The key weather and climate features in the Northern Hemisphere in May 2015
  Climate The key weather and climate features in the Northern Hemisphere in May 2015

The key weather and climate features of May 2015 in the Northern Hemisphere

Air temperature In May, as in any other month of spring this year, the main anomaly of heat in Russia has concentrated in the European north and the Urals. The unseasonable warm was mentioned there for the entire month. The maximum temperature was recorded on the Arctic islands, in the Komi Republic, the Nenets and Yamal-Nenets Autonomous District. Mean month air temperature exceeded the norm by 4-7°C. In the Urals Federal District was the warmest May in history and in the Northwest this May was the second warmest.

Heat records were registered in other parts of Russia, for example, in the Irkutsk region in the first and in the center of the country (the Middle Volga and Chukotka) in the third decade of the month. Everywhere except the above areas, the anomalies did not exceed an average of + 1 ... 2°C. In the Far East May was even colder than normal. In the last case, there were records of minimum daily temperature to be mentioned. Frosts up to -5 ... -7°C were observed not only in the east, but also in Central Russia, Crimea and North Caucasus. In the first twenty days of the month the weather in the European territory was colder than usual. Mean decade temperature anomalies reached -2 ... -3°C.

All this has led to the fact that in Russia May 2015 is not among the warmest, but it can not be said about the whole spring. It was the fifth warmest spring in the history of regular meteorological observations, though it inferior to the record warm spring of last year for about 1 °C. So as in the spring of the last year, this time large positive temperature anomalies (up to + 6°C) had formed in the north of the European territory, in the Urals and Siberia. Everywhere in the country, spring again was warmer than normal, but this time anomalies were less than the anomalies of the last year, especially in the European territory.


In Europe this May cannot be considered as very warm one. Mean month temperature was quite close to norm. While in the south of the continent in Spain, Portugal, Greece, the Balkans, the south of France and Sicily the weather was very hot and maximum temperatures, including monthly extremes, were repeatedly recorded, in the north, especially in the Scandinavian countries, it was colder than usual. In Norway the mean month air temperature anomalies were up to -2°C, whereas in Bulgaria, Italy and France – up to + 2°C, and in Spain and Portugal – up to + 3 ... + 4°C.


To the south in North Africa was a real summer heat. May 2015 there was the hottest in the history of meteorological observations. In Algeria, Morocco, Mauritania, Mali, Niger, Burkina Faso mean month air temperature norm was exceeded by 2-4°C.

It was hot in the Middle East. In Arabia and Mediterranean countries, the thermometer rose above + 40°C. In Lebanon and Israel mean month temperature anomalies were more than 2°C, in the countries of the Arabian Peninsula - + 3°C, in Iran - to + 4°C.

It was hot in Kazakhstan and Central Asia. Everywhere here the mean temperature for the month was more than the norm. In some places in the south of Kazakhstan, Uzbekistan, Turkmenistan and Kyrgyzstan anomalies exceeded + 2°C. At the same time in the mountains it was still cold. Thermometer kept near the mark of 0°C.

In India, in New Delhi, in the states of West Bengal, Orissa, Andhra Pradesh, the air glowed by almost 50°C. Heat stroke killed thousands of people. However, this is an extraordinary point. This happens almost every year on the eve of the summer monsoon. Many times before the weather in May was even hotter.

In China, slight abnormal warm was mentioned all over the country. Only in a few areas in the west of Xinjiang and in the south provinces of Yunnan and Guangdong the mean monthly exceeded the norm by 2°C or more. Similar anomalies were reported in several Japanese prefectures on the island of Honshu.

The air temperature averaged over the territory of the United States was close to normal. Nevertheless, this was achieved due to an abnormal warming of the Northeast of the country (anomalies up to + 3 ... 5°C and numerous temperature records), and lack of heat in the Midwest (anomaly up to -2°C). Of particular note is Alaska, where such a warm May have not yet seen before. Everywhere in Alaska air temperature exceeded norm by 2.5-5.0°C. Abnormally warm it was in most parts of Canada. In the west, in the provinces of British Columbia and the Yukon, i.e. in the areas adjacent to Alaska, anomalies were up to + 2 ... 4°C. Around the same they were in the southeast of the country, i.e., where it borders the northeastern United States (in Montreal the anomalies were up to + 4.1°C). At the same time in the central areas, the month was colder than normal.

