Nick F

Storm & Convective Forecast Issued 2017-08-07 22:04:31 Valid: 08/08/2017 00z to 09/08/2017 00z CONVECTIVE / STORM FORECAST - TUESDAY 8TH AUGUST 2017 Synopsis A deep upper trough will slide east and amplify across NW Europe during Tuesday, a potent shortwave trough moving SE across Ireland towards NW France into the base of the upper trough will aid in the deepening of a low pressure system drifting north across the near continent on the forward side of the upper trough. Thunderstorms will spread NE across France Monday night and through Tuesday, with a risk of storms developing across SE UK too, while a frontal wave further north and west will bring outbreaks of heavy and perhaps thundery rain. … SE ENGLAND and EAST ANGLIA … Plume of warm, humid and unstable air spreading northeast across France with low pressure system moving north ahead of approaching upper trough to the west looks to clip SE UK on Tuesday. Thunderstorms spreading northeast across France Monday night into Tuesday morning may spread across the eastern English Channel to affect SE England and parts of E Anglia, though 'home-grown' storms may also develop aong breeze convergence too. Storms will likely be hit and miss and with weak deep layer shear, unlikely to produce widespread severe weather … though models indicate rainfall totals that warrant a MARGINAL risk of torrential downpours leading to surface water flooding. Also light winds aloft, surface convergence and fairly low cloud bases will be ideal conditions for funnel clouds or even brief weak tornadoes/waterspouts. … CENTRAL S ENGLAND, MIDLANDS, YORKS and LINCS … Slow-moving frontal wave edging north across the above areas on Tuesday will bring outbreaks of heavy rain, waves rippling along the front may produce deep enough convection for a few embedded thunderstorms along the front which will move NE, particularly during Tuesday morning. A low risk of localised flooding may occur where convective torrential downpours develop along the front. ... IRELAND, SW ENGLAND and WALES ... Shortwave trough moving SE will create steep lapse rates with surface heating in expected sunny spells and create lift of cool but moist airmass ... which will support heavy showers and a few scattered thunderstorms which maybe accompanied by hail, gusty winds and locally torrential rain. Issued by: Nick Finnis http://www.netweather.tv/index.cgi?action=convective;sess=

Heavy downpours with occasional thunder here near Croydon after a sunny morning with towers building all around

Already been some thunder across parts of Wales and SW England, more recently over Gloucestershire/south Worcs/west Oxon Storm & Convective Forecast Issued 2017-08-05 06:47:51 Valid: 05/08/2017 06z to 06/08/2017 06z CONVECTIVE / STORM FORECAST - SATURDAY 5TH AUGUST 2017 Synopsis A strong belt of upper westerlies will cover northern Europe on Saturday, with an upper trough embedded in this flow crossing west to east across the UK. An unstable showery airmass will cover the UK, with a risk of scattered non-severe thunderstorms across southern Britain. ... E IRELAND, WALES, CENTRAL and SOUTHERN ENGLAND ... Diurnal surface heating beneath increasingly cold mid-level temperatures associated with upper trough moving east will create steep lapse rates and a modestly unstable airmass across the above areas - yielding around 300-500 j/kg CAPE. As a result, scattered showers this morning will turn increasingly heavy and more widespread across central and southern areas of England and Wales through the day, as lift from upper trough combined with increasing surface temperatures increases instability. Hail and occasional thunder is likely to accompany heaviest showers spreading east. Across S England - 30-40knts of deep layer shear towards strong jet stream and local wind convergence may organise showers/storms into clusters that may bring an isolated risk of surface water flooding. However, no severe weather is anticipated, given modest instability / shear. ... SE/E SCOTLAND ... Heavy showers developing or moving in across here may turn thundery this afternoon, with a risk of hail and localised flooding. Weak vertical shear will mean severe weather is unlikely Issued by: Nick Finnis

