Signs of Winter's Shift to the East Beginning to Appear

[donsutherland1]

On November 27, my idea was that winter's primary focus would be on the Ohio Valley westward through mid-December.

Among the points made then were: [L]ook for storms to continue to track somewhere to the eastern Great Lakes, up the St. Lawrence River Valley, or the Appalachians for the most part during this period. This does not mean that systems cannot jump to the northern Mid-Atlantic/New England coast. However, it does appear that the pattern remains ripe for cities such as Kansas City, St. Louis, Chicago, and Detroit to have opportunities to add to their early-season snowfall.

At this point in time, if I were to make any adjustments, I'd include areas just to the east of the Ohio Valley and also increasingly upstate New York and northern New England into the assessment for the remaining part of the period.

Having said that, there are some indications that changes could lie in the near and medium-term. If one examines the mean 500 mb height anomalies over 5-day periods over the past month, one notices that the situation has now evolved to the point where there are prominent above-normal height anomalies in the Gulf of Alaska (they've been there for around two weeks but have really sharpened in recent days) and below-normal height anomalies over the Hudson Bay region (they've inched eastward over the past two weeks and also become much more substantial in recent days).

What this combination suggests is that the dam that has been holding back some of the cold air in Canada will be opening at least somewhat. Thus, more frequent incursions of cold air will begin to flow into the USA.

However, before one expects any major Arctic outbreaks, the 10-day Canadian Ensembles say "not so fast!" With the exception of a broad area running from the Hudson Bay to Labrador, temperatures in Canada are expected to run up to 0.5 standard deviations above normal. Hence, the cold that comes into the USA will be noticed relative to the air masses that it replaces but will be nothing extreme.

I expect this situation to be maintained to at least 12/20. Thus, there will be increasingly frequent incursions of cold air into the Northern Plains and eastward but likely nothing remarkable during that timeframe.

The other feature that has shown up in recent days is the above normal height anomalies that stretch from the Gulf of Mexico to the Bahamas.

In my view, these developments portend to the gradual eastward shift of storm tracks whereby the predominant storm track will likely run northward in the area ranging from the St. Lawrence River Valley to the Coastal Plain. This does not mean that a system might not track somewhat farther to the west or the east but the most likely track would be along the lines that I described. It also does not preclude coastal redevelopment off the Mid-Atlantic or New England coasts.

In terms of actual weather, this means snow opportunities for the Ohio Valley, western/central New York and northern New England will be increasing. Moreover, as storms tap the broad reservoir of cold (not extreme) air that remains available in Canada, one might begin to see situations whereby precipitation either begins or ends in the frozen form from the Mid-Atlantic to coastal New England, expecially as one approaches and then passes mid-month.

In the medium-term, I believe the situation is pointing to the development of a positive PNA. Indeed, the ensembles are in agreement with such a prospect.

Right now, the ensembles remain stuck on a positive NAO. However, I do believe the evolution toward a negative NAO is continuing with the SSTAs. Moreover, I believe upstream developments could begin to lead to changes that could see the NAO go negative perhaps beginning in the 12/17-22 timeframe. If that happens, perhaps it might be possible to bring out the sleighs in such cities as Philadelphia.

I'm not yet fully certain of this timing. I do remain confident that for the winter as a whole, the NAO will average <0.

Finally, Saturday saw the SOI crash to -38.20. Today, it snapped back to -26.90 and a further sharp rise appears likely in the immediate term. Will this shift lead to downstream changes across the Pacific to North America as winter's slow but steady eastward march continues? Will the changes occur just as the NAO possibly begins to trend negative and the PNA has climbed the mountains into + territory?

[weatherlover427]

[Chris the Weather Man]

Wonderful Post, Don

[aggiecutter]

Looking at the latest runs of the GFS and EURO, it appears that next weekends trough is transient. It hangs around until the early part of the following week and pulls out. I think the GFS 300 hours and beyond probably has the right idea with a central-eastern trough in the means for the rest of the month into early January. IMO, the pattern wont lock in until around Christmas week. The next 2 weeks are just a period of transition.

[Brent]

GOOD.

[Lowpressure]

Might we be looking at a widespread white Christmas? Snowpack still looks a little weak albeit better in southern Canada and Northern New England.

[Chris the Weather Man]

By 12/18, the pattern will change....

[sertorius]

My question is if the GFS solution starting next Tuesday (180 hours I think) will verify-if it does, the central plains may not see much snow, but it will be plenty cold in the week before X-mass. I am not holding my breath-but it does seem that after this pretty boring and warm week upcomming that starting next Monday (there is one cold shot Friday/Saturday but next Sunday looks to be in the 50's again!!) things could turn quite wintery here in the Kansas City area-at least temps. wise. At least the GFS gives me something to think about and dream about LOL!!! It will be interesting to see if the EURO gets in on this in the 7-10 day frame. I'm hoping. Have a great day-it is raining and 42 in Lawrence today-kids are going stir crazy as were supposed to get our X-mass tree today.

[Upslope]

Looking at the latest runs of the GFS and EURO, it appears that next weekends trough is transient. It hangs around until the early part of the following week and pulls out. I think the GFS 300 hours and beyond probably has the right idea with a central-eastern trough in the means for the rest of the month into early January. IMO, the pattern wont lock in until around Christmas week. The next 2 weeks are just a period of transition.

