Nick F

If anyone thinks GFS is top dog of the models, perhaps think again: Although the ECMWF may have been too keen on easterly for the UK, an easterly is still going to happen, just a lot further south. Remember GFS was slower than ECMWF to cotton on to the blocked pattern we are now entering, preferring the much flatter and more zonal pattern across Atlantic and UK, before backtracking. Be interesting which model comes out top with a rather complex trop pattern evolving over the coming few weeks .. couple that with a warming stratosphere setting up for possible SSW late Jan/early Feb. However, there is the chance that the warming may level off like it did in late Nov/early Dec - so we may need a second warming to break the PV. However, in the mean time, the MJO is probably driving blocky pattern for the rest of January, it's just where the block sets up which is causing problems for forecasting the medium range for now, the models perhaps again not factoring in the correct MJO signal? Realtime and CFS forecasts suggest the MJO will be motoring through 6/7/8/1

Had a streamer of sleet for a good hour and half or more down here at work at Gatwick early afternoon, temp dropped to 2C in the sleet but now rising as the sun returns. Took these pictures of snow still lingering on Reigate Hill, Surrey by junction 8 of the M25 this morning:

Just light snow here at Heathrow, just enough to dampen the ground, seems the heavier snow further east. Oh well, resume the hunt for next snow potential!

Last time I witnessed 'thundersnow' was a frontal event on 28th Jan 2004' when a potent cold front and squall line raced south across the UK, think it was +4C ahead of front and -3C immediately behind, the cold air undercutting creating strong convective updrafts and lightning even well inland. Was spectacular when the rain suddenly turned to heavy snow too. Lightning on 28/01/2004 faxes

Most likely after dark, yes, though wherever rainfall is heavy, evaporative cooling may lower the temperature enough to bring the snowfall level down quite quickly - settling is another matter too, the heavier the better as the ground will be wet.

I think snow chances this evening for most of us that live at low-levels will depend very much on how quickly the colder and drier arctic air undercuts the rain from the NW - which will relate to how developed the wave low will be when it clears. If the wave is flatter than forecast by those models which are most keen on rain to snow at low-levels, then cold/dry air from the NW will be less inclined to undercut, deeper then game on. I use the partial thickness (850-1000mb) and dew points as a guide to snow potential to low-levels. Ideally need a 1290 dam or below for snow to fall, 1300 the limit with heavier precip. Also need dew point of 0C or below. Both 129 gpdm line and 0C dp lines lagging the precip to the NW at 6pm, so may still be rain by then apart from above 150m However, by 9pm, the 129 and 0C lines have caught up the rain to turn it to snow on back edge However, if we are deeper than 06z GFS, latest EURO4 from 06z nearly 10mb deeper at 6pm with developing centre of low, then we could see stronger snow signal as cold/dry air more likely to undercut from NW: 06z GFS 6pm EURO4 6pm So you can see why there is this uncertainty, even only 6-7hrs out.

Milder blip on Sunday/Monday - especially in the west. But turning progressively colder again next week, this time from the east. This time next week looking a bit raw on 06z GFS max temps - with the increasingly cold and dry flow off a cold near continent: 850-1000 hPa (partial) thicknesses show well the cold and dry continental airmass advecting west

Looking at some of the airport TAFs in the SE, Stansted (Essex) and Heathrow shows heavy snow forecast: Stansted: Temporary from 12 at 17 UTC to 12 at 21 UTC Visibility: 0600 m Broken clouds at a height of 200 ft snow TAF: EGSS 111704Z 1118/1224 28012KT 9999 SCT045 PROB30 TEMPO 1118/1121 30015G25KT BECMG 1210/1213 21007KT 7000 -RA BKN012 TEMPO 1211/1215 RA BKN008 TEMPO 1212/1217 09010KT BECMG 1215/1218 01015KT TEMPO 1215/1217 3000 RASN BKN004 TEMPO 1217/1221 0600 SN BKN002 PROB30 TEMPO 1217/1221 35023G38KT 0200 +SN BKN000 BECMG 1218/1221 29015G25KT 9999 NSW SCT045 Heathrow: Temporary from 12 at 16 UTC to 12 at 19 UTC Wind 24 kt from the North/Northwest with gusts up to 38 kt Visibility: 0500 m Broken clouds at a height of 100 ft heavy snow TAF: EGLL 111715Z 1118/1224 30012KT 9999 SCT045 BECMG 1203/1206 24008KT BECMG 1209/1212 8000 -RA BKN012 TEMPO 1211/1216 4000 +RA BKN008 BECMG 1212/1215 15010KT BECMG 1215/1217 32018G28KT TEMPO 1216/1220 0800 RASN SN BKN004 PROB30 TEMPO 1216/1219 33024G38KT 0500 +SN BKN001 BECMG 1220/1223 29012KT 9999 NSW FEW030

