Southampton Weather

Today’s ESTOFEX Risk: Level 2 — Moderate Risk

A level 2 was issued across SE France and NW Italy but also for E Corsica mainly for excessive rain. A level 2 was issued across W Sicily and offshore areas mainly for severe gusts, large hail and heavy rain, including a strong tornado risk. A level 1 surrounds all level 2 areas for heavy to locally excessive rain but also for a tornado risk. Large hail is possible mainly in the southern part of the level 1. SYNOPSIS The intense, but mobile anticyclone exits Scandinavia E towards Russia. Numerous cut-offs, which evolved S of this anticyclone now start to "feel the North Atlantic" and they respond to lowering thickness W of Europe by a gradual northward drift. This is valid for a cold-core upper low over N Germany, which lifts into S Sweden betimes and it is also valid for a French vortex, which splits apart. The northern lobe of energy lifts towards England, whereas the southern part evolves into a compact but potent/vorticity-rich low-amplitude wave, which shifts from N Spain E towards the N-CNTRL Meditterranean during the day. Finally, we also deal with a de-amplifying wave, which lifts from NW Algeria NE towards N Italy. Until the end of this forecast, we have an evolving extensive cyclonic gyre over NW Europe, with numerous waves of variable amplitude circling cyclonically around this feature. At the surface, of most interest will be a structuring depression atop the Gulf of Lion, which moves towards the Ligurian Sea. IFS-ENS indicates a rather tight clustering of members but also not much intensification of this vortex. An accompanying cold front surges E, from the W to the CNTRL Mediterranean, whereas a lifting warm front interacts with the rough terrain of the Alps. Overall, this pressure/geopotential height geometry indicates a risk of rather widespread heavy to excessive rain for the CNTRL Mediterranean area. DISCUSSION ... S France ... Along a structuring N-S aligned cold front (Gulf of Lion S/SE), we start this forecast with an extensive band of DMC activity, with excessive rain and a few coastal tornadoes the main risk. This extensive cluster shifts E betimes and this seems to be the saving graze for the coasts of SE France, as the length of the heavy rain remains rather short in time. Still, 50-150 mm of rain in just a few hours is forecast with intense hourly rainfall amounts expected during the passing MCS. There certainly is a tornado risk along the coasts, but also further inland over SE France. Of note is the bifurcating NWP field. One points to a progressive MCS event with an evolving cold pool and rather quiescent conditions thereafter. Others keep this MCS less progressive and initiate another round of slow moving/training convection further W (Cevennes and E) until noon. The latter scenario is not unrealistic, as the surface low still resides near the Cevennes until noon, before shifting E. Either way, heavy to excessive rain dominates all solutions with this MCS event, but we also point to the risk of more convection/heavy to excessive rain behind the MCS, which could impact S-CNTRL France until the evening/overnight hours (at least on a local scale). ... Corsica/Sardegna and Italy ... More foci for excessive rain with significant flash flooding exist for the following areas: Corsica and Sardegna: Ahead of the approaching MCS from the W, strengthening SE-erly flow responds to falling pressure W of Corsica. Onshore/upslope flow of a very moist/unstable airmass initiates a training MCS over E/NE Corsica, where excessive rain and a signficant flash flood risk is forecast (especially, if we get the inflow of this MCS just onshore). Some QPFs are in the 150-350 mm range for 6-9 h. In addition, a coastal tornado risk is forecast. This is also possible along E/NE Sardegna, but less onshore component of the BL flow makes it more uncertain, if training convection evolves onshore or offshore. Nowcast trends need to be monitored and an excessive rain and flash flood risk is possible. Italy: We deal with broad swaths of heavy to excessive rain and a lot depends on how the MCS behaves - is it cold pool driven /progressive or turns more stationary betimes, as the convection still awaits the surface low and upper wave from the W later the day. All of the coasts of NW Italy face a potential excessive rain risk at least on a regional scale and we would not be surprised about a few 200-300 mm reports in 24h. Betimes, this risk sags S towards W-CNTRL Italy, but also W Sicily will be affected by a heavy rain threat, where influx of very rich BL moisture next to 2000 J/kg MUCAPE would offer a favorable background for excessive rain (dependant on where CI occurs). In addition there exists a tornado risk offshore and along the coasts. From the Galite Channel into the Tyrrhenian Sea, the CAPE/shear space supports a few long-tracked supercells with all kind of severe possible, including large hail, severe gusts, a few tornadoes and heavy rain, which promted a level 2 upgrade for this area. There is some concern, when CI occurs within the best CAPE plume, upscale growth into an extensive cluster is possible despite reluctant NWP guidance. This level 2 verification heavily depends on cap strength and still has some uncertainties, but the impressive CAPE/shear space with strong EHI/STP signals and persistent CI in latest runs(including stable EPS signals) is too much for a level 1. We added the other level 1 and 2 areas, depending on the confidence level and EPS input. Finally there evolves an upslope flow heavy rain risk along the S Alps during the afternoon into the overnight hours with peaks in excess of 150 mm/12h on a local scale.