Nick F

Missed the storm passing to my south by a whisker, but so some distant lightning and heard several deep growls of thunder, here's the back edge updraft of the storm as it cleared just to my south.

Big deep, growling rumble of thunder to the south of here near Croydon, south London. Think the core will pass 10 miles to the south of me though

Storm & Convective Forecast Issued 2017-06-21 23:03:55 Valid: 22/06/17 06z to 23/06/17 06z CONVECTIVE / STORM FORECAST - THURSDAY 22ND JUNE 2017 Synopsis Shortwave upper trough, to the west of Ireland Wednesday evening, will move east across southern Britain during Thursday ahead of upper low near Iceland. At 12z Thursday, a surface cold front on the rearside of this upper trough will lie roughly North York Moors to Lands End at 12z Thursday, with an unstable warm humid airmass ahead of it across SE UK. an upper cold front clearing Kent and East Anglia east coast. By 00z Friday, the surface cold front has moved well to the east over the near continent, with cooler and more stable airmass following across the UK. DAY 1 CONVECTIVE FORECAST – UNTIL 06z THURS … N ENGLAND and E SCOTLAND … Thunderstorms that broke out across central and S Scotland along with N England this evening, in association with ascent of warm moist plume along its northern edge, should eventually clear away east into the North Sea in the early hours of Thursday. These storms may still pose a risk of flash-flooding, hail, frequent lightning and strong wind gusts in the next few hours. DAY 2 CONVECTIVE FORECAST – THURS 06Z – FRI 06Z … SW and S ENGLAND, MIDLANDS, LINCS and E ANGLIA … An upper cold front, marking the leading edge of colder air aloft associated with shortwave upper trough moving east in the morning will, in tandem with the shortwave, create forced ascent of warm and humid airmass present across S, central and E England over recent days. This forcing will likely form a linear band of thunderstorms, that will track east during the morning across the above areas, Unidirectional winds from the surface to 300mb, but strong aloft, will organise storms into a broken linear squall, with some bowing line segments, capable of producing locally strong wind gusts. 40-50 knots of deep layer shear and moderately unstable warm humid airmass could favour some locally large hail too, perhaps isolated up to an inch. Flash-flooding from sudden and intense downpours is also a concern, given PWAT (Precipitable Water) values forecast of 30-33mm. Storms could also produce frequent cloud-to-ground lightning too. Have issued a SLIGHT risk for flash-flooding, strong wind gusts (40-50mph) and large hail. These storms should clear away east into the N Sea/near continent in the afternoon. … N ENGLAND, N MIDLANDS, LINCS … Another area of storms could develop during the afternoon along the surface cold front clearing east across the above areas, forcing for ascent greater along the front here given better upper support. Vertical shear will be fairly weak, but storms may still produce locally intense rainfall leading to flash-flooding and maybe an isolated incidence of large hail – so have warranted a MARGINAL risk for this area. These storms clearing away into the N Sea early evening.

Kind of a loaded gun situation today and tomorrow across England and Wales, yes we have impressive CAPE values of 1500-2500 j/kg, but a cold front and/or surface convergence + strong heating may not be enough to overcome the stout cap in place. The 12z Nottingham sounding shows a warm nose between 750 and 950mb which prevents heated parcels from rising to create CBs. However, greater forcing for ascent, cooling aloft and falling heights from the west tomorrow afternoon should better allow the cap to erode to allow storms to develop across central and eastern England. If you are relating to the SE's storm prospects, more of a stronger cap in place today and tomorrow due to closer proximity of upper high to the south over near continent, probably mean any storms staying north of London tomorrow. However, cold front forming over Wales and SW Wednesday night and continued height falls + large scale ascent may bring a threat of storms to the SE on Thursday morning before the fresher air arrives. My 2 day storm forecast on Netweather website here: http://www.netweather.tv/index.cgi?action=convective;sess=

