Weather Photos blog

An interesting afternoon today as an unusually well-defined sea breeze front shifts across SW Slovenia (Karst) at around 5pm local time (15 UTC). Such fronts are normal for this part of Slovenia as near-surface winds turn from night/morning easterlies (land breeze) into mid-day/afternoon westerlies (sea breeze) once the inland airmass areas become warmer than the airmass above northern Adriatic sea.

The morning land breeze is usually characterized by relative humidity around 50%, while today’s airmass was drier with relative humidity around 30% by mid-afternoon hours. Land breeze usually blows from east direction as given by the topography features around here. Today, direction was more from the NE direction and was partly also a combination of light Bora wind. As higher elevations are located to the NE of SW Slovenia (Dynaric Alps with Nanos and Trnovski Gozd) the wind had katabatic nature which warms and dries the airmass going downhill. Thats why today temperature was also higher than previous days (near +30°C today) and relative humidity was lower.

As it can be seen on the graphs from my weather station below, at around 5pm the winds turned from east to west directions and a rapid moisture advection from the gulf of Trieste shifted east across Karst. The relative humidity rised from 30% to 55% very rapidly. The same ‘jump’ can be also seen on the dewpoint graph which raised for more than 7°C in a matter of a few minutes (from around +10°C to more than +17°C!). This jump was the crossing of the rather strong sea-breeze front, quite impressive passage given the boring nature of clear sunny days lately.

Such crossing of the sea-breeze front are almost daily observed over Karst, but this time it was stronger and better defined. The usual jump is for about 10% RH or a couple of degrees Celsius at dewpoint graph. The slight change of airmass has also been noted as air became more hazy as soon as front arrived. Some briefly organized cumulus clouds were then observed along the moving convergence/front, but given the strong capping inversion aloft, no deep convection was triggered.

It often happens that such sea-breeze front works as a trigger for afternoon showers and thunderstorms over SW Slovenia, it all depends how late this front arrives and blasts east. The later it is (usually it crosses between 11am and 1pm local time), the more energy builds as daytime heating was longer before.

A warm period slowly transforming into a serious heat wave across much of Europe is on going during the last few days and will most likely continue for at least the next 7 days or more. The maximum temperaratures are already around +30°C today, while higher temperature up to around +35°C can be expected towards the weekend and beginning of the next week. Stay tuned for future updates!