Looks like there will be a large swathe of severe storms over the next few days stretching from the Pyrenees NE across France, Germany and into Poland along a slow-moving boundary that separates hot and humid conditions over southern Europe and the cool and changeable conditions over NW/N Europe. Would love to be in these areas to watch supercells roll through, though could be some nasty conditions. Back home, more benign showery weather thanks to the cool conditions, but nonetheless, we could see non-severe storms today, mostly Scotland, N. Ireland and parts of N England - where lapse rates will be steepest. Chance of seeing a brief tornado / waterspout in the NW - where surface wind convergence and plenty of LL instability combined with light winds aloft will be ideal conditions for them. Storm & Convective Forecast Issued 2017-07-31 09:11:19 Valid: 31/07/2017 06z to 01/08/2017 06z CONVECTIVE / STORM FORECAST - MONDAY 31ST JULY 2017 Synopsis Upper low and collocated surface low pressure system will be parked off the west coast of Scotland during Monday. A cool and unstable showery southwesterly flow will cover the UK, surface heating will allow numerous showers become widespread away from SE UK, thunderstorms most likely for Scotland and N. Ireland. ... SCOTLAND, N. IRELAND & N ENGLAND ... An upper cold pool across northern British Isles associated with upper low centred west of Scotland will create steepest lapse rates across Scotland, N. Ireland and N England ... so here will see the greatest risk of thunderstorms developing with surface heating in sunny spells. Vertical shear will be generally weak across these areas with stronger instability, though surface wind convergence along with troughs in the flow combined with lighter upper winds may bring slow-moving lines of showers/storms that could bring a risk of localised flooding. Any storms maybe accompanied by hail and gusty winds too. Across the Western Isles, western Scotland and northern side of N. Ireland - likely local surface breeze convergence, low LCLs (cloud bases), light winds aloft and strong low-level instability will be ideal conditions for rotating non-mesocyclone updrafts, so potential for some brief tornado or waterspout sightnings here.

UK Severe Convective & Storm Forecast - Issued 2017-07-31 09:11:19 Valid: 31/07/2017 06z to 01/08/2017 06z CONVECTIVE / STORM FORECAST - MONDAY 31ST JULY 2017 Click here for the full forecastCheck the full storm forecast here

Wondering why the hot weather, that teased us earlier this summer, is reluctant to return? Blame an unusually southerly tracking jet stream. View the full blog here

Notable shortwave visible as dark stripe in WV imagery approaching NW Britain and Ireland likely to support development of heavy showers and thunderstorms in this area this afternoon Storm & Convective Forecast Issued 2017-07-26 09:21:36 Valid: 26/07/2017 06z to 27/07/2017 06z CONVECTIVE / STORM FORECAST - WEDNESDAY 26TH JULY 2017 Synopsis Upper low and collocated surface low pressure system close to the west of Scotland today will drive a band of rain along a frontal system eastwards across the UK this morning. Post frontal airmass will become unstable across Scotland, Ireland and N. Ireland through the afternoon, supporting heavy showers / thunderstorms. … SCOTLAND, IRELAND + N. IRELAND … Water vapour imagery shows a marked shortwave trough in a belt of strong upper westerlies moving east towards NW Britain this morning in wake of frontal rain currently across much of mainland UK. This shortwave trough will steepen lapse rates and create forced ascent which will support the development of heavy showers and thunderstorms. Strong westerly winds aloft and backing of winds towards the surface with approach of shortwave will create fairly strong deep layer shear in the order of 30-50 knts … which will help organise heavy shower/storms into clusters and line segments. These may produce isolated strong wind gusts and also some hail. An isolated brief/weak tornado or waterspout can’t be ruled out with stronger convection which co-incides with an enhancement of low-level shear with approach of shortwave. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2017-07-26 09:21:36 Valid: 26/07/2017 06z to 27/07/2017 06z CONVECTIVE / STORM FORECAST - WEDNESDAY 26TH JULY 2017 Click here for the full forecastCheck the full storm forecast here

