Storm Forecast
Valid: Fri 19 Jul 2024 06:00 to Sat 20 Jul 2024 06:00 UTC
Issued: Thu 18 Jul 2024 21:34
Forecaster: TUSCHY
A level 2 was issued across far S Austria and N Slovenia mainly for excessive rain.
A level 1 surrounds the level 2 with the following hazards: heavy rain, hail, strong to isolated severe gusts.
A level 1 was issued for parts of S France mainly for hail and severe gusts.
A level 1 was issued for parts of the Dinaric Alps mainly for hail, heavy rain and an isolated severe gust.
A level 1 was issued for the far E Black Sea mainly for heavy rain.
SYNOPSIS
Ongoing blocking regime with a stout subtropical ridge remains rooted over the W/CNTRL Mediterranean and bends towards E/SE Europe while delivering a prolonged heatwave for those regions. A gradual weakening trend of this ridge is noted in model data and a weak low-amplitude wave is able to move into the ridge towards the Alps.
A long-lived upper low over Finland shifts E and opens up into a broad trough structure over NW Russia with another stationary trough over Turkey (part of a wave train which points towards the Mediterranean region).
There is not much to talk about when analyzing the surface fronts as only the cold front over the E-Ukraine/W-Black Sea remains active convective-wise. This front continues to weaken while shifting E. Elsewhere weak high pressure dominates at the surface.
DISCUSSION
... France ...
Model spread continues to be substantial with BL mixing and capping issues over most of France. GFS/AROME remain on the most aggressive side with CI all the way up to Belgium, whereas ICON having more or less nothing in precipitation fields. Comparing to reality shows the ICON way too dry with other models like GFS/EZ doing a much better job.
The eastbound moving upper wave is well handled in NWP guidance although ICON has stronger thickness decrease compared to other models. All agree in mid-level cooling and regionally enhanced synoptic-scale lift. There are no substantial LL convergence zones over N/NE France to work with regarding CI so for now we stick to the EPS data, which still highlights the Massif Central and the vicinity of the Pyrenees. MUCAPE up to 1000 J/kg with DLS in the 10-15 m/s range support a few temporarily better organized thunderstorms with strong to isolated severe downburst events (dry/well mixed BL). An isolated hail event is possible as well. This activity weakens beyond sunset while drifting SE.
An isolated storm is also forecast along the E Pyrenees with MUCAPE in the 1500 J/kg range and DLS hovering around 15 m/s. In case a more robust updraft fights the environmental entrainment, hail and a strong to severe downburst event will be possible.
... Austria into NE Italy, Slovenia and far N Croatia ...
An active day with high thunderstorm coverage is forecast.
CI occurs along the Alps, where roughly 1 kJ/kg MUCAPE overlaps with 10 m/s DLS. Forecast soundings show deep moist profiles up to 700 hPa with rather high dewpoints also in the mountainous areas. The weakly capped airmass should be activated before noon with scattered to widespread CI (pulsating thunderstorms). Initial convection brings heavy rain, maybe some small hail and gusty winds, before clustering betimes and moving SE. Colliding storms and growing clusters could bring local rain amounts in excess of 50-70 l/qm in a few hours with isolated flash flood issues forecast (ID2-EPS with 60-100% for local peaks in excess of 60 l/qm in 6h until 18Z).
Outflow from this activity runs SE towards NE Italy/far S Austria and Slovenia, where more thunderstorm clusters evolve. Same here regarding hazards as healthy QPF peaks area forecast (ID2-EPS with a peak over N-Slovenia into S Styria). Flash flooding is possible next to strong gusts and isolated hail. This activity occurs during the late afternoon until midnight.
Thereafter the general pattern is rather interesting with the upper low-amplitude wave to the W and a strong MCS with a broad/deep cold pool (meso high) pushing deep into Slovenia and N Croatia. Ongoing S to SW-erly flow aloft points to an ongoing risk of clusters and even a few elevated supercells from Slovenia into N-Croatia and far W Hungary due to strong directional shear above the cold pool induced inversion. Some models show 12h rainfall amounts along the border of Slovenia into Austria in the 40-80 l/qm range with local peaks in th 100-200 l/qm range. This training conditions occur when cold pool dynamics and ongoing strong/moist inflow (plus N-ward pushing outflow from the convection along the Dinaric Alps) balance each other. Training and moist inflow cause dangerous flash flooding issues on a local scale.
EZ models drive the outflow with numerous thunderstorms far S into N Italy (e.g. Bologna and Florence) with isolated hail and heavy rain the main issue.
We upgraded parts of Slovenia and also increased probabilities into the level 2 regime for excessive rain along the Slovenish/Austrian border.
... S Germany ...
Peripheral of the upper wave, orographic CI is possible over S-Germany with a few strong storms evolving during the late afternoon. Well mixed BL conditions point to a few strong to isolated severe gusts next to heavy rain and some small hail. ID2 has peaks up to 15 m/s just before initiating convection, so even some temporal updraft organization seems possible (highlighted by a few short-lived UH tracks).
... Finland ...
Beneath the upper low, the atmosphere is pretty much worked over by the previous convection with only modest CAPE and weak shear forecast. Some diurnal heating could spark a few more thunderstorms with isolated heavy rain and a funnel/short-lived tornado report or two. This activity weakens beyond sunset.
... NE Turkey into far W Georgia ...
A pool of extremely moist air resides between the Caucasus and Canik Escarpment over the far E Black Sea with precipitable water values in the 45-55 mm range. A weak LL vortex drifts S into this area during the evening and overnight hours, which increases coastal convergence in a weakly capped 1-2 kJ/kg MUCAPE environment. DLS is in the 1-2 m/s range, so stationary convection produces excessive rain. Most of the activity stays offshore so a coastal level 1 should be eough for now.
... Dinaric Mountains...
A few strong to severe mountain storms bring hail and heavy rain on a local scale including a few strong gusts. This activity weakens during the evening.
