Convective Weather UK

[BlueHedgehog074]

Norwich has dodged most of the showers today, but there was definitely soft hail in one of the showers this morning.

That's awesome, dude. Winter is sure trying to step closer to us.

[Isolated Frost]

Norwich has dodged most of the showers today, but there was definitely soft hail in one of the showers this morning.

Isn't soft hail classed as graupel?

EDIT: According to wiki it is. Look at the description at the top.

Edited October 24, 2010 by Isolated Frost

[Phil UK]

Nice looking skies to my east within the last hour with an isolated heavy shower moving southwards, with it currently over Solihull. Be interesting to know if there's any hail falling from it, though the surface layer is relatively dry and as a result cloud height doesn't look particularly high, so perhaps not despite cold mid-levels.

Hi Weather09.

No hail spotted but plenty of quite intense rain that lasted for around half an hour. And I agree with Rainbow Snow that the shower did indeed have a wintry look about it.

Had it been say another month or so down the line then I think it would have definitaley produced snow/hail even at lower levels. Maybe even rivalling that classic, but short-lived blizzard on 17th December 2009.

Still, todays shower was totally unprecedented. (Unlike what Chris Deakin said on Radio Five Live this morning! "England and Wales sunny but cold with showers confined to north Scotland and the east coast of England").

Phil.

[Harry]

Although some way off, there appears to be potential Friday into Saturday of some thundery activity across the Southeastern quadrant of the UK - UKMO & GFS charts look favourable for some moist unstable air to be driven north from between the Bay of Biscay and the Iberian peninsula, coinciding with an active CF straddling to the West...timing is crucial in this set up but it's nice to see some potential this late in the year

[Nick F]

Yes, at the moment the models show quite an active trailing cold front running up across the SE of England on Saturday -which extends SW to a developing low over NW France, forcing of warm moist Tm air ahead of the front may create some instability near/along front ... though too far off to give any confidence in anything more exiting than heavy rain occuring.

Before then, tomorrow and Thursday looks likely to be quite active convective/storm wise across the far NW, as increasingly cold upper air spreads in from the west across N and W Scotland, with troughs in the flow, so we could see some squally showers with hail and thunder tomorrow across Western Isles, western mainland Scotland and maybe Northern Ireland, especially tomorrow afternoon onwards.

[Nick F]

Have issued a forecast for risk of t-storms over ireland this afternoon and later for western Scotland and perhaps NW England:

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

[Thundery wintry showers]

Isn't soft hail classed as graupel?

EDIT: According to wiki it is. Look at the description at the top.

Yes, as far as I'm aware, "soft hail", "graupel" and "snow pellets" are all alternative terms for the same thing.

[Evening thunder]

Just had an unexpectedly torrential shower with gusty winds briefly that brought a max rainfall rate of 111.8mm/h and gave 5.4mm of rain.

[Jane Louise]

Hi all,

Woke up this morning to see that Estofex and UKASF are forecasting storms for late afternoon onwards.No mention from Met Office or any other forecasts.

[Stuart]

Storm Forecast Issued: 2010-10-31 23:00:00

Valid: 2010-11-01 00:00:00 - 2010-11-01 23:59:00

Regions Affected

S + E Scotland, N England, Midlands, Wales, Northern Ireland, Ireland (the remainder of the United Kingdom is included in the WATCH)

Synopsis

On Monday, the United Kingdom is situated under a ridge of High pressure as a result of the positioning of deep areas of Low pressure "Yentl" and "Wanda" situated to the southwest of Iceland and over Scandinavia respectively.

During Monday a series of weather fronts approach the British Isles from the Atlantic associated with "Yentl". Particular attention is turned to the trailing cold front where there is reasonable agreement for a convective line to develop later in the day.

Generally, the cold front is expected to increase in activity as it crosses Ireland during the afternoon hours, with the convective line forming from around 16z onwards over C + E Ireland as it continues to move eastwards. During the evening hours the convective line is then forecast to continue moving eastwards into southern Scotland, Wales, northern and western England, to a line from The Humber - Portland by 0z.

