Nick F

Window does seem to be narrowing, for now on 00z EC and now 06z GFS, for next week's cold spell, may just about squeeze it out to the end of the week in the south, the north Sunday. Our modern foe the Iberian high seems to be ruining things again, despite strat-trop coupling leading to Greenland high following the SSW and supposedly favourable lag MJO trop forcing over the Pacific. But we still have at least a few days of snow potential, not really worth looking at beyond Wednesday, but 06z GFS showing potential for some back-edge snow along the cold front clearing south early Tuesday morning UKV hints at it too ...

Not sure the reason why it happens exactly, but these shallow lows moving in from the west against cold airmass more often than not make a beeline to track along the English Channel or northern France then into the Low Countries, see it so many times. So think 06z GFS track seems plausible for next Thursday. if it was a rapidly deepening low, then this would be a different matter, but it doesn't look to undergo RACY.

06z GFS doesn't pump the Iberian heights like the 00z EC / EPS, then again the 00z GEFS mean doesn't either. The heights tendency over Iberia in the medium range looks crucial to the longevity of the cold spell, too strong and greater risk of milder air flooding at least the south, some uncertainty in this area IMO. But at least one thing I've noticed in favour of prolonging the cold is the tendency for the trop PV to stay close to northeastern Europe on 06z GFS and 00z EC rather than bouncing back to Greenland as GFS was keen on previously, which makes sense - given the MJO going into high amplitude 8-1 and the continually drip down of the strat reversal following the SSW. Original post: https://community.netweather.tv/topic/98450-model-output-discussion-a-cold-start-to-spring/?do=findComment&comment=4815002

06z GFS doesn't pump the Iberian heights like the 00z EC / EPS, then again the 00z GEFS mean doesn't either. The heights tendency over Iberia in the medium range looks crucial to the longevity of the cold spell, too strong and greater risk of milder air flooding at least the south, some uncertainty in this area IMO. But at least one thing I've noticed in favour of prolonging the cold is the tendency for the trop PV to stay close to northeastern Europe on 06z GFS and 00z EC rather than bouncing back to Greenland as GFS was keen on previously, which makes sense - given the MJO going into high amplitude 8-1 and the continually drip down of the strat reversal following the SSW.

2nd warming downwelling into trop and MJO 8-1 high amplitude combo you would think reinforces high lat blocking for a while, so would expect any Atlantic milder ingress to be temporary if at all.

So, that's both 12z EC and 18z GFS with cold (sub -5C T850s) locked in until day 10. Seems to be delaying the Atlantic milder air flooding in. With the MJO heading into v high amplitude phase 7-8, which promotes higher heights and blocking to our NW, will we see the trop PV kept over NE Europe rather than bouncing back to Greenland as models were previously keen on?

I think too many are getting way too judgemental of what's going to happen and finding fault with every run, e.g. uppers not cold enough, flow too slack, sun too warm, only coastal showers the list goes on. Lets see what actually happens next week when it comes, it's going to get cold, cold enough to snow even to lower levels, some may be pleasantly surprised, some maybe disappointed, we can't predict for sure what will happen this far off. Just enjoy the fact it will turn cold enough for snow. It doesn't happen very often, especially in March.

GFS, especially, underestimates shower development inland in early spring, as the sun has enough strength by early March, to subtly warm the ground to allow convection to develop overland too.

5 day cold northerly spell next week, with snow for some, but a re-occurring theme, for now, for the Greenland block to continue to retrogress over northern Canada - which allows Atlantic lows to eventually phase with the polar vortex to our NE. This brings the risk of milder southwesterly flow flooding the UK eventually. However, can we trust the models aren't being too hasty with the retrogression of the block to the NW and the trop PV so quick to bounce back to Greenland - given the QTR to the strat-trop coupling?

12z UKMO has a more elongated upper high over S Greenland down to west of Ireland compared to GFS at T+144, so would keep.Atlantic lows at bay and allow the cold northerly to dig deeper into Europe / better CAA. Mind you, with a Greenland centric block it's always a fine balance of too far east or south and we are dry and settled, too far west or north and it allows in Atlantic lows in from the west or southwest threatening to introduce milder air. At the moment, the balance is just right for coldies on 12z GFS so far, because we are under the SW edge of the expansive low heights of the displaced trop PV to the NE, if that wasn't there pulling deep cold air down, could be a different picture.

They go out to T+168 on WZ no? UKMO EU tab Wetterzentrale - Top Karten - UKMO EU Europe 00Z WWW.WETTERZENTRALE.DE Wetterkarten UKMO EU Europe 00Z Always prefered the Europe view on WZ as meteociel has the 'flat earth' projection where Greenland appears much larger than it actually is. WZ has the cylindrical projection.

Really not worth focussing on temperatures this far off, but it can snow 4-6C if the dew point is below 0C, if the snow is heavy enough it will lower the temperature to allow it to settle anyway. Often it snows in March and April when the temperature is well above freezing, sometimes as high as 6C, because the surface air is so dry (DP below 0C), just it struggles to settle. 06z GFS showing the ideal situation where if a low does approach to the SW off the Atlantic, if it continues east with a big enough col/ridge between the next low over the Atlantic, it may pull in deep cold from the north in its wake as it moves on the continent. The lows and jet may struggle to get far north with the Greenland block and trop PV to our NE pushing cold air south.

