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Convective / Storm Discussion - 31st July onwards 2013


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Posted
  • Location: Cheltenham,Glos
  • Weather Preferences: Thunderstorms :D
  • Location: Cheltenham,Glos

    New thread here. Enjoying all your reports, photos and videos. Good luck again everybody. Posted Image

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    Maybe this will come together or maybe we're talking a day of cloud and rain.

    They mentioned Wales so I'm guessing the latter.

    UKWW suggests a chance of elevated storms across C areas/parts of Wales later today as the front clears

    Warm front brings heavy rain to much of Ireland and central England today. Some potential for elevated thundery activity on the southern flank of the warm front as Cape values increase and nudge northwards central England.

     

    The NASA model looks interesting for Saturday

    Posted Image

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    Posted
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)
  • Location: Caterham-on-the-hill, Surrey, 190m asl (home), Heathrow (work)

    Those in ROI maybe more interested in this:

     

    Valid: 31/07/2013 1000z to 01/08/2013 0600z
    Headline: ... THERE IS A SLIGHT RISK OF SEVERE STORMS FORECAST ...

     

    post-1052-0-77731700-1375266607_thumb.jp

    Synopsis
    A slow-moving long-wave upper trough continues to amplify to the W and NW of Europe, warm air advection spreads north today behind warm front lifting north across the UK and Ireland this morning. A cold front moves in from the SW across Ireland this afternoon into an increasingly warm, humid and unstable airmass across Ireland and SW UK.

    SLIGHT RISK FOR IRELAND

    Warm and moist airmass will advect north across Ireland and Sern UK this afternoon behind warm front lifting north, with a plume of steeper lapse rates moving in from the SW across Ireland and SW UK at the same time. If the general cloudiness across Ireland clears this afternoon from the SW, then insolation will likely create an increasingly unstable atmosphere as lapse rates steepen atop of warm/moist airmass, with CAPE values of 500-900 j/kg possibly realised. If convection does develop, it will do so in an environment characterised by moderate deep layer shear with values of 30 to 50 knts and low-level shear of  20-30 knts ahead of approaching cold front. So any storm developing may have the potential to rapidly organise into line segments towards the cold front, with perhaps a supercell or two where cells are more discrete. Any storms may bring the risk of strong wind gusts, excessive rainfall with risk of flash-flooding and hail. Given low Lifted Condensation Levels (LCLs) below 600m, an increasingly moist boundary layer and marked backing of surface winds, strong storm-relative helicity could mean stronger updrafts produce rotating mesocyclones - perhaps lowering to produce a tornado or two. Therefore have issued a SLIGHT risk for Ireland.

    SW ENGLAND, WALES and THE MIDLANDS

    A more isolated risk of convection here this afternoon where cloud breaks occur above an increasingly warm and humid airmass, lapse rates may steepen enough to allow rising parcels high enough to form heavy showers and perhaps a few thunderstorms, with a risk of gusty winds, hail and flash-flooding.

    Issued by: Nick Finnis

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    Posted
  • Location: Co. Down, Northern Ireland
  • Weather Preferences: Lightning
  • Location: Co. Down, Northern Ireland

    Those in ROI maybe more interested in this:

     

    Valid: 31/07/2013 1000z to 01/08/2013 0600z

    Headline: ... THERE IS A SLIGHT RISK OF SEVERE STORMS FORECAST ...

     

    Posted Imageconvmap_310713.jpg

    Synopsis

    A slow-moving long-wave upper trough continues to amplify to the W and NW of Europe, warm air advection spreads north today behind warm front lifting north across the UK and Ireland this morning. A cold front moves in from the SW across Ireland this afternoon into an increasingly warm, humid and unstable airmass across Ireland and SW UK.

    SLIGHT RISK FOR IRELAND

    Warm and moist airmass will advect north across Ireland and Sern UK this afternoon behind warm front lifting north, with a plume of steeper lapse rates moving in from the SW across Ireland and SW UK at the same time. If the general cloudiness across Ireland clears this afternoon from the SW, then insolation will likely create an increasingly unstable atmosphere as lapse rates steepen atop of warm/moist airmass, with CAPE values of 500-900 j/kg possibly realised. If convection does develop, it will do so in an environment characterised by moderate deep layer shear with values of 30 to 50 knts and low-level shear of  20-30 knts ahead of approaching cold front. So any storm developing may have the potential to rapidly organise into line segments towards the cold front, with perhaps a supercell or two where cells are more discrete. Any storms may bring the risk of strong wind gusts, excessive rainfall with risk of flash-flooding and hail. Given low Lifted Condensation Levels (LCLs) below 600m, an increasingly moist boundary layer and marked backing of surface winds, strong storm-relative helicity could mean stronger updrafts produce rotating mesocyclones - perhaps lowering to produce a tornado or two. Therefore have issued a SLIGHT risk for Ireland.

