The key weather and climate features in the northern hemisphere in April 2015
  Climate The key weather and climate features in the northern hemisphere in April 2015

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

Air temperature

The abnormal heat was recorded during the whole month in such parts of Russia as Siberia, the Urals and the Arctic Region. Throughout the month, mean decadal air temperatures exceeded the norm by 4-10 ºC. The new daily temperature maxima were registered in the North Urals, in Novaya Zemlya, in the Irkutsk Region and in the Trans-Baikal Region. The climate spring came to the Russian North three weeks earlier than usual. Yenisei broke-up in the upper reaches of the river two weeks earlier than the average.

To the west and the east of the region, in the European part of Russia and in the Far East, as it usually happens in the spring heat and cold replaced each other in the frequent manner. Thus, to the west of the Urals, the heat of the first decade of the month with the daily temperature maxima was replaced by the abnormal cold in the second decade. During that time, there were recorded the night frosts for -3…-5ºC. They were recorded not only in the Central Russia, but also in the south, where the spring fieldwork had already begun. At the end of the month, the abnormal heat returned to the Central Russia. New daily air temperature maxima were recorded in Vologda, Kostroma, Tver, Nizhy Novgorod and other places. Such a confrontation of heat and cold has led to the fact that the mean month air temperature was about normal. Only in the Crimean Federal District, Southern Federal District and in the south of the Volga Federal District the month was colder than usual, while in the north of the country (Murmansk Region, Arkhangelsk Region, Komi Republic, and Nenets Autonomous Region) it was warmer.


The same situation took place in the Far East. The cold of the first decade. In Yakutia and in Chukotka were 35 degrees of frost. Then, except for the northeast, in which the warm weather came only in the end of the month, the frost changed to the warm. In Primorye to the end of the month the air warmed up to +34ºC. The new absolute air temperature maxima for the April were recorded in Vladivostok - +27.7ºC. As the result, there, so as in the west of the country, mean month air temperature were close to normal. Only in the central parts of the Khabarovsk Region, Sakhalin, Kamchatka and partly in Kolyma the month was colder than usual.


Overall, mean temperature in April 2015 in Russia was above the norm. However, it cannot be assigned to the list of the warmest Aprils – it is outside of the top ten warmest Aprils since the beginning of the measurements in 1891. The mean temperature for the period from January to April 2015 remains the warmest in the history and exceed the norm by 3ºC, so as it was in the end of the March.

In China, in general, the mean air temperature was close to normal. However, in the north and in the northeast of the country, as well as in the neighboring Korea and Japan, the temperature exceeded the norm by 2-3ºC, in Mongolia – by 5ºC. Whereas in the west of the country in Qinghai, Sichuan, Yunnan provinces and in the Tibet Autonomous Region sometimes it was much colder than usual.

In most parts of India was mentioned cold weather that absolutely do not match with premonsoon. In the central regions, mean month air temperature for the month were lower than a normal by 1-2ºC. Only in the north of the country the air temperature corresponded to the time of the year. The thermometers rise above +40ºC.

The same weather were recorded in the neighboring Pakistan. There in general for the month the weather was above the normal for 1-2ºC. Record heat was observed in the countries of the Central Asia. In Kazakhstan, in the first decade of the month the air heated to +30ºC, in Turkmenistan – to +35ºC. In Ashkhabad on April 23 was recorded the absolute air temperature maxima for the month for +39.4ºC. South winds brought the early summer from Iran to the Central Asia. However, at the end of the month north winds made the weather twenty degree colder.

The hot air was formed above the desserts of Arabia and highlands of Iran. In average for a month, it was 2-4ºC warmer than normal. At the same time, in the Mediterranean countries of the Middle East and in the Caucasus last month became cooler than normal or near normal. In Turkey and in Georgia mean month temperature anomalies were recorded at the level of -1.0…-1.5ºC.

North Africa in April 2015 can be divided into two parts: abnormally cold east and abnormally warm west. Thus, while in Egypt, Chad and Sudan mean month air temperature was below normal by 1ºC and in Niger by 1.5-2.0ºC, in Morocco, Algeria, Tunis, Mauritania and Mali it was above the normal by 2-4ºC. In addition, mean month air temperature was insignificantly higher than norm across the Atlantic coast.

