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Costa Del Fal

European Storm Forecasts

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Friday 6th April 2007

Storm Forecast

Valid: Fri 06 Apr 2007 06:00 to Sat 07 Apr 2007 06:00 UTC

Issued: Thu 05 Apr 2007 19:36

Forecaster: TUSCHY

SYNOPSIS

A late winter-time - like storm system will affect N-Norway and Sweden at least for the next 24 hours.This vortex will bring cold and unsettled weather conditions for most parts of N-Europe.

A constantly eastward building high pressure area over W-CNTRL Europe will bring stable and dry conditions tho those regions, while a weakening upper-level disturbance over SW Europe is the focus for some convective activity during the forecast period.

DISCUSSION

...N-Norway / Sweden...

A trough axis will reach the coastal regions of NW Norway during the later afternoon/ early evening hours from the NW.

Attendant PVA field is forecast to cross the area and this will occur during a time, where some support of upper-levels ( left exit region of strong 300hPa jet streak ) will be present.

Temperatures continue a rapid cool down at all levels with GFS indicating a wide area of negative temperature advection mainly during the morning / early afternoon hours.

The main focus for an isolated thunderstorm will arise around 18Z mainly in the highlighted area.

Wrap - around moisture of the main vortex will be involved in the eastward shifting trough axis. Hence, models indicate somewhat higher Theta-E values, surging southward along the coast of NW Norway.

Lapse rates stay steep at mid-levels and some low-end instability release looks reasonable at this time.

Primary threat will be mostly sub-severe hail due to a combination of 15-20m/s DLS, rising EL temperatures and steep lapse rates.

An isolated SFLOC report SE of the highlighted area can't be excluded ( mainly over the NW part of the Gulf of Bothnia), but expected coverage will be too marginal for issuing any higher probabilities.

...SE Spain...

A weakening upper-level system over Spain will stay nearly stationary during the forecast period with strong jet systems on its base. Those streaks, although weakening, will stay east of the Strait of Gibraltar... and so do the left exit regions.

An eastward shifting vort max and a prolonged period of upper-level divergence will support scattered thunderstorm development over SE Spain .

The main focus for storm evolution will be an east / northeastward shifting moisture boundary, which will cross most parts of S/SE Spain from the west during the daytime hours.

An area of repeating thunderstorm development / A cluster of storms can be expected to evolve east of the Strait of Gibraltar, moving towards the east / northeast.

DLS of 15-20m/s will support multicells with marginal hail and an isolated severe wind gust being the main threat.

Forecast soundings of this area indicate a well saturated atmosphere and expected type of thunderstorm evolution and strong lift will also pose an excessive rainfall and hence a flash flood threat mainly between Almeria and Valencia.

Saturday 7th March 2007

Storm Forecast

Valid: Sat 07 Apr 2007 06:00 to Sun 08 Apr 2007 06:00 UTC

Issued: Fri 06 Apr 2007 14:06

Forecaster: DAHL

... SYNOPSIS ...

Upper blocking pattern persists across Europe, with a large and intense upper low covering NE Europe, Scandinavia, and NW Russia; another, albeit smaller, upper low is present over the Iberian Peninsula. Between these two features, an upper high is located over the E Atlantic and the British Isles. SFC charts feature a strengthening high pressure area over the western portions of Europe and a large low-pressure system over NE Europe/NW Russia. This system is promoting a strong cold surge into eastern portions of Europe. Quiescent conditions prevail over the Mediterranean regions.

... DISCUSSION ...

... SW Mediterranean ... Tyrrhenian Sea ...

It seems that convective activity will be limited to the Iberian Peninsula and the Mediterranean regions in association with the Iberian upper low and a small vort max at its periphery, which will linger over the Tyrrhenian Sea. Thermodynamic profiles are essentially neutral, but models suggest presence of up to 20 m/s mesoscale mid-level wind bands at the periphery of the vort maxima, which should support at least briefly/weakly organized storms. It seems that allover severe threat will be rather limited, however, due mainly to a lack of focused synoptic- and mesoscale ascent. Further limiting factor is weak/non-existent shear in the inflow region of the TSTMS. However, minimal CIN and steep LL lapse rates may be indicative of a slightly enhanced waterspout threat. Also, those storms that do organize, will pose some marginally severe wind and hail threat, but a categorical risk does not seem to be warranted at this time.

