Storm Forecast
Valid: Sat 13 Jun 2009 06:00 to Sun 14 Jun 2009 06:00 UTC
Issued: Fri 12 Jun 2009 22:08
Forecaster: DAHL
A level 1 was issued across northern France mainly for severe wind gusts and large hail.
A level 1 was issued across estreme western Russia and extreme southern Finland mainly for heavy precipitation, severe wind gusts, and large hail.
SYNOPSIS
High-amplitude upper flow pattern is developing over Europe, with an upper ridge building over central portions of Europe and two adjacent long-wave troughs over the E Atlantic and over E Europe, respectively. The SFC pattern features two low-pressure systems attendant to the upper troughs and quiescent conditions between these features underneath ther upper ridge over the central parts of Europe. Ahead of the E Atlantic trough, warm and unsstable subtropical air is advected northwards into France.
DISCUSSION
... France ...
A deep EML is expected to advect across France on Saturday, with GFS simulating a strong increase of LL moisture underneath the EML, which results in strong CAPE in the simulations. However, low-level return flow from the Mediterranean Sea is unlikely to set in before late Saturday, so it seems unlikely that dewpoints will rise as much as GFS advertises. However, some instability is likely to develop during the day, with least capping expected over N France at the northern edge of the EML.
20 to 25 m/s DLS are expected over the northern half of France on Saturday, suggesting that any storm that forms will have potential of becoming organized, including the potential for supercells. These storms are likely to produce severe wind gusts and large hail.
Lack of upward motion and strong capping should prevent much of the convective potential from being realized over central and southern portions of France, but models hint at convective development across N France in more weakly capped air mass amidst low/mid-level frontogenesis regime. It seems likely that storms will develop into a slightly elevated MCS during the evening/night hours, moving into the Benelux countries until early Sunday morning.
... W Russia .... Finland ...
Weakly capped but rather unstable air is present over E Europe ahead of the E-European deep-layer low-pressure system. Storms shoud initiate with diurnal heating, merging into weakly organized MCSs during the day. Despite rather weak shear, interaction of the cells among each other and with outflow boundaries laid out by neighboring/earlier convection may result in at least briefly organized storms. These storms are capable of producing large hail and probably damaging wind gusts. Given anticipated large storm coverage and relatively slow storm motion, local excessive rainfall is likely.
... Iberia ... and Turkey ...
Isolated high-based storms may develop over Iberia and Turkey during peak-heating hours. Though shear and instability will likely be rather weak, a dry/deep sub-cloud layer should support strong evaporative cooling within the downdrafts and lead to strong/severe outflow winds. However, coverage of severe wind gust events is expected to be too low to warrant a threat-level.
... Italy ...
Some instability appears to evolve over Italy during the day. DLS is expected to be in the 15 to 20 m/s range, which would be supportive of severe evolution, with damaging wind gusts and large hail. However, convective initiation is somewhat unlikely given mid/upper ridging, so will not introduce a categorical thunder line or a risk area.
