CONVECTIVE FORECAST
VALID 06Z SAT 05/07 - 06Z SUN 06/07 2003
ISSUED: 04/07 18:30Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the Balkan and Romania.

General thunderstorms are forecast across the eastern portion of Europe.

General thunderstorms are forecast across eastern Spain.

SYNOPSIS

Deep upper longwave trough ATTM covering central Europe ... will slowly continue east. Strong vort max at its periphery is progged to cross the Balkan States on Saturday and to reach the very SE portions of the forecast area towards the end of the forecast period. At low levels ... broad northerly flow will affect much of central and southeast Europe on Saturday in the wake of the upper trough. 850 hPa baroclinic zone E the SE European upper vort max will likewise cross the Balkan states on Saturday.

DISCUSSION

...slight risk area...
Convective scenario on Saturday remains somewhat uncertain owing to very limited model data available at this time.

Strong vort max will cross the Balkan States during Saturday and will be a potential focus for severe evolution. Friday's 12 Z soundings across the Balkan indicate nearly neutral lapse rates with a deeply mixed boundary layer. Observed surface dewpoints in excess of 18°C appear to be very shallow and are not expected to contribute strongly to the mean CAPE of the storm inflow. Expect MLCAPEs on the order of 500 to 1000 J/kg ahead of the vort max/cold front. Wind field will be quite strong ... with deep-layer shear around 40 to 50 knots. Weak low-level veering renders background SRH quite low ahead of the front.

Expect initiation of TSTMS early in the FCST period ... possibly well before 12Z due to the strong large-scale forcing for upward motion. Given rather low SRH ... the probability of supercell development will be rather small. However, local flow perturbation may cause locally high SRH and an isolated supercell or two cannot be discounted. Also ... degree of deep shear suggests that splitting storms will be possible as well. Primary convective mode, however, should be strong/damaging wind gusts producing lines of TSTMS with bowing segments. Ample shear and dry, deeply mixed low-level environment suggests that a widespread damaging wind event may be possible. However ... weak instability/DCAPE may limit vigor of the outflow winds ... thus only a SLGT is issued at the moment. Any rotating updraft will pose additional threat for large hail.

...NE Europe...
Scattered diurnal TSTMS will likely develop again beneath the thermal trough axis and ahead of weak small-scale vort maxima in the deep polar air. Minimal CAPE and minimal shear suggest minute threath of organized severe TSTMS over this region.

...Iberia...
Today's 12 Z soundings across Spain reveal too stable lapse rates/too sparse low-level moisture for positive CAPE values. DCVA-related UVV's ahead of a vort max may steepen the lapse rates somewhat on Saturday but it remains questionable if environment will finally become conductive to TSTM development. If it does ... TSTMS will be capable of producing strong outflow winds owing to a deep/dry subcloud layer. GFS assumes weak CAPE over east Spain during the afternoon/evening. However ... increasing 850 hPa temperatures may be indicative of an elevated-mixed layer advected across central and east Spain ... and low-level airmass may be too strongly capped for TSTM development. Current thinking is that an isolated TSTM or two will form late in the afternoon. Organized severe threat should be rather low although a few isolated strong wind gusts ... maybe briefly approaching severe levels ... may occur.

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