Racing the rainclouds

Big long walk today – beyond Edwardów (hitherto my furthest expedition west from Jakubowizna) – through Milanów to the edge of Drwalewice. By the early evening, massive storm clouds were building up in the east. Thunder rumbled almost continually; the interval between lightning flashes and the thunder claps was getting shorter and shorter, while the downdraft from the deluge pouring from the dark clouds was strengthening. I suddenly remembered the SMS alerts from the government security centre (RCB) warning of the possibility of intensive rain storms with hail; "If you can, remain indoors. Avoid open spaces." And here I am, with six kilometres between me and home.

Below: looking west at the sun as it sinks, nothing much to worry about. Sunset's not for another two and half hours.

Below: looking north towards Drwalew, and the Biowet plant. Beyond, the old DK50, Lasopole, and the new DK50 (Drwalew-Chynów bypass). Flashes of lightning attract my attention.

But looking east, the sky looked distinctly threatening. Downdraft can be disconcerting; the wind blows from under the deluge, and should not be confused with the prevailing wind that is actually propelling the clouds, often in another direction. 

Left: cumulonimbus calvus towering over Góra Kalwaria. The volume of water falling from it is pushing the air under it outward in my face – but which way is the cloud-mass actually moving? Those fluffy cloud tops billowing up are heading north, but the cloud base is spreading outwards and towards me. No anvil top yet; that's a real danger sign. I fear that I shall be drenched (despite the Gore-Tex jacket in my rucksack).

Below: looking toward Edwardów. A stand of silver birches tower over neighbouring fruit trees. The rushing air rustles the trees. Birdsong sounds uneasy.

I take a short-cut between the fish-ponds and orchards the lie between ulica Leśna and ul. Warecka. Strawberry pickers along ul. Wolska are working at a frenzied pace; hail could cause serious crop damage.

Below: back in Jakubowizna, I have been fortunate; the rains missed me. In the distance, it seems that Warsaw, some 45 kilometres to the north, is getting wet. 

Below: home and dry. Over 20,000 paces walked today; 16km or ten miles. My garden is dry, too. Rainfall over the past two weeks has been inadequate.

Today's weather is not that which I associate with late-May; the climate is clearly changing. Convection rainfall comes not from clouds borne west by prevailing winds from the Atlantic, but from moisture from the ground that evaporates as a result of direct sunlight. Convection rainfall is associated with late afternoons and evenings in high summer, requiring much heat energy to initiate it. Clouds gather and rise in height, leading to short-lived but heavy downpours accompanied by thunder and lightning due to electrical charges within the clouds. Convection rainfall is harder to forecast than the rain that falls from clouds carried along in weather fronts by prevailing winds. These tend to yield lighter rain over a larger area for a longer period. And here we are, still four weeks before the beginning of astronomical summer.

UPDATE SUNDAY 26 MAY: A lovely cloudless morning. Weather forecast: sunny, cloudless to 17:00. Reality: by 13:00, I can hear thunder approaching as heavy clouds build up. Further update, 14:15. The thunder is non-stop now; rolling thunder as I never heard growing up in the UK. BANG! Lighting, followed by a mighty thunderclap about a second later. And now, at last, rain. Not forecast.

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