Nick F
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Posts posted by Nick F
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2 minutes ago, Jules777 said:
Has the main focus of lightning tues night shifted slightly more favouring areas west of I.O.W.? btw have downloaded your thunderstorm guide from a few years ago..Was VERY informative and interesting Thanks for that..
What makes you think that? Don't think there's any particular focus, will have to wait and see, GFS CAPE charts would suggest more energy aloft east of I.O.W., but as ever with storms in the UK, other than N France probably getting a lot of activity, as the norm, it's up in the air for now where the focus will be Tuesday night
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Agree Brick, storms will be rooted above the boundary layer tomorrow night, can clearly see the warm nose at 900mb on the forecast skew-ts across S England. GFS painting some strong MLCAPE shifting north out of France Tuesday, probably due to the warm moist conveyor/theta-e plume spreading north overrun by an EML originating from SW Europe - creating steep mid-level lapse rates.
So Tuesday we see the theta-e plume spread N out of France ahead of increasingly negatively tilted upper trough moving in from the west coming up against high pressure retreating east.
MLCAPE increasing out of France Tuesday night, as lapse rates steepen with EML spreading N/NE over plume in low-to-mid levels
Deep-layer shear increasing too, as mid-upper winds strengthen and veer S to SWly with height with approach of upper trough while backed SEly at the surface - so this will organise elevated convection into some storm clusters that may merge into one or two MCS with a threat of hail, torrential rain and frequent cloud-to-ground lightning.
Large scale ascent indicated by vertical velocity charts:, charts for winds aloft do show a shortwave moving NE, which is likely causing the ascent
Believe it or not, elevated strong storms, which are fuelled by large amounts of CAPE aloft, can be prolific lightning producers, particularly away from heavy rain cores - this is because electrical charges tend to dissipate through rainfall without a lightning strike (water being a good conductor) - whereas drier air the electrical charge building between the elevated base and ground has to overcome it with a lightning strike.
Wouldn't take the precip charts too literally, but we may see elvated showers/storms develop initially over SW England tomorrow evening, before developing further east along N France/ E Channel and moving N across central-S and SE England Tuesday night, before spreading across Wales, Midlands, E Anglia during Wednesday morning, before reaching N England early afternoon and S Scotland later afternoon.
Meanwhile, further south, heat and humidity could spark some home-grown storms, mainly north of M4/London (due to SWly flow into southern most counties having a drier more stable element). Deep layer shear does look fairly weak and there looks like a lack of any particularly focus or forcing other than increasing larger-scale ascent from approach of upper trough from the west. Nevertheless, though, strong heating and fairly strong SWLy flow aloft and decent CAPE may compensate .. to allow some linear clusters of locally strong storms with hail and torrential rain leading to flash-flooding the main threats.
Fingers-crossed we see some good lightning shows Tuesday night, these storms drifiting N on Weds morning and then some good home-grown surface based storms on Wednesday afternoon.
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New (provisional) max temperature record of 47.3C in southern Spain yesterday. Some of this heat spreading across France early next week and clipping southern UK by Wednesday, though with it a risk of thunderstorms.
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New (provisional) max temperature record of 47.3C in southern Spain yesterday. Some of this heat spreading across France early next week and clipping southern UK by Wednesday, though with it a risk of thunderstorms.
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New (provisional) max temperature record of 47.3C in southern Spain yesterday. Some of this heat spreading across France early next week and clipping southern UK by Wednesday, though with it a risk of thunderstorms.
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Definitely the potential on models this morning for heat to return to the far south, at least, by this time next week, as an upper trough digs south to the west of the British Isles by middle of next week, causing the flow to back ahead of it and force a dome of hot air to spread N and NE from Iberia across France / Low Countries and clipping southern UK. How the trough evolves is not certain this far out and the heat may be more reluctant to reach UK or could spread further north. Anyhow, GEFS and EPS 850mb temp anomaly shows nicely the heat plume spreading NE from Iberia next week, the blues dropping down to the west over the Atlantic showing the trough digging south
00z GFS showing 31C across far south of England next Wednesday afternoon.
As often with plumes spreading up from Iberia and reaching the UK, there could be some thunderstorms breaking out too, as cooler air aloft tries to overrun from the west with approach of upper trough.
Before then looking rather quiet on the weather front. Some rain tomorrow and again Saturday for the north, but the south dry again for several days with warm sunshine bar the odd rogue shower.
