Analyse
A level 2 was issued for far NE France into Belgium/the Netherlands and far NW Germany mainly for severe/damaging gusts and large to isolated very large hail but also for heavy rain.
A level 1 surrounds the level 2 area with lowered probabilities but similar hazards. Clustering of severe reports is possible with local swaths of severe gusts, hail and heavy rain (e.g. SW into W-CNTRL Germany).
A level 1 was issued for parts of Spain mainly for large hail and a few strong to severe gusts but also for locally heavy rain.
A level 1 was issued for N Algeria mainly for large hail and severe gusts.
A level 1 was issued for S and NE Turkey mainly for hail, strong gusts and heavy rain.
A level 1 was issued for parts of SW Russia mainly for severe gusts and large hail.
SYNOPSIS
A blocking ridge extends from NW Africa towards CNTRL Europe and builds further NE towards the Baltic Sea. The strongest geopotential height anomalies exist over parts of CNTRL Europe.
A compact short wave/IPV maximum over S France lifts N/NE and approaches CNTRL Germany until the end of the forecast period.
The ridge gets framed by an extensive longwave trough over the far NE Atlantic and a quasi-stationary (positive tilted) trough over SE Europe.
Most of Europe stays avoid of noteworthy synoptic-scale front activity, although wind shift/moisture flux convergence zones will be the main players for CI (next to the wave and the orography).
Dust load will not yet be a topic to talk about for this forecast period but should be watched closely in upcoming model runs for the following days.
DISCUSSION
... NE France to Benelux into Switzerland and W/N Germany ...
First and foremost a short note of the available moisture content. With the Mediterranean and subtropical Atlantic running 2-3 K too warm from the SST background climatology, expected moisture trajectories for this event stay quite favorable for sufficient moisture input. This combined with an active and prolonged period of near unimpeted moisture advection from the far SW/CNTRL Atlantic with temporarily modest to strong IVT events result in an extensive plume of 150-250% TPW anomalies over NW into CNTRL Europe. This moisture gets either incorporated into the blocking anticyclone or will be used up in expected convection with locally efficient rainfall rates, only hampered by a deep/well mixed BL. Uncontaminated PWs will be in the 30-40 mm range.
Initial, weak convection with some elevated MUCAPE supply affects N Germany from W to E. This activity is attached to a low-amplitude wave, wich crosses N Germany east. It remains uncertain, if tail-end storms can tap into improving CAPE during the day but current expectation is that hampered diabatic heating due to extensive cloudiness should keep this risk on the lower-end side. If we get some re-development over NE Germany, hail and strong to severe gusts would be the main hazard and NE Germany was added in a low-confidence level 1 for this probability.
Thereafter, adiabatic warming of subsiding air within the anticyclone and lots of sunshine/diabatic heating create not only very deep and well mixed boundary layers from France to Germany, but also a belt of high MUCAPE, where these enhanced lapse rates meet the TPW plume from the NE Atlantic.
MUCAPE is highly variable with 800-1500 J/kg over S Germany increasing to roughly 2000 J/kg from far NE France to Benelux into N Germany. This area is also highlighted by anomalous values in the EFI MUCAPE of IFS-ENS. Of note is the DCAPE forecast, which exceeds 1000 J/kg over Benelux into NW Germany, generally pointing to very efficient evaporative cooling in structuring downdrafts.
Shear is weak for most of S/CNTRL Germany but increases towards Benelux/NW Germany into the 10-15 m/s range for the 0-6 km layer. 3km shear oscillates around 10 m/s in the latter area. Forecast hodographs remain rather short with little upper ventillation of precipitation but at least regionally somewhat curved 0-3 km hodograph signatures.
There is not much lift to talk about. We expect a short-wave over S France to lift N/NE before moving into W-CNTRL Germany during the night. Not much PV modification of this IPV maximum is expected with relative little convective activity along the periphery of this wave during the previous day. Beside that synoptic-scale support, expect a broad/diffuse area with better moisture flux convergence from NE France to Benelux into N Germany. In addition we monitor a northward surging dry line, which shifts from CNTRL towards NE France until the evening hours and a structuring sea breeze front along the E English Channel. Finally, diabatic heating could support CI along the orography on a regional scale.
