Thursday, April 19, 2007

Climate of Iraq



Brief Review:
Iraq experiences its wet season from winter through early spring, with hot, dry summers. Temperatures frequently exceed 100F during late spring and summer afternoons, and will often remain above 80F overnight during the summer. Dew points and humidities are usually quite low, except at times in areas closer to the Persian Gulf where moisture content of the air is greater, and summer heat indices can be extremely high. Iraq experiences some extremes in climate, but winters are usually rather mild with nighttime temperatures often remaining above freezing. Its wet season runs from winter through early spring, but with annual precipitation averaging less than 5 inches in driest desert areas, and most of the country having less than 10 inches of precipitation per year. In Baghdad, temperatures range from an average July maximum of 110F to an average January minimum of 38F. In much of the country, temperatures frequently exceed 100F during late spring and summer afternoons, and will often remain above 80F overnight during the summer. Dew points and humidities are usually quite low, except at times in areas closer to the Persian Gulf where moisture content of the air is greater. In these areas the summer heat index can be extremely high--over 120F.


Detailed Summary:
Terrain: A bit more than twice the size of Idaho, Iraq is nearly landlocked. Syria and Turkey border it to the northwest through north, Iran is to the northeast through southeast, Kuwait occupies most of the southern border, Saudi Arabia takes up the south through southwestern area, and Jordan is between Saudi Arabia and Syria. Iraq has only a small coastal area east of Kuwait. The Syrian Desert occupies much of western Iraq and the Arabian Desert occupies much of the country to the south-southwest through southwest.

Iraq is mostly composed of broad, arid plains, but two easily flooded river valleys, the Tigris and the Euphrates, bisect the country diagonally from northwest to southeast. These river valleys are narrow and steep-walled for the first third of their path in Iraq but open into broad flood plain valleys (just north of Baghdad) that are the lowest and best-watered terrain in the country. Fully 80 percent of these two river drainage systems are part of the region known as the Fertile Crescent.

The Tigris (locally called Nahr Diljah) flows out of Turkey into northern Iraq and flows south southeastward to the Persian Gulf. (The word nahr means river.) The river flows to the gulf through the Sha'tt Arab delta. The Euphrates (locally known as Nahr al Furat) enters Iraq from Syria and flows diagonally across the plains to join the Tigris at Hawr (Lake) al Hammar, a shallow, brackish lake in the southeastern corner of Iraq. These two rivers meander quite a bit, have many minor tributaries (most seasonal), and get close enough to be connected with manmade canals in the Baghdad vicinity before they separate once again. A number of oxbow lakes and shallow ponds dot the flood plain around both rivers from Baghdad to the Persian Gulf coast.

West of the flood plain, the terrain rises steadily toward the west onto a broad plain that is essentially a desert plateau. Wadis (seasonal streams) flow down slope toward the east into the Euphrates River. Elevations rise to 900- 1,200 feet (275-365 meters) on the plateau. In the river valleys, elevations decrease from north to south from their entry points, Syria at 1,100 feet (335 meters) and Turkey at 1,800 feet (550 meters), to 100-180 feet (30-55 meters) just a few miles north of Baghdad and to 30-80 feet (9-25 meters) in the flood plain from As Samawah southward to the gulf. Roughly the southernmost eighth of the river valleys is marshy with areas that become seasonal lakes. In eastern Iraq, both wadis and permanent rivers flow toward the west to join the Tigris River from the higher terrain in Iran. It has been reported that many of the marsh areas have been drained entirely or seriously deprived of water by reservoir construction upstream. This exacerbates dust problems as the former lake and marsh beds are exposed and dry silt lifts into the air in the wind.


The northern part of Iraq includes the southern part of the Guneydogu Toroslar (Taurus Mountain Range), which is part of the great Anatolian Plateau that occupies most of Turkey. Elevations in the Iraq portion rise from 5,000 feet (1,525 meters) to 9,000 feet (2,745 meters), near the border, with a few peaks above 11,000 feet (3,350 meters). Northeastern Iraq shares the western portion of the Kuhhaye Zagros (Zagros Mountains) with Iraq. A couple of minor outlying ridges that average 4,000-7,000 feet (1,220-2,135 meters) are in Iraq and close to the northeastern border, elevations begin to rise into the true mountains and reach 11,000 feet (3,350 meters).

There are three freshwater lakes in central Iraq near Baghdad, all lined up more or less north to south in the broad river valleys. Buhayrat Ath Tharthar is the largest of the three, but all shrink and expand dramatically with the changing seasons. Buhayrat Ath Tharthar is 48 NM (55 km) northwest of Baghdad between the Euphrates and the Tigris north of where the two rivers get close together. Al Taqaddum (TQ), also called Hawr al Habbaniyah, the middle lake, is the smallest of the three. It is 17 NM (31 km) south of Buhayrat Ath Tharthar, just southwest of the town Al Habbaniyah, which is due west of Baghdad. The third lake, Bahr al Milh, is 5 NM (9 km) south of Al Taqaddum and just southwest of the Euphrates River. It is slightly smaller than Buhayrat Ath Tharthar and its southern end is west of the town Karbala. There are also at least three manmade reservoirs in the northeastern mountains (Zagros Mountains). Dukan Reservoir is just northeast of the city of Kirkuk in the northeastern corner of Iraq. Darband-i- Khan Reservoir is just southeast of As Sulymaniyah, and a smaller reservoir built on the Nahr Diyala is northeast of Baghdad.

