Valid: Fri 12 Jul 2013 06:00 to Sat 13 Jul 2013 06:00 UTC
Issued: Thu 11 Jul 2013 22:08
A level 1 was issued for Northern Spain mainly for isolated large hail and severe downbursts.
A level 1 was issued for Northern Italy mainly for isolated large hail and heavy rain.
A level 1 was issued for Northern Romania, Northwest Moldova, West Ukraine and Southern Belarus mainly for large hail, severe wind gusts and heavy rain.
An upper level low is placed over Southeast Poland. This feature is forecast to move slowly to the East, affecting far west Urkaine during the overnight hours. Another upper level low over the extreme southwest Bay of Biscay moves slowly to the southeast. Weak height gradients prevail over the Mediterranean.
The only surface front runs from central Belarus, central Ukraine all the way into Romania.
... Northern Spain ...
An upper level low is placed over far Northwest Spain. Attendant forcing spreads East and advects an elevated mixed layer to the North/Northwest. Persistent onshore flow results in abundant low-level moisture along the coastal areas of Northern Spain. Overlap of that moisture with steep mid-level lapse rates results in MLCAPE up to 2000 J/kg. 10-15m/s deep layer shear support organized thunderstorm development on an isolated scale. Large hail and a few severe downbursts are expected.
Surface dewpoints in the mid to upper tens and cooling mid-level temperatures at 500 hPa result in widespread MLCAPE of up to 1000 J/kg. Deep layer shear remains weak, so expect multicell clusters with heavy rain and isolated large hail. Thunderstorms keep going all night long.
...Northern Romania, Northwest Moldova, West Ukraine and Southern Belarus...
An upper level low is placed over Eastern Poland. Attendant cold front moves east to the Central Ukraine and western Moldova. A 20 m/s speed maximum circles around the upper level low and crosses the cold front during the afternoon hours. This increases the deep layer shear up to 20m/s. Enhanced low level moisture along the cold front results in MLCAPE of 500-1000 J/kg. We expect scattered thunderstorm development along the cold front. This activity could produce a few large hail and isolated wind gust events. During the evening hours, thunderstorms over northwest Ukraine are forecast to grow upscale into numerous clusters. Those could produce heavy rain all the way into southern Belarus.