Nick F

06z Arpege (French model) suggests east of a line from IoW to Norwich in for a shout tonight ... ties in with what GFS is showing NMM furthest west, but does show increased backing of the 500mb flow later this evening, so this maybe why its bringing storms further NW than other models. As always with plume situations, models can have difficulty handling storm coverage and extent, so will be a case of nowcasting ...

Storm & Convective Forecast Issued 2016-06-22 08:00:56 Valid: 22/06/2016 06z to 24/06/2016 06z DAYS 1 and 2 CONVECTIVE FORECASTS - 22/23 JUNE 2016 Synopsis Amplifying long wave upper trough to the west of British Isles extends SE toward Portugal on Wednesday while flow becomes increasingly backed ahead of the upper trough across Iberia, France and UK ... this allows increasingly warm and dry air aloft (850-500mb) to be drawn north from Iberia and N Africa atop of an increasingly warm moist surface plume spreading north from France which will create an increasingly unstable airmass to develop and push NE across SE UK later on Wednesday and through Thursday. Increasingly strong SWly flow aloft and increased forcing for ascent of this unstable plume with engagement of upper trough is forecast to produce thunderstorms across parts of SE England and E Anglia late Wednesday onwards through to Friday ... some of these storms may produce severe weather. DAY 1 CONVECTIVE FORECAST – WEDS 22-JUNE-2016 Valid 22/06/16 06z to 23/06/16 06z ... SE ENGLAND and E ANGLIA ... An Elevated Mixed Layer (EML) plume, consisting of warm dry layers and characterised by steep mid-level lapse rates, will continue to advect N/NE from Iberian Plateau/N Africa towards Sern England over next 24hrs atop of increasingly warm and moist boundary layer airmass spreading NE from N/W France. GFS does build several 100 j/kg CAPE across SE England, E Midlands and E Anglia, but slow-moving frontal boundary from SW England to Lincs producing extensive cloud cover/rainfall will hinder surface heating and poor lapse rates suggest the risk of thunderstorms is low, though a few heavy perhaps thundery showers developing along breeze convergence towards E Anglia and Lincolnshire coastal areas can’t be ruled out. The main thunderstorm potential in the next 24hrs develops from the south later today. Models indicate over France today very strong surface heating (temps of 30-35C) of humid airmass (dew points 20c+) - which beneath steep lapse rates of EML will allow strong instability to develop (1500-2000 j/kg) CAPE. Increased forcing for ascent of this hot and humid airmass from approaching upper trough and subtle shortwave troughs running NE in strong SWly flow aloft combined with surface convergence is indicated to trigger strong thunderstorms across northern France in the afternoon/evening. Given strong instability combined with strengthening and veering of mid-upper flow as upper trough sharpens out west, storms here may develop supercell characteristics and produce all severe hazards before growing upscale into a MCS and other storm clusters that could affect parts of SE England and E Anglia late evening and overnight period as they continue to track NE. These storms will probably be mainly elevated once they’ve crossed the English Channel, posing predominantly a risk of locally severe wind gusts and a widespread risk of excessive rainfall leading to flooding. Therefore have issued a SLIGHT risk of severe weather. Frequent cloud-to-ground lightning and hail will be an additional hazard with such storms. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- DAY 2 CONVECTIVE FORECAST – THURS 23-JUNE-2016 Valid 23/06/16 06z to 24/06/16 06z … S ENGLAND, E MIDLANDS, LINCS and E ANGLIA … UKMO fax charts indicate slow-moving cold front will lie SW-NE from Weymouth to The Wash midday Thursday, ahead of this front – a warm/humid airmass characterised by dew points of 16-18C / PWAT values of 1.2/ - 1.6 inches. Thunderstorms are likely to be ongoing Thursday morning across parts of SE England and E Anglia from overnight storm clusters /MCS moving NE from France … residual cloud cover from these storms may tend to inhibit surface instability … but eventual cloud breaks will allow instability to rebuild as surface heating of humid airmass increases. GFS indicates 500-1200 j/kg CAPE across the above areas in the afternoon/early evening. Thunderstorms are indicated to redevelop as surface heating combines with approaching upper trough and surface convergence ahead of cold front to create forced ascent of humid airmass. Storms will form in an environment of veering and strengthening flow aloft that will be characterised by 40-50 knots of deep layer shear, so storms will likely organise quickly … initially a few supercells or bowing line segments are possible … though unidirectional winds aloft will tend to line out storms. Nonetheless, all severe weather hazards are possible from storms … mainly the risk of isolated large hail (2-3cm diameter), damaging wind gusts, flash-flooding and perhaps even a brief tornado where winds back SEly and increase SREH (Storm relative helicity). Given uncertainty of how widespread storm development will be, storms maybe isolated, have issued a SLIGHT risk of severe weather for now, though upgrade to MDT in later updates. … EIRE/N. IRELAND and SCOTLAND … Atlantic upper trough axis moves in across Ireland and W Scotland on Thursday, associated cold mid-level temperatures will create steep lapse rates atop moist maritime surface airmass, with surface heating creating 200-500 j/kg CAPE in the afternoon – so scattered heavy showers and a few thunderstorms look likely to develop across the above areas. A few organised storms can’t be ruled out … producing a risk of hail, flash flooding and gusty winds locally … though modest instability and shear will limit severe risk. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-06-22 08:00:56 Valid: 22/06/2016 06z to 24/06/2016 06z DAYS 1 and 2 CONVECTIVE FORECASTS - 22/23 JUNE 2016 Click here for the full forecastCheck the full storm forecast here