Winter (December-March)
General Weather: Winter weather generally features fair skies but migratory lows and troughs may affect the region every 3-5 days. These systems bring short periods of precipitation and occasional dust storms. The origin of these systems is important. Cyprus lows consistently produce more rain, cloud cover and thunderstorm activity in this region than any other type. A deep Cyprus low with strong cold air support can produce heavy, even severe, thunderstorm activity and associated localized flooding. Hail, although small, can occur with these systems, usually no more than once or twice per winter. Very cold mid-level troughs occasionally bring snowfall to elevations above 2,000 feet (600 meters). This occurs on an average of 1-2 days every 3-4 years.

The 24- to 36-hour shamals (shamals are strong northwesterly winds) can occur with deep polar air surges. Intense Black Sea lows sometimes contain enough polar air aloft to extend a well-defined cold front deep into Iraq. The fronts bring extensive cloudiness, rainfall and fog to the region. This appears to occur more frequently during El Niňo Years. Additionally, there is a strong correlation between El Niňo increased cloud cover and rainfall with all storm systems that move through the region. There also appears to be a good correlation between overall warmer temperatures, increased rainfall and cloud cover with negative (low gradient) North Atlantic Oscillation phases and the opposite occurs during positive (high gradient) phases.

By early December, the monsoon trough is south of the equator. A weak high over northwestern Saudi Arabia is periodically reinforced by migratory highs out of the Mediterranean. The low-level flow is mainly northwesterly, but low-level winds vary with the synoptic situation. Dust and sand lift in strong winds behind and ahead of troughs/fronts. By early January, upper-air troughs and associated surface cold fronts or troughs occur every 3-5 days. Only the strongest lows have surface cold fronts. Precipitation occurs only with fronts, but blowing dust occurs with troughs or fronts. When a strong high moves east over Turkey, flow becomes northerly or even northeasterly. This brings relatively dust-free air south out of eastern Turkey or Russia. Local dust is picked up by winds ahead of and behind the trough. By early January, secondary waves may form on fronts that cross-northern Saudi Arabia. Southeasterly flow ahead of these systems allows moist, warm Persian Gulf air to move inland, on rare occasions, as far north as Baghdad. Such flow brings isolated early morning fog or low stratus around the Tigris and Euphrates and the coast as well as isolated thundershowers with the upper-level trough axis. Such thunderstorms are rare.


Low visibility in nocturnal and early morning fog and stratus in the Tigris and Euphrates river valleys is caused by intensified thermal highs over Iran and in advance of lows out of the Mediterranean. Fog and stratus occur most at night and towards sunrise and burn off before midday in most cases.

There are two basic causes for reduced visibility or for cloud cover at any level in this season. The first relates to the Mediterranean storm tracks "A" and "B". Track A storms move through the Mediterranean just south of Turkey and curve northward into the Caspian Sea. Multiple cloud layers (low cloud to cirrus) and precipitation with the low take 2-4 days to transit Iraq. Track B Mediterranean storms come out of the sea into Jordan, Syria, and Iraq on the way into the Persian Gulf. They exit the area through the Strait of Hormuz and the Gulf of Oman into the Indian Ocean and heads toward India. These systems also cause multiple layers of cloud cover 1-2 days ahead of and 1-2 days behind the system. Most storms pass through in 2-3 days, but some stall and take as many as 6 days to move out of the area.

The second cause for cloud cover is the subtropical jet stream (STJ). In this season, the jet flows across the Arabian Peninsula and brings a band of cirrus through the area. Deep lows displace the jet south for short periods.

Foehn winds occasionally occur in the northern plains. They descend from the mountains of Turkey and Iran and are largely responsible for the absence of severely cold weather in Iraq. They occur when the Asiatic high expands and intensifies to send outbreaks of bitterly cold northerly flow over Turkey and Iran, which flows into the foothills of northern Iraq. The strongest Foehn winds are most likely when there is heavy snow cover over the mountains of the Anatolian Plateau of Turkey.

Flooding along the lower courses of the Tigris and Euphrates Rivers and some Tigris tributaries (where they cut across the lowlands of eastern Iraq to join the Tigris) occurs nearly every year. Flooding is most frequent in winter and spring when exceptionally heavy precipitation in the mountains produces torrential flow into the tributaries. Melting snow compounds the problem. In winter and spring, wadis, dry much of the year, can fill suddenly and produce flash flooding. Late winter and early spring is when these seasonal streams are most likely to contain water.

Sky Cover: Even though this is the rainy season, the mean cloud cover is still only scattered over most of Iraq. Windward mountain sites have more cloud than other locations in the country and mean cloud cover is broken there, but only the highest windward peaks remain cloud cloaked for any length of time. Cloud cover varies widely in the mountains and leeward sites are often far less cloudy than windward sites. Ceilings below 25,000 feet occur 40-50 percent of the time all winter in the mountains with a daytime maximum rate. In the rest of Iraq, they occur 25-35 percent of the time all winter with a daytime maximum rate. Ceilings below 10,000 feet occur 25-35 percent of the time all winter in the mountains and a maximum of 40 percent of the time in late morning through sunset. In the rest of the country, they occur 15 percent of the time most of the day and a maximum of 20 percent of the time during the late morning through sunset. Ceilings below 3,000 feet occur 15-20 percent of the time in the mountains with an afternoon maximum. Elsewhere, they occur 5 percent of the time or less in most places and rarely in the southern desert. Ceilings below 1,000 feet or below 200 feet are rare all season everywhere except in the windward mountains, where cloud cloaking occurs with passing storm systems.