The warm weather of the West Africa reached Western Europe. The mean air temperature in Spain, Portugal, France and Switzerland exceeded the norm by 2-3ºC. In Bordeaux was set the anomaly of +3.3ºC, in Madrid and Paris of +2.5ºC, in Geneva of +2.3ºC. The warm weather in the Arctic particularly moved to the Northern Europe. In the Nordic countries, anomalies were approximately the same as they were in the west of the continent. Peak daily maxima were recorded in Ukraine. At the same time, in the southeast Europe in Greece, Romania, different Balkan countries and in the southwest of Ukraine the month was cool. Mean temperatures there were below normal.

Abnormally warm weather was recorded in most parts of the USA. In the southwest of the country in California and Arizona, as well as in the southeast of the country in Alabama, Florida, Mississippi, Georgia, South and North Carolina the air in average warmed 2-3ºC above normal. Almost the same data were mentioned in Alaska and neighboring provinces of Canada (Yukon and British Columbia). In contrast, most part of the month was under the domination of the cold. In Quebec, Newfoundland, Labrador Peninsula and Baffin Island in April the weather was colder than usual by 1-2ºC. Cold air spread far to the east to the ocean and captured northwest Atlantic waters between Canada, Greenland and Iceland.

In the Arctic, mean air temperature exceeded the norm by 3ºC and more. Excluding the northeast territories of Canada, everywhere there was mentioned abnormal warm weather. Especially high anomalies (more than 10ºC) were formed near with the Franz Josef Land. Average area of the polar ice caps in April was 14.0 million sq. km, which is the second minimum for the month in the history if satellite observations. The absolute minimum for April was recorded in 2007.

In spite the fact that April 2015 has not reached the record value, mean temperature in the northern hemisphere at the end of the first four months of the year has the highest rank.

In Moscow, the mean temperature of April was +4.1ºC, which was for 0.3ºC higher than norm. On April 12, the new daily air temperature maxima was recorded in the capital of Russia.


The temperature of the ocean surface

It is noticeable that the average surface temperature of the Pacific Ocean in the Northern Hemisphere was above normal. Such high temperature in April was fixed 10 years ago. The equatorial and tropical latitudes in the eastern part of the ocean near the coast of America SST anomaly were over + 1º. Below-normal temperatures occurred only in the central part of the temperate latitudes and in the west of the ocean along the coast of Asia, as well as in the north of the Bering Sea. In the East China sea, the Yellow, the Japan and the Okhotsk seas and near the eastern coast of  the Hokkaido island SST anomaly reached -1º. The weak El Niño, that has been existing on its face since the end of last year, hasn`t had any noticeable impact on the atmospheric processes in the East of South America, and in the West of Indonesia and Australia yet. At the end of the month there were signs of a response from the atmosphere to the growing ocean heat. So that in the future the strengthening of El Niño may be expected. The average temperature of the surface of the Atlantic Ocean in the Northern Hemisphere was normal. Abnormally cold eastern and northern water areas opposed to the heat in the west. The temperature in the Gulf Stream is still above normal, however, it is not so noticeable as  it was in the previous months. Moreover, in its continuation - the North Atlantic flow – we can see sufficiently large negative SST anomaly (up to -1º). Here in Newfoundland area and in the south of Greenland, there were major negative air temperature anomalies (up to -2º). The water temperature in the Gulf of Mexico was noticeably higher than normal.



European Russia in April almost everywhere received normal precipitation and above. 1,5 – 2 norms went  to the Republic of Karelia in the North-West Federal District; Ryazan, Tambov, Voronezh regions in the Central Federal District; Republic of Mari El, Tatarstan, Bashkortostan, Udmurtia, Nizhny Novgorod, Ulyanovsk, Samara, Orenburg regions in the Volga Federal District; Republic of Adygea and Kalmykia, Karachay-Cherkessia, Krasnodar Krai, Volgograd, Astrakhan and Rostov regions  in the Southern Federal District. Sometimes it were not only rains, but also snowfalls. Snow fell in the Stavropol region on April 10, for a day was 70% of the monthly norm of precipitation. Then the white blanket, which thickness reached 20 cm, covered foothills of the Caucasus. Even in the third week of the month in the European territory of Russia there were heavy snowfalls. One of the snowfall lasted more than a day in the Volga region and brought the monthly norm of precipitation.

