Rischio moderato per alcuni paesi d'Europa !

**Ben** · 01/03/2008, 00:27

Storm Forecast
Valid: Fri 29 Feb 2008 06:00 to Sat 01 Mar 2008 06:00 UTC
Issued: Thu 28 Feb 2008 19:29
Forecaster: TUSCHY
SYNOPSIS

Nordhemispheric upper-level streamline pattern during the past 48h was conducive for the advection of a true tropical airmass towards the NE just east of North America. Despite modification, this column of very warm air has gained latitude refering to the latest MIMC-TPW loop and now underlays a developing high pressure area west / northwest of Portugal. This strengthening cell shifts eastwards with constantly rising geopotential heights. At the same time a broad cyclonic vortex continues to strengthen south of Iceland while racing eastwards. As a result of this strengthening baroclinic zone, an intense jet sets up over the northern Atlantic with up to 100m/s at 300hPa, pointing to NW Europe while assisting the cyclonic vortex by beneficial upper-level divergence in its exit region.
All those features result in a developing, intense wind field over NW and parts of central Europe during the next 24 hours.
Stable and cold conditions prevail over eastern Europe while dry and warm conditions continue over the Mediterranean.

DISCUSSION

.... Ireland and United Kingdom....

A concentrated swath of enhanced and possibly organized convective activity expected running from N-Ireland to central and SE United Kingdom.

An impressive temperature gradient at mid-levels sets up with 700hPa temperatures at or above 0°C on the warm side and -10°C just to its north. Cross sections also hint on a strong incline of this NW-SE orientated baroclininc zone, which only complicates the forecast more. Right now, the highlighted area will see very weak lapse rates between 2km and 4km approaching zero during the evening hours and resulting in a stout cap over the whole area. At the same time, active cold front creeps in this area from the NW, resulting in a rapid cool down below approximately 2.5 to 3 km. This cold front will have the best chance for a strongly forced line of low-topped convection. Outstanding 45m/s streak at 700hPa places the sub-3km column under the favorable left exit region. Both, dynamics and the front itself should assure adequate forcing for a strongly forced line of storms.
100-200J/kg SBCAPE at lowest 3km were persistently shown in the past few GFS runs which is enough for convection. Shear is impressive with 0-1km helicity values above 200 J/kg, winds at 850hPa at 35m/s increasing to 45m/s at 700hPa and low LCLs. Current thinking is that tail end storms or more discrete storms will pose a distinct tornado threat. Dependant on how robust convective activity will be along the cold front, widespread severe to damaging wind gusts look likely with a progessive squalline event. However we decided not to issue a level-2 as degree of instability is still uncertain, especially well inland over central UK.
Activity will rapidly shift towards the SE during the night hours.
No thunderstorm area was issued as degree of electrified storms is quite uncertain.

We went with a small general thunderstorm area over Scotland, but coverage should be more isolated.

... Belgium, the Netherlands and west-central Germany....

Overall we still deal with the baroclinic zone, which moved southeastwards, reaching Belgium and the Netherlands after 00Z. 700hPa temperatures will cool down a little bit between 00Z and 06Z which helps to weaken / lift mid-level cap somewhat. Nevertheless, capping will be too strong for deep convection and again low-topped convection along the SE-ward racing cold front will be the primary convective modus. 200-300 J/kg SBCAPE at lowest 3km are forecast and was shown persistently during the past few model runs. Speed max at 700hPa gets even stronger compared to the UK and reaches 50m/s after 00Z while attendant exit region overspreads the area of interest.
Forecast soundings show a favorable environment for tornadic thunderstorms as veering is strong, T-Td spread is small and convection should be surface based. 0-1km helicity above 150J/kg, 0-3km shear of 20-35m/s and winds at 850hPa above 30m/s point to a enhanced tornado and severe-damaging wind gust threat.
Again, dependant on the degree of convective activity along the cold front, a progressive-type LEWP squalline could evolve out of this environment with a tornado and severe wind gust risk, while racing southeastwards, reaching west-central Germany during the end of the forecast period.
Because of the persistent signals of nice shear / instability over this area a level-2 was issued.

... N-Germany...

More uncertainties exist over N-Germany as instability will be very limited and GFS only has traces along the eastward racing cold front. In contrast to the aforementioned areas we now expect deep convection as mid-level lapse rates steepen to at or above 6K/km. Potent mid- / upper-level jet is placed to the south and hence strong upper-level divergence values will be present over N-Germany. Again, the cold front, reaching NW Germany at about 00Z and eastern Germany only 6h later will be the main focus for convective activity. Despite impressive forcing, shear at all levels will be somewhat weaker than further towards the south and BL moisture somewhat worse. Current thinking is that also this part of the cold front gets convectively activated with an attendant severe-damaging wind gust / tornado risk.

Severe weather threat should continue in the postfrontal airmass especially if indeed such a well defined convergence zone can evolve like GFS wants to.
We issued a thunderstorm area as deep convection will be possible.

# # #

Storm Forecast
Valid: Sat 01 Mar 2008 06:00 to Sun 02 Mar 2008 06:00 UTC
Issued: Fri 29 Feb 2008 18:58
Forecaster: DAHL
SYNOPSIS

Vigorous upper westerly flow has established over the Atlantic and Europe ... with an imbedded wave rapidly digging from central Germany towards Turkey/the Black Sea region by Sunday 06Z. Extensive and quite intense SFC cyclone centered over SW Norway is simulated to develop a new centroid over the Baltic Sea region during the day. Associetd cold front, which will be attached to the digging upper trough will quickly surge from central Germany across the Balkans into the central Black Sea.