Visibility: The main causes of restricted visibility are fog, blowing sand and dust and dust haze. The restrictions in dust haze and blowing sand/dust are fewer in winter because of the rainfall, but rain is so limited even now, conditions are often dry in many parts of Iraq. Dust haze is frequently present, but visibility is generally somewhat better in winter than in other seasons. Fog occurs more often in winter because of the additional moisture in the air and some places are more apt to get it than others. Fog restricts visibility below 7 miles (11,000 meters) on an average of 1-2 days per month in the desert regions, 5-10 days per month in the rest of the country in December and January and 2-5 days per month in the rest of the country in February and March. Most places have only 1-2 days per month when blowing sand or dust restricts visibility below 11,000 meters. It occurs 5-8 days per month in the southern quarter of the country all season and the rate increases in the Tigris- Euphrates basin in February and March to 4-6 days per month.

Visibility below 11,000 meters occurs 55-65 percent of the time all season in the mountains. December and January show a maximum rate of 70-75 percent of the time at 06-11L but February and March do not. In the rest of Iraq, it occurs more often in urban areas than elsewhere as pollution adds particulate matter to the existing dust haze and fog. In urban areas, visibility below 11,000 meters occurs 50-60 percent of the time most of the day all season and 70-75 percent of the time at 09-11L. Pollution restrictions are particularly noticeable in Baghdad. Elsewhere, it occurs 35-45 percent of the time all season with the maximum rate at 09-11L. Visibility below 3 miles (4,800 meters) occurs 5 percent of the time or less most of the day all season in the mountains with a maximum rate of 15-20 percent of the time at 03-09L. Elsewhere in Iraq, it occurs 5 percent of the time or less most of the day all season with a maximum rate of 10-15 percent of the time at 06-11L. In urban areas, December and January show maximum rates of 30 percent of the time at 09-11L but February and March do not.

Visibility below 1 mile (1,600 meters) is rare most of the day all season all over Iraq, including the mountains and occurs 5 percent of the time or less at 03-11L. There are many places that do not get visibility this poor at all. Visibility below 1/2 mile (800 meters) occurs 5 percent of the time or less at 06-11L all over Iraq and does not occur the rest of the day. In many lowland locations, visibility this poor is very rare or does not occur even at sunrise.

Winds: Throughout Iraq, overall surface winds come from the northwest at 5-10 knots on average. Winds vary locally from west through north and the mountain sites have considerable local terrain influences. Foehn winds occur in north- south oriented mountain valleys during cold air outbreaks and up- and down slope winds are typical. Peak gusts reached 40-50 knots all over Iraq but sheltered locations, especially in the mountains, get only 30-40 knots. The strongest winds generally occur with passing cold fronts but funneled winds are the more common culprits in the mountains. Conditions are calm 15-20 percent of the time in most of the country, 35-45 percent of the time in protected mountain valleys, and only 5-10 percent of the time in the exposed southern third of the country.

Precipitation: A simple winter precipitation maximum occurs here, mainly in rain and rain showers. Thunderstorms do not occur more than 1-2 days per month all season and most places have them 1 day or less per month. Snowfall is most likely in the mountains but is possible anywhere in Iraq. In the southern third of the country snow flurries are very rare but in the rest of it, they occur every 2-3 years. Precipitation occurs 7-12 days per month in the mountains and decreases to 3-6 days per month in the middle of the country and decreases again to 1-3 days per month in the south. Rainfall distribution and amounts are erratic. Rain showers may dump a year's precipitation on a small area in a short time and leave adjacent areas, sometimes even adjacent fields or houses, dry. In many cases, the extreme monthly rainfall amounts a station reports is associated with single rainfall events of 24 hours or less. The more violent downpours often result in flash floods.

Monthly mean precipitation uniformly decreases from 4-9 inches (102 mm) per month in the windward mountains to 1-3 inches (25-76 mm) per month in the Tigris-Euphrates basin, to less than 1 inch (25 mm) per month in the rest of the country. Leeward mountain sites often get half or less the precipitation of windward sites. Extreme (record) monthly precipitation reached 12-15 inches (305-381 mm) per month in the mountains, 5-8 inches (127-203 mm) per month in the middle of Iraq, and 3-5 inches (76-127 mm) in the southern third of the country. The southwestern third of the country has the lowest mean and extreme amounts. Isolated, windward mountain sites had extreme monthly accumulations of 20 inches (508 mm) of precipitation.

Note: Rainfall and monthly precipitation are reported in inches and millimeters (mm) while snow is reported in inches and centimeters (cm). The average ratio in this arid region is 15 inches (572 mm) of snow per 1 inch (25 mm) of precipitable water.

