Storm & Convective Discussion - 01/09/14 onwards

[Dami]

 you should move to bedford, gordon! Not a peep as usual.

Edited October 17, 2014 by Dami

[Greeny]

Could be interesting, on the view of the Estofex level 1, nice to break it down a bit. Potential moving into strong sheared environment this evening. Looking strong on the lower levels. Maybe another pancake stack meso can be captured on a lightning picture, this time with a tornado? :-)

Hopefully no serious problems will be reported.

[William Grimsley]

Is that what you just experienced? I can't even imagine. Surely that would be like sheets of rain falling?

Was insane. With the wind it sounded like a train even in a house!

[William Grimsley]

William, That is a huge figure, how long did it last at that rate and do you know what the total rainfall was?

 

I was down at Sidmouth a few years back when they had major flooding following a cloudburst, but that was no more than about 30mm / hour and maybe 50mm/hr peak. 

It was. 3.2 mm of rain fell between 16/10/2014 20:05 and 16/10/2014 20:10.

That really is heavy!

Yeah, I haven't seen anything heavier in my life, unfortunately it was dark but had some flood lights on and it was just like white sheets going past the windows!

[egret]

It was. 3.2 mm of rain fell between 16/10/2014 20:05 and 16/10/2014 20:10.

Yeah, I haven't seen anything heavier in my life, unfortunately it was dark but had some flood lights on and it was just like white sheets going past the windows!

William

That gives 36mm/hr - close to what we had in Sidmouth. I think you might have got the decimal point wrong in your earlier post?

Looking at the rain radar trace for your area yesterday it was clearly a beauty - elongated intense rain along the line of the storms path so it must have lingered a while. I see Exeter got hit badly  as well.

[Andy Bown]

Sounds amazing William.

 

I looked on the Net Weather radar zoomed into your area and at 20.05 there was a very pale pink verging on white echo within the mass of rain which is just about the heaviest radar colour available!

 

It's become quite a gloomy afternoon as cloud spills in ahead of the next frontal rain, still at 16.9c despite no sunshine and wondering what the temperature will keep at in the muggy overnight air.

[Mapantz]

William

That gives 36mm/hr - close to what we had in Sidmouth. I think you might have got the decimal point wrong in your earlier post?

Looking at the rain radar trace for your area yesterday it was clearly a beauty - elongated intense rain along the line of the storms path so it must have lingered a while. I see Exeter got hit badly as well.

The Davis Vantage Vue updates rainfall every 20 seconds, so if X amount of tips have occurred in that time, it will calculate the rainfall rate for that specific moment, it's not taking an average over an hour. So if the intensity of the rain that William was experiencing when it registered 245mm/hr- kept up for 60 minutes, he would have indeed, recorded a total of 245mm. Hope that makes sense?

Edited October 17, 2014 by Mapantz

[William Grimsley]

The Davis Vantage Vue updates rainfall every 20 seconds, so if X amount of tips have occurred in that time, it will calculate the rainfall rate for that specific moment, it's not taking an average over an hour. So if the intensity of the rain that William was experiencing when it registered 245mm/hr- kept up for 60 minutes, he would have indeed, recorded a total of 245mm. Hope that makes sense?

What Mapantz said... Note that Cumulus only updates its graphs once a minute hence it showing a lower rate than actual.

[Hodgheg]

Hi, i know I'm not expecting storms here tonight, but had three storms on the second day of moving to London, took that as a good sign. Happy Storming.

[Nick F]

Have issued a storm/convective forecast for tonight and tomorrow, a SLIGHT risk of severe weather across Ireland and northern Britain over next 36hrs:

 

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

[Liam J]

Rain lashing against the front windows with a strong wind picking up. 

[egret]

The Davis Vantage Vue updates rainfall every 20 seconds, so if X amount of tips have occurred in that time, it will calculate the rainfall rate for that specific moment, it's not taking an average over an hour. So if the intensity of the rain that William was experiencing when it registered 245mm/hr- kept up for 60 minutes, he would have indeed, recorded a total of 245mm. Hope that makes sense?

Mapantz, Ah I understand now - in one 20 second period it will have recorded 1.36mm. I was thinking a 3min sample interval. For the other part of the 3 mins it will have averaged 0.23mm per sample (1/6 of the peak rate).

 

Even for 20 seconds the 245mm figure is truly impressive.

[Gordon Webb]

Well bad news I didn't win the Euromillion's jackot but the good news is that the weather was pretty uneventful

[Greeny]

Well bad news I didn't win the Euromillion's jackot but the good news is that the weather was pretty uneventful

Feels lovely out here today. Warm but not too hot and the wind feels warm too. Very pleasant. Same for you up there Gordon?

[poseidon]

Mention of locally heavy, squally, thundery showers with hail possible this afternoon, on the local weather. Lightning Wizard certainly seems to show some CAPE, convergence etc around today. Estofex have a level 1 over fair chunk of UK.