A very intense shower just clearing here at my parents just SW of Ashford in Kent Before (looking north) with radar Following a kind of 'whales mouth' below looking south had torrential rain but no thunder

More funnel sightings today, this may even a weak tornado over the New Forest

Storm & Convective Forecast Issued 2017-07-23 05:59:56 Valid: 23/07/2017 06z to 24/07/2017 06z CONVECTIVE / STORM FORECAST - SUNDAY 23RD JULY 2017 Synopsis Upper and collocated surface lows across eastern England will slowly drift east across the N Sea during the evening. An unstable Wly veerying NWly to Nly flow will cover England and Wales. … ENGLAND and WALES … Cold mid-level temperatures of upper low atop moist diurnally heated surface airmass will create steep lapse rates which will support the re-development of scattered heavy showers and thunderstorms today. A zone of wind convergence shifting southeast across England and Wales during the day could be the focus for storms to organise and train along, bringing a threat of localised flooding where they do organise. Otherwise weak vertical shear will mean showers and storms that develop will be dis-organised and pulse-type and will limit the potential for severe weather. Any showers/storms may produce hail and, like yesterday, there could be a few funnels or even brief weak tornadoes / waterspouts – especially where surface convergence combines with buoyant and strong updrafts. Issued by Nick Finnis Also on Netweather here: http://www.netweather.tv/index.cgi?action=convective;sess=

Intense rain here near Croydon and one close CG seen with instant load thunder while looking out the window at our overflowing gutter. Need to clean that out ...

*UPDATE 11AM ... have included a MARGINAL risk of severe weather (flooding) for parts of N England and S Scotland ... recent radar imagery and obs indicate convergence zone south of frontal boundary focusing persistent feed of heavy convective rain - which is also producing thunder ... there is a risk of localised flooding from this slow-moving zone of intense rainfall. Storm forecast: http://www.netweather.tv/index.cgi?action=convective;sess=

Just a had a rumble of thunder from heavy shower passing over in SE25

Storm & Convective Forecast Issued 2017-07-22 06:50:16 Valid: 22/07/2017 06z to 23/07/2017 06z CONVECTIVE / STORM FORECAST - SATURDAY 22ND JULY 2017 Synopsis Upper vortex and collocated surface low will drift east across England and Wales on Saturday. Airmass will be unstable across England and Wales and perhaps southern Scotland, with surface heating, leading to heavy showers and scattered thunderstorms. DISCUSSION … Cool mid-level temperatures of cold pool / upper low crossing England and Wales (500mb temps AOB -20C) will create steep lapse rates with surface heating in sunny spells. Heavy showers and thunderstorms will likely be ongoing across southwestern/southern coastal areas in the morning driven by warm SSTs, then diurnal heating will build cumulonimbus clouds elsewhere across England & Wales, high enough for charge separation to bring scattered thunderstorms. Given steep lapse rates, hail will be generated in heavy showers and thunderstorms, isolated up to 1cm in diameter, with any locally strong buoyant updrafts. Vertical shear will weak, so showers/storms will be disorganised / pulse-type convection. However, frequency of showers/storms towards the south coast and convergence near slow-moving frontal boundary across Wales, N England and Scottish borders could focus convection and lead to a localised flooding risk. However, organised severe weather is not expected. Most storms should fade after dark, as diurnal heating dissipates and airmass becomes stable. However, there may be sufficiently steep lapse rates from departing upper low atop moist surface airmass across SE England to keep heavy showers and isolated thunderstorms going after dark here, with an isolated risk of surface flooding. Issued by: Nick Finnis

Just hope there's no further flash-flooding from this squall moving across Cornwall, not exactly moving through too fast.

