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Storm & Convective Discussion - 16/07/15 onwards

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That Estofex forecast is awesome for my location and many in the SE but if I am honest I dont really want a tornado to hit my house, large-ish hail is probably way to much also, I haven't been on here for a few days so I have no idea how or what to expect tomorrow night. 

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as noted in the previous thread, Estofex are quite bullish about tomorrow evening, a level 2 alert for a good swathe of southern and eastern England through the period.....

 

post-4149-0-13440900-1437004250_thumb.pn

 

 

Storm Forecast
Valid: Thu 16 Jul 2015 06:00 to Fri 17 Jul 2015 06:00 UTC
Issued: Wed 15 Jul 2015 22:04
Forecaster: GATZEN

A level 2 was issued for parts of NW Germany, Benelux, N France, and S UK mainly for large hail, severe wind gusts, and to a lesser extend tornadoes and excessive precipitation.

A level 1 was issued for central and southern France, and NE Spain mainly for large hail and severe wind gusts.

SYNOPSIS

At the southern flank of low geopotential across Scandinavia and between Iceland and the British Isles, a rather zonal flow has advected moist air into Europe. Soundings from northern France/southern UK to western Germany indicate rich and deep moisture with surface dewpoints around 16°C. South of this frontal zone, a ridge is present, and steep lapse rates have spread from northern Africa into SW Europe.

On Thursday, the north-west European trough will move southward. Together with another low W of Iberia, it yields a south-westerly flow across western Europe. Advection of warm and well-mixed air masses is expected until the end of the period, when the axis of warm air will reach from central France to south-western Germany. Ahead of a cold front across the eastern UK and western France, a strong low-level jet will spread into the Benelux countries and NW Germany at the end of the period.

DISCUSSION

Southern/eastern UK into northern France, Benelux, and NW Germany

The warm air advection regime will see quickly improving lapse rates atop of a moist boundary layer from W Germany across Benelux into northern France and the southern UK. Given the rich low-level moisture, model CAPE values of 1000 J/kg MLCAPE seem to be reasonable during the afternoon and evening. Initiation becomes likely in the evening hours due to the approaching cold front and frontogenetical forcing. QG forcing will increase across the UK due to DCVA.

Storms are forecast to form across northern France in the late afternoon, spreading eastward into the Benelux in the evening. Additional storms may develop across southern and eastern UK. Due to the strong low-level jet, 15 m/s low-level vertical wind shear will be available, and storms can quickly become supercells, capable of producing large hail, severe wind gusts, and flash flood. Tornadoes are also forecast with the highest threat in the evening hours from Belgium into the SE UK. Strong tornadoes are not ruled out given the strong low-level jet and associated vertical wind shear.

In the evening and night hours, storms are forecast to cluster, spreading north-east. Severe threat will gradually weaken as storms become elevated, but given the strong low-level jet and ongoing frontogenetical forcing, threat of large hail, severe winds, tornadoes, and excessive rain is expected to continue until the early morning when the main activity is expected to shift to western Germany.

Central and southern France, north-eastern Spain

Hot and well-mixed air mass will be present ahead of an approaching cold front from the west. Low-level moisture is expected to be limited, but some moisture advection takes place from the north Mediterranean, especially to the north of the Pyrenees. Initiation of storms is forecast ahead of the approaching cold front from SE Spain to southern France and further into central France. Storms that form will have a potential to produce severe downbursts given the well-mixed low-level air mass. Additionally, vertical wind shear around 10-15 m/s in the lowest 3 km will allow for well-organized storms including supercells, capable of producing large or very large hail. Given the large cold pool potential, storms are forecast to cluster before they spread north-eastward in the evening and night hours.

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I'm not expecting anything here for tomorrow around brum, I may hop in the car and head east an hour or so if it is looking decent however.

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likewise staffs, we are on a cusp here in the mid cotswolds. anyway, maybe some warm sunshine. that'll do me. cs

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Should be interesting who is right tonight because the Met O currently disagree with Estofex and the GFS. For example the Met O only describe isolated thundery showers for London whereas for E Anglia/ E Midlands they forecast thunderstorms with frequent lightning.

 

The Euro4 model backs this suggesting much of the S/SE will see nothing as the storms will fire up across the E Midlands. I am however viewing the 18Z and shall await the 0Z. The GFS on the other hand suggests more widespread activity across much of the S/SE with this moving NE.

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Indeed, going to be a tough one to call I think in some ways, more so re severe potential.

Last week NMM5 and GFS won the storm forecast championships way ahead of MetO and Euro4, the former of which (via the invent model) fell in line around 9 hours before the event - Euro4 barely budged at all even at close range.

