Storm Forecast
Valid: Sun 08 Apr 2007 06:00 to Mon 09 Apr 2007 06:00 UTC
Issued: Sun 08 Apr 2007 00:55
Forecaster: VAN DER VELDE

SYNOPSIS

Blocking high pressure is centered over the Atlantic southwest of the British Isles, with a weak extension over the southwestern half of the forecast region. The upper air is rather cool and moisture sufficient to create small afternoon-early evening thunderstorms througout a large area, due to the weak flow much confined to elevated grounds and sea breeze convergence zones. Have noticed GFS underestimated convective potential in the southern Alpine region.

Scandinavia and eastern Europe see more active weather pattern as cold airmasses cascade southeastward. Deep convection could occur over the Baltic States, Belarus and western Russia mainly, with GFS indicating tops of -40C, but low mixing ratios suggest only sparse lightning.

DISCUSSION

A cold upper low still lingers over Spain, creating thunder chances mostly for the northern half of the Iberian Peninsula. Up to a few hundred J/kg MLCAPE is available. Deep layer (0-6 km bulk) shear reaches moderate values northwest and southeast of the vorticity maximum over central Spain (15-25 m/s), but 12Z soundings of the day before show little shear below 600 hPa with stronger winds (15-20 m/s) above. The resulting storms may persist long and locally create large precipitation sums, but severe weather threat should remain limited. An isolated landspout (high vertical vorticity, steep lapse rate and fair low level buoyancy environment) and mostly small hail seem possible.

Better shear and low level veering winds with height (NE to SW) over Algeria and the southwestern Mediterranean create a better environment for long-lived and severe storms with stronger inflow and rotation potential (0-3 km SREH up to 250 m2/s2). Although GFS does not display much precipitation, yesterday's activity seems to give away more potential for development... after all strong low level convergence signals and indicators of instability in GFS do support initiation. Large hail and severe gusts are possible, but absence of good low level shear precludes tornado chances.

These better low level backed winds occur also over the southeast coastal areas of Spain, but precipitation indications do not suggest much of a probability for storms and hence severe weather, but if anything forms it could bear a similar chance of hail and gusts.