Weather Photos blog

An interesting and rather complex setup across Europe tomorrow. I’ve been working quite a while on it during the last 3 hours. See the forecast map and outlook below. Large trough over northern Europe and weak stationary front on the northern side of the Alps. Strong instability over eastern Alpine flank and some severe storms can be expected. Finally we’re into the early summer pattern and higher temperatures now exceeding 25°C.

Storm Forecast
Valid: Tue 25 May 2010 06:00 to Wed 26 May 2010 06:00 UTC
Issued: Mon 24 May 2010 23:05
Forecaster: KOROSEC

A level 1 was issued for south-central France, NW Switzerland and SW Germany mainly for large hail and excessive convective rainfall.

A level 1 was issued for parts of Ukraine mainly for severe wind gusts and marginal hail.

A level 1 was issued for eastern Austria, SW Slovakia and much of Hungary mainly for large hail and lesser extend for strong wind gusts.

SYNOPSIS

A quite complex scenario unfolds across Europe on Tuesday. There is a large deep trough over northern Europe while a kind of omega like pattern over southern Europe slowly wipes out while making eastwards progress. There, two upper lows are located on both of its flanks. The western upper low moves into western Europe while merges with the main trough towards the Wednesday morning. The second, weaker upper low moves NE-wards from extreme southern Mediterranean into extreme SE Europe.

At surface, a cold front associated with the northern large trough moves further SE across east-central Europe while slowly weakening. The frontal boundary stays quasi-stationary over central Europe where its western flank transforms/merges with the warm front advecting across France. The frontal system pushes the cold front into western France.

DISCUSSION

… south-central France, NW Switzerland and SW Germany …

Ahead of an approaching upper low/trough/frontal system, strong WAA pushes the warm front across France during the day. Behind the front, quite rapid moisture recovery with upper 10s surface dewpoints overspreads France as well as south-western Germany. Moderately strong instability release with MLCAPEs reaching near 1500 J/kg is quite likely. Over central France, GFS pushes the values even higher, while ECMWF stays slightly above 1000 J/kg. It seems that storms initation will begin in early to mid afternoon hours when strong surface heating weakens the capping inversion across the warm sector. With forming weak surface low and increasing southerly flow, a few near-surface convergence zones can be seen besides the main cold/warm frontal boundaries, which will trigger the convection. Only marginal mid-level jet streak will be present across France/S Germany until late afternoon when deep-layer shear gradually increases up to 15m/s. Despite rather limited shear, organized storms can be still expected with the main threat for large hail given the quite high instability release. Rather slow moving storms could enhance the flash flood threat as well.

Later towards the evening, models are confidently simulating convective rainfall threat mostly along the stationary warm front from eastern France into NW Switzerland and SW Germany. One or two large convective clusters are quite probable in the evening hours trailing ENE-wards overnight due to the increased LLJ ahead of the surface low over east-central France. Therefore, excessive convective rainfall threat could lead into local flash floods.

… parts of Ukraine …

A short-wave trough on the SE side of the main large vortex will cross Ukraine/Belarus during the first half of the forecast period. In the morning hours, Ukraine lies right under the nose of relatively strong mid-level jet where a decent forcing leads into convective initiaton along the rapidly eastards moving cold front. With moderate 20-25m/s shear in place, organized storms are expected. A couple of well organized multicells as well as supercells can be possible. Posing a threat mostly for strong to severe wind gusts and marginal hail. Enhanced helicity is partly seen over narrow warm sector which could lead into LL rotating updrafts, but this threat ramains limited.

… eastern Austria, SW Slovakia and much of Hungary …

An aforementioned weakening cold front over central Europe becomes quasi-stationary during the day. It lies E-W oriented from western Ukraine across Slovakia/Hungary border westwards into southern Germany. A rather impressive moisture pooling is expected south of this boundary as healthy moisture recovery takes place over Hungary and Austria from the Balkans. Especially the GFS model is probably slightly overestimating the near surface dewpoints, but 0-1km mixing ratios of 10-11 g/kg are still quite likely. Expected clear skies will lead into strong boundary layer heating and combined with steep mid-level lapse rates, it will result in high instability between 1500 and 2000 J/kg of MLCAPE, maximized over Hungary. A relatively strong mid-level jet streak on the back side of the main trough is still placed over central Europe, which will provide moderate to strong sheared environment across the level 1 area. Its southern flank (15-20m/s in 0-3km/0-6km layer) will well overlap with instability.