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Storm & Convective Forecast
Issued 2017-07-10 08:46:33
Valid: 10/07/17 06z to 11/07/17 06zDAY 1 CONVECTIVE / STORM FORECAST - MONDAY 10TH JULY 2017
Synopsis
Upper trough will move east across the UK on Monday, clearing eastern England this evening. At the surface, a shallow area of low pressure will be centred just off the east coast of England today, before eventually drifting east towards Denmark tonight. A weakening cold front moving east clears eastern England by midnight, a warm and humid airmass, which is unstable to surface heating, resides across E England ahead of this front.
… SE and E ENGLAND …
Upper trough moving east will introduce cooler air aloft atop of warm and humid airmass (dew points of 15-16C) towards eastern England – creating steep lapse rates and thus an unstable airmass here. Modest large-scale ascent ahead of upper trough moving east and surface heating of moist airmass will support development of scattered heavy showers and isolated thunderstorms later this morning and through the afternoon / early evening during peak heating. Thunderstorms are most likely near forecast convergence zones developing across SE and E England – where lift will be maximised. Vertical shear will be weak, so no severe weather is expected … however, there is a risk of localised surface water flooding / hazardous driving conditions from any storms, given high moisture content of airmass storms will be tapping into. Any storm should fade tonight.
Issued by: Nick Finnis
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UK Severe Convective & Storm Forecast - Issued 2017-07-10 08:46:33Valid: 10/07/17 06z to 11/07/17 066zClick here for the full forecast
DAY 1 CONVECTIVE / STORM FORECAST - MONDAY 10TH JULY 2017 -
Today's Day 1 convective forecast revised from yesterday's day 2 for today in light of storms failing to materialise across the SE ... basically forcing from a subtle shortwave from the southwest delayed though now approaching East English Channel and triggering storms here, can't rule out some developing inland this morning and perhaps this afternoon across SE. Main emphasis for storms likely to be north of London across Midlands, parts of N and E England as convergence ahead of cold front and cold front itself trigger storms, which maybe surface-based.
Storm & Convective Forecast
Issued 2017-07-06 06:44:30
Valid: 06/07/2017 06z to 07/07/2017 06zDAY 1 CONVECTIVE / STORM FORECAST - THURSDAY 6TH JULY 2017
Synopsis
A broad and increasingly cyclonic SWly flow aloft covers the UK on Thursday, an area of low pressure over NW France at the start of the forecast period will drift NE across SE England during the afternoon, a plume of warm and humid air continues to advance NE across S and E England ahead of this low. A cold front on the NW edge of the plume across Ireland this morning, as cooler Atlantic air pushes in here, will move east across central UK today.
… SE ENGLAND …
Despite most model guidance developing elevated storms across SE England before/by the start of this forecast period (6am) … these have so far failed to materialise. Current thinking is lack of forcing is there to trigger storms for now … however, WV imagery shows a subtle shortwave approaching the eastern English Channel, which is triggering isolated storms across far north of France and a few heavy thundery showers across Kent and Sussex recently. There could be further heavy elevated heavy showers moving NE from the E Channel and perhaps an isolated thunderstorm or two across the far SE this morning as the shortwave glances here. Isolated instances of flash-flooding are a possibility.
This afternoon, there is some uncertainty whether the cap in place, indicated by warm nose at 850mb by 00z Herstmonceux sounding, will be eroded by falling heights and increasing convergence as low moves NE. If the cap does break, any storm that develops will tap into a ‘reservoir’ of around 1000-1500 j/kg CAPE (GFS indicates more, but often overdoes this) and have an environment of increasing deep layer shear reaching 30-40 knts … so storms may organise updrafts which will be strong enough to produce isolated large hail (1-2 inches diameter), torrential rain leading to flash-flooding, strong wind gusts and frequent cloud-to-ground lightning. However, storms that do develop will be isolated, so a MARGINAL risk of severe weather cover London and counties to the south, however a SLIGHT risk cover northern Home Counties ... see below.
… N and E WALES, MIDLANDS, N and E ENGLAND …
Cold front and upper trough behind it moving in from the west and surface heating will induce lift of an increasing warm and moist airmass with CAPE values of 500-1000 j/kg. The atmosphere here will be less capped than further south, so storms that develop here will more likely be surface-based. Vertical wind shear will be weaker across much of N England and N/E Wales (less than 30knts) but stronger (>30knts) towards Lincs and E Anglia. Therefore greatest risk of severe weather … e.g. large hail (1-2 inches diameter), strong wind gusts and even an isolated tornado … will be towards E England – so have issued a SLIGHT risk for E England. Any storms across the above areas may produce large rainfall totals in a short space of time (20-30mm / hour) leading to localised flooding, marginally large hail, gusty winds and frequent cloud-to-ground lightning – so a broad MARGINAL risk of severe weather covers areas above not covered by a SLIGHT risk.
