Valid: Sun 29 Oct 2017 06:00 to Mon 30 Oct 2017 06:00 UTC
Issued: Sun 29 Oct 2017 00:12
Threat levels were issued for large parts of central Europe mainly for severe convective wind gusts and to a lesser extent for tornadoes.
Amplified long waves govern the circulation in Europe. A 500 hPa trough over eastern Europe and a deep surface low with its center over Estonia are opposed by a 500 hPa ridge and an extensive surface high over western Europe and the near Atlantic.
In-between, a very strong NW-erly flow curves from Scandinavia across central Europe to the Aegean Sea. Embedded in this mid-level jet streak, a powerful short-wave trough ejects from Denmark (Sun 00 UTC) to the Black Sea (Mon 00 UTC) and reinforces the eastern European long-wave trough. Strong synoptic lift ahead of this short wave and in the jet's left exit also stimulates the formation of a secondary surface cyclone over the Skagerrak Sea Saturday night, which is expected to deepen below 970 hPa while it moves across Poland into Belarus on Sunday. This new cyclone will bring a remarkable autumn storm to central Europe, probably including a round of severe convection along its cold front.
... central Europe (cold front passage) ...
A tongue of moist air from the North Sea is advected eastward ahead of the cold front (2m dewpoints around 10°C across N Germany and around 12°C in the Netherlands at Sun 00 UTC, in line with the forecast models). It is overrun by steepening lapse rates, as the approaching short-wave trough lifts and vertically stretches the air. This interaction will likely create neutral to marginally unstable profiles up to 4-5 km height by early Sunday morning, and the formerly stratiform rain shield along the cold front is expected to break up into convective elements in E Germany and W Poland.
Vertical wind shear is more than supportive for storm organization below the mid-level jet streak: 0-3 km bulk shear increases from 10 m/s in central Poland to 30 m/s near the Alps, where 0-3 km storm-relative helicity also peaks above 400 m^2/s^2. The best overlap of all "ingredients" for organized convection is anticipated in the 06 to 14 UTC time frame, as the most active part of the cold front crosses east-central Europe. Linear convection with wind gusts very probably above 25 m/s and possibly, at least locally, above 33 m/s is expected to develop. Fine-meshed models agree on such a scenario.
The cold front will probably be located along a line Wroclaw (Poland) - Prague (Czech Republic) - Nuremberg (Germany) at Sun 06 UTC and will quickly move SE-ward. In the first few hours of this forecast period, the most active line segments with the highest risk of lightning and severe to localized extreme wind gusts will likely follow the Polish / Czech border. By mid-morning, the eastern line segments will gradually weaken and the most active parts should shift across the E and S Czech Republic into E Austria, W Slovakia, and finally Hungary, following the path of the strongest synoptic forcing.
The area to the east of the Alps becomes a particular focus. As the westerly flow increases ahead of the cold front, diurnal heating and westerly downslope winds (which may easily become severe themselves, but are not included into the ESTOFEX threat level scheme) may push the temperatures temporarily close to 20°C in the late morning. The deeper and drier boundary layer further increases the risk of severe downbursts as the convective line arrives. In addition, a pocket of westerly 850 hPa winds up to 40 m/s (!) overspreads this area exactly in the time frame when the cold front is expected to arrive - e.g., around 10 UTC in Vienna and Bratislava, 11 UTC in Budapest and 13 UTC at the Hungarian / Serbian / Croatian border triangle.
All in all, the setup appears menacing enough to issue a confined level 3 area. Prior to the cold front's arrival, the formation of a "dryline" boundary between poorly mixed, more humid air to the east and warmer, drier Foehn subsidence to the west should be monitored! If it appears, it would mark a preferred path for the axis of the most extreme wind gusts.
Convection will gradually weaken in Croatia, Serbia and W Romania in the late afternoon, as both the strong wind field and the synoptic lift start to disintegrate.
Valid: Mon 01 Jan 2018 06:00 to Tue 02 Jan 2018 06:00 UTC
Issued: Mon 01 Jan 2018 02:47
Forecaster: VAN DER VELDE
A level 3 was issued across southwestern France mainly for extremely severe convective wind gusts and tornado probabilities.
A level 2 was issued across western and central France, as well as the north coast of Spain, mainly for severe convective wind gusts and tornado probabilities.
