Storm Forecast
Valid: Tue 29 Sep 2009 06:00 to Wed 30 Sep 2009 06:00 UTC
Issued: Tue 29 Sep 2009 06:11
Forecaster: VAN DER VELDE
A level 2 was issued for eastern Spain and Balearic islands mainly for excessive precipitation.
SYNOPSIS
A blocking high pressure area over Western Europe with its center southwest of the British Isles diverts low pressure systems to Scandinavia, while causing eastern flow in lower levels over the Mediterranean Sea. A mid level vorticity maximum between Algeria and southeastern Spain is the cause of major problems with persisting precipitation in a zone along the east coast of Spain. Today this rainy episode continues and may become worse.
DISCUSSION
...eastern Spain...
The vorticity maximum weakens while approaching the shores of Spain, and will move inland after 21Z. Lift will at times be concentrated in narrow lines north of the vort max, with many storm cells moving onshore. Compared to yesterday, MLCAPE and ICAPE values will be 2-3x as high (in GFS), with values possibly even reaching 1500 J/kg. This could mean a stronger updraft water vapor flux and larger storm clouds with higher precipitation efficiency, which is further enhanced by very low LCL heights and hardly any evaporation in mid levels. Effective Precipitable Water indicated by GFS soars to 40 kg/mē. The maximum of precipitation appears to shift to the north, Valencia-Castellon.
LAMMA-WRF 18Z is somewhat behind (displaced to the south with respect to current developments).
Also more enhanced today is storm-relative helicity along the coast, to values of 100-200 mē/sē, and can augment updraft intensity and rotation. Large hail is possible.The large low-level instability and lapse rates combined with relatively weak flow indicate also a chance of waterspouts which can move onshore.