DISCUSSION

... S Germany ... Austria ... Balkan States ...

Convective scenario remains somewhat challenging ... with the potential severe wind/tornado threat depending on whether or not convection develops along the cold front. As global model, GFS naturally has difficulties in capturing the detailed structure of the cold front and the evolution of instability/convection along it. Based on the magnitude of upward forcing and the strong front-normal flow component, development of a split-frontal structure exists, and the development of a strongly forced slab-type convective line, several lines, or line segments, is anticipated. The main threat associated with these lines will be severe straight-line wind gusts, though large low-level hodographs suggest that any isolated updraft may attain appreciable rotation with an attendant tornado threat. Threat for convection appears to persist through the day as the cold front surges southeastwards, though wind fields seem to weaken over the Balkans and vigor of upward forcing and convection may thus also undergo some weakening.

... N Germany ... W Poland ...

Comparatively shallow moist convection, possibly organizing into small line segments, is anticipated in the wake of the cold front. This convection will develop amidst the strongest wind field this ETC has to offer, and thus augment the severe gradient background flow, and may in addition produce a short-lived tornado or two.

# # #

UPDATE

Forecast Update
Valid: Fri 29 Feb 2008 06:00 to Sat 01 Mar 2008 06:00 UTC
Issued: Fri 29 Feb 2008 13:38
Forecaster: GROENEMEIJER/TUSCHY/DAHL
SYNOPSIS

Refer to the convective forecast.

DISCUSSION

British Isles, Benelux countries, Northern and centra Germany...

As mentioned in the original forecast, strong forcing for upward vertical motion is expected within the left exit region of an intense jet streak. The cold frontal zone of an intense surface low moving eastward over Scotland is the main feature of interest. It will likely develop a split-front structure as dry air overspreads the surface front. The surface front is expected along a line Edinburgh-Shannon at 18:00 UTC, Groningen-Southampton at 00:00 UTC, Szezczin - Frankfurt- Luxembourg at 06:00 UTC. It appears likely that the juxtaposition of moist low-level air, with dew points in the 8-10 C range, and strong forcing, will suffice for the development of a convective line. The structure of such a line will likely develop better as it moves southeastward across the British Isles, the North Sea and into the continent. Hence the risk of convective severe weather will probably increase as the frontal system translates southeastward.

Current thinking is that gusts exceeding the severe limit of 25 m/s will be relatively widespread, given that 850 hPa winds of 35 m/s are forecast near the line. Locally they may even exceed 32 m/s. The forecast storm-relative helicity of 300-400 m2/s2 ahead of the line suggests that some risk of rotating updrafts will exist near irregularities in the line, or with isolated convective cells ahead of the line. These will have an attendant threat of tornadoes likely of F1 or F2 intensity.

Aforementioned threats, of which the straight-line wind is the greatest, have prompted the issuance of a level 2. In contrast to original positive forecast it is more focused now on the area that will experience the strongest forcing.

# # #

Getto quasi a fondoscala..

gabriele*80* · 01/03/2008, 00:34

Di temporali violenti a marzo.

**Ben** · 01/03/2008, 14:39

che passata!

red: tornado, yellow: severe wind gusts, green: large hail, blue: heavy rain, white: funnel cloud, pink: gustnado, orange: dust devil

al momento non è stato segnato, comunque, alcun vortice. Vediamo nelle prossime ore.

UPDATE

Forecast Update
Valid: Sat 01 Mar 2008 11:00 to Sun 02 Mar 2008 06:00 UTC
Issued: Sat 01 Mar 2008 11:28
Forecaster: GROENEMEIJER
SYNOPSIS

Refer to convective forecast...

DISCUSSION

S and E Austria, the Czech and Slovak Republics, Hungary, Western and central Balkans...

A strong convective line associated with a surface cold front is working its way SEward across Austria, the Czech Repubilc. With this strongly-forced convective event widespread severe wind gusts are being reported. The thermodynamic environment appears ahead of the line does not deteriorate in the coming hours, as dew points of 7-9 degrees have advected into Hungary, Slovenia and even SE Poland.
Across Hungary and the NW Balkans models also continue to advertise that 200-400 J/kg of CAPE will be available ahead of the line. However, the low-level wind field should weaken somewhat, so that a gradual reduction of the severe wind gust threat is expected in the late afternoon. The low level wind field should initially be strong enough to support the occurrence of a few tornadoes.

# # #

**Ben** · 01/03/2008, 14:43

questo il passaggio del fronte (radar composti germania).

ps: adsl

http://www.wzforum.de/forum2/read.php?2,1303609

**Ben** · 01/03/2008, 15:04

radar bello acceso in Slovenia

**griffa-petrucci** · 01/03/2008, 15:05

Originariamente Scritto da Ben

questo il passaggio del fronte (radar composti germania).

ps: adsl

http://www.wzforum.de/forum2/read.php?2,1303609

Si è trattato di una squall line piuttosto lunga e insolita per il periodo, ma a giudicare dal radar non c'è niente di isolato o comunque in grado di dare segnali di roazione. C'è da dire che è una rdadr piuttosto poco definito quindi non si possono dare giudizi molto precisi.

**Ben** · 01/03/2008, 15:08

Originariamente Scritto da griffa-petrucci

Si è trattato di una squall line piuttosto lunga e insolita per il periodo, ma a giudicare dal radar non c'è niente di isolato o comunque in grado di dare segnali di roazione. C'è da dire che è una rdadr piuttosto poco definito quindi non si possono dare giudizi molto precisi.

sicuramente