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Jane Louise

Uk General Convective Discussion & Forecasts, 28th August 2012>

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Carry on your discussion here folks.smile.png Let's hope we see a few more out of the NSC tomorrow.Good luck y'all wink.png Now let's chase those stormsbiggrin.png

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Good luck all,Have you managed to get out of the NSC yourself Jane?I got out with 2 storms a few weeks ago.

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CALM BEFORE THE STORMS HVY RAIN .well lets hope this wed /thurs gives plenty of us some good action as fri onwards we have the possibility of zilch for a while .already looking good on sat and radar to our far west and s/west ,best of luck gang ,i hope to be about tomorrow providing power doesnt go down with storms [heres hoping ]cheers .

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CALM BEFORE THE STORMS HVY RAIN .well lets hope this wed /thurs gives plenty of us some good action as fri onwards we have the possibility of zilch for a while .already looking good on sat and radar to our far west and s/west ,best of luck gang ,i hope to be about tomorrow providing power doesnt go down with storms [heres hoping ]cheers .

hey mate i saw your post in the USA thread where you stated you saw some good storms? where abouts were you when these happened?

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I'm off work this week so let's hope so!

that little cell passed over here about an hour ago and gave us on west mendip big spots of rain but only for about 5 mins .i can now see it on radar over north bristol ,PERHAPS a taster for tomorrow , me and my wifes rumatism playing up so something is on its way ,all of tonights charts and data also satellite images looking good for tomorrow lets just hope the synoptics all fall in place tomorrow ,must be getting tired as rheumatism was spelt wrong and punctuation all over the place ,catch up with you all tomorrow ,cheers legritter.

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So, lets check.

Metoffice looking good, well very good actually, tafs looking good, charts looking good. Could this be my turn?

Surprised to see Liverpooll airport, EGGP being very bullish with a 40% prob of heavy thunderstorm rain from 01Z to 09Z tomorrow, and again, heavy thunderstorm rain and small hail from 10Z to 18Z. As I say, looking good.

Get in!!

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hey mate i saw your post in the USA thread where you stated you saw some good storms? where abouts were you when these happened?

just noticed your post ,i will keep it short but will try and reply soon ,but basically we had a good storm in NEW YORK around the end of may , it was fantastic as from our hotel window you could see the flashes in other buildings windows .then spent june in Toronto area also LAKE HURON and also visited QUEBEC .most of the severe stuff seemed to miss us by about 10miles [AS USUAL ]BUT STILL SOME GOOD ONES .I CHECKED ON NET WEATHER MOST DAYS AND THE uk WAS HAVING A GOOD time storm wise as well .indeed on canadian weather channels britain got mentioned most days .we had a very powerfull daytime storm when we were walking in the niagra escarpment ,indeed although i am mad about storms it got a bit scary even for an old soldier .i could go on for ages about the holiday ,but perhaps some other day ,anyhow off to get some sleep as need to be alert for tomorrows ,hopefully storms .cheers

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My forecast for Wednesday, pretty widespread risk of storms in post frontal airmass.

Valid: 29/08/2012 06:00 - 30/08/2012 06:00

Headline: ... THERE IS A RISK OF THUNDERSTORMS FORECAST...

post-1052-0-60239500-1346195275_thumb.jp

Synopsis

Deep upper trough to W of the British Isles Tues night will begin to shift eastwards across the UK on Wednesday. Surface depression to W of Ireland will drift NE and expected to be centred close to the N coast of Ireland around 998mb by 12z Weds, while associated occluding cold front lies Whitby - Bournemouth with unstable post frontal airmass following with troughs in the flow moving east.

... ENGLAND, WALES, SCOTLAND and EIRE ...

Some potential exists for linear convection to develop with passage of occluding cold front which is indicated to be overlapped by fairly strong DL Shear (40-50knts) and low-level shear (15-20 knts) ... which suggests a strong wind gust threat and perhaps a tornado can't be ruled out. However, there is uncertainty over whether any strong/deep convection will occur - with GFS unkeen on the idea, so will not highlight a severe risk area.

Otherwise, post frontal airmass will be characterised by steep low-mid level lapse rates as colder mid-level air (at or below -20C) spreads in from the west with arrival of upper trough. Steep lapse rates, surface heating, large scale ascent and forced ascent near troughs will favour the development of widespread heavy showers and thunderstorms which will spread NE from fairly early on in the west across most areas by the afternoon following frontal rain pushing east. Overlap of strong jet stream across increasingly unstable post frontal airmass over England and Wales suggests storms could organise into bands - particularly near shortwave troughs moving in - with a risk of localised flooding from prolonged torrential downpours along with strong wind gusts and perhaps hail locally to 2cm or more in size with stronger storms.

