Storm Forecast
Valid: Thu 10 Oct 2024 06:00 to Fri 11 Oct 2024 06:00 UTC
Issued: Wed 09 Oct 2024 20:41
Forecaster: TUSCHY
A level 2 was issued for far NE Italy mainly for extreme rainfall amounts.
A level 1 surrounds the level 2 for similar hazards but with lowered probabilities. In addition, an isolated tornado/hail and severe gust risk exists.
A level 1 was issued for the Genoa area for heavy rain.
SYNOPSIS
The rather static wave pattern continues over Europe with an extensive N-S aligned upper trough, which runs from the Norwegian Sea down towards CNTRL Europe, before bending W into the open NE Atlantic. This trough gets framed by a belt of positive mid-level height anomalies. This configuration places most of the Mediterranean in a westerly flow regime with a dominant cyclonic regime over NW Europe into most of Scandinavia. Numerous synoptic fronts cross CNTRL Europe into E Europe and the CNTRL Mediterranean.
An anomalous deep depression evolves W of Portugal but stays W of our forecast area until the end of the day. This feature becomes the main focus for a multi-day convective event for SW Europe beyond the SWODY 1.
DISCUSSION
... N-Italy to Slovenia ...
The combination of a dragged frontal system and a broad/diffuse lee cyclogenesis over N-Italy assists in scattered to widespread CI all day long. As the depression strengthens, a marine airmass pushes N towards the S fringes of the Alps. A zonally aligned belt of better LL moisture assists in MUCAPE in the 600-1200 J/kg range. DLS stays in the 15-20 m/s range, with weaker 0-3 km shear. Any more (semi) discrete storm could become severe with isolated hail and gusts. The main risk however will be heavy rain with colliding and clustering convection.
Some changes compared to yesterday's SWODY 2 as the western level 2 was downgraded. The progressive nature of the trough and a bit more to the east displaced LL vortex keep training confined until noon with a subsequent weakening trend. Combined with the already ongoing convective precipitation from the previous night, we still see 12h rainfall amounts well in excess of 100 l/qm, but QPFs for this forecast period stay too low for a level 2. Nevertheless, flash flooding is possible.
No major change for the other level 2 area, as training convection is still anticipated with high resolution models peaking in the 150-300 l/qm range for the 24h period. Flash flooding is possible with a significant event not ruled out.
No change to the tornado/hail and gust probabilities, which extend into W-Slovenia/NW Croatia.
The Genoa level 1 is a marginal one, as drier air filters in from the W until noon. Until then, slow moving cells ride along the orography with a few heavy rain reports forecast.
... E France into SW Germany ...
Active CAA convection with a few short-lived thunderstorms produces gusty winds and graupel. A funnel or two are possible during peak heating with somewhat enhanced BL lapse rates.
However we upgraded parts of this area into a high probability lightning area, as a rather extensive confluent BL flow regime may assist in numerous broken line segments with enhanced lightning activity.
... Portugal and far W Spain ...
We added lightning areas for this region due to a somewhat faster approach of the low. Up to 1000 J/kg MUCAPE and increasing lift on the synoptic-scale should assist in numerous thunderstorms with some spotty heavy rain or graupel, although warm low/mid-levels should keep any graupel risk very isolated.