CONVECTIVE FORECAST
VALID 06Z SUN 01/02 - 06Z MON 02/02 2004
ISSUED: 31/01 23:15Z
FORECASTER: DAHL

There are no thunderstorms forecast.

SYNOPSIS

Strong upper westerly flow has established over northern and central Europe. On Sunday ... two intense vort maxima are expected to cross western and central Europe in rapid succession. Second vort max is FCST to support cyclogenesis towards Sunday evening off the British Islands over the Atlantic ... however ... timing and intensity of this development is quite incoherently simulated by various models.

Problem this period will be a very conditional severe TSTM threat ... owing to minimal instability ... in the presence of regions of quite intense synoptic- and sub-synoptic-scale forcing for upward vertical motion. Given impressive shear magnitudes ... any SFC-based TSTM will have fair chances of producing severe weather ... mainly severe straight-line winds. The scenario is additionally complicated by the strongly divergent model solutions. Hence ... significant degree of uncertainty exists with this forecast.

DISCUSSION

...W France ... British Isles ... North Sea...
First vort max will reach W France and the British Isles by the beginning of the forecast period. Enhanced Cu's/Cb's are currently present ahead of this feature. UVM is expected to increase some ... but this may be compensated for by the loss of SFC heating as convection makes landfall. Allover confidence that TSTMS will occur with this activity is rather low ATTM. Mainly the coastal regions of the British Isles ... NW France and possibly of the BeNeLux states may have slight chances of seeing a few lightning strikes ... TSTMS will act to enhance the strong/severe large-scale SFC flow through vertical momentum transfer. Also ... convection could organize into small/shallow bows or supercells given very large hodographs ... and small hail could occur as well as an isolated brief tornado or two. However ... TSTM risk is expected to be too low for a gen thunder area ATTM.

...British Isles ... North Sea ... N Germany ... Denmark...
Solution offered by the last GFS runs as well as by MM5 ... and roughly by BOLAM ... is the formation of a fairly intense SFC low over the British Isles during Sunday evening ... which will move into the Skagerrak/Kattegat region by Monday 06Z. The warm-sector air mass will likely be rather stable ... and convective threat does not appear to be large. Line convection along the cold front does not appear very likely either ... primarily owing to very weak thermal gradients along the front. Chance of deep post-frontal convection also does not seem to be particularly high given that the cold air mass will not be particularly deep. However ... any small-scale vort max ATTM not represented in the model fields ... could provide sufficient UVM for a few TSTMS in the wake of the cold front ... with an attendant severe threat owing to large hodographs. But ... current thinking is that severe TSTM threat accompanying this feature will be rather low. Situation will be monitored and if more aggressive scenario turn out to involve ... an update may be issued.

#