Using weatheronline as a guide, for what it is worth.

 

If the temperatures pan out as predicted from Sunday 27th (a long way off I know)

 

The last time when temperatures of 13-14c have occurred at Heathrow in September for more than 4 days in a row was 1994.  Even then it bounced back up to the 20's.

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I noticed the 18z GFS are showing single digit max temps for my neck of the woods by next Sunday. It will get modified as we get nearer to the time but that would come as a shock if that actually bore fruit.

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GFS - Last of the HP tomorrow, Mon 21st, declining first to W-lies then LP 995mb Ireland Thu 24th crossing the UK eventually finishing up in Germany Mon 28th with ridge of HP moving in (but not before delivering some cold N-lies). Then more W-ly/NW-ly until Sat 3rd when LP 980mb N Sea delivers a fresh batch of N-lies.

GEFS - Dip to cold Fri 25th with plenty of rain around that date. Mean of runs slowly recovers to seasonal norm Thu 1st but a great deal of uncertainty (the op in particular doesn't know what it's doing) and some rain on and off continuing to end of run Tue 6th Oct. Temps in Scotland more stepwise - stay colder for a few days longer then recover more abruptly to a little above norm. Less rain there but by no means absent. Snow row figures for low altitude locations now back to zero.

ECM (yesterdays's 12z) - More of a W-ly feel than GFS; next weekend's LP less deep but equally ridge following much flattened. New LP appears Rockall 985mb Tue 29th, not shown on GFS - UPDATE- next weekend's LP now deeper to match GFS though no ridge to follow and the LP later on is 985mb N Ireland Wed 30th rather than staying out by Rockall

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I noticed the 18z GFS are showing single digit max temps for my neck of the woods by next Sunday. It will get modified as we get nearer to the time but that would come as a shock if that actually bore fruit.

 

I'll eat my hat if that actually happens!

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0z run looks chilly and unsettled 

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6z gives us a cool unsettled start to October

 

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We have 3 months of building work starting next week, with scaffolding going up and the roof coming off.

Hence it will become wet, cold and windy and not stop raining until December.

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9 degrees  Celsiusdaytime max  showing for London Sept 30th.....remembered it before like that nearly 30 years ago....that was followed by a mild winter...

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Since that's ten days away, should be taken with a large pinch of Na Cl.

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Divergence in the models tonight. The GFS hints at the chance for quite a widespread frost on Saturday and Sunday morning especially, however the ECM brings milder air in on Saturday, which would of course stop this from happening.

Could be quite an interesting period for forecasters, with so many ex-tropical systems knocking about in the Atlantic over the next week or so.

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Jetstream buckling to produce loop around the UK Thu 24th; as this moves away the stream straightens out across the UK but furter loops develop in vicinity of UK Thu 1st and Tue 6th

GFS - LP over UK Fri 25th not as deep as previously forecast, followed by W-lies for a while before LP over Scotland Thu 1st 985mb decaying and moving S to Biscay 1000mb Tue 6th

GEFS - temps dropping to well below norm thu 24th, recovering to norm Thu1st but with little agreement between runs by then and thereafter. Less rain in S this week than previously forecast but with quite frequent big  spikes in different runs from Tue 29th onwards, less dramatic but more continuous in Scotland

ECM (as of yesterday 12z) - similar to GFS but LP Wed 30th (end of run) not as deep as GFS ALL DIFFERENT THIS MORNING'S 0Z - Lp on Wed 30th banished to Iceland

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16-dayer cool across all NW Europe for a week, recovering slightly here but focus of cold moveds to C Europe later. Swathe of rain Nw Britain to Romania.

GFS - W-ly becoming NW-ly/N'ly from LP moving across UK with ridge of HP just about making into the W Sun 27th but collapsing to more W-lies; trough of LP developing over Iceland and extending into N Sea Sat 3rd; back to more W-ly before HP arises covering UK Thu 8th. 

GEFS - cold (7C below norm) Sat 26th but back to norm Tue 29th and staying there with quite a lot of variation between runs though less than yesterday (one monstrously warm outlier 15C above norm 6th Oct!). Rain around in next couple of days and again 1st - 3rd and in some cases 7th Oct. Scotland same tendency but missing that outlier and with less rainfall, some runs pretty well dry throughout in E.