Fridays Map---------------------Saturdays Map

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Wednesday 11th April 2007

Storm Forecast

Valid: Wed 11 Apr 2007 06:00 to Thu 12 Apr 2007 06:00 UTC

Issued: Wed 11 Apr 2007 06:56

Forecaster: GATZEN

SYNOPSIS

Omega flow is present over Europe, with a high stretching from central Mediterranean to Alpine region and further to British Isles. Two lows are located W of Iberian Peninsula and Black Sea region/eastern Mediterranean. At lower levels, relatively warm air mass is present over most of western Europe. This air mass is slightly unstable underneath the trough axis from south-western France to Iberian Peninsula. Given weak vertical wind shear, organized severe thunderstorms are not expected.

DISCUSSION

Western Mediterranean

Latest ascends show relatively steep lapse rates originating from the Atlas mountains present over northern Africa. Given relatively moist boundary layer over the Mediterranean Sea, weak instability shown by latest GFS is reasonable, although the boundary-layer remains quite cool. During the period, approaching SW-erly jet will lead to some QG forcing. However, cool boundary-layer will likely limit convective development. If thunderstorms will form, some organized convective cells are not ruled out given strong veering profiles, but current thinking is that surface-based convection will not develop.

Southern Turkey

Upper cut-off will reach the region late in the period. Given warm water surface, low-level air mass is expected to become quite unstable in the evening hours. Later, instability will likely become rather deep in the range of the upper trough. Given weak vertical wind shear and strong low-level buoyancy, expect that conditions for a few waterspouts are favorable, and a couple of events may occur along the southern coasts of Turkey during the evening/night hours.

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Friday 13th April 2007

Storm Forecast

Valid: Fri 13 Apr 2007 06:00 to Sat 14 Apr 2007 06:00 UTC

Issued: Thu 12 Apr 2007 19:57

Forecaster: TUSCHY

SYNOPSIS

A well established split flow regime will persist over the western / central half of Europe with one branch affecting Iceland and Norway and the other one N-Africa.

Strong ridging over central Europe provides a continuance of the unseasonable warm conditions, while an upper-level disturbance over Spain will bring unsettled conditions for most parts of SW Europe.

A broad cyclonic vortex over western Russia continues to steer cold air far towards the south/southeast.

DISCUSSION

...NE Algeria and N-Tunisia...06-15Z...

An intense baroclininc zone has already set up over central Algeria during the past 24 hours and this will assist a strong jet on the base of the upper-level trough. This jet will race eastward and will foster a negatively tilted trough axis to shift towards the E.

At lower levels, global models indicate what could be a closed LL circulation, which will cross N-CNTRL Tunisia from the WSW between 9 and 15Z.

Keeping in mind that data input of this region is pretty sparse, models could have problems with exact strength / track of the depression and latest synop data indicate numerous possible smaller low centers over central Algeria.

Extremely dry air towards the south and strong WAA downstream of the depression will confine the area of the most robust TSTM threat under the base of the trough and along the eastward sliding frontal boundary over NE Algeria and N-Tunisia.

Intense vor max, coming out of the base of accompanying trough will cross the area from the SW and compact UVV field and just slowly weakening upper-level divergence will favor scattered thunderstorm development.

Capped areas downstream of the depression will see best LL shear / backing but favorable shear could stay enhanced along the eastward moving frontal boundary.

DLS of 20-25m/s and good lapse rates will favor mainly a large hail / severe wind gust risk although an isolated tornado can't be ruled out.

During the latter part of the forecast period, the main thunderstorm activity will shift / evolve further towards the north under the base of the NW-SE-erly elongated upper-level trough. Diminishing shear and weak lapse rates will preclude any storm organisation.

...SW / W France and SW-UK ...

After a few days of continual subsidence and strong diabatic warming at lower levels, atmospheric stratification over France was characterized by pretty steep lapse rates at lower and mid-levels and hence up to 300J/kg SBCAPE release was detected.

