The Cold Comes East
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- S2K Analyst
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The Cold Comes East
Last week's discussion focused on the core of winter remaining to the Ohio Valley westward through mid-month and the lack of severe cold through at least 12/20. However, it also pointed to the idea that the trough was slowly migrating eastward and that there would be increasing incursions of colder air in the East as the period advanced.
A look at a number of the indices and other data now points to the establishment of a more wintry regime in the East, particularly from after next weekend through perhaps the end of the month.
• For the past two days, one has seen the above-normal height anomalies link up across the Northern Hemisphere from roughly the eastern Pacific to the eastern Atlantic. This has often occurred some 8-12 days before a severe Arctic outbreak. For example, one saw this happen on November 21, 1976 and hold through the 23rd. November 1976 ended with extreme cold.
Right now, the air in Canada is not sufficiently cold for there to be such a severe Arctic outbreak. However, if cross-polar flow can be established, things could begin to fall in place after the 20th.
• The Arctic Oscillation has been negative for the past three days (even as none of the modeling pointed to such an outcome).
• Based on changes that have taken place across the Pacific Ocean and also the evolution of the Atlantic SSTAs, it appears increasingly likely that the NAO will go negative around 12/22 +/- 3 days. DT's excellent website has also pointed to the risk of such a development around the 12/20-22: http://wxrisk.com/wxalert.html.
Moreover, it should be noted that the NAO has dropped fairly sharply in the past day from above +1.00 to around +0.30. Whether or not this indicates a faster drop to negative than noted above remains to be seen.
The GFS ensemble support is not necessarily encouraging for a negative NAO but the 8-10 day average of the ECMWF is more encouraging.
• If one examines the 5-day moving average of 500 mb height anomalies, one can see that the trough has swung into the East in recent days. Moreover, the above-normal height anomalies have been growing across central Europe through Scandanavia. There are some hints of possible retrogression developing in very recent days. If such retrogression does, in fact, develop, then the idea of a shift of the NAO to negative will become far more likely.
For now, as far as the actual weather is concerned, I believe that temperatures across a large part of the East should be running 3°-5° or more below normal on a regular basis this week onward, albeit with some modest warmups. I don't expect to see the temperature at Central Park reach 59° again this month.
This coming week should mark a transition. The coldest air mass so far this season should push into the East courtesy of an energetic clipper that should move across upstate New York/southern Quebec and northern New England. While some snow flurries might be possible in the big cities from Philadelphia to Boston later tonight and part of tomorrow, most of the I-95 Corridor should not see the ground whitened. After midweek, the temperatures should begin to moderate. After next weekend, a potentially even colder air mass should arrive, perhaps next Sunday or Monday.
Afterward, given the MJO things could begin to get quite interesting, especially as abundant cold air remains available. Should blocking develop, the risk of snowfall across the Ohio Valley, Mid-Atlantic, and Northeast should increase markedly after next weekend. Whether or not any more significant storms will develop remains to be seen. Even as the risk of accumulating snow grows, should blocking occur in tandem with cross-polar flow, the possibility of severe cold could also be increasing. The best chance at that is probably 12/20 or afterward.
All said, I believe things still look good for December to end with all the major cities from Washington, DC to Boston having picked up at least some accumulation of snow and likely having seen the lowest minimum temperature in at least the upper teens.
A look at a number of the indices and other data now points to the establishment of a more wintry regime in the East, particularly from after next weekend through perhaps the end of the month.
• For the past two days, one has seen the above-normal height anomalies link up across the Northern Hemisphere from roughly the eastern Pacific to the eastern Atlantic. This has often occurred some 8-12 days before a severe Arctic outbreak. For example, one saw this happen on November 21, 1976 and hold through the 23rd. November 1976 ended with extreme cold.
Right now, the air in Canada is not sufficiently cold for there to be such a severe Arctic outbreak. However, if cross-polar flow can be established, things could begin to fall in place after the 20th.
• The Arctic Oscillation has been negative for the past three days (even as none of the modeling pointed to such an outcome).
• Based on changes that have taken place across the Pacific Ocean and also the evolution of the Atlantic SSTAs, it appears increasingly likely that the NAO will go negative around 12/22 +/- 3 days. DT's excellent website has also pointed to the risk of such a development around the 12/20-22: http://wxrisk.com/wxalert.html.
Moreover, it should be noted that the NAO has dropped fairly sharply in the past day from above +1.00 to around +0.30. Whether or not this indicates a faster drop to negative than noted above remains to be seen.
The GFS ensemble support is not necessarily encouraging for a negative NAO but the 8-10 day average of the ECMWF is more encouraging.
• If one examines the 5-day moving average of 500 mb height anomalies, one can see that the trough has swung into the East in recent days. Moreover, the above-normal height anomalies have been growing across central Europe through Scandanavia. There are some hints of possible retrogression developing in very recent days. If such retrogression does, in fact, develop, then the idea of a shift of the NAO to negative will become far more likely.
