Air Temperature

This May in Russia was extremely warm for the second year in succession. A year ago, the air temperature monthly-averaged over the entire territory of the country reached the absolute maximum for 130 years of regular meteorological observations. This year, the value was almost half a degree lower than the absolute maximum, but still higher than the normal one in most of the country. The only exceptions where this month was colder than usual were certain districts of the Pskov Region, and the vast areas around Baikal and further eastwards: the Trans-Baikal Territory, the Amur Region, parts of the Khabarovsk Territory, and Sakhalin. The highest positive anomalies (+4…6° and above) were observed in the areas from the Volga Region to the Pacific Ocean, including the Arctic region. This May was the warmest in the history of meteorological observations since 1891 in the Volga Region, and the second warmest in the Urals where the record-breaking result of the previous May remained unbeaten. The average air temperature in Siberia and in the north of the Far East entered the Top Ten of the highest values in the meteorological chronicle.
The weather in most of Russia was abnormally hot throughout the month. Sub-normal air temperature averages were only observed in the ETR in the first and third decades, and in the Trans-Baikal Territory, the Amur Region, Sakhalin and the south of Khabarovsk Territory in the third decade. In contrast, numerous daily temperature maxima were recorded in the Middle and South Urals, in the south of Western Siberia, on the Upper and Middle Volga, in the Russian North, in Central Russia, in the north-west and south of the country, in Yakutia and Chukotka, – for several days in a row sometimes. On the other hand, cold weather with frosts repeatedly returned to Central Russia and the south of the Urals in the first decade, to the south of Siberia, in the second, and to the north-west, in the third decade.
In total, spring 2021 was also very warm in Russia: its average temperature exceeded the normal value everywhere in the country. The excess was 2-3° and more in the Russian North, in the Volga Region, in the Urals, in Siberia and Yakutia, and in the north of the Far East.
In most of East Asia, the monthly-averaged air temperature was close to normal. In China, slight positive temperature anomalies were observed in general, but the weather was two or more degrees warmer than usual in a number of regions in the central and southern parts of the country. The monthly-averaged air temperature in China was among the Top Ten highest values in the history meteorological observations. The normal temperatures in some regions of Mongolia and Japan were also exceeded by 1-2°.
In the countries of South-East Asia, the temperature was approximately normal against a generally positive background of anomalies.
May was very cold in India: the monthly-averaged air temperature was below normal almost everywhere, two or more degrees below in the central part of the country. May 2021 became the third coldest since 1891, the start date of regular meteorological observations in India. The weather was even colder in May 1917 and May 1933 only.
Abnormal warmth prevailed in the Near and Middle East. The heat reached +40-45° and above on the Arabian Peninsula. The monthly-averaged air temperature exceeded the normal value by 2° and more everywhere save for the south of Arabia, or by 3-4° and more in a large area of the region.
A similar picture was observed in Central Asia where the normal values were exceeded by 2-5° and more. Numerous new temperature maxima were recorded in Kazakhstan: there, the thermometer readings rose above a +40° mark on some days.
Heat covered North Africa; as a result, this May became the warmest one in the history of meteorological observations in this region of the Globe. The record-breaking achievement of May 2017 was surpassed. Sometimes, the air heated above +40-44°. The normal monthly-averaged temperatures were exceeded by 2° or more in a significant part of the region, and by 4° or more in Algeria, Tunisia, Libya and Egypt.
Even though the thermometer readings rose above +30° on some days in Germany, Austria, the Czech Republic and Poland to produce new daily temperature maxima, the month in overall turned out to be colder than usual in most of the European continent. The above-normal monthly-averaged temperatures were only recorded in the south of the Balkans, in Greece, Spain and Portugal, and in the south-west of France. On May 12, an air temperature of +28° was observed in Finland, marking the earliest recording date of such a high value in the annual cycle.
May was cold in most of the USA and in the central and western provinces of Canada. The monthly-averaged temperature in the American states of Wyoming, Nevada, Utah, Idaho and Montana as well as in the Canadian provinces of Saskatchewan, British Columbia and Yukon was 2-3 or more degrees below normal. At the same time, the month in California, Arizona and New Mexico in the west of the United States and in Florida and partly in New England in the east was two or more degrees warmer in places. The situation was similar in the east and in the polar region of Canada, and in the US state of Alaska. The temperature in most of Mexico was above-normal as well. In the states of New Jersey, Tennessee and Alabama in the south-east of the USA and in Washington, the capital of the country, the air temperature rose above 33-34° in the third decade of May. Usually, this does not happen there before June.