This is just not an accurate read of the GFS or the EURO. Not at all. Both show the trough continuing to get reinforced as northern stream energy drops southward out of Canada. This would likely lead to some snow chances farther southward in the 7-10 day frame.

Be very cautious of the GFS solution for the end of next week as it is way off base with basically NO soutern stream system and phasing. It is lost with the STJ!

Take care!

[donsutherland1]

Aggiecutter,

I have to disagree with you on that. Even aside from the modeling, if one examines the progression of the height anomalies across North America, it appears more likely than not that once the trough is established, it will hang around for some time to come.

Overall, I believe the mean temperatures in Washington, DC to Boston will be starting a more meaningful downward trend in the wake of the storm late in the week. As earlier described, cold should continue to come into the USA, though I don't expect the air to be extreme per the Canadian ensembles.

Things could begin to change afterward, as the PNA+ gets established and later the NAO trends toward negative. Then--and probably during or just after the 12/17-22 period--there could be a chance that temperatures fall much below normal in the East. But that will depend, in part, on the NAO's making the switch, so I'm not fully confident of this. At this point in time, I am sufficiently confident to suggest that all the major cities from Washington, DC to Boston will see accumulations of snow for the month of December, with Boston having the best chance at seeing 10" or more.

[aggiecutter]

Don, I agree with you that trough will eventually lock into the east at some point this winter, but I think we're still a couple weeks away from that happening. This seems to be a pattern that is progressing slowly, rather than one that goes from a Western trough to Eastern trough in a short manner of time. I'm speaking in the means, not 3-5 days. BTW, I really enjoy your columns. They are very insightful.

[Anonymous]

Excellent discussion, Don. I'll continue to monitor this. Things should become more interesting as we progress through the month.

-Jeb

[Lowpressure]

Excellent discussion, Don. I'll continue to monitor this. Things should become more interesting as we progress through the month.

-Jeb

Jeb, the afternoon Forecast Discussion from the NWS in Sterling hints at the pattern change early the following week, ie the week of the 13th. I think you and I will have snowfall discussions before Christmas. Then you can have your Jeb walk at Potomac Mills Mall.

[Guest]

Why not Tysons Corner? lol. I think with the coming storm that Northern Virginia will start out briefly as rain, change to a mix for an hour or two, and then go to snow. South of Fredericksburg though, no snow for you. Models have been trending East with this however, so may end up with an all snow situation in the big cities. Right now (just for fun) I will guess 8" at IAD, 3.5" at DCA, 8" at PHL, 10" at CPK, and 12" at BOS.

[Guest]

BTW, if its all snow, expect significantly higher accumulations than those for PHL, DCA, IAD, and CPK (12"+???)

[aveosmth]

What does this mean for us on the west coast....we have had a very cold last 2 1/2 weeks...does this mean that temperatures will be warmer than normal out here? Thanks.

[Guest]

trof in east = warm out west

[wxguy25]

Aggiecutter,

I have to disagree with you on that. Even aside from the modeling, if one examines the progression of the height anomalies across North America, it appears more likely than not that once the trough is established, it will hang around for some time to come.

Overall, I believe the mean temperatures in Washington, DC to Boston will be starting a more meaningful downward trend in the wake of the storm late in the week. As earlier described, cold should continue to come into the USA, though I don't expect the air to be extreme per the Canadian ensembles.

Things could begin to change afterward, as the PNA+ gets established and later the NAO trends toward negative. Then--and probably during or just after the 12/17-22 period--there could be a chance that temperatures fall much below normal in the East. But that will depend, in part, on the NAO's making the switch, so I'm not fully confident of this. At this point in time, I am sufficiently confident to suggest that all the major cities from Washington, DC to Boston will see accumulations of snow for the month of December, with Boston having the best chance at seeing 10" or more.

The warm Pool has progressed eastward to about 140-145W longitude. this means that the positive height anomaly in the means will set-up right on or just off the west coast which the euro has been pushing consistently over the past several runs.

What (IMO) is more interesting is that SSTA east of the warm pool seem to be warming also along the NW coast of North America. IF this continues we may not have to wait for the actual warm pool to completely progress eastward in order to initiate a +PNA pattern assuming the warming of those SSTs continues.

Compare the current SSTA to that of a month ago. Notice NOT ONLY the eastward progression of the warm pool but also the warming of the SSTA along the NW coast of North America.

NOV 3
https://www.fnmoc.navy.mil/products/NCO ... nomaly.gif

Current
https://www.fnmoc.navy.mil/products/NCO ... nomaly.gif

ONCE the SSTA transition in the N PAC is complete, then and ONLY THEN will the trough lock off in the EUS initiating the start of the winter pattern we've been discussing for the past few months now.

BTW…great work as always, Don.

[donsutherland1]

Thanks, Wxguy25,

I like how the warm pool has been progressing and the idea that the PNA will be heading positive in the medium term. I'm looking forward to the winter pattern in the not so distant future.

[yoda]

Interesting little snippet from the LWX AFD at 9 PM....

THE 220-240 HR SUN 00Z MRF GOT MY ATTN. LET'S SEE HOW THIS PLAYS OUT
DURG THE MIDDLE OF NEXT WK.

http://www.srh.noaa.gov/fwd/productview ... &version=0


Anyone have an idea of what they are talking about? I am guessing that they mean cold air...