Feel somewhat bemused by Estofex lvl 2 - for years I wondered whether we'd ever realistically see a proper level 2 over the UK for storms - I think this is the 4th so far this year!? Not convinced personally by a lvl 2, though will take it :D

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Netweather Storm Forecast for today issued last night: http://www.netweather.tv/index.cgi?action=convective;sess=

 

Storm & Convective Forecast

 

Issued 2015-07-15 21:56:24

Valid: 16/07/2015 0600z to 17/07/2015 0600z

 

post-1052-0-12908300-1437028650_thumb.pn

 

CONVECTIVE/STORM OUTLOOK -THURSDAY 16TH JULY

 

Synopsis
 

Upper trough to the west of the British Isles will drift slowly east on Thursday eroding the ridge present earlier in the day. An upper shortwave trough in the strong upper flow rounding the base the upper trough will track northeast and aid the development of an usually deep surface low (for July) that will track N up the western side of Ireland later Thurs and early Fri. Warm front associated with the low will lift north across England and Wales during the day, introducing a warm, humid and increasingly unstable airmass from the south. A cold front will move in from the SW early Friday morning, clearing all but the far north of Scotland by 12z Friday.

 

... S/SE WALES, CENTRAL, SERN and ERN ENGLAND ...

 

Warm/moist air, characterised by high 0-1km theta-w (wet bulb potential temp) values of around 16-18C, will spread north during the afternoon and evening across the above areas. An elevated mixed layer (EML) on the near continent, characterised by steep lapse rates, will overlap this warm and moist air at the surface, yielding a pool of 400-800 j/kg MLCAPE across the above areas between 18z Thurs - 06z Fri before the cold front removes the unstable plume away to the east. The EML will most likely cap any surface based convection developing, with the temp needed to break the cap unlikely reached. However, falling heights with approaching upper trough and attendant shortwave trough moving NE should create sufficient large scale ascent, coupled with cooling mid-levels, for scattered elevated thunderstorms to develop and merge moving NE later Thursday evening and overnight into Friday morning before clearing into the N Sea. Strengthening mid-upper SWly winds while winds are backed SEly at the surface ahead of the cold front is indicated to provide 40-50 knts of deep-layer (0-6km) shear. This will support multicell line segments or perhaps even high-based supercells capable of producing large rainfall totals in a short space of time leading to flash-flooding, strong wind gusts, frequent cloud-to-ground lightning and an isolated large hail risk - therefore have issued a SLIGHT risk. Storms may merge to form a MCS, ECMWF for example has one moving NE from London across E Anglia/E England to N Sea, with excessive rain and lightning the main risks.

 

... IRELAND, N IRELAND, WALES, SW ENGLAND and N ENGLAND ....

 

Warm moist air advection ahead of low arriving close to western Ireland and cool air advection in the mid-upper levels, as upper trough edges in from the west, is indicated to yield a few 100 j/kg CAPE later in the evening/overnight. Large scale ascent ahead/along cold front will allow embedded convection with lightning in the general rain spreading in across EIRE/N Ireland in the evening and later Wales and N England. A few surface based storms developing over higher parts of Wales, SW England and Ireland in the late afternoon or early evening can't be ruled out ahead of this thundery rain, rooted in the boundary layer, these storms will benefit from strong deep layer shear and low-level shear and will quickly organise - so hail, flash flooding, strong wind gusts are possible, low LCLs and veering winds with height suggest and isolated tornado also can't be ruled out. A MARGINAL risk of severe weather seems sufficient for these areas given lower CAPE indicated than compared towards SE England

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Not too sure I want a strong tornado anywhere near me.

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00z ECM for 00z and 06z Friday:

 

post-1052-0-89441600-1437030913_thumb.jp

 

post-1052-0-36728000-1437030926_thumb.jp

 

Interestingly, 00z UKMO meso only breaks out precip from E Midlands/Cambs/Norfolk northwards across Lincs and the Yorkshire Ridings.

 

Euro4 and HIRLAM not really showing anything before 6am.

 

Netwx model showing precip breaking out across SE England/E Mids later this evening before dritting NE across E England into the N Sea

 

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post-1052-0-35668400-1437031509_thumb.pn

post-1052-0-94911800-1437031527_thumb.pn

 

The usual difference at short range ... so the usual reliance on nowcasting rather than models required!

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That Estofex forecast is awesome for my location and many in the SE but if I am honest I dont really want a tornado to hit my house, large-ish hail is probably way to much also, I haven't been on here for a few days so I have no idea how or what to expect tomorrow night. 

Erm...the real answer is probably "no" you don't want a tornado or large hail in your back garden! But as I found two weeks ago, there is absolutely nothing you can do if nature decides that's what's going to happen. So as someone said in the last thread before it closed "it's fascinating whatever the outcome"...

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An interesting day ahead, looks like I have hardly any risk but this set up looks a bit like Friday Night to me. A trough coming from the west with instability over here and eastwards. The netweather storm forecast and Estofex going for something this evening but defenitely not getting my fingers crossed here.

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We can't really say we're that good at forecasting the weather are we if we can't decide on the day whether it's gonna be in the north or south - can we?!

I'm surprised there is such a huge disparity between the models and the suggestions on here.

Considering staying-put tonight - as last time I ended up stuck in the van while all hell broke loose around me. Wasn't the most amazing experience of a storm.