Edited October 21, 2014 by poseidon

[Lynxus]

ESTOFEX.ORG have some interesting information today especially how the jet interacts with this low pressure.

 

Storm Forecast
Valid: Tue 21 Oct 2014 06:00 to Wed 22 Oct 2014 06:00 UTC
Issued: Mon 20 Oct 2014 22:47
Forecaster: PISTOTNIK

A level 1 and level 2 were issued for SE England, BeNeLux, N and E France, Switzerland, central and S Germany, the Czech Republic and Austria mainly for severe wind gusts and to a lesser extent for tornadoes.

A level 1 and level 2 were issued for NE Italy, the N Adriatic Sea, Slovenia, the N parts of Croatia, Bosnia-Hercegovina and Serbia, and the W parts of Hungary and Slovakia mainly for severe wind gusts and tornadoes, and to a lesser extent for excessive precipitation.

A level 1 was issued from Scotland into NW Germany mainly for severe wind gusts.

SYNOPSIS

A strong zonal flow is present across Europe. A first cyclone tracks eastward into Russia and brings wintry conditions into Scandinavia and northeastern Europe in its wake. Behind a transient and progressive ridge over central Europe, the next cyclone (ex-hurricane "Gonzalo") moves from Scotland towards Denmark, and a new trough ejects from the British Isles into central Europe.
Quiescent conditions prevail over southwestern and southern Europe, apart from quickly increasing Mistral and Tramontana winds over the western Mediterranean Sea at the rear flank of the amplifying central European trough.

DISCUSSION

... England into BeNeLux, NE France, Switzerland, central and S Germany, Czech Republic, Austria ...

A powerful jet streak (>50 m/s at 500 hPa) digs southeastward at the flank of the Scottish cyclone. In the course of the day, its axis is forecast to point across northern and eastern France into Switzerland and northern Italy. Very strong vorticity advection will be present at its cyclonic flank, which is forecast to catch up with the cold front around 09 UTC over southeastern England. Under the influence of its lift, a band of neutral to slightly unstable profiles will likely establish ahead of the cold front, largely overlapping with the very strong wind field of the jet streak.
In the 09 to 15 UTC time frame, thunderstorms become increasingly likely while the cold front moves from England into the Netherlands, Belgium and northern France. Storms will soon organize into multicells and bowing lines, and the risk of severe wind gusts increases betimes. In a strongly sheared and helical flow even in the lowest levels (15-20 m/s of 0-1 km shear and 200-400 m^2/s^2 of 0-1 km storm-relative helicity, respectively), any updraft that manages to stay more discrete may also acquire rotation and produce a tornado.
After 15 UTC the limited area models show convincing signals that the convective activity will be bundled into one dominant line along the cold front, as it moves into Germany, Luxemburg and eastern France. Deep-layer shear increases from 20 m/s near the northern fringe of the unstable area to almost 50 m/s beneath the jet axis over France and Switzerland. A level 2 for severe wind gusts is issued for those areas where a robust overlap of strong shear, strong synoptic lift and at least a little CAPE exists, surrounded by a broad level 1. Limiting factors are the relaxing shear towards the north and the decreasing depth of the convective line towards the south, which makes it less likely that the immense shear beneath the jet axis can be fully consumed.
Until 00 UTC, the convective line is forecast to cross central and southern Germany, the Czech Republic and much of Austria. Along the northern Alpine rim, ageostrophic flow due to channelling (indicated by forecast pressure tendencies up to 10hPa/3h) may further enhance the strength of the wind gusts.

... NE Italy, N Adriatic Sea, Slovenia, N parts of Croatia, Bosnia-Hercegovina and Serbia, and W parts of Hungary and Slovakia ...

Unseasonably rich low-level moisture is present in the range of an old frontal boundary, left over by the departing low over Russia. Backing and increasing low-level winds in response to strong pressure falls in the evening may advect further Adriatic moisture into the northern Balkans and onto the Pannonian plains, maybe even into Slovakia (depending on a possible mesolow development along the approaching cold front). The most aggressive solutions (WRF) show surface dewpoints around 14°C and 925 hPa dewpoints around 12°C over Slovenia, Croatia and western Hungary at midnight, yielding CAPE up to 500 J/kg under a strongly sheared and helical flow.
With the arrival of the vorticity lobe aloft, prefrontal storms may start to form in the late evening over eastern Austria, western Hungary, Slovenia and northeastern Italy. They will probably be elevated in the beginning, but in case they manage to root down to the surface, they can easily turn into tornadic supercells in this almost saturated and strongly sheared environment.
Any prefrontal activity will sooner or later be engulfed by the following convective line, which will cross much of Hungary and the northern Balkans until Wednesday 06 UTC. While it gradually decelerates and outruns the strongest wind field and synoptic-scale lift, the risk of severe wind gusts will start to decrease. However, a limited risk of training storms with localized flooding may evolve instead, especially in Slovenia and Croatia where storms from the northern Adriatic Sea may move onshore for a few hours while they are undercut by northeasterly surface winds and turn elevated.

