Storm Forecast
Valid: Wed 13 Nov 2024 06:00 to Thu 14 Nov 2024 06:00 UTC
Issued: Tue 12 Nov 2024 11:32
Forecaster: TUSCHY

A level 2 was issued across the Malaga/Valencia area mainly for heavy to excessive rain.

Surrounding level 1 areas and level 1 areas over the Tyrrhenian Sea and atop Greece were issued for heavy rain with isolated extreme amounts. In addition an isolated tornado risk exists mainly along the coasts.

SYNOPSIS

A blocking anticyclone stays on site and affects far NW Europe during the forecast with numerous cut-offs/cold-core lows along its eastern/southern fringe.

One of those cut-offs crosses the Iberian Peninsula during the day from E/NE to the SW and shifts atop the Tagus Basin during the overnight hours. Mass response causes a broad area of BL pressure drop including the Strait of Gibraltar, the Alboran Sea, the Golf of Cadiz and far NW Morocco. IFS-ENS member spread remains high, where a more dominant vortex might evolve but some member clustering occurs over the W Alboran Sea before shifting SW during the night.

DISCUSSION

... Spain ...

Pattern recognition points to another event, which could support high impacts on a regional scale. Despite its more western placement to the October event, it comes close to the upper vortex' position of the 57 event. In any case, extreme rainfall amounts on a local scale are once again forecast along parts of the S and E coast of Spain.

The first focus will be over far S Spain (Malaga and surroundings). A sharp BL convergence zone evolves in this area as orographically enhanced easterly BL flow streams into the broad/diffuse LL depression where it meets the vortex' circulation itself, which sits atop the Strait of Gibraltar. In this scenario, a robust/long-lived convergence zone could bend into the Malaga area.

Layered TPW data indicates a zonal plume of rich low to mid-level moisture just N of Algeria/Morocco, advecting W towards the area of interest, as TPW anomalies exceed 120% to the background climatology. Same at the BL, where a moist marine airmass gets funneled W towards the Malaga area. Main limiting factor regarding final rainfall amounts could be modest CAPE in the 300-600 J/kg range and a rather shallow warm cloud layer depth, which impacts the warm rainfall / collision-coalescence process negatively.

Still, conditions are prime from the start on for training convection along the coastal areas next to Malaga with all available ensemble data pointing to robust probabilities for QPF in excess of 80 l/qm in 24h. In fact, a few higher resolved models show swaths of 100-250 l/qm next to any persistent band of training convection with an augmented flash flood risk. In addition, constant onshore flow towards the Sierra Nevada causes a rather broad area with substantial rainfall amounts in the 30-60 l/qm range (increasing overall discharge).

Along the E coast of Spain, background conditions improve during the daytime hours and pave the way for a ramp up of probabilities for training convection on the local scale. As the mid/upper vortex shifts towards the Tagus Basin, a broad easterly flow regime impignes onto the E coast as modest offshore winds at 850 hPa increase ashore into the 30/35kt range. The quality of the offshore airmass improves with the passage of a marine front, where postfrontal 0-1 km averaged mixing ratios increase into the 9 to 10 g/kg range. So does MUCAPE, which constantly improves into the 500-1000 J/kg range (offshore) and up to 500 J/kg along the Valencia coast.

During the daytime hours, slow moving /temporarily back-building convection occurs mainly offshore between the Balearic Islands and Bareclona. Nevertheless a few quasi-stationary bands of enhanced convection may impact NE Spain on a local scale with heavy rain.
The main focus then turns more into the overnight hours, where environmental conditions once again support training convection from the Valencia area N. As the BL offshore flow funnels into the Bay of Valencia, the area with recent major flooding issues could once again become the focus for healthy amounts in a short amount of time. Some high resolved models indicate more than 100 l/qm in a few hours and this could be restrained if a dominant band is able to stays on site. Given the vulnerable area with recent destructive rainfall amounts, a serious flash flood threat could once again evolve (maybe tempered by the modest background parameters a bit and probably peaking more in the SWODY 2 period).

Please keep in mind that this event continues also into the following day.

Enhanced LL shear exists along the coastal areas but LL become more stable away from the coast. An isolated tornado event is possible, especially if convection roots into the marine airmass.

... Tyrrhenian Sea to Italy and Greece ...

A COL area over the Tyrrhenian Sea features weak mid-level height gradients along the N fringe of a brisk subtropical jet, which crosses the E-CNTRL Mediterranean.
A long-lived LL vortex drifts E atop the Tyrrhenian Sea and sparks scattered thunderstorms along its fringes. Right now the main activity with localized extreme rainfall amounts should stay offshore, so we only added a level 1 for the coastal areas. A concern exists for a few nocturnal training events from the Golf of Salerno into the Golf of Policastro area, but progressive nature of the vortex keeps the risk too low for a local upgrade. A few instances with 100 l/qm in 12h are still possible on a local scale within this area.

Persistent onshore flow of an unstable and moist airmass towards Greece brings an heavy rain event to this area with a few 100 l/qm/24h peaks possible. Flash flooding is possible on a local scale and could become significant, if a stationary band points into the complex orography. Pinpointing any peak probabilities of QPF maxima is not possible and hence no upgrade right now.

A few tornado events area possible along any more pronounced convergence zone/along the coasts.