A level 1 was issued across western Mediterranean and Tyrrhenian Sea mainly for severe convective wind gusts.
A large low pressure system with the core over western Norway remains in place over northwestern Europe. An activating satellite low pressure system tracks from the Atlantic south of Ireland through the English Channel towards Belgium and on to eastern Germany. Strong non-convective winds are forecast across northern France and southern Germany. However, the passage of its cold front from Bay of Biscay into southwestern France meets all criteria for severe convective weather. Cold upper air advection combined with 6-7 g/kg BL mixing ratio over the Celtic Sea has caused steep lapse rates and a few hundred J/kg CAPE, while models draw a sharp cold front with strong low-level convergence and differential theta-e advection, supported by a strong PV anomaly.
The cold front will likely trigger a line echo wave pattern (LEWP) with bowing line segments responsible for wind gusts of 30-35 m/s as is present in the 1-3 km layer. 0-1 km shear vectors over 15 m/s (locally even 20 m/s) magnitude will be in place across N Spain and most of France, supporting tornadogenesis as well as the bow echoes. Convection is likely to survive even inland as strong moisture advection, dynamic destabilization factors, lapse rates and orographic lifting are carried as far as central France.
As the front moves on, its structure may be torn apart between Pyrenees and Alps after 15Z, by the cut-off of moisture supply, but convection will likely recover before Corsica and Sardinia around 21Z, while the flow weakens.
Valid: Fri 08 Jun 2018 06:00 to Sat 09 Jun 2018 06:00 UTC
Issued: Thu 07 Jun 2018 23:26
A level 3 is issued for Slovenia and N Croatia mainly for large hail and severe convective wind gusts.
A level 1 and level 2 are issued for N and E Italy, SE Austria, SW Hungary and Croatia mainly for large hail, severe convective wind gusts and excessive convective precipitation.
A level 2 is issued for the Adriatic Sea mainly for tornadoes and to a lesser degree large hail and severe convective wind gusts.
A level 1 and level 2 are issued for Bosnia-Herzegovina, Montenegro, parts of Serbia and Albania mainly for large hail and to a lesser degree severe convective wind gusts and excessive convective precipitation.
Level 1 and level 2 areas are issued for S Germany, N Austria, Slovakia, S-ernmost Poland, NE Hungary, Romania and the SW Ukraine as well as for NE Turkey, parts of Georgia, Armenia and the Russian Caucasus region mainly for large hail and excessive convective precipitation, and to a lesser degree severe convective wind gusts.
A level 1 and level 2 are issued from NW Germany into Switzerland mainly for excessive convective precipitation and to a lesser degree large hail.
Another deepening polar trough and a surface cold front translate from Finland into W Russia. Otherwise, mostly weak pressure gradients remain in place across much of Europe. Cut-off lows at 500 hPa are located NW of Scotland, NW of Iberia and over central Italy.
Warm and moist air covers much of the continent south of England, S Norway and the Ukraine. It often allows moderate CAPE in reponse to daytime heating, mostly under weak vertical wind shear and weak dynamics. However, a confined window for an outbreak of organized storms opens up ahead of the Italian cut-off low, where particularly hot air wedges from SE Europe towards Austria and increasingly overlaps with enhanced vertical wind shear.
... Italian E coast, Adriatic Sea, Croatia, Slovenia, SE Austria, SW Hungary, Bosnia-Herzegovina, Serbia, Montenegro, Albania ...
Steep lapse rates, originally created over the Sahara desert and reinforced over the Appennines and the Dinaric mountains, spread over the area of interest. With 2m dewpoints of 16-20C over the Pannonian plains and up to 23C over the Adriatic Sea, around 2000 J/kg of CAPE are predicted to build on Friday, locally even more. Warm air advection will create a pronounced cap, but lift ahead of the cut-off low will start to increase from the SW as the day proceeds. At the same time, vertical wind shear rises to 15 m/s (20 m/s) across the lowest 3 (6) km under slightly veering profiles.
Scattered convection will likely still be left over from the previous night over N and E Italy or will form already before noon, aided by increasing synoptic lift and a mess of outflow boundaries and other disturbances of the low-level wind field. Competition and destructive interference may lower the severe weather risk somewhat, but at least scattered large hail, severe wind and heavy rain events are expected with this activity. Tail-end storms towards the southeast may organize best into supercells.