ECM - Similar to GFS but W-lies look warmer around 1st Oct

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GEFS gets a massive production upgrade tomorrow. Improvements include:

1) Higher resolution

2) Use of the FV3 core (used by the latest GFS)

3) 30 perturbations + control run

4) 00z cycle extended to 35 days

Today on TWO the 12z GEFS update is running the new version which is available on the parallel NCEP servers. However, there will be 20 perturbations + control run as normal. 

Later this week I will hopefully make available:

1) 35 day plots

2) All 30 perturbations  + control run

I would expect the GEFS updates will be slightly delayed due to there being more and bigger datasets.

 

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12z GFS keeps us cool and unsettled up to the end of the first week of October 

The rain will do the gardens some good 

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Jetstream in looping mode for this week, the loop transferring across the UK with the trailing edge giving a N-ly blast on Friday before modulating into a tentative sort of W-ly Mon 28th with  the main thrust running from Newfoundland to Spain by Fri 2nd i.e.just W of UK,but with occasional fragments swinging back N-ward over the N Sea. These become larger and eventually form a cut-off circulation enclosing the UK Mon 5th. This breaks up chaotically, but there is a branch running NE-wards over the SE Thu 8th

GFS - LP moving SE-wards, in southern N Sea by Fri 25th; then a W-ly pattern for a few days before LP covers England  980mb Sat 3rd; this hangs around and slowly fills, remnants 1005mb over Cornwall Fri 9th. No strong correlation with jetstream pattern after the next few days

GEFS - agreement on temps v low Sat 26th (8c below norm); back to norm Tue 29th and the mean staying there through to Fri9th but with quite a lot of variation after Sat 3rd. More rain than forecast yeaterday and frequently from Tue 29th

ECM - the new LP arrives earlier (Thu 1st) and drifts off to Norway Sat 3rd rather than filling in situ.

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12z GFS keeps us cool and unsettled up to the end of the first week of October 

The rain will do the gardens some good 

Looks very unsettled for the foreseeable. Even here the garden has dried out but we really just need a couple of spells of rain to fix that. The rest of the rain can stay away as far as I'm concerned. 

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Haven't seen it mentioned here, but starting with today's 12z run, GFS ensemble had a major upgrade:

• 31 members (from 21)


• higher horizontal resolution throughout (~25km)


• The 00z run will extend to 35 days out daily


• Runs will start ~one hour earlier and finish one hour later

These changes will probably make for a slightly better and less volatile ensemble model, but still not as good as the EC.

Haven't seen it mentioned here, but starting with today's 12z run, GFS ensemble had a major upgrade:

• 31 members (from 21)


• higher horizontal resolution throughout (~25km)


• The 00z run will extend to 35 days out daily


• Runs will start ~one hour earlier and finish one hour later

These changes will probably make for a slightly better and less volatile ensemble model, but still not as good as the EC.

See a few posts above. 

https://www.theweatheroutlook.com/twocommunity/default.aspx?g=posts&m=1258080#post1258080

 

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So, reporting as things stand:

GFS - current Lp filling and moving to Germany Mon 28th (but rather more slowly than previously? so still affecting E coast) then sequence of LPs running NW-SE across or close to UK; 975 mb Thu 1st SW Ireland, 990mb Mon 5th Cornwall. After this HP builds strongly (and looks warm) 1035mb C England Sat 10th.

GEFS - temp recovering to norm ca Tue 29th and with usual variation between runs stays there to Sat 10th (no sign of warm spell at that time unlike parent GFS) Rain in E at first, otherwise dry until Tue 29th and then on and off for the forecast period esp around Fri  2nd

ECM - holds the controlling LP stationary and  further W for a while ca Thu 1st and pushes a secondary across N England, followed by an area of LP generally covering the UK Sat 3rd with a centre 980mb Kent Sat 3rd .

 

If (see Brian's post) GEFS is significantly delayed due to upgrade, I may not be able to provide a regular daily summary which includes it owing to care commitments. ECM (while BST applies) already presents a problem

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GEFS was upgraded yesterday. Key changes: Better physics, higher res, 00z run to 35d. 31 perts instead of 21. It means IMPROVED accuracy, but even better - snowrow now goes up to 33 not 23! -:) All 31 runs should appear on TWO from this evening. https://t.co/bO5dJrQpxg pic.twitter.com/tJnoEo2JC0

— TheWeatherOutlook (@TWOweather) September 24, 2020

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