CONVECTIVE FORECAST
VALID 06Z SAT 22/05 - 06Z SUN 23/05 2004
ISSUED: 21/05 16:29Z
FORECASTER: DAHL
There is a slight risk of severe thunderstorms forecast across the N Balkan States and the W Ukraine.
General thunderstorms are forecast across southern and eastern Europe.
General thunderstorms are forecast across S Sweden.
General thunderstorms are forecast across NW Russia.
SYNOPSIS
Upper trough over central Europe at the beginning of the period ... will amplify somewhat as perturbations are rotating about the trough ... and shift eastwards into east-central Europe by Sunday 06Z. Several perturbations are expected to track eastwards amidst southern upper frontal zone stretching across the S Mediterranean. At low levels ... nearly E-W aligned baroclinic zone will stretch from N Iberia across the Alps and the central Belarus into Russia ... with cool polar air mass present N of the boundary ... and weakly unstable subtropical air present to its south. EML plume is advecting off the Sahara into the SW and central Mediterranean.
DISCUSSION
...Balkan States ... W Ukraine...
Saturday's convective scenario over E European states will likely resemble Friday's central-European scenario ... with MLCAPE generally below 1000 J/kg ... weak capping and relatively high LCLs ... and mean SFC dewpoints of about 13°C. DCVA-related lift downstream from vort max currently over the W Mediterranean ... is progged to overspread the Balkans during the day. Also ... insolation and orographic forcing ... as well as the the frontal circulation along main baroclinic zone may aid in weakening CINH.
Expect numerous TSTMS to develop during the day over the Balkans ... and over the WRN Ukraine ... maybe spreading as far NE as to extreme W Russia. Deep shear will be on the order of 20 m/s over the N Balkans ... and decrease towards the south to about 10 m/s. Though main threat with this activity will be isolated severe straight-line winds and small hail ... strong variability of low-level kinematic and thermodynamic profiles over the hilly/mountainous terrain suggests that moisture may locally be trapped ... leading to enhanced MLCAPEs ... which ... along with modified low level shear profiles may promote supercells with attendant threat for large hail ... severe wind gusts and a tornado or two. Will place a SLGT where deep shear and CAPE should be maximized.
...Iberian Peninsula ... S France...
Diurnally driven high-based TSTMS will likely develop again ahead of and underneath Iberian upper trough. Associated band of strong mid/upper winds is currently expected to be just S of where convective activity will be greatest ... and kinematic environment of the storms will likely not be very supportive to severe evolution. Nonetheless ... strong evaporative cooling of the downdrafts will likely promote a few marginally severe outflow gusts and small hail. Small threat for supercells exists if storms encounter favorably aligned outflow boundaries from Friday's convection ... primarily posing a threat for large hail. Allover chances for severe are too low for a SLGT ATTM.
Farther E over S France ... narrow plume of residual subtropical air mass will be present per BOLAM and GFS theta-e fields. TSTMS will likely develop within this air mass during the day aided by DCVA-related forcing for UVVs. About 15 m/s deep-layer shear will be in place ... and an isolated wind/hail event approaching severe levels may occur ... however ... allover severe threat is too low for a SLGT
...central Mediterranean...
As steep lapse rates move off the Atlas mountains into the SW and central Mediterranean ... weak CAPE may develop ... especially over Italy where diurnal heating will aid in destabilizing the air mass. Negatives are are strong capping and unfavorable timing of vort max ... which may inhibit initiation. If storms form ... an isolated marginally severe wind/hail event may occur given about 15 m/s 500 hPa flow and relatively dry midlevels ... but a categorical risk is not needed ATTM. A few elevated TSTMS may also form at the nose of the Saharan theta-e plume.
...S Sweden...
Shallow TSTMS may form with diurnal heating over S Scandinavia beneath upper cold pool ... severe threat will be negligible given nearly neutral profiles and minimal shear. If DCVA-related forcing at the periphery of the mean trough is stronger than currently anticipated ... TSTMS may also form in more favorable kinematic environment over Denmark and N Germany. However ... current indications are that TSTM activity will be confined to the regions beneath the upper thermal low.
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