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Posted
  • Location: Western Isle of Wight
  • Weather Preferences: Snow, Storm, anything loud and dramatic.
  • Location: Western Isle of Wight
Monday 19th March 2007

Storm Forecast

Valid: Mon 19 Mar 2007 06:00 to Tue 20 Mar 2007 06:00 UTC

Issued: Sun 18 Mar 2007 17:22

Forecaster: TUSCHY

SYNOPSIS

Dramatic changes are underway / have already occured over Europe.

Southward expanding polar vortex will reach the extreme northern part of the forecast area during the end of the forecast period .

At lower levels, a combination of a stout 1040hPa anticyclone over the Azores and a slowly filling low pressure area over Norway and Sweden will support an outbreak of arctic air over parts of western, southern , northern and central Europe. A broad area will be affected by this type of airmass and will see an active convective day.

Strong WAA on the downstream side of the impressive upper-level trough will bring warm conditions well towards the north, affecting eastern / northeastern Europe.

A developing lee-cyclogenesis over N-Italy will be another area to watch out for enhanced thunderstorm activity.

DISCUSSION

...Scotland, Ireland, United Kingdom, France, Belgium, the Netherlands, Germany, Switzerland and parts of Spain...

Temperatures of -35 to -40°C at 500hPa, -15°C at 700hPa and -5°C at 850hPa will cover a huge area, supporting mid-level lapse rates of 8-9K / km !

This kind of atmospheric stratification will admit SBCAPE release in the order of 100-300 J/kg.

Such a postfrontal convective event makes it difficult to pinpoint areas of enhanced (severe) thunderstorm activity that far out... especially over such an huge area.

GFS indicates numerous lines with enhanced moisture advection, various upper-level impulses and small UVV maxima, which will cross the area from the north. Topography and fluctuating boundary layer moisture will play a role as well as possible small-scale polar low development, which are hard to forecast by global models.

Summarized we can say that a broad area will see isolated to scattered thunderstorm development during the next 24 hours.

LL shear of 10-15m/s was calculated for Ireland, Scotland, UK and northern / western France with decreasing values further towards the east / southeast.

Boundary layer moisture is forecast to be very shallow and constant mixing will bring the LCLs to values of 750-1500m, which will lower the tornado possibility.

Storm relative helicity values stay pretty low , besides UK, Scotland and Ireland.

Decided to issue a level-1 for regions, where 850hPa flow is at least somewhat enhanced ( e.g. Ireland, Scotland and UK with 25m/s ), which poses a threat for an isolated severe wind gust. Shear / instability combination also points out the possibility for an isolated tornado in those areas.

Exactly the same for SW / W / NW / N France, where LL shear and instability favor the evolution of an isolated tornado/ severe wind gust event.

During maximum heating, storms could produce mostly sub-severe hail, although an isolated large hail event can't be ruled out, given still 10-20m/s DLS.

...Central Mediterranean...

Constantly deepening lee-cyclogenesis over N-Italy will be the focus for another area of enhanced thunderstorm possibility.

During the latter part of my forecast period, the atmosphere will start a rapid cool-down over the Balearic Islands, Sardinia and Corsica and 400-600 J/kg SBCAPE can be expected.

Despite the favorable environment, thunderstorms will have problems to evolve just south of France / east of Spain, because of expected long fetch, before dry continental airmass will be mixed out.

Further torwards the south, scattered thunderstorms can be expected in an environment with up to 50m/s DLS.

Low / mid-level flow won't be that strong, but don't want to exclude an isolated severe wind gust risk with the stronger storms.

LL shear of 10m/s, low LCLs and fine instability will also support an local tornado threat along / over Sardinia and Corsica, which was the reason for issuing a level-1.... otherwise confidence is low that storms will be able to gain severe thunderstorm status.

The same for an area between Sicily and CNTRL Italy.

Further towards the east, over Italy and the Adriatic Sea, conditions for isolated to scattered TSTMs will become favorable, too, especially during the latter part of the forecast.