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UK Severe Convective & Storm Forecast - Issued 2017-07-06 06:44:30Valid: 06/07/2017 06z to 07/07/2017 06zClick here for the full forecast
DAY 1 CONVECTIVE / STORM FORECAST - THURSDAY 6TH JULY 2017 -
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Storm & Convective Forecast
Issued 2017-07-05 09:30:05
Valid: 05/07/17 06z to 08/07/17 06zDAYS 1 & 2 CONVECTIVE / STORM FORECAST - 5TH/6TH JULY 2017
Synopsis
Trough disruption on the southern flank of the broad cyclonic upper Wly flow across the far N Atlantic leads to an upper low to drift S and SE across western Iberia over the next 36-48 hours. As a result, the upper flow across southern UK will back more towards a Sly from the generally Wly flow of recent days, allowing an unstable plume of warm and humid air over Biscay, W France and Iberia to spread N across S England by Thursday morning. A shallow surface low over the Bay of Biscay will expand north across S England with the plume spreading north, thunderstorms are likely to develop and move N within this plume across central, S and E England from Wednesday night through Thursday, some storms perhaps bringing severe weather. Some storms are also possible along a developing cold front moving in from the west across N Wales and N England on the NW edge of the plume.
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DAY 1 CONVECTIVE FORECAST – WEDNESDAY 5TH JULY 2017 (05/07 06z to 06/07 06z)
… S ENGLAND TONIGHT …
Plume of warm and humid air over France on Wednesday (with wet-bulb potential temps of 18-20C) will spread north into S England in the early hours of Thursday morning, an Elevated Mixed Layer (EML) aloft originating from the Spanish Plateau atop of the warm humid airmass will create steep lapse rates which, combined with isentropic lift on the northern edge of the plume helped by subtle surface trough moving NE over Biscay, will allow development of elevated thunderstorms over N France / English Channel areas tonight – which may move inland across southern counties of England by 6am (end of this day 1 forecast). Although deep layer shear will be weak (less than 30knts) combination of forecast MLCAPE values approaching / in excess of 1000 j/kg and strengthening SWly flow aloft will allow clusters of strong elevated storms to develop and move NE – bringing a risk of hail (isolated large), torrential rainfall leading to flash-flooding and frequent cloud-to-ground lightning. A MARGINAL risk has been issued for southern counties of England for overnight period.
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DAY 2 CONVECTIVE FORECAST – THURSDAY 6TH JULY (06/07 06z to 07/07 06z)
… S and CENTRAL ENGLAND, E ANGLIA …
Warm and humid air (WBPTs of 16-18C) will continue to advect N and NE across southern UK on Thursday in tandem with surface low drifting NE from NW France. A few clusters of elevated thunderstorms with isolated hail, torrential rain and frequent lightning maybe ongoing in the morning from the start of the forecast across parts of central-S and SE England, these will continue NE across SE England, Midlands and East Anglia, with potential for further storms, perhaps surface-based, to develop in wake of these early elevated storms into the afternoon across Midlands, SE England and E Anglia.
Model forecast skew-ts indicate that LCLs (Lifted Condensation Levels), which determine where cloud bases develop, will fall through Thursday, as surface airmass becomes increasingly moist. Also, the warm/dry nose/cap at around 850mb, which keeps convection elevated above it before then, is eroded as heights fall from the west with approach of an eastward-moving shortwave trough, so surface-based storms may develop into the afternoon as lift increases with approach of shortwave trough.
Airmass will be rather unstable across S England … Elevated Mixed Layer (EML) will create steep lapse rates atop of hot and humid surface airmass characterised by dew points in the high teens and precipitable water (PWAT) values of 33-36mm) … which is forecast to yield around 1000-1500 j/kg CAPE.
A shallow area of low pressure at the surface moving NE across SE England in the afternoon will create surface convergence which, combined with increasing large scale ascent of approaching shortwave, will create forced ascent of unstable surface airmass. As a result, organised surface-based thunderstorms may develop within an environment of increasing deep layer (0-6km) shear in the order 30-40knts … as increasing SWly flow aloft and backed winds towards the surface as upper shortwave approaches from the west. Clusters of storms, perhaps one or two with rotating updrafts / mesocyclones, may pose a risk of all severe hazards ... large hail (1-2 inches in diameter) and torrential rainfall leading to flash-flooding are the main threats – though for now any such threat should be considered isolated / SLIGHT risk. Also storms maybe accompanied by strong convective wind gusts and frequent cloud-to-ground lightning ... an isolated tornado cannot be ruled out, with any surface-based storm that forms along a wind convergence boundary - where storm-relative helicity will be maximised.