This fine stratification will get modified from the south by the influx of a warmer and humid airmass ( thick Ci-shield already present over most parts of France at 12th April 18Z ).

This will help to weaken lapse rates significantly.

In addition, GFS indicates rising geopotential heights over W / NW-France, which should also suppress any significant storm acitivty mainly during the evening hours and onwards.

Numerous vort maxima will cross the areas from the SE, weakening gradually.

A few storms can be expected to evolve mainly in the highlighted areas but shear will stay too weak for any storm organisation.

An exception will be SW France, where LL shear will be enhanced, but right now environmental conditions won't justify higher probabilities for more than an isolated thunderstorm threat

A few isolated but sub-severe thunderstorms can be expected over SW-UK, too.

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Sorry for Lack of Updates lately, I have been very busy and just been away in Woolacombe, North Devon as my Location says!

Wednesday 2nd May 2007

Storm Forecast

Valid: Wed 02 May 2007 06:00 to Thu 03 May 2007 06:00 UTC

Issued: Tue 01 May 2007 20:51

Forecaster: TUSCHY

SYNOPSIS

Split flow regime continues over Europe with high pressure in - between, centered over NW Europe.

An upper-level trough over NE Europe will start a weakening trend, while moving towards the NE. A shallow unstable layer and some forcing could be enough for a few thunderstorms over extreme western Russia , but coverage won't justify the issuance of such a large TSTM area.

The same for Estonia, Latvia and southern Finland, where ESE-ward racing cold front could suppot an isolated thunderstorm. Although parameters for an isolated tornado would be present, low confidence in any significant thunderstorm threat preclude any higher probabilities right now.

A southeastward shifting upper-level low will cross the Iberian Peninsula, while another upper-level low will bring unsettled weather conditions for SE-France.

DISCUSSION

...Portugal, Spain and the Strait of Gibraltar...

An upper - level trough continues its SE-ward motion, crossing Portugal and S-Spain during the forecast period. Latest cyclone phase evolution forecast of various models indicate some slow organisation and strengthening of this system.

Yesterday's 17-18Z stallite loop had the well defined system WNW of Portugal with a straight SE-ward motion. Warm front / sector appearance constantly improved with cooling cloud tops over the warm sector, already affecting Portugal.

Satellite based measurements denote a humid airmass ( appraised total PW values of at or above 40mm) streaming in the warm sector .

Succeeding cold front and warm front are embedded in a strong westerly jet and hence rapid eastward translation will bring them over southern Spain during the forecast period.

An accessorily hampering factor will be the predicted occlusion process, which should take place somewhere over southern Spain.

Recapitulating we have to discuss numerous fronts and attendant thunderstorm chances.

The warm front and warm sector should pose the most limited theat for thunderstorm evolution. A well saturated and warm airmass will keep lapse rates low and strong and prolonged forcing should support a more stratiform character in the warm sector although an isolated embedded storm can't be excluded.

The cold front will cross Portugal and SW Spain between 6Z-12Z and a few storms should evolve in a low-end instability and high shear environment. Best LL shear should stay displaced towards the east but DLS of 20-25m/s and at least somewhat steepened mid-level lapse rates should favor an isolated large hail and severe wind gust risk.

Models then show a complete occlusion of this fronts somewhere around the Strait of Gibraltar, while moving slowly towards the east.

Drying at upper-levels but still nice forcing should be enough for a persisting and possibly strengthening thunderstorm activity along this front over extreme southern Spain.

The main threat will be an isolated large hail and severe wind gust risk, but low LCLs and enhanced LL shear along the occlusion also favor an isolated tornado risk as far north as Madrid.

18Z onwards, most robust thunderstorm threat will shift offshore with mainly a severe wind gust risk.

High PWAT values over the level-1 region and repeated thunderstorm evolution along the eastward shifting frontal boundary also indicate a flash flood risk.

... SE - France, extreme NW - Italy...

Another area of scattered thunderstorm evolution will develop under a slowly NE-ward shifting upper-level disturbance.

Rapidly cooling atmosphere and SSTs of 17-18°C south of France are enough for up to 500 J / kg SBCAPE.

Deep layer shear of 15-20m/s and steepening mid-level lapse rates indicate a risk for hail with each stronger storm and an isolated large hail risk can't be excluded.