The convective line/cold front is likely to be accompanied by strong, gusty winds and an increased risk of a tornado developing. There is a good chance for thunder and lightning to occur in places, with small hail possible in any heavier downpours. Current thinking is the convective line will weaken and rapidly decay as it moves across East Anglia and SE England during the early hours - beyond this forecast period. The most favourable conditions appear to be over E Ireland/S Scotland/N England.

http://www.ukasf.co....orecast/id-357/

Edited November 1, 2010 by Stuart

[Coast]

ESTOFEX in agreement:

Storm Forecast

Valid: Mon 01 Nov 2010 06:00 to Tue 02 Nov 2010 06:00 UTC

Issued: Sun 31 Oct 2010 19:33

Forecaster: DAHL

A level 1 was issued for the British Isles for severe wind gusts and tornadoes.

A level 2 was issued for NE Italy mainly for excessive precipitation.

A level 2 was issued for S Italy mainly for severe wind gusts and tornadoes and to a lesser extent for large hail and excessive rainfall.

SYNOPSIS

A seasonably strong meandering upper frontal zone is stretching from the Atlantic across the northern parts of Europe into Russia. An intense jet streak imbedded in this frontal zone, and an attendant SFC cold front are expected to cross the British Isles late in the period. Meanwhile... the western European long-wave trough will be closing off into a cut-off cyclone, migrating into the central Mediterranean on Monday.

DISCUSSION

British Isles

In along the cold front that is to cross the British Isles on Monday and Monday night ... a strongly-forced line of convection is anticipated. For the given situation, the models indicate an unsusually clear signal in the CAPE/ICAPE fields. Confidence is thus rather high that a line of convection will indeed form. As usually happens with such quasi-linear convective systems ... widespread strong/severe wind gusts are to be expected, along with tornadoes associated with bow echoes/line segments. It currently seems that the majority of the gusts will be only marginally (sub)severe, so that a LVL1 should be sufficient. Comparatively shallow cellular convection is anticipated in the wake of the front. Strong wind gusts may accompany the strongest of these showers/thunderstorms.

Watch out Scotland!

[Stuart]

yes All looking good bar all the bbc weather and i am a bit :cc_confused:

[Coast]

Hi all,

Woke up this morning to see that Estofex and UKASF are forecasting storms for late afternoon onwards.No mention from Met Office or any other forecasts.

Yep, just added some other info to Stuart's post in the forecast thread, looks kinda wild up that way late afternoon into the evening!

[Stuart]

all we can do cross our fingers

[Jane Louise]

fingers crossed here again lol.Surely this is the one :lol:

[staplehurst]

Massive downgrade on the GFS today, very little chance of storms now it seems. GFS playing catchup with the UKMO eh?

[Ladyofthestorm]

Have issued a forecast for risk of t-storms over ireland this afternoon and later for western Scotland and perhaps NW England:

http://www.netweathe...onvective;sess=

Thanks Nick, look forward to persuading my little chicks to go to school in a thunderstorm tomorrow! It always happens! We never get thunderstorms in the summer always autumn and winter and the hail is huge.

[Stuart]

well i still got my hopes up still

[staplehurst]

Thanks Nick, look forward to persuading my little chicks to go to school in a thunderstorm tomorrow! It always happens! We never get thunderstorms in the summer always autumn and winter and the hail is huge.

That forecast was for last Wednesday

Reasonable agreement where exactly? Which models were in agreement? A little vague, especially considering they're monitoring the accuracy of their forecasts.

What I find quite interesting today is that they must've spotted something because they both went for similar forecasts. It's not a case of just one forecaster making a mistake, but 2 this time round. Most odd.

[virtualsphere]

What I find quite interesting today is that they must've spotted something because they both went for similar forecasts. It's not a case of just one forecaster making a mistake, but 2 this time round. Most odd.

Just out of interest, has anyone ever tried comparing the accuracy of the predictions made by all the different storm forecasting sites, ESTOFEX, UKASF etc over a sustained period of time for their area or the UK?

It's probably quite hard to do given there's only usually a small chance of a storm over any given point?

[TheToastPeople]

New UKASF forcast for tomorow Here

[Stuart]

Storm Forecast Issued: 2010-11-01 22:15:00

Valid: 2010-11-02 00:00:00 - 2010-11-02 23:59:00

Regions Affected

W & SW Scotland (Scotland, N England, N Wales, Northern Ireland, W, N + E Ireland are included in the WATCH)

Synopsis

A deep area of Low pressure "Yentl" (FU Berlin) over Iceland will dominate the weather across the United Kingdom on Tuesday.