    SW ENGLAND, WALES and THE MIDLANDS

    A more isolated risk of convection here this afternoon where cloud breaks occur above an increasingly warm and humid airmass, lapse rates may steepen enough to allow rising parcels high enough to form heavy showers and perhaps a few thunderstorms, with a risk of gusty winds, hail and flash-flooding.

    Issued by: Nick Finnis

    If only the risk was more to the north :( This would be great to see!

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    Posted
  • Location: Lancaster and East Devon
  • Location: Lancaster and East Devon

    GFS keeps showing things looking like they will be good on Saturday, good pool of CAPE moving east, this at 3am..

    Posted Image

    Only for it to be virtually gone 6 hours later, and get even less through Saturday despite surface heating.. 

    Posted Image

     

    This seems to have happened a lot recently apart from one day, Ireland/Scotland get the best instability to the west while the near continent gets the big storms associated with warmer air masses, and not much in between most days.. and this pattern shows no sign of ending on the GFS :/

     

    That's the problem with seeing a bit of convective action.. I want more lol.

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    Posted
  • Location: Kildare, Ireland
  • Location: Kildare, Ireland

    Will post if anything interesting does get going here! My biggest concern is the lack of solar heating which is often the party pooper in these scenarios

     

    a current temp of 15.8c

    rh 90%

    dp @ 14.2c

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    Posted
  • Location: Co. Down, Northern Ireland
  • Weather Preferences: Lightning
  • Location: Co. Down, Northern Ireland

    There seems to be a lot of CAPE where I am on Friday, nice negative lifted index values as well. Hopefully it will be put into action, I'm really hoping so!

    Posted ImagePosted Image

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    Posted
  • Location: Sunderland
  • Weather Preferences: Hot Summer, Snowy winter and thunderstorms all year round!
  • Location: Sunderland

    Skywarn have also issued a convective forecast ....

     

    "

    SKYWARN UK SEVERE THUNDERSTORM WATCH #027ISSUED: 0100UTC WEDNESDAY 31ST JULY 2013

    SKYWARN UK FORECASTS THE POTENTIAL FOR SEVERE THUNDERSTORM CONDITIONS AS FOLLOWS:HEAVY RAIN LEADING TO A RISK OF LOCALISED FLOODING - WALES, MIDLANDS & NORTHERN ENGLANDSTRONG, POTENTIALLY DAMAGING WIND GUSTS - MIDLANDS & NORTHERN ENGLANDBRIEF POTENTIALLY DAMAGING TORNADOES - MIDLANDS

    IN EFFECT FROM 1000UTC UNTIL 2000UTC WEDNESDAY 31ST JULY 2013

    WARM FRONT ADVANCING NORTHEAST WITH A MOIST AND SLIGHTLY UNSTABLE AIRMASS, IN A FAVOURABLE SHEAR ENVIRONMENT FOR ORGANISED THUNDERSTORMS

    DISCUSSION:THERE IS FAIR MODEL AND PARTNER AGENCY CONFIDENCE IN THE POSSIBILITY FOR SEVERE THUNDERSTORM RISKS DURING THIS PERIOD. A LOW TO THE WEST ENCOURAGES A WARM AND VERY MOIST AIRMASS NORTHEASTWARD, GENERATING AMPLE DEEP MOISTURE CONVERGENCE AND HIGH SURFACE DEWPOINTS THROUGH WALES AND THE MIDLANDS. WHILE THE FRONT ITSELF IS STABLE DUE TO PRIOR CLOUD COVER, SPARSE BREAKS BEHIND MAY ALLOW FOR LOCALISED CAPE BUILD UP OF UP TO 1000J/KG IN THE MOIST ENVIRONMENT. THIS WILL FOSTER INSTABILITY IN A WELL-SHEARED ENVIRONMENT, WITH SUFFICIENT 0-3KM AND 0-1KM SHEAR FOR ORGANISED CONVECTION, STRONG GUSTS AND POSSIBLE TORNADOES. THE HIGH PWAT VALUES OF NEAR 4CM WILL ALSO ALLOW FOR INTENSE RAINFALL TO OCCUR WITHIN MATURE CELLS, POSSIBLY LEADING TO FLASH FLOODING OVER THE HIGHER GROUND OF THE WATCH AREA. THE LIKELIHOOD OF CONVECTIVE INITIATION IS DEPENDENT UPON THE FEED OF LOW LEVEL MOISTURE AND SUNSHINE, AND IS THUS ONLY CONDITIONAL AND NOT GUARANTEED. THIS WATCH MAY BE UPDATED OR UPGRADED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

    SPOTTER ACTIVATION IS REQUESTED AND SPOTTERS ARE REQUESTED TO REPORT ALL FACTORS EXCEEDING ACTIVATION CRITERIA."