Does look a bit SE UK-centric the storm risk over the next few days - some models (ECMWF/UKMO) confine the risk to Kent, Sussex, east Essex ... others further NW. Actually tomorrow late afternoon, GFS builds some CAPE across SE/E Anglia tomorrow afternoon/evening as the warm sector that moved in is subjected to surface heating and also drier mid-level air moving aloft enhancing instability. So could see some home-grown thundery downpours develop. GFS precip Weds 18z UKMO precip weds 18z We then see models develop a potential cluster of storms / possible MCS over Nern France and English Channel Wednesday night, as forcing for ascent of warm moist plume increases from the SW. Models differ to the NW extent of these storms as they track NE. As I mentioned - ECM and UKMO furthest east: ECM UKMO ... HIRLAM looks best scenario Once any overnight MCS clears the SE on Thursday morning, GFS hinting at the potential for surface-based storm development Thurs afternoon across SE England and E Anglia. GFS indicates PWAT values approaching 1.5 inches this moisture and surface heating yielding 500-1000 j/kg CAPE, mix in strong SWly jet and veering winds aloft - GFS indicates 50 knts of deep layer shear ... so potential for supercells capable of producing large hail and damaging wind gusts. Lightning wizard highlights a significant tornado parmeter too Thurs afternoon

Some healthy looking updrafts popping up around west London as the sun gets to work on the SMZ

Trailing front of a split cold front clearing SE looks to be forcing line convection across Midlands to Lincs currently, maybe be some isolated lightning in this line as surface cold front moves SE this afternoon and creates forced ascent of a shallow moist zone (SMZ) characterised by quite rich surface moisture, current dew point obs of 16-17C across central and southern England. Models show little instability, so be lucky to see this line produce much if any thunder. Storm & Convective Forecast Issued 2016-06-20 13:27:40 Valid: 20/06/2016 12z to 21/06/2016 06z CONVECTIVE / STORM FORECAST - MON 20TH-JUNE-2016 Synopsis The UK and Ireland is on the southeastern edge of upper and collocated low pressure system over mid-N Atlantic just south of Iceland. A split cold front feature clears SE from England and Wales Monday afternoon, the trailing cold front forcing a line of convection that will clear SE across central, southern and eastern England this afternoon. … CENTRAL, SOUTHERN AND EASTERN ENGLAND … A shallow moist zone (SMZ), between split cold fronts clearing SE, is characterised by dew points of 15-17C looking at recent observations. Trailing cold front stretching from SE Wales to the Humber is creating forced ascent of the SMZ and generating line convection across Midlands and E England. This narrow line of convection will continue to clear SE across central S/SE England along with East Anglia this afternoon and early evening. Although models generate little instability, there may be sufficiently strong ascent and cloud depth along the line of convection/front for isolated lightning … main risk will be temporary risk of flash-flooding as brief line of heavy rainfall moves through, also squally winds and small hail are possible from this line. A few isolated heavy thundery showers may also develop well ahead of the cold front too. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-06-20 13:27:40 Valid: 20/06/2016 12z to 21/06/2016 06z CONVECTIVE / STORM FORECAST - MON 20TH-JUNE-2016 Click here for the full forecastCheck the full storm forecast here

Quick look at potential next week, as at work ... Low risk that a few thundery showers could develop once the rain clears across southern areas tomorrow afternoon. Then, 12z GFS sweeps some elevated CAPE across the S/SE of England early Wednesday, then some surface-based CAPE Weds afternoon across eastern parts, so be interesting if something can develop out of that: Weds 03z Weds 12z 12z GFS just has a MCS Kent Clipper Wednesday night / Thurs morning ... seems to be the way it always goes I'm afraid, but still time for it to head NE further west. 00z ECM moved an MCS over the SE on Wednesday night ... so be interesting to see what it comes up with on the 12z.

Looks like that band of heavy convective rain moving SE over N and W London currently may still squeeze out the odd flash and rumble as per recent strike activity to the W and NW of London ... but not expecting anything more than heavy when it reaches here on the south side of the big smoke.