... Scotland and E England, as well as BeNeLux and NW Germany coasts after 15 UTC...

Showers and weakly electrified thunderstorms will form in the stream of deeply mixed polar air behind the cold front. Vertical wind shear will be limited, but the strong background wind field may support wind gusts slightly above 25 m/s even with poorly organized convection. Besides, an isolated tornado is not ruled out along windward coasts where the sudden increase of surface friction ramps up low-level wind shear.
The exact track of the compact center of the cyclone is still uncertain. The majority of forecast models simulate a landfall in Denmark towards the end of the forecast period, which could result in a dramatic increase of wind speeds in a confined area in northwestern Germany near its back-bent occlusion. Since it is unclear how much deep convection will be involved and if this will happen at all until Wednesday 06 UTC, no level 2 was issued.

[BlueHedgehog074]

Has really felt October-esque with the menacing showers and wild winds today. It's nice to have had a North-Westerly flowing producing frequent showers of a good quality, and also seeing colder than 0*C 850 hPa temperatures spilling across the country for the first time this season. Reminds you of the fact that Winter is slithering like a snake closer to the UK (but obviously not close enough to pounce and bite at it yet)...

Having said that, some of the particularly juicy showers today seemed to have missed here by a few miles to the South or North (as the way these shower setups can go with their hit and miss affair). To be fair, though, their had been quite a decent one around 3(ish) this afternoon producing heavy rain mixed in with a bit of hail. As with some of the other reports from other places, the showers exhibited some squally characteristics with winds whipping the rain about all over the place.

Not the best quality, but had also taken a pic of some convective shower clouds passing by to the North-East in the distance against the darkening blue skies earlier,

[Nick F]

Storm & Convective Forecast

 

Issued 2014-10-24 09:11:19

Valid: 24/10/2014 0600z to 25/10/2014 0600z

 

 

THERE IS A RISK OF THUNDERSTORMS FORECAST

 

Synopsis

Upper trough close to the NW of the UK will drive a deep cyclonic SWly flow across the British Isles today. A cold front clears SE England this morning, while another waving cold front moves SE across England and Wales today. Troughs in the southwest flow will bring showers/storms to the NW.

 

... S/E MIDLANDS, S/SE ENGLAND and E ANGLIA ...

 

Warm air advection in the warm sector ahead of waving cold front moving SE is indicated to yield a few 100 j/kg CAPE from late morning across the above areas. General large scale ascent of airmass with falling heights and forcing from cold front may support the development of a few thunderstorms in this modestly unstable airmass. Fairly strong winds aloft will support some storm organisation into multicells, capable of producing strong gusty winds, hail and torrential rain leading to localised flooding.

 

... NW SCOTLAND ...

 

A shortwave trough and associated pool of cold air at mid-levels will serve to steepen lapse rates as it crosses N Britain today. These cold mid-levels atop of moist rPm airmass warmed by SSTs will support frequent heavy showers and thunderstorms across northwest Scotland today, accompanied by hail and squally wind gusts.

 

Issued by: Nick Finnis

 

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

Edited October 24, 2014 by Nick F

[Staffordshire]

Something developed across west mids past half hour

[timeless]

are you sure? just been generally dry and grey day in herefordshire tho there was a few mins of light rain which has already dried up. a far cry from the percentage of storm possibility given to this area. then again l suppose its likely to be quieter given we are going into the winter months soon.

[timeless]

been looking at the will it thunder pages and the GFS and it doesnt seem to make much sense, the LI for tuesday night doesnt look anything special (at least not by the charts)  and same with wednesday yet there seems to be a higher percentage possibility considering that fact on at least a couple of time on the storm forecast page it shows 0% convective cloud which lm sure storms need.

[timeless]

just curious about the potential for thunderstorms this week, the storm forecast page has started to confuse me as it doesnt seem to match what l see on the gfs lve seen, then again lm not the most knowledgeable as lm still picking things up as l go along, however dont thunderstorms require "convective" cloud? as the storm forecast page shows 0% convective cloud for my area and its gone up to 52% possibility of storm overnight.

Edited November 1, 2014 by timeless

[Mokidugway]

Line echo developing over Northern Irish sea .....

[Convective]

Line echo developing over Northern Irish sea .....

 

Annnnnnd....... its gone! Didn't even make it 30 miles off Ireland! 

[Greeny]

I don't know if this is anything that significant but the signs are there for something tomorrow..

 

 

 

Although no picture, Cape isn't that significant but enough. Temps Maxing at 15oC according to GFS, can't see any convergence so not sure if any triggers are that readily available.