CONVECTIVE FORECAST
VALID Fri 29 Jul 06:00 - Sat 30 Jul 06:00 2005 (UTC)
ISSUED: 28 Jul 21:19 (UTC)
FORECASTER: TUSCHY

There is a moderate risk of severe thunderstorms forecast across North central and northeastern Germany, northwestern Poland, extreme western parts of Lithuania and Latvia, southern Sweden and most parts of Denmark

There is a slight risk of severe thunderstorms forecast across central and southern Germany,Switzerland,southern France, Austria,Czech Republic and Poland

SYNOPSIS

Major upper level trough located over Great Britain and Ireland. This system should start to lift northeastward , in response to a strong upper level streak, circling around the base of the system...This slightly negative tilt helps to assist downstream weak ridging and transport of a very hot and humid airmass over most parts of southern, central and eastern Europe.
Conditions are favorable for an active severe weather day over parts of central Europe!

DISCUSSION

...North central and northeastern Germany, northwestern Poland, extreme western parts of Lithuania and Latvia, southern Sweden and most parts of Denmark...
Remnants of convective systems from yesterday [28. July]should continue to weaken during the early morning hours due to chilling of the boundary layer, but strong 500hPa jet and forcing along the cold front could sustain storm complex till the early noon hours, while moving northeastward over parts of northwestern Germany.

Otherwise, most parts of the MDT risk area will see a couple of hours of strong insolation under weak ridging....Last model runs showed very interesting solution by developing a low level depression somewhere over central and eastern Germany....Again, global models show significant differences in handling this system and adjacent precipitation ( in each model run and between different models )...Beside those uncertainties,forcing of northward shifting warm front and prefrontal convergence zone ahead of eastward moving cold front, upper level divergence induced by coupled jet structure and very strong insolation ( low CIN values )should be conducive for widespread storm initiation during the afternoon hours over the risk area.... Instability forecast of each model too optimistic...WV loop showed infiltration of relatively dry mid level airmass and yesterday sounding reports confirmed this trend...partial downward mixing of this drier airmass helped to reduce instability release yesterday and current thinking is that in the MDT area, only 500 to locally 900 J/kg will be released... If low level depression develops over central Germany, broad backing wind field north of this depression can be expected...in fact, low level shear of 15m/s +, 0-1 SRH values of 200 - locally 400 m**2/s**2 ( especially next to retreating warm front )and low LCLs would be more than adequate for each storm to organize...if this backing wind field can be established, discrete cell evolution can be expected whith main threat being very large hail, severe wind gusts and a few tornadoes - one or two of them could be strong .
Further to the north, along the warm front over parts of Denmark, southern Sweden and the Baltic Sea, storms will form in an environment with 20 - 30m/s DLS...TSTMs should string in a line pretty fast and severe MCS expected to race eastward with main threat being widespread severe wind gusts...Strong mid level jet from the south could help to build the MCS southward and parts of Poland could be affected, too...MCS should arrive in the morning hours in Lithuania and Latvia.
Final focus for TSTM development in the risk area will be the eastward moving cold front in the evening hours over northeastern Germany and Poland...being nearly parallel to background-flow, front won't be that progressive but conditions seem favorable for strong to severe storms to develop....500hPa jet could cause backbuilding of storms further to the south, where kinematic parameters are weaker...however a few organized storms could develop with a sever wind gusts and large hail risk.

...central and southern Germany,Switzerland,southern France, Austria,Czech Republic and Poland...
In the last few runs, global models showed pretty consistent the arrival of a short wave in the early evening hours over parts of Switzerland and southern Germany... This system should move further to the northeast during the night hours over parts of southern and central Germany...Forecast soundings show a pretty dry boundary layer with strong veering profilers...forecasted dew points of about 13°C looks reasonable (stations in southeastern France reported dew points of about 11-16°C at 16 UTC yesterday )... Current thinking is that increasing upslope flow over Jura Mountains and Black Forest will be conducive for scattered TSTM development during the afternoon hours over southwestern Germany...Main risk will be large hail and severe wind gusts and although low level shear is slightly enhanced, tornado threat should be only marginal...Deep layer shear will increase significantly in this time period to about 25m/s and severe MCS could develop and race northeastward with a pronounced severe wind threat...again global models disagree on the exact track of this convection line and upgrade may be needed later in the period.
Switzerland and southeastern Germany should also see isolated to scattered TSTM development during the evening hours next to a developing convergence zone...deep layer shear strong enough for some storm organisation... Forecasted dry boundary layer would be supportive for a few large hail and severe wind reports.
Parts of Austria should also see isolated to scattered TSTM initiation during the afternoon and evening hours in a weakly sheared environment....instability values up to 1000 J/kg and locally modified wind field in the alpine region should be enough for a slight severe weather risk of large hail and isolated severe wind gusts.
Weakening cold front over southern France will be a focus for TSTM initiation, too. Deep layer shear of about 20m/s will be enough for storm organisation...main threat will be a severe wind threat, especially in bowing line segments.

...parts of Great Britain and northern France...
Base of trough will shift slowly eastward over parts of southern Great Britain. North of a low-level pressure center, a warm and humid airmass will be advected from the east...Instability forecast of NMM with up to 600 J/kg too optimistic, but a corridor of slightly unstable airmass should develop...Although kinematic parameters are very low, slightly enhanced 0-1 SRH values and very low LCLs will pose a risk for an isolated tornado and severe wind gust threat.... Further southward, especially over northwestern France, arrival of cooler mid level airmass and steepening of mid level lapse rate will also cause a slightly unstable airmass and isolated to scattered TSTM initiation...an isolated wind gusts and marginal hail threat will be the main risk.

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