Convective / Storm Risk Discussion - 23rd July 2013 onwards

[nitro_deluxe]

I can guess, but that's all it'd be - very Paxman-esque....there is a risk of cloud, rain, thunder, lightning, large hail, gusty winds, tornadoes, sunshine and flash flooding with the highest risk of severe further east but possibly extending further west too.Any good????? :DGenuinely though, not a scooby and on balance I think the MetO have played it well thus far - there is a risk of severe weather but nobody can know yet where, when and how much!?!?

Exactly.If they were to completely rule out severe weather, there'd be others saying..hang on? Surely not.Blimey it's the UK, a relatively small island with a predominantly maritime type climate. Anything else is a bonus/mystery/maker of good arguments lol. Harder to predict..My guess a line Portsmouth to Brum and east most at risk. Bristol to Liverpool slightly less so. Swansea to Belfast a notch lower. Or is it other way round

[Richie V]

I know exsactly what is going to happen... In the morning it is going to get light, comes fri eve it will get dark. Saturday is where the fun really starts, quite early on it will get light, minutely less light than fri but light all the same. Saturday night will see yet more darkness arriving from the east, a touch more than fri night.....

Damn, anyone seen my coat?

[ZONE 51]

There was a funnel cloud today http://www.thejournal.ie/tornado-kildare-1007910-Jul2013/ 

Image below:

(bnw conversion/contrast to show cloud/funnel structure) 

 

[Robbie Garrett]

What is interesting is Estofex suspect at this stage the thundery low moving up across C-UK...the MetO have it skirting East of Kent/Sussex/Essex....if Estofex are right, then this could change prospects entirely!!

 

Well result, let's hope they are both wrong and it just head straight for the center of those two, me in Central London. HAHA!

 

Latest NMM does say it's heading this way...

 

[paul m]

BBC weather now have it hitting the south during the day and heading up through Yorks overnight.

[ZONE 51]

My views on the weekend storms.

 

As we know there is potential for a large scale thundery feature to affect the UK this weekend, there is a great deal of uncertainty with the track of this system, one option is for the main area of thundery rain or MCS to move up across Central Southern England and into the Midlands moving up from the continent, this is the most likely track at this stage that I see occurring, if this happens I expect more thunderstorms to still affect the SE and EA even if the main event misses these areas to the west. Another option is for the main storm to affect only the SE and EA and near the east coast, if this happens then the storm activity likely to be on the east side of the MCS/TRain, Also NAE is indicating some very heavy rain across Central South but incl parts of the SW.

 

I have done a map to show these tracks as an image. This is something that is rather different to your normal MCS set-up/track (what we are used to these days) I have great interest in this as many of you do, did we expect another thundery set-up after the lack of them over many summers? only just had one so this is amazing after all we have had hardly any night action up until recently!

(note this is not a forecast)

 

ESS

Edited July 26, 2013 by ElectricSnowStorm

[Mesoscale]

Estofex has the SE in a level 1, this is an extended forecast so its likely to change later today.I think its 50% forecasting and 50% luck to be honest, forecasting for the knowledge that there could be storms and luck if one actually hits you. Unfortunatley for me luck wasn't on my side the other night but the forecasting was right. Somebody said that the GFS had the cape and li splitting over them but in fairness for my area I had high cape levels and didn't get anything within 5 to 10 miles of my house.

 

Its frustrating when you don't get anything though, especially when you can see and hear it but not quite be in it. Nothing is garanteed until it actually happens.

Edited July 26, 2013 by Mesoscale

[AWD]

Latest NAE for Saturday night;

Ouch!

[The PIT]

Sheffield shield chuckles in anticipation.

[East_England_Stormchaser91]

Morning all, apologies for my rant last night about the METO! I understand where Harry was coming from and I do understand that it can't be too easy predicting these kinds of scenarios. It can get highly frustrating if you are a die hard storm lover and big potential possibly looking like it will be going to waste, or affect the typical places (Holland/Belgium who are lets face it, spoilt rotten with MCS's every summer almost!)

At least there has been some sort of slight shift with this and we may see a little bit of convective activity after all.

