End of the week & weekend storm risk

[Speedway Slider]

What are these floating around in the English Channel? Are they extremely heavy but small showers, or are they some sort of annaprop? Screen shot from 02:25 Friday am..

 

[Mesoscale]

1 hour ago, Speedway Slider said:

What are these floating around in the English Channel? Are they extremely heavy but small showers, or are they some sort of annaprop? Screen shot from 02:25 Friday am..

 

Definitely Anaprop see how close the different colours are together, Netweather radar shows this far more clearly. 

[weather09]

Meso. models still going for shower/storm activity overnight, initially over far SW, then into tomorrow morning over more of the SW and into Wales where shortwave destabilizes warmth/moisture 'plume' aloft, ahead of cold front to the SW.  

One concern is any elevated convection will leave residual cloud debris for a good part of Saturday, with temps being slow to recover, which would affect CAPE build-up. Still, would seem there's an increasing likelihood that afternoon/evening period will see good insolation and heating of increasingly moist sfc air mass, where dewpoints are modeled generally to be 12-14C, perhaps 15C per GFS outputs.  There has been the concern that GFS might be overstating DPs for tomorrow/Sunday given that it has slightly overdone them for last couple of days, when many sfc obs were recording low single or minus figures DPs. Don't think that will be the case tomorrow. Euro4 generally backing GFS with DPs to 12-13C, so where possible this is 1-2C under actual observations, would appear current CAPE progs are realistic. 

Having looked at France's Arome outputs for tomorrow- though not making much of early day elevated activity (which is difficult for models to get a handle on anyway), does blow up storms from mid-afternoon over Midlands, and then further north and west as sfc heating is maximised.  Converging low-level winds another lift mechanism toward western coasts.  Shame that, on the whole, shear is weak and more obvious forcing aloft is absent.  Would have made a decent looking period more significant. 

[Speedway Slider]

6 hours ago, Mesoscale said:

Definitely Anaprop see how close the different colours are together, Netweather radar shows this far more clearly. 

Confirmed!! Still same place, same size, lapping each other!! Busted!!

[Mapantz]

Yellow warnings issued:

  

[Harry]

13 minutes ago, Mapantz said:

Yellow warnings issued:

  

Limited use of the T word I notice...

[Convective]

6 minutes ago, Harry said:

Limited use of the T word I notice...

Essentially because that warning is only really covering the more organised rain expected through Wales during tomorrow. Later in the afternoon and into the night period is when the real storms are meant to begin firing, I would imagine these warranting at least a yellow warning, if not amber.

[Mapantz]

5 minutes ago, Harry said:

Limited use of the T word I notice...

Yeah - Just lightning mentioned.

Nothing significant in terms of thunderstorm probability during the first part of the afternoon, but that probability increases further North in the late afternoon..

 

Scattered being the operative word I guess? Still, nice to see opportunities arising quickly considering we haven't been under any warmth for that long- hope it continues!

[Harry]

10 minutes ago, Mapantz said:

Yeah - Just lightning mentioned.

Nothing significant in terms of thunderstorm probability during the first part of the afternoon, but that probability increases further North in the late afternoon..

 

Scattered being the operative word I guess? Still, nice to see opportunities arising quickly considering we haven't been under any warmth for that long- hope it continues!

Blimey, Mapantz

Those maps - are they your handy-work or are they computer generated?

[Mapantz]

1 minute ago, Harry said:

Blimey, Mapantz

Those maps - are they your handy-work or are they computer generated?

They're computer generated, I wouldn't even be able to use MS Paint to that level! lol

They use all of the convective parameters to generate a map of where severe weather might occur. It's not 100% accurate of course, but it has done well on numerous occasions.

[Pat Butcher]

Hi folks,

Just a quick one - in a non-sheared environment, do CAPE values actually matter above a certain threshold in terms of storm strength/probability? These CAPE maps tend to throw up anything from 200 to 1,500 j/kg CAPE on weekends like this one, but is it a variable that matters?

[Azazel]

32 minutes ago, Mapantz said:

They're computer generated, I wouldn't even be able to use MS Paint to that level! lol

They use all of the convective parameters to generate a map of where severe weather might occur. It's not 100% accurate of course, but it has done well on numerous occasions.

They're awesome:) where can i view these maps if you dont mind me asking?

[Mapantz]

13 minutes ago, Azazel said:

They're awesome:) where can i view these maps if you dont mind me asking?

On my site @Azazel http://www.warehamwx.co.uk/cumulus/ewn/forecast/map.php

[Azazel]

4 minutes ago, Mapantz said:

On my site @Azazel http://www.warehamwx.co.uk/cumulus/ewn/forecast/map.php

awesome! Thanks mate:)

[weather09]

18 minutes ago, Davethedog said:

Hi folks,

Just a quick one - in a non-sheared environment, do CAPE values actually matter above a certain threshold in terms of storm strength/probability? These CAPE maps tend to throw up anything from 200 to 1,500 j/kg CAPE on weekends like this one, but is it a variable that matters?

