Nick F

Certainly tomorrow's date record of 28.3C set back in 1934 is under threat. Ironically, eastern England is forecast to be hotter than southern Spain tomorrow, which has just come out of a record heatwave when last week temperatures reached 45C (114F) Max temps last Tuesday across Spain: Looking at the medium range of the operational runs today, GFS appears to have been more progressive in keeping a deeply cyclonic flow close or over the UK, whilst the ECM keeps the Atlantic trough further west towards the end of the run, with a ridge being thrown north across the UK, so summer warmth may return again. 12z EC and GFS comaprison reflacts this difference:

Southern UK this week taps into some of the record heat that's bothered Spain, before the supply of heat is cut-off by the weekend heralding more autumnal weather to take over. View the full blog here

Bit of toing and froing from the models over how much influence the persistent ridge over central Europe will have on the UK against an rather active jet roaring across the Atlantic toward NW UK. The Euro ridge relaxes from Thursday and through this coming weekend to allow a succession of low pressure systems to brush NW UK and bring cooler/fresher conditions, wet and windy conditions in the NW from Thursday and rain for all by the weekend. But model uncertainty grows next week over whether the Euro ridge gains more influence across S/SE UK next week, returning summer warmth as per 00z EC op or whether Atlantic upper trough will be the dominant force across the UK as per 00z GFS op. 00z EPS and GEFS 500mb mean/anomalies for Wednesday next week indicates trough disruption off SW Europe, which indicates Atlantic trough being pushed back by the Euro ridge, so 00z GFS op maybe a little over-progressive in pushing in Atlantic trough axis across the UK

Newton has deepened into a Category 1 hurricane overnight, currently has max sustained winds of 90 mph with a central pressure of 979mb, closing in on the southern end of the Baja California, could strengthen into a Cat. 2 briefly before it crosses Baja Cal. then continues across the Gulf to mainland NW Mexico. SUMMARY OF 1200 AM MDT...0600 UTC...INFORMATION ----------------------------------------------- LOCATION...22.2N 109.5W ABOUT 60 MI...200 KM SSE OF CABO SAN LUCAS MEXICO ABOUT 145 MI...235 KM SSE OF LA PAZ MEXICO MAXIMUM SUSTAINED WINDS...90 MPH...150 KM/H PRESENT MOVEMENT...NW OR 325 DEGREES AT 17 MPH...28 KM/H MINIMUM CENTRAL PRESSURE...979 MB...28.91 INCHES FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 21.3N 109.0W 80 KT 90 MPH 12H 06/1200Z 23.3N 110.3W 90 KT 105 MPH 24H 07/0000Z 26.1N 111.5W 65 KT 75 MPH...INLAND 36H 07/1200Z 29.2N 111.8W 60 KT 70 MPH...INLAND 48H 08/0000Z 32.1N 110.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 09/0000Z...DISSIPATED Public Advisory: http://www.nhc.noaa.gov/text/refresh/MIATCPEP5+shtml/060559.shtml? Forecast Advisory: http://www.nhc.noaa.gov/text/refresh/MIATCMEP5+shtml/060254.shtml? Discussion: http://www.nhc.noaa.gov/text/refresh/MIATCDEP5+shtml/060255.shtml? Flash-flooding and mudslides the main issue, particularly in the mountainous areas, as 5-10 inches expected to fall along coasts, locally as high as 15 inches. Wind damage likely over southern Baja Cal. and coastal areas of mainland NW Mexico for a time too before Newton weakens. Could bring a flash-flooding risk to parts of Arizona and western New Mexico later in the week, as the remnants arrive here, so some relief for the moderate drought affecting much of the desert SW of the U.S. I did a blog yesterday about the 2016 hurricane season ramping up now, coming on the back of 7 years of a hurricane drought for the N Atlantic, though currently the wave over the eastern Caribbean has a low chance of tropical cyclone formation, while the wave over the eastern N Pacific has 50% chance of TC formation over next 5 days, though far away from land.

