Convective / Storm Discussion - 22nd October onwards 2013

[Clair_Witch]

Rain just arriving in Cardiff.

[paul m]

Rain just arriving in Cardiff.

Anything convective in it ??

[Panayiotis]

Nope ^ good night!

[lottiekent]

Pouring and very windy here at the moment!

[Clair_Witch]

Nope. Not even heavy rain.

[paul m]

Pouring and very windy here at the moment!

Looks like there is a squall line near you

[Supacell]

A difficult one to forecast for the next 48 hours relating to convective activity what with so much change in the models from run to run. GFS has downgraded the storm system and also appears to push it through that bit earlier but this is just one run of one model. 

 

Latest GFS and lightning wizard (which very much uses the GFS to my knowledge) shows the chance of some thundery activity in the showers today, more so in the north and west of the country where the risk is there from the word go - maybe western Scotland and NW England in with the highest risk. Any heavy showers and thunderstorms that do form across the England portion will have some 30-50 knts of DLS and moderate to high levels of helicity to play with which will allow activity to organise and bring the risk of strong convective gusts of wind/tornadoes (hence a level 1 from Estofex although more relating to after midnight for England). Convective activity does look to die out in England after around mid afternoon. Further north in Scotland the risk goes on into the evening, but these look to be more pulse type storms, albeit with lightning possibly more prevalent here due to lower ELT's and higher CAPE.

 

Tonight, as part of this storm system, there looks an interesting zone to the south of the UK - although this is based on an ever changing suite of runs - whereby a small amount of CAPE (100-200j/kg) overlaps DLS of up to 100knts, 0-1km helicity that is off the scale and 0-3km helicity of over 400m2/s2. Currently this region is in a line from around the IOW to the Wash eastwards. To my eye this combination brings the risk of some very high convective wind gusts in association with any convective activity and a high risk of one or two, perhaps quite sizeable, tornadoes. Rainfall rates in southern parts could also pose a problem, with a lot of rain likely to fall in a 6-9 hour period. This activity is in addition to storm force winds gusting up to 80-90mph along the south coast, particularly to the eastern half of the south coast - which are bound to create havoc for the morning commute tomorrow.

 

After this there is the risk of further convective activity in southern and central parts tomorrow in the sunshine and squally showers regime in the wake of this storm.

Edited October 27, 2013 by Supacell

[Bobby]

Some torrential downpours here this morning, heard 2 loud rumbles of thunder an hour or so ago but no lightning seen, just missed us I think. Very heavy rain now.

[Chris.R]

Wow just had a stupidly huge squall pass over here, monumental rain, hail and gusty winds. No thunder though surprisingly.

[4wd]

Interesting report here relating to last Friday evening.http://www.yorkpress.co.uk/news/10766191.SUNDAY_UPDATE___Tornado__storm_hits_North_Yorkshire_village/

[Raidan]

Rumble of thunder here followed by torrential rain.

[Coast]

Sorry, too tied up on the other stuff:

 

 

 

Storm Forecast

Valid: Mon 28 Oct 2013 06:00 to Tue 29 Oct 2013 06:00 UTC

Issued: Sun 27 Oct 2013 23:15

Forecaster: GROENEMEIJER

 

Note: ESTOFEX forecasts address only convective storms, not windstorms unrelated to deep, moist convection. The level areas do therefore not represent regions affected by non-convective severe wind 

 

A level 2 was issued for SE England, N France, Benelux, NW Germany and S Denmark mainly for severe wind gusts and isolated tornadoes.

 

A level 1 was issued for an area surrounding the level 2 mainly for severe wind gusts and isolated tornadoes.

 

SYNOPSIS

 

An amplifying trough approaches Europe from the Atlantic ocean with a very strong SWly jet situated ahead of it. A frontal wave within the associated baroclinic zone is expected to translate very rapidly NEward during the day. The associated surface cyclone should be located over the southern North Sea by 06 UTC, near Stockholm by 18 UTC and over Karelia 06 UTC on Tuesday. The wind field on the cyclone's SE flank is expected to be very strong with severe (25 m/s) and isolated extreme (32 m/s) wind gusts occurring even in the absence of convective storms.

 

DISCUSSION

 

... SE England, N France, Benelux, N Germany, Denmark...

 

NWP guidance suggests that the cold front in the wake of the surface cyclone will be accompanied by narrow segments of convection with tops in the mid-troposphere. On Monday at 06 UTC, this line should be located over SE England and the English Channel extending into Brittany. It is expected to move ENE ward across the level 2 area reaching NW Germany in the mid-afternoon, and then gradually weaken. However, is not ruled out that some convective activity will also affect southern Sweden.

 

The strong surface wind field in which the convection will be embedded will be further by the storms to produce widespread severe and isolated extremely (>32 m/s) severe wind gusts. Given the extreme wind shear expected ahead of the convective lines (20-25 m/s 0-1 km shear) and high 0-1 SRH (400 - 500 m2/s2) some tornadoes may also develop. The threat of large hail, however, will be relatively small since the updraughts will be not that deep and probably strongest a low levels. Modest mixing ratios and high storm speeds will mitigate the threat of extreme rainfall.

 

... British Isles NW of the front ...

 

Additional convective storms are expected to the NW of the front. These will be rather poorly organized and should not pose a significant threat of severe weather. Nevertheless, small hail and mostly- non-severe winds will probably occur with some of these. 

 

 

 

[poseidon]

Sky just went very dark here in Herts as a smallish developing anvil cloud passed over. Just a few spits of rain though and moved away pretty quick eastwards. I notice that there's a lightning strike showing up west of London now also.

[Coast]

Still time for some convective action yet:

 

 

[Robbie Garrett]

Just had IC lightning and thunder here in SE17

[Panayiotis]

Lots of CB's around me in Cardiff, producing some moderate showers. Maybe more convection will kick in later...

[Bobby]

Gone very dark here with some heavy rain starting. Some nice convective skies today, pretty CB anvils.

[AWD]

Deep booming thunder heard in Bristol associated with one of many torrential downpours today.

[Supercell 89]

Just had the lights flicker followed almost instantly by a clap of Thunder here in Reading, very dark to our North 

[Cloud 10]

Some impressive looking cloud just to my South-west and the wind has dropped completely.

 

 

Satellite loop shows developments nicely.

 

Meteociel - Observations satellite - images satellite infrarouge et visible

 

 

Interesting report here relating to last Friday evening.http://www.yorkpress.co.uk/news/10766191.SUNDAY_UPDATE___Tornado__storm_hits_North_Yorkshire_village/

 

 

Very interesting report from Yorkshire,thanks for posting.

 

Some pretty unusual weather in the NE of the UK last friday.

[Panayiotis]

Hail and heavy rain here in Cardiff, no thunder heard!

[Raidan]

Lightning seen and thunder heard over Bristol.

[Chris K]

Torrential rain and had a couple of flashes and rumbles here just now! Didn't realise anything was due to happen today!

[virtualsphere]

Nothing too exciting here in SW Wales today, but plenty of picturesque skies around with some dramatic Cbs against a backdrop of blue skies -

[carl1980]

Just had a hail storm,no thunder though,roads were like rivers..mad !!