Forecast Update
Valid: Fri 21 Jul 2006 14:00 to Sat 22 Jul 2006 06:00 UTC
Issued: Fri 21 Jul 2006 14:09
Forecaster: TUSCHY

SYNOPSIS

Please refer to the outlook, issued at Thu 20 Jul 2006 18:22 UTC !


DISCUSSION

A few adjusments regarding the TSTM line //mainly in the SE-quadrant // were necessary.

... NW / N-France and parts of the United Kingdom ...

Despite the fact that GFS and NMM nearly stashed the whole low-level circulation away, conditions will be still fine for a few organized storms to form .

Main reason for E/SE-ward expansion of the level-1 area are the currently developing storms over NW France... Storms are aligned along a NW-SE oriented boundary and are still well seperated. The NE-ward waved anvil shows the arrival of a stronger mid-level flow.
Latest sounding reports indicate a well mixed boundary layer in front of those storms.... Steep mid-level lapse rates are present, so up to 1200 J/kg instability were released.
There is a concern that those storms will still have a limited time frame for isolated tornado development.
Decreasing T-Td spread in front of those storms and a still more discrete appearance on the latest VIS loop are a fine initial position for a few low-based and organized storms.
DLS of 15-20m/s is on track but low-level shear ( model forecast )is still pretty slim.
Current thinking is that mesoscale features like a developing sea-breeze front along the coastal area of the English Channel could locally enhance the shear...hence I continue to mention the possibility for an isolated tornado // mainly during the next few hours // over NW France.

I canceled the level-1 over NW Germany and
the Netherlands due to the diminishing eastward trend of convective signals in the models and the continually weaker calculated circulation over France.
Instability and shear will be still high enough for an isolated large hail and severe wind gust threat.