Storm & Convective Forecast Issued 2017-06-20 12:03:56 Valid: 20/06/17 12z to 22/06/17 06z DAYS 1 & 2 CONVECTIVE / STORM FORECAST - TUES 20TH & WEDS 21ST JUNE Synopsis An upper high which has persisted over southern Britain over recent days will begin to weaken and retreat SE during the rest of this week, as an upper trough approaches and moves in across western Britain by early Thursday. A surface high will drift east across northern Britain on Tuesday, pushing a weakening boundary southwards across England and Wales, separating hot and humid air to the south and cooler and fresher conditions to the north currently over Scotland. Surface convergence to the south of this boundary moving south may, with heating, trigger a few isolated afternoon storms. The same boundary will stall late Tuesday before drifting north as a warm front across northern Britain Tuesday night and through Wednesday, warm and humid plume returning north across below this warm front will likely destabilise across northern Britain early Wednesday, then further south later in the day. DAY 1 CONVECTIVE FORECAST Valid: Tuesday 12z to Wednesday 06z … WALES, MIDLANDS … Although forecast isolated storm development failed to materialise over last few days across England and Wales due to stout cap caused by upper high and warm/dry profiles, continued weakening of heights and slight cooling aloft from the NW in tandem with surface breeze convergence just to the south of boundary shifting south and stalling may breach the stout cap to allow a few isolated thunderstorms. Should a storm develop, it will tap into a reservoir of hot and humid air with CAPE values forecast in the order of 1000-1500 j/kg CAPE. High rainfall totals in a short-space of time leading to localised flooding with be the main threat from any storm that does develop, given high PWAT (Precipitable Water) values of 30-36mm pooling along convergence zones. High CAPE may also support sufficient buoyancy for isolated large hail too, though limited by lack of any appreciable vertical shear. Despite favourable parameters for storms, there are doubts that upper ridging will weaken enough to allow storms to develop, like last few days, so have refrained from severe probabilities for now. … N. IRELAND, N ENGLAND and S SCOTLAND … A shortwave trough moving NE on forward side of long wave trough approaching Ireland will likely cause large scale ascent of warm/moist conveyor returning north across the UK/EIRE Tuesday night, leading to an increase in mid-level convection and eventually the development of elevated thunderstorms by 06z Wednesday 30-50 knot SWly flow at 500mb and 30-40 knot 0-6km effective shear will support storm organisation into clusters, capable of isolated large hail, high rainfall totals leading to localised flooding, gusty winds and frequent cloud-to-ground lightning. Have issues a MARGINAL risk for severe weather across N England and Scotland. DAY 2 CONVECTIVE FORECAST Valid: Wednesday 06z to Thursday 06z … N IRELAND, far N of ENGLAND and SCOTLAND … Elevated thunderstorms are likely to be ongoing across N. Ireland, N England and Scotland during the morning with further storms perhaps developing through the day and moving NE, though they will be hit and miss in nature. Like the day 1 forecast, storms will be capable of hail, gusty winds and frequent lightning, though high rainfall totals leading to localised flooding will be main threat. Have carried over MARGINAL risk of severe weather before storms eventually clear east into the N Sea Wednesday evening. … N ENGLAND, MIDLANDS and E ENGLAND … Some elevated thunderstorms may be ongoing in the morning across the far north of England in association with destabilisation of warm moist plume returning north and destabilising across northern Britain as per forecast above, this activity clearing by afternoon. GFS and ECM forecast a highly unstable hot and humid airmass in place across much of England and Wales on Wednesday afternoon, with CAPE values in the order of 1000-2500 j/kg. Again, there is uncertainty whether the strong cap created by upper high across the south and EML (Elevated Mixed Layer) aloft will weaken, however with temperatures reaching 33C inland across central England, weakening heights and strengthening divergent winds aloft, along with weak surface trough moving east across central and northern UK creating convergence coupled with orographic lift, there may be sufficient forcing to break the cap to allow a few thunderstorms to develop across the southern Pennines, Midlands and parts of E England. Strengthening 500mb SWly flow aloft reaching 40-50 knots along with 30-40 knots of effective 0-6km shear suggests any storms that develop will quickly organise … with scope for a supercell or two … capable of producing large hail (1-2 inches), damaging wind gusts, flash flooding and frequent cloud-to-ground lightning. Also, likely discrete nature of storms and forecast strong storm-relative helicity may favour the development of tornado. However, given uncertainties of convective initiation in this region and isolated nature if storms do develop, have refrained from issuing more than a SLIGHT risk of severe weather for now, but may upgrade with the DAY 1 outlook update, if initiation looks more probable and widespread in one area. ... WALES and SW ENGLAND ... Later in the night until end of forecast at 06z Thurs, models indicate another round of thunderstorms, mostly elevated, forming along developing cold front shown on fax charts across Wales and SW England. These storms may bring a risk of torrential rain leading to flash-flooding.

UK Severe Convective & Storm Forecast - Issued 2017-06-20 12:03:56 Valid: 20/06/17 12z to 22/06/17 06z DAYS 1 & 2 CONVECTIVE / STORM FORECAST - TUES 20TH & WEDS 21ST JUNE Click here for the full forecastCheck the full storm forecast here