With regards to question (1), current wind obs can be useful in showing wind convergence, as Jo suggests the reason for the clouds 'colliding', xcweather I sometimes use to pick out winds converging (i.e. opposing wind directions meeting): http://www.xcweather.co.uk/ Netweather extra (and maybe free?) has GFS wind streamline charts that can pick out lines of covergence too, bearing in mind wind conv. can form from synoptic flow as well as sea breezes which aren't modelled so well:

Hermine hit Florida last Friday as a Cat. 1 Hurricane. But with a hurricane drought for the U.S. over recent years, 11 years since a major hurricane hit the mainland, could the 2016 hurricane season be starting to ramp up? View the full blog here

As much as I love watching storms, don't envy anyone in a tent on Exmoor right now! Hopefully in a nice warm and dry pub or in the car, that's where I'd be ...

TORRO have a Convective Discussion out for S Wales, central and S England too ... which echoes my thoughts earlier http://www.torro.org.uk/forecast.php

Some pretty intense echoes with lightning moving in across N Devon / N Somerset currently, must be wild on Exmoor. First band of moderate rain clearing here in Kent where I am this evening, but it's the second band along second cold front coming through SW England and S Wales that is more active, be interesting if these bowing line segments continue to track further east with the thunder risk, certainly wise to have issued the alerts for flooding. Nice little storm headed for Dublin too.

Think there is a risk of thunder embedded in linear convection that may develop along cold front as it slowly clears S England this evening and overnight. Otherwise, post frontal airmass with steeper lapse rates could support one or two storms amongst heavy showers moving in from the west across western areas and Ireland overnight. Say the risk is small of catching a storm, but given decent shear, could be potential for isolated severe weather. Storm & Convective Forecast Issued 2016-09-03 14:57:12 Valid: 03/09/2016 06z to 04/09/2016 06z CONVECTIVE / STORM FORECAST - SAT 3RD-SEPT-2016 Synopsis An upper trough to the west of Ireland Saturday morning will shift east across the UK later and overnight into Sunday morning. An area of surface low pressure also west of Ireland this morning will move east across N England this evening before moving out across the N Sea. Associated fronts will bring a spell of heavy rain across most parts today, cold front clearing SE England and E Anglia in early hours of Sunday could produce convection/thunderstorms and post cold front Pm airmass will also support heavy showers and some thunderstorms … EIRE, ENGLAND and WALES … Upper trough and associated cold air aloft moving in from the west this evening will steepen lapse rates across the above areas this evening and overnight, behind the frontal rainfall clearing east today. Some lines of convection/embedded storms may develop along or just ahead of the cold front clearing this evening/overnight across S England – as this colder air aloft overruns the warm/moist airmass ahead of front which is being forced to ascend along the front. Otherwise, scattered heavy showers and perhaps a few isolated thunderstorms will likely affect western areas of England along with Wales and EIRE later today and overnight. Fairly strong DL shear in the order of 30-50 knots maybe supportive of storm organisation, with strong convective wind gusts and torrential rain leading to localised flooding possible – particularly with any line convection along or near the cold front . Strong low-level shear just ahead of the cold font, with winds veering with height, may support long-lived linear cells or bowing line segments that may produce hail and an isolated brief/weak tornado too. Have issued a MARGINAL risk across S England and perhaps S Wales for the low severe risk along cold front as it slowly clears this evening and overnight. Otherwise, post frontal storm risk is covered by a general thunderstorm area for isolated risk of storms that may produce hail, gusty winds and localised flooding. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-09-03 14:57:12 Valid: 03/09/2016 06z to 04/09/2016 06z CONVECTIVE / STORM FORECAST - SAT 3RD-SEPT-2016 Click here for the full forecastCheck the full storm forecast here

