The December AO: An Ominous Signal

[donsutherland1]

In the opening post in my December 23-31 thread, I expressed my concern that cooler weather that occurs in that period could be "fairly short-lived with the potential for a dramatic warmup during the first week in January."

If the guidance is right, the Arctic Oscillation is likely to remain predominantly positive to very positive through December after a brief decline.



For December as a whole, that’s not good news. Worse, if that news were not bad enough, there is a strong tendency for the Arctic Oscillation to remain predominantly positive in January following a highly positive figure in December. Through today, the Arctic Oscillation is averaging +2.360. If that average were to be maintained, it would be the highest December figure on record.

The 10 highest figures on record are:

Code: Select all

1951   1.987
1988   1.679
1992   1.627
1991   1.613
1998   1.353
1979   1.295
1975   1.290
1990   1.277
1972   1.238
1999   1.043


In 9/10 (90%) of the cases in which the Arctic Oscillation averaged +1.000 or above in December, January's figure was also > 0. The lone exception occurred in Winter 1979-80.

The outcomes in terms of composite temperature anomalies for the East are ugly.

December:


January:


This outcomes would be quite consistent with what Joe Lundberg talked about in his column earlier today, specifically that the Euro monthly forecast for January was warm.

In terms of snowfall, such winters proved generally less snowy than average across much of the East. Median seasonal snowfall for select cities:

Boston: 23.5"
Buffalo: 80.7"
Burlington: 77.6"
Chicago: 39.6"
New York City: 14.6"
Philadelphia: 15.4"
Pittsburgh: 30.5"
Washington, DC (DCA): 9.2"

How December fares in terms of snowfall could provide a crucial indication as to how snowfall in the East will fare. Back in November, I provided the following select data:

Boston:
The indicators of below to much below normal seasonal snowfall following a November in which the mean temperature was 47° or above (November 2006: 49.1°) were:
∙ December snowfall of 5" or less
∙ December mean temperature of 36° or above

In such cases when December snowfall came to 5” or less, the mean seasonal snowfall was 17.9”. The most was 24.9”. In such cases when the mean December temperature came to 36° or above, the mean seasonal snowfall amounted to 20.9”. The most was 32.7”.

Current December snowfall: 0.4”

Mean December snowfall for the sample of strongly positive Arctic Oscillation years came to 5.4”. Moreover, 6/10 (60%) of those seasons had 5” or less snowfall in December. Through 12/15, December 2006 has a mean temperature of 41.7° in Boston. For Boston to finish with a mean temperature of < 36°, it would need to have a mean temperature of 30.6° for the remaining 16 days of the month. Model guidance suggests that this is not likely.

New York City:
The indicators of below to much below normal seasonal snowfall following a November with a mean temperature of 49.0° or above (November 2006: 51.9°) was less than 3” snowfall in December. In those seasons, the mean seasonal snowfall came to 13.1”. The median figure was 12.5”. The most was 30.6”.

Current December snowfall: None

Mean December snowfall for the sample of strongly positive Arctic Oscillation years came to 2.0”. Moreover, 7/10 (70%) of those seasons had less than 3” snowfall in December.

Washington, DC (DCA):
Indicators of below to much below normal seasonal snowfall following a November with a mean temperature of 48.0° to 52.0° (November 2006: 50.7°) were those in which December snowfall came to less than 6”. In those seasons, the mean seasonal snowfall came to 13.8”. The median figure was 13.0”. The most was 31.4”.

Current December snowfall: Trace

Mean December snowfall for the sample of strongly positive Arctic Oscillation years came to 1.1”. Moreover, 10/10 (100%) of those seasons had less than 6” snowfall in December.

The bottom line is that the December 23-31 pattern, which should provide cooler conditions in the East will need to see storminess coincide with the presence of sufficiently cold air to generate snow. There is still a realistic possibility that each of these cities might be able to receive enough snowfall to avoid falling into the very low snowfall category. Nonetheless, the risk of a very low snowfall winter is of growing concern.

For now, the idea of a return of meaningful blocking episodes as indicated by the historic experience with long-duration NAO+ regimes that began at the time the current one commenced, leaves the door open for colder weather especially later in January and February. Historic experience with El Niño events also lends some support to that idea. Therefore, I’m not yet ready to write off the idea of at least average snowfall, but I do believe December’s figures will be indicative of how things will turn out.

If, by some chance, that unhappy outcome of little or no December snowfall occurs and the Arctic Oscillation comes out with a stratospherically positive average for December, perhaps snow geese can urge their cities’ and towns’ governments to follow Lepe Spain's cue per a December 15, 2006 Associated Press report. Excerpts follow:

The last time it snowed in the sun-baked town of Lepe in southern Spain was in 1954. Now the stuff is falling every day — promptly at 8 p.m., for exactly 15 minutes — thanks to a mayor keen on concocting a white Christmas.

