24-05-2009 | Estofex | m.b.t. 25-05-2009 t/m 26-05-2009
A level 2 was issued for N France and Benelux mainly for severe wind gusts, large hail, tornadoes and excessive precipitation.
Storm Forecast
Valid: Mon 25 May 2009 06:00 to Tue 26 May 2009 06:00 UTC
Issued: Sun 24 May 2009 22:55
Forecaster: PUCIK/GROENEMEIJER/TUSCHY
A level 2 was issued for N France and Benelux mainly for severe wind gusts, large hail, tornadoes and excessive precipitation.
A level 1 was issued for much of England for excessive precipitation and large hail.
A level 1 was issued for Germany, Switzerland, Austria, Slovenia for large hail and severe wind gusts and excessive precipitation.
SYNOPSIS
A mid-level cut-off low with its center over western Spain will slowly connect with a short wave trough, which is travelling in a strong westerly flow above the Atlantic. This trough will deepen during the day and a blocking situation will be established with a significant ridge stretching from the central Mediterranean to southern Scandinavia. Strong southerly flow is simulated between these two features. To the east, yet another trough will stagnate over Eastern Europe. Strong WAA is already underway on the lee side of the ridge and a tropical airmass is expected to reach Northern Germany and Southern Britian. Wavy cold front will slowly propagate eastwards and a surface low has developed under the left exit region. This low will rapidly propagate northeastwards and deepen and its center is forecast to be over the Northern Sea by Tuesday morning.
DISCUSSION
....N France, Benelux....
Two waves of thunderstorms are simulated by models in this region.
The first one is expected with an isolated storm development in the afternoon hours. Impressive instability release is predicted with MLCAPEs probably reaching locally more than 3000 J/kg and in combination with moderate wind shear ( 15 m/s in 0-6 km layer), any developing thunderstorm will have a chance to produce large, or even giant hail. Delta Theta E values should reach more than 16 K, implying a threat of downbursts in the storms. A development of MCS is not ruled out as storms will progress to the north. The initiation of storms seems to be most likely over NW France along the warm front that is moving northward.
The second wave of storms will reach the region in night hours, probably in form of one or more well developed MCS. At the same time a surface low will undergo a deepening process and strenghtening wind speeds at lower levels. At 850 level, strong southerly flow is anticipated wind windspeeds over 20 m/s. Increasing low and mid level shear suggest a serious wind gust threat with those MCS, especially in case bow echoes form. Furthermore, tornadoes are possible given the strong low level wind shear, low LCLs and a possibility that some embedded rotating structures will develop within MCS ( this is supported by the strenghtening SREH in the vicinity of the surface low). Very strong low level convergence, humid airmass and high rainfall amounts simulated by both GFS and ECMWF models point to the threat of heavy convective rainfall with MCS.
....England...
A threat of large hail is anticipated over the SE England in the evening hours, as more than 1000 J/kg of MUCAPE are quite probable as well as moderate to strong DLS ( 15 - 20 m/s). Storms will likely cross the region in form of MCS and during the night hours the system should reach the Northern Sea. Also here a threat of excessive precipitation is present especially over the NW part of Level 1.
Hagel(-schade) | Onweer/blikseminslag | Tornado/hoosverschijnsel(en) | Verwachtingen/waarschuwingen | Wateroverlast/(zware) neerslag | Wind/storm (-schade)