Convective / Storm Discussion - 31st July onwards 2013

[Darren Bown]

It's warmer here (ellemsmere port) than it has been all day now the rain has stopped. Must be due to the warm front moving through.

[IanR]

is that skywarn  forecast just having a laugh, the predictions for decent thundry activity over these parts of northwest very rarely comes off,, seen it many many times, this the northwest , not east midlands,.....move along, nothing to see here

[staplehurst]

is that skywarn  forecast just having a laugh, the predictions for decent thundry activity over these parts of northwest very rarely comes off,, seen it many many times, this the northwest , not east midlands,.....move along, nothing to see here

 

Not sure any of the convective forecasts for today explicitly say there will be 'decent thundery activity', just that the potential is there for some local severe convective weather in the form of primarily tornadoes, but if a supercell could develop mid afternoon through to mid evening over N Wales and NW Eng then there could be some moderate hail too.

[Darren Bown]

It's a case of 80% of the ingredients are there, but the 20% missing seems to be the most important factors in this setup. Stayed dry in Manchester so far, with some nice sun coming out travelling along the M56.

[Supacell]

At first glance I cannot see the potential for today but then I remembered it's not all about CAPE. Having said that, although GFS are forecasting only a small amount of CAPE - the values shown by NMM and WRF are more substantial.

 

However, we then have the fact that we have 30-40 knts of deep layer shear, 30knts of 0-1km shear which increases to 40-45knts overnight, strong helicity (with some very strong helicity moving through Wales and into NW England overnight) and you can see why the storm forecasting's clever people think there is the risk of something this evening and overnight. A lot of rain to come too, so flooding may be of biggest concern.

 

Although storms are by no means guaranteed, IF they do form they will likely become organised with the possibility of supercells, large hail, 40-50mph wind gusts and possibly a tornado. I don't see this being a widespread lightning fest though, but clearly lightning and thunder would be present.

 

Low risk but moderate to high impact I would say.

[The PIT]

Some convection going on around midday since then nothing really and judging the way the rain has been decaying suggests there's little prospect of anything later on.

[Chris.R]

Agree Supercell, that's what I was thinking. The sun is trying to come out now after the half an hour of heavy rain as the warm front passed. Feeling very humid and close indeed now.

[Darren Bown]

So this evening is the 'breeding time' for any developments? N Wales seems to showing some intensification.

[nitro_deluxe]

These set ups are always rather tricky to pinpoint much detail re storm or convective potential, indeed things are developing quite quickly, making it all that bit more difficult to predict with much accuracy or timing etc - saying this, similar set ups have in the past produced the 'goods' for some. Not widespread by any means, but if you're directly beneath it, you're very likely to know about it   others wondering what the fuss is about.

 

Even now, after a brighter drier slot, a pretty sharp downpour inbound..

Edited August 4, 2013 by triple_x1

[Supacell]

So this evening is the 'breeding time' for any developments? N Wales seems to showing some intensification.

It is later in the day when things may start to happen and you would want to be looking around mid and north Wales for development as it is this air that would later be over NW England.

[Darren Bown]

BBC are just concerned with the amounts of rainfall tonight rather than anything particularly windy/thundery.

Quite a development of rain between now and 10pm too.

Edited August 4, 2013 by Darren Bown

[Chris.R]

Well the met office are now talking about the risk of thunder in their text forecast for both tonight and early tomorrow. Interesting.

[Chris.R]

A heavy shower here now with huge convective drops

[Stuart]

Synopsis

A waving front will continue to affect many parts of Britain through Monday, beneath the base of an upper trough and a weakening jet aloft. At the surface, a low pressure centre will track northeastwards from the Celtic Sea, across Wales, the Midlands and northern England, and ultimately across the northern North Sea during this forecast period. To the south and east of this low and associated frontal boundary, a tongue of warm, moist air (characterised by WBPT >14C and 10g/kg 1km mixing ratio) will continue to be advected northeastwards. There is scope within this airmass for some convective activity.

 

Discussion

Strong DLS and LLS will be present during the first half of the forecast period, allowing embedded (probably largely non-thundery) convection to form distinct lines along both the cold front and occlusion, and hence giving large rainfall totals on some southern and western slopes across western Britain (PWAT >35mm).

Greatest focus for convective weather will be between 12z-20z, beginning over the West Country during the early afternoon, then shifting progressively northeastwards towards East Anglia by late afternoon and into the evening. Surface troughing underneath an upper trough axis is likely to result in a zone of low-level wind convergence or confluence. Provided sufficient insolation amongst frontal boundaries allows a build-up of 600-800 J/kg CAPE, scattered showers and thunderstorms can be expected to develop, perhaps into a distinct NE-SW orientated line.

By this stage, the upper jet will have weakened but with 20-30kts DLS still present this should allow cell organisation, with perhaps a CZ-induced funnel. Perhaps of greater concern is local flash flooding, given fairly slow storm motion and/or backbuilding/training over similar areas combined with PWAT values >30mm. Some small hail is possible in any stronger cells. All activity will generally shift northeastwards offshore during the evening hours.

 

http://ukasf.co.uk/storm-forecasts/269

 

[Chris.R]

A stupidly torrential shower just went through here.

[Chris.R]

The sun is out now LOL.

[iand61]

Rain here on and off since early afternoon.

Mainly fairly light but with heavier bursts at times although IMO nothing to warrant a warning.

Maybe things will change later and the warnings will be proved correct but it's not looking likely at the moment.

[The PIT]

Warning in effect from 23:00 hours here so will have to wait too see what happens. 20:00 for the South West.

[Chris.R]

Yes, 2000 hours here as well so you can't say the warning isn't needed when it hasn't even come into effect yet!

[Allseasons-Si]

Here is a still i captured on last fri night's storm

 

 

 

[nitro_deluxe]

Some tidy looking showers now nearing Pembrokeshire.

[Darren Bown]

Some tidy looking showers now nearing Pembrokeshire.

Yes, the radar should be starting to intensify over the next 4 or 5 hours. Looked quite nasty on the Metoffice precipitation forecast for overnight period.

[The PIT]

Interesting some lightning in the Irish sea. Just now.

[paul m]

Really heavy showers passing through

[Mokidugway]

thunder in barrow in furness