… E IRELAND, N WALES, N MIDLANDS, N ENGLAND …
A cold front developing over Ireland in the morning on the NW edge of the plume spreading into Sern UK will arrive across the above central areas of the UK in the afternoon. Lift by this front of warm/moist air to the SE of front is forecast to support the development of a band of heavy showers and thunderstorms across the above areas in the afternoon/early evening – before this activity clears east into the N Sea. Hail, flash-flooding, strong winds gust and frequent lightning may accompany these storms, so have issued a MARGINAL for these areas.
Issued by: Nick Finnis
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UK Severe Convective & Storm Forecast - Issued 2017-07-05 09:30:05Valid: 05/07/17 06z to 08/07/17 06zClick here for the full forecast
DAYS 1 & 2 CONVECTIVE / STORM FORECAST - 5TH/6TH JULY 2017 -
Storm & Convective Forecast
Issued 2017-06-30 07:10:27
Valid: 30/06/17 06z to 01/07/17 06zCONVECTIVE / STORM FORECAST - FRIDAY 30TH JUNE 2017
Synopsis
Upper low drifts SE across N France during Friday, an upper ridge of high pressure slides in from the west across northern and western UK. At the surface, a shallow low over eastern England will fill and merge with low pressure system on the near continent, a light northerly flow will cover much of the UK, unstable across S England.
... S ENGLAND ...
Cooler mid-level temperatures across S England than further north, in association with the upper low over France, will create steep lapse rates here as diurnal surface heating increasing into the afternoon. As a result, models indicate a few 100 j/kg CAPE across southern counties of England, highest instability likely to the south of the M4/London - where surface convergence of moisture is likely from sea breeze moving inland against light northerly synoptic flow. So, with convergence inland from south coast, scattered heavy showers and a few thunderstorms are likely to develop by or through the afternoon. Main risk will be potential for localised flooding due to slow-movement of any showers/storms. No severe weather is expected.
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UK Severe Convective & Storm Forecast - Issued 2017-06-30 07:10:27Valid: 30/06/17 06z to 01/07/17 06zClick here for the full forecast
CONVECTIVE / STORM FORECAST - FRIDAY 30TH JUNE 2017 -
It is a common misconception still, but it's not the sun's heat that causes skin to burn or tan, it's actually UV radiation from the sun, which is both invisible and can't be felt during exposure.
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It is a common misconception still, but it's not the sun's heat that causes skin to burn or tan, it's actually UV radiation from the sun, which is both invisible and can't be felt during exposure.
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It is a common misconception still, but it's not the sun's heat that causes skin to burn or tan, it's actually UV radiation from the sun, which is both invisible and can't be felt during exposure.
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UK Severe Convective & Storm Forecast - Issued 2017-06-27 22:14:56Valid: 28/06/2017 06z to 29/06/2017 06zClick here for the full forecast
CONVECTIVE / STORM FORECAST - WEDNESDAY 28TH JUNE 2017 -
Funny how the radar always goes down when there is interesting weather to keep an eye on!
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So far, though, storms coming up from the south seem be dying before they reach here in south London
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Just now, chrisbell-nottheweatherman said:
Cheers Nick - I'm not surprised given the storm forecast on the site, where you discussed the inversion. I just wondered what you thought might be causing that interesting signal - you can see I think why an idiot like me might have wondered!Think it's just co-incidence more than anything more sinister
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Just now, chrisbell-nottheweatherman said:
Seems similar in form to this one:
May look similar on radar, but that's where any similarity ends, very unlikely to be a mesocyclone, shear too weak, CAPE in the mid-levels and storms too elevated today.
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3 minutes ago, chrisbell-nottheweatherman said:
Is this what I think it is (over Essex on N-W radar)?
Unlikely to be a hook because of a mesocyclone in that storm (that can produce tornadoes) - as storms are elevated today and also deep layer shear is fairly weak and unsupportive of rotating storms.
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Some sferics already across Cambs to W Suffolk
00z GFS showing 31C across far south of England next Wednesday afternoon.
Convective/Storm Discussion Thread - 8th July onwards
in Storms & Severe Weather
Posted
BBC forecast I saw showed storms initially across SW England, but developing and moving north further east Tuesday night. The Beeb forecasts often don't always pan out like they depict with storms, which are tricky to model by even the best supercomputers for the UK, so will be IMO, as usual, a case of nowcasting tomorrow evening!