Storm Forecast
Valid: Sat 27 Jan 2007 06:00 to Sun 28 Jan 2007 06:00 UTC
Issued: Fri 26 Jan 2007 20:40
Forecaster: TUSCHY
SYNOPSIS
A baroclinically unstable flow is present over the northern Atlantic and Europe with an intense high pressure area just west of France and United Kingdom. Very cold air spreads southward downstream of this high pressure area, covering most parts of eastern Europe.
Compared to the past few days, conditions for thunderstorm development over the Mediterranean will become somewhat worse, but still a few convective events can be expected.
DISCUSSION
...Coastal areas of Norway...
19Z IR images show a wide field of cumuli-streets north of Norway moving towards the south. Cloud top temperatures are pretty warm and there are no indications of any electrified storm development.
A strengthening baroclinic zone around Svalbard will support an intensifying low pressure area north of Norway. As a result, background wind-field will start a veering trend and a warmer airmass will begin to affect the coastal areas of Norway. An isolated topographically enhanced storm could still develop during the early part of the forecast period, but expected coverage is too low for highlighting any specific areas.
...Parts of the Baltic Sea and Poland...
Very cold thermodynamic environment will support steep mid-/low level lapse rates over a broad area. Main difficulty right now is to determine the length of the fetch until PBL moistens enough for deeper convective evolution.
The background-flow will be from the NNW during the daytime hours becoming more NW-erly during the evening hours as a consequence of weak ridging over S-Sweden and Norway.
This constellation would favor the highlighted area, where a few thunderstorms can be expected mostly on the cyclonic side of a 150kt UL jet.
A few waterspouts can be expected due to maximized instability release at lowest levels.
Environment for storm development over Poland should be enhanced due to a fine jet position and very steep lapse rates. No clear forcing signals present, but a few storms should be able to form. Low LCLs and somewhat augmented LL shear would pose a threat of an isolated tornado report.
...Strait of Gibraltar and parts of extreme SW-Mediterranean...
A nearly stationary and slowly weakening UL low over the Strait of Gibraltar will support an environment for scattered thunderstorm development. The threat will start to decrease during the late evening hours ( 18Z onwards ) due to warming at mid-levels from the south.
Any developing thunderstorm would pose a risk for severe to damaging wind gusts, given DLS of about 40m/s.
Don't want to exclude an isolated tornado report over extreme S-Spain, where strengthening onshore flow will support an overlapping area of low-end instability and significantly enhanced LL shear. Therefore, extreme S- Spain was also included into the level-1 area.
...Aegean Sea and W-Turkey...
A channel of low pressure develops over the area of interest and scattered thunderstorms will evolve over the area of interest. Right now, there are no indications of a closed LL depression to form over the Aegean an UL support is not that impressive to assist a rapidly developing depression.
Anyhow, strengthening onshore flow and arriving cold front ( at about 00Z ) will provide a favorable environment for isolated - scattered storms to form.
Enhanced LL shear and marginal instability values over extreme NW Turkey and along the coastal areas of W Turkey favor an enhanced tornado and severe wind gust threat.
Confidence in more robust thunderstorm development is pretty low and hence will stick with a 1.
The threat for storms will shift southwards during the latter part of the forecast period.
...Adriatic Sea...
A few storms will form during a 06Z and 18Z time - frame, while activity will rapidly shift towards the south, also showing a weakening trend. Storm coverage will be low but very steep LL lapse rates and very weak background flow will support a risk of a few waterspouts mainly along the coastal areas.
