Extended Forecast

Extended Forecast
Valid: Thu 10 Oct 2024 06:00 to Fri 11 Oct 2024 06:00 UTC
Issued: Tue 08 Oct 2024 22:17
Forecaster: TUSCHY

Two level 2 areas were issued across N-Italy for extreme rainfall amounts.

A level 1 surrounds both level 1 areas for a similar hazard with lower probabilities. In addition, severe gusts are also possible with an isolated hail and tornado risk.

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 2.

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 and 0-3 km shear stay in the 10-15 m/s range, so any more (smei) discrete storm could become severe with isolated hail and gusts. The main risk however will be heavy rain with colliding and clustering convection.

Two confined level 2 areas were issued over N/NE Italy, where a more unidirectional flow regime alinges with robust CAPE, which supports training convection along the orography. The Lombardy level 2 is valid for the morning hours until noon (probably ongoing from the previous night) with 12h rainfall amounts in the 100 to locally 200 l/qm range. Flash flooding is possible. The other one over NE Veneto into N-Friuli Venezia Giulia evolves more in the afternoon/evening time-frame with 50 to locally 150 l/qm forecast in a 12h time frame. Both events probably see mentioned rainfall amounts in a much shorter time frame, so flash flooding is possible in both level 2 areas and a significant event is not ruled out.

Beside the rain risk, semi-discrete (probably tail-end) convection also poses a tornado and hail threat along the path of a few eastward traveling supercells. This risk could be maximized towards NE Italy, where best CAPE/shear space evolves during the afternoon/evening.

During the night, a weakening cluster of storms works its way into Croatia/Slovenia with a decreasing rain threat. W-Slovenia could see a lingering tornado risk with maturing cells approaching from NE Italy. A broad level 1 should cover that risk.

A level 1 may be needed in later updates for the SE coast of the Adriatic Sea but right now late CI keeps the severe risk (heavy rain) below the level 1 threshold.

Another level 1 was issued for the Genoa area for the morning hours with still ongoing and training convection. Heavy rain is likley with this activity.

... 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. This risk is too marginal for an upgrade for now.

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