Higher chance than yesterday n next few hours of cumulus vertical growth breaking the cap IMO, as today we have weakening heights towards northern UK and strengthening flow aloft combining with the surface breeze convergence. Storm & Convective Forecast Issued 2017-06-19 13:28:42 Valid: 19/06/17 06z to 20/06/17 06z DAY 1 CONVECTIVE FORECAST - MON 19TH JUNE 2017 Synopsis An upper ridge covers much of central and western Europe including southern Britain on Monday, an upper trough slow-moving mid-Atlantic extending south near the Azores. Breeze convergence from development of heat low inland across central England this afternoon could trigger a few isolated heavy showers and/or thunderstorms. ... N ENGLAND, E WALES, MIDLANDS, LINCS, NORFOLK ... Satellite imagery shows cumulus field bubbling up inland across the above areas, also wind observations show some weak convergence zones developing inland across the Midlands, Yorkshire and Lincolnshire. Slight fall in heights aloft and strengthening SWly flow aloft towards northern UK this afternoon combined with surface convergence and orographic lift of hot and humid airmass in situ for last few days maybe enough to overcome the capping inversion present in a few spots in the above areas for isolated rapid cumulus growth and a few late afternoon / early evening thunderstorms. High precipitable water values of airmass indcates main concern of any storm would be large spot rainfall totals leading to localised flooding. Any heavy showers/storms should fade overnight.

My storm forecast for today: http://www.netweather.tv/index.cgi?action=convective;sess= You'll be lucky to catch one, if they do develop at all, could be a bust

Fascinatingly large differences between 00z ECMWF and GFS high res and ensemble means for 7-8 days' time (middle of next week), though the 06z GFS high res seems to be coming more round to the 00z EC idea with amplifying an intact trough just west of the UK, though not quite there with the hot plume spreading north across the UK later next week like the EC. Have talked more about the GFS vs EC debacle for next week in my blog for Netweather below:

The European ECMWF weather suggesting a heatwave for the UK later next week, but the American GFS weather model disagreed on the 00z runs this morning. Who's likely to be right? View the full blog here

Latest from Paul on the storm they are chasing over near Pine Bluff, Wyoming, looks like they caught a rope earlier!

A stunning tube captured in Wyoming this evening 4 inch hail from these supercells in Wyoming too ...

Yep, the 12z GFS and Netwx-MR shunted the instability further east, staying on near continent and clipping far east of Kent. Mind you, ECMWF all along so far has not been keen at all for a thundery plume across the SE Weds night / Thurs morning. Teach me to be led astray by the BBC forecast earlier today!

Some isolated potential for storms showing middle part of this week atm, though may change. Warm and humid air looks to be drawn north across England on Wednesday between low pressure to the west and high pressure close to the east. Some weak CAPE showing across central and northern England - weak upper forcing but orographic uplift of Pennines could trigger a few isolated heavy showers or storms. Then attention turns to Wednesday night/Thursday morning, as theta-e plume / elevated mixed layer (characterised by steep lapse rates) advecting NE across SE England / E Anglia shows signs of destabilising - as upper trough moves in from the west and surface convergence creates increased large scale ascent of the warm/moist conveyor. This could trigger some elevated storms overnight and through Thursday morning before the cold front moves through from the west in the afternoon/early evening.

Just saw some IC out toward east London from my 10th floor office view in west London

Quite a few sferics over Ireland now, line convection along cold front crossing Wales and SW England atm. though no sferics as yet, probably too shallow convection for charge separation.

Storm & Convective Forecast Issued 2017-06-08 12:17:39 Valid: 08/06/2017 12z to 09/06/2017 12z DAY 1 CONVECTIVE / STORM FORECAST - 8TH JUNE 2017 Synopsis Two upper vortices/lows are present over the far N Atlantic on Thursday, one just east of New Foundland will dig SE over the NW Atlantic, the other further east will move in across Ireland this evening and UK tonight. At the surface, a low pressure system to the west of Ireland will slide east to be across Scotland by 00z Friday, associated frontal system moving NE will bring rain NE across northern and western areas on Thursday, cold front clears east across Sern UK this afternoon, an unstable showery flow follows cold front across Ireland and western UK this afternoon, cold front clearing SE UK early hours Friday ... EIRE / N. IRELAND ... Behind cold front now moving E over Wales and SW England, an increasingly unstable SWly flow will follow, as lapse rates steepen from the west in response to upper vortex/low and associated colder air aloft spreading east. GFS shows 400-800 j/kg CAPE this afternoon/early evening across EIRE/N. Ireland as colder/drier aloft spreads atop moist airmass (dew points of 12-14C) combined with surface heating in sunny spells. This will support increasingly heavy showers and thunderstorms which will spread NE. 30-40 knot 500mb SWly flow and 20-30 knt deep layer shear will tend to organise storms into linear or bowing line segments, capable of producing large rainfall totals in a short space of time leading to flash-flooding. Also there could be some isolated marginal large hail (up to 1 inch) in some of stronger storms, given fairly large CAPE values indicated, though weak shear will tend to limit this risk. Also, low LCLs (Lifted Condensation Level) and low dew point spread combined with some locally enhanced low-level shear may support isolated brief tornado / waterspout with more bouyant updrafts. ... SW ENGLAND, WALES, NW ENGLAND and SW SCOTLAND ... Cold front may produce sufficient lift for some shallow convection which may locally produce isolated lightning, heavy rainfall and gusty winds. Also post front, steepening lapse rates from the west will promote some modest instability with late afternoon / early evening surface heating to support scattered heavy showers and isolated thunderstorms. No severe weather is expected from these. These showers and storms may continue into the night near coastal areas. ... SE ENGLAND ... Low level convergence and surface heating of moist airmass ahead of the cold front and the front itself moving from the west may support some heavy showers and isolated thunderstorms later this afternoon and into the evening. Some hail and localised flooding is possible with any of this activity. Although this activity may ease for a time, further showers with isolated lightning may arrive from the west later in the night