Over Ireland, backing winds ahead of approaching surface low moving in close to the W/NW may enhance low-level shear with a tornado or two not ruled out with any stronger cells here

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Maybe not as explosive as saturday was but later today could be fun

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Thanks Nick and just to point out if I'm not reading it wrong that the forecast dates are wrong I think its supposed to be 29/8/12 30/8/12

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Latest NMM model suggests precipitation should increase dramaticly between 2-4am so should be intresting to see what happens :)

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Up watching the Isaac feeds all night so no doubt if anything pops-off in the Irish Sea overnight i'll be catching it on the RADAR, but should look better CAPE wise into the late morning once the sun gets to work.

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Have heard one sferic in the last half an hour on the radio, I think there will be some more lightning before long. Still dry here but the wind has just started to gust sharply.

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Usual old waffle from me again today:

Nothing from ESTOFEX or TORRO so far, must be too early in the day? UKASF broadly backing up the NW forecast (my bolds):

post-6667-0-42887100-1346222060.png

Synopsis:

A mature surface low migrates eastwards under an upper trough, becoming elongated and multi-centred. Widespread showers and thunderstorms are forecast to develop beneath the upper trough, behind an eastward-moving occlusion.

Discussion:

An occlusion will move eastwards (and northwards) across much of Britain during the day, becoming rather fragmented across England. Here, with jet aloft creating 60kts DLS, some line convection/convective elements are possible. Dry air intrusion in the mid-levels, combined with backed surface winds and up to 30kts LLS could lead to bowing segments capable of producing a tornado and/or strong wind gusts. With such saturated profiles, lightning activity, if any, is more likely on the back edge where the dry air intrusion is most pronounced.

In the wake of the front, cold mid-levels (-21 to -23C at 500mb) will overspread much of the British Isles and Ireland, steepening lapse rates substantially. As such, diurnal heating will allow 600-1000J/kg CAPE to be available, with widespread showers and thunderstorms expected to develop.

A few shortwaves will move anticlockwise around the low's periphery, providing an increased focus for shower/storm initiation (primarily NW Eng and W Ireland) with the general steering winds allowing such showers/storms to migrate to the east. Low-level convergence across Scotland and Ireland will also help shower/storm development and organisation, primarily due to proximity to the low's centre, and/or convergence on the trough axis.

Cold and dry air aloft, combined with local strong updrafts, could produce some moderately-sized hail in any stronger cells, potentially up to 3.0cm in diameter. Slow storm motion over Scotland and northern portions of Ireland/Northern Ireland, combined with backbuilding, significantly increases the threat of local flash flooding. Given this criteria, this is borderline SVR in terms of it's impact, but such an event is likely to be quite localised. Currently we are unable to pinpoint any region most at risk (out of Scotland and Ireland/Northern Ireland) but an upgrade to SVR may be necessary on Wednesday to accomodate this risk.

Perhaps attention should also be given to southern Ireland (Munster in particular) during the late afternoon/evening hours where an increase in LLS may allow any showers/storms there to become better organised and may perhaps exhibit supercellular-characteristics, capable of producing a tornado.

SkyWarn also going with Scotland and Ireland to kick of with:

SKYWARN UK SEVERE THUNDERSTORM WATCH #055

ISSUED: 2130UTC TUESDAY 28TH AUGUST 2012 (GJ)

SKYWARN UK HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR THE FOLLOWING REGIONS:

NORTHERN IRELAND SCOTLAND SOUTHWEST ENGLAND WALES NORTHERN ENGLAND MIDLANDS

ISLE OF MAN

IN EFFECT FROM 0000UTC UNTIL 2359UTC WEDNESDAY 29TH AUGUST 2012

SHALLOW LOW PRESSURE UNDER A STRONG CYCLONIC JET INFLUENCE, WITH UNSTABLE FRONTAL AND POST-FRONTAL ENVIRONMENT THERE IS A POSSIBILITY OF SEVERE WEATHER AFFECTING THE INDICATED REGIONS IN THE TIME PERIOD SPECIFIED. THREATS WITHIN THIS WATCH INCLUDE, BUT ARE NOT LIMITED TO: HEAVY RAIN...FLASH FLOODING...STRONG GUSTS...FUNNELS/TORNADOES...LARGE HAIL...FREQUENT LIGHTNING

DISCUSSION:

THERE IS GOOD MODEL AND AGENCY CONFIDENCE OF A SEVERE THUNDERSTORM RISK THROUGH WEDNESDAY, BEGINNING IN THE EARLY HOURS. A SHALLOW LOW ~990MB APPROACHES FROM THE WEST WITH A STRONG JET INFLUENCE OVERTOPPING THE COLD FRONT AND FOLLOWING SHORTWAVES. THE FRONTAL ZONE IS SLIGHTLY UNSTABLE AS MID-UPPER LEVELS COOL, AND SHOULD FRAGMENT OVERNIGHT, WITH BROKEN LINE SEGMENTS LIKELY INTO THE SOUTHWEST WHERE DLS IS STRONGEST. STRONG GUSTS AND TORNADOES ARE POSSIBLE WITH ANY SUSTAINED RADAR ECHOES, WITH THE RISK DIMINISHING FURTHER EAST AS THE UPPER JET MOVES AHEAD AND SURFACE CONVERGENCE DECREASES.