The capping over eastern Alpine flank/Hungary gives some uncertainities to the forecast, but it seems that convective temperature (near 26°C) will be easily reached in the late afternoon hours to initiate the convection. Organized and rather isolated severe storms are expected across the level 1 area, where quite a few well organized multicells and supercells will be possible. Given the high instability release, large to very large hail (3-5cm in diameter) will be the main threat, while severe wind gusts cannot be ruled out either, but remain limited. This threat should diminish in the evening hours, when instability vanishes.

The current thinking is that no widespread activity is expected over these areas, but the activity and the next model runs will be closely monitored for a possible upgrade/adjustments later tomorrow if conditions change significantly.

Source: ESTOFEX outlook from May 25th 06z until May 26th 06z 2010

Stay tuned for future updates!

Nothing too impressive across southern Alpine region over the next following days, we’re experiencing under average temperatures for mid May as large upper low remains quasi-stationary over eastern Europe and the Balkans and precludes an Azoric high to expand into central Europe and bring signifficant warming.

So I am just posting a convective outlook for tomorrow across Europe. There will be some organized storms on this low’s northern flank, while only diurnal driven showers and thunderstorms are expected at some places. So quite a boring period continues.

Storm Forecast
Valid: Tue 18 May 2010 06:00 to Wed 19 May 2010 06:00 UTC
Issued: Mon 17 May 2010 22:46
Forecaster: KOROSEC

A level 1 was issued for Belarus, Baltic states and parts of western Russia mainly for large hail and lesser extent for excessive convective rainfall.

SYNOPSIS

A large scale upper low with moderately cooled mid-levels dominates over eastern Europe and the Balkans and remains mostly stationary during the forecast period. On the eastern flank of the northwards building ridge, another, rather small scale upper low moves southwards across Germany and reaches the Alps on Wednesday morning. At surface, a weak surface low with an attendant quasi-stationary front over parts of eastern Europe and western Russia serves as a focus for main convective activity.

DISCUSSION

… Belarus, Baltic states and parts of western Russia …

With the main upper low vortex staying stationary today, a daytime driven convective activity is expected along the well defined surface frontal boundary again. Mixing ratios near 10-12 g/kg suggest that MLCAPE of around 1500 J/kg will result. It seems that the main jet streak along the northern flank of this upper low is only partly overlaping with the instability, as the most CAPE stays to its north. Given the almost uncapped environment, its expected that widespread coverage of showers and thunderstorms will be mostly around the surface front. Despite the only weak to moderate shear, it will still support organized storms as numerous multicells as well as isolated supercells. Some of them with a threat for marginally large hail as well as excessive convective rainfall given the weaker wind field where CAPE is maximized.

… southern Germany…

An afforementioned small scale vorticity maxima crosses Germany from NW towards the Alps. A rather cold mid-levels with steep lapse rates will result in moderate destabilization. Marginal instability of several hundreds J/kg is likely given the expected good daytime surface heating. Favorable ascent associated with DCVA will lead into storms intiation along the progressing trough axis by midday and will continue towards the evening hours. Instability overlaps with moderate 20-25m/s deep-layer shear and therefore mostly elevated storms could be quite well organized. A threat for marginally large hail will exist, but the currently expected low coverage and especially only marginal instability precludes a threat level 1. However, the situation will be closely monitored for a possible upgrade if conditions improve significantly.

The rest of low probability lightning areas in central Italy and western Balkans (Apennini and Dynaric mountain range) will only see isolated storms where some of them could support some hail, but with sub-severe threat.

Source: ESTOFEX outlook from May 18th 06z until May 19th 06z 2010

Stay tuned for future updates! Hopefully heating starts soon and some significant trough digs in.