It is worth mentioning that the majority of the model pool, including convection-permitting models like WRF and MOLOCH, predict scattered activity across the northern and central Adriatic Sea throughout the forecast period. Scirocco winds would advect a very moist boundary layer with enhanced 0-1 km shear into these storms, which would very likely become supercellular. If such a high storm coverage over the Adriatic Sea indeed verifies, numerous tornadoes could form, most of them well off the coastlines, though.
In the evening and overnight, clustering storms will increasingly move onshore or form anew in coastal Croatia, Montenegro and Albania with a gradually decreasing but still enhanced risk of all kinds of severe weather.
Further north and east of the Adriatic Sea, it is most difficult to assess where and when the cap will be broken. Convective initiation will stay isolated at best until mid-afternoon. Possible sites for solitary early "cap breakers" are the southern Alps (if upvalley flow is strong enough) or outflow boundaries, laid out by several storm clusters from the previous night that are moving northward in E Austria and W Hungary near the nose of the warm air advection regime at the time of writing (Thu 22 UTC). Despite an expected struggle against the cap, these early storms, if they form, may already organize well and bring large hail.
In the course of the afternoon, the probability of convective initiation rapidly increases over the Dinaric mountains in W Slovenia and NW Croatia. While vertical mixing will keep both CAPE and wind shear lower in these initiating regions, storms will quickly intensify and organize as soon as they tap into the abundant CAPE reservoir and better shear further northeast. Convection-resolving models agree on quick upscale growth into a large MCS with a most likely track across much of Slovenia in the evening, including the bordering regions of Croatia and Austria. Supercells will likely bring large to very large hail in initiating stages or generally at the southern flank of such a system. In addition, a tornado is not ruled out, though this risk is mitigated by not too low cloud bases and rather inconspcuous low-level shear. Along the MCS's main body, severe straight-line winds will betimes become the main risk. They may become quite widespread and include some extreme events (>32 m/s).
The mature and finally slowly weakening MCS could persist well into the night or even into the next morning while it continues its track northeastward into E Austria, Hungary and possibly even Slovakia. It will likely bring a prolonged period of heavy rain, and flash floods become another dangerous hazard in the course of the night, especially in S and E Austria where soils are often already saturated. In addition, severe wind gusts or large hail are still possible at the leading edge or under more discrete updrafts, respectively.
Similarly abundant CAPE and enhanced vertical wind shear is expected over the eastern parts of Croatia and Bosnia-Herzegovina as well as in Serbia, but the capping inversion will be stronger towards the south (indicated by the Thu 12 UTC Trapani, Pratica di Mare and Brindisi soundings) and synoptic lift arrives later and stays weaker. It is uncertain whether the cap can be broken at all. However, every storm that forms over the Dinaric mountains and descends into the Pannonian plain can easily become supercellular with a risk of large to very large hail. Severe downbursts and flash floods become additional hazards in case convection manages to grow upscale. In that case, it may also persist into the evening and night. | Gewijzigd: 8 juni 2018, 19:05 uur, door Lako
13 Oktober 2018
Valid: Sat 13 Oct 2018 06:00 to Sun 14 Oct 2018 06:00 UTC
Issued: Fri 12 Oct 2018 23:45
A level 3 was issued for parts of Portugal surrounded by a level 2 covering also parts of Spain mainly for severe to damaging wind gusts and to a lesser extent for (strong) tornados and excessive precipitation.
A level 2 was issued for parts of Sicily and Malta for excessive precipitation.
A level 1 was issued for parts of Turkey and Cyprus for excessive precipitation.
A strong and widespread upper level high is influencing large parts of the forecast domain with stable conditions. South of the high-pressure system two separated upper-level lows can be found over the Mediterranean Sea - one close to Turkey and the other over Southern Italy and Sicily.
Over the near North Atlantic Ocean, a strongly amplified and broad trough is active, leading to that southerly /southwesterly flow over most parts of Europe and thus to unusually warm temperatures over most parts of Europe. On the forward flank of the trough, several surface lows have traveled northeastward brought mostly non-convective severe wind gusts to parts of the British Isles. On Saturday another low is influencing that area that however is much weaker.
The most interest on that day is hurricane Leslie that is quickly traveling eastward and will probably reach the Iberian Peninsula during the night from Saturday to Sunday posing a high risk for severe and damaging wind gusts.