Hi, yes unfortunately they are premium, so can't post them on here. They are increasing their subscription rates soon too, so I don't think it's worth justifying to continue with their sub, just for the benefit of seeing their CAPE, snow, 32 days ahead charts, etc. Precip charts out 240hrs are freely available and generally the GFS CAPE charts are a reasonable guide, albeit you need to tone down their projections by a few 100 j/kg ... more in line with EC. Don't think EC are always closer to reality to where instability develops as it projects, but I suppose this is because the higher resolution of the modelled CAPE projections is never going to match the reality of actual local conditions (which can be affected by changes in cloud cover, topography, temperature and moisture changes, wind shifts) which can affect storm development on a local scale to make it inherently difficult for models to reslove accurately.

Storm clouds over north Kent near Sevenoaks looking SE from the North Downs this afternoon, not very electrically active but turned the hillier roads into rivers driving around under it. With regards to the next storm potential, both 12z GFS and ECMWF hinting at strengthening WAA ahead of digging trough to west of Iberia and Biscay Weds/Thurs combining with a thundery low moving NE across northern France to bring a threat of convective rainfall to the SE early Thurs. ECMWF CAPE charts on wxbell show several 100 j/kg Thursday morning too. Long way off though, with the usual shift of the risk away on to the near continent possible! Here's precip from ECMWF for 06z Thursday ...

Having seen numerous supercells in the U.S.A, I can confidently sat that isn't one in the video, a supercell would have a rotating mesocyclone in the updraft area with separate rain core and evidence of striations around the perimeter of the storm. Can't see any signs of rotation in the storm, think the way the camera is angled in different positions gives the illusion of rotation. Need strong wind shear for a supercell in this country, been little or no vertical wind shear this week, which has meant pulse type storms where downdrafts aren't separated from updrafts - which eventually suffocates the storm. We have see funnel or weak tornadoes this week, but you don't necessarily need a supercell to produce those, just surface convergence, low cloud base and weak wind aloft. Supercell would produce a stronger updraft rotation = larger hail and stronger tornadoes, given right conditions, than covergence / weak shear environment ever could.

Watching a line of cells over North Kent looking from the west on a mini chase

Emphasis for storms shifting south today, I favour areas south of M4 and London seeing some nasty storms later, convergence indicated towards English Channel coasts - so expect funnels or even brief/weak tornadoes. Here in south London, just a few distant rumbles heard so far this week from storms that were across west London yesterday evening, so hoping for some storms overhead today being the last day of this thundery period. Anyway, storm forecast for today: Storm & Convective Forecast Issued 2016-06-17 08:21:43 Valid: 17/06/2016 06z to 18/06/2016 06z CONVECTIVE / STORM FORECAST - FRI 17TH-JUNE-2016 Synopsis Upper low that's been over the UK these past few days will drift slowly east onto the near continent by Saturday morning, while a ridge of high pressure over the N Atlantic builds in from the west. At the surface, a shallow area of low pressure centred across the far SE of England at 06z will drift E over the Low Countries today. A deeply unstable airmass will hang on across southern Britain today, bringing another round of scattered diurnally-driven thunderstorms, while cooler, drier and more stable airmass moves in from the NW across central and northern Britain. ... SE WALES, S ENGLAND and E ANGLIA ... Fairly steep lapse rates atop of stagnant moist surface airmass across southern Britain today, characterised by dew points of 12-14C / temps reaching the high teens, will become unstable to surface heating where sunny spells develop ... triggering heavy downpours / thunderstorms. Lack of vertical shear again today will mean storms will mostly be pulse-type, i.e. downdrafts will not be tilted away from the updraft and so downdrafts will evenually suffocate storm updrafts and kill the storm, while new storm updratfs pop-up nearby. However, models indicate 300-900 j/kg CAPE, which combined with weak winds aloft will favour slow-moving intense burst of rainfall that will lead to flash-flooding and treacherous driving conditions in places. So have highlighted a MARGINAL risk for the flooding. Storms may also be accompanied by isolated hail up to marbe-size, gusty winds and occasionally frequent bouts of cloud-to-ground lightning. Wind convergence is indicated by models and current obs across southern coastal areas - so here we could see stronger updrafts rotate to create funnel clouds or even brief/weak tornadoes. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-06-17 08:21:43 Valid: 17/06/2016 06z to 18/06/2016 06z CONVECTIVE / STORM FORECAST - FRI 17TH-JUNE-2016 Click here for the full forecastCheck the full storm forecast here

Wind map shows a convergence zone running roughly from Norfolk down toward Hampshire, with an area of low pressure centre over Hants. Some other smaller more subtle convergence zones possible elsewhere too. The funnel spotted near Didcot/West Berks likely formed from a rotating updraft due to the spin created by opposing winds meeting along the convergence zone running through there.