While snow flurries are possible all over the country, they are rare in the southern half and accumulations are rare except in the mountain. Winter snows occur occasionally on the lower slopes and snow cover may last for several days before it melts. In the higher reaches, above 3,500 feet (1,065 meters), snow is frequent and continuous snow cover may last for several months. A deep snow cover may persist on sheltered plateaus above 5,000 feet (1,525 meters) and snowdrifts often close down mountain passes. January and February are the biggest snow months.

Temperature: Winter temperatures are generally mild except in the high mountains. Temperatures at or above 100F occur as early as March in some places and are most likely in the southern half of the country. Freezing temperatures are observed as early as October and as late as April in most places and as early as September and as late as May in the high mountains. There, temperatures hover near freezing much of the winter. Mountain temperatures provided below are for inhabited areas, commonly valleys.

Mean highs are 45 to 55F (7 to 13C) in December-February in the mountains and 55 to 65F (13 to 18C) in March. In the interior plains, they are 55 to 65F (13 to 18C) in December-February and 65 to 75F (18 to 24C) in March. Extreme highs reached 70 to 80F (21 to 27C) in December-February in the mountains and 80 to 85F (27 to 29C) in March. In the plains, they were 90 to 95F (32 to 35C) in December and February 80 to 85F (27 to 29C) in January, and 95 to 100F (35 to 38C) in March. The southern third of the country is typically the warmest region of Iraq. The temperature rises to or above 90F (32C) on an average of 1 day or less just about everywhere in Iraq in March and very rarely in December. Temperatures above 90F (32C) do not occur in January or February.

Mean lows are 35 to 45F (2 to 7C) all season in the mountains. In the plains, they are 35 to 45F (2 to 7C) in December and January and 45 to 55F (7 to 13C) in February and March. The southern third of Iraq has 45 to 55F (7 to 13C) for mean lows all season and the southern Tigris Euphrates valley has 60 to 65F (16 to 18C). The extreme lows were 15 to 25F (-9 to -4C) all over Iraq except for the southern third of the country, which had extreme lows of 25 to 35F (-4 to 2C). The temperature falls to or below freezing on an average of 1-3 days per month in December and January for most of Iraq, 8-12 days per month in the low mountains, and as much as 20-25 days per month in the high mountains. In February and March, most of Iraq gets subfreezing temperatures 1 day or less per month and rarely in the southern third of the country. The low mountains get them 2-5 days in February and 1-2 days in March while the high mountains get them 8-10 days in February and 3-5 days in March.

Spring (April-May)
General Weather: This season is usually at least warm and often hot. Temperatures have been known to reach 112F (44C) as early as March in the desert areas and well above 100F (38C) in the river valleys. The monsoon trough shifts back north of the equator by early April. The summer heat low over interior Iran and southeastern Saudi Arabia begins to form. Weak highs cross the northwestern Arabian Peninsula behind ever-weaker cold fronts and upper air troughs from the Mediterranean Basin. Occasional strong cold air outbreaks may move southwestward and southward across Turkey and Iran behind intense lows that move southeastward into Iran. Cyprus, Black Sea and Atlas lows all reach this region in spring but move farther and farther north as the season progresses until they no longer affect Iraq by late in the season. In El Niňo years, the period of activity sometimes extends into June.

Low-level winds remain northwesterly over Iraq and slowly strengthen. By late May, these winds become sustained northwesterly over Iraq as the heat lows dominate the region. Low-level winds in April and early May vary with the synoptic situation. Dust haze becomes more common during May. Shamal winds, strong northwesterly that carry sand and dust far downwind, gradually intensify and occur with greater frequency as the summer heat low strengthens.

Frontal systems and their upper-level troughs cross Iraq every 5-7 days in early April; by late May, these systems are weak and very rare. Blowing sand occurs over the Tigris Valley with strong frontal associated winds over areas of loose soil or fine sand. In early April, a rare secondary low can occur on fronts in southern Iraq or northern Saudi Arabia. Onshore flow ahead of these systems allows moist, warm Persian Gulf air to move inland, on very rare occasions, inland as far as Baghdad. This flow brings isolated early morning fog or low stratus to the Tigris and isolated thundershowers over the Tigris-Euphrates River valley with the upper level trough axis. Such infrequent thunderstorms reach maximum frequency during April. By May they are rare.

Sky Cover: The mean cloud cover is scattered almost everywhere in April except for windward mountain sites. There, broken or nearly broken conditions are the norm. Cloud cover varies widely in the mountains and leeward sites are often far less cloudy than windward sites. By May, scattered conditions prevail everywhere except for a few windward mountain sites where cloud cloaking still occurs, especially early in the month. By the end of May, scattered skies are the norm everywhere in Iraq. Clear or nearly clear skies prevail over much of Iraq by mid-May.

Ceilings below 25,000 feet occur 25-35 percent of the time in the mountains all season with a maximum rate of 40 percent of the time in the afternoons. In most of the rest of Iraq, they occur 15-25 percent of the time with the maximum rate in the afternoons. In the southern quarter of Iraq, they occur only 10-15 percent of the time all season. Ceilings below 10,000 feet occur 25 percent of the time in the mountains in April and 10-15 percent of the time in May. In the rest of Iraq, they occur 5-10 percent of the time in April and 5 percent of the time or less in May. In southernmost Iraq, they are rare all season.

