Convective / Storm Discussion - 1st May 2014 onwards

[Supacell]

A slight downgrade on the GFS as to be expected but despite this still things look good for some thunderstorm activity later this afternoon. CAPE in the region of 700-900j/kg along with Lift indicies of -2 to -3 develop over Central England and head east into the East Midlands and East Anglia this afternoon/evening behind and eastward moving warm front:

 

 

It looks to be the cold front following on afterwards that brings the risk of thunderstorms, with cold drier air aloft increasing lapse rates. (It is worth still bearing in mind that this forecast is based on the GFS only, currently the Met Office and BBC have no mention of thunderstorms, although do pick up on an eastward moving band of heavier rain in association with this cold front):

 

 

Even so, any thunderstorms that do develop will do so in an environment of fairly good DLS of around 20-30knts which will be enough to separate the updrafts/downdrafts and allow organisation into multicell clusters, possibly even supercells. The supercell parameter charts are showing the highest risk I have seen so far this year for an area around the East Midlands into East Anglia:

 

 

 

With these storms there is also the risk of a tornado or two, this something that has also been picked up by Estofex who have given a level 1 for this reason.

 

 

 

Lightning activity, should these storms develop, would likely be fairly decent to with decent CAPE and high lapse rates. Estofex offer a 50% lightning risk in conjunction with their level 1.

 

 

Overall I have concerns about cloud cover and would be more confident if the Met Office and BBC were on board, but I do hold a lot of respect for Estofex for their accuracy as they do often forecast these scenarios well. If cloud does not break then we are unlikely to see such storms, but the risk is there for possibly the best risk day for a few of us so far this year.

 

It is then worth mentioning too that a band of showers expected to move from west to east tomorrow morning could also contain convective potential, once more bringing the risk of organised multicell activity of some form:

 

Edited May 8, 2014 by Supacell

[SalopWatcher]

Interesting I have a drive through the Estofex level one from Shrewsbury yo Leicester for a 1.30 meeting and then back about 4ish, so will keep a good eye on the sky and netweather. If a slight diversion is required to get some storm action I will be all over it.

 

Right now heavy rain in Shrewbury.  

[Candice]

SkyWarn UK Severe Thunderstorm Watch No:18 issued, http://www.skywarn.org.uk/current.html

[Nick F]

Cloud today concerns me, despite the potential, could easily be a now show/bust today!

 

Full forecast here: http://www.netweather.tv/index.cgi?action=convective;sess=

 

 

THERE IS A RISK OF THUNDERSTORMS FORECAST

Synopsis
Low geopotential heights/surface pressure dominate NW Europe and far N Atlantic area today, with a strong 100mph+ westerly jet stream ploughing across the UK today. A frontal system will push east across the UK today, with the 'warm' sector pushing across England and Wales followed by clearance east of a cold front - which will clear the east coast this evening.

... IRELAND/N IRELAND, WALES, CENTRAL, SOUTHERN and EASTERN ENGLAND ...

GFS has, for several runs, indicated the potential for thunderstorms to develop today across southern Britain and Ireland, but the risk will be conditional on clearance of total cloud cover this morning to allow surface heating to help destabilise sufficiently the moist maritime airmass in place. Warm sector crossing southern UK is characterised by weak lapse rates and is fairly stable for now, with stratiform cloud cover producing dynamic rainfall. Shortwave trough moving in from the west will introduce colder air aloft from the NW as the day goes on, which will steepen lapse rates and combine this with increase forcing with this approaching trough and covergence near eastward-moving cold front, the airmass may become unstable. Should any surface heating develop this afternoon, the moist airmass under steepening lapse rates will likely produce sufficient CAPE for thunderstorms to develop. Any storms will benefit from an environment characterised by strong vertical shear, given strong westerly flow aloft veering southwesterly or even southerly towards the surface. The 40-50knts of deep-layer shear and 25-30 knts of low-level shear indicated by models suggests any storm could organise into multicell or even isolated supercell structures - capable of producing large hail and damaging wind gusts, additionally, low LCL (Lifted Condensation Levels) and very moist surface airmass may enhance risk of an isolated tornado with any strong rotating updrafts that form.

However, will not issue a SLIGHT risk of severe weather, given concerns over cloud cover not clearing to allow convection to develop. But given the potential, a conditional forecast was thought appropriate.

Edited May 8, 2014 by Nick F

[Greeny]

Yes total cloud cover here in Norwich. Doesn't look that great with all the cloud cover at the moment in the areas of interest. We can only wait and see if anything develops.