Not slating it, it just seems to be the bearer of bad news this winter but unfortunately often right while GFS often teases us ad infinitum with deep cold synoptics. ECM often on the conservative side of things, but I guess eventually it will tease us too. Not when I'm away.

Our patience is wearing thin with the ECM. Away this weekend in Wales and plan not to look at the models until Monday evening, if we are still chasing deep cold synoptics after day 10 by then, may have to employ the banging head against a brick wall emoji.

My concern is high pressure remains stuck to us like a limpet and the deep cold remains out of reach just to the east with occasional scraps of cold ejected south, southwest or west from this cold pool around the high over the UK. If we have a true reflection of the strat in the trop, the displaced polar vortex looks too far east and the ridge over us. Really could do with some retrogression of the upper patterns. But we'll see, but, doesn't looks to be a mobile westerly March. But we are hoping for deep cold to counteract the increasing daylength and solar radiation, which is a tall ask the way our luck has gone in recent winters.

I saw a video on twitter of snow in Pau, SW France near where you used to live, just to rub salt in wounds, and although the city is in the foothills of the Pyrenees, it's not that high up. I share your frustration, it's unfortunate that the SSW may not bear fruits for us until towards mid-month, given the 2nd more potent warming and reversal doesn't occur until Monday and the lag from that. But given the EC weeklies were showing high lat blocking throughout March, there is some hope, but will be too late unless we get proper deep cold? There's still a chance that the UK's limpet high may budge far enough west to allow a cold shot to drop down from the arctic late next week / following weekend, but may be just eastern areas that get chance of deep cold. For now, MJO cycling in out of phase 7 and perhaps 8 suggests limpet high near UK next week and perhaps beyond (phase 7), but maybe a drift towards Greenland (phase 8) but this is up against possible westerlies at higher latitudes being flushed down by the SSW

Probably not worth reading too much from the model output past day 7/8, GFS op keeps chopping and changing with how quickly the blocking high near UK retrogrades west or northwest and declines, how far west or east the cold plunge moves south towards northern Europe and how much undercutting of the block there is over the N Atlantic by lows. But the broad idea of blocking high near northern UK loitering into next week before drifting west or northwest to allow a deep cold plunge towards UK / North Sea tail end of next week has been on the cards for a while from most model ensemble guidance. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4810126

Probably not worth reading too much from the model output past day 7/8, GFS op keeps chopping and changing with how quickly the blocking high near UK retrogrades west or northwest and declines, how far west or east the cold plunge moves south towards northern Europe and how much undercutting of the block there is over the N Atlantic by lows. But the broad idea of blocking high near northern UK loitering into next week before drifting west or northwest to allow a deep cold plunge towards UK / North Sea tail end of next week has been on the cards for a while from most model ensemble guidance.

A very valid point, I tend to look at the Northern Annular Mode for a quick picture of reversal downwelling during a SSW, the GFS NAM below, although updated yesterday, it clearly shows coupling between strat and trop.

A Sudden Stratospheric Warming (SSW) is now underway, with the stratospheric polar vortex already displaced from the pole over northern Russia. A second warming next few days likely to lead to a coupling with the troposphere - which will increase the risk of cold and wintry weather in early March. View the full blog here

Arctic express inbound day 10

I think cloud cover in March is key for keeping temperatures supressed if we can't get sub -10C uppers like we saw with the BFTE in 2018, which gave sub-zero day maxes even in the first few days of March. If it's sunshine and showers northerly or northeasterly, temperatures likely to be up and down like a yo-yo in early March if the airmass is not extremely cold, warms up in the sun then plummets towards freezing in any showers. The plus side, with annual SSTs at their coolest in March, is that dew point will normally be sub-zero in a northerly or northeasterly sourced from the arctic, so snow will still fall even if temperatures aren't near freezing, just the snow may struggle to settle unless heavy. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4809312

Combination of convective downdrafts typical of showers, pulling cold air down from aloft and cooling of the air created by the precipitation absorbing latent heat from the surrounding air. The heavier the more cooling. Original post: https://community.netweather.tv/topic/98326-model-output-discussion-into-february/?do=findComment&comment=4809329

Combination of convective downdrafts typical of showers, pulling cold air down from aloft and cooling of the air created by the precipitation absorbing latent heat from the surrounding air. The heavier the more cooling.

Looking at the 00z EPS mslp mean out to day 10 to 15, there is definitely a northerly signalled after day 10, how cold it will be too far away to be worth speculating on. But with time low pressure in the means moving out of N America over the N Atlantic could be a concern for prolonging any deep cold flow due to the high near Greenland retrogressing too far west towards Northern Canada - like GFS ops have been showing. Yesterday's NOAA CPC 8-14 day reflects the EPS mean in a way too with potential for lowering heights extending out over the N Atlantic from N America but still with Greenland/Iceland Ridge and the troughing close to our east and northeast. But it must be stressed, it is a mean, so masks a range of possible future outcomes which are uncertain given the models may not have a handling on the strat-trop coupling following the 2nd warming which looks evident on the GFS NAM index: If we can firm up on a deep cold northerly first then that would be the first hurdle to overcome, the threat of lows moving over the N Atlantic to phase with low pressure to the northeast is too far off to worry about for now, but is certainly a possibility that may limit the window deep CAA potential to our small islands.