I really can't believe how messed up our weather is, all winter it was westerly based mild/wet crap yet now when you expect the warmth to be building an Arctic plunge is f/cast, that's after 3 weeks of easterly based weather and low temps here on the east coast which was bad enough, if this was January it would get downgraded day after day and then disappear but i bet this one turns up and kills off the summer visitors that have arrived and most insects will perish too, absolutely ridiculous...!!

Vineyards in southern England saw bud burst several weeks ago in the second week of April (some earlier) and many now have flower inflorescences well developed. If we get air frost on the vines it will be catastrophic: worse than 2017.

3 things that give some hope: 1. there looks like being a keen North wind which may keep valleys above zero, 2. The last two harvests were very big so most vineyards have plenty of stock, 3. My vineyard isn’t yet planted until next year so it’s not a personal risk this time

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I think the risk of damaging frost will be more once the high starts pushing in calming the winds down .

I doubt if we’ll get an air frost with a northerly. Even in the depths of winter a stiff northerly rarely gives an an air frost down here when the wind is blowing. Looking like low double figures during the day and 3-4C overnight. Maybe a touch of ground frost once the wind dies down. If it ever does. The nagging wind has been a feature of this spring so far, doing far more damage to the plants than the frost ever does. I’ve been putting my courgette plants out to harden them off and the wind is snapping the leaves off as fast as the plants can grow them. 

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Mid teens by day, and mid to high single figures overnight here would be my guess Cold wind yes. However in the countryside it might be a tad cooler, and that's were the vines would be, no?

The chilly weather at the weekend will be problematic for the sheltered west where there may well be a frost Sunday and Monday night.
Looking at the model output I would expect it to be gloomy here during the coldest upppers Sunday night and around 2c at the lowest perhaps with some light wintry showers so shouldn't damage any plants.

This morning is frosty in many parts too.

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I wouldn’t expect southern parts to notice much more than a cold wind to be honest. As for up here, there are still air frosts quite regularly in many parts anyway. What is more unusual (not unprecedented of course) is the potential for snow showers.

https://www.wetterzentrale.de/maps/ECMOPEU00_120_1.png 

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GFS - HP drifts S-wards this week, gradually pushing that depression in the SW out of the way, and by Sat 9th the last traces of it are gone. New HP , Iceland 1030mb, opens the door to cold NE/N-lies for a few days; that too drifts S-wards and is over UK Thu 15th (expect to see some frosty nights midweek if this verifies). A short-lived LP over France affecting the south before the Atlantic fires up with LP 990 mb Hebrides Mon 18th and (very deep for the time of year) 960mb S of Iceland Thu 21st, with W/SW winds.

ECM similar but treatment of HP is critically different in that the midweek period the HP is just that bit further west and retains a reasonable circulation over the UK, which may mean that damaging frosts are avoided.

GEFS has the well-forecast drop in temp Sun/Mon 10/11th to about 9C below norm, slowly recovering but not until Thu 21st is it back to norm. The SW may see some rain around Mon 11th but otherwise mostly dry; some chances of rain at end of forecast period.

 

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Crazy. Both pinks

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Still looking like Monday and Tuesday nights could see damaging frost in the South, particularly West of London. Essex and Kent benefiting from onshore flow off the sea keeping night temperatures higher.

Nothing truly arctic, but -2C is enough to see off tender plants (and vine shoots) at this time of year.

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Jetstream persisting with N and S branches for the rest of this week, then on Sun the N branch peps up and dives south over the N Sea (all the better to guide that Arctic plunge). That fades and by Wed 13th all the flow is to the S, looping as far down as N Africa. That looks unstable, and indeed by Sat 18th it's back in the usual place across the UK where it remains for the following week, with occasional loops.

10-day summary has temps recovering in week 2, and mainly dry

GFS as previously has HP declining this week and replaced by another centre from Greenland with cold N-lies over UK (swinging E-ly in S) but  N flow cut off by Tue 12th as the HP centre moves to UK. Temps should be brought back up by LP affecting the S on Thu 14th and then by Sun 17th there's a familiar situation with LP on the Atlantic and a ridge from the Azores giving a zonal flow from the W or SW. 

ECM similar though later stages are still yesterday's 12z run.

GEFS shows the expected dramatic dip in temp on Sun 11th after warmth this week but the recovery to seasonal norm is sooner than previously shown with the majority of runs back there by Fri 15th and then warm (S)/ mild (N) for the week. Some rain about in the S towards the end of the run on Fri 22nd. otherwise not much pptn (Inverness has one snow row figure of 22)

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GFS 12z goes all scorchio after the cold spell 17c 850s on day 10

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GEFS portraying a lengthy dry couple of weeks in most parts after initial showers over the weekend...

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Regarding the cold blast from the north, I think this image says it all. 