DLS of 30-40m/s and locally up to 17m/s LL shear favor an isolated tornado / severe wind gust risk. Expected pretty strong forcing will compensate the warm temperatures at low / mid-levels.

...Aegean Sea...

A weakening upper-level trough will cross the Aegean Sea from the SW during the late hours and a few thunderstorms will manage to develop. Strongest shear will just be out of my forecast area ( south of Turkey ) and therefore no organized thunderstorms can be expected .

That looks very interesting for today Blizzards, i look forward to some fun :)

Regards,

Russ

Edited by Rustynailer
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

yes today may turn out like yesterday. Hope so!

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Posted
  • Location: Western Isle of Wight
  • Weather Preferences: Snow, Storm, anything loud and dramatic.
  • Location: Western Isle of Wight
yes today may turn out like yesterday. Hope so!

i think better today, the northerly flow has got going properly.

R

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Monday 19th March 2007

Today has been a busy day for storms. Ther has been Strong gusts and Hail in France, Lightning in France, Spain, Italy, midlands, Southern England and East anglia and some other areas.

post-6797-1174330627_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

thanks for that!

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Tuesday 20th March 2007

Storm Forecast

Valid: Tue 20 Mar 2007 06:00 to Wed 21 Mar 2007 06:00 UTC

Issued: Tue 20 Mar 2007 02:53

Forecaster: VAN DER VELDE

SYNOPSIS

A large amplitude, long wave upper trough filled with very cold air has settled over Europe. Cold air with wintery thundershowers is advected south and eastward, as far as the African coast and the cold front over southern Italy into the Balkan.

Ahead of the cold front, GFS indicates possibilities for deep convection in the much warmer airmass streaming up into Albania and western Greece.

DISCUSSION

...extreme southeastern Italy, Albania, western Greece...

A tongue of higher theta-e and very strong low level convergence and MLCAPE >250 J/kg in GFS creates a setup favourable for widespread or violent severe weather events in this area. 00Z Brindisi (45 kts at 925 hPa) and Trapani seem to confirm instability and strongly veering winds with height in the warm sector. GFS calculates deep layer shear >25 m/s, low level shear of >10 m/s and 0-3 km SREH >250 m2/s2 overlaying the area with CAPE between 12Z-18Z.

Given strong forcing due to warm air advection, arrival of a mid level vorticity maximum, and frontal convergence, thinking is that one or several MCSes may form with a chance of severe convective gusts, but supercells with a chance of tornadoes and large hail appear quite possible. Local flash flooding may occur as well.

...northern Spain...

A continuation of the previous day with little change. Instability should slowly decrease, but expect a few hundred J/kg to remain possible. Deep layer shear and low-level shear (over land) are sufficient to sustain a small tornado chance with any storms that manage to develop a mesocyclone.

...northern Algeria and Tunesia...

With the jetstream overhead and a pool of unstable air advecting onshore, waterspouts and tornadoes are possible. GFS indicates only low storm tops and subsidence, but given solid 0-3 km CAPE, >10 m/s low level shear and very strong >40 m/s deep layer shear, a risk for isolated severe weather seems warranted.

...southwestern Turkey...

During the morning hours, instability is present in a zone of highly veering winds with height and moderate deep layer shear, and low level convergence. Storms may develop long-lived or rotating characteristics with a chance of large hail. Instability seems to become suppressed a bit and sliding eastward during the day.

post-6797-1174376176_thumb.png

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Posted
  • Location: Western Isle of Wight
  • Weather Preferences: Snow, Storm, anything loud and dramatic.
  • Location: Western Isle of Wight
post-4726-1174379754_thumb.pngThats definitely accurate, look at SE Italy :) Edited by Rustynailer
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Tuesday 20th March 2007

!Warning: Severe Weather in Southern Italy!

There has also been Severe gusts around Southern France and Lightning Scattered all over the Place.

post-6797-1174413073_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Wednesday 21st March 2007

Storm Forecast

Valid: Wed 21 Mar 2007 06:00 to Thu 22 Mar 2007 06:00 UTC

Issued: Tue 20 Mar 2007 21:52

Forecaster: TUSCHY

SYNOPSIS

A strong upper-level trough over south / central Europe will start a transformation towards a closed upper-level low.

