Storm Forecast
Valid: Mon 02 May 2011 06:00 to Tue 03 May 2011 06:00 UTC
Issued: Mon 02 May 2011 03:04
Forecaster: DAHL

A level one threat has been issued across the western and central Mediterranean regions for severe wind gusts, large hail, and tornadoes.

... SYNOPSIS ...

Upper-air analyses show a blocking pattern over Europe, the main feature being a quasi-stationary cut-off cyclone over Scandinavia/northern Europe. A meandering southern frontal zone is stretching across the Mediterranean regions. A trough imbedded in this frontal zone will cross the SW and central Mediterranean during the period and maintain a weak attendant SFC low.


... DISCUSSION ...

... Iberia ... France ...

Scattered diurnally driven thunderstorms are anticipated across Iberia and France. Large-scale shear and CAPE will be weak, so the overall severe threat should be rather low. Still ... outflow boundaries laid out by Sundays convection ... orographic modifications of the low-level flow field, and in situ cold-pool formation ... may support a brief/isolated severe wind/hail event or three. The overall threat is not focused enough, however, to highlight a particular region.

... southern Germany ... interalpine regions ...

The convective activity may extend into southern Germany and Austria, where DLS will exceed 20 m/s per GFS. However, instability is progged to be quite shallow where shear becomes acceptable ... farther into the inter-Alpine regions, instability will improve but the shear will be weak. It seems that an isolated marginally severe hail event or two cannot be ruled out but minimal instability over S Germany currently precludes LVL1 severe probabilities.

... SW and central Mediterranean ...

It seems that a somewhat more robust severe weather threat might evolve over the western and central Mediterranean ahead of a compact vort max. DLS should be in excess of 25 m/s, with LLS in the 10 to 15 m/s range. Regarding the thermodynamics ... a Saharan EML should be advected into the region, contributing to steep lapse rates. The boundary-layer moisture may be on the weak side, but sufficient for positive CAPE. Given the strong large-scale ascent, at least scattered storms are anticipated to develop. The shear magnitude and inferred GFS hodograph shape seem to favor supercells, which could potentially produce large hail, severe wind gusts, and possibly a tornado or two. The only negative is somewhat weak instability and possibly strong capping owing to the EML ... precluding the introduction of more solid severe-weather probabilities at the moment.