Extended Forecast
Valid: Thu 07 Nov 2024 06:00 to Fri 08 Nov 2024 06:00 UTC
Issued: Tue 05 Nov 2024 15:08
Forecaster: TUSCHY

A level 1 was issued for heavy to isolated excessive rain and a low-end tornado threat.

A level 1 was issued for NE Algeria and Tunisia mainly for hail and gusts next to heavy rain and an isolated tornado event.

SYNOPSIS

Not much change to the SWODY 1 as mid-level height anomalies increase over far N Europe, creating a long-lived blocking pattern for most of Europe. The upper low over the W-Mediterranean splits with one part shifting NW towards the Bay of Biscay while opening up into the NE Atlantic through, while the other part drops S towards Tunisia. The net result is an elongated channel of lowered heights, which runs from W Europe S towards Tunisia.

There is no synoptic-scale front, which affects our SWODY 2 DMC-wise.

DISCUSSION

... W into S-CNTRL Mediterranean ...

A residual marine layer beneath somewhat steeper mid-level lapse rates over and just N of Algeria/Tunisia create a broad area with MUCAPE in excess of 500 J/kg but also peaks in the 1000-1500 J/kg range just N of the African coast. There is no clear signal of any BL vortex so it is a bit tough to detect any potential hotspots for DMC activity.

One probably exists over and N of the Balearic Islands, where erratic/slow moving thunderstorms and small clusters pose an ongoing (from the previous night) heavy to excessive rainfall threat on the local scale. Ensemble data point to variable QPF maxima but nowcast will tell, if f.ex. an onshore pointing convergence zone could support a longer-lived coastal MCS event as shown by COSMO just W of Barcelona. This risk extends into SE France and a broad level 1 was issued. In addition, if stationary storms occur over the Balearic Islands, local precipitation maxima in excess of 100 l/qm are not ruled out.

Another focus for heavy (convectively driven rain) exists between the east coast of Sardinia towards the Tyrrhenian Sea but also over psrts of/S of Sicily. NWP guidance is still divergent regarding showing any dominant LL convergence zone, as low-tropospheric pressure gradients remain weak. Marginal shear but good moisture up to 600 hPa point to slow moving convection with heavy to excessive rain on a local scale. Storm motion could become stagnant next to BL convergence zones. Ensemble and deterministic data indicate some weak signals for a few high rainfall events in excess of 80 l/qm/24h, but ongoing uncertainties of the placement of any QPF maxima cause a broad level 1 issuance for now.

Similar to yesterday, an overlap of robust MUCAPE in excess of 1000 J/kg with a drier 900-750 hPa layer support a few hail and strong gust events next to the mentioned rain threat.

For the level 1 area, there exists also a low-end tornado (spout) risk mainly along well established BL convergence zones.