Numerous small-scale impulses will rotate around this broad cyclonic vortex, resulting in unsettled weather conditions over a broad area.

Merging polar front / subtropical jet will produce an impressive at or above 160kt jet core over N-Africa, causing a slow shift of the main upper-level trough axis towards the east.

Exceptionally warm and stable conditions prevail for the northeastern parts of Europe.

DISCUSSION

...Extreme western Turkey / eastern Greece and southern Bulgaria...

Conditions become favorable for a small area to experience severe thunderstorms mainly between a 12Z-18Z time-frame !

At upper-levels, a rapidly northeastward racing vorticity maximum will cross the area of interest between aforementioned time-frame and accompanying UVV field looks pretty compact and intense.

Main support will be warranted by a coupled upper-level jet configuration with outstanding UL divergence spreading rapidly towards the north over Bulgaria and southern Romania.

At lower levels, the focus for evolving / ongoing thunderstorms will be a very slowly eastward shifting frontal boundary ( cold front ), becoming more and more diffuse during the later afternoon / evening hours.

So dynamics look favorable for intense thunderstorm development. The main uncertainty will be the degree of instability release.

Yesterday's 19Z synop datas showed dewpoints of 11-13°C over / along the Aegean Sea, which will be advected towards the north, given the strong southerly flow.

Expect nice conditions for surface based thunderstorms mainly in the level-2 area , given increasing influx of moisture and a cooling atmosphere at lower - / mid-levels.

LLS of 15-20m/s and DLS of about 35m/s will be present and although veering at lower levels is not that strong, tornadoes and severe wind gusts will be a distinct possibility...as well as an isolated large hail report.

Threat will decrease rapidly towards the north, but a risk for a few storms with mainly an marginal - isolated large hail risk will stretch up to southeastern Romania.

Only slowly eastward shifting north-south aligned frontal boundary, the intense LLJ pointing into the level areas and impressive upper-level dynamics favor the risk of possible training thunderstorm development with an attendant flash flood threat !

... Belgium, France and parts of Spain...

A borderline thunderstorm area was issued for those areas.

Yesterday's 12Z soundings already indicated that despite the steep lapse rates the boundary layer moisture was pretty shallow and rapid mixing was possible during the afternoon hours.

Same for this forecast period with a few modifications becoming necessary.

Models indicate a constant but faint warming of the mid-levels from the north with an attendant rapid decrease of the lapse rates' slope.

This would bring down TSTM chances significantly, but in contrast surface dewpoints will rise 2-3°C compared to yesterday over parts of central / northeastern France .

In addition, GFS indicates a weak wave, crossing Belgium and NE France during the peak heating from the north...UVV not that impressive, but still enough to issue a large TSTM line that far towards the north.

Further towards the south, conditions will be the same like yesterday and hence isolated thunderstorms can be expected.

In all areas, shear will be too weak for expecting any organized thunderstorm activity.

...Central Mediterranean...

Scattered to widespread thunderstorm development can be expected under the base of this huge upper-level cyclonic vortex. Shear won't support any storm organisation.

Weak shear and steep lapse rates in all levels favor an enhanced waterspout risk, stretching from the Balearic Islands to Italy to the Adriatic Sea.

post-6797-1174462693_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Thursday 22nd March 2007

Storm Forecast

Valid: Thu 22 Mar 2007 06:00 to Fri 23 Mar 2007 06:00 UTC

Issued: Thu 22 Mar 2007 02:27

Forecaster: VAN DER VELDE

SYNOPSIS

A large upper cut-off low pressure system remains stationary over Europe (S-Scandinavia to Algeria, Spain to W-Turkey). Two cores circle around inside this system: one moving over Poland into Germany, the other moving from Italy to the Aegean Sea. The cold airmass aloft guarantees widespread thundery convection (with probably a few waterspouts) over the relatively warm Mediterranean Sea. More isolated thunder is expected over the Balkan up to Poland.

