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• 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… 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 ensembles have grown significantly more supportive of such a scenario. A look at the ensembles suggests that the Arctic Oscillation will go negative. The NAO likely will go negative for a short time around the timeframe noted, return to positive, then go negative (possibly strongly negative) around or after mid-month and possibly lock in there. The PNA should go positive:
• Much of the eastern United States will average warmer than normal through the first 7 days of January. 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.
Through January 6, this idea has been holding up reasonably well, though temperature averages are even warmer than I had expected. The monthly temperature departures from normal and monthly extremes through January 6 follow:
Boston: +8.1°; Highest: 53°, January 3, 2005
New York City: +12.8°; Highest: 60°, January 1, 2005
Philadelphia: +11.9°; Highest: 64°, January 1, 2005
Washington, DC: +13.4°; Highest: 69°, January 1, 2005
• 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.
Some snow did penetrate as far south as northern New Jersey with Newark picking up 0.1” on January 6. A series of waves brought snow to both Boston and Providence and a trace to New York City. Boston and Providence set daily snowfall records for January 6. Total snowfall for the aforementioned cities:
Boston: 6.9” (5.5” on January 6 set new daily record)
New York City: Trace
Providence: 4.5” (4.5” on January 6 set new daily record)
Philadelphia: None
Washington, DC: None
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.
This idea generally worked out quite well. Kansas also witnessed a major ice storm during the January 4-5 period. Total snowfall through January 6 for the above-mentioned cities:
Chicago: 9.8”
Cleveland: 3.6”
Detroit: 6.0”
Kansas City: 1.2”
• 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 latest model guidance, and I’m relying more heavily on the ECMWF given its performance in the medium-range, suggests that the second week of January should prove cooler than the first week. However, temperatures could spike after mid-week ahead of the advance of a potentially much colder air mass.
• 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 latest model guidance suggests that a series of deep troughs should move through the Pacific Northwest. Today and tomorrow, some parts of Washington State could receive some snow. It remains to be seen whether the snow reaches Seattle. Another cold shot could arrive at mid-week next week. Afterward, the PNA is expected to be rising and as mid-month approaches, a noticeable warming trend could commence.
• 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.
Precipitation Amounts through January 6:
Houston: 0.07” Below Normal
Los Angeles: 2.15” Much Above Normal
Omaha: 0.48” Much Above Normal (14.1” snowfall January 5-6)
San Francisco: 1.13” Above Normal
The January 9-22 Ideas:
In the East, the unseasonable warmth has defined the opening days of January. Even as New England has been able to experience brief periods of cold along with snow, readings have averaged above to much above normal along the East Coast. That situation is likely to continue into the second week of the month.
However, there are growing signs that a significant pattern change could be unfolding, especially around or just after mid-month. One can see hints of this in the ensembles depicted earlier, specifically with growing support for the PNA shifting to positive, and the Arctic Oscillation and NAO to negative, especially around and after mid-month.
While there may be doubts about whether such a pattern will be sustained, a look at the historic experience given similar ENSO regional profiles argues that the pattern change will occur and be sustained.
Of the 11 seasons in which the average ENSO regional temperature was less than +0.5°C from that of December 2004 (Regions 1+2, 3, 4, and 3.4), 7 (64%) saw a trough predominate in the East for the January 16-31 period. Moreover, for the regional profiles most similar not just to December but also over the past 3 months, 7 of those 10 (70%) seasons saw a trough predominate in the East during the January 16-31 period. The two seasons that saw similar December and October-December ENSO setups and January 1-6 500 mb anomalies also saw a trough predominate in the East during the January 16-31 period.
Atlantic SSTAs would still argue against a sustained negative NAO but there have been exceptions to the SSTA rule. Moreover, changes that have occurred upstream in the Pacific also argue for the change. Given the ensemble trends, upstream Pacific changes, and the historic experience with similar ENSO regional temperatures, I believe that the trends one has been seeing in the ensemble forecasts for some of the major indices (AO, NAO, and PNA) are pointing toward the proverbial real deal. A pattern change is nearing and it should ensure that the second half of the month sees a predominant trough in the East/ridge in the West configuration.
Some things to look for over the next two weeks or so:
• Cold air will continue to make its presence felt in the Pacific Northwest and there might yet be another snowfall opportunity around the January 11-13 timeframe. After the 14th, a significant warming trend could evolve.
• After January 10, the water-logged Pacific West Coast (especially Los Angeles and San Francisco) should begin to dry out. Warming should follow.
• The East should see readings continue to average above normal from Richmond to Washington, DC through January 14. During that period, it is possible that the temperature might reach 60° on one additional day as far north as New York City. Philadelphia, Washington, DC and Richmond should see readings into the 60s on one or more occasions. A conservative estimate of the highest temperature in each of those cities for the January 9-14 period would be:
Boston: 57°
New York City: 60°
Philadelphia: 63°
Richmond: 71°
Washington, DC: 66°
The January 15-22 period should see temperatures average below normal across New England and a large part of the Mid-Atlantic region, including Washington, DC. It’s still speculative but given the very cold air in Canada, at least one day where highs stay in the 20s and lows fall into the teens from Philadelphia northward cannot be ruled out. The potential for even colder air lies ahead as the month advances and the pattern locks in.
The colder January 15-22 period might see the opportunity for accumulating snow even in such snow-deprived (to date) cities as Washington, DC and Philadelphia. But this is not yet certain.
• As the trough shifts toward the East, I expect that there will be additional accumulations of snow in such cities as Detroit and Chicago, which have enjoyed good snowfall so far and appear well on their way toward the 40”-50” amounts set forth in my winter outlook.
As this happens, cities such as Bismark, Rapid City, Omaha, and Kansas City will likely see their coldest readings so far this season probably during the January 13-16 timeframe. The air that could be spilling into the region is forecast by the Canadian 10-day ensemble to average, in cases, more than 1 standard deviation below normal.
ENSO Regional Update and Seasonal Snowfall:
Finally, the following are some seasonal snowfall scenarios for seasons in which the ENSO regional profile was most similar to the current one:
• Top 15 similar seasons:
Boston: 49.5”
Chicago: 39.2”
New York City: 29.8”
Philadelphia: 24.7”
St. Louis: 21.0”
Washington, DC: 19.4”
• Similar both for December and October-December Periods (10 seasons):
Boston: 53.0”
Chicago: 40.0”
New York City: 32.1”
Philadelphia: 25.4”
St. Louis: 19.9”
Washington, DC: 18.6”
• Similar to December 2004 with QBO that averaged below +6.00 and above –6.00:
Boston: 57.8”
Chicago: 46.5”
New York City: 42.6”
Philadelphia: 36.2”
St. Louis: 30.1”
Washington, DC: 26.0”
• Similar to December 2004 with Positive PDO:
Boston: 55.5”
Chicago: 43.1”
New York City: 32.6”
Philadelphia: 26.8”
St. Louis: 24.5”
Washington, DC: 21.4”
• Similar to December 2004 with Negative PDO:
Boston: 33.0”
Chicago: 28.8”
New York City: 22.1”
Philadelphia: 18.9”
St. Louis: 11.3”
Washington, DC: 13.9”
Note: Given additional global parameters, the most similar negative PDO season (assuming that 2004-05 holds negative) with the ENSO regional anomalies would be 1968-69. Snowfall amounts for that season follow:
Boston: 53.8”
Chicago: 29.4”
New York City: 30.2”
Philadelphia: 23.7”
St. Louis: 12.1”
Washington, DC: 13.9”
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