Hurricane Leslie is rapidly approaching Portugal and will likely bring severe to damaging wind gusts during the night hours of Sunday
Looking at the current satellite images Leslie still looks well organized with a symmetric cloud shield and cloud top temperatures of almost -70 degree C. The central pressure is estimated to be around 971 hPa.
At the moment Leslie can be found to the south of the upper-level trough. It is forecasted that it should be taken up by the trough in the upcoming hours leading to a further acceleration of its movement to the east and also leading to a beginning transition into an extratropical system during the forecast period. However, models keep Leslie as a system with a tropical appearance for a long time when approaching the Iberian peninsula. It is also forecasted that the system should stay rather strong until it will make landfall. Although increasing shear and somewhat lower SSTs should normally weaken Leslie, the interaction with the through is probably the reason why its central pressure is forecasted to not rise significantly or even drop again during the night time.
The symmetrical appearance will probably disappear in the evening hours due to the aforementioned transition process. Models forecast the strongest pressure gradient to the south and to the west of Leslie. Together with the movement speed of Leslie, the regions of the southern flank of Leslie should see the strongest gusts but with that strong gradient west of the core, the whole coastline can be affected by severe wind gusts. Winds in 925 hPa are forecasted up to 50 m/s.
Ensemble forecasts show a significant probability of wind gusts in the excess of 30 m/s in the aforementioned area. Depending on the model damaging wind gust higher than 40 m/s are well possible. A few solutions also show more than 50 m/s. The risk of severe wind gusts can also affect parts of Western and Northwestern Spain although the storm is significantly weakening more inland.
There are still uncertainties in the exact track of Leslie and in the strength it makes landfall. ICON and ECMWF are the models that show Leslie making landfall at hurricane strength on a northerly course from Lisboa to northeastern Portugal. GFS, however, has a much weaker storm that is also moving on a more southerly track. However, models are getting more and more confident concerning a strong landfall.
The time of the landfall is expected to take place at around midnight (MESZ).
Although it is rather questionable if convections (in form of lightning) may develop we decided to issue an LVL3 area for the wind risk that comes from a convectively driven system that is only slowly transforming into a low with extratropical character.
Besides the wind risk, a locally excessive precipitation threat exists since the system brings a lot of liquid water. However, models do only give little hints for higher amounts of precipitation which is probably due to the rather fast movement of Leslie and the orography of the affected area. But amounts of 30 to 80 mm in a short time frame may lead to local flash floods.
Strong low-level shear together with low LCL would lead to an enhanced threat for tornados that may also be strong. This risk is highest to the south of Leslie where also notable CAPE values of a few hundred J/kg can be expected along a developing cold front. Also, a nice maximum of moisture convergence traveling eastward can be found in the models. This is the reason why the LVL2 area was extended to the south.
There will be an update on Leslie during the day.
22 juni 2019
Valid: Sat 22 Jun 2019 06:00 to Sun 23 Jun 2019 06:00 UTC
Issued: Sat 22 Jun 2019 00:10
A level 3 is issued for parts of Croatia mainly for large hail and to a lesser degree for severe convective wind gusts.
A level 3 is issued for a small area in NE Italy mainly for large hail and to a lesser degree for tornadoes and severe convective wind gusts.
A level 1 and level 2 are issued for N Italy, SE Austria, Slovenia, Hungary, parts of Croatia, Bosnia-Herzegovina, Serbia, Romania and Bulgaria mainly for large hail, excessive convective precipitation and to a lesser degree for severe convective wind gusts.
A level 1 and level 2 are issued for the rest of Austria, Germany and the S Czech Republic mainly for excessive convective precipitation.
A level 1 and level 2 are issued for Slovakia, SE Poland and the SW Ukraine, as well as for the W half of Turkey for excessive convective precipitation, large hail and to a lesser degree for severe convective wind gusts.
A level 1 is issued for parts of Belarus and NW Russia mainly for excessive convective precipitation and to a lesser degree for large hail, severe convective wind gusts and tornadoes.
A level 1 is issued for NE Turkey, Georgia and the Russian Caucasus region mainly for large hail and severe convective wind gusts.