...Aegean Sea...

During the second half of the period, a narrow plume of warm theta-e over the southern Mediterranean/Aegean Sea is re-intensified by strong advection of Saharan warm air, creating a small wave. Under the jetstream there is over 30 m/s deep layer shear, >15 m/s low level shear and strongly veering winds with height. If surface-based convection could develop, a strong potential exists for storm rotation and threats of large hail, a tornado, and severe gusts... but GFS-12Z and 18Z runs show hardly signs of deep instability and a band of rather weak 2-4 km lapse rates. Most-unstable parcel parameters come to higher cloud tops in the same area, indicating some chance of elevated convection which would be mostly harmless as it would not profit from most of the shear and helicity. However, the situation and any developing convection should be monitored closely.

post-6797-1174549360_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Thursday 22nd March 2007

Since todays forcast there has been lots more lightning in the forecasted area especailly around Italy.

post-6797-1174583066_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Friday 23rd March 2007

Storm Forecast

Valid: Fri 23 Mar 2007 06:00 to Sat 24 Mar 2007 06:00 UTC

Issued: Fri 23 Mar 2007 11:24

Forecaster: VAN DER VELDE

SYNOPSIS

Two low pressure centers circle around in a large, cold upper cut-off low, one from Germany to France, the more important other over the Balkan. A tongue of high theta-e air moves out of the area of Turkey and albeit associated with strong shear and helicity, has not proven to be active convectively due to lack of instability, apparent in 00Z profiles. Widespread convection is continuing over the Mediterranean Sea area, with more isolated thunder possible over the southern Balkan. A few isolated waterspouts are expected. The western Mediterranean stabilizes, with cloud top heights decreasing. A new impulse comes during the night when convergence near the Balearic Islands can trigger some convection with fairly good low-level instability (GFS and MM5 precip signals).

DISCUSSION

Over the eastern Aegean Sea, Crete and the S/W coast of Turkey a jetstream is present, creating strong deep layer shear over 35 m/s (0-6 km). Decent low level (0-1 km) shear >10 m/s is also progged to be present over Turkey due to friction over land. GFS keeps somewhat enhanced (up to 150 m2/s2) 0-3 km SREH over Turkey as well in the late afternoon and evening in co-existence with postfrontal instability of up to 300 J/kg MLCAPE. Additionally, potential instability is present (boundary layer WBPT of 8C and 700 hPa WBPT of 4 indicated in GFS) that could enhance CAPE by layer lifting.

This combination of parameters is thought to result in strong, long-lived storms, mostly along the Turkish southwest coast and further inland (low level convergence and near PV intrusion) , with a chance of rotating updrafts and hence a threat of large hail and perhaps a tornado.

post-6797-1174672940_thumb.png

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Sunday 25th March 2007

Storm Forecast

Valid: Sun 25 Mar 2007 06:00 to Mon 26 Mar 2007 06:00 UTC

Issued: Sat 24 Mar 2007 19:39

Forecaster: TUSCHY

SYNOPSIS

An high over low blocking pattern will persist for the next 24 hours over Europe with a strong high pressure area over Sweden and Finland and a channel of low geopotential heights over the Mediterranean.

Cold conditions will prevail for NE and E Europe .

Main convective acitivty can be expected around the Mediterranean.

DISCUSSION

....Mediterranean...

A few hundred J/kg SBCAPE will be available and a broad area will see thunderstorms.

The more difficult task will be to define the area with a more significant thunderstorm threat, which will be highlighted by the TSTM line.

A few more sentences for an area, stretching from Sicily towards the east / northeast.

Instability signals indicate the evolution of a more robust release of up to 500 J/kg SBCAPE.

During the evening hours, DLS will increase from the SW and will reach up to 20m/s.

Although the main storm activity can be found ahead of this enhanced DLS belt, a few storms can be expected to evolve in this environment.

Storms should not be able to organize and hence no severe weather threat can be expected.