A Pm airmass is advected southwards across the country as a cold front clears the far SE around dawn. Scattered showers and isolated thunderstorms are forecast to affect the western side of Scotland and the Northern Isles during the day. Given the airmass, hail is likely in many of the showers, perhaps locally moderate in size across the Northern Isles. There exists a risk of a weak tornado developing.

Showers will persist into the night period over the same areas, whilst further south a frontal feature moves eastwards across central U.K..

http://www.ukasf.co.uk/module-Storm/mode-forecast/id-358/

[staplehurst]

It is indeed odd. And I notice UKASF have taken down their forecast for today and have now issued one for tomorrow. Don't they usually wait until the end of the forecast period before issuing the next forecast? I think they couldn't wait to take down their forecast for today, given its inaccuracy (lol).

My guess is that given the strong upper flow over the UK and significantly backed surface winds ahead of the cold front, resulting in strong DL and LL vertical wind shear, this has lead ESTOFEX to issue a level one as any rising parcels would give rise to the possibility of rotating updrafts. But, for an updraft to develop we must have instability, and this is where I get confused with their forecast. They seem pretty confident that conditions look favourable for sufficiently buoyant updrafts aided by forcing of the cold front.

Going by the recent GFS model runs, no instability has been modelled. There is, however, significant intrusion of dry air in the mid levels modelled to pass over Wales and England this evening. So perhaps at a fairly long reach, you could say there's a slight possibility of severe convective wind gusts if some instability did happen to be released; this would arise if updrafts were strong enough to mix with the dry air, and then transfer the strong mid-level winds down to the surface. But given little moisture at the surface and rather neutral lapse rates, instability is non-existent.

Yeah, it is very weird - shame it didn't come off! :lol:

UKASF operate like ESTOFEX in the sense that they create their forecasts usually before midnight for the following day. They can both be viewed here http://ukasf.co.uk/module-Storm/ until midnight when the old forecast is removed from that page leaving the new one. However, when a new forecast is issued it supercedes the old one on the home page.

Could be a long wait for a storm in Norwich then.

[Coast]

and again this morning, ESTOFEX are following that with:

Storm Forecast

Valid: Tue 02 Nov 2010 06:00 to Wed 03 Nov 2010 06:00 UTC

Issued: Tue 02 Nov 2010 01:04

Forecaster: KOROSEC

A level 2 was issued for south-central Italy and Adriatic sea as well as for eastern Adriatic coast mainly for excessive convective rainfall, strong winds, tornadoes and large hail.

A level 1 was issued for surrounding areas of level 2 mainly for excessive convective rainfall.

A level 1 was issued parts of British Isles, north Sea and Denmark mainly for strong to severe wind gusts.

SYNOPSIS

A strong zonal flow has established across northern Europe, where deep surface low is placed west of Scandinavia. The main cold front rapidly moves east while another one stretches across British Isles.

Over southern Europe, a slowly weakening large upper low makes only slow SE progress from across central Italy. Along/ahead of an attendant surface frontal zone, another round of excessive rainfalls and severe storms is expected.

A building upper ridge moves into SW Europe with high pressure system expanding towards central Europe by Wednesday morning.

DISCUSSION

British Isles, North Sea...

Strongly sheared environment with deep-layer shear exceeding 30m/s is embedded within the zonal flow, wraping around the deepening surface low north of UK. The main frontal zone moves east into Scandinavia in early morning hours and should locally support some strong winds where stronger convective cells will occur. Behind this front, cold maritime airmass will spread into North sea and UK, showers and a few thunderstorms could occur. While southern UK will be affected with belt of WAA coming from SW ahead of a new front, environment will become supportive for convection and/or convective lines once the frontal zone moves through. Though models are showing only weak instability signals, very high shear is well favorable for some strong cells/lines across the level 1 area. Expect strong to severe wind gusts locally along these line(s). However, very high speed shear and quite high SREH, but limited instability, could as well support stronger cells with embedded rotating updrafts.

[Stuart]

Going to cross my fingers Today Agan