January 1-January 15, 2005 Pattern Discussion

[donsutherland1]

Last week’s discussion raised a number of issues of what one might expect for the December 26-January 7 period.

• [C]oming shots of cold for the period covered (December 26-January 7) will probably not be as harsh as the outbreak that sent temperatures into the low teens from New York City southward and 6° in Boston (December 20 and 21)… There will be at least another shot of cold air later this weekend into the first part of next week [12/26-27], but it won’t rival the magnitude of the air mass that sent temperatures to their coldest levels of the season so far. In addition, moderation should occur as the month draws to a close.


This idea has verified and model data shows no suggestion of anything comparable through January 7. Lowest temperatures for the timeframe to date:

Boston: 11°, December 28 vs. 6°, December 20, 21
New York City: 18°, December 28 vs. 11°, December 20
Philadelphia: 17°, December 28 vs. 10°, December 20
Washington, DC: 20°, December 28 vs. 11°, December 20

• The only area that stands a chance at picking up perhaps a moderate or significant snowfall is easternmost New England as a clipper and offshore low attempt to phase this weekend. Downeast Maine and Cape Cod probably have the greatest possibilities of seeing at least an appreciable snowfall, but it is not out of the question that at least some snow backs into Boston, Providence, and even eastern Connecticut.

Appreciable to significant snowfall occurred somewhat farther to the west than outlined. The heaviest snow was confined to southeastern Massachusetts, Cape Cod, Nantucket, and eastern Long Island. However, Boston and Providence saw significant snowfall (6” or more) and accumulating snow also reached such cities as New York City and Newark. Some accumulations from the December 26-27, 2004 snowstorm included:

Boston: 6.6”
Brewster, MA: 18.0”
Bridgehampton, NY: 8.5”
Chatham, MA: 18.0”
East Hampton, NY: 8.7”
Eastham, MA: 16.0”
Montauk, NY: 8.0”
Nantucket: 13.6”
New York City: 2.1”
Newark: 1.4”
Providence: 7.5”
Worcester: 7.4”

• In the Deep South, I believe opportunities remain for at least the threat of snow. Best prospects for that, in my view, lie across northern Alabama, northern Georgia, and northern Mississippi. [earlier discussion] This threat has materialized to some extent and even southeast Texas, parts of Louisiana, and the Florida Panhandle have some chance at seeing minor snow or mixed precipitation today and tonight [12/24 into 12/25].

This threat worked out well. However, parts of southeastern Texas received a substantial snowfall. All in all, this proved to be a historic snowstorm in parts of the U.S. Gulf Coast region.

• As the month nears an end…there is some danger that ridging might begin to retrograde toward the East.

As of now, the pattern features a trough in the West and ridge in the East.

• The PNA turned negative on December 20 and continues to plunge. The ensembles continue to take it to near the bottom of the charts by early next week. Afterward, there is much uncertainty as to how negative it will hold for the remainder of the month and first days of January.

The Arctic Oscillation is strongly positive and there is strong ensemble support that it will remain that way through the end of December.

As December nears its end, the PNA is negative and the Arctic Oscillation positive. Ensemble data strongly supports this remaining the case for the opening days of January.

• The warmth in the West should peak this week [December 19-25] and then likely begin to fade… With the PNA continuing to plunge and the latest model guidance, next week [week beginning 12/26] looks to be colder than the one that is now concluding.

Temperature anomalies for December 19-25 included:

Los Angeles (Downtown): +0.2° (cooling trend began 12/23)
Portland: +1.7° (cooling trend began 12/27)
Seattle: -0.2° (cooling trend began 12/28)

The January 1-15 Ideas:

As 2004 nears an end, there are some hints that a large-scale pattern change could begin to evolve, mainly after the first week in January. For starters, given the changes occurring over the Pacific Ocean, there are some indications that the NAO could be trending downward toward the end of the first week in January and perhaps reach negative January 11 +/- 3 days. Unlike the last false alarm earlier this month, there is some ensemble support for this trend. However, on a cautionary note, the SSTAs are not very favorable.

At the same time some of the ensembles are hinting at a falling NAO, they are also hinting that the Arctic Oscillation could be falling and the PNA heading positive but this ensemble support concerning the PNA has diminished in recent days.

After crashing to –34.70 on December 25, the SOI had rebounded to +10.40 by December 30 before falling back to +6.30 a day later.

In recent days, the 500 mb height anomalies have shown that the ridge anchored over the Central Atlantic has shifted farther to the east. It is possible that it progresses more toward the north and east in coming days and then begins to retrograde toward Greenland around or after January 10. Whether or not retrogression occurs much less takes these above normal height anomalies toward Greenland is still very uncertain given the SSTAs.

