In light of a transition from La Nina to El Nino and coverage of warmer-than-average ocean and atmosphere, a flip from abnormal dry to wet was anticipated for the UK and Ireland. This proved to be the case during summer 2023 with a dramatic flip from record warm, dry June to one of the wettest July’s on record.
The below 500mb geopotential height anomalies from 1 Jul-17 Oct show the strong and persistent block over Greenland and Europe with a channel of low heights in between, connecting the tropics with N Europe.
A pretty wet pattern featuring several unusually deep depressions for time of year (July-August), magnified by a busy tropical Atlantic and warmer than normal Atlantic.
The tropics combined with blocks to the north set the stage for some extreme rainfall events, especially into late September and October as colder air began to expand over the pole.
The combination of tropical/subtropical depressions lifting north and warmer SST’s likely contributed to increased rainfall amounts but what further enhanced the wet conditions has been the slowing or stalling of fronts due to blocking. Throw in hills and mountains along with these stalled or slow moving fronts and you see big rain totals.
October has been quite exceptional for some.
Scotland’s Wettest 2-day period on record!
Between 6-7th of October, Scotland observed widespread heavy and persistent rain thanks to a channel of moisture rich air running along a boundary separating cold/dry air pushing south from the Arctic and unusually warm, moist air lifting up from the Bay of Biscay.
Model projections.
Credit: TropicalTidbits
Credit: wxcharts
Credit: BBC Weather
An atmospheric river connecting the subtropics with Scotland ran the unusually sharp thermal boundary.
https://twitter.com/MatthewLehnert/status/1710219951204687967
The stalled nature of the boundary, the amount of water vapour within the atmosphere, warm origin of system and topography all played a key role in delivering a truly soaking 36-hour period for the south and central Highlands and most of the country.
Credit: weatheronline
https://twitter.com/MarkVogan/status/1710612862253564128
https://twitter.com/RoostWeather/status/1710797483322782135
https://twitter.com/MarkVogan/status/1710680290492809480
https://twitter.com/NetworkRailSCOT/status/1710579288192307238
https://twitter.com/NWTrunkRoads/status/1710634733766353291
https://twitter.com/NetworkRailSCOT/status/1710641120286233019
https://twitter.com/SWTrunkRoads/status/1710579214649364913
https://twitter.com/NWTrunkRoads/status/1710925855306690916
https://twitter.com/dmacphers1/status/1710976926481871070
On the Saturday when much of Scotland was under a radar of bright yellows indicating heavy, persistent rain, large swathes of England and Wales enjoyed a summer-like sunny day.
A high of 25.7C was recorded at Faversham, Kent while it only warmed to 7.7C in Aviemore.
Some interesting swings even for the south.
https://twitter.com/SnowbieWx/status/1713840808732791230
https://twitter.com/wanstead_meteo/status/1714202237071659086
STORM BABET: One for the Record Books?
A complex synoptic situation with low pressure driving warm, moist air into a block of cold air. The result, two spells of extreme rainfall within a 72-hour period.
https://twitter.com/SnowbieWx/status/1714573524256362582
https://twitter.com/PaulBlight6/status/1715357523090256339
Not one but two lows pushed north taking subtropical energy with it. Due to the strong wall of cold high pressure over Scandinavia, all the warm, juicy air was stopped from continuing it’s journey northward and as a result, further heavy, persistent rain combined with gale or severe gale-force winds out of the SE.
This came less than 2 weeks after the 100-175mm rain swept through central Scotland within 24 hours (well over 200-250mm in 48 hrs), we had yet another extreme event and example of tropical origin air pushing north only to see the boundary stall.
1st night radar
1st red warning for rain valid from 6pm Thu to midday Fri
Credit: BBC Weather
The result in parts of Angus.
https://twitter.com/STVNews/status/1715334973450850325
https://twitter.com/theiaincameron/status/1715287244477460964
2nd night radar
Credit: weatheronline
2nd red warning for rain valid midnight Fri through all of Sat.
Credit: BBC Weather
https://twitter.com/MarkVogan/status/1716129629893759012
When you have a phase 2 MJO combined with El Nino in October, the pressure pattern correlates to the below.
I think you’ll agree this looks almost exactly like the pattern which brought Babet, it’s stalled nature as it bumped up against the Scandi high. Throw in unusually warm SST’s and you increase rainfall further, despite the moisture coming out of a warm, moist source region in the first place.
FEATURED IMAGE CREDIT: Amey SW Trunk Roads
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