Convective / Storm Discussion - 14th May 2014 onwards

[NO LONGER POSTING]

May I ask what the "lifting index" determines?

 

• LI 6 or Greater, Very Stable Conditions
• LI Between 1 and 6 : Stable Conditions, Thunderstorms Not Likely
• LI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, ...)
• LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting Mechanism
• LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting Mechanism

[Candice]

Nice few days into the weekend for everyone, then all change as of Sunday. A sharp and southward projecting upper trough drives a weak Icelandic low down the Wrn side of the UK before the upper trough cuts off and leaves a complex surface low situation, which the globals see wallowing around through next week. This puts a plume of Biscay/Continental air up the UK, with widespread precip between the 5 and 10oC isotherms at 850mb - some of this may be convective, though most will be smeared murk and downstream effects of Continental convection. Nevertheless, some periods of warm sector thermodynamic convection likely given the ascent provided by the jet persistently rounding the base of what becomes a cut-off upper low. Some hints of a Continental heat low generated from Benelux/Germany and drawn NWwd over the UK later in the period.

Either way, some flooding concerns given much higher PW values than we've seen so far creating heavy rain rates, though on the plus side temps hovering around 20oC for most away from the far W.

[East_England_Stormchaser91]

A slight westward shift by the GFS on the latest 06z run. This is looking to be getting quite interesting now. If this continues to shift gradually further West, it could be quite explosive !

[shaky]

A slight westward shift by the GFS on the latest 06z run. This is looking to be getting quite interesting now. If this continues to shift gradually further West, it could be quite explosive !

yup I was just about to post the same thing on the model thread!!sunday is now looking to be a very warm and sunny day across eastern england aswell!!cape values have been downgraded in the midlands and south for saturday though but on the other hand temps are higher more widely across england!weird that!! Edited May 15, 2014 by shaky

[East_England_Stormchaser91]

yup I was just about to post the same thing on the model thread!!sunday is now looking to be a very warm and sunny day across eastern england aswell!!cape values have been downgraded in the midlands and south for saturday though but on the other hand temps are higher more widely across england!weird that!!

I expect upgrades if things keep going the way they are. Very interested as mentioned above about a possible heat low coming up from the Benelux, that could well be in the form of a MCS if we're very lucky!

[NO LONGER POSTING]

When importing storms from France the one thing that plays a part is SST (Surface sea level temperature) 

 

Simple to explain... If a thunderstorm is over land it has it's power source to grow or keep going.. As it moves over a cold area of water.. Hey presto you shut off the power source BUT if you have warmer SSTs then you have a chance it can maintain the journey and or develop once again as it hits land (VERY RARE!) 

 

Back in January I mentioned the fact that due to a very mild winter the SSTs where in fact much higher than they usually are..

 

I can't find the site where I check the average but I believe they are in fact a few degrees warmer than usually this sort time of year.. 

 

Edited May 15, 2014 by Surrey

[Summer Sun]

Could be some problems with localised flooding next week in parts of north west Scotland and northern Ireland if these accumulated totals come off almost 120mm for some in NW Scotland river levels are certainly going to be high some big differences in Scotland it has to be said 120mm for some western parts but just 20mm for the likes of Aberdeen

 

[Azazel]

When importing storms from France the one thing that plays a part is SST (Surface sea level temperature) 

 

Simple to explain... If a thunderstorm is over land it has it's power source to grow or keep going.. As it moves over a cold area of water.. Hey presto you shut off the power source BUT if you have warmer SSTs then you have a chance it can maintain the journey and or develop once again as it hits land (VERY RARE!) 

 

Back in January I mentioned the fact that due to a very mild winter the SSTs where in fact much higher than they usually are..

 

I can't find the site where I check the average but I believe they are in fact a few degrees warmer than usually this sort time of year.. 

 

 

Depends if the storms are elevated above the boundary layer does it not?

 

Most MCS' we import from France (when that used to happen, somewhen before 2007) are elevated and therefore unaffected by the relatively frigid channel.

 

Surface-based storms would indeed struggle moving over a cold mass of water, but elevated storms would be unaffected.

 

That's not to say an elevated storm cant become rooted in the boundary layer and surface-based later on once it has crossed the channel.

 

But anyway, we all know the drill now. MCS develops over France, moves north then dramatically East avoiding the UK entirely apart from the very south eastern corner.

 

I do live in an absolute graveyard for decent thunderstorms though (apart from one noteable storm that became organised and sheared last year..she was a beaut)

Edited May 15, 2014 by Nick L
Fixing quote

[Mapantz]

^ yup.

 

In some circumstances, I have seen MCS' maintain their energy when crossing the channel out of the Summer months, when SST's are lower but are warmer than the land. Many an elevated storm has survived the pitiful journey and given a great display here, in the past, not so much now though, as they pass east and and west of me.

Edited May 15, 2014 by Mapantz

[Nick L]

I propose we have a whip round to fund a heated platform to cover the Channel.

[Bobby]

^ yup.

 

In some circumstances, I have seen MCS' maintain their energy when crossing the channel out of the Summer months, when SST's are lower but are warmer than the land. Many an elevated storm has survived the pitiful journey and given a great display here, in the past, not so much now though, as they pass east and and west of me.

