Storm Forecast

Storm Forecast
Valid: Sun 12 Jun 2016 06:00 to Mon 13 Jun 2016 06:00 UTC
Issued: Sat 11 Jun 2016 19:18
Forecaster: TUSCHY

A level 2 was issued for the N-Ionian and SE Adriatic Sea including surroundings mainly for excessive rain.

A level 1 surrounds the level 2 mainly for a few large hail, excessive rain and tornado reports.

A level 1 was issued for Italy mainly for isolated large hail and excessive rain.

A level 2 was issued for N-Tunisia mainly for large/very large hail and severe wind gusts.

A level 1 surrounds that level 2 for a lesser risk of aforementioned hazards.

A level 1 was issued for far W-Russia mainly for an isolated large hail and tornado event.

SYNOPSIS

Pronounced diffluent upper trough amplifies over CNTRL Europe to the SE. Otherwise, the only feature of interest at mid/upper levels will be a cold-core low over NE Europe, which rotates NE/N over far W-Russia. This vortex is accompanied by a sub-995 hPa depression, which pushes cold/warm fronts to the east and northwest. A residual boundary extends from the Ukraine all the way to the S-North Sea. Numerous frontal boundaries emanate from an extensive depression over the far NE Atlantic and affect the Bay of Biscay and surroundings. Another front sharpens over the Ionian Sea with increasing pre/postfrontal moisture and thermal gradients. This boundary extends towards N-Tunisia.

DISCUSSION

... CNTRL Mediterranean ...

Diffluent upper trough interacts with a moist and moderately unstable air mass. Both, synoptic forcing and large-scale upper divergence, combined with weak capping support scattered to widespread CI. CIN increases towards S-Italy and Sicily, which may limit coverage of storms. Else, early initiation is anticipated with convection ongoing all day long. DLS increases from N-Italy to the south from 10 m/s to 20 m/s with roughly 1 kJ/kg MLCAPE. Hence, Italy will see adequate shear / CAPE interaction for organized multicells with large hail, strong wind gusts (isolated severe downbursts especially over CNTRL Italy) and heavy rain. Complex interaction of outflow boundaries may support an isolated tornado event.

The N-Ionian Sea towards Montenegro and Albania was upgraded to a level 2, as enhanced BL convergence beneath upper divergent flow regime and undisturbed / capped very moist inflow from the S-Ionian Sea probably result in a growing MCS during the night with only slow eastbound motion. Excessive rain is the main hazard, although tail-end storms/more discrete storms also pose a large hail and isolated tornado threat.

... N-Tunisia ...

The level 1 from S-Italy was expanded to N-Tunisia, where a SE-ward moving front advects a moist air mass well ashore. Overlap of 20m/s DLS and 25 m/S 0-3 km shear with 1kJ/kg MLCAPE indicate an augmented chance for supercells with large or very large hail despite gradually weakening mid-level lapse rates. In addition, severe wind gusts are forecast with mature storms and hence a level 2 was added.

... N-France to Benelux to Germany to Austria ...

Placed beneath the upper trough, once again an overlap of cool mid-tropospheric air atop a moderately moist BL results in an active day with widespread thunderstorm activity. Weak mid-level lapse rates atop BL mixing ratios of 9-10 g/kg cause 300-700 J/kg MLCAPE with effective PWs of 20-30 mm. Early and widespread CI will limit chance for any discrete activity and CAPE will gradually consumed by high convective activity including limited diabatic heating with expanding cirrus (anvil) clouds. Slow moving/clustering storms bring heavy rain, but the excessive rain threat should be limited by increasing storm motion vectors and confined CAPE.
Although a few rainfall reports will probably be received, meager CAPE and moderate low/mid-tropospheric moisture content kept probabilities below the level-1 threshold.

...E-Hungary to Romania to S-Ukraine...

Similar conditions are expected as discussed in the paragraph above. The main difference will be stronger winds at mid-levels, which increases 0-6 km shear to 10-15 m/s. In addition to heavy rain, an isolated large hail event can't be ruled out ... especially over E-Romania.

... SE of the White Sea ...

Warm sector features rather dry BL air mass with enhanced values due to moisture pooling along gradually north-/northwestward surging warm front. Kinematics remain weak over the warm sector but increase a bit toward the warm front. There, enhanced backed low-tropospheric flow and DLS of 15 m/s support a few better organized multicells with large hail and an isolated tornado threat. The threat diminishes after sunset.

Further to the SW, postfrontal convection has to be monitored, as 500 hPa temperatures drop to -25C with GFS indicating 400-800 J/kg SBCAPE. In case of deeper updrafts, 15-20 m/s DLS may support a few better organized storms during peak heating with an isolated large hail risk. Hence the level 1 was expanded to the SW.

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