Forecast Update
Valid: Thu 05 Dec 2013 11:00 to Fri 06 Dec 2013 06:00 UTC
Issued: Thu 05 Dec 2013 11:39
Forecaster: GROENEMEIJER/PISTOTNIK/GATZEN

A level 3 was issued for NE Netherlands, NW and N Germany and extreme S Denmark mainly for extreme wind gusts, and to a lesser extent for tornadoes.

SYNOPSIS

Please refer to the original forecast.

DISCUSSION

A convective line with ample lightning activity has developed along a cold front across the North Sea.
This activity is collocated with the left exit of a particularly strong mid/upper-level jet streak.

Near the line, a very strong low-level wind field is in place with wind speeds around 40 m/s at 850 hPa. A combination of downward momentum transport and squall-line internal dynamics will likely be capable of producing gusts of around 35 - 40 m/s.

The line is expected to move quickly SEward reaching the Dutch, German and Danish coasts during the early afternoon. Upon interacting with boundary-layer induced friction over land, storm-relative helicity ahead of the system should increase strongly with NWP guidance yielding values in excess of 800 m2/s2 0-1 km SRH. At the same time, buoyancy should gradually diminish as the air ahead of the line gradually becomes drier. Nevertheless, some risk of tornadoes will exist, which, if they develop, may be strong.

During the 16 UTC - 18 UTC time frame the storms will likely start to reduce their intensity, but it is well possible that some linear convective activity will continue to progress well into parts of the Czech Republic and western Poland. Some convection may make it even further east across Slovakia, eastern Poland and the western Ukraine overnight.