Storm Forecast
Valid: Thu 19 Sep 2024 06:00 to Fri 20 Sep 2024 06:00 UTC
Issued: Wed 18 Sep 2024 21:34
Forecaster: TUSCHY
A level 2 was issued across the Gulf of Valencia and adjacent areas mainly for excessive rain.
A level 1 surrounds the level 2 mainly for heavy rain and a tornado risk (offshore and along the coast) and also for rain/gusts onshore.
A level 1 was issued for N Morocco into N Tunisia mainly for heavy rain.
A level 2 was issued for parts of Italy, the Adriatic and Ionian Sea mainly for excessive rain.
A level 1 surrounds the level 2 for similar hazards including a few tornadoes and isolated hail/gusts.
A level 1 was issued for parts of W-CNTRL Germany for a low-end hail and tornado risk.
A level 1 was issued for the Gulf of Alexandretta and surroundings mainly for large hail, severe gusts and heavy rain.
SYNOPSIS
Not much change on the large scale with ongoing high-over-low blocking for most of Europe. Impressive/extensive anticyclone remains in place over Scandinavia with lowered geopotential heights atop the Mediterranean Sea.
The leisurely eastbound moving upper trough shifts towards the Adriatric Sea, as a dominant/progressive second vortex races W while crossing Germany into France. DMC activity is confined to these upper vortices and is also dictated by numerous convergence zones offshore over the W/CNTRL Mediterranean Sea.
DISCUSSION
... Gulf of Valencia into CNTRL/E-Spain ...
A convergent mid/upper flow pattern is forecast downstream of a weak vortex over Portugal and upstream of the broad one over Italy/Adriatic Sea.
Stationary storms occur over the Gulf of Valencia ongoing from the previous night until noon and once again beyond midnight as offshore blowing (daytime/outflow driven) winds meet the synoptic background flow from the E and create a rather strong convergence zone. Slow moving storms with excessive rain and a few spouts/tornadoes are forecast with spotty rainfall amounts in excess of 100 l/qm. NWP guidance diverges regarding extent of how far inland those peaks occur but we added the coastal areas into a rainfall driven level 2. Layered moisture products show no real connection to a mid-level moisture source, so this should stay a rather confined/regional event.
A level 1 extends more inland for slow moving convection with 500-1000 J/kg MUCAPE. Some hail/gusty winds are also forecast next to the heavy rainfall threat. Convection peaks during the late daytime hours but continues with lowered coverage all night long.
... N Morocco to N Tunisia ...
A belt of enhanced mid/upper subtropical moisture remains entranched over this region and overlaps with strong winds next to the subtropical jet in the 15-25 m/s DLS range (although effective values remain more on the modest side). Some spotty hail is possible but the main risk will be heavy rain with clustering convection. The highest rainfall and isolated flooding risk evolves from NE Algeria into Tunisia, where spotty 50-80 l/qm/12h are possible.
... Italy and the Adriatic Sea ...
A decaying upper vortex drifts E over the Adriatic Sea with no clear imprint of any LL vortex sin-up.
The long-lasting band of convection, which bends from the CNTRL Adriatic Sea into the Bologna/Florenze area probably lasts well into the afternoon hours, before finally drifting S while weakening. This adds spotty 50-100 l/qm/6-8h for parts of Emilia-Romagna into Marche regions.
Beyond noon a broad cyclonic flow regime becomes established atop the Adriatic Sea, which results in unstable (500-1000 J/kg weakly capped MUCAPE) and weakly/moderately sheared conditions as DLS increases from the CNTRL into the S Adriatic Sea from 1 to 15 m/s. Hence a bimodale severe risk exists with slow moving/training convection mainly along the E-Adriatic Sea, where convection may train along the coastal convergence zone with highly variable 24h rainfall amounts in the 20-200 l/qm/24h range. An isolated spout/tornado risk exists.
Further south, including SE-Italy, the S-Adriatic Sea into the Ionian Sea, DLS improves and multicells/a few supercells are forecast. Some hail and gusty winds are possible but the main risk will be excessive rain and a locally augmented tornado risk (mainly along LL convergence zone).
A rather extensive level 2 was added for this mixture of severe risks.
... Germany into Belgium/Netherlands ...
The crossing cold-core low during peak heating sparks numerous thunderstorms, which evolve in a not too bad environment: 500-1000 J/kg MUCAPE, 15-20 m/s DLS and 100-150 m2/s2 SRH1/3. Would not be surprised about a few rotating cells with some hail, gusts and heavy rain. LCLs in the 700-1000 m range and local 0-3 km CAPE peaks of 100 J/kg even support a low-end/spotty tornado risk with strongest storms. The marginal level 1 was placed, where strongest storms seem plausible/possible e.g. along the W/NW fringe of the cold-core low and the upgrade was driven by rather aggressive ID2/EZ/UK10 with GFS more of an outlier, firing storms more to the W. Storms decay beyond sunset.
... Gulf of Alexandretta and surroundings ...
Onshore flow advects a very moist marine layer beneath steep mid-level lapse rates, resulting a belt of sizeable belt in the 1000-2000 J/kg range. 15 m/s DLS is forecast and numerous storms occur as weak short waves cross the area of interest to the E. The level 1 was expanded S towards W Syria with similar hazards.
