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ENSO Analogs:
As a general rule, in times of changing patterns where uncertainty is highest, analogs can provide invaluable guidance. Based on both the December and January ENSO regional data, 9 of the 10 closest matches to December 2004 and January 2005 saw February come out with an NAO that averaged negative. From that mix, in each case, 7 of the top 10 analogs were cold for the second half of February. Moreover, 5 of those 7 continued cold through at least the first week of March. When one factors in the QBO, this data is reinforced.
In terms of February snowfall, using a broader pool of 15 ENSO analogs, one comes up with the following:
Averages:
• Boston: 16.4" (5/6 years when January saw > 30" also saw > 15" in February
• New York City: 8.7"
• Washington, DC: 5.0"
If one throws in the winter QBO, the snowfall totals are even more impressive:
• Boston: 19.4"
• New York City: 11.8"
• Washington, DC: 8.0"
Finally, if one considers the winter ENSO pattern (R1+2 averages < 25.25°C for the winter; R3.4 averages 27°C or above) in combination with the January regional data, the signal is again a snowy one:
• Boston: 21.4"
• New York City: 10.4"
• Washington, DC: 5.9"
Major Teleconnection Indices:
Both the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) are forecast to go negative by most members of the GFS ensembles after mid-month. The important thing at this point in time is to avoid embracing the ensemble means but to (1) focus on the number of members supporting a given trend and (2) identify the trend.
The ensemble forecasts are also generally consistent with February climatology. From 1950 through 2004, in 43/55 (78%) cases, the NAO was negative when the AO was negative and the NAO was positive when the AO was positive.
Climatology associated with Stage 8 of the MJO also typically supports a negative NAO. At last word, the MJO had moved into Stage 7 and should reach Stage 8 within 5-7 days.
In short, strong arguments can be made for the NAO to head negative. There are also hints of a shift to a strongly negative NAO. If one reads through some of the earlier threads at the Eastern United States Weather Forum, Boston NWSFO Lead Forecaster Walt Drag mentioned a recent presentation by heather Archambault who researched the impact of large-scale regime changes in the NAO and PDO. She found that a phase change of more than 2 standard deviations was correlated with daily precipitation. In other words, there may be a hint of a possible significant precipitation event for the Northeast in the GFS ensembles. Given the active southern jet, this adds confidence to the overall idea that February could prove snowier than normal in the East.
One objection might be the SSTAs. However, since 1982 (when the detailed Long Paddock SSTAs are available), in one third of the cases, the NAO averaged negative without the presence of the classic tripole pattern that has been associated with the negative NAO.
Madden-Julian Oscillation (MJO):
The Madden-Julian Oscillation (MJO) is advancing toward Stage 8 and should reach there within 5-7 days. If one examines the typical impacts of the Stage 8 MJO, one finds a general tendency toward a PNA+, NAO- and a trough in the East:
ECMWF Model:
The latest 12z run of the ECMWF is supporting the pattern change idea. It also suggests that ridging could be building into Greenland in a fashion consistent with the evolving MJO.
Snowfall Climatology:
• In 5/6 (83%) of seasons that saw Boston receive 30” or more snow in January, February saw 15” or more fall there. The average was 20.4”. Since regular recordkeeping began in 1891-92, 36/113 (32%) of seasons saw February receive 15” or more snow and the historic average snowfall for February came to 12.7”.
• In 8/15 (53%) of seasons that saw New York City receive 15” or more snow in January, February saw 10” or more fall there. The average was 11.1”. Since regular recordkeeping began in 1869-70, 46/135 (34%) of seasons saw February receive 10” or more snow and the historic average snowfall for February came to 8.5”.
• In 11/42 (26%) of seasons that saw Washington, DC receive 6” or more snow in January, February saw 6” or more fall there. The average was 4.8”. Since regular recordkeeping began in 1888-89, 35/116 (30%) seasons saw 6” or more fall there and the historic average snowfall for February came to 5.5”.
By itself, each piece of evidence makes a reasonable argument for an upcoming pattern change. Taken together, given both the number of factors and the consistency involved confidence in a mid-month pattern change should be strong.
Consistency of Signals:
• Mid-month Pattern Change: ENSO analogs, ECMWF, MJO
• Negative NAO: ENSO analogs, ENSO climatology, MJO, ECMWF, GFS Ensembles (both NAO and AO)
• Above Normal Snowfall: ENSO analogs, ECMWF (split flow, active southern jet), GFS Ensembles (NAO signal), Snowfall Climatology (Boston and NYC)
Overall, I have above average confidence that a mid-month pattern change will occur and that the eastern United States, including the Mid-Atlantic region, will see both colder than normal readings during the February 15-28 period and above normal snowfall for that time. I would estimate that Boston will likely see 15” or more snowfall, NYC 10” or more, and Washington, DC 6” or more.
Finally, there have been some perceptions that the February pattern change that is now highly likely has been “delayed” and “pushed back.” Going back to one of my January 28 posts at another message board, I noted: Relative to normal, the first 10-14 days should probably come in reasonably close to normal with some below normal readings but also some somewhat above normal readings. No extreme cold nor blowtorches appear likely. The second half of February looks to average colder than normal… Interestingly enough, 3 of those cold analogs were suppressed and this points to increasing opportunities for snowfall accumulations in the lower Mid-Atlantic. Overall, things remain on course for February to prove colder than normal and snowier than normal in the Northeast and Mid-Atlantic region.
This summary was based on the ENSO analogs noted above. The point of bringing this up is to note that perceptions notwithstanding, the facts are as follows concerning February (at least from my general idea that was expressed prior to the beginning of the month):
• The early February pause in the cold and snow was supposed to happen. It was not unexpected. To be sure, this stretch is milder than I had envisioned but it is not extreme.
• The idea that the Mid-Atlantic would see its snows was a second-half of February proposition, not something that was supposed to occur in the first 10 days of the month.
• There was no “pushing back” or “delaying” the onset of the pattern change. The timing was well-defined by the ENSO analogs. I know that others shared a similar perspective.
In the end, I believe those in the Mid-Atlantic and Northeast, even in areas that will not receive a flake of snow from the February 10-11 event, should cast aside pessimism and frustration and hang in there. A change to a colder and snowier pattern appears highly likely and the far stronger weight of evidence is in favor of just such a change. Once in place, if the ENSO analogs again hold true, it could be sustained for 2-3 weeks and perhaps a little longer.
As a final note, I intend to verify this at the end of February regardless of whether the outcome is good, bad, or downright ugly.
Great pattern ahead!!!