Spring 2015 in the Northern Hemisphere is the warmest in the entire 125-year history of regular meteorological observations on the planet. Its average temperature accurate to 0.1ºC repeated record achievement established in the spring of 2010.

Everywhere on the Eurasian continent, except for some small areas, the mean temperature has exceeded the norm of spring. Like in the last year, the record warming remains in Russia. As noted above in the north of the European part of the country, in the Urals and Siberia ended spring was warmer than usual by 2-6ºC. In the North-West Federal District, this is the warmest spring in the history of meteorological observations, and in the Urals, it has the third rank.

In the republics of Central Asia, Afghanistan, Iran and the Arabian Peninsula, in Japan, in the northwest of Africa and in neighboring European countries (Spain, the south of France), the average temperature in spring exceeded the norm by 2ºC and more. A similar pattern was on the North American continent. In most parts of the US and Canada this spring can be attributed to the abnormally warm one. This applies especially to the western territories of these countries, where the average temperature exceeded the norm by 2-3ºC more. Only in the northeast of Canada (Labrador Peninsula the island of Newfoundland) the weather in spring turned colder than usual.

As at the end of April, so as after the first five months of the year the average temperature in Russia and in the whole Northern Hemisphere is record high.


Sea surface temperature

The development of El Niño continues in the Pacific. Throughout the equatorial zone of the Western Hemisphere, temperature anomalies on the ocean surface are over + 1°C, and in some places they are more than + 2°C. The NOAA assume that El Niño persist until the end of summer with a probability of 60%, and with a probability of 60% that it will persist even in autumn. In general, the waters of the Pacific Ocean in the Northern Hemisphere can be assessed as very warm. Though, in the temperate latitudes and along the coast of Asia water temperature is colder than normal, but the heat is much prevalent in the rest area. The surface of the Pacific Ocean in the Northern Hemisphere for the last time was so warm in May 2005.

The average temperature of the surface of the Atlantic Ocean in the Northern Hemisphere was close to normal. Much of the water area in the central part of the ocean, and especially in the north is occupied by negative anomalies, which in the area of Newfoundland, Greenland and Iceland reached 1°C or more. Water temperature on the surface of the Gulf Stream is still higher than normal, but a transfer of warm water to the northeast remains difficult.

At the resorts of the Eastern Mediterranean in May the water warmed up to + 20-22°C, which made it possible to open a full bathing season.



In the European part of Russia, May was very rainy. Almost everywhere the amount of precipitation in the past month was normal or more. In the central area the excess amounts 1.5-2.5 times, in the southern region, the Lower Volga and the Crimea - 1.5-2.0. Rains have often been strong and continued for several days, which had led to a new record amounts of rainfall. In the northern parts of European Russia, it was still snowing, as the result of it even in late spring snowdrifts formed up to half a meter in height. At the same time, the distribution of precipitation over the territory is uneven. For example, It fell more than 2 precipitation norms in the Central Federal District in the Kaluga region, and only half of it fell in the neighboring Belgorod and Lipetsk regions. The same pattern can be seen in the Volga Federal District. Over 1.5 precipitation norms fell in the Republic of Bashkortostan and the Orenburg region, and only about 50% - in the Perm Territory, the Republic of Mordovia, the Penza and Ulyanovsk region. The abundance of rainfall went southern part of Urals. In the Chelyabinsk and Kurgan region the amount of precipitation blocked the norm is 2 times or more in the past month. At the same time in the north of the Khanty-Mansiysk and Yamalo-Nenets Autonomous Districts it fell only 50% of the norm.

Most of the regions of Siberia and the Far East, with the exception of the northern territories of the Krasnoyarsk Territory, the Kamchatka and part of the Kolyma got normal precipitation and above. In some parts of the Kemerovo region, Khabarovsk and Primorye territories they turned 2 times, and in Chukotka in 3 times, more than the norm. Often, especially in the first decade of the month, it was still snowing, and very abundant, which led to an increase of the height of the snow cover.

