Storm Forecast
Valid: Tue 28 Jul 2009 06:00 to Wed 29 Jul 2009 06:00 UTC
Issued: Mon 27 Jul 2009 23:23
Forecaster: PUCIK

A level 1 was issued for Northern Russia mainly for excessive precipitation.

SYNOPSIS

In strong zonal flow a short wave trough is forecast to affect British Isles, turning northeastwards during its progress. At the same time, yet another trough will travel from the west, having reached almost the longitude of western Ireland by Wednesday 06Z. To the east, a ridge over Eastern Europe will slowly decay during the course of the day and a new one will start to build from the Mediterranean into Central Europe. The trough that is now situated over Western Russia with slow eastward movement will slowly decay, leaving a cut-off with center over the northeastern coast of the Black Sea. Large area of diurnally driven thunderstorms is expected over Russia around the axis of the trough. A frontal zone will stagnate in this region, having a wavy structure with several small surface lows possible, as suggested by GFS output. Weaking cold front is expected to pass over Western Poland and Czech republic during the day. At the surface a large high pressure area will start strenghtening over Central Europe. Northewestern and Northern Europe will be under the influence of surface lows.

DISCUSSION

... Ireland and Scotland...

As an impulse passes over the region, strong forcing is anticipated both from mid and upper levels of troposphere, especially in the late afternoon hours. GFS and ECMWF simulate low-end instability release, with GFS being the optimistic one with possible values over 400 J/kg, whilst ECMWF keeps the values very low, just around 100 J/kg. With low level flow strenghtening, LLS values might approach, or even locally exceed 10 m/s. Shear in the lowest 0-3 km should stay meager, only around 10 m/s, as well as SREH values in 0-3 km layer only up to 100 J/kg, so no well organised convection is expected . In case that GFS is right and strongly forced convection forms with better CAPE than in ECMWF a slight chance of tornadic event or marginally severe wind gust in these areas will exist. At this moment, it is not possible to say which model is correct and due to many uncertainities, mainly regarding the available instability, Level 1 is not warranted. However, an update might become necessary later on.

...Northern Russia ( Arkhangel´sk region)...

A belt of enhanced MLCAPE values are simulated with a tongue of high Theta-E airmass ahead of the stagnant cold front (values locally above 1000 J/kg). The aforementioned trough over Russia should provide sufficient forcing (in combination with front) for widespread initiation of thunderstorms with several rounds of deep, moist convection possible over the region. Moderate wind shear with values of 15 - 20 m/s at 0-6 km should provide sufficient organisation for storms, which might cluster into convective system, especially in the late evening / night hours in the Eastern part of the area. High moisture content, slow storm movement and high precipitation amounts simulated by models point to the possibility of heavy convective rainfall. In stronger, well organised multicells, marginally severe hail is not ruled out either.