Beyond the Urals the rainfall was close to norm, but still it is possible to note some areas, where there were significantly more than it (about 1.5 times), or - less. The first group includes southern Siberia: Altai Republic, Tomsk region; the second - the polar areas and Trans-Baikal. In the Far East, especially in the northern regions, April mostly is a winter month. So, even at the end of the month, no one was surprised by heavy snowfalls in Sakhalin and Magadan region. Mainly in the Far East for a month there were norm of the precipitation, and only in the Chukotka region, as well as throughout the north of the country, the precipitation turned out to be small - about 50% of normal. In China in April were the rains. That is why everywhere there the precipitations exceeded the norm, 2-3 time in some places. Especially heavy rainfall took place in the beginning of the month. They have led to numerous floods in the central part of the country. In the Henan and Hubei provinces, they suffered more than 1.5 million people. Tens of thousands of hectares of farmland were flooded. At the same time rains took place in Japan. In the north of the country, there was the snow.

Surprisingly rainy weather was in India. Despite the fact that the summer monsoon season has not started yet, torrential downpours and hail passed over the country. Up to 100mm of heavenly moisture dropped out during the day. In central, eastern and southern provinces of the country, as well as in the neighboring Nepal and Bangladesh monthly precipitation exceeded the norm by 3-4 times.

A lot of rain was in the eastern part of Pakistan. In the northeast of the country, they fell about 2 times more than the norm, while in the southwest - in the province of Gujarat – there was not rain at all. There were a lot of rains over the steppes of Kazakhstan, especially in the west of the country. Дожди напоили степи Казахстана, особенно на западе страны, in the republics of Central Asia, as well as in neighboring Afghanistan, there was little rain.

Middle East left in April was left without precipitation. Only in the Caucasus and in some places in Turkey there were heavy rains. During the day, fell out up to 30 mm of precipitation.

There was a dry weather in Africa. The rate of precipitation was recorded only in some coastal states. There was little precipitation in Europe. The norm was recorded in the Nordic and Baltic countries, partly in the Ukraine, the individual area of the Balkan States and in France. In early April, in Central Europe (Czech Republic, Slovakia, and Austria) there was heavy snowfall and snowpack returned for some time.

The abundance of rainfall was observed in the United States except California and border territories with Canada. In most of the country, monthly norm of precipitation was exceeded by 1.5-2.0 times. Especially a lot of rain fell on the Gulf of Mexico. Over the last month, they have made here 2-3 norms. Catastrophic drought continues in California. In April, here precipitation was significantly less than the norm, and in some places, there were not rains at all. The state imposes restrictions on water consumption. Experts believe that if in the coming months the rain still would not coming, underground reserves would be completely depleted of moisture, and then people would have to bring water to the state in tankers. The drought persists in neighboring island states of the West Indies. There were less than a half of the norm of the precipitations during the last 4 months on Cuba.

Continental neighbors of the United States Mexico and Canada are in different situations. If Mexico not for the first month is poured by rain and in April rainfall here has fallen about 3-4 times more than the norm, Canada experienced its deficit, especially the southwestern and northeastern territories of the country.

In Moscow, the amount of precipitation for the month was 44 mm, which exactly corresponds to the norm.


Atmospheric Circulation


There were the reorganization of the circulation to the summer mode in the upper stratosphere (at the level of AT-10) in April. Stratospheric anticyclone over the Canadian Arctic was quite intensive in the beginning of April, however deep cyclone did not let him to take a place at the North Pole. Only at the end of the second decade, significantly weakened cyclone gave way to the anticyclone. Restructuring of the stratospheric circulation was complete by April 20.


In the equatorial stratosphere the eastern phase of the winds of the quasi-biennial cycle were persisted. However, at the time the tendency of its weakening had already begun. In the middle troposphere (at the level of AT-500), averaged over the month geopotential field, in general, consisted the climate. However, troughs and ridges were smoother: anomalies of both signs were quite high. Polar vortex had one center that had almost permanently located during the month above the Baffin sea, where the anomalies of geopotential amounted -7 dam. The second climate center above Taimyr during the month on the mean month charts was absent. However, it was well expressed on the mean decade charts in the second and the third decades of April. It was located to the West far more than usual – on the coast of the Kara Sea or above Novaya Zemlya. The deep tropospheric trough and connected to it extensive zones of negative anomalies of the geopotential located over eastern Canada and  western Atlantic (up to -4 dam over Hudson Bay and up to -6 dam near Newfoundland) and over Eastern Europe (up to -9 dam over European territory of Russia). A large area of negative anomalies of the geopotential was also connected to a forked trough that occupied the eastern Siberia, Russian Far East and the entire North Pacific. The greatest anomalies in this region (up to -9 dam) formed over the Gulf of Alaska. Reduced geopotential in the eastern subtropics of the Pacific Ocean (anomalies up to -3 near Peninsula CA) in which polar troughs always extended during the month also needs to be mentioned.

