Storm Forecast
Valid: Thu 12 Dec 2024 06:00 to Fri 13 Dec 2024 06:00 UTC
Issued: Wed 11 Dec 2024 15:04
Forecaster: TUSCHY

Numerous level 1 areas were issued for parts of S/NE Spain and the W-CNTRL Mediterranean mainly for heavy rain (with isolated extreme peaks) and an isolated tornado risk.

SYNOPSIS

A blocking high-over-low pattern persists for most of Europe. A deep vortex over SW Europe retrogrades a bit west beneath an extensive anticyclone to its N, which covers most of N Europe. A more pronounced cold air outbreak in response to an amplified streamline pattern occurs over far NE Europe into Russia. Most of the S/E Mediterranean remain beneath an active subtropical jet, which rounds a broad/low-amplitude ridge over far N Africa.

The synoptic-scale fronts over N/E Europe remain detached from today's DMC activity.

DISCUSSION

... W-CNTRL Mediterranean ...

A rather static pressure/height pattern persists and features a brisk SE-erly near BL flow, wich turns SW-erly with height (although some modifications occur as described below).

Starting from the main vortex just W of the Iberian Peninsula, a broad and zonal aligned low pressure channel extends E towards the CNTRL Mediterranean. An embedded transient spin-up of a vortex next to the Balearic Islands pushes the overall low pressure channel N during the day. This gradually ends the brisk SE-erly BL flow next to Sardinia including best moisture advections as winds turn S and weaken. The rather deep plume of LL moisture balances rather warm mid-levels, so at least weak to modest MUCAPE is forecast during the day (weakening as the best BL moisture shifts E).

Kinematics show a bimodal behavior with weak/modest shear next to the Balearic Islands and N, before increasing significantly to the SE as we approach the subtropical jet (with 30 m/s next to the Strait of Sicily).

Expect CI all day long on an isolated to scattered scale with weak cap and neutral/slighly positive upper divergence. The main drivers for CI however become extended LL convergence zones e.g. SE of Sardinia or between the Balearic Islands and Sardinia. Expect slow moving thunderstorms either along those convergence zones, or with deviating cells (due to favorable background shear next to Sardinia), which brings the Bunkers motion near the center on forecast hodographs. An isolated tornado event is possible.

Level 1 areas were added for the rain threat but there is a risk of spotty extreme amounts, when updrafts remain anchored to the boundary with favorable moisture influx. Level 2 conditions could evolve just SE of Sardinia, but this risk remains offshore. Still healthy amounts can occur over SE/E Sardinia.

A deep moist and slightly unstable onshore flow becomes established during the day along the N fringe of the zonally aligned trough. This flow points towards NE Spain and extreme SW France. 24h rainfall peaks in excess of 100 l/qm are possible along the orography but the same is valid for coastal areas, where training convection evolves. Flash flooding is possible and could include Barcelona. A broad level 1 was issued for this risk, as background ingredients stay moderate.

This is also valid for the Malaga area.