Ceilings below 3,000 feet occur 10-15 percent of the time in the mountains in April and 5 percent of the time or less in May. In the rest of the country, they occur 2-3 percent of the time in April and are rare or do not occur at all in May. They are rare or do not occur at all in southernmost Iraq all season. Ceilings below 1,000 feet or below 200 feet are rare in the mountains in April and do not occur except where cloud cloaking occurs at high elevations in May. In the rest of Iraq, they are very rare or do not occur in April and do not occur at all in May.

Visibility: Visibility is generally fair to good with dust haze in the air frequently. As the scanty winter rainfall falters, fog rates decrease. Blowing sand and dust and dust haze are the main causes of restricted visibility. By the end of May, dust haze is in the air more often than not in the plains. Fog that restricts visibility below 7 miles (11,000 meters) occurs 3-5 days per month in mountain valleys and 8-10 days per month on cloud cloaked mountain slopes. In the Tigris-Euphrates valley, it occurs 1-2 days in April and is rare in May. Fog that restricts visibility below 11,000 meters is rare all season in the rest of the country. Blowing sand or dust occurs 1-3 days per month in the mountains and varies widely site by site depending on exposure. It occurs 6-9 days per month in most of the plains and 8-11 days per month in the southern third.

Visibility below 11,000 meters occurs 55-60 percent of the time all season in the mountains. In the rest of Iraq, it occurs 35-40 percent of the time most of the day and 55-60 percent of the time at 03-05L all season. Urban areas, like Baghdad, have higher rates because of pollution. There, visibility below 11,000 meters occurs 55-60 percent of the time all season with a maximum rate of 70 percent of the time at 06-11L.

Visibility below 3 miles (4,800 meters) occurs 3-5 percent of the time all season in the mountains. In the rest of Iraq, it occurs less than 5 percent of the time in April and is rare in May. Urban areas have higher rates. There, it occurs 5 percent of the time or less most of the time and 8-10 percent of the time at 09-14L in both months. Visibility below 1 mile (1,600 meters) or 1/2 mile (800 meters) is very rare or does not occur at all in spring. In most places, only sand storms, dust storms or dust devils cause visibility this low and only for the duration of the event. Windward mountain sites at high elevation may get poor visibility in cloud cloaking in April.

Winds: Overall surface winds continue to come from the northwest at 5-10 knots all season. The circulation pattern is like that seen over the top and to the east of a high-pressure system to the south of the area. Western Iraq has westerly winds, the desert west of the Tigris-Euphrates valley has northwesterly, and the remaining eastern part of the country has northerlies. As always, mountain winds are highly variable because of the terrain. Wind direction is decided by terrain steering and terrain effects such as upslope/down slope winds more often than by large-scale weather features. Conditions are calm 15-20 percent of the time in most of the country, 35-45 percent of the time in protected mountain valleys, and only 5-10 percent of the time in the exposed southern third of the country.

Precipitation: Rainfall decreases toward the summer dry as storm systems move north out of the region. By the end of May, the summer regime is in control and little to no rainfall occurs. Rain showers are the main rainfall type with occasional steady rainfall with the last of the winter systems in April. Thunderstorm activity, never great increases a little where local water sources supply fuel for them. Snowfall is still possible in the mountains but accumulations only occur above 3,500 feet (1,065 meters) and linger only above 5,000 feet (1,525 meters) by the end of April.

Precipitation occurs on an average of 2-5 days in April in most places and 6-9 days in the mountains. By May, it occurs 1-3 days in most places and 3-5 days in the mountains. By the end of May, rainfall is very limited across the whole country. Thunderstorms occur on an average of 1-3 days per month in most places and some of them are dry, especially after early May. A few places in the Tigris and Euphrates valley get 3-4 thunderstorm days per month.

The mean monthly precipitation is 2-4 inches (51-102 mm) in April in the mountains and 1-2 inches (25-51 mm) in May. In the middle third of Iraq, April mean monthly rainfall is 1-2 inches (25-51 mm) and in May, it is 0.5 inch (13 mm) or less. In the southern third, April mean monthly rainfall is only 0.3-0.6 inch (8-15 mm) and in May it decreases to a trace to 0.3 inch (8 mm). Extreme monthly precipitation was 5-7 inches (127-178 mm) per month in the mountains with one or two isolated windward sites that got records of 15-18 inches (381- 457 mm) in April. In the rest of the country, the extreme monthly rainfall was 3-5 inches (76-127 mm) in April and 2-5 inches (51-127 mm) in May with the southern third of the country the driest. In spring, the heaviest rainfall events occur with rain showers or thunderstorms and are often very localized and highly erratic (hit or miss). Flash flooding can occur with a sudden downpour.

Temperature: Temperatures warm quickly once rainfall begins to taper off and skies clear of the last storm clouds. Because of the arid atmosphere, the diurnal temperature spread between daily highs and lows spread as rainfall slows and then stops. Temperatures cool roughly 3-4 Fahrenheit (1-2 Celsius) degrees per 1,000 feet (300 meters) of increase elevation. Mountain temperatures provided are for inhabited areas, commonly valleys.

