Kasim Awan

The upcoming set up has potential for lower areas of the region. The hills could get very high amounts. Low heights, forget any significant precipitation shadow. Lots of shortwave activity & slow moving precip.

This upcoming set up is less marginal on average. The "base" snow line will be ~150m lower than 4th Dec if the current output is correct. This means more places will come into the snow potential, and snow will be easier to achieve. Potential is the key operator here.

Yes, from experience the set up screams rain to snow event potential to lower levels. Throw in stalling, an offshore breeze, nocturnal cooling & heavy ppn. Some decent amounts on the cards locally. All snow for most >200m with -4.5 uppers at 525DAM. Not everywhere will see the precip.

Inversions erode the <1000ft temps just like evap cooling etc can erode the >500ft temps. In both instances, more moderated uppers can support snow.

In the shorter term, ICON has a trough development early Xmas eve. Notice the lift in 850ThetaE values off the NE coast, which highlights the trough.. If this gains support it could produce a few cm in places.

I've seen snow with uppers of 0C in the occassion where heavy ppn erodes the top-down temperature lapse rates.. It's about the soundings rather than the uppers. Higher humidity reduces the 850 requirements due to lesser lapse rates.

The pattern is rife for producing "polar lows". The point I'm making is, the GFS can predict them, plus additional deeping is possible under a nowcast situation.

It's the trough energy associated with the larger scale low responsible for the polar lows not them directly. They don't always appear at very short notice, though they do have a short duration. The GFS is quite good at modelling troughs embedded in 500mb temps below -35C, 528dam or lower in an unstable northerly flow with low heights. The 6Z does appear to form a polar low.

GFS 06Z evolution is sensible. Has a polar low diving SSE at D7 creating room for further amplification, I expect the SE Greenland / Iceland area to have higher heights forecast by upconing output for D8-9. This could well yield a surface easterly into the first week of January.

Extremely unlikely given the WAA is glued to the lows near Newfoundland. Will keep the strong Mid Atlantic omega ridge well west.

The ECM provides an ideal set up for continued bouts of meridional amplification following trough disruption around southern GL. Other output i.e. GFS keeps us looking to the NE instead. Anyway, that'll be all from me this AM.

I find use of the "laughing" emoji without any discussion leaves me a little confused @matthugo P.s., I'm not stating this solution is favoured within the model bias - the gfs' dealing of the GL high is most likely to verify. However, in model analysis consideration of other solutions is very useful.

ECM has a muchhh flatter Greenland ridge. As explained this is a positive, allows for a build in low heights to our east. Please don't misinterpret this as a negative. It is actually a potential route to prolonging cold.

GEM also in with excellent polar low injection... permitted by weaker GL heights.

Just checked and the GFS op has sided towards the solution I was discussing yesterday, lower heights over Greenland and trough energy sliding south east. Less clean wave break. This continued cold source also means uppers are colder on the run. This had some support from ens. Will be interesting to see how the eps deals with the wave break.

It obviously can't be determined whether the model was forecasting a SSW from that. I don't think long range output forecasts SSWs as such - more just a general stratosopheric disruption. I believe there are certain surface conditions more conducive for SSW surface waving. This may have lead the model down this disrupted PV path. We have some of these requisites now. Also note Jan 13 seems a good match for the SSW and split forecast. Interesting. I'm not a huge fan of the strat, so this will probably be my only contribution.

Good summary. Amazing consistency now, 9/10 times this consistency is had the cold follows in. Something significant afoot.

Said sunny spells 4 days before BFTE

I think an eventual easterly isn't completely off the cards either... combine continued amplification & a trend for the ridge to collapse SE and you have surface easterly. Albiet, weak and quite temporary, it's fate also dependent on pressure near Svalbard.

I like the smaller low on gfs 18z. Notice more shortwave activity as a result..

Northern Hills getting clobbered now.

GFS East by 0.5 miles In all seriousness, heights a little less low, and a little further east. Good start.

ICON 18Z strengthens the Russian high a little more. From a longtitudinal perspective, this would send the low further south west. Being realistic in suggesting more moderated uppers and marginal surface conditions is also a completely possible scenario for the D7-11 range. The strengthening of this pattern described could outweigh any bias which pushes the system further east. Hopefully both factors meet somewhere in the middle as per EC mean.

I believe there is a significant distinction between an isolated Greenland high and a ridge extending into Greenland. Regarding onwards opportunity the high option would be slightly more promising for easterlies. Most model output shows an extensive ridge with little low pressure to the south (isolation). Hence, the 240h EC outcome is more conducive to activity associated with the ridging & eventuall loss of Greenland pressure.

ECM mean has us in the optimal place. Indicates that some runs are further east like the gfs mean. Area 1 would have a lack of convection, area 2 an optimal combo of convection / cold air, and area 3 a higher risk, potential greater reward scenario. Air not as cold but more potential for higher precip totals. Area 2 please.