Nick F

Storm & Convective Forecast Issued 2018-08-06 21:33:50 Valid: 07/08/2018 00z to 08/08/2018 00z THUNDERSTORM OUTLOOK - TUESDAY 7TH AUGUST 2018 Synopsis North Atlantic upper trough will begin to amplify S and SE across the far west of Britain during Tuesday, with a strengthening upper flow across the UK – as SWly jet stream shifts S and E across the UK. Ahead of the jet streak, a weak surface cold front will progress slowly east, to lie North York Moors - West Sussex by 00z Weds. A very hot, humid and increasingly unstable airmass ahead of the cold front across SE England and East Anglia is forecast to destabilise and produce thunderstorms in the evening here before the front clears through and introduces cooler and more stable air. … SE ENGLAND and E ANGLIA … Surface-based CAPE will build up through the day due to surface heating of humid plume in conjunction with lapse rates steepening in association with advection north of EML (elevated mixed layer) aloft. However, this surface instability is likely to remain capped. However, a shortwave in the strengthening flow aloft will move NE from Bay of Biscay area in the morning crossing NW France in the afternoon. The increased lift by the shortwave along NW edge of hot and humid plume over France and SE UK combined with increasing mid-level instability as dry air intrusion punches NE overlapping plume, is forecast by many models to break out thunderstorms across Brittany and Normandy by early evening, before spreading / expanding NE across SE England then East Anglia through the evening. Thunderstorms are likely to be elevated, though 40-50 knots of 0-6km shear forecast will allow storm organisation into clusters, perhaps even an MCS passing over parts of Kent and eastern E Anglia, so there is potential for strong storms that may bring locally intense downpours leading to flash-flooding, isolated hail, strong wind gusts and frequent cloud-to-ground lightning. These storms should clear away NE into the North Sea after midnight. Issued by: Nick Finnis

Quite alarming wind gusts with Sunday low on 12z GFS, further south too, be bad enough in depths of winter, but with trees in full leaf … Be interesting to see if the 12z ECMWF begins to run with the deep low idea later.

Big storm GFS keeps showing headed across the UK this weekend looks like containing the remnants of post-tropical cyclone Florence, the U.S. pressure chart shows it off NE seaboard tomorrow - then follow the GFS pressure loop from tomorrow through to Sunday. Remnants of Florence and frontal boundary between tropical and polar air engaging with sharp shortwave trough in the upper westerlies coming out of NE Canada/new Foundland - this serves to deepen the low on the forward side of the trough moving east, also note the steepening thermal boundary through the low ahown by 850mb temps in animation above which will aid in cyclongensis,

Yep, 00z GFS and ECMWF chalk and cheese for early next Sunday (T+120) at the surface, while the 500mb flow is broadly similar. I guess much depends on how a sharpening shortwave trough in the strong upper westerlies / jet leaving New Foundland on Friday interacts with the frontal boundary stretching west from Iberia to the north of the Azores and further west. If the shortwave phases ideally with the frontal boundary, cyclogenesis will occur which may carry a deepening low towards the UK. GFS has been keen on this for the weekend last several runs and again on the 06z run. EC not buying the weekend deep low last few runs. Be interesting to see who's right, as GFS threatens a nasty low on 00z with widespread gales or severe gales on Sunday, which with trees in full leaf will cause widespread disruption.

Yikes

Although Florence has weakened to cat 2, the weakening associated with increased shear and dry air entrainment at the unusually higher latitude which Florence has been tracking west than would be the case with track further south, but the weakening only of max wind speeds while the strong wind field has become larger as the storm expands in extent, couple this with slowing down as it approaches North Carolina coast, the threat from catastrophic flooding from storm surge and heavy/prolonged rainfall remains and coastal areas of NC and SC will still be affected by hurricane force winds.

22 foot wave height WNW of Florence, good idea to evacuate low lying coasts and islands

Florence looking rather ragged in appearance on its SW side, likely due to undermodeled slight shear from PV streamer with dry air aloft on south side, which maybe why Florence is drifting slightly further north than models suggest too. unlikely to make landfall as category 5, given weakening today, but likely to hold steady in strength before landfall, possibly sustained winds of 110-120 mph at landfall along western end of Atlantic coast of North Carolina, eye perhaps passing over/near Bald Head Island in NC before maybe mov8ng back out to sea to make second landfall over South Carolina as then moves west, such is the shape of the coastline.

