ESTOFEX going with the French storms, but nothing reaching our shores:
Quote
Extended Forecast
Valid: Sun 21 Aug 2011 06:00 to Mon 22 Aug 2011 06:00 UTC
Issued: Fri 19 Aug 2011 23:35
Forecaster: TUSCHY
A level 1 was issued for parts of France and Germany mainly for large to very large hail and severe wind gusts.
A level 1 was issued for parts of Spain and Portugal mainly for large to very large hail and severe wind gusts. An isolated tornado threat may evolve along the coastal areas.
SYNOPSIS
A cut-off low west of the Iberian Peninsula becomes trapped in the westerlies and starts to move northeastwards, eventually approaching the Bay of Biscay during the night hours. A sharp frontal boundary over parts of W-Europe will be the focus for isolated to scattered thunderstorm initiation. Stable and hot conditions prevail over most of the Mediterranean.
DISCUSSION
... France to Germany ...
Stalling stationary front from the 18th/19th cold front event continues to retreat northwards during the day and seems to be placed somewhere over central France and central Germany as an active warm front boundary. Air mass over far S-France/W-Mediterranean features a rich BL moisture content with surface dewpoint readings in the upper tens/lower twenties. As an upper low moves towards the Bay of Biscay, WAA strengthens over France and helps to sharpen the boundary during the day with EZMWF/GFS indicating a quite intense moisture gradient along this boundary....with moisture pooling bringing surface dewpoints well above 20°C on a local scale. Steep mid-level lapse rates atop this air mass feature a confined area with high CAPE build-up....probably in the order of 1-2 kJ/kg. However major uncertainties exist in the exact placement of this front due to numerous weak short waves crossing that boundary during the severe weather outlook day-1 period, each of them being able to generate strong to severe thunderstorms, which may modulate final boundary position.
Despite that, overall conditions favor rapid to explosive thunderstorm development on an isolated to scattered scale regarding thunderstorm coverage. Shear in order of 20-25 m/s (6 km bulk shear) will be more than adequate for intense multicell/supercell evolution with the main risk being large to very large hail and severe downbursts. Near parallel alignement of the deep layer shear vector to the frontal boundary also favors the development of numerous smaller scale and progressive clusters with a more widespread severe to damaging wind gust risk.
However, major uncertainties in the meso-alpha/beta scale preclude any higher probabilities for now. Also, latest QPF outputs hint on more isolated thunderstorm coverage especially over central France, which also neglects a level 2 for now.
UKASF:
Quote
Storm Forecast - Slight
Forecaster:
Dan
Last Updated: 20:02 Friday, 19th August 2011
Valid: 00:00 Saturday, 20th August 2011 - 23:59 Saturday, 20th August 2011
Areas Affected:
SLGT: W + SW Scotland, Northern Ireland, SW England, SE Wales, West Country, S + E Midlands
Synopsis:
Upper ridging slowly weakens and moves eastwards as an upper low approaches from the Atlantic. The associated upper trough weakens progressively during the forecast period. Limited convection is expected.
Discussion:
In the post frontal airmass, numerous showers are forecast over SW + W Scotland and Northern Ireland during the morning. Slight instability is indicated with a few hundred J/kg CAPE, and ELT's marginally conducive for lightning. Chances for isolated thundery activity increase here during the evening hours across Northern Ireland and SW Scotland in particular.
Further south, in the redeveloping warm sector as a wave develops along the cold front, slight instability is also signalled to run NEwards along/ahead of the front between 12z-23z from SW Eng towards Lincolnshire. Isolated lightning is possible from embedded convection, but not expected to be widespread given weak support.
During the evening hours it is likely an area, possibly linear, of showers and thunderstorms may develop in the W English Channel, drifting NEwards just offshore of Cornwall and Devon, and possibly making landfall somewhere in S/E Dorset (Swanage, Poole etc for example). However, this is expected to be beyond this forecast period and thus we will monitor this situation and will provide an update in the Forecast issued for Sunday.
EXTENDED OUTLOOK: There exists a chance of a few thunderstorms over the C + E English Channel during Sunday morning,
which may move onshore at times, although this remains uncertain. Further activity is expected next week.
21st OWS have nothing even close!
Their Met O interpretation shows it way too far South for our interest:
WAFC Aviation chart looks better:
KO index looks in about the right place:
CAPE doesn't really get going until the early hours of tomorrow, but is encouraging:
Gone by lunchtime tomorrow:
I'm not convinced for daylight hours at all during today, but later overnight and into the morning, still has the merest smidgen of a chance for the South coast:
Maybe even a funnel in the Channel if you can see out there?
Yet again down to radar and lightning detector watching - presupposing you want to be up in the wee small hours in Hants, Sussex and Kent coastal areas!!!!!
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Ok, l thought I'd start a new thread. Now, UKASF seems to think that some of us have a slight chance Saturday and according to them the areas affected will be W + SW Scotland, Northern Ireland, SW England, SE Wales, West Country, S + E Midlands I expect Stu will be along to post up a more detailed forecast from UKASF later on .