South and east of S-Italy, strong instability signals, weak shear and steep lapse rates will pose a risk for a few waterspouts.

Although maximized in this area, the spout index and expected thermodynamic / kinematic environment indicate that an isolated waterspout report mainly in the highlighted area will be a possibility.

A few SFLOC reports will be possible outside of the highlighted areas, but should stay sporadic.

Monday 26th March 2007

Storm Forecast

Valid: Mon 26 Mar 2007 06:00 to Tue 27 Mar 2007 06:00 UTC

Issued: Sun 25 Mar 2007 19:49

Forecaster: GROENEMEIJER

SYNOPSIS and DISCUSSION

A large blocking-high is located over eastern Sweden. Weak mid-level cyclones are expected over the Bay of Biscay, southwest of Portugal and the northern Tyrrhenean Sea. they are characterized by relatively steep lower tropospheric lapse rates that induce a couple of storms in their vicinity. The amount of instability is expected to be low as well as the vertical wind shear, so that the threat of organized severe storms should be low.

Sundays Map-----------------------Mondays Map

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post-6797-1174854664_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Monday 26th March 2007

There has been scattered Lightning all aroung the Forecast Areas today.

post-6797-1174942788_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Tuesday 27th March 2007

Storm Forecast

Valid: Tue 27 Mar 2007 06:00 to Wed 28 Mar 2007 06:00 UTC

Issued: Tue 27 Mar 2007 02:26

Forecaster: VAN DER VELDE

SYNOPSIS

Blocking high pressure is situated over northeastern Europe while weak low surface pressure and mid level cold air cause a slightly unstable episode with isolated to scattered thunder. Within the weak flow, expectations for storms to yield severe weather are low, with cells being mostly short-lived.

Moderate deep layer shear is available around southern Italy and the Adriatic Sea (10-20 m/s 0-6 km), where storms can persist for most of the period over a stationary tongue of high theta-e and strong low level convergence. At most some low-end severe hail is forecast, or a waterspout, but the situation seems too marginal for a level 1 as the higher shear is not always co-located with instability according to GFS.

post-6797-1174977515_thumb.png

Edited by Blizzards
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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Tuesday 27th March 2007

Yesterday there was lightning around all the forecast areas Especially around Spain.

post-6797-1175063539_thumb.png

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Thursday 28th March 2007

Storm Forecast

Valid: Thu 29 Mar 2007 06:00 to Fri 30 Mar 2007 06:00 UTC

Issued: Thu 29 Mar 2007 09:04

Forecaster: VAN DER VELDE

SYNOPSIS

Shallow low pressure area is present from the North Sea over France/Germany into the western half of the Mediterranean Sea. Cold upper air in combination with sufficient low-level theta-e leads to convective temperatures in the 12-15 C range over land evidenced by 00Z soundings, while tops can reach -40 C. GFS has confidence LFC will be reached over a large area. Hence, widespread thunder from mostly single-cells (weak shear environment), like the previous day over northern France, is likely over much of the Benelux, France, Germany and Switzerland. An isolated landspout and small hail are possible. A zone of slightly enhanced theta-e in weak SW-ly flow and plenty of solar irradiance moves slowly eastward over France and Benelux, while a small but high vorticity upper low enters the western part of the thunder area, behind the theta-e tongue. This may trigger additional convection later into the period, possibly in the form of a comma cloud over western France.

Ahead of this feature the tight upper pressure gradient causes very good deep layer shear, but thinking is that air only unstable enough behind the shear zone and over sea, so a marginal level 1 is drawn only for a small coastal strip, with some chance of marginally large hail and a tornado.

Within the Mediterranean low pressure zone, several low level convergence features trigger convection, as well as a more dynamic trough coming out of Tunesia. Most absolute moisture is over the Italian waters, while an upper jet touches the unstable airmass over Malta, Sicily and southeastern Italy. With deep layer shear over 15 m/s, low level shear around 10 m/s and 0-3 km SREH up to 150 m2/s2, storms developing under the jet can develop rotation and cause large hail and tornadoes. However, instability is higher to the northwest and GFS is rather confident that convective precipitation is not going to occur within most of the level 1 region until the night, apparently due to capping, and only sparsely so.

