MAIN WEATHER AND CLIMATE TRAITS IN THE NORTHEN HEMISPHERE AS OF MAY 2023
 
Air temperature

From the first days of May, colds were pouncing upon Central Russia. Frosts in the Tula, Ryazan, Tambov, Orel, Kaluga, Lipetsk and Smolensk Regions reached the record-breaking strengths. The same took place in the Volga region (the Ulyanovsk and Samara Regions as well as the Republic of Tatarstan), although the air temperature in this area exceeded +30° as lately as on the first of May. And eventually, the average air temperature in the first decade turned out to be one to four or more degrees lower than the normal value.
The weather in the second decade did not become milder. Frosts were still recorded in the Kostroma, Yaroslavl and Tver Regions. However, warm weather already came to the Russian North were the temperature could reach +25° in some places, and new daily temperature maxima were observed.
It was only in the third decade when anomalous warmth occupied almost the entire European Territory of Russia (ETR) and resulted in the decade-averaged anomalies reaching +8-10° in the north and +4…6° in the Volga region.
In the Urals, this May was the fifth warmest in history, whereas in Siberia and in the Far East, cold prevailed over heat for all its duration, and new temperature minima were recorded in certain locations. In the south of Western Siberia, frosts were observed, yet abnormally warm air broke through sometimes to result in new daily temperature maxima almost reaching +30° in the Tomsk, Kemerovo and Irkutsk Regions as well as in the central and southern regions of the Krasnoyarsk Territory.
The average air temperature in May was 2-4° higher than normal in the Russian North, in the Urals and in the north of the Volga region. In the rest of the country, the temperature conditions were close to normal, except for the Republic of Tyva where the weather was colder than usual by about 2°.
As regards the ETR, this spring may be considered abnormally warm: its average temperature is among the top five highest in the meteorological chronicle. The normal temperatures in the Volga region, in the south of the Urals and in some places in the Russian North were exceeded by two or more degrees. The spring was the second warmest in history in the Volga and Southern Federal Districts, and the fifth warmest in the North Caucasus. As regards the ATR (the Asian Territory of Russia), this spring was noticeably warmer than usual in the Primorye only, where it was the second warmest in the meteorological chronicle. In the rest of Russia to the east of the Urals, the temperature background was close to normal.
This May, the monthly-averaged air temperatures in China and in the other countries of the Far East were close to normal, with negative anomalies in the north of China and in Mongolia, and with positive ones in the rest of China as well as in Korea and Japan. In the third decade, extreme heat settled over the eastern provinces of China. In Shanghai, the absolute maximum of temperature in May equal to +36.1° was set. But in the north of the country, negative air temperatures and new daily temperature minima were recorded in the Gobi desert roughly at the same time.
The weather in the countries of South-East Asia was very hot sometimes: the thermometers showed above +40° in the northern and central regions of Thailand, and the absolute maximum of air temperature was set to +44.2° in Vietnam.
In India, this May was very cold, which is quite untypical for a pre-monsoon month. In Delhi, it was the coldest May in 36 years, and in the country as a whole, among the eight coldest in the entire history of meteorological observations. Negative anomalies of monthly-averaged temperatures prevailed almost everywhere save for the south-western regions, reaching -2° in the north.
In the Near and Middle East, and in Central Asia alike, the monthly averages were close to normal, albeit that the background of anomalies was different: negative in the Near East, and positive in Iran and in the ex-Soviet Asian countries. In the west of Kazakhstan, the thermometer readings sometimes rose above +30° at the beginning of the month, and new daily temperature maxima were set at times.
In North Africa, the monthly-averaged temperature was about normal, against the background of negative anomalies in the north of the continent and within the Horn of Africa, and of positive anomalies in the rest of the territory.
Central and Eastern Europe received less heat than usual, while Western Europe, more heat than usual, if only in small amounts both. At the beginning of the month, new daily temperature minima – all accompanied with frosts – were recorded in Sweden, in the Baltic countries and in the south of Ukraine, but at the same time, temperature maxima were observed in Portugal in the extreme western part of the continent.
As for the Arctic, the average temperature in May was the tenth highest in the history of observations.
In Canada, this May was the warmest in the meteorological annals, beating the previous record-breaking May 1998 by almost a degree. The USA, Canada's southern neighbour, also received a lot of heat: there, the month was the fifth warmest May in history. The monthly-averaged temperatures were 4-8° higher than normal in Canada, and two or more degrees higher in the northern US. The weather in the USA was colder than usual on the east coast and in Alaska only. New daily temperature maxima were set in Canada and in the north-western US.
The air temperature in Mexico and in the other Central American countries was close to the normal value or slightly higher than that.
In the Northern Hemisphere, the monthly-averaged air temperature calculated to an accuracy of 0.1°C was ranked the second highest since 1891, just as in 2021 and 2016. May 2020 remained the warmest in history.
Regarding the whole spring in the Northern Hemisphere, it was the third warmest along with springs 2019 and 2022, spring 2016 being the record-holder. The Japan Meteorological Agency deemed this spring in the country as the warmest in the past 125 years. Spring was warmer than usual by some 2° in Central Asia, in the north-east of Canada and in the north-west of Africa, while the seasonal air temperature averages in the rest of the Hemisphere were about normal, with weak negative anomalies in Eastern and Northern Europe, in the south of Arabia, within the Horn of Africa, in India and Pakistan, in Alaska (where the anomalies reached -2°) as well as in the water bodies of the Atlantic and Pacific Oceans, and with weak positive anomalies elsewhere.
In Moscow, the average air temperature in May was 12.7° with an anomaly of -0.9°, so that the month turned out to be cold. May in the capital was even colder in 2022 – almost 3° colder than normal, just as cold in 2017, and almost 2° colder than normal in 2020. So, cold May weather in the capital has become a frequent phenomenon in recent years. The average temperature in spring in Moscow was +7.9°, implying an anomaly of +2.3°. As a result, this spring was the eleventh warmest since 1891.

