The first European heatwave is coming and already on Wednesday, 31. March should temepratures in southern Spain reached +33°C, while in Portugal and southwestern France, +30°C is forecasted.
In the UK, extremely warm weather will be peaking around 30. March with maximum temperatures up to +24°C and Thursday, 31. March should be already in very cold air, below -5°C in 850 hPa and regional snow showers.
In southeastern parts of Central Europe (Austria, Slovakia, Hungary, southern Poland...) extremely warm air will stay on 1. April, yet, then both air masses - from NW and SE Europe, will start fighting.
The newest outputs of GFS are warmer than outputs from previous days and there is a match in possible temperatures up to +25°C in large region of Central Europe and +27°C, later even over +30°C in Balkan, after an Easter in Greece and Turkey maybe up to +35°C!
About evolution of weather after Easter 2021 in Europe we will write more in the next article.
Now, we should look at criteria for reaching of tropical day, summer day and possibility of snow cover according to 850 hPa temperatures.
Tropical days are usual in air masses with T850 hPa above +15°C in Europe. During clear weather, we should add maximally +17°C to 850 hPa temperature for expected maximum temperature. Usually it is only +15/+16°C thanks to wind, cloudiness and other factors, during cloudy and windy weather lesser. In winter season is situation sometimes totally different, with warm T850 hPa layer and temperature inversion with fogs and frosts in basins, valleys andd lowlands. +15°C in 850 hPa rule is valid for all summer half-year.
With summer days it is very similar, only +10°C in 850 hPa is needed to reach for summer temperature +25°C in lower altitudes during sunny, anticyclonic days.
For snow showers in every season of the year, T850 hPa below -5°C is a predictor of snowing in many climate zones from Arctic to Tropical. Below -5°C we should consider about winter or semi-winter conditions in mid-latitudes.
Such we should notice on maps below, above the Spain will be during expected March 2021 heatwave hot air above +15°C in 850 hPa and only day later, above almost all British Islands very cold air below -5°C in 850 hPa.
Winter is therefore still fighting with a summer.
In the next 2 articles we will look at this fight after an Easter 2021 and too at the newest ECMWF Weather Regime forecast until early May 2021.