ESTOFEX Storm Forecast

ESTOFEX Forecast www.estofex.org

A level 2 was issued across N to NE Spain mainly for large to very large hail, excessive precipitation and to the lesser extent for severe wind gusts.

A level 1 was issued across N Spain, France, N Italy, S and E Austria, Slovenia, S Czech Republic, W Hungary, E Croatia and Bosnia mainly for large hail, excessive rainfall and to the lesser extent for severe wind gusts.

A level 1 was issued for S-Central Italy mainly for excessive rainfall and large hail.

A level 1 was issued for parts of Turkey mainly for large hail, severe wind gusts and excessive rainfall.

A level 2 was issued for S Caucasus mainly for large to very large hail, severe wind gusts and excessive rainfall.

A level 2 was issued for W Russia mainly for excessive rainfall, tornadoes, severe wind gusts and to the lesser extent for large hail.

A level 1 was issued for Algeria mainly for large hail.

SYNOPSIS

A large part of Europe will experience isolated to widespread thunderstorms during the forecast period. One of the reasons for this will be synoptical situation, which will feature a trough shifting from U.K. towards France and Iberia and a large, stationary, cyclonic vortex centered over Belarus and N Ukraine. The base of the vortex will rotate as a short-wave trough from Greece towards Turkey. In the evnrionment of modest lower tropospheric moisture, widespread thunderstorms are forecast in a belt from W Spain through France, S Alpine range into Romania and Belarus. Another belt of pronounced thunderstorm activity is forecast from Turkey towards the Caucacus and W Russia. Over many of these areas, NWP simulates an overlap of DLS around 15 m/s with several hundreds to around 1000 J/kg of MLCAPE. In such conditions, well-organised storms, including multi- and transient supercells will be possible with severe weather threat.

DISCUSSION

... Spain to France ...

Widespread storms are forecast to occur over this area during the forecast period in a combination of synoptic-scale lift from the approaching trough, rich topography and a cold front lingering over the northern part of the area. NWP models consistently simulate overlap of substantial MLCAPE, ranging from 500 to 2000 J/kg and moderate to strong DLS. The best overlap of CAPE and shear is forecast across E Spain, where DLS will likely exceed 20 m/s in the afternoon hours. Well organised storms, including multi and supercells are forecast with primary threats of large hail and excessive precipitation. Very large hail may occur as well, especially over E Spain. Severe wind gust risk may be lower in the beginning, owing to the rather moist profiles and low LCLs, but may increase as the storms congeal into numerous large systems in the late afternoon to evening hours.

... S Alps towards Balkans ...

Yesterday, numerous severe storms, capable of large hail have occurred over N Italy. Similar situation will continue today, with storms developing over the local topography and progressing S-SE in the prevailing NW-ly flow. While the DLS will be modest, mostly between 10 - 15 m/s, local upslope winds on the southern slopes may enhance the DLS to reach around 20 m/s and again support formation of several supercells, capable of large hail and excessive precipitation. The degree of DLS will increase from W to E and the most organised and strongest storms are forecast along the eastern fringe of the Alpine range by high resolution NWP.

... W Russia ...

A WAA regime is forecast over the area with a tongue of CAPE spreading northward during the forecast period. Models are uncertain about the exact location of the individual convective clusters, but it looks like one or two will develop and move N along the warm front, yielding some excessive rainfall events. As pressure falls along the frontal wave, isallobaric winds will contribute to curved hodographs with 0-1 km SRH locally exceeding 200 m2/s2. Combined with low LCLs, this would point to a substantial tornado threat. Convective mode and the stability of boundary layer remain concern as the highest SRH area is confined to the zone, where models simulate widespread rainfall just to the north of the warm front.

... N Turkey to Caucasus ...

NWP simulates a pronounced overlap of non-zero MLCAPE and DLS exceeding 20 m/s, as well as numerous storms developing over the area. Both the strongest shear and the highest CAPE is simulated just south of the Caucasus, where any forming storm will pose a risk of large to very large hail and severe wind gusts. It is possible that storms will congeal into severe wind producing MCS that will quickly move towards NE. However, should it cross the Caucasus, it is likely that its cold pool will be distrupted, weakening the system.

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