Slight update to my storm forecast issued last night, to include a SLIGHT risk of severe weather from central S England NE to E England, can't ignore large SBCAPE values showing and potential for low-level inversion to be breached where CZ develops inland here. It is small/isolated risk, but should sfc based storms develop, they could quickly turn severe: Storm & Convective Forecast Issued 2016-08-26 23:02:33 Valid: 27/08/16 06z to 28/08/16 06z CONVECTIVE/STORM FORECAST - SAT 27TH-AUG-2016 Synopsis Upper trough to the west of the British Isles will slowly advance eastwards during Saturday. Ahead of the trough, a plume of warm and moist air, characterised by WBPT/Theta-w values reaching 16-18C, advects north in across S England early Saturday. A warm front will move in across S England by 12z Saturday marking the boundary of warm and humid air moving in from the south at the surface. … E WALES, S ENGLAND, MIDLANDS, E ANGLIA, N ENGLAND … An elevated mixed layer (EML) characterised by steep mid-level lapse rates will move north in tandem with plume of warm/moist air below. Isentropic lift of the plume ahead of the warm front may create sufficient instability in the mid-levels above a stable cooler and drier boundary layer to support development of scattered heavy showers and perhaps isolated elevated thunderstorms early on in the day across southern counties of England. These early showers and isolated storms tending to drift NE across The Midlands and Eastern parts of England during the day north of the warm front above a stable cool/dry boundary layer. Any elevated storms could produce frequent cloud-to-ground lightning locally and also a risk of flash-flooding. So have issued a marginal risk for severe weather. Drier and sunnier conditions returning to S/SE England late AM into PM, where surface will likely remain capped, but with strong surface heating of humid airmass, where skies clear, yielding towards 1000 j/kg CAPE. There is a small risk that surface breeze convergence and surface heating will be sufficient to overcome the cap to produce some isolated thunderstorms here later afternoon/early evening. Any sfc-based storm that does develop may organise, given 30-40 knts of DL shear, to produce large hail (2-3cm), strong winds gusts and torrential rain leading to flash-flooding. Large CAPE modelled, enhanced LL shear near/along warm front and low LCLs look favourable for storm rotation that may lead to a tornado too. Have higlighted a SLIGHT risk for this potential for severe weather near the warm front from central S England NE across S Mids, Nern Home Counties, Lincs and E Anglia. BUT it should be stressed that surface-based storm development is rather uncertain given cap, cloud clearance and forcing (or lack of). Further N and W, increasing large scale ascent by upper trough approaching from the west, lift from shortwave trough moving in across the SW early evening and increasingly cyclonic and strengthening mid-level flow may trigger some surface-based storms along the edge of unstable plume across E Wales, Midlands and parts of N England during the evening. These storms could produce large hail, gusty winds and a risk of flash-flooding, but given uncertainties over extent, will stick with the MGNL risk for here for now Issued by: Nick Finnis

Storm & Convective Forecast Issued 2016-08-26 23:02:33 Valid: 27/08/16 06z to 28/08/16 06z CONVECTIVE/STORM FORECAST - SAT 27TH-AUG-2016 Synopsis Upper trough to the west of the British Isles will slowly advance eastwards during Saturday. Ahead of the trough, a plume of warm and moist air, characterised by WBPT/Theta-w values reaching 16-18C, advects north in across S England early Saturday. A warm front will move in across S England by 12z Saturday marking the boundary of warm and humid air moving in from the south at the surface. … E WALES, S ENGLAND, MIDLANDS, E ANGLIA, N ENGLAND … An elevated mixed layer (EML) characterised by steep mid-level lapse rates will move north in tandem with plume of warm/moist air below. Isentropic lift of the plume ahead of the warm front may create sufficient instability in the mid-levels above a stable cooler and drier boundary layer to support development of scattered heavy showers and perhaps isolated elevated thunderstorms early on in the day across English Channel and southern counties of England. These early showers and isolated storms tending to drift NE across The Midlands and Eastern parts of England during the day north of the warm front above a stable cool/dry boundary layer. Any elevated storms could produce frequent cloud-to-ground lightning locally and also a risk of flash-flooding. So have issued a marginal risk for severe weather. Drier and sunnier conditions returning to S/SE England late AM into PM, where surface will likely remain capped, but with surface heating of humid airmass yielding towards 1000 j/kg CAPE. There is a small risk that surface convergence and surface heating will be sufficient to overcome the cap to produce some isolated thunderstorms here later afternoon/early evening. Any sfc-based storm that does develop may organise, given 30-40 knts of DL shear, to produce large hail and torrential rain leading to flash-flooding. Parameters, such as LL shear and LCLs look favourable for storm rotation that may lead to a tornado too. But risk is too low to warrant more than the MGNL risk for the elevated storm risk as above. Likewise, increasing large scale ascent by upper trough approaching from the west, lift from shortwave trough moving in across the SW early evening and increasingly cyclonic and strengthening mid-level flow may trigger some surface-based storms along the edge of unstable plume across E Wales, Midlands, Lincs and parts of N England during the evening. These storms could produce large hail and a risk of flash-flooding, but given uncertainties over extent, will stick with the MGNL risk for now. Issued by: Nick Finnis http://www.netweather.tv/index.cgi?action=convective;sess=

UK Severe Convective & Storm Forecast - Issued 2016-08-26 23:02:33 Valid: 27/08/16 06z to 28/08/16 06z CONVECTIVE/STORM FORECAST - SAT 27TH-AUG-2016 Click here for the full forecastCheck the full storm forecast here

Think we all understimated how deep the cap was and the lack of forcing to break it, there's been some rainfall, but from mid-upper level instability through differential thermal advection. These plume breakdowns are often notoriously difficult to forecast, or rather, I and maybe others maybe get too optimistic that something interesting will develop. Lessons learned to be more cautious when there are heavy caps in place! Seems to be increased forcing moving up from the Channel now as per strikes over Channel isles and off Brittany, so it ain't over yet.