Steering cyclones are placed over Finland and over the Atlantic near 50N 15W. A meandering W to SW flow at 500 hPa and a diffuse frontal boundary near the surface stretch from the Bay of Biscay to NW Russia at their southern flank. South of this frontal boundary, very warm to hot, often moist and unstably stratified air covers the majority of the continent. Under mostly weak geopotential/pressure and temperature gradients, a cut-off low moves from the Alpine region to the N Balkans and another one is stationary over the Black Sea, whereas mid-level ridging and a surface anticyclone dominate from France to Germany and Poland.
... Alpine region, N Italy, N Balkans, Hungary ...
Particularly rich low-level moisture has gathered on the warm side of the frontal boundary and is overspread by the fringes of a Saharan elevated mixed layer. Widespread, daily convective overturning limits CAPE over the Alps to some hundred J/kg, whereas the airmass south of the Alps remained largely capped until Friday evening, yielding CAPE on the order of 1500 J/kg per 12z Rivolto, Zagreb and Belgrade soundings based on 2m dewpoints around 18C, and regionally up to 2500 J/kg where 2m dewpoints exceed 20C.
On Saturday, a confined mid-level jet curves around the cut-off low over the Alpine region. In its left exit, strong lift and increasing mid-level flow overspread this potent airmass from the west. By afternoon, 0-3 km shear up to 15 m/s and 0-6 km shear up to 20 m/s should become available. Interaction with the cut-off low also creates a subtle wave within the diffuse frontal boundary with temporary warm air advection and veering wind profiles.
While everything points to an outbreak of severe thunderstorms, details are still difficult to assess. In the northern part of the concerned area, both CAPE and vertical wind shear will be limited, but very moist air and plentiful synoptic and orographic lift create a typical environment for excessive precipitation and flash floods. This risk is maximized in the Italian Alps, S and E Austria and W Hungary, where most models agree on precipitation peaks exceeding 100 mm. A wedge of CAPE will likely also wrap around the cut-off low and be squeezed out in a strongly convergent wind field over the southern parts of the Czech Republic and Bavaria.
Towards the south, the main risk shifts to discrete and well-organized storms. Possible initiation sites include the tail ends or outflow boundaries of the storm clusters over the Italian and Austrian Alps, or individual storms forming over the northern parts of the Appennines and Dinaric mountains and moving onto adjacent forelands. These storms can easily turn into strong multicells or supercells with a main risk of large to very large hail.
The further south, the more CAPE is available (possibly well in excess of 2000 J/kg in inland parts of Croatia and Bosnia-Herzegovina), but the less favorable the balance between the capping inversion and the synoptic lift will be. As usual in these volatile setups, the margin between a "null event" and a memorable severe weather outbreak is therefore quite narrow, and the southernmost updrafts that still manage to persistently break the cap will likely develop into the most extreme storms.
In case convection grows upscale into an MCS later on, additional risks of cold-pool driven severe wind gusts and excessive rain would evolve and such a feature could travel as far east as E Hungary, N Serbia or even SW Romania overnight. This scenario is rather questionable, but still reflected by an eastward expansion of the lightning and risk level areas across much of the Pannonian plains.
Two small areas are upgraded to a level 3 after awaiting the Friday 12z and 18z runs:
(1) Inland Croatia: all convection-resolving models agree on strong supercell signals, hence confidence in some extreme hail events is high enough.
(2) NE Italy between the Appennines and the lower Po river: Onshore and uslope flow of very moist air from the Adria might create more than 2000 J/kg CAPE under strongly veering low-level wind profiles. Whereas a premature reduction of CAPE either by dry downslope winds or by morning convection pose limiting factors further west, an undisturbed sea breeze regime should be maintained and not disturbed until the afternoon closer to the Adriatic Sea. By then, a second vorticity maximum on a more southerly track will erode the cap and convective initiation at the sea breeze front or outflow boundaries appears to be only a question of time. Supercells with all kinds of severe weather are very likely, including a possibility of extremely large hail and one or two tornadoes. | Gewijzigd: 22 juni 2019, 12:59 uur, door Lako
Estofex level 3 27 juni 2019
Valid: Thu 27 Jun 2019 09:00 to Fri 28 Jun 2019 06:00 UTC
Issued: Thu 27 Jun 2019 09:40
Forecaster: GATZEN/PISTOTNIKA level 3 is issued for E-most Hungary and W Romania mainly for large hail and severe convective wind gusts.