Mean highs are 70 to 75F (21 to 24C) in the mountains in April and 80 to 90F (27 to 32C) in May. In the interior plains of Iraq, mean highs are 78 to 88F (26 to 31C) in April and 90 to 98F (32 to 37C) in May. Extreme highs reached 100 to 106F (38 to 41C) in April in the mountains and 108 to 110F (42 to 43C) in May. In the plains, they reached 105 to 110F (41 to 43C) in April and 115-118F (46 to 48C) in May. The central Tigris-Euphrates valley has the highest reported record temperatures but other areas of the country have undoubtedly reached them as well. Isolated locations, especially in the desert, have probably had extreme highs that reached 120 to 125F (49 to 52C) by the end of May. Temperatures rise to or above 90F (32C) on an average of 1-2 days in April in the mountains and 8-14 days in May, depending on elevation. In the plains, they occur 8-14 days in April and 25-30 days in May.
Mean lows are 45 to 55F (7 to 13C) in April in the mountains and 55 to 65F (13 to 18C) in May. In the plains, they are 55 to 65F (13 to 18C) in April and 65 to 70F (18 to 21C) in May. In plains areas around water, additional moisture in the air moderates mean lows. In these places, mean lows are 70 to 75F (21 to 24C) in April and 80 to 85F (27 to 29C) in May. Extreme lows reached 30 to 35F (-1 to 2C) in April in the northern half of Iraq and 40 to 50F (4 to 10C) in the southern half. In May, they are 45 to 50F (7 to 10C) in the northern half and 55 to 60F (13 to 16C) in the southern half. The temperature falls to or below freezing on an average of 8-10 days in April at elevations above 3,000 feet and 1-2 days below that level in the mountains. In May, they occur 4-6 days above 3,000 feet and are rare below it. In the plains, subfreezing temperatures are very rare in April and do not occur at all in May. They occur mainly in early April.

Summer (June-September)
General Weather: The summer thermal lows over interior Iran and southeastern Saudi Arabia are at peak strength. Conditions are clear, hot and dry, often extremely hot. Winds persist from out of the northwest over Iraq as the heat lows dominate the region. Dust haze is common and visibility, especially in the south, is often restricted. Sustained northwesterly winds in the lower 15,000 feet maintain a persistent dust layer throughout the summer. Frontal systems no longer reach this area and what little rainfall occurs, rare, is from local moisture sources, mainly the lakes in the center of the country. Even here, the heat is such that rain showers typically only produce virga (rainfall that evaporates before it hits the ground) and thunderstorms are practically nonexistent.

Rainfall drops to the annual minimum; rainfall essentially stops; and Shamal winds cause dust storms and sandstorms. Shamals, northwesterly winds, can set in very suddenly and persist for 1-5 days. Shamals weaken overnight and strengthen during the day as the heat low that parents them waxes and wanes with the diurnal heating and cooling typical of such an arid area. The shamals reach maximum intensity in June and July when they may continue without cessation. This is often called the time of 40-day shamals, an indicator of the persistent nature of these conditions. The fine silt of the Tigris and Euphrates lowland is typically a significant source of visibility restrictions associated with shamals.

Sky Cover: The mean cloud cover all over Iraq is clear or nearly so all summer, including over the mountains. Ceilings below 25,000 feet occur 5 percent of the time or less in June and September over the mountains and are rare or do not occur in July and August. In the rest of Iraq, they are rare or do not occur all season. Ceilings below 10,000 feet are very rare or do not occur all over Iraq all season. Ceilings below 3,000 feet are very rare on June afternoons in the mountains and do not occur the rest of the season. They do not occur all season in the rest of the country. Ceilings below 1,000 feet or below 200 feet do not occur.

Visibility: Overall, visibility is generally good most of the time but summer visibility is also the worst of the year. Dry, hot winds lift the fine silt in the Tigris-Euphrates valley high into the air, sometimes as much as 15,000 feet, where it lingers for long periods. Blowing sand and dust are the main causes of restricted visibility and dust haze is a permanent feature in the summer sky. Fog is all but non-existent. Blowing sand or dust that restricts visibility below 7 miles (11,000 meters) on an average of 1-3 days per month in the mountains, 5-10 days per month in most of the remaining country and 12-15 days per month in the central Tigris-Euphrates valley.

Visibility problems have worsened in the last twenty years as lakes are depleted and shrink and wetland areas are drained for agriculture. This shrinkage (sometimes disappearance) of water exposes the fine silt of former lake and marsh beds, which is then easily lifted by the wind. This not only exacerbates visibility problems but increases respiratory problems experienced by the local populace as well.

Visibility below 11,000 meters occurs 50-60 percent of the time all summer in the northern mountains. Rates are lower at night than during the day. In the rest of Iraq, they occur 45-55 percent of the time in most places and 65-75 percent of the time in the central-southern Tigris-Euphrates valley and southeastern mountains.

Visibility below 3 miles (4,800 meters) occurs 5 percent of the time or less in June in the northern mountains and is rare the rest of the season. In the rest of Iraq, it is rare in most places all season and occurs 5-10 percent of the time in the southeastern mountains and the central and southern Tigris-Euphrates valley with a maximum rate of 15-20 percent of the time in the afternoons.