18z GFS indicates some leading edge snow as the rain pushes SE, but not supported on other models so far and probably change next run - too far out to forecast snow anyhow.

My latest blog covers the risk of snow, ice, gales and coastal flooding over the next few days: http://www.netweather.tv/index.cgi?action=news;storyid=7895;sess=

View the full blog here

There are various ways of gauging MJO activity, other than using the more easier to understand RMM plots. tropical and ex-tropical interactions can be seen through the magnitude of the upper winds and the waves in them, as GP suggests, as shown on plot below: Found at: http://mikeventrice.weebly.com/tropical-waves.html Also the velocity potential (CHI-200) charts can show the propagation of the MJO, if you know how to read them, but charts below do show eastward propagation of an MJO wave https://ncics.org/portfolio/monitor/mjo/ So the RMM plots we are used to don't always pick up the MJO activity well, as they may not filter out other modes, such as Kelvin and Rossby waves.

Yes, I have been keeping tabs on Kyle MacRitichie's realtime MJO and 30 day CFS MJO forecasts - which have been propagating MJO out of COD, unlike the EC/GFS/JMA/UKMO, from phase 6 (today) through phase 7/8/1 later this month

Agree, an interesting period coming up mid to late January and beyond. Whether we get an easterly or not early-mid next week depends on how the surface high orientates which is uncertain for now, big EPS spread this morning, from as early as this Sunday/Monday, compared to yesterday, increases the uncertainty. However, there is still decent chance next week of a slack cold continental feed, though any snow is a big ask from that direction for now. But more consistently at upper levels for the medium range a 500mb ridge is drawn NE across the UK into Scandi in the EPS means, and there are signs that mid-Atlantic troughing may go under toward day 10 to thee SW of the mean ridge. Further ahead, we have the MJO wave heading into phase 1 (often = colder phase for UK) on GEFS, EPS, JMA and trending that way on UKMO too. So we could see impetus for amplification to pull the block further north later in January. Couple with that, the GFS and EC keen on shifting the strat PV back toward Russia/Siberia by day 10 - which suggests that, if indeed connected with the tropospheric pattern, could pull deep cold pool south into NW Russia - which may eventual pull west if the block drifts further N or maybe NW. Given the background of unprecedentedly long westerly QBO, and recent muted MJO, AAM and GWO signal, we are doing quite well atm with the pattern we are seeing. But now it looks like 10 hPa zonal winds are on the decrease, the sPV looking perturbed and perhaps drifting to Siberia and the MJO waking up, interesting times ahead.

06z GFS still has the heavy snow signal on the back edge of Thursday's wave low running across the far south

The Euro4 precip type charts have been a little over optimistic with snow in the past, so we'll see and believe it when I see it. At least we have some model consistency now with the track of this wave on Thursday and it's heavy rain and possible back edge snow. Fancy the North Downs getting a good covering, not far from me so may jump in the car to Biggin Hill, as doubt it'll settle in lowland London.

I will ask Paul in the morning and see if he can put it up. 12z EC ens for London suggest determisitic pretty consistent with the mean of the ens - with what looks like clustering of similar or colder solutions too. So nothing to worry about there again.

There is, but hard to find : https://flood-warning-information.service.gov.uk/5-day-flood-risk GFS showing sustained northerly winds of 40 to 50 mph and gusts of 70mph+down the North Sea, combine that with water bulge created by 974mb low and morning spring tide, could be some spectacular waves and coastal flooding for eastern England. Surge could be worse for Belgium and Holland maybe?