[AWD]

WRF-NMM model has the heaviest rainfall even further west than the NAE;

Before moving east/ north east across the south of the UK and into the South East, showing some immense rainfall;

Edited July 26, 2013 by AWD

[Petorious]

Is Saturday afternoon/ evening going to be one of those things I haven't seen for so many years, were looking across my south over fields and the whole skyline turns jet black with lightning across the lot. I would say the last time that happened for me was probably in the 1999 - 2003 period of time, been so long.

[Captain Shortwave]

The UKMO which has been the party pooper in this scenario has shifted the low west this morning, still further east than the rest but it now crosses through the north sea rather than through Belgium. So it looks like the chances of some great storms Saturday night is on the up *touchwood*

[Coast]

ESTOFEX for today:

 

 

 

Storm Forecast

Valid: Fri 26 Jul 2013 06:00 to Sat 27 Jul 2013 06:00 UTC

Issued: Thu 25 Jul 2013 22:05

Forecaster: TUSCHY

A level 2 was issued for parts of extreme N-Spain, parts of France, Belgium, the Netherlands, Luxembourg and NW Germany mainly for large to very large hail (hail diameter in excess of 5 cm possible), severe to damaging downbursts, excessive and potential flash flood producing rainfall amounts and an isolated tornado event.

 

A level 1 surrounds the level 2 for a similar hazard but with a low chance for extreme events.

 

A level 1 was issued for extreme SE-France and far N-Italy mainly for excessive rainfall amounts, isolated large hail and strong to severe wind gusts.

 

SYNOPSIS

 

A constant blocking pattern remains in place with strong ridging over S/C-Europe flanked by two stout troughs, one over the far E-Atlantic and the other one over far W-Russia.

 

At the surface, a quasi-stationary and wavy frontal boundary runs from the SE Bay of Biscay all the way to Denmark. Numerous small-scale disturbances evolve along that boundary and serve as foci for severe DMC. Probably the most pronounced surface pressure fall is expected during the night hours over the SE Bay of Biscay and SW France.

No other synoptic fronts play a role in today's thunderstorm forecast.

 

DISCUSSION

 

... NE France, Benelux, parts of Denmark and parts of Germany ...

 

The big issue with this pattern is the absence of any serious forcing. A short wave over UK and Benelux rotates north until noon and leaves a more or less undisturbed mid/upper level flow regime behind over N-France. Weak mid-level height falls are forecast in all models over N-Germany/Denmark, so initiation there becomes more likely during the latter part of the forecast. For a better overview we split the forecast in certain time-frames:

 

06 - 18Z:

 

The aforementioned short-wave probably caused the development of one or two large thunderstorm clusters from the night before, affecting mainly Benelux and W/NW Germany during the morning hours. This activity is probably also tied to a warm front, which crosses the area of interest from SW to NE during that time frame. Diurnal heating on both sides and the departing short wave result in a decelerating and mitigating warm front. Most models show only a temporal weakening trend of thunderstorms during the early morning hours, but rapid re-strengthening is forecast as diabatic heating starts. Forecast data and soundings reveal 500 to 1000 J/kg MLCAPE and 15 to 20 m/s DLS at 9 Z over Benelux with PWs in excess of 40 mm. Ongoing WAA induces also strongly veered profiles, so current thinking is that we will see one or two severe thunderstorm clusters before noon, affecting Benelux and NW-Germany. Those clusters will gradually move offshore around noon. Expect all facets of severe with those storms, including large hail (a first very large hail event already possible), severe wind gusts and flash flood producing excessive rainfall amounts.

 

In case those clusters either don't evolve or remain smaller than currently anticipated, a more supportive environment will be in place for the next round of DMC.

 

