Issued October 25, 2007

This winter will feature a battle between the Atlantic pattern and the Pacific pattern. More specifically, the weather across the nation will be determined by La Nina and the strength and location of blocking across North America and the North Atlantic. Right now, the northeast is coming off of a relatively average summer temperature wise. High pressure to the northeast and periodic backdoor fronts kept heat out of the region while the Mid Atlantic, Southeast, and Ohio Valley baked. The AO and NAO averaged negative through August and began to rise above 0 SD in September. The PNA has been positive through the summer and into September, dropping to around neutral this past month. The PDO has been dropping for the past two years, and will likely become negative later this winter. La Nina has built through the summer and two weeks ago was on pace for a moderate to strong phase this winter.

Analogs for this autumn:
1954
1964
1970
1995
1998

At least a weak La Nina was featured in all of these years. -PDO occurred in 1998 and 1970. The NAO in 1954, 1964, and 1995 was positive for September and October. Also, as an additional interesting piece of information, the Solar Flux was at an all-time low in the 1995-1996 winter, which is where it is heading right now. 1995-1996 featured significant cold and snow including a famous blizzard in January.

ENSO: While it appeared La Nina was in a freefall downward, in recent days SST anomalies in Nino 1+2 have decreased, and the progress of falling anomalies in the Nino 4 region has halted. It is possible that the peak of the La Nina will occur well before Christmas this year and may be nearing neutral by late February to March.

ENSO Forecast:
November: -1.3 to -1.6
December: -1.2 to -1.5
January: -0.7 to -1.0
February: -0.5 to -0.8
March: 0.1 to -0.4

Blocking: The analogs listed above with a moderate or stronger Nina had a much more zonal flow all winter long. This along with a weak southern jet meant warmth and little in the way of precipitation. This year, the GFS and EURO are already indicating the NAO dropping negative within the next 10 days. A positive NAO in September and October correlates strongly with a negative NAO winter. The main helping hand in keeping a trough in the east will be low pressure setting up in the Gulf of Alaska, if this holds strong, a +PNA will remain intact longer than what a normal La Nina winter would feature.

NAO Forecast:
November: 0.0 to -0.2
December: -1.0 to -1.2
January: -0.2 to -0.4
February: +0.6 to +0.8
March: -1.3 to -1.5

:::FORECAST:::

November: NAO fluctuating, AO negative, PNA positive. Rain to snow event followed by unseasonably cold weather between the third and the fifth. NAO goes positive briefly around the middle of the month which could bring another snow event around the 15th. First snow event with advisory accumulation is possible on the 23rd when the NAO should drop negative for good. While the NAO may not hold negative for long periods, a positive PNA will help block a strong northern Pacific Jet, and assist in the AO staying negative and generally below average temperatures across the heart of the nation.
Temp anom: -1
% of norm Precip: 90%
Snowfall: 5"

December: NAO and AO are negative, PNA flucuates. Storm possible around the 5th. Cold and dry weather will be the rule through the middle of the month. Another snow storm, possibly significant, will arrive before Christmas. White Christmas probability is high.
Temp anom: -2
% of norm Precip: 70%
Snowfall: 20"

January: AO is positive, NAO goes positive around the 10th. PNA is negative. Major storm around the 10th at the time of the NAO shift. January thaw likely mid month. La Nina will be weakening, and anomalies will be around -.8 by the end of the month with Nino 1+2 region possibly nearing neutral anomalies.
Temp anom: 0
% of norm Precip: 150%
Snowfall: 30"

February: NAO is at its peak, AO is in transition, PNA is negative. Not blowtorch, but very warm across the northeast. Precipitation will be average.
Temp anom: +3
% of norm Precip: 110%
Snowfall: 5"

March: NAO tanks. La Nina will be weakening, and New England will have much below normal temperatures for the month. A couple major snow events are possible during the period - one in the beginning of the month, and one towards the end. With a strong pVs moving south, clippers with advisory to warning snowfall are possible around the middle of the month when the NAO is at its lowest.
Temp anom: -3
% of norm Precip: 100%
Snowfall: 20"

Overall winter: Above average snowfall (80 to 90"), temperatures average -1 to -2 below normal.