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Pattern Discussion 12/15 and beyond


ORH_wxman

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What you have here is above normal heights to begin with across Canada so that when you get some ridge from a Mid Latitude Wave, the anomaly charts appear to look amazing. This is a case where you actually have to look at the means and the anomalies. If you just look at the h5 anomalies, you'd think 2009 or 2010 was on the way or something. In reality, the Arctic Heights took a hike back to Asia and we are left with generally above normal heights throughout Canada, so any small ridge will appear like a huge block on anomaly charts.

The thing about "models not realizing the strength of the 50-50 low and block" is usually when there is a strong cold air source / suppressive high / polar vortex. The situation after Christmas is another hybrid, bootleg scenario that could possibly benefit the interior and portions of New England. Even we could see a snow to rain but I'm about 50, 50 myself on that one. This is NOT a classic 50-50 low / -NAO setup; otherwise, I'd be on board with DT.

Yeah I agree. I suppose it could be more of a SWFE for us with that set up, but for now...I'm sort of meh about it with it being so far out. It would be nice for that to come through, however. I know I could use a little. There are some signs of the block trying to help force it out under last minute, but then you risk already flooding the atmosphere aloft with more marine air.

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one things for sure, lack of moisture will not be an issue with the day10 system.

The dry pattern is over. We've definitely entered a stormy pattern. That is a good thing to have...you keep that going in late December into January...climo will catch up with temps a little bit and probably give some good events.

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Yeah I agree. I suppose it could be more of a SWFE for us with that set up, but for now...I'm sort of meh about it with it being so far out. It would be nice for that to come through, however. I know I could use a little. There are some signs of the block trying to help force it out under last minute, but then you risk already flooding the atmosphere aloft with more marine air.

Where we are in the global AAM budget and tropical forcing is similar to around mid October or so (our last really strong +EPO period). This is a very promising time to be in with extreme -AAM tendency going on in the Tropical Regions (this was a possible Hadley Cell feedback from West Pac/Asia I was talking about and warm equatorial stratospheric temperatures). These anomalies will propagate poleward along with a strong 30mb wave 1 between Christmas and New Years. Both will help cool the equatorial temperatures and get the EPO negative.

Starting to look very promising as we move into the New Year and the possibility of a snowstorm is growing 1/5-1/10.

This is my 1 positive post of the day (haha). I'll revisit this in the coming days. For now, it's speculative.

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Nice post HM and I agree as well. It's easy to get caught up in the bright red colors on the model height anomalies but when push comes to shove if there's not a physical blocking ridge there it doesn't do you much good at all. This retrogression of above normal heights into Central Canada has been as bootleg as they come.

But the ridge splitting from the PAC into Alaska is good and I think the changes will start to manifest themselves in the form of shots of colder air and a rapidly shifting pacific by the last few days of Dec into the new year.

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What you have here is above normal heights to begin with across Canada so that when you get some ridge from a Mid Latitude Wave, the anomaly charts appear to look amazing. This is a case where you actually have to look at the means and the anomalies. If you just look at the h5 anomalies, you'd think 2009 or 2010 was on the way or something. In reality, the Arctic Heights took a hike back to Asia and we are left with generally above normal heights throughout Canada, so any small ridge will appear like a huge block on anomaly charts.

The thing about "models not realizing the strength of the 50-50 low and block" is usually when there is a strong cold air source / suppressive high / polar vortex. The situation after Christmas is another hybrid, bootleg scenario that could possibly benefit the interior and portions of New England. Even we could see a snow to rain but I'm about 50, 50 myself on that one. This is NOT a classic 50-50 low / -NAO setup; otherwise, I'd be on board with DT.

Thanks for the explanation..For a time I was thinking that this may be more of a legitimate blocking setup this go around after this week's system forms into a 50/50..I was mistaken though.

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The GFS has a pretty legit Baffin Island block during the 12/27 threat...its not just a fake high heights there as it joins the ridging from the 12/21 storm with the block that migrates east from N of AK. The Euro isn't quite as good as it shoves evrything further north toward northern Greeland which gives room for higher heights to build ahead of the system in SE Canada.

It would be nicer if they teleconnected more directly to a North Atlantic ridge as this would hold in a 50/50 type low better. But I won't be shocked if that 12/27 system ends up pretty nasty in the interior with a lot of frozen if we can get that thing to come in a bit stronger.

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The GFS has a pretty legit Baffin Island block during the 12/27 threat...its not just a fake high heights there as it joins the ridging from the 12/21 storm with the block that migrates east from N of AK. The Euro isn't quite as good as it shoves evrything further north toward northern Greeland which gives room for higher heights to build ahead of the system in SE Canada.

It would be nicer if they teleconnected more directly to a North Atlantic ridge as this would hold in a 50/50 type low better. But I won't be shocked if that 12/27 system ends up pretty nasty in the interior with a lot of frozen if we can get that thing to come in a bit stronger.

Yup . It's this week shifted 200 miles south
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Thanks for the explanation..For a time I was thinking that this may be more of a legitimate blocking setup this go around after this week's system forms into a 50/50..I was mistaken though.

Well, it still is blocking in a good location, so maybe the correct word isn't legitimate as much as it's "effective."

Even as the N PAC block forms and pinches off into the north pole, the Arctic Air retreats westward toward Alaska. The air simply isn't cold INVOF the blocking setup. Also, conditions appear pretty ripe for wave amplification along the lee-Rockies so you are going to need an equally strong force to block its developing downstream ridge. Now, if this wave trends weaker for some crummy reason with s/w timing or whatever, then suddenly much of New England becomes a snowstorm. I still don't think it's quite the right setup for coastal CT-NYC-NJ yet. But if you are looking to see anything at this point, then of course the upcoming stormy pattern is a good one.

This same news I'm spouting off as "bad" is actually great news for northern guys and the Midwest, who wouldn't see see heavy snow with a very effective -NAO block. This is one of the reasons why a while back I said that the anomaly placements were suggesting near-historic snowfall potential in the Midwest.

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fwiw

Wxrisk.com

‎***ALERT *** 12z wed A afternoon run of the European ensemble Model is WAAAAAY EAST of the 12z operational or regular European Model ( which has the Low near Chicago).

12z ECMWF ensemble mean Has 2ndary LOW off the southeast VA coast on morning of DEC 27 with the 0 degree ISOTHERM at 850 MB (rain snow line) ROA to DCA to RDG to ABE to POU to PVD... BOS mostly snow

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The low goes over SNE on the ensembles, so the mostly snow in SNE is probably not correct, verbatim. Not that it means much this far out, but DT weenied out a little.

The way you described it seemed pretty good...its a snow to ice/wintry mix in the interior type storm on the Euro ensembles. Prob snow to rain on the coast.

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