The average May temperature in the Arctic exceeded the normal value by more than 2° and entered the Top Ten highest values in the history of meteorological observations.
As for the Northern Hemisphere in overall, the average May temperature was among the top three highest values since 1891, and the average temperature of spring, among the top five ones. The latter temperature was above-normal almost everywhere in Eurasia except for some parts of Europe and India, and excluding Alaska. This spring in China and North Africa was ranked as the 3rd or 4th warmest in the history of meteorological observations.
In Moscow, the average temperature in May was +14.3°, corresponding to an anomaly of +1.2°. Spring was about as much warmer than normal in the capital.

Ocean Surface Temperature

La Niña in the Pacific Ocean continued to weaken. The average SST anomaly in the La Niña zone was the same as when this phenomenon initiated, i.e., as in August, 2020. All negative anomalies In the equatorial zone of the Northern and Southern Hemispheres were lower than 1°.
The average SST anomaly of the Pacific Ocean in the Northern Hemisphere preserved its April level (+0.6°) identical to the one in May of the previous year. The anomalies of monthly-averaged SST at subtropical latitudes in the central part of the Ocean and at tropical latitudes in the west exceeded +1…2°. In addition to the equatorial zone, negative anomalies were also observed along the coast of Northern America, in the Sea of Okhotsk, and in the Bering Strait.
As for the Atlantic Ocean, its average SST anomaly in the Northern Hemisphere was the same as in the previous month (0.5°). Positive anomalies in excess of 1° were observed in the subtropics and along the coast of North America, while negative ones, at high latitudes on the border with the Arctic Ocean, and in the North Sea.


In the ETR, May that followed "wet" April was also profuse as to precipitation: its monthly totals were above-normal everywhere except for the Volga Region and the republics of the North Caucasus, and often amounted to 1.5-2.0 or more times the normal value, or even 2.5 or more times in the Leningrad and Pskov Regions in the North-West Federal District and in the Kaluga, Bryansk and Tula Regions in the Central Federal District. In St. Petersburg, this May was the rainiest one in the entire history of observations. Heavy rains during the month pounced upon many ETR regions. In the first decade, they came to Central Russia and to the North Caucasus (the Krasnodar Territory and the Republic of Adygeya), and brought record-breaking daily precipitation totals of up to 28-47 mm. In the second decade, the north-west of the country (the Leningrad and Pskov Regions, and the Republic of Karelia) suffered from lavish rainfalls. And in the third, the north-west (the Leningrad Region), the North Caucasus (the Republics of Adygeya, Dagestan and Kabardino-Balkaria, and the Stavropol Territory) and Central Russia were the victims again, along with Crimea now. Daily precipitation maxima were updated anew, with the rain intensity reaching 50 mm/day. In Simferopol, more than the normal monthly amount of rain fell for a single day.
In the Volga Federal District, the precipitation figures were normal or above-normal in the north, and normal or subnormal in the south. The latter was most spectacular in the Orenburg Region where the monthly precipitation totals were just one third of the normal value. A similar picture was observed in the Urals: normal or above-normal precipitation in the north, and very scarce in the south, e.g., less than 30% in the Chelyabinsk Region or less than 10% in the Kurgan Region. Snow was still falling in the north of the Urals.
Rains were rare guests in Siberia: their amounts were much less than normal everywhere except for the southern regions. In contrast, they were abundant in the south of the Krasnoyarsk Territory as well as in the Republics of Altai and Tyva where the normal figures were exceeded by 1.5-2.0 or more times, and up to 50-70 mm of rainwater accumulated for one night in certain places. Snowfalls were observed in the Baikal area.
This rainy belt extended further to the southern territories of the Far Eastern Federal District, namely, to the Republic of Buryatia, to the Trans-Baikal Territory and Amur Region, to the south of the Khabarovsk Territory, and to the Primorye Territory. There, the monthly precipitation totals exceeded 2.5-3.0 times the normal amounts in some locations. Snow was falling in the Trans-Baikal Territory and Amur Region. In the north of the Far East, the monthly precipitation quantities were less than normal.
