Storm Forecast
Storm Forecast  Thunder Storms 2009-07-04 00:00 - 2009-07-04 23:59
Statistics
Forecasts Issued
- Watches: 52
- Thunderstorms: 110
- Severe: 5
- Extreme: 0
- Total: 178
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Posted on Tuesday, 26th May 2009 by Mike
Many of our readers will be aware that Bank Holiday Monday`s forecast didn`t go to plan (see blog below for full details).
The main problem was the inconsistency with the models, especially with the first MCS that developed over Biscay/W France on Sunday evening and tracked north. Many, if not all, of the models were indicating it would turn showery and head for the Southwest corner. However, instead it took more of a NNE route through northern France, across the Channel and into the Southeast corner.
Lightning strikes significantly decreased during its crossing over the Channel, and as a result it quickly dissipated with very little rain falling away from the extreme southeast (Kent and Sussex).
However, in its wake it left a lot more cloud cover than any of the models had predicted (which we warned about in the blog below issued some 8-9 hours beforehand). The cloud was also much further east, and this significantly hampered the temperatures. The lack of insolation meant that the maximum reached in the south was 25C, rather than the 28C which had been the forecast the day before.
Due to the change in the path of the MCS, it meant that all the models were incorrect and would then be unreliable for storm forecasting later in the day. It became increasingly apparent during Monday morning that Severe storms would be unlikely across the UK, but still possible across the continent during the evening and night hours. Indeed reports of large hail, severe wind gusts and funnel clouds have been reported from prone areas of North/Northeast France and Benelux.
The extensive cloud cover did eventually break along southern counties during the early afternoon, with the sunshine slowly spreading north. As a result, the temperatures rapidly increased into the 20`s, but it wasn`t high enough to break the cap in most places. Sea breezes allowed a convergence zone to develop along east Kent and the Dover Straits, and satellite imagery reveals convection rapidly developing in a loaded gun type scenario, as did the upper air soundings at the time.
Another convergence line over NW France allowed storms to rapidly develop in under an hour and these then drifted north into the Channel.
The synoptic charts reveal the centre of LOW pressure over West Sussex at 7pm yesterday evening, which is a good indicator as to why the storms moved in the Channel, but then headed east, curving around the coastline of Kent. The plotted lightning strikes on our maps also reveal the path of the storm cores were basically in-line with the Channel, all rotating anticlockwise around the centre of the LOW over Sussex. This explains ground reports from the South Coast indicating that the lightning wasn`t getting any nearer but seemed to be staying out to sea.
Synoptic chart at 7pm Monday evening: 
Further pulses of storms attempted to cross the Channel during the late evening, but yet again they rapidly decayed as they crossed the cold Channel. Despite it being a really poor day for storms across the United Kingdom, no doubt people along the South Coast saw some good lightning at times yesterday.
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| Severe Weather - Bank Holiday Monday |
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Posted on Saturday, 23rd May 2009 by Mike
UPDATE #5 Updated Monday 25th May 2009 at 00:01
The weather over a Bank Holiday weekend in the UK is well-known for being wet and windy. However this time it appears to be behaving itself - at least until Monday.
Please bear in-mind that our forecast just issued is remaining on the cautious side, and is mainly focusing on areas that are 60% certain to see storm development today.
A decaying MCS is forecast to drift into SW England during the late morning, turning increasingly showery but still with the potential for torrential downpours, and as a result a risk of flash flooding. Whilst it may be initially electrically active, it is expected to rapidly decrease in terms of electrical activity as it moves into Wales during the afternoon.
All areas to the east of this (Midlands/E Anglia/SE & CS England) will be in a very favourable evenironment for thunderstom development. Initiation time is likely to be late afternoon into the evening, but once cells start to develop, they may shows signs of turning marginally severe. Cells over SE/CS England are expected to drift northeast and merge into an MCS over Home Counties/E Anglia/E Midlands during the evening, exiting into the North Sea during the late evening. The atmosphere will very favourable to sustain thunderstorms for a large portion of the night. There is a risk of supercellular development, especially for areas within the SEVERE region on the map - this would bring a threat of moderate to large hail, and moderate tornadoes.
Further storms may arrive into the SE corner from the nearby continent, though this risk remains quite uncertain at the moment. Given the very favourable atmosphere, storms will persist for much of the night, slowly moving northeastwards into the N. Sea.
There may be a few problems however:
(a) The decaying MCS forecast to move into SW England - Wales - N England may provide extensive cloud cover, or more cloud cover than the models are currently predicting. This may inhibit thunderstorm growth in some areas due to lack of insolation.
(b) The SE may be used as a breeding ground, where cells may mature in areas north of London. There therefore remains a risk that the SE may miss out on any potential thunderstorms.
We will monitor the situation very closely through the next 24 hours or so, and may issue further updates to this blog before the main forecast for Monday is issued later this evening.
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