Sea Surface Temperature
 
Whereas high positive SST anomalies (higher than 2°) were observed off the coast of South America in the east of equatorial latitudes of the Pacific Ocean, the temperature conditions in the rest of the Ocean remained close to normal still, both in the Northern and Southern Hemisphere, meaning that the Ocean was not yet prepared for the birth of new El Niño.
In the Pacific Ocean, high positive SST anomalies were recorded at temperate latitudes in the central part of the Ocean and off the Asian coast, while high negative ones, at tropical latitudes (especially high, off the American coast), as well as in the Sea of Okhotsk and the Bering Sea the north (of -1° or below).
The surface of the Atlantic Ocean in the Northern Hemisphere was extremely warm: there, a new maximum of monthly-averaged temperature for May was established. Remarkably, the monthly-averaged SST in each month starting from January (i.e., for the fifth month in a row) either reached a new record-breaking value, or reproduced the previous highest achievement. This has been never observed before. This May, the highest anomalies (in excess of +1-2°) were recorded in the east of the Ocean, from the equator to Europe, but the conditions were close to normal in the rest water areas: as a rule, against the background of weak positive SST anomalies, but in some places (off the coast of North America, and in the Norwegian and Greenland Seas), against the background of weak negative anomalies.
 
Precipitation
 
This May, the distribution of precipitation in Russia was primarily distinctive by the absence thereof in most of the country. The normal monthly amounts in the ETR were only achieved in the Murmansk Region, the Republic of Komi and the Nenets Autonomous District in the North-Western Federal District, in the Kostroma and Ivanovo Regions in the Central Federal District, in the Kirov, Nizhny Novgorod, Penza, Saratov and Orenburg Regions as well as the Republics of Mari El, Mordovia and Chuvashia in the Volga Federal District, and throughout the Southern and North-Caucasian Federal Districts in the south where heavy rains pelted during the entire month, bringing up to 20-40 mm of daily rainwater to some places in the Crimea, Krasnodar and Rostov Regions as well as the Republic of Kalmykia. As for Central Russia and the Volga region, rains came in the third decade only: up to 20-30 mm of atmospheric moisture accumulated there per day in the Kursk, Voronezh, Belgorod, Smolensk, Kostroma, Yaroslavl and Penza Regions and in the Republics of Mari El and Chuvashia. In contrast, 2 mm of rainwater fell during the first twenty days in Belgorod, 1 mm in Voronezh and Lipetsk, and nothing at all in Kursk.
The weather in the Ural Federal District was altogether dry: there, the normal precipitation amounts were solely reached in the Yamal-Nenets Autonomous District in the north. Drought took place in some areas of the Southern Urals.
Precipitation was lacking in Siberia where the normal value was only reached in Taimyr in the Far North, and in the Republics of Altai, Khakassia and Tyva as well as the Irkutsk Region in the south.
The Far East contradicted the basic trends of dryness in May. There, precipitation was ample in most of the territory, or excessive in some locations. The normal figures were exceeded by 1.5 times in the Magadan Region and by 2.5 times in Kamchatka. Precipitation in Buryatia and Yakutia, in the Khabarovsk Territory and Jewish Autonomous Region, and on Sakhalin was normal. The Primorye Territory and Chukotka were the only areas to experience a shortage of precipitation.