The anomaly becomes more widespread a few hours later albeit not as extreme https://www.wetterzentrale.de/maps/GFSOPEU00_102_34.png

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GFS has the well-forecast decline of this week's HP to give cold N/NE winds Sun/Mon 10th/11th but the cold air cut off fairly quickly by new HP over N Ireland Wed 13th (Spare a thought for Finland, much colder air and violent gales from LP 970mb). HP then transfers E across the UK with shallow LP coming up from the S by Mon 18th. Pressure remains fairly high through to Sat 23rd but with UK under a col between HP centres over the Baltic and the Azores. (Maybe showery?)

ECM similar but suggesting a deeper LP from the south and warmer air around Mon 18th EDIT the 0z now available places this low over Holland with the UK getting 'the colder side of the circulation

GEFS shows the forecast warmth this week and big dip on Sun 10th as before ( a little rain at this time), recovering to seasonal norm by Thu 14th and most runs clustered around that norm through to Sat 23rd, no great warmth, and some rain on individual runs, more general towards the end of run but still not a lot of it.

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Well the Northerly now arriving later down here (Sunday rather than Saturday) as first forecast and not the same depth of cold either. We might even squeak 14c on Sunday afternoon in London. Still a bit of a shock to the system though.

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There was an inadvertent duplication - ignore this!

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GFS: HP devloping near Iceland Mon 11th to give that forecasted northerly but not lasting as long as the HP moves S to UK and cuts off the flow. By Fri 15th it is over Scotland 1025mb and with LP now shown more strongly over France menacing the S Coast. That fades and by Wed HP is over S England and LP on the Atlantic with warm SW. The HP coverts itself into a strong extension of the Azores High and the activity on the Atlantic fades through to Sat 23rd.

 

ECM puts a bit more emphasis on the LP over France but otherwise similar.

 

GEFS Temps doing the big drop on Sun 11th but back close to seasonal norm on most runs Fri 15th - Sat 23rd  (though IMO the synoptics suggest warmer later on). A little rain on the 10th/11th in the east, otherwise intermittently but with greater chances later on, from ca Sun 18th

 

10 day forecast http://www.wxmaps.org/pix/temp4 very cold over Scandinavia  and  N Europe week 1 but much warmer week 2, Pptn shown in the extreme S week 1 (doesn't match GEFS but does accord with ECM) otherwise dry.

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The astonishing observation for me, just catching up withe the N hemisphere GFS run, is just how the cold pool over the North Pole (arctic circle region- to be more precise) dissipates so completely after the simultaneous cold plunges towards the uk and Canada. By the 17th May, there is very little sub minus 10 air left. I have checked back over decades from the 60s onwards and can't find a year that this happened so comprehensively by this time.

In my youth occasional May snow or sleet flurries have occurred - and indeed did so in 1991, down here in East Anglia. I can't imagine that now though. This plunge may bring a flurry to Aberdeen but there is not enough puff to bring it down south...

With little air craft - are we witnessing a window in global dimming, so the true heating of Co2 is being felt??? It might end up being a super heated summer sizzler for the N hemisphere temporate countries...if so. This is potentially a massive event unfolding before us and needs watching.

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I posted the equivalent image yesterday just to highlight how anomalously cold the upper air is for the time of year.

I know it has happened before but I cannot remember snow falling here in May before (and I guess it may not happen this time either) but the -10°C t850hPa hPa air really is quite remarkable in May all the more so given the comparative lack of it at any stage in winter!

Regarding the the GFS run and the lack of cold t850s on the 17th of May, here the N Hemisphere view for that date on this run showing the anomalies compared with the 1981-2010 long term average showing the notable positive anomaly (and the corresponding cold air displaced over Canada):

However looking a week further ahead the t850s for what it is worth at that stage are a mix of both above and below average over the Arctic.

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Re snow in May, I can clearly recall a morning in mid-May back in 1995 when we had falling snow wher I live, and this was only a week after we had had several days of sun and clearl blue skies with temperatures in the low 20s.

Just goes to show how fickle the British climate is.

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I think the last time I can recall snow falling here was in May 1997. 

There has been sleet on a few occasions (falling in the form of afternoon wintry showers) since then.

There is a good chance of some snowfall on Sunday across northern and eastern Scotland, particularly over higher ground and most likely during the earlier hours of the day.

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Thanks Doc, yes the anomalies make it clearer. Worth keeping an eye on this. Makes me wonder how much reduced the net carbon gain/ deficit cycle will be this year and the effect of the drop in dimming will have on these anomalies. Is any organisation recording this data - and is it accessible??

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June 1975 - Yes I am that old!

https://www.espncricinfo.com/story/_/id/22539954/rewind-1975-snow-stopped-play

I lived in Colchester then where snow stopped play and remember the massive snowflakes falling at lunchtime!

Funny how we talk about extreme weather nowadays, but the summers of 1975 and 1976 were about as extreme as you can get!

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