BEHIND THE FRONT, EARLY IN THE MORNING FOR NORTHERN IRELAND AND WESTERN SCOTLAND, AN UNSTABLE ENVIRONMENT IS FURTHER ENHANCED BY DRY AIR ADVECTION ALOFT AND THE ENCROACHMENT OF THE SURFACE LOW. SUCCESSIVE HEAVY SHOWERS AND THUNDERSTORMS MAY PROVIDE A RISK OF HIGH RAINFALL TOTALS FOR THE WATCH PERIOD, WITH COMMENSURATE FLASH FLOODING RISK. DESPITE A LACK OF SHEAR, FUNNELS AND POSSIBLE WEAK TORNADOES MAY OCCUR OWING TO THE EFFECTS OF FURTHER SHORTWAVES AND PROXIMITY TO THE CENTRE. TOWARDS LATE MORNING, INSTABILITY INCREASES ACROSS THE WATCH AREAS OWING TO DAYTIME HEATING WITH GOOD CLEARANCE OF FRONTAL CLOUD. WHILST AGAIN SHEAR IS REDUCED BEHIND THE FRONT, ANOTHER STRONG SHORTWAVE INTO THE SOUTHWEST ENHANCES LOW-MID LEVEL WINDS AND MAY PROVIDE SOME VEERING THROUGHOUT THE WATCH AREAS, LEADING TO FURTHER POSSIBILITIES FOR FUNNELS AND WEAK TORNADOES. WITH THE COLD FRONT HAVING LITTLE IMPACT ON DEWPOINTS, THERE EXISTS A POSSIBILITY OF LARGE HAIL WITH STRONGER STORMS, FIRST EARLY IN THE MORNING WITH OROGRAPHIC INFLUENCE ACROSS THE WESTERN MAINLAND BUT ALSO ANYWHERE INLAND LATER IN THE DAY. THIS WATCH MAY BE UPDATED OR UPGRADED. PLEASE MONITOR WEATHER AND TRAVEL INFO AS NECESSARY.

061152Z_21OWS_ATLANTIC-EUROPE_FITL_THUNDERSTORM-STANDARD_12082912.GIF

061254Z_21OWS_ATLANTIC-EUROPE_FITL_THUNDERSTORM-STANDARD_12082918.GIF

PGNE14_CL.gif

Plenty of CAPE around:

hir_cape_eur12.png

hir_icape_eur12.png

Messy!

hir_layer_eur12.png

hir_lfc_eur12.png

SBCAPE too with spout chances off the North coast of Scotland and Irleand?

hir_spout_eur12.png

Lapse rates increasing, especially in the Irish Sea:

hir_lapse2_eur12.png

Rain through out the day moving through the country from the West:

hir_prec_eur12.png

Widespread tornado possibilities:

hir_stp_eur12.png

hir_srh_eur12.png

Already getting breezy with convective gusts later up to 35kts:

hir_gusts_eur12.png

Chances of thunder through out the day starting in the West:

12_20.gif

Moving through Scotland and the Midlands right down to the SW:

18_20.gif

Exiting out through the North Sea in the early hours:

24_20.gif

Good luck all!

post-6667-0-42887100-1346222060_thumb.pn

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Currently having some very intense rain here as this front pushes through.

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just had that here, nothing special though. Windy now.

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Plenty of it to come I think:

post-6667-0-12147300-1346224630_thumb.pn

12_34.gif

18_34.gif

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Good luck all,Have you managed to get out of the NSC yourself Jane?I got out with 2 storms a few weeks ago.

Hi Raidansmile.png Yes, I managed it Saturday lol. So glad you're out too.biggrin.png

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Nice big rain-drops as the front passes this morning, clearer skies behind look to be making it's way through fairly quickly so i'm hoping to see a dividing line before we get into storm territory later this afternoon into the early evening.

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A few reports from back home about a small thunderstorm in the North West corner of Wales and there seems to be a small evidence on the 8:45am radar. Today is looking good! A few shower activity to the West of Cardiff now!

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ESTOFEX

post-3685-0-60796300-1346228138_thumb.pn

DISCUSSION

... Southern UK ...

Some window for isolated severe threat might exist over this area as the trough with attendant frontal system spread eastwards. The main time-period should be probably the beggining of the forecast period, possibly between 9 and 12 Z as the cyclonically curved jet-streak favorably moves over the region, with some attendant forcing. Consequently, some marginal instability with more than 20 m/s of DLS will be available in the region. Sounding profiles from 00 UTC also suggest quite strong LLS, around 10 m/s and enhanced SREH, as south-southeasterly surface flow underlies the mid and upper level southwesterlies. The biggest limiting factor might be the fact that instability will be marginal and also the factor of embedded storms within larger scale precip. Nevertheless, isolated severe wind gusts and tornadoes are forecast in case that supercells manage to develop in this setup.

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