Storm Forecast
Valid: Wed 25 Mar 2009 06:00 to Thu 26 Mar 2009 06:00 UTC
Issued: Tue 24 Mar 2009 21:52
Forecaster: PUCIK
SYNOPSIS
Strong prevailing NW-ly flow has established over Europe. Several mid and upper level disturbances are embedded in this flow, having a dominant influence on the weather conditions. The first one is predicted to affect Western Europe by Wednesday morning, associated with a deepening surface low, which should reach BENELUX coast by 12Z. The second one over Central Europe will move eastwards and in strong cold advection aloft, some thundery convection is expected over Ukraine, as suggested by general thunderstorms area. The last one is as of Tuesday 21Z supporting widespread thunderstorm activity over Italy. This impulse will rotate around the base of the large-scale trough, subsequently influencing Greece and Turkey.
DISCUSSION
... Nothern France, Belgium....
A mid-level disturbance will start to affect the region by early morning with very favorable dynamics. We are expecting this area to be under the left exit region of both mid and upper-level jet ( having speeds of more than 50 m/s), which suggests strong vertical motion. Strong QG forcing is also anticipated ahead of the trough. Split-front characteristic may result with a strongly forced convective line trailing behind the main stratiform rain shield. Deep layer shear will reach more than 40 m/s, with more than 10 m/s confined to the lowest km. Moreover, SREH values will be very high in vicinity of the front, with more than 300 J/kg for 0-1 km layer. Despite the fact that only weak instability release is anticipated with simulated CAPEs around 100 J/kg, it is quite probable that strong dynamics will compensate for lack of instability and deep moist convection will form. Due to the strong shear and helicity, some embedded rotating circulations might occur in the convective line so tornado or two can not be ruled, as well as marginally severe gusts.
...Greece....
With the help of strong impulse moving rapidly eastwards, quick build up of instability is expected, with several hundred J /kg of MLCAPE. Thunderstorms will already ongoing on Wednesday 06Z and should increase their coverage especially with the cold front arriving later on. Deep layer shear will be in excess of 25 m/s, with shear in lowest 3 km over 20 m/s. Also, high SREH values are anticipated inland and therefore, well organized storms are anticipated. Marginally severe hail will probably be the most prominent threat with low chance of severe wind gusts, in case that supercells or strong squall line manage to form. Storms will quickly dimnish after 15Z.
...Turkey....
The same disturbance as in case of Greece, will also affect Turkey. MLCAPEs more than 500 J/kg are predicted to form over Aegean Sea and such unstable air will be advected inland ahead of the frontal system. Strong forcing ahead of the trough and frontal uplift will initiate numerous thunderstorms. The deepening of the surface low over the sea is expected to strenghten the low level flow and more than 15 m/s of wind shear 0-1 km is forecast inland. SREH values will also rise to more than 250 J/kg with the backing flow ahead of the low. Whole palette of severe weather is possible, marginally large hail might occur with supercells, severe wind gusts are quite possible too, with more than 25 m/s of flow at 850 level. Due to the strong low level wind shear, favourable forcing and low LCLs, also tornadoes could be a risk over this area.
