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Thunderstorm Outlook - Mon/Tues 28/29th

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Author Topic: Thunderstorm Outlook - Mon/Tues 28/29th  (Read 928 times)
martinastro
Martin Mc Kenna
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« on: July 27, 2008, 11:08:58 pm »

There is alot going on here. Britain is a very interesting place to be for storms this week. First forecast from ESTOFEX.



Storm Forecast
Valid: Mon 28 Jul 2008 06:00 to Tue 29 Jul 2008 06:00 UTC
Issued: Sun 27 Jul 2008 21:18
Forecaster: GROENEMEIJER

DISCUSSION

France, British Isles, Benelux, W Germany...

During the afternoon, 1000-2000 J/kg MLCAPE will likely form over northern France, extreme W Germany and the Benelux. There, dew points near 20 C are expected. Scattered thunderstorms will probably develop, that could produce some localized large hail and flash flooding problems. Shear is weak in this area.

Isolated storms are expected to develop over Great Britain and eastern parts of Ireland as well, where CAPE should be a bit lower.

Towards the evening, moisture is expected to spread further westward across W France and southern England on approach of the upper-level system. As deep-layer shear increases to 15-20 m/s and forcing for upward vertical motion overspreads the area, convective storm activity is expected to increase. A likely scenario is that convective storms form over western France during the afternoon and merge into a large MCS moving into England.

With 850 hPa winds near 15 m/s some strong and locally severe wind gusts are possible on the passage of this system. Overnight, as the system moves slowly, large amounts of precipitation will likely accumulate across southern and southwestern England, so that flooding problems are likely to occur there.

Balkans...

Across the indicated area of the Balkans rather widespread thunderstorms are expected to develop. Low to moderate CAPE and weak shear suggest that the threat of severe weather will be low. rather slow-moving storms could, however, cause some local flooding problems.
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martinastro
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« Reply #1 on: July 27, 2008, 11:12:04 pm »

From UKWeatherworld...

There is nothing in the 12Z Suite of model guidance that goes against earlier ideas.  WV imagery shows the major longwave trough currently to the west of Iberia. Ahead of this an area of advancing high WBPT air is moving north (showing marked Mid level instability already to the west of Biscay.  This plume moving NE and merging with the plume already in the N Sea and effectively expanding the area to cover England by tomorrow evening. Greater than 18C WBPT air in the SE by then so quite juicy to say the least.

Aforementioned trough swings NE and extends then partially disrupts leaving an active part of the trough and slow moving upper level low over the Celtic Sea by 00Z Tues. THis is quite a complex development.  Large scale ascent takes place ahead of this trough with large amounts of PVA at 500 and 300mbs and large scale 700mb Vertical Velocity, this effectively meaning that above this plume, the airmass will be destabilising and become very unstable. 

During the afternoon Surface Convection may develop from London up through the Midlands to NW England and Wales (temps again nr 30C) spawning scattered T-Storms and downpours.  More general cloud dervied from an ELevated Moist Layer will move NE towards the SW.  Models are consistent in at least one MCS developing over N France and swinging NW. It is unclear whether this will be derived from the B/L however given the type of event and time of day it seems likely that most of the activity coming NE tomorrow evening and night will be from Mass synoptic ascent and therefore derived from above the B/L. However feeding from possible homegrown events means there may be a mixture.

Even Global Models and their limited resolution are indicating 20-30mm falling in some places within a few hrs and up to 50mm is possible in isolated spots in a 6hr period.  Locally Gusty winds and Strong Thunderstorms are possible if MCS's develop and move N.  Isolated Hail is possible =if= any severe storms develop.

Rain will move NE into Tuesday with increasing trends towards a curling occlusion developing bringing more rain into the SW and Wales on Tuesday.

From Tony Gilbert...

Whilst further general thunderstorms are on the cards for Monday. Once again initial convection is likely to be delayed well past the suggestion of the GFS model. Upper saturation inhibits potential instability and surface temps are less that what we saw for Sunday. So low level lapse rates may be less than what we saw today (Sun). An environment of weak shear and less convergence will all but preclude any severe weather potential. GFS are once again overdoing the CAPE.

Storms likely to be more wide spread across UK and NW Ireland but I see limitations here!

PS. Watch out for Tues is my advice!

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martinastro
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« Reply #2 on: July 28, 2008, 11:08:06 am »

UPDATE 8.45am Mon by Tony Gilbert



Slight Risk Gen Tstorms 12Z-21Z UK and Ireland

Slight Risk of Strong Tstorm & Tornado Development 21Z-03Z Tues Wales

As per earlier forecast for gen thundery activity today though GFS are now more generous with moisture advection earlier in period.

Specific attention is focused on a small prefrontal trough which looks to develop late evening and move north effecting Wales and parts of Glouc region. Strong low level jet overruns the last of the instability creating a moderately sheared environment. It is quite possible that a notable increase in convective activity could take place with the added risk of tornado development. This specific part of the forecast requires a later update.