     

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    Posted
  • Location: Newton-le-Willows, Warrington, Merseyside
  • Location: Newton-le-Willows, Warrington, Merseyside

    This warm front seems to have stalled as a stream of rain runs into England ATM.

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    Posted
  • Location: Belper, Derbyshire
  • Weather Preferences: Thunderstorms
  • Location: Belper, Derbyshire

    GFS 6z shows some decent CAPE for this afternoon as this rain band clears, supposing it does clear in time. Already some heavy showers developing around Worcester and Coventry post warm front. Infact a band seems to forming from Swansea to the Wash, these need watching IMO.

     

    And for tomorrow:

     

    Extended ForecastValid: Thu 01 Aug 2013 06:00 to Fri 02 Aug 2013 06:00 UTCIssued: Wed 31 Jul 2013 05:03Forecaster: TUSCHY

    post-2719-0-41961200-1375281655_thumb.pn

    A level 1 was issued for Ireland mainly for heavy rain, severe wind gusts and tornadoes. An isolated large hail event is possible, too.SYNOPSIS and DISCUSSIONA potent upper trough continues to amplify west of Europe with strengthening ridging downstream over S/C Europe. Another upper trough over N-Europe weakens and breaks open into a closed low which exits the N-Baltic Sea to the southeast.An extensive surface high pressure area over most parts of Europe keeps conditions stable regarding initiation of deep moist convection.Scattered thunderstorms are expected to develop from C-Sweden, S-Finland further to the SE. This activity evolves along and ahead of a gradually eastward moving surface cold front. DLS of 15 m/s might support an isolated organized thunderstorm event with large hail the primary risk. A marginal level 1 may be added in later outlooks in case CAPE either remains in the 500 to 800 J/kg MLCAPE range or even improves over S-Finland.An augmented severe risk might evolve over Ireland and parts of UK. A warm front continues to lift north with a N-S aligned cold front approaching slowly from the west. Hence a broad warm sector covers most of Ireland and UK during the forecast. Some improvement of the mid-level lapse rates is likely with a northward spreading EML plume, which finally covers S/C-UK during the afternoon and evening hours. Rich BL moisture with mean BL mixing ratios in excess of 11 g/kg and improving lapse rates offer increasing MLCAPE over most parts of UK in the order of 500 to 1000 J/kg. Further west, over Ireland, the characteristics of a true subtropical air mass with weak lapse rates remain, which also lowers MLCAPE build-up substantially. Only SW/W Ireland might see 400 to 800 J/kg MLCAPE due to deepening BL moisture along the gradually eastward moving cold front.Initiation over Ireland will be most probable due to the eastward sliding cold front and the placement beneath the left exit region of a powerful 40 / 50 m/s 500 / 300 hPa jet streak. 20 to 30 m/s DLS overspread the cold front and should offer plenty of shear for temporarily organized storms. The near parallel alignement of the cold front to the jets should support rapid thunderstorm clustering and upscale growth with numerous clusters affecting and leaving Ireland to the north. A sub-1000 hPa depression just west of Ireland increases ageostrophic deflection of the BL wind field, so substantial LL shear (15 m/s and 200 m^2/s^2 SRH-1) is forecast. Combined with LCLs blow 800 m, an enhanced tornado risk exists with any more discrete thunderstorm. Otherwise, severe wind gusts and flash flood producing rain is possible. The level 1 was extended towards E-Ireland mainly for the rainfall risk.Further east over UK, missing forcing and moderate capping keep CI probabilities low for now. Foci for isolated initiation could arise along inland moving sea-breeze fronts or along a confluent LL flow regime over N-UK/Scotland during the afternoon hours onwards, but confidence in that scenario remains too low for issuing a level 1 that far out. In case of CI however, strong shear and moderate CAPE would support organized convection with large hail, strong to severe wind gusts and an isolated tornado event. A 50-% lightning area was added for the offshore areas just E of UK due to persistent signals of an overnight thunderstorm cluster.

    www.estofex.org

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    Posted
  • Location: Newton-le-Willows, Warrington, Merseyside
  • Location: Newton-le-Willows, Warrington, Merseyside

    The warm front is making painfully slow progress northwards. Should feel much warmer here soon as the warm sector takes hold.