Although 06z GFS doesn't make much of Thursday's wave low scooting along the south coast, can see why MetO have their concerns re: heavy snow/rain looking at their own 00z UKMET-G model which develops some heavy rain on the rear side of the wave low - thanks to a diffluent upper trough behind the cold front which induces heavy precipitation near and along cold front - plus a wedge of cold air (sub -6C T850s) with this trough and 2m temps not much to drop to freezing, especially through evaporative cooling in heavy ppn. SLP and ppn + 500 hPa vorticity T850s and 2m temps Could do with dew point and wet bulb temp forecast charts too ... but will really come down to nowcasting at the end of the day and not certainty over exact track at t+48-60 hrs out. ECMWF had similar track and also turns precip heavy on back end of wave as upper trough arrives and engages Tm airmass wrapping up into low Other than this feature, of course there will be plenty of snow showers Thursday for EIRE, N. Ireland, SW England, Wales, NW England, northern and western Scotland, NWly flow could bring a Cheshire Gap streamer through the Midlands toward the SE too? Friday similar, but with winds veering more northerly toward the east, could see snow showers down eastern counties too So plenty of fun and games to look forward to, before some uncertainty over a low dropping SE on 06z GFS over the weekend, which could bring less cold air and rain preceded by some snow. 00z had it further west I think. Then of course the will it or will it not Scandi high and easterly.

All this talk of easterlies this morning and it's the 30th anniversary in a few days of the start of the infamous January 1987 beasterly, the Holy Grail of easterlies. The 13th of Jan '87 saw sub -15C T850s spread from the east. Only seems like yesterday I was helping to dig through a snow drift in Kent, aged 11, with my father so we could get our car back home. How time flies! Anyway, enough reminiscing, looking at the 06z GEFS postage stamps, main concern re: easterly potential is that quite a number of members not really building the high far enough north and northeast so we don't get a decent a cold easterly flow, with only a few members with a strong and cold easterly flow, but at least the Atlantic looks blocked and will be cold under high pressure inversion. Still chance of cold easterly - despite this IMO.

Come on Nick, you are talking like a man who has not recovered from the previous traumas of easterlies failed ... we've come on a long way with GFS since only very recent zonal express runs. The downside of the 06z Scandi high is that it's only the south that benefits from deep cold and only then the far SE that gets snow showers. But it's a step in the right direction and a far cry from what was being served up early yesterday's 00z suite - especially GFS. At last we have GFS on board with ECM, just hope that ECM doesn't climb down on the 12z from showing a Scandi high - as it will be traumatic!

Equatorward returning jet heading SW over France further west on 06z GFS - BINGO an EASTERLY for UK 00z for 06z Tues 06z chart for 06z Tues

The broadscale mid-upper level flow differences between 00z GFS and EC ops start after t+144 (though we do have surface differences before then at the weekend) As the comparisons show ECM extends troughing / low heights further SW across southern/western Europe early next week compared to GFS, as the ridge builds NE - which prevents to much ridging in the Atlantic pushing east - whilst GFS also pushes more energy east out of Greenland. N.B. see that deep low west Azores too on EC - that suggests more energy in STJ pulling Atlantic troughing further south You can see on the ECM 300 hPa winds - the jet returning SW on southern flank of block building NE is further west - allowing cold air troughing over Euro land further west GFS has equatorward jet further east + poleward jet to the NW of UK further east - which doesn't allow as good position of block for UK cold advection from east So we can see the upper pattern differences and it maybe that GFS may not be handling as well the returning equatorward jet over Europe and extention of troughing SW and W to our south. Also worth mentioning that the polar stratosphere is undergoing changes that may benefit blocking over and to the NE of the UK too, a huge ridge in the stratosphere will weaken winds above northern and western Europe and may help re-inforce ridging building NE

Looking at the 18z GEFS postage stamps, plenty of easterly options in there to say that the GFS high res may continue to slide towards this kind of evolution tomorrow just hope for sanity's sake that GFS and EC can settle their differences and come to a more mutual agreement very soon, as this is getting exhausting not knowing whether there's still a chance of an easterly or not, though odds are decreasing thankfully.

Good EC ens again, some cold clusters, the mean below 5C much of extended, GFS op a warm outlier