Level 1 and 2 areas are issued for parts of Belarus, SW-most Russia, the Ukraine, Moldova, Romania, Slovakia, Hungary, Serbia, Bosnia-Herzegovina, Croatia, Slovenia and Austria mainly for large hail and to a lesser degree severe convective wind gusts and excessive convective precipitation.
A level 1 is issued for the Celtic Sea south of Ireland mainly for large hail.
A level 1 is issued for NE Turkey, Georgia and the Russian Caucasus region mainly for large hail and to a lesser degree for severe convective wind gusts.
A level 1 is issued for the E Black Sea mainly for non-supercellular tornadoes (waterspouts).
A high across northern Africa extends over France and ridges into the British Isles. At its western flank, a highly amplified trough is situated west of Europe. A plume of very warm, well-mixed air had spread into east Iberia, most of France, the Bay of Biscay, and southern British Isles. Another trough across Scandinavia amplifies over eastern Europe, associated with intense cold air advection over large portions of Europe. A frontal boundary extends from northern France to southern Germany, Hungary, and across the Ukraine and east Belarus, where a surface low moves east. Rich low-level moisture along this frontal boundary overlaps with steep lapse rates especially from France to Romania, where high CAPE develops. Finally, a weak trough is situated from Turkey to the south Mediterranean.
Kaart alle level 3 forecasts van Estofex
| Gewijzigd: 28 juni 2019, 18:58 uur, door W. in t Erland
Ik heb een overzicht gemaakt van alle level 3 forecasts. De uitkomst vond ik vrij verrassend, Oost-Nederland heeft van Estofex de meeste level 3 forecasts gekregen, gevolgd door Slovenië en Noordwest-Roemenië. (Natuurlijk staat een level 3 forecast niet gelijk aan de hoeveelheid extreem weer.)
Een mogelijke verklaring voor de hoge hoeveelheid is de samenstelling het publiek en het team achter de forecasts. Ik denk dat Estofex toch beter bekend is in onze regio en dat ons gebied daarom ook wat meer aandacht krijgt door het team. Daarnaast is deze regio ook dichtbevolkt en daardoor lopen er misschien meer mensen risico bij noodweer.
3 juli 2019
Valid: Sat 06 Jul 2019 06:00 to Sun 07 Jul 2019 06:00 UTC
Issued: Fri 05 Jul 2019 23:27
A level 3 is issued for NE Italy and S Austria mainly for large hail and to a lesser degree for severe convective wind gusts. In addition, tornadoes are possible in NE Italy.
A level 1 and level 2 are issued for a belt from central France to W Hungary and Slovenia mainly for large hail, severe convective wind gusts and excessive convective precipitation.
Level 1 areas are issued for S France and E Spain for large hail and severe convective wind gusts.
A level 1 is issued from the E Ukraine into W Russia mainly for excessive convective precipitation and to a lesser degree for large hail and severe convective wind gusts.
Low 500 hPa geopotential stretches from Iceland to Scandinavia and NW Russia. An unseasonably strong mid-level jet is present at its southern flank. It gradually connects with a second jet streak over SW Europe ahead of a cut-off low west of Portugal, resulting in a broad zone of enhanced zonal flow across central Europe.
The associated frontal zone near the surface stretches from France to the Ukraine and remains stationary. Hot air is present to its south.
... France and greater Alpine region ...
An elevated mixed layer (EML), originally created over NW Africa and the Spanish plateau, is picked up by the increasing westerly flow and advected over the Alpine region, where it is reinforced by strong daytime heating. Low-level moisture has recovered well under the capping inversion on Friday. Since the upstream regions over France and Spain where largely devoid of convective overturning, the robust CAPE predictions that are offered by the forecast models for the warm side of the frontal zone on Saturday appear realistic or even too conservative. Expected CAPE magnitudes by Saturday afternoon are 500-1500 J/kg over central France, Switzerland and S Germany, 1000-2000 J/kg over S France and 2000-3000 J/kg over N Italy, but peak values along convergence zones may still be 1000 J/kg higher. The highly unstable airmass is overspread by steadily increasing vertical wind shear, often reaching or even exceeding 20 m/s across the 0-6 km layer in the afternoon and evening. This impressive CAPE-and-shear overlap sets the stage for the first day of a severe weather outbreak of possibly extraordinary dimensions.