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    Posted
  • Location: Grimsby
  • Weather Preferences: Severe weather.
  • Location: Grimsby

    Cape values very high for some tomorrow and overnight Thursday, am I right in believing that despite this nothing is likely to happen due to very high levels of CIN?

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    Posted
  • Location: King’s Lynn, Norfolk.
  • Weather Preferences: Hot and Thundery, Cold and Snowy
  • Location: King’s Lynn, Norfolk.

    Seen some very tornadic looking skies North and East of Peterborough, saw some real low level cloud moving at a rapid pace, pity I didn't have my camera on me.

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    Posted
  • Location: Darlington
  • Weather Preferences: Warm dry summers
  • Location: Darlington

    Synopsis:

     

    A sharpening upper trough over the Atlantic amplifies the jet pattern, forcing the jet and a surface frontal zone to move progressively northwards across the British Isles. Behind the front, a very warm, moist airmass is advected northwards, particularly across England and Wales.

     

    Discussion:

     

    Behind more general stratiform rain along the warm front, increasing insolation in the warm, humid airmass will build 500-800 J/kg SBCAPE across the shaded ISOL areas. There appears to be a small zone of opportunity, beginning across the West Country/SE Wales and also W Munster around noon, and shifting progressively northwards and eastwards with time towards the northern extent of the ISOLs by 17z-18z onwards; to the south, this will be replaced by continuous warm air advection in the lower levels, providing a significant cap which will continue to shift northwards through the afternoon and evening.

    Within the ISOL and to the south/behind the surface front, if any sufficient insolation can develop and utilise the available CAPE there is scope for a few scattered showers or thunderstorms to form during the afternoon and early evening hours, in an environment of 40-50kts DLS enabling such cells to become well-organised. Low LCLs and a favourable vertical wind profile on forecast soundings suggest the potential for an isolated tornado event, the risk greatest if cells can form immediately behind the surface front where low-level flow will be increasingly backed (albeit with more excessive cloud likely to be present). Indeed, with close proximity to the surface front, there may be the (rather low) potential for a low-topped supercell to develop.

    Given the degree of uncertainty currently, especially since there is some inter-model disagreement on timings of front clearance, we remain with an ISOL threat for now, but with the potential to upgrade to SLGT during Wednesday as and when necessary.

     

    http://ukasf.co.uk/storm-forecasts/265

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    Posted
  • Location: Belper, Derbyshire
  • Weather Preferences: Thunderstorms
  • Location: Belper, Derbyshire

    Yes i don't think that ukasf forecast is still valid now considering the caveats of the speed the front clears have come to play in keeping surface temps down over the risk area.

     

    Tomorrow looks explosive if only the cap can be broken. Looking at the skew-T it would probably take a temperature of 31c along with a dewpoint of 16c to do this.

     

    I am new to Skew-T's so any advise welcome but from what I can see you would need a temperature of 30c with a dp of 18c to break the cap at 6pm in Birmingham. If the dp is lower then the temp would need to be higher.

     

    post-2719-0-30163600-1375292563_thumb.gi

     

    In Newcastle we would need a temp of 26c at 6pm with a dp of 18c.

     

    post-2719-0-44231100-1375292703_thumb.gi

     

    In other words, I think the cap tomorrow will be too strong in the south, touch and go in the north.

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    Posted
  • Location: Brongest,Wales
  • Weather Preferences: Stormy autumn, hot and sunny summer and thunderstorms all year round.
  • Location: Brongest,Wales

    Risk of convective weather?Posted Image

     

    No chance of that around here today, its been overcast with bits of drizzle all day.

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    Posted
  • Location: West of Ireland
  • Location: West of Ireland

    Trying to get someone to chase out west 2moro here in Ireland !!!! #hatenothavingacar !!!! 

    You think there's a risk of thunderstorms here 2moro?!!

     

    Edit: just saw estofex forecast above, looking good for us!

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    Posted
  • Location: Stanwell(south side of Heathrow Ap)
  • Weather Preferences: Thunderstorms, squally fronts, snow, frost, very mild if no snow or frost
  • Location: Stanwell(south side of Heathrow Ap)

    I like the weather front on Nick F's storm risk map! not seen those on one before. Is this something new or was it a special?

