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!

Here is a report of a storm chase I had on Sunday when I intercepted an intense squall line with embedded mesocyclone in SW Friuli, right on the border with Veneto region. I first drove to Portogruaro and then headed north towards Pordenone where intercepted a mesocyclone to my left. Its structure can be seen on the first images below, though more obvious look beneath it can be seen on the video at the bottom of this message (first 30s of video). Later I turned east to be ahead of it and I’ve been blasted with intense RFD gusting near 80km/h while driving towards Udine. Meanwhile took a few more shots of shelf cloud structure before left it to run over me with intense rainfalls just SW of Udine. The lightning activity was quite frequent. Also, quite a lot of debris was flying in the air when RFD hit.

Here is a radar image at the time when I was recording the video… I was right there near that 65dBz reflectivity:

And the radar animation of the squll line passage from Veneto to Friuli region…

4 hours radar animation from 15 to 19 UTC

A couple of shots… first taken between Portogruaro and Pordenone…

And later on towards Udine ahead of the squall…

Here is the video of the whole event. Looking over the first 30s of the video, there is a obvious wall cloud structure beneath the main supercellular/mesocyclonic structure. I actually doubt these could be only a scud clouds, especially when taking in account the radar image above:

• Video of intense squall line on June 13th 2010 in SW Friuli

I was quite happy with the chase, though the season this years is still pretty poor and less intense than one would want it to be. But we will see how continues. Stay tuned for future updates.

An early summer pattern continues over central Europe and the Balkans. It seems that this pattern will continue during the few days as well, with daily temperature slowly rising above 30°C. High BL moisture content will likely limit the more extreme temperatures as one would expect given the expected T850 values of around 20-24°C over northern Balkans.

There is some severe storms threat tomorrow over Europe… parts of E-CNTRL France along an active front and parts of central Europe with mostly large hail threat given the high instability release in the afternoon hours. Here is the ESTOFEX outlook for tomorrow through my eyes:

Storm Forecast
Valid: Tue 08 Jun 2010 06:00 to Wed 09 Jun 2010 06:00 UTC
Issued: Mon 07 Jun 2010 21:08
Forecaster: KOROSEC

A level 1 was issued for NW Russia mainly for severe wind gusts and lesser extent for tornadoes and large hail.

A level 1 was issued for Czech Republic, SE Germany and N Austria mainly for large hail and strong wind gusts.

A level 1 was issued for east-central France mainly for marginally large hail and a brief tornado.

SYNOPSIS

Weak geopetential heights are placed over much of Europe while a large trough over western Europe slowly shifts southwards and transforms into an upper low towards the Wednesday morning. Another short-wave trough continues eastwards from Baltic states into NW Russia.
At surface, a frontal boundary extends from NW Russia into central Europe where it advects northwards as a warm front during the second half of the period. Another front extends from the large surface low over UK SW-wards across central France into Iberian peninsula. The third front races onto western Iberia overnight when the upper low/new system approaches.

DISCUSSION

… Czech Republic, SE Germany and N Austria …

Placed beneath the weak upper ridge over central Europe/Balkans, weak wind field will be in place. Near surface mixing ratios of around 12 g/kg south of the weak/quasi-stationary surface front should result in moderately strong instability with MLCAPEs locally exceeding 1500 J/kg. Expect mostly diurnal driven storms, where some of them could bring threat for large hail and strong wind gusts. Locally, rather slow moving storms can lead into some flash flood risk.

… east-central France …

The convective activity will be mostly aligned to the frontal zone and areas ahead of it once the diurnal heating takes place. Pre-frontal initiation is more likely over the Massif central. Given the marginal instability overlaping with 10-15m/s 0-6km shear, mostly multicells are likely. Storms may tend to cluster into a larger system. In the late afternoon/early evening hours, when the upper trough approaches northern Iberia, a weak surface low forms over NE Spain and an increasing LL jet results in enhanced shear in the lowest levels across the level 1 area. More backed wind field leads into several hundreds of m^2/s^2 of SREH3 as well, rising the potential for more organized severe storms. Given the near 20 m/s of deep-layer shear, a couple of more isolated supercells with threat for large hail and weak tornado could result.

… NW Russia …

Ahead of an eastwards moving short wave trough, warm and ustable airmass advects NE-wards behind the warm front. Rather strong deep-layer shear around 25 m/s and MLCAPE near 500-1000 J/kg spreaded across the warm sector should created environment for some severe storms. A maintaining cluster of storms is possible along the leading cold front with a few embedded supercells. Posing a threat for mostly severe gusts and marginally large hail. With at least 10 m/s of LL shear and rather low LCL heights, a tornado threat is not ruled out either.

… western Iberia …

Weak to moderate instability builds up ahead of an approaching surface front coming onto western Iberia towards the evening hours. With moderate mid-level jet streak and deep-layer shear near 15-20m/s in place, a few organized severe storms could occur over Portugal. But rather limited threat and coverage preclude any threat levels attm. However, a marginally large hail and strong wind gusts threat exist with the strongest storms.

Source: ESTOFEX outlook from June 08th 06z until June 09th 06z 2010

Stay tuned for future updates!