Both GFS and ECMWF stall Florence around the Carolinas coastal areas through Friday, Saturday and Sunday. So although hurricane force winds and resultant storm surge will be an issue at first with landfall, Florence may be remembered for its historic devastating flooding from prolonged heavy rain.

12z ECMWF blows the cobwebs away early next week, as a deep low formed of the remnants of ex-Helene barrels across the UK. 12z GFS and UKMO also track an ex-Helene low NE over the UK but not as deep

Issac is heading west towards the southern Caribbean, it's Hurricane Helene which is forecast to swing NW then N towards the Azores this weekend then, if EC is to be believed, moving N/NE west of Ireland early next week, while 00z GFS took the much weakened ex-TS NE into SW UK while the 6z GFS takes it towards Iberia … big uncertainty!

Millions in SE U.S.A are bracing themselves for the arrival of major Hurricane Florence on Thursday, which will likely bring major impacts. View the full blog here

Millions in SE U.S.A are bracing themselves for the arrival of major Hurricane Florence on Thursday, which will likely bring major impacts. View the full blog here

Storm & Convective Forecast Issued 2018-08-24 09:34:26 Valid: 24/08/2018 00z to 25/08/2018 00z https://www.netweather.tv/weather-forecasts/uk/convective THUNDERSTORM OUTLOOK - FRIDAY 24TH AUGUST 2018 Synopsis Large-scale upper trough axis will lie across the British Isles Friday morning, before the axis tends to shift east toward Scandinavia into the evening. A low pressure system centred off the coast of Norway will pull in a cool polar maritime W to NWly flow across the UK, which becoming increasingly unstable to surface heating - supporting increasingly widespread showers and thunderstorms. ... UK and IRELAND ... Showers from the word go this morning across western areas, frequent and heavy across the NW, will spread or develop more widely through the day across much of mainland UK, as surface heating beneath mid-level temps of minus 20C at 500mb creates steep lapse rates. Some of the heavier showers will produce hail and sporadic lightning, where heavy showers merge, there is potential for some localised flooding. Difficult to highlight where thunderstorms are most likely, though W Scotland, NW England and N. Ireland / NW Ireland seem at greatest chance based on models. Showers may not arrive across SE England until the evening. Late afternoon and through the evening, models indicate a shortwave trough, marked by flow veering from W to NW, moving E/SE across Ireland, Wales and then southern England bringing a more organised area of heavy showers and perhaps embedded isolated thunder with it. 40-50 knts of deep layer shear enhanced by strong jet stream across Sern UK will perhaps organise convection into clusters which will bring mainly a threat of localised flooding and also strong wind gusts (35-45 mph)

UK Severe Convective & Storm Forecast - Issued 2018-08-24 09:34:26 Valid: 24/08/2018 00z to 25/08/2018 00z THUNDERSTORM OUTLOOK - FRIDAY 24TH AUGUST 2018 Click here for the full forecastCheck the full storm forecast here

A look at the impacts of Cat. 4 Hurricane Lane passing Hawaii and why the Atlantic Hurricane season is so quiet. View the full blog here

Narrow squall line blasting through here in south London, made the cat run in from outside, shame no thunder.

UK Severe Convective & Storm Forecast - Issued 2018-08-16 09:21:48 Valid: 16/08/2018 00z - 17/08/2018 00z THUNDERSTORM OUTLOOK - THURSDAY 16TH AUG 2018 Click here for the full forecastCheck the full storm forecast here

Storm & Convective Forecast Issued 2018-08-13 05:48:04 Valid: 13/08/2018 00z to 14/08/2018 00z THUNDERSTORM OUTLOOK - MONDAY 13TH AUG 2018 Synopsis Upper trough towards the eastern side of the UK this morning will drift away eastwards into the Low Countries this afternoon, weak ridge building across the west, shallow surface low situated over south North Sea at noon, with associated wrap around occlusion close to east coast of England, the low deepening a little as it moves east across Denmark by midnight. Heavy showers and a few thunderstorms likely to develop across eastern England this afternoon. ... E ENGLAND ... Models indicate surface breeze convergence / moisture pooling not far inland of east coast of England this afternoon, steeper lapse rates towards the east closer to colder air aloft of exiting upper trough and scope for some surface heating will generate sufficient instability combined with lift of convergence to support heavy showers and increasingly into the afternoon a few thunderstorms too. Steering flow towards eastern UK will be fairly slack, so main threat will be slow-moving showers/storms bringing a risk of localised flooding. Issued by: Nick Finnis