In May, southern China regions suffered from heavy rains. In the provinces of Jiangxi, Guangdong, Guizhou, Fujian, Guangxi weather led to massive flooding, mudslides, rock falls, the deaths of dozens of people and, consequently, the damage in the amount of more than $ 5 billion. At the same time, in the north of the country and in neighboring Mongolia was the drought, that has affected about 5 million hectares of agricultural land. In May little rain went to neighboring Korea and Japan. The same pattern can be seen in south-east Asia, where the amount of precipitation was about half the norm in the past month.

In most part of India, it was dry. Heavy rains were just to the south of the peninsula and to the north on the border with Pakistan, where the precipitation norms were exceeded by 2-3 times. Kazakhstan has got a lot of rains, especially its northern territories. Here, and especially in the Caspian region, monthly precipitation exceeded the norm by 3-4 times. Heavy rains were in the mountains of Tajikistan.

It was dry in most part of the Middle East. Although some downpours, such as in Azerbaijan, led to the formation of mudslides that washed away the roads, bridges and buildings. There was a dry weather In North Africa. Significant rains occurred only in the Gulf of Guinea.

There was almost no precipitation in Western Europe. In Spain you can find areas, where there were no rains in the past month. In France, Belgium, Holland and northern Germany, total precipitation for the month amounted to only about half of normal. But there were a lot of rains in the north of the continent in the UK and Scandinavian countries, as well as in Eastern and Central Europe. In Ireland, England, Scotland, Finland, Sweden, Austria, Hungary, and in Ukraine precipitation norm was exceeded by 2 times.

Mostly dry weather persisted in the Balkans. Torrential rains that hit the Midwest and Southwest US., led to massive flooding. From Canada to Mexico precipitation for the month fell by 2-4 times more than the norm, and in the most affected areas - by 6 times. Dozens of people were killed or disappeared, numerous destructions have been registered. And in other parts of the country, except for the coasts of two oceans, the amount of precipitation in May was enough. The rains caused by El Niño just moderated drought in California. Only the south-east of Canada monthly precipitation totals conformed to standards, and in the rest part of the country they were few. American precipitations through Oklahoma and Texas went to Mexico. In the most part of the territory, the rainfall rate reached or exceeded the norm, sometimes in 2-3 times.

In Moscow, the amount of precipitation for the month amounted to 120 mm, or 235% of the norm. This is the second maximum in the history of 125-year recording. Only once, in May 1976 precipitation in the capital was even more - 143mm. The first month of spring of this year – March – was very dry in Moscow, the second - April - was normal, and the third – May - significantly the norm. As a result, the spring of 2015 in Moscow was wet. Its amount of rainfall - 178mm has the second rank, and the spring was the wettest, as well as in May in 1976. Then there were 244mm of rainfall dropped in the spring.


Atmospheric Circulation

In May in the upper stratosphere (at AT-10), there was a strengthening of the stratospheric anticyclone that steady over the North Pole in the second decade of April. It’s average monthly intensity was about the norm.

In the equatorial stratospheric winds persisted eastern phase of quasi-biennial cycle with a tendency of weakening.

In the middle troposphere (at AT 500) monthly averaging field of geopotential had a number of unique features: troughs and ridges were expressed more sharply than usual, so the anomalies of both signs were quite large. The main center of polar vortex, which normally resides in May over the Kara Sea, was shifted to the pole, as the result the average for the month geopotential between Greenland and the North Pole was lower by 6 dam. The second center of the polar vortex, the average long-term position of which was marked on the Baffin Sea, shifted to the south to Davis Strait in May 2015, where mean month geopotential anomaly was -10 dam. In addition, there was a very deep trough during the entire month over Iceland and the Norwegian Sea, because of that geopotential here was below the norm by an average of 12 dam. Another abnormally deep trough was observed over the Bering Sea during the second and third decades of the month; the average geopotential here was also below normal by 8 dam.

Along with the deeper-than-normal troughs, also there were more intensive tropospheric ridges. One of them existed over West Siberia (anomaly 15 dam). The displacement of the center of the polar vortex from the Kara Sea to the North Pole is connected with its existence. The second intensity ridge at the level of 500 hPa was observed over Alaska, where the average monthly geopotential anomaly reached +14 dam. In two more ridges over the Iberian Peninsula and over the northeastern United States, the mean month geopotential anomalies amounted to +10 dam and +9 dam respectively.

