Nick F

Despite the difference at the surface between 12z and 18z GFS beyond t+144, one thing they have in common is a similar upper pattern. I.e. split / bifuricated jet due to block near UK ... but eventually all energy goes into southern split branch, diving SE towards Iberia and Morocco, while the northern arm weakens. This weakening of the northern arm, in effect, allows cold air to start pouring south from the arctic toward the UK. So we have an upper low over Iberia and troughing over northern Scandi, ridge in between, then eventually the ridge is squeezed out and a large trough is carved out over much of northern and western Europe, as cold air pours down from the north. Time for some diagrams again to illustrate the above pattern evolving using jet charts: And ... if you are still in doubt that the pattern may bring riches in the coming few weeks, take a look at the NAO and AO forecasts, all keep negative. Also, despite zonal winds at 10 hPa showing signs of increasing at higher polar latitudes, the PV maybe strengthening a little, at least the core of the vortex is shifting toward Eurasia. Also note, not any serious deep cold over N America either, it's all over Russia, Siberia and E Asia. So no huge temp gradient over NE N America to fuel a strong zonal jet and Atlantic storminess for the UK for weeks on end

More jet/upper flow energy diving SE toward Iberia, Canary Isles and Morocco than over the top of the UK past T+144 - which can often lead onto good things cold and snow wise! How the jet plays end of this week, most energy over the top of UK ridge toward Scandi with some heading SW round the block into the Iberian cut-off low: By early next week, though, less energy over the top of UK ridge but a lot of energy now piling SE towards Canary Isles and Morocco - which will ultimately keep low heights over Iberia Roll further on, the jet buckles over Atlantic and forms an omega block before being undercut below as jet continues to head toward far SW Europe. this is a GOOD UPPER PATTERN for cold and snow lovers on 12z GFS ... but model volatility recent runs has shown don't get hopes up yet beyond t+144!

Risk of some intense and squally convective downpours accompanied by hail and isolated thunder pushing NE along cold front from late morning and through afternoon across southern counties, flooding main concern, more in my storm forecast here: http://www.netweather.tv/index.cgi?action=convective;sess=

UK Severe Convective & Storm Forecast - Issued 2016-11-21 10:34:49 Valid: 21/11/2016 06z to 22/11/2016 06z CONVECTIVE / STORM FORECAST - TUES 21ST-NOV-2016 Click here for the full forecastCheck the full storm forecast here

Looks like Northern France took the brunt of #stormangus with gust of 105mph on Cherbourg Peninsula and 91mph at Cap Gris Nez near Calais, for example.

Hardly any wind of note in south London, looks like the low tracked on a more southerly track than models suggested yesterday. Most seem to exit centre of low over E Anglia rather than the actual exit around Thames Estuary/ N Kent, so strong winds confined to Channel and immediate S coast. Picked up a lot of rain overnight though here, 31mm at nearby Kenley in 12hrs. Peak gusts overnight of 84mph Guernsey Airport, 74mph at Jersey Airport, 68mph Langdon Bay in Kent (exposed), 62mph at Shoreham on Sussex coast and also Isle of Portland in Dorset (exposed): not really that remarkable for exposed mainland coasts, Channel Isles worst off. http://www.weatheronline.co.uk/weather/maps/current?LANG=en&DATE=1479614400&CONT=euro&LAND=UK&KEY=UK&SORT=3&UD=0&INT=12&TYP=windspitzen&ART=tabelle&RUBRIK=akt&R=310&CEL=C&SI=mph

Oh forgot to mention I issued a storm forecast Saturday evening for a marginal risk of severe convective weather Sunday morning along southern coastal counties ... namely a low risk of a tornado or two, given highly sheared environment,and some instability, as we've seen across E Devon recently in the form of storms and some strikes appearing in the mid-E Channel now too. http://www.netweather.tv/index.cgi?action=convective;sess=

Guernsey Airport gusting to 71mph at 01z, had 84mph at Brignogan-Plages in far NW tip of Brittany earlier at 00z. Angus may have a sting in its tail like a scorpion!

