Storm Forecast
Valid: Sun 18 Sep 2016 06:00 to Mon 19 Sep 2016 06:00 UTC
Issued: Sat 17 Sep 2016 18:13
Forecaster: BEYER
A LVL1 was issued for parts of Southern Italy mainly for excessive precipitation, and to a lesser extent for large hail and severe wind gusts.
A LVL1 was issued for parts of Southern Croatia, parts of Bosnia y Herzegovina, Albania and Montenegro mainly for excessive precipitation and to south with a lesser extent also for large hail and severe wind gusts.
A LVL1 was issued for the Crimean Peninsula for large hail, severe wind gusts and tornados.
SYNOPSIS
The general weather over the northern half of Europa is dominated by a persistent omega pattern. A trough can be found between Iceland and Greenland as well as over far Eastern Europa /Western Russia. In between a strongly amplified ridge influences most parts of Scandinavia with stable conditions.
South of the ridge a upper level low can be found over the central Mediterranean influencing most parts of the neighboring countries of the Tyrrhenian Sea, the Adriatic Sea as well as the Ionic Sea. But also parts of Central and Eastern Europe are under the influence of quite humid airmasses belonging to this extensive upper level low. On its southern flank an upper level Jet maximum is travelling eastward during the forecast period.
Southwestern Europe is influenced by a ridge with corresponding surface high.
DISCUSSION
... Parts of Southern Italy ...
With the low pressure center situated over Northern Italy surface and low level winds are from the west so that constantly humid airmasses are advected to the Italian coast. Mixing ratios of around 11 g/kg are expected to overlap partly with somewhat steeper lapse rates developed more inland. This will result in about 1000 J/kg along the Italian coastline.
Having this constant advection of humidity in combination with the orography excessive precipitation should be the main threat with the expected storms especially in regions where also coast convergence effects may play a role.
In addition DLS has values of 15 to 20 m/s so that also better organized storms are possible. In such a case an isolated severe wind gust and locally large hail cannot be ruled out.
... Parts of Southern Croatia, parts of Bosnia y Herzegovina, Albania and Montenegro ...
Humid airmasses are advected constantly from the Adriatic Sea. Although lapse rates are not that prominent, slightly enhanced instability is enough to produce a few hundred up to 1000 J/kg of MLCAPE. With the same reasoning as for Southern Italy excessive rain will be a prominent threat with developing storms.
More to the south (Albania, Montenegro) the overall situation is more dynamic. The left exit region of the upper level jet enters the region in the afternoon. In addition DLS is enhanced with values of 20 to 25 m/s. This should allow for better organized storms that may also bring severe wind gusts and locally large hail.
For the whole LVL1 area an IPV maximum is visible that should enhance convective activity. This maximum travels from north to south. Thus convection in the first half of the forecast period is primarily present over the norther parts of the LVL1, whereas the southern parts are mainly influenced beginning with the late afternoon/evening hours.
... Far Eastern Algeria and Tunisia ...
A well pronounced upper level jet maximum is situated south of the upper level low centered over Northern Italy. The right entrance region influences central part of Tunisia and parts of Eastern Algeria. At this area a maximum of mixing ratios up to 12 g/kg are present, overlapping with steep lapse rates and thus resulting in CAPE values that reach 2000 J/kg in the afternoon hours. In addition a well-defined surface convergence line can be found in the model forecasts.
These rather high values of potential energy overlap with quite high DLS (0-6km: around 25 m/s): Thus storms that develop along the convergence line can easily organize into supercells bringing especially large to very large hail and severe wind gusts. Where several storms move over the same area also excessive rain is possible.
The explained scenario should develop just at the southern border of the outlook map so no LVL-area was drawn.
... Ligurian Sea ...
Near the center of the upper level low weak upper level winds and low LCLs favor the development of waterspouts along developing local surface convergence line (e.g. sea breeze).
... Crimean Peninsula ...
This region is situated near the frontal boundary that is separating cooler airmasses to the north and warmer airmasses to the south. During the day a convergence line is forecasted near the coastline of the Black Sea. With southerly winds humid and warm airmasses are advected over the Black Sea.
Quite high values if mixing ratio (11-13 g/kg) can overlap with steeper lapse rates (around 6.5 K/km) . This should lead to CAPE values of more than 1000 J/kg. Mainly affected by this high instability values is the Peninsula of Crimea which is at the border of our forecast map. Thus only a small line could be drawn. The region of interest, however, is extended also more eastward.
Shear values of 15 to 20 m/s (0-6km) are forecasted. Therefore organized storms and supercell are possible. They can bring large hail and locally severe wind gusts.
In addition enhanced LLS (0-1km) is predicted (>10 m/s). This together with low LCLs (around 1000 m) offers the risk for one or two tornados. This is also supported by SRH1 values of locally more than 200 m2/s2.