Timing and extent of the aforementioned clusters determine the strength and position of afternoon convection due to temporarily cooler/stable outflow air behind those storms and limiting heating due to an extensive anvil canopy. The current plan is, that both, rapid air mass recovery behind the storms from forenoon and also scattered development along the synoptic front (W-Benelux) result in another round of severe thunderstorms with the highest coverage of storms probably over the Netherlands and Belgium. Overlap of unseasonably high BL moisture (effective PWs in excess of 40 mm) and moderate mid-level lapse rates offer 1000 to 2000 J/kg MLCAPE build-up within 15 to 20 m/s DLS. Similar shear magnitude is forecast within the lowest 3 km, which raises concerns regarding bowing segments, racing NE-wards along the quasi-stationary synoptic front. Missing forcing limits that risk, but cold-pool driven bowing segments are still very well possible. In that case, expect swaths of strong to severe wind gusts and very heavy rainfall amounts. Despite that risk, limited forcing and strongly veered profiles also support more discrete storms towards NW Germany and well organized multicells and supercells with large to very large hail, severe wind gusts and heavy rain are likely. Despite mainly weak LL shear signals, lowering LCLs during the late afternoon hours (combined with anomalous high BL moisture content), regionally enhanced LL shear especially along outflow boundaries or the synoptic front and expected mature supercell storm mode also points to an isolated tornado risk especially during the evening hours.

 

A short side-note to the rainfall risk. Despite the progressive nature of the convection, the leisurely NE-ward moving warm front and also the quasi-stationary synoptic front will be the main foci for potential training thunderstorm activity either due to a near normal alignment to the strong background flow (warm-front) or due to repeatedly developing DMC along the wavy frontal system. Flash flooding could become a distinct possibility.

 

Despite ongoing uncertainties, we upgraded most parts of that area to a level 2 as confidence in numerous severe and a few extremely severe events is high enough.

 

An high-end level-2 situation however is forecast over NE France during the afternoon and evening hours. GFS and EZ both agree in the development of a plume with very high CAPE on the order of 2000 to 3000 J/kg. Similar shear (speed and directional) is forecast as described above, which is supportive of long-lived and well organized supercells. Current thinking is that either initiation due to a breaking cap (either due to diabatic heating or constant BL moisture increase) or southbound moving outflow boundaries from Belgium result in isolated thunderstorm development over NE-France. Expect explosive development with any cell, which experiences an uncontaminated inflow of very moist and unstable air. Large to very large hail (hail diameter in excess of 5 cm), severe to damaging wind gusts, excessive rainfall amounts and an isolated tornado threat exist with those storms. Despite a SW-erly steering flow regime, deviant storm motion should bring those storms near Paris-Nancy and Luxembourg / S-Belgium. 

 

... 18Z - 06Z ...

 

The main story probably will be any ongoing supercell over NE France, S-Belgium and Luxembourg, which gradually approaches far W-Germany during the late evening hours. A slow weakening trend should occur with decreasing CAPE and storms also start to outrun strongest shear, but nevertheless, an ongoing risk of supercells/well organized multicells exists over Benelux, NW and W-Germany and NE France until midnight. Large to isolated very large hail, severe wind gusts and locally excessive rainfall amounts are possible next to an isolated tornado event.

A thunderstorm cluster probably affects Denmark during the night as a result of upscale growth of the Benelux activity from the daytime hours. Again, severe wind gusts and heavy rainfall amounts will be the main hazard, but we can't exclude an isolated large hail and tornado event (e.g. with advancing discrete cells).

Models diverge regarding thunderstorm development over C/E-Germany during the night. We think that decreasing mid-level heights should assist in thunderstorm clusters to move more to the E or NE and therefore also affect areas further south (including C/E-Germany). This activity however experiences weaker shear and becomes more elevated in nature, so a decreasing risk is anticipated. Heavy rain, marginal to isolated large hail and gusty winds will be the main risk with 15 m/s DLS and 400 to 800 MUCAPE.

 

... N-Spain, SW/W and N-France ...

 

Initiation during the daytime hours is a bit uncertain with no noticeable forcing mechanism seen until 18Z. Overnight thunderstorm activity (from last night) likely continues until noon with numerous clusters moving to the N/NE. This activity however either weakens until noon (W-France) or moves towards Benelux (see paragraph above). Thereafter, forecast soundings show only weak capping until 18Z and either orography, outflow boundaries or the frontal circulation of the quasi-stationary front might assist in isolated CI over W/N-France. 1500 to 2500 J/kg MLCAPE, 20 to 25 m/s DLS and ongoing pronounced veering indicate a high possibility for any developing thunderstorm to achieve rotation with all kind of severe possible ... including very large hail (hail diameter in excess of 5 cm), severe downbursts and heavy rainfall amounts.

