CONVECTIVE FORECAST
VALID 06Z SAT 03/07 - 06Z SUN 04/07 2004
ISSUED: 03/07 00:12Z
FORECASTER: DAHL

General thunderstorms are forecast across central ... NRN and ERN Europe.

General thunderstorms are forecast across E Spain.

SYNOPSIS

At the S periphery of extensive upper low centered over the North Sea ... band of strong upper westerlies is present over central Europe ... progged to back somewhat as the upper low slowly translates east during the period. Main frontal boundary at low levels is roughly paralleling the upper flow ... expected to curve from N Spain across N Italy... the N Balkans and W-central Russia into N Scandinavia by Saturday 12Z. Weak but extensive SFC low is covering the NWRN portions of Europe ... with weak SFC ridging expected to spread into S and S-central Europe.

DISCUSSION

...Central and E-central Europe...
It looks that main convective activity will occur within the deep polar air mass present across large portions of Europe. Air mass will be nearly uncapped ... and widespread showers and scattered TSTMS should form with daytime heating over Holland ... Germany ... and over E-central Europe. Low-level shear profiles are progged to strengthen during the day ... with late afternoon/early evening 0-1 km shear in the 7.5 to 10 m/s range over much of Germany ... Benelux ... E England and N France. Also ... deep-layer shear should increase some ... with the strongest shear likely remaining outside the region of deepest convection.

Especially the increasing low-level shear suggests that a few shallow mesocyclones may form ... posing the threat of an isolated marginally severe hail/wind event or two ... also ... any mesocyclone that forms will have the potential of producing a tornado ... especially late in the day as LCL heigts decrease and shear strengthens. Highest probabilities for severe appear to exist over the Netherlands and NW Germany in strongest low-level shear regime. Somewhat unfavorable timing of the increase in shear ... and weak instability suggest that allover severe threat will be limited ... and a SLGT does not appear to be warranted ATTM.

...E Europe ... Scandinavia...
Ahead of strong Ukrainian vort max ... a few TSTMS could be sustained or re-develop during the day. Degree of instability is quite uncertain ... but it looks that nearly neutral/saturated profiles will be present ... improving to the north of the Ukraine and towards Scandinavia where low LCLs ... little CINH and appreciable CAPE densities in the lowest few kilometers appear to be present. Large-scale shear will me marginal with ~ 15 m/s shear magnitude in the lowest 6 km and weak large-scale 0-1 km shear. But local flow perturbations along with the favorable low-level thermodynamic fields may support a few supercell tornadoes ... along with large hail and damaging winds. However ... allover setup is rather marginal and somewhat uncertain ... and a SLGT is not justified ATTM.

...E Spain...
Models hint at possibility of a few Cb's late in the day over Spain ... if relatively deep SFC-based layer of cool air apparent in Friday's 12Z ascents can be mixed out. If convection initiates ... its high-based nature will likely allow for strong evaporative downdraft cooling ... promoting very gusty outflow winds ... which may briefly reach severe levels.

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