Air Temperature
The first two decades of April were abnormally warm in the ETR. During the second one, the decade-averaged temperatures exceeded their normal values by 4-6°. In the North Caucasus, the air warmed up to +30° sometimes. New daily temperature maxima were recorded in Central Russia, as well as the Russian North where the daily-averaged temperature never dropped below the normal value on any of the twenty days. Yet, the weather became cold in the third decade: its average temperatures everywhere in the ETR save for the Arctic territories were subnormal, down to 2-3 or more degrees below the normal values in some places. Even in the Volgograd and Rostov Regions in the south, April ended up with occasional night frosts.
In the Urals and in Siberia, anomalous warmth with the normal average monthly figures exceeded by 4-7° and more was steadily observed in the north only, whereas in the southern areas, the weather was more volatile. For example, the record-breaking warmth in the Irkutsk Region alternated with the record-breaking cold in Altai and in the south of Western Siberia.
Such volatility was even more noticeable in the Far East. While the temperature anomalies from Taimyr to Chukotka reached -2…-5° in the first decade, the weather in this area became as much as 2-7° warmer than usual in the second and third decades. Unprecedented warmth at this time came to the northern regions of Yakutia and to Chukotka. There, new maxima of daily temperatures were recorded in bulk. The temperature background in the rest territory of the Far East was more stable during the month: in each decade, the average temperature fluctuated around its normal value and did not exhibit large anomalies. The only exceptions were Kamchatka and Primorye where the weather was 2-3° warmer than usual in the first decade, and the Amur Region or south regions of the Khabarovsk Territory where the anomalies turned out to be negative (-1…-3°) in the second decade.
The monthly-averaged air temperature in Russia was higher than normal everywhere apart from Crimea and the southern islands of the Kuril ridge, by 4-6° in the north of the Urals and Siberia, and on the Arctic islands. Its April value averaged over the whole Russian territory entered the second ten of the highest ones recorded since the start of meteorological observations in the country, i.e., since 1891. The monthly-averaged temperatures in individual federal districts were also outside the Top Ten of the highest-ranked values, with the exception of the North-West Federal District.
In most of China, the average temperature in April was about normal. Its value was noticeably higher in the north-east of the country only and in neighbouring Mongolia and Korea, by two or more degrees in certain locations. In Hong-Kong, a new absolute maximum of April temperature was established.
In major part of South-East Asia, the air temperature was close to normal. The same was true for India, while in Pakistan, the air temperature background was shifted up to result in +2…3° or higher anomalies in the west of the country.
The heat which descended upon the countries of Near and Middle East and of Central Asia was quite summer-like. There, the normal monthly-averaged values of air temperature were exceeded by 2-4° or more. Ever hottest air spread over Kazakhstan and the republics of Central Asia at the end of the month. New temperature maxima, remarkably, monthly in addition to daily ones, were recorded in Kazakhstan (Ust-Kanemogorsk), Uzbekistan (Fergana and Samarkand), Tajikistan (Dushanbe), Kyrgyzstan (Bishkek) and Turkmenistan (Ashgabat). Yet on some days of April, cold Arctic air reached there to set up new temperature minima in these regions.
Abnormally hot weather settled in South Africa, with the anomalies of monthly-averaged temperatures up to +2…4° or more in a number of countries. The thermometer readings rose above +40° on some days, and the average temperature of this April hit the Top Five of highest values in the entire history of meteorological observations.
At the end of March, air temperature maxima were overridden in many European countries. But the weather turned cold at the beginning of April already and remained cold at least until the middle of the month. In London, the air temperature dropped down to -2°, and in Scotland, new daily temperature minima were recorded. The same happened in France where the temperatures decreased to -7°. Colds as low as -5° were observed in Spain, while in the Balkan mountain regions, air temperatures of -15…-20° were recorded. The average temperature of April was subnormal all over Central Europe, and in the south-east of the continent, and was above the normal value solely in the far west (Portugal and Spain), in the east (Ukraine, Belarus and the Baltic countries) and in Scandinavia. According to meteorological observations, April 2021 was the second coldest since 1917 in Germany, and the coldest one since 1922 in England. As for the entire continent, it was the coldest April in the 21st century.