Visibility below 1 mile (1,600 meters) is very rare or does not occur all season in most places. The southeastern mountains and the central and southern Tigris- Euphrates valley get it 5 percent of the time or less all season with the highest rates in the afternoons. Visibility below 1/2 mile (800 meters) does not occur outside of the immediate area of where sandstorms, dust storms or dust devils begin and then only persists the life of the events.

Winds: Overall northwesterly winds at the surface are stronger and more persistent in summer than in any other season. Average wind speeds are 10-15 knots with periods when winds persist above 25 knots for hours or days at a time. Shamals occur more often now as well and, in June and July, can persist for weeks at a time. They are weakest at night and strongest in the afternoons. Calms occur only 5-10 percent of the time in most of the country, with the majority in the low end of the range, and 30-40 percent of the time in the mountains. Peak gusts reached 40-50 knots in most places and 50-60 knots in a few.


Precipitation: Rainfall drops to nothing all over Iraq. Rain showers and thunderstorms that can gather together enough moisture to develop are typically dry or produce only virga (rainfall that evaporates before it hits the ground). Rainfall occurs on an average of less than 1 day per month all summer, meaning it does not occur in every month or every year. There are many places in the southern third of Iraq that never get rainfall in this season. Thunderstorms, even the dry ones, are rare. The mean monthly rainfall is 0 to a trace all over Iraq all summer. The extreme monthly rainfall does not exceed 0.5 inch (13 mm) anywhere in this arid country.

Temperature: Summer is hot and dry throughout Iraq and the desert is the hottest part of the country. Diurnal temperature spreads are the widest of the year in summer because the air is so dry it cannot retain heat after sunset. The mountains offer some respite from the unrelenting heat but it is only comparatively cooler there. Mountain temperatures provided below are for inhabited areas, commonly valleys.

The mean highs are 85 to 95F (29 to 35C) in the mountains in June 95 to 105F (35 to 41C) in July and August, and 90 to 95F (32 to 35C) in September. In the rest of the country, mean highs are 102 to 110F (39 to 43C) all summer. Extreme highs were 115 to 125F (46 to 52C) all summer. Although the desert areas are typically the hottest places, even the mountain valleys have reported record highs around 120F (49C). The temperature rises to or above 90F (32C) on an average of 25-31 days per month over most of the country all summer. The high mountains are the exceptions.

Mean lows are 65 to 75F (18 to 24C) all over Iraq in June and September and 70 to 80F (21 to 27C) in July and August. The exceptions to this are the wetland areas, where lows remain in the 90 to 95F (32 to 35C) range all summer because of the higher relative humidity. Extreme lows reached 45 to 50F (7 to 10C) in June and September all over Iraq and 55 to 60F (13 to 16C) in July and August.

Fall (October-November)
General Weather: By the end of September, the monsoon trough has moved south off the Arabian Peninsula into the Arabian Sea. The Saudi Arabian thermal low is weakening steadily; by late October, it has been replaced by a weak high center over northwestern Saudi Arabia. Predominant low-level flow is northwesterly; speeds decrease steadily after mid-September. By mid-September, the prevailing dust haze of summer slowly diminishes; however, it is still present in a lesser form through late November.

The first upper-level westerly troughs cross the area in late October. These first troughs do not have surface fronts; only surface troughs mark their positions. These troughs are followed by relatively dust-free air from eastern Turkey or Russia. Surface troughs rarely reach Basrah before early December. Southeasterly flow ahead of these systems brings warm, moist Persian Gulf air inland past Basrah. This flow brings isolated early morning fog or low stratus on/near the Tigris and Euphrates and the coast and isolated thundershowers with the upper-level trough axis. Thunderstorms rarely reach Baghdad until mid- December and even then, they are not common.

Sky Cover: Mean cloud cover is scattered all over Iraq in both months but slowly increases from the summer minimum to winter norms by mid-November. High windward peaks are cloud cloaked with passing storm systems and this occurs more and more often as winter approaches. Ceilings below 25,000 feet occur 15-25 percent of the time over the mountains in October and 25-30 percent of the time in November with a maximum rate of 35 percent of the time on November afternoons. In the rest of Iraq, they occur 10-15 percent of the time in October and 15-20 percent of the time in November.

Ceilings below 10,000 feet occur 10-15 percent of the time over the mountains in October and 15-20 percent of the time in November. Over the rest of Iraq, they occur 5 percent of the time or less in October and 5-10 percent of the time in November, with a few northern plains sites reaching a maximum rate of 10-15 percent of the time during November afternoons.

Ceilings below 3,000 feet occur 5 percent of the time or less over the mountains in October and 5-10 percent of the time in November. In the rest of Iraq, they are very rare or do not occur in October and occur less than 5 percent of the time in November. The farther south a site is, the lower the occurrence rates become. Ceilings below 1,000 feet and below 200 feet do not occur anywhere except on high windward mountain slopes, where cloud cloaking occurs with passing storm systems.

Visibility: Blowing sand or dust and dust haze continue to be the main causes of reduced visibility but as rainfall begins to occur, visibility improves. Visibility is generally fair to good in October and good in November outside of actively blowing sand/dust areas. Fog that restricts visibility below 7 miles (11,000 meters) begins to occur as relative humidity creeps upward with the first rains. It still occurs 1 day or less practically everywhere in October and in most places in November. In some mountain valleys and in sites close to water sources, fog occurs 2-6 days in November. Basrah, in the southeastern corner of Iraq is an exception. It gets fog 4-5 days per month all season. Blowing sand/dust that restricts visibility below 11,000 meters occurs 1-2 days per month in most of Iraq and 3-6 days per month in the southern Tigris- Euphrates valley and the southern desert areas.