With any luck, ex-Gaston will throw a strong ridge N or NE across the UK, via WAA, if it follows the usual path NE towards the gap between Iceland and Scotland ... dependent on how quickly its absorbed and keeps or loses its intensity as merges with the upper westerlies/Atlantic trough. But as John says, expect some model wobbles on the way as they try to get to grips with the energy it will pump into the atmosphere and how this will affect the upper pattern over the Atlantic.

Temperature rocketing to 28C under blue skies at a few stations in Suffolk and Kent now. Close to 29C Headcorn aerodrome. Will we hit 30C? Nothing electrical anywhere near the UK for now, though forcing currently over Biscay, producing some mid-level storm activity, should arrive across southern England early evening before moving NE over central and eastern England.

just looking at the 12z Herstmonceux radiosonde ascent and it looks quite unstable in the mid-levels upwards but a notable warm and dry nose (cap) at around 900mb which would likely prevent any surface based convection in the flow across the SE, unless some substantial forcing develops. PWAT of 37mm is ringing the alarm bells if storms that form do root into the boundary layer though! Some surface convergence apparent across central S England and The West Country to Welsh Borders could trigger something, though a lot of mid-level cloud cover may inhibit the 'spark'. May have to rely on the mid-level convection pushing up from the SW for the thunder fix.

Bit late with my forecast, but a lot to take in and tricky to forecast the potential for severe weather, which despite favoured by parameters is dependent on forcing breaking the cap, but will give it my best shot ... Storm & Convective Forecast Issued 2016-08-25 08:53:04 Valid: 25/08/2016 0600z to 26/08/2016 0600z CONVECTIVE / STORM FORECAST - THURS 25TH-AUGUST-2016 Synopsis Upper trough over the N Atlantic continues to slowly advance across western British Isles, ahead of it a slow-moving waving cold front lies SW-NE across England and Wales during Friday, with an unstable warm and humid airmass ahead of the front across central, southern and eastern England. There will be a continuing risk of thunderstorms along and ahead of the cold front on Thursday. Also, EIRE, N. Ireland and western Scotland will be at risk of a few storms later as upper trough and associated cold mid-levels moving in steepens lapse rates. … E WALES and ENGLAND … A departing shortwave or vort max bringing some elevated storms to E Anglia this morning now clearing, otherwise, forcing for ascent will initially be too weak this morning to produce much in the way of convection from the potentially unstable warm and humid conveyor continuing to advect NE across England. However, WV imagery this morning shows a subtle shortwave trough moving NE over the Bay of Biscay, currently producing storms over the same area. This shortwave may engage cold front to develop another wave to ripple NE across England. Increased low-level convergence ahead of frontal wave and large scale ascent aloft from shortwave and approaching large scale trough to the west will favour the re-development of elevated storms tracking NE embedded in more general heavy rainfall expected to re-develop close to or along slow-moving cold front across northern and western parts of England on Thursday. There is a risk of localised flooding produced by these storms, particularly this evening and through into the overnight period across central and eastern parts of England, when most models expand coverage of heavier rainfall as forcing increases with approach of upper trough from the west. So have included a MARGINAL risk of severe weather. Further east across SE England and E Anglia, capping of warm and humid surface airmass will be present, good sunny spells spreading NE here this morning should allow strong surface heating by this afternoon, with CAPE values approaching 1000 j/kg indicated by models. Surface heating, low-level convergence, increasing lift aloft from approaching shortwave trough and approaching large scale upper trough to the west may produce sufficient forced ascent to break the cap this afternoon to allow a few surface-based storms to develop across eastern England. A SLIGHT risk has been highlighted for E England for the potential of surface-based storms which will tap into a rather warm and moist surface airmass (dew points of 17-18C) and will likely quickly organise within an environment of strong deep-layer shear in the order of 40-50 knots. Supercells may develop briefly, capable of producing isolated large hail (2-3cm), torrential downpours leading to flash-flooding, strong winds and frequent cloud-to-ground lightning. Also, low-level wind convergence from sea breeze interaction with synoptic flow and outflow from convection further west near cold front may even produce an isolated tornado or two, given large CAPE and sufficiently low LCLs. However, there remains a question mark over whether there will be sufficient forcing to break the cap to produce such storms, so stuck with a SLIGHT risk. Cold front is expected to gradually clear east from E England during first part of Friday morning, any severe surface based storms will clear into the N Sea late evening, then more general heavy rainfall with embedded elevated storms will move in from the west overnight before clearing the east coast by dawn. There will be continued risk of isolated flash-flooding overnight from these embedded storms. ... EIRE, N. IRELAND, SCOTLAND ... Lapse rates will steepen here later as Atlantic upper trough moves in aloft and introduces colder air aloft. So scattered heavy showers and thunderstorms will be on the increase here today. Deep layer shear and upper wind strength will be sufficient for some storms organisation, with hail and gusty winds possible, though cooler surface temperatures and modest moisture will tend to limit severe potential. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-08-25 08:53:04 Valid: 25/08/2016 0600z to 26/08/2016 0600z CONVECTIVE / STORM FORECAST - THURS 25TH-AUGUST-2016 Click here for the full forecastCheck the full storm forecast here