Elsewhere in the Mediterranean, an isolated waterspout is not ruled out.

post-6797-1175182130_thumb.png

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Friday 30th March 2007

Storm Forecast

Valid: Fri 30 Mar 2007 06:00 to Sat 31 Mar 2007 06:00 UTC

Issued: Thu 29 Mar 2007 18:10

Forecaster: TUSCHY

SYNOPSIS

A pool of lower geopotential heights can be found over western / central Europe, surrounded by high pressure areas.

A well established cold front will affect parts of Norway and Sweden with adjacent intense CAA during the daytime hours. An isolated SFLOC report can't be excluded, but coverage will be too low for warranting a TSTM line.

DISCUSSION

....Central and eastern Mediterranean....

A pretty strong at or above 160kt jet over N-Egypt will help to push a negatively inclined upper-level trough over southern Italy towards the NE.

This kind of constellation will support capped conditions under and on the anticyclone side of the jet and this is also captured by yesterday's 12Z sounding report of Heraklion, indicating a nice EML layer with pretty steep lapse rates between 900-600hPa ( also observably in model outputs).

Hence the main focus for storm activation will be under the base of the NE-ward shifting trough, characterized by slowly warming mid-levels and a surge of a pretty moist BL airmass on its upstream side towards the north.

Keeping in mind that SSTs will be around 15-16°C, lapse rates at the mid-levels stay pretty steep and dewpoints will be about at or above 10°C, an area of 200-400 J/kg SBCAPE looks reasonable.

The suggestion of GFS with up to 800 J/kg looks somewhat overdone, comparing the atmospheric stratification of yesterday and today.

DLS of 10-20m/s ( increasing southwards ) will be enough for an isolated large hail risk.

Further towards the north, background shear will be weaker and this would enhance an isolated waterspout threat.

The final reason for a level-1 area was the fact that both, thermodynamic and kinematic parameters look fine for a low-end severe TSTM threat over Sicily and S-Italy.

The same for the coastal areas of western Greece and the Aegean Sea, where enhanced DLS would pose a risk for a few severe wind gusts and an isolated large hail report.

...France,S-UK, Germany , the Netherlands and Belgium....

Upper-level low pressure area will continue to spin around over France although a final SW-ward movement will arise during the latter part of my forecast period.

Diffuse upper-level forcing and no real "frontal" boundary signal at lower-levels makes it difficult to define locations of enhanced thunderstorm development that far out.

Re-circulated tongue of higher PBL moisture - stretching from SE / E France NW-wards - attained the main advertence for storm initiation during a 12Z-20Z time frame.

Mixing ration values of 6g/kg, enhanced convergent flow along this Theta-E tongue and steep lapse rates at mid-levels will support 100-200 J/kg SBCAPE mainly over Belgium and the Netherlands, where diabatic heating and moisture advection will be maximized. Again, GFS looks like to be somehwat too aggressive regarding the expected instability values ( although dewpoints were acquired pretty well ). No significant thermodynamic change at 800-700 hPa will occur, which should keep instability values pretty slim.

Expected minimal instability values and weak shear will support weak pulse storms, which should not produce gusts/hail, reaching the severe weather criteria.

post-6797-1175236679_thumb.png

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Monday 2nd April 2007

Storm Forecast

Valid: Mon 02 Apr 2007 06:00 to Tue 03 Apr 2007 06:00 UTC

Issued: Sun 01 Apr 2007 19:45

Forecaster: GROENEMEIJER

SYNOPSIS

In the mid-troposphere, a large blocking dipole pressure structure persists over the eastern North Atlantic with a low west of northern Portugal and a high south of Iceland. Flow is weak over much of central and southern Europe. Another low pressure system is present over northern Turkey. A trough over the Barents Sea embedded in a strong westerly flow should sharpen implying a strong northerly jet will develop over the Norwegian Sea and Norway southward.

