CONVECTIVE FORECAST
VALID 06Z SAT 09/08 - 06Z SUN 10/08 2003
ISSUED: 08/08 18:44Z
FORECASTER: DAHL
General thunderstorms are forecast across SW ... central and eastern Europe.
SYNOPSIS
Quasistationary high-amplitude upper flow pattern has firmly established across Europe ... with large-scale upper ridge covering northern parts of Europe ... slowly pushing east ahead of extensive upper trough over the N Atlantic. Downstream upper trough is covering entire east Europe. Over central and SW Europe quiescent conditions continue ... while the W British Isles and parts of E Europe are progged to be affected by vorticity maxima at the periphery of the upper longwave troughs.
DISCUSSION
...SW ... S ... and SW-central Europe...
Problem with the current setup is the weak synoptic-scale forcing and weak capping ... and foci for convective initiation are widely distributed across S ... SW and W parts of Europe. Weak vort max is apparent over central Europe on WV imagery ... and current convective activity appears to be associated with this feature. Numerical models show quite weak signals in the vorticity and vorticity advection fields during the period ... looking rather noisy and offering little guidance finding regions where initiation will be most likely. Thus ... over W Germany ... France and Iberia ... as well as over the central and W Mediterranean Islands/peninsulas ... widely scattered TSTMS may develop during the afternoon ... primarily along orographic features and weak baroclinic boundaries indicated by BOLAM's 850 hPa theta-e fields. Though CAPE and shear will be minimal ... impressively deep dry-adiabatically mixed subcloud layer will promote strong evaporative cooling withing convective downdrafts ... and potential for strong outflow winds exists across the entire region ... with the potential of locally/briefly exceeding severe levels. Coverage is expected to be too low for a SLGT.
...E parts of Europe...
Stronger signals in the vorticity fields are found at the W periphery of the east European long-wave trough ... and stroms will be likely ahead of various vort maxima rotating about the main trough. Shear is expected to remain fairly weak ... possibly on the order of 20 to 30 knots in the lowest 6 km. Given very limited CAPE ... and rather moist environment ... severe threat appars to be minimal. Merging cells/outflow-cell interaction may locally promote mesocyclones ... posing a threat for large hail ... but coverage/duration of severe TSTM events is expected to be very limited ... and a gen thunder outlook is sufficient ATTM.
...British Isles...
Strong DCVA-related UVV's are progged to overspread the W British Isles on Saturday night. 12Z soundings indicate weak lapse rates ... and a SFC-based stable layer caused by advection of rather cool maritime air at low levels. PRIND that environment will struggle to become supportive to deep convection. Chance of a few elevated TSTMS appears to exist as steep lapse rates are advected from France into south GB early Sunday morning. Prefrontal airmass needs to be monitored and an upgrade may be necessary ... but chances for TSTMS appear to be rather small ATTM.
...Finland...
Vigorous vort max is expected to cross Finland during the day. Airmass ahead of the vort max may become weakly unstable ... and with 0-6 km shear magnitude expected to reach 70+ knots ... brief bow echoes and a few low-top supercells may occur. Only ... but substantial negative is possible drying of the airmass in the lee of the Scandinavian mountains ... and TSTMS may completely fail to initiate. Region should be monitored for a possibly upgrade.
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