UK Severe Convective & Storm Forecast - Issued 2016-11-19 23:10:31 Valid: 20/11/2016 00z to 21/11/2016 00z CONVECTIVE / STORM FORECAST - SUNDAY 20TH-NOV-2016 Click here for the full forecastCheck the full storm forecast here

Have done a blog going into more detail about approaching Storm Angus and also another troublesome low deepening tomorrow to the SW before swinging across England and Wales on Monday, here: http://www.netweather.tv/index.cgi?action=news;storyid=7785;sess=

#StormAngus, the first named storm of the season, will bring severe gales and heavy rain to southern Britain tonight and Sunday morning. Then followed by another deep low bringing heavy rain and gales for Monday. View the full blog here

Radar between 1035 and 1045 shows a 'hook' coming ashore just north of Aberystwyth - the hook then maintains across Wales and N Midlands all the way to the Lincolnshire coast some 3 hours later!! Could have been multiple spin ups or tornado touch downs in this time within the hook: Hook appears to be where the 'triple point' was in the frontal system, an area well-known in the storm-chasing community for strong ascent, shear and tornadoes

A rant over the British media's misleading use of the incorrect term 'mini-tornado' View the full blog here

Difficult to ascertain for now whether there were tornadoes causing this reported damage or just strong straight-line winds from the squall line based on anecdotal rather than pictorial evidence, though wouldn't be surprised there were tornadoes. 94mph gust at the RNLI weather station in Aberystwyth is astonishingly strong and unlikely to be synoptic driven and surprised it would be straight line wind gust either. Will have a look at the radar images for the time it went through places which reported tornadoes. I somehow managed to be in a gap/break in the squall line when it came through the SE, lol:

Storm & Convective Forecast Issued 2016-11-17 10:48:10 Valid: 17/11/2016 0600z to 18/11/2016 0600z CONVECTIVE / STORM FORECAST - THURS 17TH-NOV-2016 Synopsis A deep and cold upper trough, originating from Greenland, approaches British Isles from the NW on Thursday. A strong cyclonic W/SWly flow runs along the bottom and forward side of this approaching upper trough, with a 150 mph+ jet running east across Sern EIRE and Sern UK. A frontal wave within this strong westerly flow will track east across Wales and England this morning and through the afternoon, bringing a spell of squally rain with a risk of hail and thunder. ... WALES, CENTRAL and S ENGLAND, E ANGLIA ... Frontal wave moving in across Wales this morning from the Irish has a distinct 'comma' shape of heavy convective rainfall on radar. Strong deep layer shear in the order of 50-70knts is indicated, as the wave moves through beneath a strong jet and creates strong veering and strengthening of winds with height. So convection along the cold front/triple point of this wave moving east into England will be well organised and displaying line squall characteristics. Main risk from the squall moving east will be strong convective wind gusts, some convective allowing charts show 50-60 knt gusts, so have issued a MARGINAL risk for Wales, Midlands, S England and E Anglia. CAPE forecasted looks fairly meagre, but updrafts should be strong enough along the cold front to support hail and isolated lightning. There is also a risk of minor localised flooding from brief high rainfall rates along the squall. An isolated and brief tornado can't be ruled too along the squall, especially given strong low-level shear indicated. ... W and NW UK ... Besides the frontal wave and its squall running across Sern UK, rather steep low to mid-level lapse rates will overspread northern and western parts of the UK as increasingly cold air aloft (AOB -30C at 500mb) spreads aloft from the W and NW with approaching upper trough. As a result, scattered heavy showers accompanied by hail and isolated thunder will affect the above areas today, thunder most likely near western coasts where CAPE will be enhanced by cold air atop relatively warmer SSTs. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2016-11-17 10:48:10 Valid: 17/11/2016 0600z to 18/11/2016 0600z CONVECTIVE / STORM FORECAST - THURS 17TH-NOV-2016 Click here for the full forecastCheck the full storm forecast here

