Storm & Convective Discussion - 02/07/15 Onward - Heat & Plumes

[Staffordshire]

Convective Weather forecast out.

Interesting read, noting the huge caveats.

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Day 2 Convective Outlook

VALID 06:00 UTC Fri 03 Jul 2015 - 05:59 UTC Sat 04 Jul 2015

ISSUED 21:54 UTC Thu 02 Jul 2015

ISSUED BY: Dan

... NW HIGHLANDS ...

Some wind convergence and upslope flow may develop a couple of locally heavy showers, perhaps a local flash of lightning in the mid/late afternoon.

... ENGLAND AND WALES ...

Rapid warm air advection will develop across southern Britain through the evening hours, causing surface dewpoints to increase as a warm front lifts northwards. Meanwhile, the Atlantic upper trough will pivot NEwards, overlapping with the arrival of this plume during the evening, and providing sufficient lift. Consequently, expect thunderstorms to develop through the evening hours, initially fairly well-scattered across SW England, with activity expanding farther N and E as the evening progresses.

With the approaching trough, DLS will strengthen with favourably-backed surface winds. This combined with 800-1,200 Jkg-1 MLCAPE suggests the potential for storms to become organised, perhaps into supercells capable of producing large hail. Forecast profiles suggest most storms will be elevated above 700mb, thus limiting the tornado risk, but if any storms do become rooted within the boundary layer, then there would be the risk of a tornado developing. There exists some uncertainty with developments farther east, namely across SE England and the Channel Isles.

Capping may be too strong or upper forcing not strong enough to generate storms here (as per consistent signals in EURO4/UKV/ECMWF) while GFS is more keen to develop storms over northern France and run them northwards into CS/SE England. Given these uncertainties have opted to go for the general consensus for now (hence reducing probabilities towards the SE, the MDT placed where best agreement exists amongst most models) but cater for the risk of large hail and heavy rain (given PWAT 35-40mm) as the primary threats with any strong storms that may develop in central and southern Britain. In either case, mass ascent will see storms become more numerous as instability axis moves north, merging into an area of thundery rain and eventually losing most lightning activity during the early hours of Saturday as instability weakens and clears eastwards to the North Sea.

It is likely that this forecast will need updating during Friday with threat level areas tweaked depending on convective trends.

i don't quite understand the meaning of the black outline on here even after reading the info, could you elaborate for me, is this between MDT and SVR?

[Snowshine]

Next week - Boring weather 

[Mokidugway]

Next week - Boring weather 

Screen Shot 2015-07-02 at 22.50.07.png

I love those technical charts ..

[Harry]

i don't quite understand the meaning of the black outline on here even after reading the info, could you elaborate for me, is this between MDT and SVR?

The black line denotes where severe potential exists. The coloured zones highlight probability of storms. Areas in the MDT but outside the black zone have good chance of seeing a storm but unlikely it will be severe. Areas in the brown or green zone but in the black zone, have less chance of a storm, BUT, if there is a storm, it has a higher probability of being severe.

Hope that makes sense.

Edited July 2, 2015 by Harry

[Vestan]

I'm just on the edge of 'severe' in the South Midlands, but have seen this before and ended up with nothing.

 

This week, it seems that everything forming in France has split into two and gone up the West coast or towards London. Nothing has made it to this area

 

Waiting more in hope than anticipation for tomorrow

[stainesbloke]

I'll believe the hyped storm predictions when I actually see a decent storm. Not expecting anything more than patchy drizzle as per usual. Some heavy convective summer rain would be very welcome now as it has been so dry.

Edited July 2, 2015 by stainesbloke

[Mapantz]

Re; Southeast

 

Capping may be too strong or upper forcing not strong enough to generate storms here (as per consistent signals in EURO4/UKV/ECMWF) 

 

And back to my old chestnut again.. 

 

The tropospheric ducting forecasts show the possibility of an inversion for the Southeast tomorrow.

I'm looking forward to how all this pans out lol

Edited July 2, 2015 by Mapantz

[Noahjoe]

i don't quite understand the meaning of the black outline on here even after reading the info, could you elaborate for me, is this between MDT and SVR?

I think the moderate is for the overall storm risk whereas the black line is signalling where IF thunderstorms were to occur they are more likely to be severe....or at least that was my understanding of it.

[I Cumbria Marra I]

Next week - Boring weather 

Screen Shot 2015-07-02 at 22.50.07.png

true

[Staffordshire]

The black line denotes where severe potential exists. The coloured zones highlight probability of storms. Areas in the MDT but outside the black zone have good chance of seeing a storm but unlikely it will be severe. Areas in the brown or green zone but in the black zone, have less chance of a storm, BUT, if there is a storm, it has a higher probability of being severe.