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    Posted
  • Location: STEVENAGE, HERTS (100M ASL)
  • Location: STEVENAGE, HERTS (100M ASL)

    Are we still on for storms on Fri eve in the east / south east? GFS cape doesn't look too great now :(

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    Posted
  • Location: Nairn
  • Location: Nairn

    Synopsis:

    Atlantic upper trough continues to sharpen west of Ireland, the forward side situated over Ireland and western Britain during Thursday. A very warm, moist airmass characterised by high WBPT is advected northwards within the warm sector of a surface frontal system. Warm mid-levels creates a capped environment across the bulk of England and Wales, albeit with improving mid-level lapse rates through the day as an EML plumes slides northwards across C/E Britain. Meanwhile destabilisation will result in thunderstorms across parts of Ireland and western Scotland.

     

    Discussion:

    ... REPUBLIC OF IRELAND, NORTHERN IRELAND, W SCOTLAND ...

    Along and behind the surface cold front, cooling mid/upper levels and the placement of the left exit of the upper jet will generate 600-800 J/kg CAPE, and is likely to lead to the development of scattered thunderstorms, particularly across SW and S Ireland from the latter half of the morning onwards. With a strong jet aloft, some 40-50kts DLS will allow cells to become well-organised, forming multicell clusters and becoming quite linear/backbuilding given rather parellel flow throughout the vertical. Such clusters/lines of thunderstorms are then expected to continue to drift towards the N/NNE, particularly across western parts of Ireland, through the afternoon and evening hours.

    A surface low centre offshore over the Atlantic will migrate northwards through the afternoon, backing the low-level winds across Ireland and increasing SRH and low-level shear, thus increasing the potential for a supercell to develop if any thunderstorms can remain discrete. Even with clustering, given strong shear embedded mesocyclones are possible capable of producing a tornado. The strongest cells have the potential to produce hail 2.0-3.0cm in diameter, and given PWAT values of 35-40mm initially, some flash flooding is possible in places from prolonged torrential downpours and backbuilding over similar areas. Therefore, a SVR threat level may be introduced for W and SW Ireland to cater for the excessive precipitation, moderate-sized hail and tornado threat if conditions continue to look favourable by Thursday morning.


    ... NE, N, NW, W + SW SCOTLAND, IoM, NW WALES, CORNWALL ...

    As the cold front continues to advance from the west, an increase in elevated convection is expected through the evening hours, particularly towards the very end of the forecast period (ie towards midnight). As a result, have introduced an ISOL to cater for potential elevated lightning activity late in the day.


    ... E/NE ENGLAND, SE SCOTLAND ...

    With an EML plume advected northwards through the day, capping will subsequently increase, inhibiting SB-convection. However, strong insolation resulting in surface temperatures peaking at 25-30C, seabreeze convergence and upslope flow/orographic forcing may allow isolated convection to occur, utilising some 1000-1300 J/kg SBCAPE. 40kts DLS and backed surface winds, particularly near the east coast with onshore surface wind component, suggest the potential for supercell development, capable of producing hail 2.0-3.0cm in diameter and a tornado. PWAT near 35mm would also increase the risk of flash flooding from torrential downpours. However, given some uncertainty over initiation (eg several models remain capped, and in recent runs are less-backed at the surface) have included an ISOL for now, but with the potential to upgrade to SLGT and/or SVR threat levels. In either case, if initiation does occur it is likely to be quite late in afternoon or even into the evening.

     

    http://ukasf.co.uk/storm-forecasts/266

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    Posted
  • Location: STEVENAGE, HERTS (100M ASL)
  • Location: STEVENAGE, HERTS (100M ASL)

    Seems met office are downgrading the risk on Friday...

    There is a low probability that heavy, thundery showers may affect parts of southeastern England later on Friday and at first on Saturday.

    Since the issue of this Alert yesterday, the probability of heavy rain appears to have decreased, and if this trend continues, the Alert could yet be removed. But for the moment, the public should be aware that there is a possibility of localised disruption, should this occur.

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    Posted
  • Location: Warminster, Wiltshire
  • Location: Warminster, Wiltshire

    Risk of convective weather?Posted Image

     

    No chance of that around here today, its been overcast with bits of drizzle all day.

    Interesting to read this thread for the first time today as after the early drizzle had cleared there was some warm sun in the West Wiltshire area amongst a lot of low Stratocumulus and mist.

    When the sky cleared a little it was possible to see plenty of Altocumulus suggestive of a disturbed atmosphere and, on our way to Salisbury late morning, we drove through several brief sharp showers with large convective drops ; this surprised me until I read posts made earlier in the day.

    Since midday though it's been mostly cloudy, increasingly humid and is now drizzly again.

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    Posted
  • Location: Douglas, Isle of Man - 380ft/116m ASL
  • Weather Preferences: Warm summers, cold winters.. How it should be!
  • Location: Douglas, Isle of Man - 380ft/116m ASL

    Wind picking up here now. Temperature 16°C, dewpoint 16°C....

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