The above normal height anomalies that prevailed over the Central Plains in recent days should shift eastward. However, the below normal height anomalies that have been off the West Coast might move only slowly through the West over the next 7 days.

My quick thoughts on the NAO, PNA, and AO:

• AO: Begins a steady decline after January 7 and goes negative sometime between January 10-15.
• NAO: Begins a gradual decline but holds strongly positive through January 7. After January 10, it heads toward neutral territory.

• PNA: A slow rise occurs but it holds mainly negative through January 10 and then perhaps goes neutral a few days later.

In terms of the resulting weather, at this point in time, I believe the following is likely:

• Much of the eastern United States will average warmer than normal through the first 7 days of January with no prolonged sieges of cold. New England could see above normal anomalies begin to diminish a few days before then. Before then, look for highest temperatures to reach at least 54° in Boston, 59° in NYC, 60° in Philadelphia, and 64° in Washington, DC. Through at least January 10, none of these cities should see any new low temperatures for Winter 2004-05.

• None of the big cities from Washington, DC through New York City should see accumulating snow through the first week in January. There is a possibility that a system could bring a rain ending as snow scenario to Boston and perhaps even Providence in the January 5-7 period.

• The Central United States and Midwest should see a trend toward cooler readings during the first week in January. Some of the cities that have already experienced snowfall this season including Kansas City, Chicago, Detroit, and Cleveland likely will see additional accumulations during the first 10 days of January.

• The January 8-15 period should see readings in the East trend downward and cities from Philadelphia to Boston could see their readings average somewhat below normal. Washington, DC might be closer to normal but even there the possibility does exist for a turn to colder than normal conditions particularly after January 10.

• The pattern looks to be progressive. Consequently, while Winter is likely to visit the Pacific Northwest through perhaps the middle of the first week in January—with at least the possible opportunity for some snow in Seattle—that region should be warming during the second week of January.

• The first 10 days of January should see continued above normal rainfall on the West Coast. Rainfall should not be as extreme as the recent 3-day total of 6.84” in Los Angeles but it could still be significant. Cities where above normal precipitation should occur extend beyond the West Coast and include Los Angeles, San Francisco, Omaha, and Houston.

Seasonal Snowfall Update:

In this discussion, the focus will be on Boston and New York City. December saw total snowfall of 7.2” and 3.0” fall respectively in those cities. At this point in time, both cities remain on course for the initial seasonal estimates of 50”-60” and 20”-30” respectively.

Boston:

Criteria: November 1” or more; December 7” or more:
• Average seasonal snowfall: 56.0"
• 50" or more: 10/18 (56%) seasons
• 40" or more: 16/18 (89%) seasons

New York City:

Criteria: October: None; November: Trace; December: 3” but less than 10.0”
• Average seasonal snowfall: 28.7”
• 30” or more: 6/18 (33%) seasons
• 20” or more: 13/18 (72%) seasons

New Year’s Day fun tidbit for New York City:

On 22 prior occasions, NYC saw a high temperature of 50° or above. 7 (32%) seasons saw 30” or more snowfall; 8 (36%) seasons saw less than 20” snowfall. Average seasonal snowfall: 27.6”. However, for those seasons that had seen 3” or more snow in December, the average climbed to 34.1” with 6 of those 12 (50%) seasons seeing 30” or more. Just 2 of those 12 seasons (17%) received less than 20”.

Snowiest such season: 53.2”, 1906-07
Least snowy such season: 2.8”, 1972-73

Reference for a January 2005 Outlook:

For those looking for a thorough and well-written national outlook for January 2005:

WxGuy25’s January 2005 Forecast

To all, a happy New Year!

[wx247]

great as usual don!!! I learn a little more everytime I read one of your outlooks.

[sertorius]

Don:

Thanks o much for the info-awesome as usuall!! It really is beginning to look know that Kansas City/Lawrence couls see a little accumalating snow this Wed. night into Thursday-esp. if the 0z euro today verivies and the low tracks thru southern Missouri-both gfs and euro have the 850 0 line well thru the area by Wed. afternoon-we shall see-thanks again!!

[donsutherland1]

A number of quick updates:

Some points made in the initial discussion:


• AO: Begins a steady decline after January 7 and goes negative sometime between January 10-15.
• NAO: Begins a gradual decline but holds strongly positive through January 7. After January 10, it heads toward neutral territory.
• PNA: A slow rise occurs but it holds mainly negative through January 10 and then perhaps goes neutral a few days later.

The latest ensemble data continues to support these ideas. However, support for a negative AO has diminished, so this is a trend that will bear watching.

• Much of the eastern United States will average warmer than normal through the first 7 days of January with no prolonged sieges of cold. New England could see above normal anomalies begin to diminish a few days before then. Before then, look for highest temperatures to reach at least 54° in Boston, 59° in NYC, 60° in Philadelphia, and 64° in Washington, DC.