 

Around sunset and during the night, conditions for scattered CI improve over the SE Bay of Biscay and SW France with falling surface pressure next to an approaching PVA maximum at mid-levels from the west. Scattered intense multicells/supercells likely evolve over N-Spain into SW-France around sunset with 20 to 30 m/s DLS and 2000 J/kg MLCAPE. Very large hail (hail diameter in excess of 5 cm), severe downbursts, excessive rainfall amounts and an isolated tornado event are forecast. Rapid upscale growth into a large MCS over the SE Bay of Biscay is forecast which moves to the NE, affecting W-central France during the night with heavy rain, large hail and severe wind gusts. Another large thunderstorm cluster probably evolves over W-France in response to increasing BL convergence ahead of the consolidating broad low-level surface pressure area over SW-France. Despite the overnight hours, forecast soundings still show a good chance for surface based activity along and south of the frontal boundary, where 800 to 1500 J/kg MLCAPE and 20 m/s DLS overlap. Multicells and a few supercells with large to very large hail (hail diamater in excess of 5 cm), strong to severe wind gusts and flash-flood producing rainfall amounts are forecast. In addition, improving LL wind field enhances the tornado risk over W-France. Those severe thunderstorm clusters continue until 06Z (and beyond) over NW/N/NE France.

 

The level 1 area was expanded a bit to the southeast over NE Spain to include the low chance for a few mountain storms during the evening and overnight hours. Shear/CAPE would favor organized DMC with large hail and severe wind gusts.

 

 

 

[Coast]

Now the important one, ESTOFEX for tomorrow:

 

 

 

Extended Forecast

Valid: Sat 27 Jul 2013 06:00 to Sun 28 Jul 2013 06:00 UTC

Issued: Thu 25 Jul 2013 21:33

Forecaster: GROENEMEIJER/PUCIK

... An outbreak of severe storms is expected across France, the Benelux countries and northwestern Germany...

 

A level 2 was issued across parts of France, the Benelux countries and northwestern Germany for severe winds and large or very large hail, excessive precipitation and tornadoes.

 

A level 1 was issued across a larger part of France, the Benelux countries, northwest Germany as well as southeast England, parts of Denmark and north Spain for the same risks. 

 

A level 1 was issued across the southern Alps, mainly for excessive precipitation and large hail.

 

DISCUSSION...

 

Saturday, the synoptic situation will be dominated by a strongly amplified trough over the Eastern Atlantic and a ridge that stretches from the Mediterranean towards Central Europe. Between these features, a strong and gradually strengthening south-southwesterly mid- and upper level flow is simulated, with wind speeds between 20 and 35 m/s at 500 hPa level.

 

The mid-level winds will advect a plume of steep lapse rates off the Spanish Plateau into France, the Benelux Countries and Germany. A corridor of convergent low-level winds and high low-level moisture flanks the western and northern side of the area of steep lapse rates, stretching from southwest France across the southeast Benelux toward north Germany. A pronounced overlap of this low-level moisture and steep mid-level lapse rates should result in CAPE exceeding 1500 J/kg across a large area with pockets up to 3000 J/kg.

 

A shortwave trough forecast west of the Iberian Peninsula on Saturday morning moves northeastward, reaching central Britain on Sunday morning. In response, a baroclinic wave is expected to develop with pressure falls over central France, and increasing warm air advection over north and west France.

 

It appears likely that scattered to widespread convection will be ongoing early on Saturday across NW France and the Benelux, probably producing outflow boundaries. New convective storms are simulated to develop along these boundaries during the afternoon, and during the evening in south-central France along the advancing cold front of the wave. 

 

Strong deep-layer shear of 20 - 30 m/s suggests that some storms will become supercells, capable of producing produce large or very large hail. 

 

A southwest to northeast oriented surface warm front is forecast to develop during the afternoon and evening by most NWP guidance, and stretches from north France across the Benelux into northwest Germany. Storm-relative helicity and low-level (0-1 km) wind shear are forecast to be around 200-300 m2/s2 and 10 m/s respectively. Together with relatively low cloud bases, this suggests that some threat of (possibly strong) tornadoes will exist during the late afternoon and evening along and north of the surface front. 

 

Across south-central France, the inflow from the Mediterranean is quite helical too, so that tornadoes cannot be ruled out there either. 