[Mapantz]

Yep, lots of cloud. There are some breaks moving in from the west, but few and far between!

[Harry]

Still awaiting my first rumble of thunder in 2014 (shambolic form!) - frantically revising for my last exam of this year tomorrow, so for once might be grateful for the lack of distraction

Judging by the extensive cloud cover here also, and the satellite imagery, am confident most of us will be seeing nothing of interest. 

[Nick L]

Looking like it might be yet another potentially interesting day scuppered by cloud cover.

[poseidon]

I don't understand how GFS can put out such favourable CAPE and LI figures given the fact that it was also predicting complete cloud cover (along with UKMO). Were these numbers based on instability associated with the cold front alone or is this a fault in the way that the model interprets this kind of situation? Can anyone offer any insight?

[Greeny]

Looking like it might be yet another potentially interesting day scuppered by cloud cover.

 

Yes time is getting on and it certainly looks that way

 

Oh well maybe worth turning your heads across to the west over in America and watch some live storm chase streaming from over there this evening. Moderate risk and a potentially big day for storms and tornado's. Last storm system 27th, 28th of April they had over there I was watching the stream while the tornado was hitting Mayflower and a large debris ball was being seen on radar. It was a big tornado outbreak.

[vladthemert]

been raining all morning here.  Last night did have convection down pour missed my location by 50 yards   weird the car park  getting right pounding of wall of rain so could not say how much raiin fell.  Today just cloud steady stream rain 4mm so far.

[Nick L]

I don't understand how GFS can put out such favourable CAPE and LI figures given the fact that it was also predicting complete cloud cover (along with UKMO). Were these numbers based on instability associated with the cold front alone or is this a fault in the way that the model interprets this kind of situation? Can anyone offer any insight?

 

You can have favourable CAPE and LI, but without a "trigger" then nothing will happen. A trigger in this case would be surface heating in order to enable air parcels to ascend (i.e. convection). But seeing as it's cloudy, this surface heating isn't really happening. The atmosphere is unstable, but we need something to kick-start that instability so-to-speak. Other forms of triggers can be convergence zones (where opposing winds meet or converge, forcing air upwards) or a frontal boundary to provide that lift. Even sea breezes can act as a sufficient boundary.

 

In short, favourable CAPE and/or LI values don't automatically mean thunderstorms are going to occur.

 

Over the weekend (have an exam tomorrow...) I'll add a more extended and full explanation in the learners area.

Edited May 8, 2014 by Nick L

[Chris.R]

Sun is out here. 500 J/kG and -2 LI showing for here. Why could stuff not happen here?

[Nick L]

Sun is out here. 500 J/kG and -2 LI showing for here. Why could stuff not happen here?

 

It could well do, very early days yet! The days are long at this time of year so plenty of heating time left

[Bobby]

The conditions feel ripe for something thundery but yes the cloud cover and lack of surface heating will probably prevent it, might be a few downpours though. Shame as with some breaks in the cloud I can imagine some tasty storms.

[Mapantz]

There's a bigger clear slot to the south of Ireland, moving in to Wales, on the 13:15 update. I reckon some might get lucky in the next few hours.

[Biggin]

Yes time is getting on and it certainly looks that way

 

Oh well maybe worth turning your heads across to the west over in America and watch some live storm chase streaming from over there this evening. Moderate risk and a potentially big day for storms and tornado's. Last storm system 27th, 28th of April they had over there I was watching the stream while the tornado was hitting Mayflower and a large debris ball was being seen on radar. It was a big tornado outbreak.

Any good sites for this ??

[Nick L]

Any good sites for this ??

 

If you keep an eye on threads in the US storm chase section, links to streams will be posted when things look lively

 

http://forum.netweather.tv/forum/168-storm-chase-2014/

[Biggin]

If you keep an eye on threads in the US storm chase section, links to streams will be posted when things look lively

 

http://forum.netweather.tv/forum/168-storm-chase-2014/

Thanks Nick

[Convective]

Ireland and perhaps the furthest parts of Northwest England in with the best chance this evening, in my opinion. 

[Harry]

Oh look areas of blue sky....typical

[Greeny]

So there are ingredients for storms to fire overnight but what are the trigger factors and how would I go about finding the chances of a trigger? I see some in places overnight sweeping eastward according to these charts.

[vladthemert]

been raining here all day with odd break some heavy.  Not sure anything convective will happen still alot cloud.

[Tom Jarvis]

Cloud has broken up here and looks like first cell has fired north of Portsmouth May get to my location

[East_England_Stormchaser91]

Ay up, towers seem to be sprouting up, don't count this one out too soon!