CONVECTIVE FORECAST
VALID Sat 25 Jun 06:00 - Sun 26 Jun 06:00 2005 (UTC)
ISSUED: 24 Jun 20:07 (UTC)
FORECASTER: DAHL
There is a slight risk of severe thunderstorms forecast across
SYNOPSIS
As Atlantic upper long-wave trough closes off into a cutoff low ... residual NRN-stream trough will accelerate eastwards ... mainly affecting NE Europe on Saturday. Meanwhile ... upper ridge will build over the western and central Mediterranean ... with weakening slowly eastward-moving upper low present over Turkey. Main low-level frontal boundary is progged to stretch from the NW Iberian Peninsula across the Gulf of Biscay ... the S British Isles and the SRN North Sea into NE Europe ... with the NRN segment of this boundary expected to make some eastward progress ahead of the upper trough. Extensive SFC high over the Atlantic should spread into NW and central Europe ... while rather quiscent conditions persist across the SRN portions of Europe. Weak SFC lows/SFC-pressure trough is progged to exist over SWRN and central portions of Europe E of the main frontal boundary.
DISCUSSION
...central Europe and France...
Air mass over France and Germany should become moderately unstable again ... with maximum MLCAPEs locally probably exceeding 1500 J/kg. It seems that mid-level ridging will limit TSTM potential across France ... so that TSTM coverage should be somewhat lower than on the previous days ... though several outflow boundaries may provide sufficient mesoscale ascent despite weak QG sinking motion.
Coverage over Germany is somewhat uncertain as well ATTM as models strongly disagree on the amount of convective precip. However ... confidence is high that deep low-level moisture will continue to advect NEWD ahead of the front ... and that air mass will be rather weakly capped. Though distinct focus for mesoscale ascent is not apparent ATTM ... at least scattered TSTMS should form in the afternoon hours in the vicinity of mesoscale pre-frontal SFC lows/SFC-pressure trough ... and outflow boundaries from Friday's convection.
Deep shear should be sufficient for multicellular storms ... capable of producing large hail and damaging winds. Isolated mesocyclones may form despite the weak large-scale shear if locally LL shear is augmented along outflow boundaries and orography ... especially in the Alpine regions ... and should augment the hail/wind threat. TSTMS may merge into larger clusters in the evening hours ... and should slowly decay during the night. An upgrade to SLGT may be required across France and Germany if confidence in widespread vigorous convection increases.
...N Poland ... Baltic States...
Farther NE ... instability/low-level moisture should be somewhat weaker ... but large-scale forcing for UVVs and kinematic profiles will be substantially stronger. Current thinking is that lines of TSTMS/bow echoes will form along and ahead of the cold front ... mainly posing a threat for damaging wind gusts. Strong low-level shear may also favor development of some supercells ... capable of producing severe wind gusts ... large hail and maybe a brief tornado or two.
...N Spain...
Another round of isolated high-based TSTMS is expected over NRN Spain ... capable of producing severe straight-line winds and some hail given deep/dry subcloud layer and 15 to 20 m/s deep shear. Lack of large-scale upward motions should limit TSTM coverage ... and a SLGT does not appear to be necessary ATTM.
...Italy...
weak vort max at the N/E periphery of building Mediterranean upper ridge will affect Italy ... supporting development of scattered TSTMS during peak-heating hours mainly at along orographic features. Minimal shear will likely limit organized-severe TSTM threat ... though strong thermodynamic profiles may allow storms to briefly attain severe levels.
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