Nevertheless, in the geopotential field was mentioned the dominance of the positive anomalies. During the first two decades of the month, intensive ridges were formed over the Western Europe and the eastern Atlantic, where the mean month anomalies showed the degree of +12 dam. In the western Siberia geopotential was significantly higher than norm. In the first decade of April, strong tropospheric ridges regularly spread from the Middle Asia and Mongolia to the coast of the Kara Sea, which led to the formation of the anomalies in the north of Mongolia up to +8 dam and up to +14 dam over Taimyr. In the second decade of April, over the territory of Taimyr and Severnaya Zemlya existed independed tropospheric anticyclone, which was the reason of the destruction of the normal regime of the circulation over the region when the area of low pressure situated over Taimyr. The geopotential was also significantly higher than norm on pole, which in the first two decades of the month was influenced by the Siberian and Canadian ridges. As a result mean month anomaly in Canadian Arctic was recorded at the level of +9 dam.  High geopotential was mentioned almost everywhere in subtropics: anomalies up to +12 dam were formed in the north of Africa, up to +8 dam on the Arabian peninsula, from +2 up to +6 dam – over the eastern part of Eurasia and the Pacific Ocean, up to +4 dam near Bermuda.

In general, the position of high altitude frontal zone in April was close to climatic. Only in the areas of deep tropospheric troughs, it was located a bit south than usual. The largest deviations over the eastern Europe didn’t exceed 7°C.

In general for the hemisphere and for the separate natural synoptic regions (NSR), the difference with the norm of zonal and meridional indices was not that mentionable. Only in the temperate latitudes III NSR meridional transport was more intense than usual by 21%.

During the month, all the atmospheric centers of action of the average surface pressure field were well expressed. In Atlantic pair of atmospheric centers of action was the dominance of Azores anticyclone. During the first two decades of the month, its eastern ridges were very active; their activity was one of the main factors of the formation of anticyclones in the Western Europe, which provided dry and warm weather in the region. Even with the fact of the rapid cyclonic activity over the region in the third decade of the month, an independent anticyclone with the center in the north of France was mentioned on average monthly map. Pressure anomalies in the Western and Central Europe and in the northern Africa accounted for +5…+7 hPa. In most of these areas was a serious shortage of rainfall. Just to the west of Spain, in France, in the alpine countries and in central Italy monthly precipitation totals were near normal or slightly higher. However, most of them dropped out, mainly in the third decade of April. In the Icelandic Low, western center had a normal position and depth, the eastern one which was located near the northern coast of Scandinavia, was much more intensive than usual and had the pressure in the center 5 hPa below the norm. Atlantic cyclones were active during the month, however in the first half they were mostly influencing the north and the west of Europe and the western part of  West Siberia: mean month pressure anomalies in these regions amounted -9 hPa in the east of the European territory of Russia and -5 hpa in the Caucasus. Despite the north of the European territory of Russia, in April all the listed territories had a considerable excess of the rainfall. In Greece, Turkey, in the Caucasus and in the south of the European territory of Russia April was colder than usual. However, negative temperature anomalies were small. In most of Europe, the temperature background was normal. Under the influence of the warm anticyclones, positive temperature anomalies were generated in Western Europe and North Africa. Regular warm advection from the south have significantly increased average temperatures in the northern part of Scandinavia and northern European Russia.

Siberian anticyclone was very intense in the first decade of April. However, it was dismissed to the north, where it actively interacted with the polar anticyclone, which was abnormally intensive too. As a result, on the coast of the Laptev Sea average monthly pressure anomalies amounted to 5 hPa. Powerful advection from the south along the western periphery of the anticyclone resulted the generation of the large positive temperature anomalies over the entire area of Western Siberia, especially, in the northern regions over the Kara Sea and the Franz Joseph Land. In the second decade of April, the Siberian maximum sharply weakened and divided. Its northern part has shifted to the east (in Chukotka and the Sea of Okhotsk) and South - west Mongolia. In the third decade, the anticyclone absolutely disappeared. On the mean month map, it was located in the eastern Kazakhstan and looked a little weak in the its northern and western parts: pressure anomalies for -2…-4 hPa. The Atlantic cyclones hosted in Siberia throughout the second and the third decade of April. Mostly, they shifted to the central regions. In connection with this, substantial excess rainfall was observed in almost the entire southern half of Siberia, except for the Trans-Baikal. In the first half of the month active cyclogenesis took place in Central Asia, in the second half of the month it took place in northeastern China. In onnection with this, the monthly precipitation norm was significantly exceeded in northern Kazakhstan, in the north of Afghanistan, in some Central Asian republics, as well as in the northwestern, central and eastern provinces of China. Stormy cyclonic activity in the east of the Eurasia contributed to the formation on the mean month map of the seasonal low-pressure centers over the northeast of China. Nevertheless, it was weaker than usual: pressure anomalies amounted +1…+3 hPa.