Quite a different results today against the simulations by the models yesterday. Severe weather period over southern Balkans was less robust than expected, only marginally severe storms and excessive rainfalls occured. Over Slovenia and Croatia, continuous stratiform rainfalls are still on going, but only up to 50mm acumulated so far. The positions of the deep surface low was more to the south and pressure gradient was less pronounced, resulted in weaker Bora (only up to 100km/h locally) and less precipitation as the richer WAA did not affect northern Balkans as expected.

However, surface low is now weakening while moving across the Balkans and some severe weather could still be expected tomorrow along the main frontal boundary. I’ve prepared an ESTOFEX outlook for tomorrrow:

Storm Forecast
Valid: Sun 16 May 2010 06:00 to Mon 17 May 2010 06:00 UTC
Issued: Sat 15 May 2010 22:35
Forecaster: KOROSEC

A level 1 was issued for parts of NE Sweden, central Finland and parts of NW Russia mainly for marginally large hail.

A level 1 was issued for coastal areas of Montenegro, Albania, NW Greece and western Macedonia mainly for excessive convective rainfall.

A level 1 was issued for NE Bulgaria, extreme eastern Romania and south-central Ukraine mainly for large hail and severe wind gusts.

SYNOPSIS

A deep trough/upper low which brought a severe weather period across the southern Balkans finally fills while slowly translating northeastwards on Sunday. At surface, deep low with an attendant cold front weakens while moving towards central Ukraine. The surface front quite rapidly shifts eastwards off the Balkans onto the Black sea. The rest of Europe stays stable while mostly daytime driven convective activity is expected along the difuse frontal boundary extending from NW Russia into eastern Scandinavia, as well as within the quasi-stationary unstable airmass across parts of western Russia.

DISCUSSION

… NE Bulgaria, eastern Romania and south-central Ukraine …

Convective activity will continue along the rapidly eastward progressing cold front, beneath the upper-level dvergence where strong forcing will remain in place. A few hundreds of MLCAPE seem reasonably available ahead of the surface boundary. Despite the position of the strong mid-level jet with deep-layer shear above 25m/s a bit south of the main instability release, it should allow storms to organize into multicells as well as a few rotating storms. Large hail and especially strong damaging winds seem like the main threat. Minor threat for a LL mesocyclones development seem over the Ukraine, however.

… coastal areas of Montenegro, Albania, NW Greece and western Macedonia …

Strong westerlies with moderate to strong deep-layer exceeding 30m/s shear will again support strongly forced convection onshore into over the coastal areas of Albania and surroundings as well as more inland onto the complex topography. Marginal instability seem enough to support excessive convective rainfall locally. Persisting upslope flow and possible organized/maintaining storms could enhance the risk for local flash floods. This threat should diminish late in the afternoon when jet streak moves towards southeast.

… parts of NE Sweden, central Finland and parts of western and NW Russia …

Mainly diurnal driven showers and thunderstorms are expected over parts of eastern Scandinavia and western Russia where somehow difuse frontal boudaries/LL convergence zones remain quasi-stationary. Latest soundings from western Russia showed rich BL moisture with mixing ratios near 10-11 g/kg. With strong diurnal heating and temperature insolation this should yield instability with MLCAPEs exceeding 1000 J/kg, though in only marginal shear. Numerous storms will take place with threat for marginally large hail across the level 1 area. More to the south, slow moving storms could support excessive convective rainfall locally as well. Given the high LL instability and weak wind field, funnels/spouts cannot be excluded either.

… southern Poland, eastern Czech Republic and northern Slovakia…

The situation over these areas will be most likely non-convective excessive rainfall, while minor chances exist for some embedded convection. Placed on the back side of the surface low, strongly forced upslope flow over Tatra mountains will support lots of stratiform rainfall which could result in total accumulations locally reaching or even exceeding 100mm per 24hr period. However, if some convective rainfall occur as well, higher accumulations are therefore even more likely. Local flooding can be expected over these areas.

• ESTOFEX outlook from May 16th 06z until May 17th 06z

The following days will depends on the position of the large scale upper low over the eastern Europe and the Balkans which could mean things will not become stable yet over our region. Scattered showers and thunderstorms could be possible again later next week.

Stay tuned for future updates!