In Canada, abnormally warm weather was observed in the north and the east of the country. The anomalies of monthly-averaged air temperatures were as high as +4…+6° in the Arctic regions, and +2…4° in Quebec, Nova Scotia, New Brunswick and partly Ontario provinces in the east. The monthly averages in the west of the country were roughly normal, slightly higher in some locations and slightly lower in the others.
A similar picture was observed in the United States, with the difference that the weather was warmer than usual in the west, from California to Washington, and in the north-east, from Virginia to the Great Lakes and the Canadian border (with anomalies up to +2° and more). And, just like as in Canada, the temperature conditions in the rest territories were close to normal. Likewise, they slightly deviated to higher or lower degrees in some or other places.
In most of Mexico and in the Central American countries below it, the air temperature was above the normal value.
The average temperature of April in the Northern Hemisphere as a whole was last among the Top Five of highest values in the history of meteorological observations, i.e., since 1891.
In Moscow, the monthly-averaged temperature in April was +7.5°, with the anomaly of +1.7°. New daily temperature maxima were recorded several times in the first half of the month.
Ocean Surface Temperature
La Niña in the Pacific Ocean continued to degrade. Negative anomalies exceeding 1° were no longer observed in the Northern Hemisphere, while in the Southern Hemisphere, they were present along the coast of South America only, up to about 10-12° S. The area occupied by negative anomalies shrunk in both hemispheres.
The average SST anomaly of the Pacific Ocean in the Northern Hemisphere remained the same. In subtropical latitudes, the SST anomalies exceeded +1° over a large part of the water body and reached +2° in some places. Negative SST anomalies took place in the equatorial zone (La Niña), along the coast of North America, as well as in the Sea of Okhotsk and its adjacent water area of the Ocean.
The average SST anomaly of the Atlantic Ocean in the Northern Hemisphere increased noticeably. Most of the water body was occupied by positive anomalies that exceeded +1° of coasts of North America and North Africa in certain locations. Negative monthly-averaged SST anomalies were recorded in the north along the Greenland coast, in the North Sea and at the junction with the waters of the Arctic basin. The water temperature in the Black Sea and in the east of the Mediterranean Sea was significantly higher than normal (by 1° or more).
April in the ETR proved to be really "wet." The normal monthly precipitation totals were either reached in almost all constituent territories of the Federation, or exceeded by 1.5-2.0 or more times in many of them. Subnormal precipitation was observed in the Republic of Komi, in the Kaliningrad Region and in parts of the North Caucasian Federal District (Kabardino-Balkaria, Chechnya and Dagestan) only. In the second decade, heavy rains fell in the Krasnodar Territory (up to 20 mm of precipitation per day). As for the Central Russia, the major amount of rainfall, often with sleet, was measured in the third decade: up to 20 mm of precipitation fell during the night, sometimes even creating a new snow cover. In the south of Moscow region, it reached 17 mm on April 26. It was the latest date when a new temporary snow cover formed in the 21st century.
A shortage of precipitation was observed in the Ural region, as well as in most of Siberia where the normal precipitation totals were only recorded in the south of the Krasnoyarsk Territory, in the republics of Tyva and Altai, and in the north (in Taimyr and Evenkiya). In the middle and at the end of the month, winter snowfalls returned several times to the southern regions of Siberia (the south of the Krasnoyarsk Territory and the republics of Khakassia and Tyva).
The Far East excluding the Primorye received abundant precipitation. The normal amounts were exceeded by 1.5-2.0 times in Kamchatka, in the east of Yakutia, in the Magadan Region and in the north of the Khabarovsk Territory. In Kamchatka and Chukotka, new record-breaking daily precipitation totals were measured. Heavy snowfalls were observed on Sakhalin, in the Khabarovsk Territory and in the Amur Region.