UK Severe Convective & Storm Forecast - Issued 2018-08-13 05:48:04 Valid: 13/08/2018 00z to 14/08/2018 00z THUNDERSTORM OUTLOOK - MONDAY 13TH AUG 2018 Click here for the full forecastCheck the full storm forecast here

Storm & Convective Forecast Issued 2018-08-11 23:47:55 Valid: 12/08/2018 00z to 13/108/2018 00z THUNDERSTORM OUTLOOK - SUNDAY 12TH AUG 2018 Synopsis Upper trough embedded within in westerly jet will move east from Ireland across the UK on Sunday. A waving cold front will slowly progress east on forward side of this trough, parallel to a belt of modest SWly flow aloft. Pulses of heavy and perhaps thundery rain moving NE along front will shift east from Wales and SW England towards eastern England through the day, cold front not reaching eastern England until late evening, in wake of front heavy showers and thunderstorms may develop across the west. … SW ENGLAND, WALES, NW ENGLAND and S SCOTLAND … Pulses of heavy rain moving NE across SW England, Wales and NW England during the morning, ahead/along waving cold front moving in from the west, may be driven by pockets of strong enough mid-level convection to produce isolated lightning strikes at times. There is a risk of localised flooding from the heavier convectively-driven downpours. The heavier convective burst of rainfall and isolated lightning risk will ease for through the morning, as lead impulse moving NE enhancing convection weakens and the surface front moves away eastwards. However, post-frontal airmass will be characterised by steep lapse rates as cold mid-levels spread aloft with advancement east of upper trough, surface heating will destabilise moist airmass which, combined with forecast N-S surface breeze convergence inland of above areas creating lift, will support heavy showers and some thunderstorms in the afternoon and evening, focused near convergence, though may develop with orographic lift elsewhere too. Vertical shear will be weak (0-6km 20-30 knts), so main risk will be localised flooding where storms train along convergence, along with hail too. … CENTRAL S + SE ENGLAND … Further east, cold front will arrive from the west into the afternoon, with potential for another impulse in the upper flow moving NE to generate another wave or two along the frontal boundary, which will serve to enhance lift and generate pulses of heavy convective rainfall with perhaps some embedded thundery activity, again, main risk will be localised flooding.

UK Severe Convective & Storm Forecast - Issued 2018-08-11 23:47:55 Valid: 12/08/2018 00z to 13/108/2018 00z THUNDERSTORM OUTLOOK - SUNDAY 12TH AUG 2018 Click here for the full forecastCheck the full storm forecast here

UK Severe Convective & Storm Forecast - Issued 2018-08-11 23:47:55 Valid: 12/08/2018 00z to 13/108/2018 00z THUNDERSTORM OUTLOOK - SUNDAY 12TH AUG 2018 Click here for the full forecastCheck the full storm forecast here

Storm & Convective Forecast Issued 2018-08-11 09:32:51 Valid: 11/08/2018 00z - 12/08/2018 00z THUNDERSTORM OUTLOOK - SAT 11TH AUG 2018 Synopsis An upper trough in the broad cyclonic westerly upper flow over N Atlantic will approach the west of Ireland today, a surface depression containing the remnants of ex-tropical storm Debby will also approach to west of Ireland while filling. A warm front will lift N across England and Wales today, with warm and moist southwesterly flow becoming unstable ahead or along cold front then following in from the west. ... SW ENGLAND, WALES, IRELAND, IRISH SEA ... Cloud and patchy rain will spread NE through the day across Wales and western England in warm sector, then through this evening a cold front will move in from the west. differential thermal advection as cooler air moves in aloft ahead of surface cold front and lift from the front itself will cause the warm and moist conveyor to destabilse mostly in the mid-levels upwards - supporting increasing elevated convection across the above areas this evening and into the night - with potential to bring isolated thunder and lightning and heavy downpours leading to localised flooding.

UK Severe Convective & Storm Forecast - Issued 2018-08-11 09:32:51 Valid: 11/08/2018 00z - 12/08/2018 00z THUNDERSTORM OUTLOOK - SAT 11TH AUG 2018 Click here for the full forecastCheck the full storm forecast here