Storm Forecast
Valid: Tue 19 Oct 2010 06:00 to Wed 20 Oct 2010 06:00 UTC
Issued: Mon 18 Oct 2010 19:20
Forecaster: KOROSEC
A level 1 was issued for North sea and coastal areas of Netherlands, NW Germany and parts of Denmark mainly for funnel clouds and non-mesocyclonic tornadoes (waterspouts).
A level 2 was issued for western Turkey mainly for excessive convective rainfall, severe wind gusts, large hail and a couple of tornadoes.
A level 1 was issued for areas surrounding the level 2 as well as for the whole Greece, southern Albania, Aegean sea and parts of southern Mediterranean sea mainly for excessive convective rainfall, strong winds, large hail and a couple of tornadoes or waterspouts.
SYNOPSIS
Between the two persisting upper ridges, one over eastern Atlantic and another over western Russia, a deep polar trough spreads SE-wards towards central Europe and Scandinavia. Accompanied by this powerful trough, a strong surface pressure with an attendant surface cold front moves across North sea in the early morning hours of Tuesday where front continues racing towards the Alps during the forecast period. More to the south, a filling robust upper low slowly moves towards ENE and merges with the coming polar trough by Wednesday morning. Another strong cold front serves as a focus for severe convective storms over Aegean sea and western Turkey, continueing from the nighttime activity.
DISCUSSION
... western Turkey, Greece and parts of southern Mediterranean sea...
A rather strong WAA will be spreading northwards towards Turkey ahead of the slowly moving surface front across Aegean sea and western Turkish coast. The convective activity will actually continue from the previous night and should intensify more during the daytime hours. Models, especially GFS, have high to extreme instability in place, peaking well above 2000 J/kg with MLCAPE just ahead of the surface front. Supported by moderately strong mid-level jet, deep-layer shear between 20-25 m/s seems reasonably expected. This will lead into well organized severe storms, posing a threat for very intense rainfalls, as well as very large hail and strong to severe wind gusts. Impressive LL shear near 15 m/s in the lowest 1km brings quite a high threat for a couple of tornadoes (signifficant event possible) as well. Locally, flash floods will be possible where any convective clusters will form, as their progress should be quite slow. Combined with strong orographic lifting, large precipitation sums can be expected.
The second round of convective activity seems to arrive later during the day when the upper low, placed over southern Italy, slowly moves eastwards. Large scale ascent ahead of the trough axis/diffuse surface front suggests that numerous showers and thunderstorms will form again, though in weaker shear. Given their slow motion vectors and steep LL lapse rates, non-mesocyclonic funnels/waterspouts and locally heavy rain will be the primary threat.
... North sea and coastal areas of Netherlands, NW Germany and parts of Denmark ...
Behind the rapidly SE-wards moving strong surface cold front, polar airmass will be spreading across the North sea and coastal areas of Netherlands, extreme NW Germany and Denmark. Models release a marginal instability once the steep lapse rates overspread the still warm SSTs there. Given the low EL temperatures, CAPE will be tied in the lowest levels and combined with steep LL lapse rates and weak shear (although surface winds will be quite strong from the NW), shallow convection is likely within the maritime airmass. A couple of funnel clouds or waterspouts could occur in these conditions as well. However, a marginal level 1 threat area has been placed over parts where the potential for some spout type tornadoes or some strong gusts seems maximized.