In overall, this May can be considered dry in Russia. Many meteorological stations entered zero in "Monthly Precipitation Totals" column.
In China, rains were abundant in the east and south of the country only. Heavy rains caused floods in the province of Guangdong. Severe floods due to downpours were also observed in the province of Jiangxi, leaving more than half a million people affected and damaging or destroying crops over an area larger than two thousand hectares. New daily maxima of precipitation totals were set. Precipitation in Japan and Korea was normal.
As reported by the meteorological service of Thailand, the rainy season in the country began on May 22; at first, the rains started falling in the south of the country, in its neighbouring Cambodia and Vietnam, and in the south of Myanmar.
A lot of precipitation went to India and Pakistan.
The weather in Central Asia was mostly
In the Near East, precipitation was abundant in Saudi Arabia, Turkey and Transcaucasia. On the last days of the month, heavy downpours hit the western and southern regions of Turkey, causing landslides in certain locations. Heavy rains in the west of Georgia brought up to 50 mm of atmospheric moisture per day.
Rains in North Africa were only observed along the Mediterranean coast and the coast of the Gulf of Guinea; their monthly totals were normal or above-normal. The weather in the rest of North Africa was dry.
This May was dry in most European countries; the normal precipitation figures were only reached in the Balkan countries, and partly in Spain and Italy. In the latter country, rains were observed during the entire month and flooded the province of Emilia-Romagna in the north. This flooding was the most severe in the past 100 years, causing the rivers to overflow their banks, leaving 41 settlements under water, and triggering more than three hundred landslides. In the third decade, heavy showers hit the south-west of the country where they also led to massive floods. In Spain, rains were falling for several days and brought up to 120 mm of rainwater alongside an unusual drought in the country.
Dry weather prevailed in most of North America. The central regions of the US and Canada along with California and the north-east of Canada were the only areas to receive the rains, and to obtain precipitation in normal amounts, or in above-normal amounts in some places.
This spring, precipitation in Russia was adequate in general. The amounts less than normal were only recorded in the southern regions of Western Siberia and of the Urals, and partially in the central region of the country. The above-normal quantities of precipitation during the spring fell in Siberia as well as in the north and south of the ETR.
In Europe, the precipitation totals for the entire spring were normal or increased. The same picture was observed in most of the US and China as well as in Mexico, India and Pakistan. A shortage of atmospheric moisture was noticed in Central Asia, in most of the Near and Middle East, in the south of China, in South-East Asia and in Canada.
In Moscow, 38 mm of precipitation fell in May, amounting to 62% of its normal quantity; thus, this May in the capital was dry. The total precipitation in spring matched its normal figure.
 
* The air temperature anomalies have been calculated basing on the normal values for 1991-2020, the anomalies of precipitation totals in the Northern Hemisphere, on the normal values for 1961-1990, and the anomalies of precipitation totals in Russia, including Moscow, on the normal values for 1991-2020.