 

It appears likely that individual storms will cluster over time. Some may develop into north-northeastward moving bow echoes producing swaths of damaging winds. Along the cold front that progresses only slowly eastward, subsequent convective cells may train over the same areas, possibly leading to very high rain accumulations and an attendant flash flood risk.

 

 

 

 

[Nick F]

Yes the track of the low/frontal wave a bit further west coming north tomorrow night looking at the UKMO and fax charts, GFS further west still though keeps CAPE mostly on the near continent - which suggests heavy rain rather than thunderstorms.

 

However, it's still worth nowcasting to see if any storms develop far enough west along the frontal wave and drift across S/SE England and E Anglia. 

 

NAE looks interesting for tomorrow night:

 

[Coast]

GFS further west still though keeps CAPE mostly on the near continent - which suggests heavy rain rather than thunderstorms.

 

Maybe a Kent Clipper from them?

 

[Guest William Grimsley]

 

Edited July 26, 2013 by William Grimsley

[Guest William Grimsley]

Hi there,I'm asking about Saturday Night's thunderstorms.I live in East Devon and I am just wondering if I might see any action then?BBC Weather shows me getting a lot of activity from 16:00 to 19:00 especially but others don't.Please can I have your opinions on what you think?Thanks,William

[Guest William Grimsley]

My views on the weekend storms.

 

As we know there is potential for a large scale thundery feature to affect the UK this weekend, there is a great deal of uncertainty with the track of this system, one option is for the main area of thundery rain or MCS to move up across Central Southern England and into the Midlands moving up from the continent, this is the most likely track at this stage that I see occurring, if this happens I expect more thunderstorms to still affect the SE and EA even if the main event misses these areas to the west. Another option is for the main storm to affect only the SE and EA and near the east coast, if this happens then the storm activity likely to be on the east side of the MCS/TRain, Also NAE is indicating some very heavy rain across Central South but incl parts of the SW.

 

I have done a map to show these tracks as an image. This is something that is rather different to your normal MCS set-up/track (what we are used to these days) I have great interest in this as many of you do, did we expect another thundery set-up after the lack of them over many summers? only just had one so this is amazing after all we have had hardly any night action up until recently!

(note this is not a forecast)

Wknd Thundery rain potential tracks July 2013.gif

 

ESS

It looks like I'm only at risk of very heavy rainfall instead of thunderstorm, then? Oh, well.

[Coast]

 

Thunderstorms will threaten to unleash blinding downpours, severe winds and hail across a large swathe of Europe Saturday and Sunday.

Paris will be at risk of powerful thunderstorms on Saturday into Saturday night, as will a wide belt reaching from southwestern and central France north into Belgium and the Netherlands.

 

The worst of these storms will have potential to damage property. London could also get thunder and lightning as rain breaks out over much of England Saturday and Saturday. However, severe storms are not expected. The trigger for the thunderstorm outbreak will be a cold front from the Atlantic Ocean that will dislodge a mass of hot air originating in northwestern Africa.

 

Sunday, the threat area will shift eastward along with the cold front, spanning much of Germany into eastern France and Switzerland. Strong, gusty thunderstorms could reach Berlin by Sunday evening. Serious heat will precede these thunderstorms with Sunday temperatures soaring as high as 38 or 39 degrees C (100-102 degrees F) in Berlin and nearby eastern Germany.

 

 

http://www.accuweather.com/en/weather-news/strong-thunderstorms-paris-to/15747365

[Coast]

Still so much conflicting information and views, NMM:

 

 

 

 

 

[Pixel]

A juicy storm develops out of nothing from the Bay of Biscay (nr Bordeaux) heading NE through France… and it's still going.  

 

http://www.weatheronline.co.uk/cgi-app/satellite?CONT=euro&CREG=im00&LOOP=12&LANG=en&STRUCTUR=_

 

Droooool....

 

If only…. (-:

[Radiating Dendrite]

Looking as though this could be similar to the MCS that moved up through the country on July 22nd 2006.

[Coast]

Looking as though this could be similar to the MCS that moved up through the country on July 22nd 2006.

 

http://forum.netweather.tv/topic/31465-storm-reports-22nd-july-2006/