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« Reply #3 on: July 28, 2008, 11:47:27 am »

North Antrim - Nothing imminent according to my migraine status
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martinastro
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« Reply #4 on: July 28, 2008, 12:12:17 pm »

Altocumulus Castellanus visible over Maghera at minute. Very warm and humid to. Feels encouraging.
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« Reply #5 on: July 29, 2008, 12:14:29 am »

Im just back from walking the dog and to my east looking out the Irish sea there was some electrical activity but it was to far away for any audio i have a feeling it might disspate by the time it reaches land.
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« Reply #6 on: July 29, 2008, 12:32:46 am »

A couple of distant booms here about 2300BST but saw no lightning!
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martinastro
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« Reply #7 on: July 29, 2008, 12:37:38 am »

Thanks for the reports guys!. There are heavy showers and t-storms in Ireland at the minute but nothing showing on radar near N. Ireland, however a batch of showers leaving Wales are to cross the Irish Sea later tonight. May hit during the morning. Will keep an eye out here. It's clear at the moment with mist and fog.

No show at my end today. Darn hot though!!. Another outlook has been issued for Tues.
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martinastro
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« Reply #8 on: July 29, 2008, 12:41:52 am »

Tuesday's outlook from Tony Gilbert.



Slight Risk Gen Tstorms UK & Ireland 09Z-21Z

Further general thunderstorms possible through Tues as better moisture spreads NE through the said period. Wrapped occlusion expected to set off some rather sharp thunderstorms within a contued unstable environment. Upper troughing finally edges NE increasing lapse rates at all levels of the atmosphere. Lowered freezing point will mean that small hail showers are much more likely to accompany these storms. The shear tries very hard to avoid the occlusion as it runs around it periphery but some overlap is inevitable suggesting that tomorrow has a slightly better potential for stronger thunderstorm activity than of recent days. Conditions will need to be monitored to assess as to what degree this risk will develop.

Tornadoes at this point cannot be rules out but shear looks to me rather straight lined ATM and speed shear will not compensate.

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« Reply #9 on: July 29, 2008, 12:57:52 am »

OK Martin, my migraine is just starting so maybe something will happen.

Also the medium level cloud which was around all day cleared up at dusk, but still very hazy, calm, humid & warm but about half an hour ago stratocumulus started forming, a force 4 wind has appeared from somewhere and the temp has jumped from (min) 17.2 to 18.4. No immediate signs of thundery activity though.
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« Reply #10 on: July 29, 2008, 08:47:02 am »

Hi Martin, Just to let you know that there was thunder in Dromore & Banbridge area this morning!
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Thanks,
         Steven..

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martinastro
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« Reply #11 on: July 29, 2008, 11:39:10 am »

Thanks for that Steven!

TORRO CONVECTIVE DISCUSSION 2008/017

A TORRO CONVECTIVE DISCUSSION has been issued at 0900GMT on Tuesday 29th July 2008

Valid from/until: 0900-1900GMT on Tuesday 29th July 2008 for the following regions of the United Kingdom & Eire:

Much of Eire

N Ireland

Scotland

Much of England

Wales

THREATS

Isolated tornadoes, marginally severe wind gusts, CG lightning, hail, torrential rain.

SYNOPSIS

Plume of moisture and cold front across N England and portions of Eire/N Ireland will continue to move north and west through today. Ahead of this across N Scotland, diurnal heating should provide sufficient low-level theta-e for thunderstorm development later this morning and through this afternoon. Shear will be sufficient for multicell storms capable of producing marginally severe wind and hail. Post-front, across the remainder of the forecast area, surface heating will promote the development of scattered showers and thunderstorms, in a regime characterised by weak to moderate shear values. Gusty winds are possible, and given quite steep low-level lapse rates, isolated tornadoes too. Northern parts of Wales could be most at risk from the latter, with backed surface flow relative to the 850 flow. N Ireland and parts of NW Eire could also see backed surface flow, and a tornado risk.

At this stage, WATCHES are not anticipated. However, the situation will be monitored, especially across N Scotland

Forecaster: RPK.


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« Reply #12 on: July 29, 2008, 11:42:36 am »

Went for a walk this morning, obvious signs of convective activity but what I saw of the heads looked more like cumulus congestus than cumulonimbus. Saw no lightning, heard no thunder, precipitation a few minutes of very light drizzle from stratus fractus under the darker patches. No feeling of "electric charge" in the air but very muggy despite a steady force 3-4 SE breeze, with no gusts or sudden direction changes which would be typical of strong convective activity.

Looking to the SW right now, apparently the back edge of a front or trough, a line of transparent clear sky is appearing.

I wish it would thunder (and, having been struck 3 times by lightning within 20 minutes whilst in the French Alps, I really hate it) - perhaps it would cool down enough to be able to sleep!
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martinastro
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« Reply #13 on: July 29, 2008, 12:19:51 pm »

I stayed up to 05.00 last night and seen nothing of interest except some convection over the Sperrins. Went to bed shattered. In my sleep during the early morning I head torrential rain outside. I was gutted to hear about the convective activity at this stage. However, today and Wed looks very interesting.

At the moment I can see good cumulus congestus clouds with towers tilted over with obvious wind shear. A good visual cue for organized storm and funnel/tornado development if these turn into Cbs.

Brian, If you don't mind sharing, I would be fascinated to hear more about your lightning strike encounters. A lady from the UK emailed me sometime ago and described how she saw her friend get hit and killed by a c-g about 6ft away. I would love to hear from someone who has got directly hit.
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martinastro
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« Reply #14 on: July 29, 2008, 03:30:26 pm »

Very good convection in the form of widespread cumulus towers. Very impressive line over Slieve Gallion all afternoon, no doubt enhanced by tropographic lifting. No cbs visible yet though. Some showers have moved into eastern parts of N. Ireland now. Might turn thundery.

Met Office have a severe weather warning for N. Ireland on Wed.
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