DISCUSSION

Iberia...

In the range of the low near Portugal, a zone of stratiform precipitation over the NWrn third of the peninsula will be followed by convective showers, many of them thundery. Low instability and weak to moderate wind shear strongly limits the potential for severe convection.

post-6797-1175549134_thumb.png

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Tuesday 3rd April 2007

Storm Forecast

Valid: Tue 03 Apr 2007 06:00 to Wed 04 Apr 2007 06:00 UTC

Issued: Tue 03 Apr 2007 01:27

Forecaster: VAN DER VELDE

SYNOPSIS

Northwestern Europe is dominated by a large high pressure area with its center northwest of Scotland. At its eastern flank, colder air is transported southward and forms a cold front reaching from Bretagne to southern Poland. The stagnant warmer, slightly unstable airmass is expected to yield isolated to scattered thunderstorms over France and southern Germany, probably somewhat more than yesterday as the cold front may provide a more organised source of lift. Insolation should not be a problem. Isolated to scattered thunderstorms are likely to occur over the Iberian Peninsula, parts of the Mediterranean Sea, as well as Italy and the western Balkan, where sea breeze circulations may trigger isolated convection. Vertical shear is mostly weak to moderate, leading to single cells and some clustering storms with negligible severe weather threat.

DISCUSSION

The strong upper jet over southern Iberia and the Tunesia-Srn Italy area increases chances that convection may produce a few severe weather events:

southern Portugal and southwestern Spain:

The secundary core of the upper low near Portugal should trigger convection also over land during daytime, with 0-6 km bulk shear values of 20-30 m/s. Although there is not much veering with height or increased low-level shear and only a few hundred J/kg CAPE, the area could yield more organised and/or more sustained convection with better chances of marginally large hail.

Tunesia, Malta:

Up to 25 m/s 0-6 km shear is forecast to be present, but here low-level winds should be veering with height so that 0-3 km storm-relative helicity of more than 250 m2/s2 could be present in areas with CAPE of a few hundred J/kg and steep mid level lapse rates. This area lies at the left exit of the jet and strong low-level convergence is forecast within the 9-10 g/kg moisture pool. Supercells may develop (Tunesia after 12Z) with a chance of large hail, though the strong linear forcing may favour more of a squall line later in the period with perhaps a few severe gusts. The southern parts possibly remain capped by heat advecting off the Sahara.

north of Sicily:

Stronger instability and convergence near a low pressure core likely will cause some thunderstorms, while enhanced storm-relative inflow under moderate shear conditions is expected to result in long-lived storms, capable of a few large hail events.

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Wednesday 4th April 2007

Storm Forecast

Valid: Wed 04 Apr 2007 06:00 to Thu 05 Apr 2007 06:00 UTC

Issued: Tue 03 Apr 2007 21:02

Forecaster: GATZEN

SYNOPSIS

South-east of amplified high pressure over north-eastern Atlantic, a broad upper-level trough is located over most of Europe, with an axis from Baltic States to northern Balkans, central Mediterranean and Iberian Peninsula. While cold and stable air mass spreads southeastward at the eastern flank of the high, Mediterranean regions are dominated by warmer air mass that is characterized by relatively steep lapse rates and some boundary layer moisture. This region will be the focus of expected convective development. Given weak vertical wind shear and forcing, most thunderstorms will be not organized. Two short-wave troughs embedded in the westerly flow at the southern edge of this trough are expected to lead to slightly better thermodynamic profiles, where chance for organize convection is enhanced compared to surrounding areas. Another region of interest is south-eastern Europe, where steep mid-level lapse rates have formed. Although boundary-layer moisture is weak, instability will likely develop during the period, as upper trough axis moves eastward and will likely produce some lift, and chance for showers and thunderstorms is expected to increase gradually.

