Storm Forecast
Valid: Mon 28 Jul 2014 06:00 to Tue 29 Jul 2014 06:00 UTC
Issued: Sun 27 Jul 2014 21:53
Forecaster: GROENEMEIJER
A level 1 was issued for northeast Sweden and parts of Finland, mainly for heavy rain and to a lesser extent for large hail and severe wind gusts,
A level 1 was issued for parts of eastern France, for Belgium, the Netherlands, Luxembourg, Germany, and for north, west and south Poland, as well as for the Alpine countries, the Czech Republic, Slovakia parts of Hungary, northern Italy and the northwestern Balkans. It is issued mainly for heavy rain.
A level 1 was issued for cental and south Romania, eastern Serbia and NW Bulgaria.
A level 1 was issued for NE Spain, mainly for large hail.
SYNOPSIS
A broad trough covers most of western and central Europe. The air-mass is rather warm, humid and somewhat unstable. Within the through, a fairly strong cold-core mid-level cyclone located over the English Channel will move to south France by Tuesday morning. An embedded shotwave trough stretching from the eastern Alps across the western Balkans moves slowly eastward. Within a westerly flow across northern Europe, an embedded shortwave trough should reach the Norwegian coast by 00 UTC.
DISCUSSION
... northeast Sweden, parts of Finland ...
A more or less stagnant relatively humid air-mass will once again be destabilized by the diurnal cycle, and during the evening hours by the approaching shortwave trough. As a result, convective storms with a high precipitation efficiency will once again break out, which may lead to localized flash flooding problems. Some severe hail will also be possible, as well as very local severe wind gust.
... Benelux and central Europe ...
On the eastern flank of the southward moving low, several processes including diurnally-driven destabilization, frontogenetical lift (across eastern France and Belgium) and low-level warm air-advection and associated ascent (Benelux, Germany) will be responsible for creating a fairly unstable (1000-1500 J/kg) environment in which scattered storms should manage to form. Given the overall humid air-mass and weak wind shear, storm with a high precipitation efficiency are expected to form once again, yielding a large enough threat for excessive precipitation to warrant issuing a level 1. In addition, some marginally severe hail (2-3 cm) and, very locally, strong wind gusts may occur. Across the Benelux and western parts of Germany some weak tornadoes cannot be ruled given the very humid and ample large-to-mesoscale vertical vorticity present.
... central and south Romania, eastern Serbia and NW Bulgaria ...
As the shortwave trough over the Western Balkans moves eastward, an interplay of QC lift and orographically-enhanced lift is expected to cause the development of widespread storms, of not an organized mesoscale convective system across the indicated area. High humidity, weak to moderate wind shear and persistent convergence hint at a significant risk of flash floods. Some marginalyl severe hail or very local severe wind gusts may also occur.
... NE Spain ...
Ahead of the southward moving mid-level low, rather strong ~25 m/s deep-layer shear is excpected over northern Spain. Diurnally-driven inland/upslope winds enhanced by QC forcing should allow moist air to be advected inland, that may be sufficient to sustain a few well-organized storms along the eastern mountains. Any such storms may well turn into supercells and produce large hail. That said, NWP guidance is quite reluctant in developing storms, so that a level 1 without a >50% thunder probabilty seems the best choice.
