Storm Forecast
Valid: Mon 06 Jun 2011 06:00 to Tue 07 Jun 2011 06:00 UTC
Issued: Mon 06 Jun 2011 10:23
Forecaster: DAHL

(this forecast was issued 22:03 UT but posted late)

A level one threat has been issued across N Spain and SW France mainly for excessive convective rainfall.

A level one threat has been issued across N Italy, W Slovenia, and S Austria, mainly for large hail, severe wind gusts, and excessive convective rainfall.

A level one threat has been issued across the SW Mediterranean mainly for large hail and damaging wind gusts.

SYNOPSIS

An amplifying Atlantic upper trough remains anchored off the continental European west coast. East of this trough, weak southwesterly
upper flow exists over western and central Europe. A weakening small upper low is embedded in this flow and will
migrate from N Italy into the Czech Republic/S Poland on Monday. Warm moist air is present over central and southern Europe, and although the lapse-rates in this air mass are consistently weak, sufficient low-level moisture is present to result in weak to moderate instability.

DISCUSSION

... SW Europe ... central Europe ... SE Europe ... N Mediterranean ...

The large-scale setup seems to be rather homogeneous from SW and central Europe into SE Europe and the northern and central Mediterranean.
It seems that some 500 to 1000, locally up to 1500 J/kg of MLCAPE will exist in an essentially uncapped air mass in the afternoon hours.
Though there is no focus for large-scale ascent, outflow boundaries and orography will likely initiate thunderstorms in the early afternoon
hours. Given a lack of vertical shear, storms should remain disorganized, limiting the severe-weather threat. However ... storms may congeal
into larger clusters towards the evening hours, which may locally/briefly result in a marginal hail and severe-wind threat. Given slow storm
motions, locally excessive rainfall may occur. The average severe threat across this large area seems to be too small for a categorical
risk ... however, a few regions can be highlighted where the threat is slightly enhanced:

Over N Italy, W Slovenia, and S Austria, some 20 m/s DLS should exist near the compact upper low. This will likely support multicellular and mesocyclonic storms capable of primarily large hail and severe wind gusts.

Over N Spain and SW France, there seems to be a potential focus for storm clustering/heavy rain according to WRF and GFS guidance.

Over the Czech Rep., Slovakia, and Poland, low-level shear will increase beyond 10 m/s in the evening hours. Although this probably will not aid in storm organization, a brief funnel/tornado could occur, if convection persists despite the loss of daytime heating. Overall confidence in severe weather is too low for a LVL1, however.

... SW Mediterranean ...

Steep Saharan lapse rates will overspread the SW and S-central Mediterranean on Monday. It seems that convection will form near the western edge of the EML plume ahead of a mid-level vorticity maximum. Shear should be sufficient for organized storms that will pose a threat mainly for large hail and damaging winds.