08-07-2024 20:39 | Estofex | m.b.t. 09-07-2024 t/m 10-07-2024
Storm Forecast
Valid: Tue 09 Jul 2024 06:00 to Wed 10 Jul 2024 06:00 UTC
Issued: Mon 08 Jul 2024 20:39
Forecaster: TUSCHY
A level 2 was issued across far NE France into Benelux and far NW Germany mainly for damaging gusts.
A level 1 surrounds that risk for similar hazards but with lower probabilities. An isolated tornado is possible along the cold front over Belgium/the Netherlands. In addition, a few heavy rain and large hail events are forecast.
SYNOPSIS
A low-index pattern over Europe continues with a broad upper trough over the far NE Atlantic into the Bay of Biscay and Ireland, facing positive height anomalies over E and S Europe.
This rather static pattern drives a well clustered (IFS-ENS) depression towards the UK in the 1005 hPa range, with some member spread regarding a secondary depression developing over the German Bay during the night hours.
This (potential dual low pressure area) drives a cold front E with a well clustered placement over Benelux around 00Z (10th July).
Elsewhere, a flat/progressive upper trough over Finland causes a broad belt of low-end to moderate instability in a weakly sheared background flow.
DISCUSSION
**AMENDMENT**
This outlook was re-issued to correct a more enhanced morning/forenoon thunderstorm risk over NW France with some hail/heavy rain issues. This more elevated convection shifts NE towards the level 1/2 areas and could play a role in initiating surface based convection in this area. The level 1 was adjusted a bit W in this area. Otherwise no changes were done to the level areas.
... France into Benelux and Germany ...
Regarding CI, the main focus evolves along the gradually eastward moving cold-front over E/NE France probably all the way down towards the Massif Cental/Toulouse area. Enhanced background forcing due to a passing NE-ward traveling upper trough, strong diabatic heating and the orography combined should assist in scattered CI along the cold front.
Forecast soundings indicate a deeply/well mixed prefrontal air mass with surface temperatures in the upper twenties/lower thirties and dewpoints in the mid to upper tens. In addition, the low-tropospheric airmass will mix up to 700 hPa with plently of MUCAPE aloft in the 800-1500 J/kg range. This BL configuration assists in a gradual stabilization trend during the late evening and into the overnight hours, which should induce a gradual decrease in intensity.
Regarding shear, a 50 kt mid-level speed maximum grazes most of the area with a better overlap towards Benelux. In addition, winds at 700 hPa also increase to 40-50kt from SW-erly directions over NE France into Belgium/the Netherlands, which pushes 0-3 km shear values along the front into the 15-20 m/s range from NE France further E/NE.
This area has the best support for bow echoes with swaths of damaging wind gusts both due to the the strong background shear but also due to intense cold pools in a well mixed prefrontal BL airmass. Hence a wind-driven upgrade to a level 2 was performed. This risk may extend into extreme NW Germany before CIN induces a weakening trend.
Beside the gust risk, large hail becomes another issue, especially in case of semi-discrete supercells, driven by substantial directional shear along that boundary. In case of a storm riding the lower LCL environment of the immediate boundary, we even cannot exclude an isolated tornado event.
Further S along that boundary into CNTRL France, convection remains a bit more discrete with somewhat weaker background forcing but upscale growth into numerous smaller bow echoes is also forecast, as cold pools grow betimes. A few severe wind gusts and hail reports are forecast before the activity weakens while driving a pressure wave into SW/CNTRL Germany. Over SW France (Massif Central to Toulouse area), forecast soundings/hodographs and modest forcing could support a few longer-lived supercells with damaging gusts and large hail. More isolated nature keeps this risk in a level 1.
The mentioned pressure wave (probably a structuring leading pre-cold frontal convergenze zone) becomes the focus for spotty/nocturnal CI (e.g. along the orography) over CNTRL-/S-Germany with MUCAPE in excess of 1000 J/kg. This points to an ongoing, but localized severe wind gust/hail threat with any stronger cell (e.g. SE Germany with impressive MUCAPE values all night long). A broad level 1 was issued to capture that risk.
In addition, a second round of thunderstorms erupts along the main cold front over NE France into W Germany during the overnight hours. They remain elevated in nature with a local heavy rain threat.
(alleen de voor NL en aangrenzende gebieden relevante tekstdelen overgenomen, klik hier voor de volledige forecast, red.)
Hagel(-schade) | Onweer/blikseminslag | Tornado/hoosverschijnsel(en) | Verwachtingen/waarschuwingen | Wateroverlast/(zware) neerslag | Wind/storm (-schade)