Although not explicit hinted in the models a low-end tornado risk may be possible due to some veering and low LCLs.

...Rest of France, Switzerland...

No significant changes compared to the past few days.

W / SW-wards shifting moisture convergence zone will start to slowly retreat towards the north as a consequence of a weak LL depression over extreme SW France.

Pulsating storms with mostly subsevere wind gusts and small hail will be the primary threat over west-central France.

Stronger DLS (up to 20m/s ) and steeper lapse rates will be present over eastern France, Switzerland and extreme SW Germany.

Stronger cells may be able to produce locally hail, matching the severe hail criterion.

Slowly northward retreating convergence zone could help to increase PBL moisture as far towards the east as extreme SW Germany which is the main reason for the far eastward expanded level-1 area.

....S-Bulgaria and NW-Turkey...

A cold front from the north will reach S-Bulgaria and some low-end instability release looks reasonable. Limited instability will likely preclude a more significant severe weather event , because DLS of 25-30m/s and still fine lapse rates will be present. Developing storms will mainly produce isolated large hail / severe wind gusts.

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Thursday 3rd May 2007

Storm Forecast

Valid: Thu 03 May 2007 06:00 to Fri 04 May 2007 06:00 UTC

Issued: Thu 03 May 2007 06:38

Forecaster: GATZEN

SYNOPSIS

A high pressure area is present over NWrn Europe. At its eastern flank, cold air mass has advected into eastern Europe in the range of broad long-wave trough. Region of low geopotential spreads across the Alpine region into SWrn Europe, where intense upper cut-off lows will slowly propagate north-eastward. A strong south-westerly upper jet is present at the south-eastern boarder of the low, affecting the central Mediterranean. At lower levels, warm air mass spreads into central and eastern Mediterranean, while most of south-western/western Europe is affected by rather cool, but unstable air mass. On Thursday, cyclogenesis is forecast over north-western Mediterranean, where focus of convective activity is expected. Latest models forecasts show a cold front that moves across the western Mediterranean during the day. An occlusion is expected from southern France into Balearic Islands. To the north of this system, another occlusion is forecast from the eastern Alps to southern Germany and farther to the Pyrenees.

DISCUSSION

Northern Tunisia region

A strong upper south-westerly jet affects this region at the eastern flak of upper trough over Iberian Peninsula. Rather strong QG forcing is expected to continue as upper trough center slowly moves north-eastward and warm air advection spreads across southern Mediterranean. Given moist but quite cool boundary-layer as well as many stratiform clouds, development of steep lapse rates and associated strong instability is not likely. Best chances exist in the northern Tunisia region, where strong insolation will be possible during the day. Given moist boundary-layer, some convective cells are forecast to develop especially over mountainous regions. Limiting factor will be weak QG forcing at the anticyclonic flank of the upper jet. Given strong (25 m/s) deep layer wind shear as well as favourable veering profiles, some supercells are expected to develop, posing a threat of large hail and severe wind gusts. A tornado is not ruled out as low-level wind shear of about 10 m/s and 0-1 km SRH of 100 J/kg is forecast. Convective cells are expected to weaken in the evening hours, as QG forcing will remain weak.

Central Mediterranean

Only weak instability is forecast to develop in the warm sector air mass given cool boundary-layer and stratiform clouds over most places. Some insolation may occur during the day, helping for some low-level instability. Some thunderstorms, especially along the cold front moving towards the east, are forecast to develop. Given strong (20 m/s) deep layer wind shear in the warm sector, embedded thunderstorms may produce isolated large hail. Overall threat is weak, though, given cool boundary-layer and weak lapse rates. Chance for tornadoes is rather weak given weak low-level wind shear over the region.

South-western portions of Europe

In the range of the upper trough, air mass is characterized by rather cold mid-level air mass/steep mid-level lapse rates. The boundary-layer is rather moist and some sunshine is forecast, yielding to weak instability. Thunderstorms are forecast to develop, and given weak vertical wind shear, organized thunderstorms are not expected.

