CONVECTIVE FORECAST
VALID 06Z TUE 25/05 - 06Z WED 26/05 2004
ISSUED: 24/05 20:34Z
FORECASTER: DAHL
There is a slight risk of severe thunderstorms forecast across the E Ukraine ... portions of W-central Russia.
General thunderstorms are forecast across extreme W Russia ... E and SE Europe ... S-central Mediterranean.
General thunderstorms are forecast across the Iberian Peninsula.
SYNOPSIS
Upper long-wave trough is present over E Europe ... with its SRN periphery expected to close off into an intense upper cut-off low ... rotating about the mean trough across the N Black Sea on Tuesday. Other vort max upstream will affect N-central Europe during the period. Weak southern upper frontal zone persisting across the Mediterranean ... with several weak and ill-defined eastward tracking vort maxima imbedded. W European upper high is finally in the process of weakening ... and will move into the N Mediterranean towards the end of the period. At low levels ... main baroclinic zone is alligned nearly parallel to main upper frontal zone ... 850 hPa frontal boundary is progged to stretch from the S-central Mediterranean Sea across the NW Black Sea northwards into NW Russia by Tuesday 06Z. Cyclogenesis is FCST to occur along the boundary N of the Black Sea early in the day ahead of strong upper low. Weak cyclonic circulations at the SFC will accompany vort maxima at the periphery of E European trough ... while SFC high over W/NW Europe is progged to weaken some.
DISCUSSION
...E Ukraine ... W-central Russia...
Air mass ahead of the developing ... vigorous ... E European upper low is poorly sampled by radiosonde data. Indications are that convectively-undisturbed profiles will be characterized by deep/dry-adiabatically mixed boundary layers ... and minimal CAPE. GFS' CAPE fields are inheriting substantially overdone SFC dewpoint forecasts ... and based on Monday's and the last days' observations ... air mass will likely be weakly unstable at best.
Despite the meager instability ... Shear and large-scale forcing for UVVs will likely be immense on Tuesday ... with 500 hPa wind speeds likely inceasing to 35+ m/s N of the Black Sea towards late Tuesday afternoon. Though insolation may be limited in the pre-frontal air mass ... weak CAPE should be present throughout most of the pre-frontal theta-e plume. TSTMS should develop along the cold front during the day ... most of them being rather short-lived owing to weak thermodynamics ... however ... a few supercells or bow echoes may occur ... posing a threat of large hail and damaging winds. Given degree of large-scale upper forcing and large hodographs ... a SLGT is marginally warranted.
...S Mediterranean...
Soundings farther S across the Mediterranean do not suggest much convective potential ... However ... ribbons of weak DCVA will overspread the low-level front ... and assuming patches of enhanced low-level moisture will persist [ref. Monday's LICT 12Z launch] ... a few TSTMS may develop along the front. Given moderately strong mid-level flow ... some hail approaching severe levels may occur if persistent updrafts can be realized. However ... low confidence in TSTM development ... low TSTM coverage if storms form ... and degree of severe threat once a TSTMS has formed do not warrant a categorical severe outlook
...Iberia...
Another round of diurnal TSTMS is expected over Iberia ... CAPE has effectively been mixed out over the last days ... and thermodynamic profiles are quite meager now. Towards northern Spain ... boundary layer appears to increase in depth ... which may support a few strong outflow wind gusts. Given that air mass is nearly uncapped ... resulting in quite large TSTM coverage ... chance of a rotating updraft or two exists as cells/low-level flow may interact with outflow boundaries/orography ... resulting in somewhat enhanced probabilities for large hail. However ... allover severe threat will likely be too low for a SLGT.
...Otherwise ...
Scattered showers ... capable of producing a few CGs ... may develop beneath upper thermal lows over E Europe and N-central Europe. TSTM coverage should be too low for a TSTM outlook.
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