DISCUSSION

South-western Mediterranean as well as southern Adriatic

Both regions will be affected by weak short-wave troughs embedded in the westerly flow. Weak to moderately strong jet streaks/vort-maxima travel eastward at the eastern flank of both short-wave troughs, providing some QG forcing. Affected air mass will likely destabilize due to some boundary-layer moisture indicated by latest ascends as well as relatively steep lapse rates, that may improve due to mid-level height falls. Showers and thunderstorms that are expected over a rather widespread region will likely concentrate in this regions. Given some vertical wind shear reaching 20 m/s 0-6 km shear, some thunderstorms may organize into multicells. There is also a potential for supercells as low-level winds shift to the south due to deepening surface pressure underneath the trough axis. Most significant severe thread is expected to be some large hail, while strong wind gusts and an isolated tornado is not ruled out. Thunderstorms will likely merge into clusters during the period and may go on through the night hours, while severe potential is forecast to weaken.

South-eastern Europe

Although low-level moisture is weak, a few showers and thunderstorms are not ruled out as upper level trough migrates eastward providing some forcing. Steep mid-level lapse rates and expected high cloud-base as well as locally inverted-V profiles (dependent on diurnal heating) may increase the potential of strong wind gusts. By now, we do not expect severe wind gusts given weak winds as well as weak forcing.

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Posted
  • Location: Truro, Cornwall
  • Weather Preferences: Winter - Heavy Snow Summer - Hot with Night time Thunderstorms
  • Location: Truro, Cornwall

Thursday 5th April 2007

Storm Forecast

Valid: Thu 05 Apr 2007 07:00 to Fri 06 Apr 2007 06:00 UTC

Issued: Thu 05 Apr 2007 07:25

Forecaster: GATZEN

SYNOPSIS

Strong arctic trough over Scandinavia supports cold air advection into north-eastern Europe. To the south, a rather strong frontal boundary is present from the North Sea to southern Scandinavia and further to western Russia. Rather warm air mass remains in the range of a weak ridge that stretches from a high over British Isles to northern Balkans. South of the ridge, low geopotential present over Mediterranean weakens during the period. A cut-off is forecast to remain over southern Iberian, while a short-wave trough over eastern Mediterranean moves into Black Sea region. At lower levels, only weak instability is present over most of Mediterranean, where low clouds may also inhibit insolation over most places. Weak forcing and vertical wind shear are also expected and chance for severe thunderstorms is forecast to be low. Vertical profiles seem to be more interesting over the southern regions of the Mediterranean.

DISCUSSION

Southern Mediterranean

A tongue of low-level instability has developed over southern Mediterranean as indicated by a few soundings. Steep low-level lapse rates as well as rich boundary-layer moisture are present especially near southern Iberian Peninsula and southern Italy. Today, some vort-maxima/jet streaks are forecast to move eastward, affecting southern Iberian Peninsula as well as Sicily. While regions with moderate deep layer wind shear and deep instability are not expected to overlap, some QG forcing will likely affect those regions. Showers and thunderstorms are forecast to develop. Given rather strong low-level buoyancy and almost no CIN, a few waterspouts are forecast to develop. Increasing DLS over southern Iberian Peninsula in the range of propagating short-wave trough/jet streak may increase the chance for a few organized storms, capable of producing locally hail and strong wind gusts. As vertical veering is not expected to be favorable for mesocyclones, tornadoes or large hail seem to be unlikely.

Turkey

In the range of strong south-westerly jet, strong to very strong vertical wind shear will affect most of Turkey during the period. Approaching vort-max over Aegean/Black Sea will likely provide DCVA, and QG forcing is forecast to go on. Although weak instability is forecast by latest models and sounding over Istanbul indicates an EML above the dry boundary layer, chance for thunderstorms is weak over most places given lack of diurnal heating due to low clouds. Current thinking is, that a few mostly embedded thunderstorms will form during the day. Best potential seems to exist over the central regions where QG forcing will be strongest as well as over the southern mountains, where upslope flow is expected. Chance for a few supercells is not too high, but will not exclude some reports of large hail, severe wind gusts and also isolated tornadoes. Due to many limiting factors (stratiform clouds, weak forcing), we do not issue a level 1 ATTM. However, the situation has to be monitored closely.

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