Precipitation was generally subnormal in the central provinces of China, but its monthly totals significantly exceeded the normal amounts in the north, in the south-east and especially in the west of the country. Approximately normal amounts went to Korea, and to Japan where heavy showers brought up to 120-180 mm of rainwater per day in the west of the country and established new maxima of daily precipitation. In South Korea, snowfalls were observed in May for the fist time in 22 years. The depth of the snow cover reached 15 cm.
In most countries of South-East Asia, the weather in May was dry. As a rule, the monthly precipitation totals amounted to half the normal value or less. Malaysia and Indonesia were the only countries where the normal figures were reached, or even exceeded in some locations: there, heavy downpours caused floods and landslides. The floodwater depth exceeded 50 cm. In a number of meteorological stations, the precipitation totals recorded for several days exceeded the normal monthly amounts.
Rains in the countries of South Asia inundated India, Sri Lanka and Pakistan (its central regions). The monthly precipitation totals were 2-4 times the normal amounts. More than 200 mm of rainwater poured on the western coast of India for one day. New daily maxima of precipitation amounts were set. The Republic of Sri Lanka received even more precipitation: more than 300 mm per day.
Dry weather with very scant precipitation prevailed in Kazakhstan and in the countries of Central Asia. Heavy rains fell in the north of Afghanistan only; they caused floods that killed people and livestock.
In Iran, occasional torrential rains in otherwise dry weather conditions that settled this May caused floods that led to fatalities. The weather in the Middle East was even drier: not a drop of rain fell there in some regions. At the same time, heavy rains occurred in Oman and Yemen at the beginning of the month, ending up in large-scale floods that affected people, with the residents of Sana'a, the capital of Yemen, among them.
Most of North Africa received no rains at all in May. The exception was the north of Algeria which was hit by heavy downpours causing floods in the first decade. There, the normal monthly precipitation amounts were exceeded by 1.5-2.0 times in a number of places. In the mean time, rains came to Ethiopia and Somalia, also leading to floods and bringing more than 80 mm of rain moisture per day. Dry weather in North Africa sharply contrasted with the one in the south-west region where the monthly precipitation totals were either normal or above-normal..
In Europe, much precipitation was recorded save for the Iberian Peninsula as well as for the most of the Balkans and of the southern regions of the "Italian boot." The normal precipitation figures were exceeded by 2-3 times in the Baltic countries and in the Great Britain, and by 1.5 times in many countries of Central Europe. Snowfalls that came to the continent at the beginning of May covered Finland, Lithuania and Scotland. The snow cover reached 6 cm in its depth. Heavy rains that fell in Latvia, Switzerland and the south-east of France did not stop for several days. In Lyon, a new maximum of daily precipitation equal to 140 mm was set. Rains flooded Slovakia, Romania, Bulgaria, the north of Italy and the Scandinavian countries, viz., Sweden and Finland. Up to 50 mm of daily precipitation accumulated in certain places.
The Pacific coast of the USA and the territories adjacent to it received virtually no precipitation in May. A state of emergency was declared due to the draught. The same picture was observed in the south-east from North Carolina to Florida. In the rest of the country, precipitation was quite noticeable: either normal, or more than that. Abundant rainfalls took place across the south of the USA, bringing 380 mm of rainfall in twelve hours in Louisiana. Severe floods occurred in Texas, Louisiana, Mississippi, Arkansas and Oklahoma. Heavy rain with hail descended upon Pennsylvania, and upon Quebec in Canada where the precipitation amounts were normal in the south of the country and almost completely absent in the northern territories. In Mexico, the drought which persevered in the north of the country contrasted with plentiful rains in the central regions.
In Moscow, 94 mm of atmospheric moisture fell in May, amounting to 184% of the normal quantity. Recall that the precipitation totals in May 2020 thrice exceeded their normal values. New daily maxima of precipitation totals were repeatedly set during this month, with the total monthly amount in spring 2021 being as large as 221 mm. This is the fifth result in the meteorological annals of the capital, yielding to the ones observed in 1976 (the highest value equal to 244 mm), 2020, 2013 and 1998 only.