Increased geopotential was observed in most parts of the Northern Hemisphere subtropics: highest anomalies were formed over the Arabian peninsula (up to +6 dam), over the West Africa, Iran and the West Pacific (up to +4 dam). In the subtropical zone in the east of the Pacific Ocean, geopotential on average was below normal by 6 dam. in May, mainly corresponded to the climate norm. Only in areas of intensive tropospheric ridges, it was located farther to the north than usual. The largest deviations were observed over Alaska, where on average for the month, they accounted for about 15°C. Over the North Urals The position of the planetary high-altitude frontal zone in May was located seven degrees north than usual.

Zonal and meridional circulation indices in general for hemisphere insignificantly differed from the norm. However, the zone transfer was significantly weakened in the high latitudes of II NSR (28%) and in temperate latitudes of III NSR (23%), meridional transfer was more intense in the II NSR and in the high latitudes of III NSR (24%).

All main centers of atmospheric action (CAA) are presented in the monthly averaged surface pressure field, but their position and intensity had a number of specific features. Instead of one center associated with the Icelandic depression, usually located on the southern coast of Greenland, two separate centers were noted. On the mean month map were noted two of its center instead of one, usually located on the southern coast of Greenland. One center, which was much deeper, located over the Norwegian Sea, and the other - over the Baffin Island. Because of this, in these areas, as well as on the Scandinavian Peninsula, the anomalies of mean monthly pressure reached -8 hPa. Negative pressure anomalies were noted throughout the European territory of Russia, where they averaged for month ranging from -7 hPa in the north to -4 hPa in the south. This pattern was caused by stormy cyclonic activity: Atlantic cyclones moved mainly over the northern seas of the Atlantic Ocean, and then - over European Russia. Cyclones brought heavy rainfall in Ireland, the UK, Scandinavia, the north and the center of European Russia; advection of cold air in their rear led to negative temperature anomalies. Promotion of the Atlantic cyclones to the east was often blocked by the ridges that were formed over Siberia, the Urals and European Russia. The most intensive they were over northern Siberia, so the greatest positive pressure anomalies on mean monthly map were located over the Taimyr Peninsula and reach 5 hPa. There were frequent changes of circulation last month over the European Russia. After passing through the cyclones and temperature lowering the ridges of high pressure were established after their cold fronts, the air temperature at the same time increased to very high values.

Center of Azores anticyclone located in the usual place, its pressure conform to the standards. However more intensive was the western ridge, which provided the anomalies of mean monthly pressure up to 6 hPa off the coast of the United States. As expected, the ridge of the Azores anticyclone dominated over Western and Central Europe in May, but the Atlantic cyclones influenced the weather in these areas less than usual, so the precipitation here was below norm.

Siberian anticyclone was still quite intense for May. All Eastern Siberia Under, where prevailed positive anomalies of mean monthly pressure, was under its influence. In the north, the anomalies reached 5 hPa. The ridges of the anticyclone often spread to the west to the Ural Mountains, and to the European Russia. As a result, in the north of the Urals and Siberia, fell little rain, the temperature here was much higher than normal. The West Atlantic cyclones often reached the south of Western Siberia and Kazakhstan, so precipitation here was more than the norm. At the same time over the south of the Far East formation of seasonal low-pressure center continued. Its position on the average monthly map corresponded to the climate and was observed over the Amur region, the intensity of it was even deeper than usual (anomaly for -4 hPa). The increased cyclonic activity caused abnormally high rainfall over the northeast China and south of the Far East.

In May, the formation of the monsoon depression began over Hindustan and Indochina, this depression was deeper in the north Indochina (pressure anomalies to -3 hPa), but the precipitation here was below norm. Abnormally large for May precipitation in some regions of India is connected with the ongoing active convection over the Bay of Bengal and the influence of tropical disturbances on the coast. The monsoon came to the southeast China. 2-3 monthly norm of precipitation fell in some places of the coast of the South China Sea.