Good spot! No location under your name, where are you? Swear London has a storm shield this week, anything heading this way just evaporates, one last day tomorrow of storms which should in theory deliver around here.

Storm & Convective Forecast Issued 2016-06-16 09:09:38 Valid: 16/06/2016 06z to 17/06/2016 06z CONVECTIVE / STORM FORECAST - THURS 16TH-JUNE-2016 Synopsis A long-wave upper trough extends across western Europe as far south as Morocco. An area of low pressure will be centred over S England on Thursday, with a deeply unstable showery flow circulating around this low across England and Wales. … S ENGLAND, E ANGLIA, MIDLANDS, WALES, NW ENGLAND and ERN EIRE … Cool mid-level temperatures in association with upper trough atop of moist surface airmass heated in sunny spells will create steep lapse rates which will yield around 300-900 j/kg CAPE across the above areas this afternoon. As a result of this instability, low pressure and surface convergence – heavy showers and thunderstorms will develop widely across the above areas. Storms will tend to focus near a slowly SE-ward shifting wind convergence zone separating Sly winds to the south and NEly winds to the north. Currently lying between Severn Estuary and The Wash it will drift further SE through the day. Here will see the greatest severe threat from flash-flooding and treacherous driving conditions – so have, like recent days, issued a MARGINAL risk near the convergence where storms will be most numerous. Funnel clouds or even a brief/weak tornado can’t be ruled out beneath storms that form along the convergence zone. Otherwise thunderstorms will be scattered pulse-type downpours elsewhere in above areas, but may pose a local/isolated risk of flash-flooding. Storms will tend to fade after dark, as diurnal heating wanes, though some showers will continue through the night Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-06-16 09:09:38 Valid: 16/06/2016 06z to 17/06/2016 06z CONVECTIVE / STORM FORECAST - THURS 16TH-JUNE-2016 Click here for the full forecastCheck the full storm forecast here

Interesting lowering from a storm over the Black Country earlier. Haven't heard any thunder since last week here in south London, few more days left before the thunder risk dies off over the weekend.

Just hung my washing out in the garden, which will mean the rain will now arrive after a dry day so far. Still waiting for my first thunder of the week, not heard any since last week!

UK Severe Convective & Storm Forecast - Issued 2016-06-15 12:56:46 Valid: 15/06/2016 12z to 16/06/2016 06z CONVECTIVE / STORM FORECAST - WEDS 15TH-JUNE-2016 Click here for the full forecastCheck the full storm forecast here

Looks like parts of north North Wales could see some flooding issues, a lot of slow-moving heavy downpours there in last few hours.

Pretty much agree with what Brick mentions above, bit more of a head start with insolation here in London this morning compared to yesterday, though sunny spells are brief -so modest surface heating at best today with a lot of cloud for my liking. Still - should be some storms around, and N Wales, N Midlands to Lincs /Norfolk could be prime spot for funnels or even brief/weak tornadoes due to convergence between E/NE and SW winds here. -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Storm & Convective Forecast Issued 2016-06-14 08:53:44 Valid: 14/06/2016 06z 15/06/2016 06z CONVECTIVE / STORM FORECAST TUES 14TH-JUNE-2016 Synopsis Upper low that has been to the west of the UK over recent days finally shifts across the UK by the end of Tuesday. At the surface, area of low pressure centred over N Wales this morning will shift slowly east to be centred off the north Norfolk coast by midnight. A showery circulation around this low will cover England and Wales, with increased surface heating triggering scattered thunderstorms. ... ENGLAND, WALES and EIRE ... Airmass covering UK will be cooler than recent days, but still moisture rich with dew points of 12-14C typical. Cloud breaks should allow modest surface heating of the moist surface airmass to yield 300-600 j/kg CAPE beneath increasingly steep lapse rates as cooler air edges in aloft with arrival of upper low from the west. As a result, scattered heavy showers and thunderstorms will develop. Like recent days, unidirectional winds from the surface to upper levels and little increase aloft means weak vertical shear with little organisation of storms likely. However, storms will likely be slow-moving across central, northern and eastern parts of England where winds are weak aloft - so have highlighted a MARGINAL risk for flash-flooding here. Additionally, models indicate a zone of winds convergence from N Wales to Norfolk this afternoon between E/NE winds to the N and SW winds to the south - which may allow storms to train along this zone increasing risk of localised flooding ... Also weak winds aloft, fairly low LCLs (Lifted Condensation Level) around 600-800m and surface convergence may allow funnel clouds or even a few brief/weak tornadoes to develop in the Marginal risk area. Storms will move through quicker in the south - with faster mid-level steering winds. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-06-14 08:53:44 Valid: 14/06/2016 06z 15/06/2016 06z CONVECTIVE / STORM FORECAST TUES 14TH-JUNE-2016 Click here for the full forecastCheck the full storm forecast here