Over Hindustan and Indochina in April began the formation of the monsoon depression, which was more active over the West India and the Arabian Sea (pressure anomalies up to -2 hPa).  The high rainfall in India and in the north of Indochina, which is unusual for April, was connected with the turbulent convection over the Bay of Bengal and the output of several tropical disturbances on its coast.

Atmospheric centers of action in Pacific in the past April were very active. Hawaiian anticyclone was close to normal, but it was harder than usual: pressure anomalies near the center amounted to +4 hPa. Its ridges continuously extended to the west and contributed to the formation of anticyclones in the western and central Pacific Ocean, where pressure anomalies for the month amounted to +2…+6 hPa. That is why the western part of the Aleutian Low was mostly weakened. The polar anticyclones also influenced this process. The pressure in the eastern sector of Russian Arctic and in the western sector of Canadian Arctic because of them was higher than norm (anomalies up to +5 hPa over the Laptev Sea). However, the center of the eastern Aleutian depression, dislocated to the southwestern tip of Alaska, was very deep: pressure anomalies near the center amounted to -7 hPa in western Alaska - -8 hPa. Pacific cyclones were deep and active in the first two decades of April. They influenced mainly western provinces of Canada, where in April was a high level of rainfall and the temperature was significantly higher than normal because of the warm advection in the southern sector of the cyclone. Fronts of cyclones that ran south through the West (pressure anomalies to -3 hPa) and Midwest of the United States sharpened, they repeatedly caused heavy showers, thunderstorms and hail in the central states. On April 9 sixteen tornadoes were recorded in Iowa, Missouri, Illinois, Oklahoma; some of them had a category F4 on the Fujita scale.  Moreover, there was hail to 7cm in diameter. The tornadoes caused very strong destructions in Oklahoma, which also caused some deaths. Rapid cold falls and its interaction with the warm and moist air of the gulf of Mexico caused cyclogenesis in the southern and southwestern parts of the United States. As a result, much more than normal precipitation fell in the southern states and the northern half of Mexico. In Texas and Louisiana flooding, severe thunderstorms, hail and separate tornadoes were recorded many times. The southern cyclones that shifted to the northeast brought to the eastern United States heavy rains, there the monthly precipitation norm were also significantly exceeded. The temperature in most parts of the country conformed to the standards. Warmer than usual was only in the southeastern and some central regions, where tropical air of the warm sectors of cyclones arrived in the first half of the month, and where in the second half of April was the domination of the anticyclones weather. Much colder than usual in April was in eastern Canada, particularly in Newfoundland. The weather there has been varied, mostly cyclonic (anomalies to -5 hPa over Hudson Bay), but anyway Nord Stream dominated at cold rear of cyclones or at the eastern periphery of the anticyclones. On the shores of Hudson Bay in connection with the active cyclonic activity, the weather was rainy.

In the tropical zone of the northern hemisphere, in the west of the Pacific Ocean, in April there was a tropical cyclone at a rate of 0.8. The cyclone was weak and existed for a while in a long distance from the land.

In the tropical zone of the southern hemisphere in April were formed four cyclones (the norm is 2.5). One of the cyclones originated south to the Solomon Islands in the Pacific Ocean, got through the islands of Vanuatu and filled before reaching New Caledonia. maximum winds there did not exceed 30 m / s, so it didn’t cause the serious damages. In the Indian Ocean in April there were 3 tropical cyclone at a rate of 1.7. All cyclones were very intense, but only one of them, «QUANG», was dangerous. It was the most intensive cyclone in April (рmin – 945 mb, Vmax – 55 m / s). It appeared not far from the northwest coast of Australia. By shifting to the southeast, the cyclone on May 1 came to the west coast of Australia. However, just before the landfall it rapidly weakened and quickly filled over the coast. It only caused winds up to 30 m / s and heavy rains.

Hydrometcentre of Russia

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