New Year's Day saw record temperatures across parts of the Mid-Atlantic and warmth into the Northeast. Already, most of these conservative estimates were exceeded with the exception of Boston:

Minimum estimate for highest temperatures:

Boston: 54°; Actual to date: 52°
New York City: 59°; Actual to date: 60°
Philadelphia: 60°; Actual to date: 64° (record for 1/1)
Washington, DC: 64°; Actual to date: 69° (record for 1/1)

The warmth from Philadelphia northward did not reach the levels I thought it would yesterday afternoon as the wind shifted and temperatures began to retreat. Select high temperatures:

Baltimore: 67° (record for 1/1)
New York City: 60°
Philadelphia: 64° (record for 1/1)
Richmond: 72°
Washington, DC: 69° (record for 1/1)

• None of the big cities from Washington, DC through New York City should see accumulating snow through the first week in January. There is a possibility that a system could bring a rain ending as snow scenario to Boston and perhaps even Providence in the January 5-7 period.

Model guidance has grown somewhat colder for the aforementioned timeframe. It now looks like a good bet that Boston and possibly Providence will see at least some accumulations of snow. New York City still appears to be too warm. Farther south, snow is not likely for the event which should occur on January 5-6.

• The Central United States and Midwest should see a trend toward cooler readings during the first week in January. Some of the cities that have already experienced snowfall this season including Kansas City, Chicago, Detroit, and Cleveland likely will see additional accumulations during the first 10 days of January.

So far, so good. All of the cities specifically mentioned appear reasonably likely per the computer guidance to see at least some accumulations of snow during the January 5-6 timeframe; a significant snowfall of 6" or more can't be ruled out in some of the noted areas, though it's a little soon for me to try to pin this down just yet. After the event, with the pattern remaining relatively progressive, a moderation in temperatures is likely and there is some support from the computer guidance for such a trend.

[sertorius]

Don:

Thanks again-the models have def. trended things south a bit more and have become more aggressive with the cold-the euro, had this storm further south all along. The NWS service out of Topeka is growing quite concerned and was caught by surprise with the cold front that passed thru here last night-we are at 33 degrees with topeka below freezing-were supposed to be in upper 40's to close to 50 today. NWS has not ruled out that we could see significasnt snow here Wed./Thursday, but right now a siginifiacnt ice storm is comming into focus-this set up is very similar to the massive ice storm that hit us in Jan. 2002. ETA espec. on the 12z run has us in quite a mess with the 0 line well thru us before Wednesday-It def. bears watching and I know things could change quickly as I am in this scenario pretty far south, but at least I have something to think about!! If the front last night is any indication, then we are in for a mess!! By the way Topeka is in a winter weather advisory thru tomorrow-I'm not and that really accentuates how tricky this forcast will be for Wed. 30 miles from could get ice while I stay liquid!!!

[donsutherland1]

A quick update...

The event that should bring at least some accumulating snow to such cities as Kansas City, Chicago, Detroit, Cleveland, Boston, and Providence is underway/getting underway. Chicago and Detroit could see a significant snowfall and should keep Chicago and Detroit headed toward the idea of 40"-50" for the winter.

In the larger overall pattern, there are some hints of change down the road:

• The ensembles have grown more supportive of the Arctic Oscillation trending neutral and possibly negative toward mid-month.
• Ensemble support for a negative NAO is higher than it has been just a few days ago.
• The evolution of events in the Pacific remains consistent with downstream changes in the Atlantic

Finally, and I'll offer more details on this in my next larger pattern discussion, a look at ENSO profiles suggests that odds generally favor a pattern change after mid-month.

For today, the Windy City will be transformed into the Snowy City, Kansas will be the great skating rink in the Plains, and overrunning will defy the Southeast ridge to bring some frozen precipitation to interior New York State and parts of New England.

[donsutherland1]

Earlier, I had noted:

As 2004 nears an end, there are some hints that a large-scale pattern change could begin to evolve, mainly after the first week in January. For starters, given the changes occurring over the Pacific Ocean, there are some indications that the NAO could be trending downward toward the end of the first week in January and perhaps reach negative January 11 +/- 3 days.

The latest trends in the ensembles suggest that the issue is increasingly becoming not whether the NAO will go negative but whether a negative NAO will be sustained.

January 3 and January 6 Ensembles:



Now, most of the ensembles point to at least a briefly negative NAO around the timeframe noted above. The SSTAs would argue for a short-lived negative NAO. However, the changes that have occurred upstream in the Pacific would suggest that it would have a chance at being sustained should it go negative.

For now, the trend in the ensembles is encouraging.