 

Lost count of the times I've seen big thunderstorms from the continent maintain their activity way up into the North Sea also. I think SST's are overrrated, we just need any 'plume' to be far west enough, unfortunately the boundary is usually too far east, grrr.

Edited May 15, 2014 by Bobby

[Mapantz]

Lost count of the times I've seen big thunderstorms from the continent maintain their activity way up into the North Sea also. I think SST's are overrrated, we just need any 'plume' to be far west enough, unfortunately the boundary is usually too far east, grrr.

 

There's no doubt that things have changed over the years, but I believe it works in cycles.

This year has started off well, so let's hope the pattern continues when it matters most, when those temps rocket and humidity goes up!

I'm not a huge fan of that type of weather at night, but if there's a chance of storms sparking off, then it's worth it.

[Mokidugway]

Cape of 1100 and li of -4 , for Tuesday afternoon for my area ,I hope it doesn't downgrade !!!!.....

[Robbie Garrett]

MCS are normally so big that by the time the front has crossed the channel the first cells keep the rest going before re-exploding over the South East. It's an amazing sight that's for sure.

[Supacell]

Estofex have the 15% lightning risk over C-UK tomorrow. WRF and GFS build CAPE across this same area through the afternoon and are expecting precipitation to break out. The Met Office now also showing showers breaking out on their precipitation forecast. Are these all expecting that showers will break out despite the high pressure lid sitting over us? It would be interesting to know what temperature is needed to break through the CAP tomorrow because if we can achieve that temperature then there may be a surprise or two later on tomorrow.

[Cloud 10]

Estofex have the 15% lightning risk over C-UK tomorrow. WRF and GFS build CAPE across this same area through the afternoon and are expecting precipitation to break out. The Met Office now also showing showers breaking out on their precipitation forecast. Are these all expecting that showers will break out despite the high pressure lid sitting over us? It would be interesting to know what temperature is needed to break through the CAP tomorrow because if we can achieve that temperature then there may be a surprise or two later on tomorrow.

 

Yes,it would be impressive to get something decent tomorrow but i suppose stranger things

have happened.

 

[Nick F]

A look at the GFS wind charts for tomorrow afternoon indicates convergence zone from the Severn Estuary up to the Humber - moisture converging here, temps 20-22C and slight cooling off of 500mb temps probably building the CAPE GFS shows - however, think we may struggle to see convective cloud develop high enough for a shower/storm to develop - will probably 'turkey tower'. though there will plenty of convective infill developing.

 

Next week looking interesting on both 12z GFS and ECM, with storms starting as early as Monday across central, southern and eastern areas on GFS - both home-grown and maybe overnight imports. Strong southerly jet indicated would help organisation of storms into multicells and maybe upscale into an MCS or two - maybe supercells if conditions are right. Low/trough sticks around near the SW for much of the week, and become increasingly negatively tilted - which may help increase vertical shear too. Still too far off for specifics, with some uncertainties over the position and shape of the upper trough and surface low pressure system which evolves over Biscay, France and Spain late weekend.

Edited May 15, 2014 by Nick F

[Greeny]

Yes for me im not convinced about tomorrow or Saturday cause of the high pressure possibly keeping everything down or at least causing a restriction somewhat. However according to GFS sunday shows an Atlantic low creeping in for monday and Tuesday and I feel that is the time to focus on the probability of storms and gearing up for a possible show.

(Amateur perspective)

[Dancerwithwings]

Yes for me im not convinced about tomorrow or Saturday cause of the high pressure possibly keeping everything down or at least causing a restriction somewhat. However according to GFS sunday shows an Atlantic low creeping in for monday and Tuesday and I feel that is the time to focus on the probability of storms and gearing up for a possible show.

(Amateur perspective)

The fax charts agrees with the GFS for Sunday

 

 

But then gets pushed back West...ish, come Monday!... but for the probability of storms, well it's too early to say just yet!

 

Edited May 15, 2014 by Dancerwithwings

[SnowJoke]

Looking very exciting next week as regards storm potential. A few possible thunderstorms over the weekend if temperatures can break the cap aided by any wind convergence zones. Next week dare I say it looks good for some overnight MCS development pushing up from the continent on a warm humid south easterly wind. If the residual cloud from any MCS clears there is also a chance of home grown storms during daylight hours.... Time to check my camera and HD camcorder me thinks in anticipation 

[Darren Bown]

The fax charts agrees with the GFS for Sunday

 

 

But then gets pushed back West...ish, come Monday!... but for the probability of storms, well it's too early to say just yet!

 

That Monday chart is juicy, very warm, dry air being driving north from S Spain, with the cold front out west holding moisture. Everything is looking good at the moment!

[Dancerwithwings]

That Monday chart is juicy, very warm, dry air being driving north from S Spain, with the cold front out west holding moisture. Everything is looking good at the moment!

True .... I still think Tuesday looks best, especially what may (come up/come off) from the continent.... WOW!

 

[East_England_Stormchaser91]

Can't believe these charts are becoming closer to reality after being in fairy land not so long ago. The scary thing is that they seem to be upgrading too!

[Convective]

[lassie23]

http://www.weatherweb.net/wxwebtv2.php

 

Some news on the latest shower potential and unsettled spell next week!

Edited May 16, 2014 by lassie23