Storm Forecast
Valid: Thu 02 Jul 2009 06:00 to Fri 03 Jul 2009 06:00 UTC
Issued: Wed 01 Jul 2009 19:31
Forecaster: PUCIK

A level 1 was issued for Great Britain and Ireland mainly for excessive precipitation

A level 1 was issued for Northern Spain and Pyrenees area mainly for excessive precipitation and large hail.

A level 1 was issued for Western France mainly for excessive precipitation.

A level 1 was issued for mainly for Poland, Czech republic, Southern Germany, Eastern Austria and Balkan states for excessive precipitation.

A level 1 was issued for Vologda oblast and surroundings mainly for tornadoes.

SYNOPSIS

Rather inconspicuous synoptic setup has established over Europe and no major changes are anticipated during this forecast period. A ridge of slightly higher geopotential heights at midlevels will stretch from SW Mediterranean into Scandinavia. To the east, a shallow trough will reside over Russia, Ukraine and Balkan states. The only apparent change to the setup is an approaching short-wave trough, which is predicted to affect the weather across Great Britain, Western France and Spain. Frontal system, associated with it, will cross the area in the late evening and night hours.

Widespread diurnally driven thunderstorms are expected over most of Central, Western and Southeastern Europe. In weak wind shear, thunderstorms will stay mostly poorly organised. Due to the slow motion of individual cells, high moisture content , local heavy rainfall event is quite possible, especially over the mountainous areas.

DISCUSSION

...Great Britain...

Ahead of the approaching cold front, soundings suggest that an unstable air mass has developed over the islands.
air-mass or air mass, not airmass, as far as I know Thunderstorms have already commenced (as of 18Z Wednesday) and for this forecast period, two rounds of convection are possible. GFS suggests that an MCS will affect southern parts of England, Wales and Ireland by early morning and noon hours, developing in vicinity to the cold front and moving northwards. Another round is possible in the afternoon and evening hours, mainly over Scotland and England, where models hint on enhanced CAPE values. Due to the high moisture content of the troposphere, slow motion and predicted formation of convective system, it seems possible that significant precipitation amounts could accumulate locally.


...Northern Spain / Pyrenees area...

This area will see slightly better wind shear, with values around 15 m/s in 0-6 km layer, especially for the Spanish part of Level 1. Moreover, slight veering of the winds with height will result in locally enhanced SREH values, which might add in the development of brief rotation in storms. Combined with moderate values of instability ( MLCAPE > 1000 J/kg with the highest values across southern France), isolated large hail event is not ruled out. Moreover, slow thunderstorm motion and high moisture content in troposphere might result in local excessive precipitation event, especially in the northern Pyrenees.

...Western France...

Widespread thunderstorms are expected to form along the approaching cold front in the belt of moderate instability, with MLCAPE values over 1000 J/kg as suggested by GFS and due to their very slow movement and high values of precipitable water, we can not rule out that isolated heavy rain event will ensue. In case that multicells manage to become better organised, a very isolated occurence of large hail might be another risk within this area.

....Poland, Czech republic, Southern Germany, Eastern Austria, Italy and Balkan states...

12Z Tuesday soundings have shown that moderate instability has developed in this region, with MLCAPEs even above 1500 J/kg at a few locations. A very similar situation will also develop this forecast period, with rapid destabilization as surface heating commences. Warm, well-mixed and humid airmass will therefore allow for another round of convection. Wind shear will stay very weak, so the storms will not become better organised than in multicell clusters. Nevertheless, slow storm motion and high moisture content (Tds approaching 20°C) will allow for localized heavy rain events, especially in the mountainous areas. In multicells, we can not even rule out a large hail event, mostly over Poland or northern Italy, where the highest values of instability should be realised. Enhanced Delta Theta-E values ( locally over 16 K) suggest that slightly severe wind gusts might also occur (again, with Poland being the place with the highest probability of this threat when compared to the rest of Level 1 regions). Due to low LCLs, weak wind fields and high CAPE release in the lowest 3 km, landspout type tornadoes might occur, especially tied to the local convergence zones.

... Vologda oblast and surroundings....

With the approaching trough from NW and associated PVA, cyclogenesis is forecast by models and a low level flow should strenghten considerably, resulting in high LLS values, locally up to 15 m/s as forecast by GFS. Moreover, prominent veering of the winds with height will result in high SREH values. Slight instability, with MLCAPE values less than 1000 J/kg will develop in vicinity of the surface low. As models show that instability will overlap with enhanced LLS and SREH, slight chance of tornadoes is forecast for the region in Level 1.