Extended Forecast
Valid: Wed 30 Sep 2026 06:00 to Thu 01 Oct 2026 06:00 UTC
Issued: Mon 28 Sep 2026 22:01
Forecaster: TUSCHY
A level 2 was issued across parts of S France mainly for excessive rain.
A level 1 surrounds the level 2 for heavy rain but also for a few tornado events.
A level 1 was issued for parts of Ireland and UK mainly for an isolated tornado and strong to severe wind gust risk.
A level 1 was issued across Crete mainly for heavy rain and an isolated tornado event.
A level 1 was issued for NW Georgia mainly for heavy rain.
SYNOPSIS
An intense extratropical cyclone/warm seclusion pushes N W of Ireland and backs the strong ridge downstream over CNTRL Europe. A broad upper trough with numerous embedded vortices still affects SE Europe with unsettled conditions for a broad area.
DISCUSSION
... S France ...
A classique episode cevenol or Marin event continues for the level 2 area with a significant flash flood risk forecast including a risk of a few damaging/life threatening events.
Ahead of a slowly eastward advancing cold front over W- to CNTRL France, a persistent S/SE-erly onshore flow persists, which still roots into a plume of anomalous moist and unstable air atop the W-CNTRL Mediterranean with MUCAPE in the 2000 J/kg range over offshore areas. This restless LLJ pumps the moist airmass ashore with a gradual shift to the E, as tropospheric winds veer betimes.
During the day, expect repeated training onshore convection with excessive rain on the local scale and mainly along the orography. Local 12h amounts in the 100-200 mm range are possible with most of this occuring in a short amount of time.
During the night, upper divergence improves and the result will be a growing cluster of convection with erratic motion, dependant on storm-internal dynamics like cold pool development. This more dynamic background supports an increasing excessive rainfall risk during the night with an expanding QPF imprint of serious rainfall amounts. Some models point to 6h amounts in excess of 350 mm and this back-building cluster brings extreme amounts for a rather broad area (Cevennes E towards Nimes). This increases the flash flood risk also away from the orography with significant/life threatening events well possible.
Latest guidance takes this cluster S over offshore areas during the end of this forecast, which would also bring this multi-day excessive rainfall event to an end.
A few coastal tornado events are possible, although the favorable LL thermal/kinematic background extends well inland into the level 2 area and a few tornado events are also forecast mainly in the southern part of the level 2 area.
We also expect more isolated to scattered WCB convection further W, which affects SW to CNTRL France. Warm mid-levels preclude any serious CAPE build-up, but spotty heavy rain will be a risk with this activity due to the high moisture content in the troposphere.
The cold front activity over SW/W-CNTRL France needs to be monitored during the afternoon into the night for a confined CAPE/shear space, which could support a few rotating updrafts with some hail and a tornado risk. There remains uncertainties, like if this cold front is already affected by CAA, which would limit LL SRH. Hence no level 1 upgrade was performed that far out. However, latest ID2 run f.ex. has a nice low amplitude wave passage over NE France in the afternoon, resulting in an impressive CAPE/shear space for an augmented/isolated tornado risk with low-topped convection. Overall, this risk runs from NE/N-CNTRL towards SW France.
... Parts of UK and E Ireland ...
This area resides upstream of an eastward departing cold front and downstream of an approaching upper trough from the SW, placing this area in at least modest upper divergence.
A moist and unstable airmass advects towards NW Europe and with some diabatic heating forecast, 200-600 J/kg SBCAPE evolve with bottom-up profiles. Shear is decent to support a few rotating updrafts and there exists an isolated tornado risk especially for semi-discrete cells or merging updrafts in a low LCL setup. SRH is not the best in the 1km and 3km layers respectively, but we see strong SR inflow with somewhat enhanced streamwiseness in forecast hodographs, which indicates effective streamwise vorticity advection into updrafts. Strong to severe gusts will be another issue with this activity and hence we issued a broad level 1 area for now. This is also valid for E Ireland.
... E Black Sea ...
Despite a lingering shallow vortex, this area will stay avoid of adequate instability to support stronger updrafts and hence no serious DMC risk is forecast (including a low chance for any subtropical development). Still, heavy rain is possible along the eastern fringe of this vortex and this area was upgraded to a level 1.
... Crete ...
Persistent N-erly flow atop the warm Sea of Crete assists in repeated onshore moving convection with heavy to locally excessive rain and 24h amounts in the 100-200 mm range (mainly along the orography). Flash flooding is possible and an isolated tornado risk along the coasts is also forecast (next to a general augmented waterspout risk over the E Mediterranean beneath cooling mid-levels).