Brief hail shower here at Heathrow. Same line of showers that stretches along M4 corridor, sferics currently on cells over Wiltshire.

Nice line of storms to SW about to run over Chez Moi near Croydon, frequent thunder rumbling now to the south.

Some nice convection going up to north of where I am now in Beckenham, SE London

Warm but hazy sunshine now here in south London with high thin cloud, should get hot and humid enough.

Storm & Convective Forecast Issued 2017-06-02 06:50:23 Valid: 02/06/2017 06z to 03/06/2017 06z DAY 1 CONVECTIVE/ STORM FORECAST - 02 JUNE 2017 Synopsis Upper longwave trough over the North Atlantic advances eastward towards the UK on Friday, a cold front lying from SE Scotland down across NW England, Wales and far SW England at breakfast time pushes slowly east today, to lie appox. Humber to Dorset by midnight tonight. A warm and humid airmass across SE UK ahead of the cold front will become unstable this afternoon with surface heating, supporting development of a few thunderstorms. … SE ENGLAND and EAST ANGLIA … Warm/moist flow off the near continent across the above areas ahead of the cold front to the west will become increasingly unstable into this afternoon, as temperatures reach the high 20s centigrade in sunshine while low to mid-level lapse rates steepen as colder air arrives aloft with eastward advance of upper trough. GFS develops 300-600 j/kg CAPE this afternoon across the above areas, weak surface convergence and increasing large scale ascent as upper trough approaches from the west should be sufficient to allow a few thunderstorms to develop this afternoon during peak heating. 30-40 knot 500mb SWly flow may organise storms into a few linear clusters capable of producing localised high rainfall rates (20-30mm per/hour) which may lead to localised flooding. Directional shear will be fairly weak though, so storms will tend to produce only small hail and locally gusty winds. But have included a MARGINAL risk of severe weather for the risk of flooding/treacherous driving conditions.

Yep, some warm moist pooling combined with surface heating yielding enough CAPE for some storms ahead of the cold front across SE England and E Anglia Friday afternoon/early evening, triggered by some surface convergence ahead of the front. Latest fax doesn't clear front from SE and EA untill after midnight, however, speed of front clearance, as Dan mentions in his forecast, may change, quicker clearance and storms less likely to have chance to develop before the instability is removed by the cold front.

Yep, can just about see the cauliflower Tcu and dark base from my office in west London through low cloud, been some cloud breaks over central London + UHI (Urban Heat Island) effect downstream triggering the heavy shower, though no lightning yet.

My convective/storm forecast for today, just updated. Storm & Convective Forecast Issued 2017-05-28 22:08:52 Valid: 29/05/2017 06Z to 30/05/2017 06Z CONVECTIVE/ STORM OUTLOOK- 29TH MAY 2017 Synopsis Upper trough axis approaches western Britain from the west, as upper ridge extending north from the Mediterranean across Central Europe begins to relax. A plume of warm, moist and unstable air will be present across central, southern and eastern England on Monday, ahead of cold front moving in from the west, which will clear eastern England Monday night, diurnal heating of this warm humid air combined with breeze convergence could trigger some isolated thunderstorms. DAY 1 OUTLOOK - 06Z MONDAY 29TH MAY - 06Z TUESDAY 30TH MAY ... S ENGLAND, E WALES, MIDLANDS, LINCS AND E ANGLIA ... Atmosphere in the morning will likely be largely turned over by overnight storms, with a cap in place. However, abundant mositure (dew points 16-17C) and surface heating combined with breeze convergence ahead of cold front moving in from the west across England and Wales may trigger isolated thunderstorms during the afternoon across the above areas. 30-40 knts of deep layer shear should favour organisation of storms, bringing a risk of localised torrential rainfall leading to flash-flooding, isolated large hail and gusty winds. Also, an isoalted tornado can't be ruled out with storms forming along breeze convergence zones