Storm Forecast
Valid: Sat 02 Dec 2006 06:00 to Sun 03 Dec 2006 06:00 UTC
Issued: Fri 01 Dec 2006 21:29
Forecaster: TUSCHY

SYNOPSIS

An outstanding dynamic weather pattern continues over the North Atlantic.
Latest CMC analysis (01.12.) indicated a whopping upper level jet streak with up to 185 kt over far eastern Canada, also supported by the 12Z sounding of YZV Sept-Iles, reporting even 190 kt at 300 hPa.
This intense jet will rapidly develop towards the SE during the next 24 hours, inducing an intense cyclogenesis somewhere around 55N 20W, nearly matching the criteria for a rapid cyclogenesis.
The 12Z outlook of the Ocean Prediction Center levels it off at about 953 hPa north of Ireland just after the end of the forecast period.
Further towards the south, a spacious upper-level trough will cross Portugal and Spain, supporting an active period regarding convective activity.
Strong high pressure area will still be present over the rest of Europe although smaller scale disturbances support localized enhanced convective activity over parts of the Mediterranean.


DISCUSSION

...Ireland, United Kingdom and Scotland...

Again, multiple rounds of enhanced convective activity can be expected over a broad area, where kinematic parameters will be favorable for some kind of severe weather !

First area to look at will be Ireland, Scotland and the northern and western parts of United Kingdom during the 06 Z - 15 Z time frame.
An upper-level short-wave trough is forecast to cross the region from the SW and 19Z IR images ( 01.12.) already indicate a pool of enhanced convective activity just west of Ireland.
Advection of a cold mid-level airmass supports widespread steep mid-level lapse rates over Ireland and Scotland and isolated to scattered thunderstorm development can be expected.
Kinematic environment looks fine with up to 15m/s DLS and LLS and also up to 200 J/kg 0-1km SRH.
LCLs will also stay low and hence storm rotation and an attendant tornado threat will be a distinct possibility mainly along the coastal areas of SW / W - UK and Scotland.
Otherwise, severe wind gusts and marginal hail can accompany the stronger cells.

Then the attention turns towards the west due to the arriving cold front of the intense low pressure system noth of Ireland (21Z onwards).
Exact coverage and location of the best severe weather threat is still somewhat uncertain due to the importance of smaller scale features, which are not handled that good by global models that far out.
Well developed, eastward racing cold front will cross Ireland around 18Z . Strong CAA will cause an area of steep mid-level lapse rates to spread eastward and still at or above 11°C SSTs will support vigorous convective activity behind the cold front.
Shear values will be more than adequate for an enhanced tornado risk and severe wind gusts over Ireland.

12Z GFS meso-analysis indicates that the cold front will reach western UK during the 03 - 06 Z time frame and was pretty consistent with this solution during the past few model runs.
Main concern will be the rapidly ENE-ward movement of a weak dry slot, which is forecast to intersect the cold front somewhere over SW UK during the 03 - 06Z time frame.
This trend has to be closely monitored due to possible convective activation on the backside of a well developed warm conveyor belt in an environment with extreme shear values( more than 50 m/s DLS and 20m/s LLS ).
End of forecast validity and uncertain final front position hampers me to introduce a broader level region over SW - UK, but aforementioned update may become necessary later on.

... Portugal and parts of Spain...

Upper-level trough will drip off just west of the Iberian Peninsula and is forecast to cross Portugal and SW - Spain from the WNW during the daytime hours.
DLS will be significantly enhanced over Portugal and an area west of the Strait of Gibraltar and therefore included the region into a level 1 due to the severe wind gust risk.
Betimes ( after 15 Z ), separation of best shear and instability will lower the risk for organized thunderstorms.