Hope that makes sense.

yeah cheers, looks like I'll be getting in my car and heading E'wards tomorrow then

[Harry]

Re; Southeast

And back to my old chestnut again..

The tropospheric ducting forecasts show the possibility of an inversion for the Southeast tomorrow.

I'm looking forward to how all this pans out lol

Indeed...but if that cap goes then expect explosive storms.

Edited July 2, 2015 by Harry

[Evening thunder]

12z ECM charts for 00z-06z Saturday, heaviest precip towards the NW, less towards the SE, though like you say, not immune.

 

ecm0125_036.jpgecm0125_042.jpg

 

 

It's interesting how the choice of scale affects things, on those charts the SE precip look relatively insignificant whereas on ones I was looking at it looked more significant, if not as heavy as the rainfall further north.

 

My general thoughts, though not as knowledgeable as some, is that storms are most likely from say the SW up through the Midlands towards the east/NE, but the further east storms can take hold the more potential strength and chance of developing severe characteristics they have, in fact the forecast map from Convective Weather posted by Harry sums up my thoughts very well.

Edited July 2, 2015 by Evening thunder

[Nick F]

Re; Southeast

 

 

And back to my old chestnut again.. 

 

The tropospheric ducting forecasts show the possibility of an inversion for the Southeast tomorrow.

I'm looking forward to how all this pans out lol

 

Ridging will be more evident aloft towards the SE of England, thanks to an omega high over much of Europe, lets hope it doesn't completely cap the atmosphere despite the high CAPE pushing up from France tomorrow night.

[Mapantz]

Indeed...but if that cap goes then expect explosive storms.

 

I think it will, with 28 to 30°C on offer in some places.

[ThunderBuddy21]

I'll rent you my loft conversion with velux windows for the night if you like, clear views over the downs where the storms kick off once they've been swept in off the sea, a view wasted on me, I'm pretified. Might sedate myself tomorrow!!

[Condor Vitesse]

Nothing will ever beat last night. Was not overhead but the Lightning was amazing. I have never seen anything like that before.

[Harry]

Estofex out

Storm Forecast

Valid: Fri 03 Jul 2015 06:00 to Sat 04 Jul 2015 06:00 UTC

Issued: Thu 02 Jul 2015 22:17

Forecaster: GROENEMEIJER

A level 2 was issued for NW France and the channel region, for very large hail, severe wind gusts and tornadoes and to a lesser extent for extreme precipitation.

A level 1 was issued for a greater part of Northern and Western France and the Southern United Kingdom for large hail and extreme precipitation.

A level 2 was issues for parts of Northern Germany and Southern Denmark, for large hail, and to a lesser extent for severe wind gusts and extreme precipitation.

A level 1 was issued for Northern Denmark, Southern Germany and the Alps for for large hail, and to a lesser extent for severe wind gusts and extreme precipitation.

A level 1 was issued for the Southwest Ukraine, Southeast Moldova and East Romania for extreme precipitation and large hai.

A level 1 was issue for parts of Northwest Russia including Southern Karelia, and the oblasts Leningrad, Vologda, Tver, Novgorod and Yaroslavl, mainly for severe wind gusts and tornadoes.

SYNOPSIS

Friday morning at 06 UTC...a ridge extends from the Western Mediterranean to the Baltic States and a cold core low is slowly drifting southwestward over the western Black Sea. Very high lower-troposperic temperatures are present the ridge. An eastward intrusion of cooler near-surface air has made its way into Germany ahead of a second northward impulse over France of particularly hot air.

DISCUSSION

NW France...

The forecast for this area is particularly difficult. NWP guidance suggests that a warm front will set up over the area during the afternoon and evening, and that steep lapse rates and moisture will lead to ample surface-based CAPE of 1000 (ECMWF) to 2000-3000 J/kg (GFS). In addition, a substantial elevated CAPE is forecast to develop during the evening over the Channel and Southern England.

During the evening, the warm frontal zone features easterly surface winds, a brisk 10-18 m/s southerly flow at 850 hPa and 15-20 m/s southerwesterlies at 500 hPa. This yields a large curved low-level hodograph with 400 m2/s2 of SREH. Hence, strong rotation is expected in any boundary-rooted storm that might develop. A risk of very large hail producing supercells with - given the 10-15 ms/ 0-1 km shear forecast in the 18-21 time frame - a risk of (strong) tornadoes exists.