Storm & Convective Forecast Issued 2017-07-20 21:37:59 Valid: 21/07/2017 06z to 22/07/2017 06z CONVECTIVE / STORM FORECAST - FRIDAY 21ST JULY 2017 Synopsis A collocated upper and surface low will move in off the Atlantic across Ireland, becoming slow-moving. Associated occluding cold front will push east across England and Wales during Friday, lying Cumbria to East Sussex by 00z Saturday. SUMMARY … A band of heavy rain will accompany the occluding frontal boundary pushing east across, with some convective elements that may produce isolated thunderstorms along its length, with a risk of strong wind gusts and isolated flooding, as it moves in from the west across SW England, Wales and NW England during the day. A lower risk further east as the heavy rain reaches here in the evening and overnight. Also there is a risk of thunderstorms developing across Ireland in the afternoon, with a risk of localised flooding and isolated tornadoes. DISCUSSION … ... SW England, Wales, Midlands, NW England ... Models indicate fairly strong upward motion in association with lobes of strong positive vorticity wrapping around upper low moving in the west – particularly along/ahead frontal boundary pushing slowly east. A tongue of fairly warm and moist air drawn north ahead of the occluding cold front pushing east from the Irish Sea / SW approaches will produce some marginal low-level instability ahead of the front – due to weak lapse rates. But surface and upper support for strong lift of warm moist conveyor indicated by models along front, overlapped by strong deep layer shear of 30-50knts provided by divergent flow aloft of southerly jet streak parallel to front may be enough to produce some linear / squall convection. Main threats from this line convection, if it develops, will be brief but intense rainfall leading to flash-flooding. But strong low-level jet winds aloft may be brought towards the surface by downward momentum in any convective lines leading to a risk of strong convective gusts of 40-50mph … so have issued a MARGINAL risk for severe (flooding and strong winds). Lightning is expected to be isolated / sporadic with these frontal convective lines … given weak lapse rates forecast. ... Ireland / N. Ireland ... Post frontal airmass across Ireland / N. Ireland in the afternoon will have steeper lapse rates due to surface heating in any sunshine beneath cold pool of upper low aloft. So there is greater risk of thunderstorms/lightning developing here, though small hail and localised flooding will be the main threat here. Worth highlighting that the cold core upper low, low-level instability, steep lapse rates and low Lifted Condensation Level (LCL) here will be favourable conditions for brief funnel/tornadoes where surface convergence forms in the low pressure system crossing the area. Have issued a MARGINAL risk for localised flooding and isolated tornado risk. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2017-07-20 21:37:59 Valid: 21/07/2017 06z to 22/07/2017 06z CONVECTIVE / STORM FORECAST - FRIDAY 21ST JULY 2017 Click here for the full forecastCheck the full storm forecast here

Is a MCV (Mesoscale Convective Vortex) - look at the swirl or circulation!

Blitzortung going berserk atm!

Plenty of warmth aloft tonight spreading north out of France to fuel this elevated storms threatening the south coast, 850mb temps of 17-18C as per radar with T850 overlay

Looks like it has its own circulation the storm system NW of London ... interesting! A MCV indeed. hoping the storms over the Channel get a move on, as got be up early in the morning ...

Look like we may see a new area of storms developing over the English Channel as another 'surge' of the high theta-w plume spreading out of France interacts with shortwave, shown by dark stripe on WV image below: storm development may focus along theta-w plume 'axis' , shown by streamlines on chart below, as the plume spreads north overnight

Can see on the winds at different levels, steering winds generally mid level say 700-500mb, more backed Sly in the west to SWly over to the east, The 12z radiosonde ascent for Herstmonceux in E Sussex (SE England) shows steering flow SWly ... whereas Camborne in far SW England the steering flow is more Sly

Looking at recent satellite, looks like two storm systems with an arc SE across northern France along northern edge of plume of further Tcu and potential storms to spread north Plenty of mid-level instability above warm nose at 800-850mb upstream looking at 12z Brest and Trappes (Paris) radiosonde ascents - some shear evident with winds backed at the surface - so upscale growth into one or two MCS likely.