The day may start with elevated and initially weak convection across central France near the forward rim of the EML. It is not ruled out that this convection will already start to root down until noon and bring first severe storms that move from E France into SW Germany and Switzerland. Otherwise, convective initiation becomes increasingly likely over orographic features from early afternoon onward. Model agreement about its timing and placement is limited, but subtle warm air advection, numerous crossing vorticity maxima and persistent upvalley and upslope circulations offer plentiful sources of lift across all scales, and the question is not IF, but rather WHEN convection will form. Towards evening, secondary initiation at outflow boundaries and other convergence zones becomes increasingly likely as well.
Storms will quickly organize into strong multicells, supercells and bowing lines or grow upscale into large clusters. Large hail and severe wind gusts are likely and scattered extreme events are foreseen across the entire level 2 area. Supercells with extremely large hail are more likely over the Alpine forelands, where enough low-level moisture is maintained beneath the capping inversion to allow fat CAPE profiles. in contrast, possible swaths of widespread severe to extreme wind gusts can explixitly include the Alpine terrain as well - deeper mixing and higher cloud bases can compensate a somewhat weaker storm organization, and the expected storm motion from west to east appears favorable for their gust fronts to burst out into major west-east running valleys.
The risk of extreme developments culminates on the southern side of the Alps in the late afternoon and evening. From 14 UTC onwards, storms from the southern Alps will likely start to descend into the Klagenfurt Basin (S Austria) and the plains of Friuli and Veneto (NE Italy), where they encounter the highest CAPE and the best wind profiles on the moist side of a dryline. Fine-meshed models agree on several right-moving supercells which can bring large to giant hail, downbursts and very heavy rain. In addition, a remarkable tornado risk unfolds in the NE Italian plains, where sea breezes enhance low-level shear and may boost 2m dewpoints to 24 or 25C by sunset. A few tornadoes are possible and even a strong tornado is not ruled out in case the track of a supercell can connect with an outflow boundary, the sea breeze front or another convergence zone.
Uncertainties of this forecast grow towards the east (E Austria, Slovenia, N Croatia, Hungary), where the CAPE buildup needs some hours more, the capping is stronger and synoptic lift arrives later. A few "cap breakers" over orographic features can organize well and turn severe, but could fall victim to the cap again soon after they detach from the mountains. There is some consensus that a large storm cluster will cross Austria and Slovenia overnight with an ongoing risk of severe wind gusts, excessive rain and localized large hail before it gradually decays over Hungary and Croatia. Tail-end storms to the south may still turn supercellular and propagate towards the unconsumed air further south, hence N Italy could repeatedly be affected by corridors of all kinds of severe to extreme weather throughout the night.
7 juli 2019
Valid: Sun 07 Jul 2019 06:00 to Mon 08 Jul 2019 06:00 UTC
Issued: Sat 06 Jul 2019 21:33
A level 3 was issued across NE Italy, Slovenia, N Croatia and N Bosnia mainly for damaging wind gusts, large to very large hail and excessive rainfall.
A level 2 was issued across N Italy, N Adriatic, N Bosnia, N Serbia into extreme W Romania mainly for large to very large hail and damaging wind gusts.
A level 2 was issued across E Slovakia into SW Ukraine and extreme NW Romania mainly for large to very large hail, severe wind gusts and excessive rainfall.
A level 1 was issued across Massif Central, N Alpine forelands mainly for large hail, excessive rainfall and severe wind gusts.
A level 1 was issued across Romania, Ukraine and Belarus mainly for severe wind gusts and large hail.
A level 1 was issued across E Spain mainly for severe wind gusts and large hail.
A level 1 was issued for the Caucasus region mainly for excessive rainfall and severe wind gusts.
In a broad belt of strong zonal flow at mid to upper troposphere, several short-waves troughs are forecast to track from the Northern Sea through N Poland towards the Baltics and Russia. At the same time, closer to the surface, a low pressure system will move from the Baltic Sea towards Russia. Associated cold front, which will be located over N France, S Germany, Czech Republic and SE Poland on Sunday 06 UTC, will move towards the Alpine range and cross Austria, Hungary, much of Romania and Ukraine by the next morning. As strong mid-tropospheric flow will overlap moist boundary layer ahead of the front, large area over Europe, in a belt from E France towards Belarus, may experience at least isolated severe convective storms.