Visibility below 11,000 meters occurs 40-50 percent of the time all day in October in the mountains and most of the day in November. It occurs a maximum of 60 percent of the time at 09-14L in November. In the rest of Iraq, it occurs 25-35 percent of the time all season in most places and 50-60 percent of the time in the central and southern Tigris-Euphrates valley and in the western parts of the southeastern mountains. It occurs a maximum of 75 percent of the time at 18-20L in October in those places.

Visibility below 3 miles (4,800 meters) is rare or does not occur all season in most places. It occurs 5-10 percent of the time most of the day in both months in central and southern Tigris-Euphrates valley and southeastern mountains with the peak rate at 09-11L. Visibility below 1 mile (1,600 meters) or below 1/2 mile (800 meters) is very rare or does not occur at all in this season all over Iraq. Most places do not get visibility this low. The most vulnerable places are in the southern Tigris-Euphrates valley.

Winds: Overall surface winds continue to come from the northwest but are lighter than they are in summer, at an average of 5-10 knots. There is also a greater westerly component in more of the country. West-northwest winds are as common in central Iraq as they are in western areas, where they are typical. Mountain winds are highly variable because of the terrain and upslope/down slope winds vary wind direction and speed diurnally. Calm conditions occur 5-10 percent of the time in the southern third of the country, 25-35 percent of the time in the remaining plains, and 45-55 percent of the time in mountain valleys. Peak gusts reached 25-35 knots in most places but sandstorms, dust storms, and dust devils still cause 50-60 knots in a few places. As storm systems begin to push cold fronts through the region once again, pre and post-frontal winds increase.

Precipitation: Precipitation, still mostly rain showers and very isolated thunderstorms, gradually increases over the fall as the first winter systems begin to shift southward close enough to the region to push through cold fronts. Although snow is possible by late November in the plains and by mid October in the mountains, it does not generally do much more than light, brief flurries in the fall, except at high elevations. Rainfall occurs on an average of 1-2 days in October just about everywhere. In November, it occurs 3-4 days in most of Iraq and 6-8 days in the mountains. Windward sites have higher, sometimes double, precipitation rates than leeward sites. Leeward sites generally have the same rates as plains locations. Thunderstorms occur on an average of 1 day or less per month in most sites. Places near water sources in the Tigris- Euphrates valley and in a few windward mountain locations get them 2-3 days per month in the fall.

The mean monthly precipitation is 0.5 inch (13 mm) or less everywhere in October. It is 0.5-1 inch (13-25 mm) in most places in November, 3-5 inches (76-127 mm) in lower elevation mountain valleys, and 6-8 inches (152-203 mm) in higher elevation, windward sites. The extreme monthly precipitation was 1.5-2.5 inches (38-64 mm) just about everywhere in October. In November, it was 3-6 inches (76-152 mm) in the plains, 6-8 inches (152-203 mm) in the mountain valleys, and 11-14 inches (279-356 mm) in the high, windward mountain sites. While snow does not accumulate significantly below 5,000 feet (1,525 meters) elevation, the high passes sometimes close due to snowdrifts in early winter storms in November.

Temperature: Temperatures cool from the blistering heat of summer but October is still quite warm. Mean highs are 85 to 95F (29 to 35C) in October in the plains and 75 to 85F (24 to 29C) in the mountains. In November, they are 75 to 85F (24 to 29C) in most lowland sites and 60 to 70F (16 to 21C) in the mountains. Extreme highs were 95 to 105F (35 to 41C) in the mountains in October and 90 to 95F (32 to 35C) in November. In the plains, they are 105 to 115F (41 to 46C) in October, with a few desert sites approaching 120F (49C). In November, extreme highs reached 95 to 105F (35 to 41C). The temperature rises to or above 90F (32C) on an average of 8-10 days in the mountains in October and 3-5 days in early November. In the plains, they occur 15-20 days in October and 1-5 days in November (most have 1-3 days in November). A few sites in the central and southern Tigris-Euphrates valley and in the southern desert have temperatures above 90F (32C) 25 days in October and 8-10 days in November.

Mean lows are 55 to 65F (13 to 18C) all over Iraq in October except near water sources, where they are 70 to 75F (21 to 24C). In November, they are 45 to 55F (7 to 13C) in most places and 60 to 65F (16 to 18C) around water. The extreme lows were 25 to 35F (-4 to 2C) in the mountains in October and 20 to 30F (-7 to -1C) in November. In the plains, they were 30 to 40F (-1 to 4C) in October and 25 to 35F (-4 to 2C) in November. The temperature rarely falls to or below freezing in the mountains in October and only 3-5 days in November. Higher elevation sites have progressively more subfreezing days with increasing elevation. In the plains, they occur 1-2 days in November and are very rare in October.

1 comment:

Bobillw said...

From my first perusal of your Iraq 101 article, I find very interesting and instructive. Thank you for the piece and for your service to America.