With all that, we expect numerous areas for CI, like most of the W Alps into SW Germany but also along the orogrpahy of W-CNTRL Germany. The highest probabilities for sure exits from NE France towards Benelux.
Initiating convection over the W Alps into SW Germany will see a supportive background for initial slow moving storms with heavy rain, large hail and strong to severe downburst events. The rain risk could become noteworthy for stalling or colliding convection (locally in excess of 50 l/qm/h) and the gust risk for maturing and merging outflow events. A confined level 2 upgrade was considered, where latest EPS/deterministic data has sufficient support for numerous severe events with an isolated extreme event not ruled out. However inconsistency in CI within NWP guidance kept this area in a level 1 for now.
Along the orography of W-CNTRL Germany, the risk of large to isolated very large hail increases for initiating cells but also for severe/damaging gusts with local peaks up to hurricane-force. This pulsating but intense convection spreads E/NE betimes and weakens due to increasing cap and probably an outward spreading rain-cooled outflow. No level 2 was added due to the local coverage of thunderstorms and some issues in how scattered CI will be. However a temporal severe and cold pool driven MCS is possible.
Best CAPE/shear overlap exists for firing thunderstorms over far NE France towards Benelux, where large to very large hail with intense pulsating updrafts/multicells is forecast and even a few supercells are possible. Severe/damaging gusts are likely and EPS data gives enough back-up to support an evolving and cold pool driven MCS event betimes. No supportive speed maximum at 700 hPa is found upstream, which could increase RIJ strength but even without that support, a severe MCS event can unfold admits very efficient evaporative cooling. Severe to damaging gusts could affect most of CNTRL/E Belgium and Netherlands before moving into NW Germany thereafter. ID2-EPS supports that idea for Belgium/the Netherlands but looses track into NW Germany. Uncertainties also exist in case of overperforming convection over W-CNTRL Germany, which could send an outflow into W Germany, lowering the general risk.
Therefore only a confined level 2 was added, where confidence in CI and clustered severe coverage (with isolated extreme) is highest. Swaths of level 2 conditions can occur also outside of that polygon however.
Ouside of the mentioned areas, any initiating thunderstorm can produce hail, strong to severe gusts and/or heavy rain. This was highlighted by a broad level 1. Some parts of that level area could see a more focused severe coverage whereas other areas could stay avoid of DMC activity.
During the night, we expect a further upscale growing large cluster over NW Germany moving towards N Germany/Denmark, possible evolving into an MCV. A swath of strong to isolated severe gusts seems possible but the increasing cap should lower that general risk. Some hail and heavy rain will be another issue.
Besides that, the arriving short wave sparks additional thunderstorms over CNTRL Germany during the night, which shift NE until the end of this forecast period. This activity should stay sub-severe with some spotty rain issues.
... Spain to NW Africa ...
A plume of rich BL moisture intersects steep mid-level lapse rates, resulting in up to 3000 J/kg MUCAPE build-up. A very warm sub-700 hPa layer causes strong capping for most parts. However, passing weak waves, strong diabatic heating and upslope flow into the orography over SE Spain increase the risk of a few cells along the orography. As EPS data also stays rather reluctant regarding CI, we placed a level 1 with low to high lightning probabilities. Hail, severe downdrafts and locally heavy rain would be the main issue mainly for CNTRL into SE Spain. This however is a low confidence forecast.
We also added a level 1 for the Atlas Mountains mainly for large hail and severe downdrafts. Isolated CI is possible.
... S and NE Turkey ...
Two more level 1s were added for far S and NE Turkey, where a confined belt with rich CAPE and weak to moderate DLS overlaps. Scattered thunderstorms bring hail, strong gusts and heavy rain.
... Parts of SW Russia ...
Strong DLS overlaps wit sufficent CAPE for organized DMC activity with large hail and severe gusts the main hazard.
TUSCHY / ESTOFEX