Got an elevated storm just to the south of Heathrow where I am at work this evening with several white/pink forks of lightning seen, though fairly infrequent. Planes still landing despite the lightning close by...

Storm & Convective Forecast Issued 2016-08-24 09:26:16 Valid: 24/08/2016 0600z to 25/08/2016 0600z CONVECTIVE/STORM FORECAST - WEDS 24TH-AUGUST-2016 Synopsis Amplifying upper trough to the west of the British Isles will continue to advect a plume of hot and humid air north across south and east England on Wednesday ahead of a slow-moving cold front lying between NE and SW England. Although the cold front is inactive for now, a wave will develop from the SW this evening and overnight, bringing an increased risk of thundery downpours across southern, central and eastern England tonight. … S and E ENGLAND, SE WALES, MIDLANDS … Hot and humid airmass across S and E England on Wednesday will be strongly capped by upper ridge on near continent, despite models indicating several 100 j/kg CAPE building this afternoon thanks to strong surface heating. However, slowly falling heights from the west and shortwave upper trough, visible on WV imagery, triggering storms across NW Iberia this morning, will move NE toward S England later. This increase in upper forcing and subsequent re-activation of cold front as it develops a wave moving NE will allow the development from this evening of isolated elevated thunderstorms pushing NE from the English Channel and central southern England up through the Midlands towards Yorks, Lincs and Norfolk. There is some uncertainty over eastern extent of these storms, with some isolated storms possible across SE England too later in the night. Some organisation into multicell clusters of storms is possible, given strengthening mid-upper SWly flow aloft and 40-50knts of deep layer shear. However, much of the rain falling from these elevated storms may evaporate before it reaches the ground, given very warm dry air at the surface, so rainfall will not pose much of an issue until perhaps later in the night across The Midlands and NE England as moister air and greater forcing moves in. Frequent cloud-to-ground lightning and perhaps isolated strong wind gusts will be the main hazard from these storms. Have not issued a categorical severe risk for storms overnight into Thursday for now, but may later today if storms become organised. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-08-24 09:26:16 Valid: 24/08/2016 0600z to 25/08/2016 0600z CONVECTIVE/STORM FORECAST - WEDS 24TH-AUGUST-2016 Click here for the full forecastCheck the full storm forecast here

Have issued a storm forecast for Saturday, plenty of showers and the odd storm in the strong flow rotating around the unseasonably deep low crossing northern Britain tomorrow, can't rule out a storm almost anywhere, but central and northern areas most at risk where greatest forcing will be near the low: http://www.netweather.tv/index.cgi?action=convective;sess=

UK Severe Convective & Storm Forecast - Issued 2016-08-19 08:02:49 Valid: 20/08/2016 00z to 21/08/2016 06z CONVECTIVE/STORM FORECAST - SATURDAY 20TH AUGUST 2016 Click here for the full forecastCheck the full storm forecast here