In most of China, the weather was dry. The quantities of precipitation were normal or slightly increased in the Yellow River Valley only, or in the south-east provinces of Zhengjiang and Jiangxi. The above-normal precipitation was also observed in the north of the Korean Peninsula and in Japan, but the figures were especially large in Mongolia where the monthly totals were exceeded by 2-4 or more times.
A lot of precipitation fell in the countries of South-East Asia where the normal values were exceeded almost everywhere: moreover, by 2-3 times or more in a significant part. Pelting rains caused floods in the north of Vietnam and in Indonesia. In Singapore, more than 90% of the normal monthly amount of precipitation fell in just three hours. This was one of the highest figures recorded in the last forty years.
In most India and Pakistan, precipitation was ether altogether absent, or very scarce. Yet, it caused much trouble in some areas. Up to 100-150 mm of rainwater fell in a couple of days in the south of India and in neighbouring Sri Lanka: this is much greater than the normal monthly value. A snowfall in the north of the country and in Pakistan nearby resulted in severe harm to blossoming fruit trees. There, the monthly precipitation totals were about normal.
The weather was dry in the Near and Middle East. No precipitation at all was observed in many regions. The more surprising was that the sand dunes in Saudi Arabia were covered with a white blanket, however, consisting of solid grains of hail rather than flaky snow. In the central regions of Turkey, the depth of freshly fallen snow reached 40 cm in some locations.
In April, almost no precipitation was observed in North Africa. The amounts were sufficient in the countries of the Gulf of Guinea only.
In Central Asia, the precipitation quantities were normal or somewhere increased in the north-west of Kazakhstan only, but meagre in the rest of the region, with zero amounts recorded in places. A severe drought took place in Turkmenistan where only 2-4% of the normal monthly figure was accumulated. In Kazakhstan, snow was falling in certain locations.
In Europe, snowfalls were also observed during April in Germany, Slovenia, Croatia, Czechia, Belgium, Hungary, Romania, Sweden, Ukraine and even in warmth-pampered Majorca. Freshly fallen snow that covered the ground was up to 10-30 cm deep. In Majorca, snow in April fell just for the fourth time in the entire history of observations. This April became one of the snowiest in Germany over the past 25 years. In the UK, heavy downpours caused a landslide never seen in the country for more than sixty years. Yet, the monthly precipitation totals were subnormal in most of Europe, with the normal or above-normal amounts observed only in some regions of Ukraine, Belarus, Slovakia, Hungary, the Balkan countries, Spain and Portugal. In the latter two countries, the normal figures were exceeded by 1.5-2.0 times in places.
Much precipitation went to the central and northern territories of Canada, amounting to twice the normal value or more in places. The precipitation amounts were close to or greater than normal along the Atlantic coast and, conversely, very scarce along the Pacific coast. In most of the US territory, the observed precipitation was close to the normal value everywhere excluding the west of the country where it was much less than that. This April entered the Top Five driest for the whole history of meteorological observations off the Pacific coast from the Mexican to Canadian borders. At the end of the month, winter returned to North America and brought the snowfalls in the Canadian province of Ontario and the US state of Kansas. The trees that were in bloom by that time were covered with flaky snow.
Pouring rains hit Central America. In Guatemala and Salvador, from 70 to 135 mm of rainwater fell in three days, which is 1.5-2.0 times the normal monthly amount. This natural disaster destroyed the houses and damaged the infrastructure. Heavy rains caused flooding in Panama and Haiti, and submerged thousands of houses under water. At the same time, Mexico was suffering from the worst drought in the last thirty years with 85% of its territory in severe lack of moisture.
In Moscow, 91 mm of precipitation, i.e., twice the normal amount, fell in April. This month was the third wettest April in the meteorological chronicle of the capital, and the wettest one in the 21st century. No such large amount of precipitation in Moscow was observed in April since 1986 with its ever-highest value of 98 mm, or since 1903 when the second highest value of 97 mm was recorded.
Hydrometcentre of Russia