... N Italy towards W Romania ...
A severe weather outbreak is forecast over the area given overlap of 15 - 25 m/s of DLS with 1000 to 3000 J/kg of MLCAPE, yielding high probabilities of severe weather in any convective storm that forms. Scattered to widespread coverage of storms is forecast from NE Italy to Romania with cold front serving as a lift factor of virtually uncapped airmass. Coverage of storms becomes more questionable over NW Italy, given the fact that cold front does not reach this area and initiation will likely depend on the local topography.
Abundant convective activity may already be ongoing over the Alpine range and over N Italy / Slovenia on Sunday morning. Given the environment, this activity may already be severe and may impact the consequent development over the northern part of the area. As day progresses, further rounds of severe convective storms are forecast. It is likely that isolated supercells will form on the Alpine and N Appenines foothills in the early afternoon to evening hours and progress SE-wards, merging into one or more convective systems. High res NWP currently suggests that one such system may cross from NE Italy towards the Adriatics and another one from Slovenia towards Croatia, N Bosnia and Serbia. Towards the late evening and night hours, storms are forecast to reach and/or initiate over Romania.
Large to very large hail will accompany supercells, while well organised systems, including bow-echoes, may produce multiple swaths of damaging wind gusts. Tornado threat will be low initially given weak low level shear, but may increase towards the evening with strengthening wind field around the Adriatic Sea. Level 3 is introduced for the region where widespread storm activity is simulated in high CAPE and strong shear parameter space.
10 juli 2019
Valid: Wed 10 Jul 2019 09:00 to Thu 11 Jul 2019 06:00 UTC
Issued: Wed 10 Jul 2019 08:59
A level 3 was issued across Puglia, Italy, mainly for very large hail, damaging wind gusts, tornadoes and excessive rainfall.
A level 2 was issued across Central - South Italy, Albania, Montenegro, North Macedonia, Northern Greece mainly for large to very large hail, damaging wind gusts, tornadoes and excessive rainfall.
A level 1 surrounds Lvl 2 for areas with lower probablities of severe weather.
Satellite imagery reveals a short-wave trough crossing Corsica and Sardegna at the moment, accompanied by isolated thunderstorm activity over these islands. The short-wave is forecast to rapidly translate E-wards, across Italy towards the S Balkans and NW Turkey. As the short-wave crosses the region with very moist airmass and the cold front sweeps across the Adriatic and Balkans towards the Ionian and the Aegean Sea, widespread thunderstorm activity is forecast from Central Italy to N Greece.
Scattered thunderstorms are also forecast over parts of Ukraine, Belarus and Russia, underneath an extensive cyclonic vortex, in the environment of marginal CAPE and weak vertical wind shear.
... Central Italy to N Greece ...
Ahead of the rapidly moving short-wave, mid-tropospheric wind field is forecast to strengthen considerably. Forecast hodographs reveal unseasonably strong bulk vertical wind shear, with 0-6 km values reaching 25 - 35 m/s and 0-3 km values 20 - 30 m/s. While hodographs will stay rather straight, enhanced SRH values are forecast particularly over the coastlines of Puglia with 0-3 km SRH reaching up to 400 m2/s2. Combined with 1000 to 2500 J/kg of MLCAPE in very moist airmass, any developing storm may either become a long-lived intense supercell or a bow-echo, capable of extremely severe weather. Convective mode, isolated cells or a large system, will likely impact the dominant type of severe weather.
As of 9 UTC, a long-lived, right-moving cell is moving along the western Adriatic Sea coastline and several elevated cells are ongoing across S Italy and parts of Balkans. Towards the early afternoon, convective coverage is forecast to rapidly increase over Italy and subsequently also over Balkans, in conjunction with the passage of the short-wave and the front. Storms will spread S and SE during the forecast period and are forecast to reach NW Turkey by Thursday morning.
Storms will be capable of all kinds of severe weather, including tornadoes and excessive precipitation, but the primary threats will be very large hail and damaging wind gusts. A level 3 is introduced for the area where NWP simulates widespread storms in high CAPE, strong shear and high SRH environment as the low level wind field backs to E-ly direction. However, it is possible that the cores of some of the storms will remain over the sea and in such case, severe weather would impact only the offshore areas. | Gewijzigd: 10 juli 2019, 12:28 uur, door Lako