Finally some agreement between GFS and ECM on Sunday's deep low track, at T+84 (12z Sunday) both have the centre tracking across SE England, as does the MetO fax updated this morning: GFS and ECM indicating some high rainfall totals for southern counties south of M4, also GFS shows some strong southerly wind gusts Channel coasts ahead of the low. France bearing the brunt of strong winds (60mph+ gusts). Still time for the low to shift further north.

12z ECMWF ensembles highlight the sudden increase in uncertainty in the mesoscale associated with the track of Sunday's low. London ENS show a sudden spread in wind and rainfall on the 20th (Sun) and also the standard deviation for MSLP across southern UK on Sunday is quite high - giving low confidence in the low's track. Shame they have got rid of the EPS postage stamps on the ECMWF old site which they've now closed. 12z GFS, GEM, UKMO and Arpege all took the low across the UK, most far south, Arpege central UK. EC sticking with its guns along N France. Be interesting where the low tracks on tomorrow's runs.

Darn west-based -NAO developing T+264 onwards on 18z GFS ... good job it's deep FI!

Although high latitude blocking is certainly evident on today's runs, it still seems a long route to deep cold that would bring any lowland snowfall on current runs I've seen. The problem appears to be the stalling of highly amplified upper trough over western Europe next week, and slow-moving low pressure system near the UK, which ends up drawing mild air into its circulation before eventually the low sinks south as high pressure builds to the north over Iceland and Greenland. Blame the Russian high for the lack of progress eastwards - if those lows did dig deeper into eastern Europe on the southerly track - it could pull down much colder air from the NE. Alas, this doesn't look favourite for now. However, patience may eventually be rewarded with the signal for high latitude blocking to persist, but we may have to wait for the final days of November or into early December for real cold and snow potential. But that's if the blocking and jet configuration positions favourably ...

The polar vortex, which normally strengths this time of year, is weak and may remain so as we head into winter, which will increase likelihood of blocking and cold outbreaks for the UK/Europe in early winter. View the full blog here

The flow becomes increasingly meridional or buckled into the medium range across the N Atlantic and Europe, probably in lagged response to the MJO which is motoring through to phase 1 and corresponding changes in the upper flow pattern upstream across N America and NE Pacific. Upper trough amplifies deep across western Europe next week and eventually disrupts into a cut-off upper vortex across SW Europe while ridges over N Atlantic and Wern Russia/Ukraine could eventually bridge across UK to form a mid-latitude high belt. Warm upper air pumped north across central and eastern Europe on forward side of Wern European trough before then though, so like you say, not cold uppers to tap into to from the east and the split flow with jet to the north of the UK as well as the south would prevent much cold infiltration from the north too. ECMWF ENS mean GEFS mean So, synoptics not evolving perfectly yet to tap into deep cold arctic air, but the blocks are forming to prevent the usual W/SWlies to perhaps favour something colder down the line ... just the blocks aren't positioning right just yet ... If high pressure does build over the UK, it may still be cold at the surface, despite the seemingly warm uppers, especially if cold polar air was present when the high builds.

Bit of a rainbow looking east toward central London on back end of passing hail shower

Quite a heavy hail shower here at work in Hounslow, west London.

In another news ... the AO is still looking to dip negative in the medium range as cross polar height rises gain hold. Closer to home, 500mb polar vortex moves across Greenland bringing us into a Wly/NWly regime, but the mid-tropospheric vortex is on the move rather than sticking there like a limpet. On route to Scandi? EPS and GEFS seem to hint at this, but no clear signal how long this will take, get this vortex to the NE and it may allow height rises to the west and NW toward Greenland - this looks the most likely route for arctic cold to return (from the N) for now.