Forecast Update
Valid: Fri 16 Feb 2007 13:00 to Sat 17 Feb 2007 06:00 UTC
Issued: Fri 16 Feb 2007 13:00
Forecaster: TUSCHY

SYNOPSIS

Please refer to the outook issued at Thu 15 Feb 2007 19:25 !


DISCUSSION

...Portugal and Spain...

An update became necessary because of an northward expansion of the level-1 area.

Latest WV/IR images indicate clear conditions over most parts of Spain with a few more hours of insolation possible. The cold front has finally arrived along the coastal areas of W / SW -Portugal and the MCS is about to reach W/SW Spain.
Temperatures boom and 10-17°C can already be found over Portugal and Spain with a few spots of 20-21°C along the N-/SE coast of Spain ( although those are likely foehn effects, which occured during the morning hours ). This strong diabatic warming at lower levels goes hand in hand with a beginning cool-down at upper-levels and this should support ongoing convection along the eastward shifting cold front.

Highest tornado threat still expected along the SW-/S coast of Portugal and S-Spain, where LCLs are pretty low and LL shear will be maximized due to backing winds.
DLS of 35m/s and steep mid-level lapse rates will also favor an isolated large hail / severe wind gust risk.

The attention then turns northward. Latest thinking is that the threat for possibly severe hailstorms will expand westward, too. Cold front is forecast to reach W-Spain during the next few hours.
The main reason for the northward expansion of the level-1 area was the developing LL depression over N-Spain, which seems to be more robust than during the latest model runs ( also indicated by a more pronounced wind field, covering central Spain during the afternoon hours ).
PBL should undergo constant modification well to the north and hence a broad area of at least low-end instability release can be expected. Lapse rates of up to 8K / km will be present and although LCLs will lower somewhat, still expect pretty nice inverted-V-soundings over central Spain, indicating an enhanced severe wind gust / hail threat. DLS will stay impressive with up to 40m/s possible.
Evaporational cooling due to the dry PBL will also support strong downdrafts and a few severe wind gusts can be expected.

Into the bargain the latest GFS run also indicated an enhanced tornado potential over W-central Spain. The main uncertainty is if storms will stay mostly elevated or if moisture advection along the cold front could support thunderstorms, which root into the highly sheared boundary layer ( LL shear of 17-20m/s ). Strong diabatic heating assissted a rapidly mixing of the PBL with decreasing dewpoints also supported by humidity reports of the INM varying between 27 and 50%.
Any spot with higher dewpoints would foster an enhanced tornado threat.
Datas from this region are sparse for such small-scale discussions and topography very craggy so will mention the chance for an isolated tornado with each more discrete cell and with storms, which tend to develop more in the postfrontal airmass.

During the early evening hours, thunderstorms will shift towards the NE and severe weather threat will taper off because of rapidly decaying instability.

Parts of Morocco were downgraded because of the model consent that trough will arrive a little bit later than expected.