A pair of cannons blasting frozen precipitate over the town square have proven such a hit in Lepe — a town of 22,000 better known for its beaches and lush crops of strawberries — that human and traffic gridlock ensue every evening when it is time to snow.

"More than anything we are doing it for the younger people, who have never seen snow," Mayor Manuel Andres Gonzalez said last week, according to the newspaper El Pais.

[Yankeegirl]

Hi there... Just a quick question.. I am going to RI at the end of January, hopefully to see some snow, what are your thoughts on that... Ya think it might snow by then?

[donsutherland1]

Yankeegirl,

If Winter 2006-07 is similar to a number of moderate El Niño winters, the late January-February timeframe will probably offer a growing risk of snowfalls. Enjoy your trip to RI.

[jasons2k]

Hey Don,

Excellent analysis. Thanks!

[Brent]

Ugh... I don't like that. Oh well.

[JonathanBelles]

not to make any work but can you do a forecast for miami as you do fro NYC and Boston.

[Stephanie]

I don't think that "artificial snow" is in the city's budgets.

Well, we'll just have to enjoy it. However, when the first day of Spring arrives, I don't want any snow falling afterwards!

[MGC]

Well, if you like warmer than average weather in the East this is good news. I know a few folks who like it cold but I'll take the warmth any day. Another outstanding analysis Don!.......MGC

[sphinx]

In Don's last post he indicated that this mid-December warm spell would have people predicting a year without a winter.

...

I just didn't expect one of those people to be Don.

Sigh ... At least he does hold out some hope!

[Dean4Storms]

This is good news in that with less cold and snow we could see gas prices drop significantly after the Christmas rush as oil supplies become less tapped for heating.

[donsutherland1]

Fact789,

The NYC, DCA, and BOS data in this thread concerned snowfall. If the data from the Arctic Oscillation is representative, January could wind up warmer than normal in the Miami area.

[donsutherland1]

Sphinx,

I also added, "For now, the idea of a return of meaningful blocking episodes as indicated by the historic experience with long-duration NAO+ regimes that began at the time the current one commenced, leaves the door open for colder weather especially later in January and February. Historic experience with El Niño events also lends some support to that idea. Therefore, I’m not yet ready to write off the idea of at least average snowfall..."

FWIW, the GSM is cooler than it was in last week's run with respect to January.

[bob rulz]

I like that forecast. They put it colder than normal in the West, if history is anything to go by.

[Stephanie]

In Don's last post he indicated that this mid-December warm spell would have people predicting a year without a winter.

...

I just didn't expect one of those people to be Don.

Sigh ... At least he does hold out some hope!

There definately will be those that will predict "no winter" - but it will only be those that don't know how to read trends and weather maps. We're fortunate to have people like don, derek, etc. to shed a light on what the atmosphere is REALLY telling us.

[jinftl]

just to make sure i understand correctly, in the context used here, ominous = lack of severe arctic cold or harsh winter weather?

[Stephanie]

just to make sure i understand correctly, in the context used here, ominous = lack of severe arctic cold or harsh winter weather?

Lack of severe arctic cold/snow for the Eastern CONUS. For snow buffs it's an ominous sign.

I love the change of seasons and a good snow storm or two. However, winters like these that tend to take it's good old time in becoming winter can be frustrating. I love the warm weather, but I would just as well have it be spring.

[donsutherland1]

Just to clear up some points:

1) I'm not yet writing off winter as a whole. I'm arguing that some patience might be required. However, I do want to alert people that there is a possibility for below to much below normal snowfall in some areas. I'm not arguing that it will occur, but there are some signals toward that end.

2) If I see big changes, I'll certainly post about it, as I have in the past. FWIW, I most definitely prefer winter weather, especially with respect to snowfall.

3) There are some indications that the "perpetual" positive Arctic Oscillation (AO+) regime of 2006 will be eroding toward the end of the month i.e., 10 mb stratospheric warming shown on the ECMWF (and an area that has been progressing across the north Pacific) and model forecasts for the votex to become less vertically-stacked over time. As it is stretched out, it will become less intense. Add the stratospheric warming to the mix, and the seeds are being planted for a change, though that change is still down the road.

4) Given historic experience, this AO+ event will likely linger until the January 10-20, 2007 timeframe. However, the super-long duration events have typically seen above average blocking (NAO-) in the 30-day period following their demise.

5) Such a return of blocking and the timing of a shift toward what might be a colder pattern would be consistent with a number of El Niño winters that saw their coldest period anywhere from later in January through February.

6) There will be potential for severe cold. There is currently a large area of colder-than-normal readings centered near the North Pole. Once the blocking develops, one will have to watch for at least an outbreak given the magnitude of the cold that is building. Whether it directs its icy breath to Asia, North America, or Europe remains to be seen. But somewhere, beach beauties will again be transformed into ice beauties. Moreover, given ENSO climatology and historic experience following the demise of very long duration AO+ regimes, I believe North America will see at least one severe Arctic outbreak once the tyranny of the positive AO falls.