Not probability, but strength, yes. CAPE being a measure of instability and indicator of potential updraft speed (strength), higher CAPE generally translates to stronger updrafts, and increased risk for severe weather. Provided, of course, there is a lifting mechanism to release the potential energy, and aren't any significant inhibitive factors such as general subsidence aloft or a stout capping inversion. So lots of CAPE doesn't necessarily increase the risk of there being storms, being just an indicator of how much energy there is to be utilized , but it does matter in terms of storm severity should they develop.  

Despite the lack of forcing aloft and adequate shear for tomorrow/Sunday, should current CAPE progs (several 100j/kg MLCAPE) be actualised during afternoon/evening period then any surface based storms that develop will likely be active (frequent lightning) and pose a low risk of moderate size hail, as well as gusty downdraft winds. The problem is with the limiting factors mentioned, as storms look likely to be scattered given lack of forcing in the mid-upper levels and deep layer shear to increase storm coverage and organisation/longevity.  

[Supacell]

New Met Office warnings out for the central portion of the UK with more emphasis on intense thunderstorms but also highlighting the low probability:

"Whilst the majority of places within this warning area will see a dry and very warm Saturday with a good deal of hazy sunshine there is a very low likelihood of isolated intense thunderstorms developing during the afternoon and evening. Please be aware that if these occur they are likely to be associated with torrential downpours as well as frequent lightning and hail leading to disruption to travel, outdoor activities and potentially flooding or temporary power disruption. Some very localised strong and gusty winds are also possible."

http://www.metoffice.gov.uk/public/weather/warnings/

 

[Pat Butcher]

16 minutes ago, weather09 said:

Not probability, but strength, yes. CAPE being a measure of instability and indicator of potential updraft speed (strength), higher CAPE generally translates to stronger updrafts, and increased risk for severe weather. Provided, of course, there is a lifting mechanism to release the potential energy, and aren't any significant inhibitive factors such as general subsidence aloft or a stout capping inversion. So lots of CAPE doesn't necessarily increase the risk of there being storms, being just an indicator of how much energy there is to be utilized , but it does matter in terms of storm severity should they develop.  

Despite the lack of forcing aloft and adequate shear for tomorrow/Sunday, should current CAPE progs (several 100j/kg MLCAPE) be actualised during afternoon/evening period then any surface based storms that develop will likely be active (frequent lightning) and pose a low risk of moderate size hail, as well as gusty downdraft winds. The problem is with the limiting factors mentioned, as storms look likely to be scattered given lack of forcing in the mid-upper levels and deep layer shear to increase storm coverage and organisation/longevity.  

Amazing, thanks a lot for your help - I understand now. You're spot on as well - Met Office echoed your sentiments immediately after you posted that.  

[sn0wman]

46 minutes ago, Mapantz said:

On my site @Azazel http://www.warehamwx.co.uk/cumulus/ewn/forecast/map.php

This is such a good resource! Thanks for this  

[Arnie Pie]

50 minutes ago, Mapantz said:

On my site @Azazel http://www.warehamwx.co.uk/cumulus/ewn/forecast/map.php

There`s a real good live stream on this excellent site

[keithm]

1 hour ago, sn0wman said:

This is such a good resource! Thanks for this  

this livestream bournemouth pier looking out to sea.

http://www.bournemouth.gov.uk/AttractionsLeisure/BeachesandWaterfront/PierApproachWebcam2.aspx

[Frosty hollows]

Met O warning for tomorrow for my area

"In the warm airmass over the UK there is the potential for thunderstorms to develop thanks to high temperatures triggering convection during Saturday. Many places are expected to remain dry and the development of the thunderstorms is by no means certain and they may not form at all. However, if storms do develop the atmospheric conditions are there for the showers to generate frequent lightning, torrential downpours, large hail of up to 20 mm and gusty winds. The development of these showers is likely to remain uncertain even up to very short lead times and this warning is likely to be updated as confidence increases."

 

So maybe there'll be thunderstorms. Maybe not.

[William Grimsley]

Lots of Altocumulus Castellanus cloud has moved through here this afternoon, I think we're on!

EDIT: Just seen the latest Met Office forecast. Looks like lots of thunderstorms will move through this area through early tomorrow morning and later in the afternoon! Goodie!

Edited May 6, 2016 by William Grimsley

[William Grimsley]

Looking SW!

Looking WSW!

Looking SSE!

Quite muggy outside too!

Edited May 6, 2016 by William Grimsley

[William Grimsley]

Looking WSW!

[A.J]

what you have their is a cirrus veil with some patchy Ac, Ac Cas at a stretch which isn't towering...nothing really that would have me jumoing up and down in excitement..best to wait a few hours to see if anything develops over northern France, but at the moment 'all is quiet on the western front'.....some showery rain over biscay and western france with the odd lightning flash over northern Spain (something which is pretty much seen every day from May to October)