Storm Forecast
Valid: Mon 06 May 2024 06:00 to Tue 07 May 2024 06:00 UTC
Issued: Sun 05 May 2024 23:26
Forecaster: BEYER

A level 2 was issued for SE Germany, S Czech Republic, and N Austria mainly for excessive precipitation and large hail as well as severe wind gusts

A level 2 was issued for N Ukraine, SE Belarus, and small parts of W Russia mainly for severe wind gusts, large hail, and tornadoes.

A level 1 was issued for several countries in E Europe mainly for large hail and severe wind gusts.

A level 2 was issued for far SE Turkey, N Iraq, and far W Iran mainly for large hail and severe wind gusts and to a minor extent for excessive precipitation and tornadoes.

A level 1 was issued for NW France mainly due to the risk of landspouts

A level 1 was issued for SW Spain mainly for large hail and severe wind gusts.


SYNOPSIS

On Monday the general weather situation is quite persistent over the entire outlook period. Several low pressure areas that may lead to severe convection can be found over Europe.

One upper level low is present over NW France. It is only slowly moving SE ward into C France while weakening. On its S flank a trough axis will pass Spain and the E Mediterranean during the forecast period.

Another UL low is moving slowly from the German Baltic areas to Lithuania and will finally incorporated into the trough to the N. Its diffluent forward flank will influence many parts in E Europe and far W Russia.

While a shallow ridge influences most parts of the C Mediterranean a stationary UL low is influencing the E Mediterranean. Especially its diffluent forward flank is influencing parts of the Middle East.

DISCUSSION

... SE Germany, S Czech Republic, and N Austria...

A southerly component of the mid-level flow will lead to a developing foehn on the N flank of the Alps. As a result, the Lapse Rates are forecasted to steepen. However, there is also a drying of the lower troposphere and thus the forecasted 500 to 1000 J/kg of MLCAPE will initially be capped. This inhibition of convection is supported by a weak anticyclonic UL flow. During the afternoon hours, a small short wave feature is forecasted to enter the area of interest, as visible in the IPV320K field.

This feature serves as a trigger to initiate convection starting in Bavaria around 12 UTC and moving eastward during the afternoon hours. In the late afternoon hours and during the evening N Austria will be influenced.

DL shear does not look too impressive but some high-resolution models indicate the development of a small patch with around 15 m/s mainly thanks to the local wind regime influenced by the Alps. As a result, two or three supercells are forecasted to develop over Bavaria which can be nicely seen by looking for the UL tracks. Later on, as the short wave feature travels eastward, also Austria and parts of the Czech Republic may see some rotating supercells. Those supercells do have the potential to bring large hail and severe wind gusts. The latter is supported by enhanced values of DCAPE (due to previous Foehn winds).
Later, when the cold front is approaching from the W, storms are forecasted to cluster into a larger system. Some LAMs indicate the development of a mesoscale convective system. Due to high ppws (25 to 30 mm) and only moderate movement, an enhanced risk for excessive precipitation is present that may bring flash floods. On the forward flank of the MCS, a few model solutions show bowing segments. If this verifies widespread severe wind gusts are possible. While the self-dynamic of such a system is an argument for their development only moderate 0-3 km shear values are and counterargument.

During the night the system will move further eastward while weakening.

...N Ukraine, SE Belarus, and small parts of W Russia...

Several parts of E Europe and W Russia are situated on the diffluent forward flank of an UL low with its center of the S Baltic Sea. One can find a supporting UL jet to the S of the low pressure center. Another jet maximum coupled to the trough further to the N can be found over W Russia. There is an area that is situated at the sweet point of the left exit and right entrance region of both jet maxima. This location will be the N Ukraine, parts of Belarus, and far W Russia.

A lot of uncapped MLCAPE is forecasted to develop as a result of steep lapse rates and enhanced LL moisture (600 -1200 J/kg). Shear is improving during the day from the west. A small short wave feature will move W to E and may serve as an additional trigger. In addition, a small surface low can be found over Belarus that will lead to a backing of the LL winds to the east. As a result, LL shear I quite strong. Right-moving supercells can benefit from a lot of streamwise vorticity (SRH0-1:200-400 m2/s2).

Therefore, rotating storms are forecasted especially in the LVL 2 area that can bring large hail and severe wind gusts. Since LCLs are low one or two tornadoes that may even become strong, are possible.

For the rest of the surrounding LVL 1 area, the risk of severe weather is lower but still locally large hail, severe wind gusts, and excessive precipitation are possible. The lower risk is mainly due to less shear or weaker CAPE values. The risk of severe weather will lower significantly during the night hours.

...SE Turkey, N Iraq, and far W Iran...

A strong UL low is situated to the W of the area of interest. Its active diffluent forward flank has the potential for a lot of lift. That is also supported by the left exit region of an accompanying UL jet.

Steep lapse rates and enhanced LL moisture lead to MLCAPE values of 500 to 1000 J/kg that can overlap with a lot of DLS (25-30 m/s). As a result, supercells are forecasted that bring large to locally very large hail. In addition, severe wind gusts are possible, especially in regions where a large spread can be found in the lower troposphere.

The latter leads also to some difficulties concerning the question of initiation. However, LAMs show regions with convection. LL wind profiles look very impressive. Although the best profiles do not overlap with developing convection they are still good enough for severe weather. The question is whether LCLs can be lowered in some areas which as a consequence would enhance the risk of tornadoes. Excessive precipitation is most likely in the area of the LL convergence zone and in connection with orography.

With the persisting UL support convection will also be active during the upcoming night but with lowering risk of severe weather.

...NW France...

A low pressure center with UL cold airmasses is present over NW France and will lead to repeated convection in that area. Steep LL lapse rates, weak UL winds, and LL convergent flow as well as low LCLs lead to an enhanced chance of seeing landspout-type tornadoes in the indicated area.

...SW Spain...

To the S of the low pressure center over NW France, a significant trough axis is moving eastward over Spain. On its forward MLCAPE values of 400 to 800 J/kg can develop during the day as a result of steep lapse rates and enhanced LL moisture.

Convection is forecasted during the afternoon. With shear values of 15 to 20 m/s better organized storms and supercells are possible that can bring large hail and severe wind gusts. The latter is mainly due to enhanced DCAPE values (enhanced LL spread).
The risk of severe weather will extend into the W Mediterranean and can also influence the Balearic Islands.