Storm Forecast
Valid: Sun 29 Apr 2007 06:00 to Mon 30 Apr 2007 06:00 UTC
Issued: Sat 28 Apr 2007 20:55
Forecaster: DAHL

SYNOPSIS

Not much of a change compared to Saturday is expected on Sunday ... except that the Iberian upper cut-off cyclone will make further eastward progress, reaching the central Mediterranean regions late in the period. Downstream vort max over the Aegean region will likewise move east and leave the forecast region during the day.The cold front at the S/E periphery of the north European SFC high will continue its southward progression and curve from southern Germany across the N Balkans and the E Ukraine into central Russia by Monday 06Z.

DISCUSSION

... France ...

Another round of diurnal TSTMS is expected over France in weakly unstable and weakly capped environment. Shear remains minimal, and allover severe threat should be accordingly low. However, numerous mesoscale boundaries should be in place mainly as a result of previous convection, and locally, the low-level shear profiles may be augmented along the boundaries and support at least brief mesocyclones. These would be capable of the entire facet of severe convective weather. However, threat is too conditional for a categorical risk.

... east-central Europe ... north Balkans ...

Challenging forecast over the Balkans and E-central Europe. Weak DCVA-related ascent will accompany the southward digging E-European upper long-wave trough, and which should also support low-level mesoscale ascent along the cold front. Instability is unlikely to be large, but sufficient for scattered TSTMS. Deep-layer shear will be on the order of 15 to 20 m/s per GFS, which would be marginally adequate for some of the cells to become severe, possibly even mesocyclonic. Main threat appears to be marginally severe hail/wind. Given the evolution as of Saturday evening, which has been slightly underestimated by the models, a categorical threat will be issued despite the weak CAPE signals in the models.

Isolated storms will likely form farther SE, as well, but in less strongly sheared environments. Deep and dry CBLs may nonetheless promote strong outflow winds, but their intensity and coverage should be too weak for a categorical risk.

... Sardinia ... W Tyrrhenian Sea ...

Some severe threat should accompany the W Mediterranean upper low. Though instability will likely remain minimal, a small spatial juxtaposition of 20 m/s deep-shear and positive CAPE contours is anticipated towards the late afternoon. Main threats should be marginally severe wind and hail, though moist maritime boundary layer may boost the LL buoyancy and increase the threat for an isolated tornado or two.