North-western France to southern Germany/Alpine region

At the northern flank of the low pressure area over Mediterranean, a weak occlusion/low-level convergence is present over France, and Germany. Along this boundary, latest soundings indicate steep mid-level lapse rates and rather moist layers above the boundary layer. Given strong insolation during the day, low-level CAPE may be realized locally, but poor boundary-layer moisture is present over most places. There is also a potential for elevated convection along the occlusion as increasing QG forcing is expected during the day. Thunderstorms that root to the boundary-layer may become organized given some (about 10 m/s) deep layer vertical wind shear, and isolated large hail is not excluded. Overall threat is weak, though.

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Sunday 13th May 2007

Storm Forecast

Valid: Sun 13 May 2007 06:00 to Mon 14 May 2007 06:00 UTC

Issued: Sun 13 May 2007 02:14

Forecaster: VAN DER VELDE

SYNOPSIS

A significant low pressure system is forecast to move from the Atlantic west of France to the English Channel region and Denmark. The axis of a strong upper jet is predicted to cross Galicia, western France and the Benelux. At the time of strongest diurnal heating, the nose of the jet will be situated over northern France, with very high speeds also in the lower levels: 25 m/s at 850 and more than 30 m/s at 700 hPa forecast by GFS 18Z.

Models predict a few hundred J/kg MLCAPE in the warm sector, also near the frontal wave over Belgium at 15Z (GFS, NMM, MM5). The timing, location and magnitude of CAPE and shear has varied slightly over the past few GFS runs, but the presence of instability, shear and forcing has remained constant and indicative of a significant severe weather episode.

DISCUSSION

...France, Benelux, western Germany...

Scattered convection under weak instability is expected to occur during the morning hours over western France, which can already profit from strong vertical shear conditions (deep low level) and create isolated severe weaher as gusts or a tornado. As the day proceeds, forcing and heating are expected to increase and start to build more organised and stronger convection around Paris and near the wave over Belgium.

With 0-6 km shear vectors around 25-30 m/s, 1-8 km vectors of 15-20 m/s, 0-1 km vectors of 12-17 m/s and veering winds with height yielding more than 200 m2/s2 0-3 km SREH (even over 400 m2/s2 along the warm front north of the instability), supercells are very likely and will have a good probability to produce tornadoes (lowest LCLs, strongest LL shear over Benelux), as well as large hail and severe gusts in the level 2 area.

In the level 2 area, the deep layer shear vector is under some angle with the forcing, as judged from GFS mixing ratio advection fields, which is favourable for discrete cells initially, until the late afternoon, when cells are likely to merge and form a squall line, which will be effective in transferring strong wind speeds to the surface over a large area, thought to warrant a level 2. This system will proceed to affect the Netherlands and western Germany during the evening and move rapidly northward. It should lose strength when reaching Denmark. A somewhat limiting factor is instability and probably not very dry air except over Germany.

The 12Z sounding of Trappes should become representative of the environment.

...central and southern France...

More isolated storms are expected here after about 15Z along the front, with weaker low level shear southward but stronger deep layer shear, and SREH still higher than 100-200 m2/s2 giving a high probability that cells will develop more persistent mesocyclones or split. Large hail is the primary threat here. Severe gusts can occur helped by cold downdrafts (>12 degrees negative buoyancy at surface). During the evening, a band a enhanced low level shear may increase tornado chances a bit over the northeastern Massif Central. As the shear vector is much parallel to the front here, storms may have formed a line by then.

...Czech area...

GFS and MM5 have indicated some convective precipitation here. While there should be quite considerable instability and favourable deep layer shear and SREH, chances seem a bit slim as no clear forcing is going to be present... perhaps orography. Would not exclude Bavaria totally... an update may be required but everything is likely staying localized. The warm front might set off a storm near the Czech/Polish border during the evening if GFS has it right. Large hail would be the primary threat in this area.

...Ukraine...

Another area where the jet crosses slight instability. >100 m2/s2 SREH and >20 m/s 0-6 km shear, so a few storms may display rotation and a slight chance of marginally large hail. A weak shortwave trough provides lift.

...Galicia, northern Portugal...

Have indicated area of slight instability crossed by deep layer/low level shear. Not much over land though.

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Update: Some more strikes in the map but needs updating to include strikes in england etc!

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