Pacific CAA last May were quite unusual. Hawaiian anticyclone was shifted to the north, so that the pressure anomalies in the Gulf of Alaska in average for the month amounted to 9 hPa. Unusually intensive was its ridge over the center of the Pacific (anomaly for 3 hPa). Because of the displacement of the Hawaiian anticyclone to the north, the Aleutian Low has been significantly moved to the West, which had led to the formation of the area with negative pressure anomalies over the south of the Bering Sea (anomaly for -9 hPa). Stormy cyclonic activity over the Bering Sea has led to an excess of precipitation in Chukotka and the west Alaska.

Positive anomalies of pressure prevailed over the North American continent in May. Ridges spread from the Pacific Ocean and from the north to the central regions of Canada (the anomaly +4 .. +6 hPa), to the east of the continent they spread from the Atlantic (anomalies +3 .. + 4 hPa). Only in the southwest there was a trough connected with emerging California Low, however over the north of Mexico, where the center of this Low should be located, pressure on average per month was above normal by 6 hPa. Cyclone center on average monthly map was located in the north of the Gulf of California, which led to a negative pressure anomalies (-4 hPa) on the Pacific Coast. Thus, the northern and western regions of Canada most of the month was under the influence of anticyclones; they experienced precipitation deficit; the temperature here was abnormally high. Similar weather was observed on the Atlantic coast of the United States. Pacific cyclones gave their moisture reserves to the western and central regions of the United States, the highest precipitation anomalies were observed in the southwest of the country. The west of the USA was the most frequently exposed to the cold air advection in the rear of cyclones, which led to a negative temperature anomalies.

Also in May, it was observed characteristic for this month tornado. Tenth of May, the strongest F2 of the Fujita scale tornado was recorded in South Dakota. It has passed the path length of about 25 km, the width of the destruction strip in its path reached 400m. The most affected was city of Delmont, where the tornado damaged about 20 buildings. An unusual phenomenon was snowfall over the cold front, which formed the tornado. In Rapid City, South Dakota, fell 32cm of snow, in Denver, Colorado - 10cm. May 11, tornado brought destruction in the city of Van, Texas. According to media reports, 30% of city buildings were damaged.

Four tropical cyclones formed in the tropical zone of the northern hemisphere (the norm is 2.8).

Two cyclones formed in the western Pacific (norm for 1.1). Both were very intense and reached the supertyphoon stage, i.e. their wind speed exceeded 50 m / s. Typhoon "Noul" was very close to the coast of the island of Luzon (Philippines). Just at this time, it reached the peak of its activity: the wind speed at its center reached 53 m / s and the pressure dropped to 915 hPa. It became possible to avoid casualties only because of the fact that the northeast of this island is sparsely populated. Another typhoon, "Dolphin", passed at more eastern trajectory, it influenced the South Mariana Islands, where about 200 mm precipitation fell in just 12 hours, the wind speed reached 38 m / s. After passing through the Mariana Islands, cyclone amplified even more: its maximum wind speed reached 50 m / s, the minimum pressure amounted 925 hPa. It should be noted that the season of tropical cyclones in the western Pacific began very actively. Seven tropical cyclones has formed since the beginning of the year (norm for 4.8), five cyclone reached the stage of the typhoon, and three – the stage of the supertyphoon. The first tropical cyclone of the season formed in the Atlantic Ocean. In May, tropical cyclones form very rarely, the rate is only 0.1, i.e. once in ten years. Initially the cyclone was classified as a subtropical storm "Anya," but the next day it acquired the status of a tropical storm. Unusual for May was the shift of the cyclone to the land. National Hurricane Center of the US registered only eight cases, when tropical cyclone shifted to the land before June 1 for the period from 1900 to 2014. Cyclone "Anya" was shifted on the coast of North Carolina on May 10 in a strong tropical storm stage (maximum wind - 25 m / s).

Also, the season of tropical cyclones started in the eastern Pacific Ocean. There formed one cyclone (normal 0.7), named "Andres", which became the first superuraganom (maximum wind of 63 m / s, the minimum pressure - 938 hPa). It did not influence the land. Hydrometeorological Centre of Russia

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