All said, the ugly duckling (has anyone seen the latest ensemble guidance for the AO? It can be found here: http://www.cpc.ncep.noaa.gov/products/p ... .sprd2.gif) may still turn into a beautiful swan (blocky pattern) but that transformation will require some time. For now, the Empire of the Positive AO rules with an iron fist--perhaps as never before on record in December (a monthly record is possible given the current figure and ensemble forecast)--and all cross-polar flow has been shut down.

[ohiostorm]

I know that I would take this 65 degree stuff everyday this winter if thats what Moterh Nature wants us to have here in Ohio! I could do without some snow. Maybe a bit for Xmas but I dont see that happening.

[Ptarmigan]

Interesting. Here's what I have noticed for extreme cold weather in Houston and AOI index.

January 1973=1.232
February 1973=0.786
December 1983=0.186
February 1989=3.279
December 1989=-0.644

AO Index 1950-2006

[donsutherland1]

At last word, the Arctic Oscillation (AO) remains at a towering +1.898. Moreover, the seemingly perpetual AO+ regime is forecast to hold through the rest of this month, which would be consistent with the experience concerning super long-duration AO+ regimes that commenced in the fall. Yesterday, the GFS ensembles hinted at a brief negative period in coming days. Today, in Scrooge-like fashion, the GFS ensembles have returned to their former idea of a positive AO through the remainder of this month. To add insult to injury, the NAO is forecast to rise and the PNA to fall.

All said, the wait for sustained winter weather will go on, even as some cool shots tease the East from time to time and modeled solutions flirt with the desires of snow geese. However, given the historic experience, modeled "stretching" of the polar vortex, and warming that continues to build and spread northeastward from the north Pacific, I expect the AO+ regime to end in the New Year, probably in the January 10-20, 2007 timeframe. Afterward opportunities for colder weather and snow will probably grow more likely.

In the meantime, December is increasingly likely to pass with little meaningful snow in the major cities of the East Coast. However, there have been past situations where the October-December period saw little or no snow, yet ample snow followed afterward.

Baltimore:
1885-86: Snowfall through December: 0.0”; Seasonal snowfall: 30.3”
1891-92: Snowfall through December: Trace; Seasonal snowfall: 44.3”
1906-07: Snowfall through December: 0.2”; Seasonal snowfall: 31.1”
1934-35: Snowfall through December: 0.1”; Seasonal snowfall: 29.2”
1986-87: Snowfall through December: 0.1”; Seasonal snowfall: 35.2”

Boston:
1891-92: Snowfall through December: Trace; Seasonal snowfall: 46.8”
1957-58: Snowfall through December: 0.1”; Seasonal snowfall: 44.7”

New York City:
1874-75: Snowfall through December: 0.1”; Seasonal snowfall: 47.9”
1891-92: Snowfall through December: 0.0”; Seasonal snowfall: 25.4”
1895-96: Snowfall through December: 0.3”; Seasonal snowfall: 46.3”
1913-14: Snowfall through December: 0.3”; Seasonal snowfall: 40.5”

Washington, DC:
1906-07: Snowfall through December: 0.5”; Seasonal snowfall: 28.3”
1913-14: Snowfall through December: Trace; Seasonal snowfall: 28.6”
1965-66: Snowfall through December: 0.2”; Seasonal snowfall: 28.4”
1986-87: Snowfall through December: Trace; Seasonal snowfall: 31.1”

So there is still reason for the snow geese to hang onto their belief that, in time, the snow will return. However, there is also historic precedent to inspire the rapidly growing ranks of the “Warministas” who are basking in the season’s seemingly unrelenting mild breezes.

From Winter 1750-51:
Rev. Thomas Smith of Portland, Maine wrote:

January 15, 1751: “The frost is entirely out of the ground; weather like May.”

February: This month has been more like spring than winter, moderate generally, and several days as warm as May. The winter ends a wonder through the whole.”

From Winter 1753-54:
In February, John Adams wrote, “This winter, we had a vacation. In the winter of 1754 we had no snow at all save a smattering or two, but perpetual rains and warm weather thro’ought the whole.”

In March, he added, “Had a small flurry of snow.”

From Winter 1827-28:
The following was reported from Norfolk, Virginia:

On the 5th, 6th and 7th of January the weather was so very warm, that the doors and windows of dwelling houses were thrown open to court the passing breeze, and parties were seen promenading the street by moonlight as in summer. Vegetation has of course, felt the genial influence of this delightful temperature of the atmosphere. Asparagus of mature growth—Hyacinths in bloom—apples and figs in a forward state—Trees and shrubs budding… To conclude, our oldest inhabitants aver that they have never known so warm a winter.