The difficulty is caused by the fact that NWP models are not uniformly producing surface-based convective storms. Indeed, a significant hindrance to surface-based development is the warm air at 850 hPa of around 18 C. The GFS model initiates what is likely surface-based convection within the level 2 area during the afternoon, but there is very little precipitation in ECMWF.

I have decided to go with a level 2, with the understanding that there is a risk that surface-based convective over NW France may not occur at all, in which case the severe weather threat is limited to large hail and extreme rainfall from any elevated storms.

England, Channel region, Benelux...

Elevated convection should move in from the south during the late evening and after midnight. There is a small risk of large hail and extreme precipitation with these storms.

Germany, Denmark...

The boundary of cooler air generated on Thursday will likely be the focus of new convective development during the late afternoon and evening. For this area, the level 2 was issued. Along that boundary, relatively high surface moisture should be available, that in combination with the steep lapse rates lead to 2000 or more J/kg CAPE. 0-6 km shear is weak, but with 10 m/s it should sustain multicellular modes. The strong updrafts will likely cause large hail in some places, and the deep boundary layer may lead to strong local downbursts.

Away from the boundary the probability of convective initiation decreases, but ample buoyancy still implies a large hail and downburst threat. Across Denmark, convective coverage is not a concern, but the risk of severe weather should decrease with the somwhat lower CAPE forecast there compared to Germany.

Alps...

In an environment similar to that over Germany, i.e. very hot with a relatively deep, dry boundary layer, scattered storms should develop during the day in response to the mountain circulation. The sizable CAPE forecast to develop over the Alpine slopes indicates that these storms, despite a lack of shear may produce very isolated severe weather, specifically extreme precipitation and large hail, and possibly strong downbursts.

NW Russia...

Within a strong west-northwesterly flow some CAPE is expected to develop to the warm side of a WNW-ESE oriented frontal zone. NWP guidance indicate modest signals for convective coverage. Nevertheless, the high shear prompts a level 1 to be issued for severe wind gusts but also for tornadoes.

Eastern Balkans...

On the western fringe of the md/upper-level low ample large-scale upward motion is forecast that should aid storm initiation. Indeed, NWP models simulate widespread convection. The shear is in the 10-18 m/s range, indiicating that some storm systems may be rather well-organized multicells. Some marginally large hail and, in particular extreme precipitation are forecaste to occur on an isolated basis.

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[Nick F]

It's interesting how the choice of scale affects things, on those charts the SE precip look relatively insignificant whereas on ones I was looking at it looked more significant, if not as heavy as the rainfall further north.

 

My general thoughts, though not as knowledgeable as some, is that storms are most likely from say the SW up through the Midlands towards the east/NE, but the further east storms can take hold the more potential strength and chance of developing severe characteristics they have, in fact the forecast map posted by Harry from Convective Weather sums up my thoughts very well.

 

Yes, you have it in a nutshell, less capping and greater forcing for ascent across northern and western areas will likely mean storms will develop earlier here and be more widespread before quickly merging into a mass of thundery rain, locally torrential with risk of flooding. Whilst capping further east/SE will allow more CAPE to build and potentially allow more energy to be released - which means more discrete storms that are more likely to have supercell charactertics - whether it pans out that way is not quite clear, as always in the UK!

[Flash bang flash bang etc]

Whatever happened to regular common or garden storms you can set your (admittedly lo-tech digital) watches to?

I think GPS satellite radiation and the bee vacuum is to blame...

Edited July 2, 2015 by Flash bang flash bang etc

[ChezWeather]

So GFS UKMO and NMM all going with a swathe of storms moving NE across Southern England / Midlands? 

[Mokidugway]

Whatever happened to regular common or garden storms you can set your (admittedly lo-tech digital) watches to?

I think GPS satellite radiation and the bee vacuum is to blame...

nah , it's windturbines bending the molecules ..

[tomp456]

good vibes are oozing out of me for tomorrow now the word 'cap' has been mentioned.

I won't have to buy everyone a beer. (See list few pages back)

Although I think I'd rather.

Come on Mother Nature, ma'am!!!!!!!

[Cableguy]

Now I'm confused after seeing the estofex forecast which goes against many showing the SE in with a chance, can't make my mind up whether to head west or stay put tomorrow evening will just have to watch the radar and make the decision as it unfolds I guess

[PersianPaladin]

Warning....strong language...

 

[mhielte]

Amazing video! You weren't wrong about the language warning, but somehow it makes it better