For now, as far as the actual weather is concerned, I believe that temperatures across a large part of the East should be running 3°-5° or more below normal on a regular basis this week onward, albeit with some modest warmups. I don't expect to see the temperature at Central Park reach 59° again this month.
This coming week should mark a transition. The coldest air mass so far this season should push into the East courtesy of an energetic clipper that should move across upstate New York/southern Quebec and northern New England. While some snow flurries might be possible in the big cities from Philadelphia to Boston later tonight and part of tomorrow, most of the I-95 Corridor should not see the ground whitened. After midweek, the temperatures should begin to moderate. After next weekend, a potentially even colder air mass should arrive, perhaps next Sunday or Monday.
Afterward, given the MJO things could begin to get quite interesting, especially as abundant cold air remains available. Should blocking develop, the risk of snowfall across the Ohio Valley, Mid-Atlantic, and Northeast should increase markedly after next weekend. Whether or not any more significant storms will develop remains to be seen. Even as the risk of accumulating snow grows, should blocking occur in tandem with cross-polar flow, the possibility of severe cold could also be increasing. The best chance at that is probably 12/20 or afterward.
All said, I believe things still look good for December to end with all the major cities from Washington, DC to Boston having picked up at least some accumulation of snow and likely having seen the lowest minimum temperature in at least the upper teens.
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Chris,
I don't know for sure whether the cross-polar flow will develop. If it does and if there is blocking, the potential would exist for at least some severe cold. For now, I'm taking a more conservative approach, looking for temperatures that will fall at least into the upper teens in DCA through Boston (probably single digits or lower teens outside the big cities) before the month is over.
By later this week or next weekend, there should be much better evidence concerning both the issue of cross-polar flow and blocking.
I don't know for sure whether the cross-polar flow will develop. If it does and if there is blocking, the potential would exist for at least some severe cold. For now, I'm taking a more conservative approach, looking for temperatures that will fall at least into the upper teens in DCA through Boston (probably single digits or lower teens outside the big cities) before the month is over.
By later this week or next weekend, there should be much better evidence concerning both the issue of cross-polar flow and blocking.
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Eric,
For this week alone, it would not surprise me if there were at least a day where the mercury failed to reach 40° in Raleigh with nights well into the 20s on several occasions.
Next week's air mass might be colder with highs perhaps in the lower or middle 30s/lows in the teens in Raleigh. But for now, there's still time to get a better assessment on next week's possible Arctic outbreak.
For this week alone, it would not surprise me if there were at least a day where the mercury failed to reach 40° in Raleigh with nights well into the 20s on several occasions.
Next week's air mass might be colder with highs perhaps in the lower or middle 30s/lows in the teens in Raleigh. But for now, there's still time to get a better assessment on next week's possible Arctic outbreak.
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- therock1811
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Don, excellent Discussion. Your ideas regarding the AO are very solid IMO. the SSTA configuration out there is now starting to favor a classic Aleutian low (both WRT intensity and position) this should help maintain the blocking over the Arctic and keep the AO more negative in the means.
Furthermore, I noticed the beginnings of a slpit flow near 70E in central Asia on the D10 ECMWF. that seems to be supported by the GFS ensembles also. IF that happens we'll be able to reverse the pattern in europe by sending the longwave trough into Scandinavia while the PV slides SW into to a position over Hudson Bay. This would result in the NAO going strongly negative.
Furthermore, I noticed the beginnings of a slpit flow near 70E in central Asia on the D10 ECMWF. that seems to be supported by the GFS ensembles also. IF that happens we'll be able to reverse the pattern in europe by sending the longwave trough into Scandinavia while the PV slides SW into to a position over Hudson Bay. This would result in the NAO going strongly negative.
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Good luck to everyone in the East, South East, and Carolina's-I hope you get something in the next two weeks. Besides being hit by plunges of cold air (which moderate in 2 days!!) the weather in the Central Plains will be pretty dull for at least the next 10 days. I will live vicariously thru you!!! Have a good night
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therock1811 wrote:Well we have a pretty good outbreak setting up here in Cincinnati this week. Just how cold will it get here next week? It couldn't be worse than the 15° we expect here this week, could it?
The implications are much colder than this week's weather, sometime during Christmas week.
Meanwhile, temperatures have dropped all morning, currently it's 27 here with a wind chill from 10-15 - not too far to the NW wind chills are 10-15 below zero! There have been some healthy snow showers passing over from time to time as well, mostly lake enhanced showers aided by the deepening upper low and strong cyclonic flow. Winter is here...brrr..
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- Cat5survivor
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Mr. Sutherland
What about Central Minnesota (Twin Cities Area)? All our weather people do is make jokes about how warm it is but never tell us why?
This morning was actually cold (about 12 degrees). Other than that...nada! I can't even get in the mood to shop. I need to see some snow and have it last. That's my Christmas wish. Any explanations would be appreciated!



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- Cat5survivor
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Thank you
Today (which none of our meterologist saw) we have a coating of snow, very little but none the less it white. So maybe, just maybe, there will be a white Christmas. 

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