Storm Forecast
Valid: Tue 24 Jun 2008 06:00 to Wed 25 Jun 2008 06:00 UTC
Issued: Mon 23 Jun 2008 21:49
Forecaster: SCHLENCZEK
SYNOPSIS
A ridge is building over western-central Europe, surrounded by two upper lows. The low pressure system west of Ireland will slowly move northeastward which supports WAA over France and Germany during the day. An upper longwave trough with an attendant occluding surface low over Scandinavia will translate northeastward. On the warm side of a frontal boundary that stretches from western Ukraine via Czech Rep. and southern Belgium towards the Bay of Biscay and extreme western Portugal, diurnal heating as well as WAA at lower levels will create significant instability in the hot and moist airmass. Latest GFS runs develop a surface low over southern France in the vicinity of a weak upper level cut off low. Stable conditions in a hot and dry airmass will prevail over eastern Mediterranean.
DISCUSSION
...Iberia, Balearic Islands...
Low-end instability is expected to form in an environment with an impressive EML as shown by the last 12 UTC soundings from Murcia and Barcelona. Even though moderate DLS is forecast, a lack of forcing should preclude severe convection and a thunderstorm / level area is not warranted at the moment.
...France...
Ahead of the upper low, about 2 kJ/kg MLCAPE may form during the day. The surface low that is expected to develop over central France will lead to veering winds as shown by slightly enhanced (100 J/kg) SRH3 values. In the vicinity of the upper jet streak, deep layer shear in order of 15 to 20 m/s is expected. Forcing is expected to be rather weak and convection should develop more isolated. Vertical shear as well as huge CAPE may lead to organized multicells and a few supercells, capable of producing widespread large / isolated very large hail and severe gusts. Rather weak LLS and quite high LCLs should reduce the tornado risk but an isolated tornado is not ruled out though.
...S Germany, Switzerland, Austria, N Italy, Hungary...
During the afternoon, a 25 m/s jet streak at 500hPa will overspread southeastern Germany, Austria and Czech Rep. where about 1 kJ/kg MLCAPE should be available. Although forcing is rather weak, organized multicells and some supercells may develop, posing a risk of large hail and severe gusts. GFS is quite uncertain where the best BL moisture could be expected. A level-two threat may be issued later on when soundings or satellite / radar images hint at storms with a threat of very large hail and / or damaging winds. Convective activity will probably decrease after sunset.
...N Romania, W Ukraine...
In a moderately unstable environment with 15 m/s deep layer shear, organized multicells and perhaps a few supercells may develop during the afternoon. Forcing is rather weak and storms will probably stay more isolated which increases the chance for large hail and severe gusts.
As a side-note for all areas with moderate to high instability: Storms may persist for a long time and intense convective rainfall may lead to an enhanced flash flood threat.
...S Finland...
In the wake of the trough, some hundred J/kg of CAPE should be sufficient for diurnally driven thunderstorm development with small hail and gusty winds. Weak vertical shear, especially at lower levels, and strong LL buoyancy indicated by forecast soundings with a moist boundary layer may allow a few funnels / short-lived tornadoes.
...Ireland, N UK...
In the vicinity of the approaching frontal zone with some QG forcing, some showers and thunderstorms may form in an environment with a few hundred J/kg of CAPE. Strong (25 m/s) low level winds suggest that isolated severe gusts are not completely ruled out. Despite the relatively good kinematic features, a threat level is not introduced as instability is probably too marginal for organized severe convection.
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