Storm Forecast
Valid: Mon 25 Jul 2011 06:00 to Tue 26 Jul 2011 06:00 UTC
Issued: Mon 25 Jul 2011 00:08
Forecaster: DAHL

A level-one threat has been issued across the E Baltic States, E Poland, the W Ukraine, and Belarus mainly for excessive rainfall and to a lesser extent for marginally severe hail.

A level-one threat has been issued across Romania and the S Balkans mainly for large hail, damaging winds, and excessive rainfall.

A level-one threat has been issued across NW Italy and NE Spain mainly for large hail.

A level-one threat has been issued across the NE Maghreb States, the Ionian Sea, and Greece mainly for large hail and severe wind gusts.

SYNOPSIS

A deep, quasi-stationary upper longwave trough is anchored over central Europe. East of this feature, unstable subtropical air is present, which will be the focus for convective development on Monday. At low levels, rather quescent conditions prevail.

DISCUSSION

... E Europe ...

1000 to perhaps 2000 J/kg MLCAPE should become available over parts of eastern Europe towards peak-heating hours. Given the presence outflow boundaries from Sunday's convection, some DCVA associated with perturbations imbedded in the large-scale trough, and orographic forcing ... expect scattered to widespread storms to develop in the afternoon hours. GFS indicates some 15 m/s DLS over the S Balkans, Romania, and the Black-Sea region, which will be sufficient for multicells and a few mesocyclones. The primary threats should be marginally severe winds/hail, as well as excessive rainfall. However, serendipitous encounters of local augmentations of the kinematic fields may support very sporadic, somewhat more high-end hail. Weak low-level synoptic-scale shear suggests that tornadoes are unlikely, though a brief spin-up can never be ruled out completely once a supercell in a low-LCL environment moves over complex terrain.

The best CAPE/shear combination is advertised over the Black Sea ... where convective initiation seems rather unlikely, though.

To summarize ... the overall evolution should thus include mainly disorganized cells over the northern portions of E Europe, with the main threat being excessive rain, and to a small extent, marginally large hail. Towards the south, storm organization should gradually increase, so that an additional hail/wind threat is anticipated. Will include the Black Sea in the LVL1 despite somewhat unlikely convective initiation (CI) there, given high conditional severe probabilities (the condition being CI).

... France ... NW Italy ... NE Spain ...

It seems that somewhat shallow convection will occur over France in a weakly unstable air mass. DLS should be in the 15-20 m/s range, but given the minimal thermodynamic support, the overall setup is too marginal for an appreciable severe threat. However, more robust CAPE might linger over N Italy, which will be grazed by the mid-level speed max. It thus seems that there is a small probability of a hailstorm or two. A similar, small-scale region where models suggest CAPE of order 1000 J/kg and about 20 m/s DLS is extreme NE Spain and parts of the adjacent Sea. Two small LVL1 regions seem to be justified for these areas mainly for large hail.

... N Maghreb States ... Ionian Sea ... S Greece ...

Rather strongly capped but sufficiently unstable, and strongly sheared air mass will exist across the the NE Maghreb States and the Ionian Sea into Greece. The thermodynamic profiles will likely vary between high-based (N Africa, intermountain Greece) and Miller-type-1 over the Ionian Sea and the coastal regions of N Africa and Greece. Storm coverage will likely be rather small, but the setup should be supportive of isolated large hail and damaging winds.