It's gonna be a frustrating year if every storm event is gonna take place a 2 hour drive away...

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We can't really say we're that good at forecasting the weather are we if we can't decide on the day whether it's gonna be in the north or south - can we?!

I'm surprised there is such a huge disparity between the models and the suggestions on here.

Considering staying-put tonight - as last time I ended up stuck in the van while all hell broke loose around me. Wasn't the most amazing experience of a storm.

It's gonna be a frustrating year if every storm event is gonna take place a 2 hour drive away...

 

Some sources have you fairly well placed...still a bit undecided whether storms will fire C/W of London or C/E of London, as the most reliable models are stuck between these options. I am doubtful as to the merits of the Euro4 or MetO models so am not giving them much attention.

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Some sources have you fairly well placed...still a bit undecided whether storms will fire C/W of London or C/E of London, as the most reliable models are stuck between these options. I am doubtful as to the merits of the Euro4 or MetO models so am not giving them much attention.

 

I'm not criticizing anyone here but models should not be discounted just because they don't show preferred outcomes

 

 

edit - seems to a be a focus of storms more across E/SE areas from late evening onwards met office only has light rain in early hours for my area

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bbc graphics seem to have the heavier rain and storms to the north of here tonight

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you can tell that things have downgraded according to the models  , not by the posts in here but by the lack of them

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If memory serves it was the much derided gfs that nailed the areas where storms broke out during the last event,with just about every other model and forecast organisation producing error strewn predictions.

Laterly the met office web page had a pretty decent effort as to where storms would fire,however that was an update during the afternoon before the evening event.

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If memory serves it was the much derided gfs that nailed the areas where storms broke out during the last event,with just about every other model and forecast organisation producing error strewn predictions.

Laterly the met office web page had a pretty decent effort as to where storms would fire,however that was an update during the afternoon before the evening event.

 

and looking at that model it indicates that it is more focused over E/SE parts just like the rest doesn't mean there won't be heavy showers with the odd rumble elsewhere , I just cannot see the same activity of that severity or as widespread as was 3rd July

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Meteo Group "While not as potent as the setup we saw the Friday before last

The area of the UK most likely to see thunderstorms and quite frequent lightning is across the SE quarter, between 19:00 today and 02:00 on Friday morning. Gusty winds and hail may accompany a few of the storms."

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Day 1 Convective Outlook

 

VALID 06:00 UTC Thu 16 Jul 2015 - 05:59 UTC Fri 17 Jul 2015

 

ISSUED 21:53 UTC Wed 15 Jul 2015

 

ISSUED BY: Dan

 

On Thursday, an Atlantic low will be located to the SW of Ireland, moving progressively due north. At the surface, a warm front will migrate northwards across the southern half of Britain, allowing poleward-advection of a very warm, moist low-level airmass across the aforementioned areas. The arrival of this high ThetaW air will be quite late in the day, as diurnal heating begins to subside, and will probably act as a cap to any potential surface-based convection given limited maximum temperatures in the upper 20s Celsius, despite increasing dewpoints through the evening hours.

However, there is some scope across parts of Wales/West Country for isolated sfc-based convection to develop late afternoon/evening hours, given 700-900 Jkg-1 SBCAPE, increased forcing from aloft and some surface convergence. Forecast profiles look quite dry, and so whilst convective cloud will likely develop, it is uncertain whether it will reach a depth sufficient for lightning activity - hence for now we remain with an ISOL and will monitor convective trends for any potential upgrades.
 
Greatest attention is then turned to the potential for elevated thunderstorms to develop during the mid/late evening hours and thereafter, as the forward-side of the large-scale Atlantic upper trough, and an attendant shortwave, serve as the focus for convective initiation. Naturally there is still a reasonable amount uncertainty as to the exact detail in development and areas affected.
 
Current thinking is a few scattered thunderstorms may develop during the mid/late evening hours across some southern counties of England, with activity becoming more widespread as the plume axis tracks northeastwards, eventually exiting to the North Sea - areas at greatest risk are thus highlighted with a SLGT and MDT (20z-04z), with instability increasing (but upper forcing decreasing) as one heads farther to the SE.
At present there appears to be a lack of upper forcing to generate imported elevated convection from France (especially Cherbourg and environs), and hence for now Channel and adjacent coastal areas remain at ISOL. 
 
Several models also simulate an increase in lightning potential over the Irish Sea, running NNEwards into adjacent parts of Cumbria / S/SE Scotland 00z-06z. Have included a SLGT here for now to highlight slightly higher chances of lightning, albeit this signal less clear compared with NWP guidance yesterday. Retaining SLGT for now, but may need a downgrade if this trend continues.
Conversely, parts of Ireland/Northern Ireland may need an upgrade to SLGT, especially northern and western areas.
 

post-11178-0-58966500-1437036071_thumb.p

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I would say I am in with a good chance of seeing some action tonight :-) that's brilliant because us in Lincolnshire always miss out .........*dons crash helmet* :rofl:

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Level 2 by estofex? They've got to be kidding.

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