Forecast Update
Valid: Wed 26 May 2010 09:00 to Thu 27 May 2010 06:00 UTC
Issued: Wed 26 May 2010 09:24
Forecaster: PUCIK
A level 1 was issued for Southern to Central France mainly for large hail.
A level 1 was issued for Eastern France to Central Germany mainly for tornadoes.
A level 1 was issued for Slovakia, Northern Hungary, extreme Southwestern Ukraine, Northern Romania mainly for large hail and tornadoes.
SYNOPSIS
A prevailing zonal flow is observed over most of Europe with two separate cold-core lows at 500 hPa level over Northern Europe - one centered over the Northern Sea, with little movement and another one over Western Russia moving to the east-northeast. Strong westerly flow over 20 m/s is observed at the southern flank of both lows. From the low centered over the Northern Sea a trough will extend to Southern France, moving eastwards during the day.
At the surface a major feature will be a warm front, stretching from Belgium to Central Germany, Northern Czech Republic, Northern Slovakia/ Southern Poland. As the separate surface lows deepen on this frontal system, it will become wavy in its nature with cold front passing over France during the evening. In the warm sector of the lows, slightly to moderately unstable airmass will be present. A deep surface low will be centered over Northwestern Russia.
DISCUSSION
... Eastern France to Central Germany ...
Behind the warm front, high Theta-E airmass will advect over the region with slight instability built-up behind the warm front. Surface observations reveal very low dewpoint depressions and therefore, low LCLs. With enhanced wind shear, in the 0-6 km layer reaching 20-25 m/s, well organised storms are probable, including few low topped supercells. Backed flow due to the deepening surface low, wind shear in the 0-1 km layer reaching 10 m/s and abundant boundary layer moisture point to the threat of isolated, weak tornado which might accompany supercells. Stronger cells might also be capable of marginally severe hail.
... Southern to Central France...
Ahead of the approaching trough and the cold front, slightly to moderately unstable airmass, with MLCAPE values locally over 1000 J/kg should be present over the region. Wind shear values will reach 15-20 m/s, with the highest values observed in the southern extent of the Level 1. Over this area, GFS simulates a blob of enhanced SREH (over 200 J/kg in 0-3 km layer) and therefore, the highest potential for well organised, rotating storms will exist here. Scattered storms will likely form over the area during afternoon. A low end level 1 is issued for this region, as marginally large hail might occur with the stronger storms.
...Slovakia, Northern Hungary, extreme Southwestern Ukraine, Northern Romania...
Behind the warm front, a moderate destabilisation is expected with MLCAPE values locally likely exceeding 1000 J/kg in the belt from Slovakia to Northern Romania. Moderate wind shear values, reaching around 15 m/s point to the formation of mostly multicellular structures. Stronger wind shear will be observed to the north or in the close vicinity of the warm front. However, backed flow due to the approaching surface low will likely sustain enhanced SREH values, reaching over 150 J/kg, over Eastern Slovakia even over 250 J/kg in 0-3 km layer. Therefore, brief supercells are not ruled out either. In the stronger cells, large hail might be a threat. With quite strong low level shear, over 10 m/s and low LCLs, tornadoes might occur as well, especially in case that supercells manage to develop. Level 1 is therefore introduced for this region.
