Storm Forecast
Valid: Thu 23 May 2024 06:00 to Fri 24 May 2024 06:00 UTC
Issued: Wed 22 May 2024 20:50
Forecaster: TUSCHY

A level 1 was issued across parts of Turkey mainly for heavy rain and isolated large hail/severe wind gusts.

A level 1 was issued across parts of N Algeria mainly for large hail and severe wind gusts.

Numerous level 1 areas were issued for parts of W/E-CNTRL Europe and NW Poland into SE Norway mainly for heavy rain.

SYNOPSIS

A building anticyclone over Scandinavia with low heights over W-CNTRL Europe create some kind of high-over-low blocking pattern. This static pattern features weak MSLP gradients over most of Europe with slow moving convection the main risk.

The main feature of interest frontal-wise will be a wavy boundary, embedded within this low pressure channel, which extends from UK to Poland and further to the SE towards the Black Sea. A filling vortex just E of UK moves little with otherwise only subtle vorticity maxima present within this channel. Using the Okubo-Weiss parameter one discovers two more pronounced vorticity dominated maxima with one just mentioned (E of UK) and another one evolving over far NW Poland while drifting to the NW into far S-Sweden. In addition another very weak signal emerges from the Alps northward during the evening into the overnight hours, affecting parts of S-Germany.

This blocking pattern keeps split-flow regime going with a pronounced subtropical jet stream affecting parts of SE Europe.

DISCUSSION

... Turkey ...

A brisk and zonally aligned subtropical jet is placed just S of Turkey. An embedded disturbance exits Greece E during the morning hours and grows into a deep vortex over Turkey - some models even try to evolve this feature into a cut-off during the end of the forecast.

Hence most parts of the level 1 see weak shear conditions beneath the vortex with slow moving DMC activity. Thin and elongated CAPE profiles with 300-600 J/kg MUCAPE and weak CIN support scattered to widespread CI with clustering convection. Small hail and heavy rain will be the main risk.

Further S, DLS increases rapdily to values in excess of 20 m/s but the troposphere becomes very dry as an arid African airmass is advected into the area. Hence anticipated 1-2 kJ/kg MUCAPE may be too much with lots of entrainment forecast. Effective ECAPE may cut the final instability in half or even lower. Current idea is the one or two storms manage to form next to the Gulf of Iskenderun with better onshore flow of rich BL moisture. An isolated large hail/severe downburst event is possible.

... W-CNTRL Europe, E-CNTRL Europe and NW Poland into SE Norway ...

Heavy to excessive rain on the local to regional scale will be the main story for:

NW Poland into far NE Germany with an ongoing and gradually NW-ward expanding heavy rain event next to the weak vortex, which lifts into S-Sweden during the afternoon hours. Slow moving/back-building convetion with heavy rain remains the main hazard. This risk extends well into N Denmark.
We also upgraded parts of SE Norway/coastal areas of SW Sweden as the convection moves into the orography with a few heavy rain events forecast.

W-CNTRL Europe: Daytime driven slow moving convection is forecast with DLS mainly below 10 m/s. This activity grows upscale into numerous slow moving clusters, which weaken during the overnight hours. The main risk will be heavy rain but over N-Italy, hail (probably lots of small hail) is also possible as MUCAPE peaks higher.
An exception of the overnight weakening trend will be S-Germany, where a weak vortex becomes the focus for slow moving and clustering convection well into the night with heavy to excessive rain.
The same for E-CNTRL Europe along a N-S aligned LL confluence zone with enhanced MUCAPE up to 1 kJ/kg on a local scale. Deep moist profiles combined with this CAPE amount and weak shear also point to lots of small hail next to heavy rain.

Not highlighted in our level 1 scheme due to missing thunderstorm activity but still mentioned:

N-UK into Scotland: Placed along the W fringe of the quasi-stationary low, a heavy rainfall event is forecast with local 24h peaks in the 40-80 l/qm range.

... N Algeria ...

This area of interest is placed downstream of a deepening trough to the SW of Portugal. Weak short-waves cross the area and may spark a few elevated storms along the orography. Severe downbursts and isolated hail will be the main risk.