December 16-31, 2005: Pattern Thoughts

[Stephanie]

Have a great vacation!

[Margie]

In the last years we've had many wimpy winters, even no snow on the ground at the end of the year, but this year winter came early.

We've already had some weeks of single digit weather, and by the end of the week we'll easily have a foot of snow on the ground, and are headed back to the low temps.

Usually we get a couple very cold days the end of Dec and then about 10 days to two weeks of extreme cold the end of Jan. But since we're already into an early snowy and cold winter, any feedback as to what we'll be seeing come first of the year?

If things keep going at this rate, we'll end up with three or four feet of snow on the ground by the end of Jan, and I haven't seen that since 1994 (or 93? can't remember).

[VoodooCadillac]

Hope Don is having a good vacation and keeping up with his research so he can start a January pattern thread when he returns! His December stuff has been fairly accurate.

[invisible]

Thanks, Don

I think your prediction of the indicies will be right. The weather will be much milder and wetter in the Pacific Northwest for the next two weeks. When the PNA changes its position, the trough will move to the Pacific Northwest to give some colder weather. I think this trough will eventually move to our region in the early or middle of January. The Northwest should be snowy and cold at that period because of the indicies .

[donsutherland1]

Thanks, Stephanie. It was nice to see close friends from University.

[donsutherland1]

Thanks, VoodooCadillac.

[donsutherland1]

Pacific Northwest Verification for 12/16-22:

∙ ...the December 16-17 period could start cool but moderation will likely quickly commence as the PNA builds to strongly positive levels.

December 16 saw the temperature average 9° below normal in Seattle and a low there of 23°F (-5.0°C). December 17 had a mean temperature that was normal for the date.

∙ Per ensemble guidance and the PNA forecast, the 12/20-25 period could be especially warm. Readings could run 4°-8° above normal, especially in interior sections and parts of British Columbia.

December 20-22 were very warm days. In Seattle, the temperature came to 11°, 13°, and 14° above normal respectively. December 22 also saw the mercury reach a record high of 57° in Seattle.

Vancouver also warmed up to record levels. On December 20, the temperature reached 12.3°C (54.1°F), which beat the old record of 11.7°C (53.1°F) set in 1940. Today (12/22), Vancouver had unofficially reached 13°C (55.4°C), which easily surpassed the previous record of 11.3°C (52.3°F) established in 1986.

[vbhoutex]

Welcome back Don. Glad you enjoyed your vacation.

[VoodooCadillac]

Welcome back Hawkeye - of course that's Southerland with an "O." I'm sure you've heard all those jokes before.

[donsutherland1]

Final data on the 12/22 record high in Vancouver:

13.5°C (56.3°F).

[donsutherland1]

Thanks Dave and VoodooCadillac. Yes, I'm certainly familiar with those jokes

[VoodooCadillac]

Hey Don - not nearly as official as you - but I think the weather here in the WNC mountains has been at or below normal (temperature) virtually all of December (since December 4th). Moisture seems to be about normal. A couple of icing episodes (one serious) and a couple of snow flurry days (one enough to make the ground white). I often think of us as "mid-atlantic" since the increased elevation makes our temperatures more like northern Virginia/Maryland/etc. So I've been reading with great interest your mid-atlantic predictions. Thanks.

[donsutherland1]

Some cleaning up and additional thoughts…

Milder weather has moved into the East. At the same time, record-breaking warmth has covered parts of the Pacific Northwest. Yesterday saw record highs of 57° in Seattle and 56° in Vancouver.

Overall, the magnitude and duration of the cold was less than what I had indicated. The most severe outbreak was more temperate than what I had anticipated. Moderation also came earlier than I thought.

In my view, the two big reasons for this were that the PNA never rose as high as I thought it would. Instead, it peaked at +1.614 on December 19. The NAO was slightly positive on 4 of the last 7 days. I had expected a mainly negative NAO though not sharply negative.

In my view, a moderate pattern (with some intervals of cooler than normal weather but also milder than normal weather) likely will prevail through the rest of the month. I don’t believe there will be any severe Arctic outbreaks for the remainder of December. There may be a few days where low temperatures fall into the 20s, particularly in Philadelphia, New York City, Providence, and Boston. At the same time, I don’t expect much above normal readings for any prolonged stretch.

I also believe at least part of the East Coast will see some snowfall in the closing days of the month. New England will likely be the prime candidate for the 12/25-26 system. Another system might spark coastal development off the Delmarva and bring at least the threat of some snow to the northern Mid-Atlantic and New England in the 12/28-29 period. There is ensemble support for both systems. The latter system has the potential to bring 0.50” of precipitation, particularly to eastern New England, according to a significant cluster of ensemble members. The 12/23 6z ensembles have a much larger area of 0.50” than the 0z run.

Looking farther ahead, there are some hints of perhaps an important amplification during the first week in January, with perhaps the middle or latter part being somewhat favored. One will need to watch the guidance over coming days to see if such a prospect has a greater chance of coming to fruition.

Overall monthly prospects for the East are also not all bad. In 10/10 (100%) cases where December saw the Arctic Oscillation average -1.500 or below, the Arctic Oscillation came to < 0 in January. 8/10 (80%) cases saw January average near normal to below normal in terms of temperatures in the East. In 6/7 (86%) cases where the January Arctic Oscillation averaged -0.500 or below, temperatures were normal to below normal. Furthermore, in 6/6 (100%) cases where the NAO averaged < 0 and the AO averaged < 0 in January, the East saw near normal to below normal temperatures.

In the 10 seasons in which the AO averaged -1.500 or below in December, the greatest likelihood of warmth in January was in the Southwestern U.S. There, 7/10 (70%) cases averaged warmer than normal in January and 10/10 (100%) averaged normal to warmer than normal. In the Pacific Northwest 6/10 (60%) cases averaged warmer than normal in January and 7/10 (70%) averaged normal to warmer than normal. In the Ohio Valley, 8/10 (80%) cases were normal to cooler than normal in January.

Given the ENSO anomalies and PDO-, there is a risk of warmth in the East. However, odds are probably much against unrelenting warmth. Rather, warmer periods should be balanced out by colder ones.

Finally, to all, have a great Christmas and Hanukkah. Don’t let the rain wash away one’s fondest memories of winter. Don’t let the warmth melt one’s hopes for snowstorms to come. Just as the joy of these special holidays is renewed year after year, Winter 2005-06’s cold and snow will blossom again. For many, the autumnal snows that preceded the Winter Solstice, will likely prove to have been the appetizer for a much richer feast to follow. In my view, I believe it remains likely that Winter 2005-06 will see 30” or more snowfall in New York City for the 4th consecutive winter, 25” or more seasonal snowfall in Philadelphia and 20” or more seasonal snowfall in Washington, DC.

For now, enjoy the milder break, as it will only make the return of winter’s finest weather feel even more special.


Winter morning in the country (Currier & Ives, c.1873)
Source: Library of Congress

[donsutherland1]

Pac NW: Another Day, More Extreme Warmth:

12/23 Data:

Seattle: High: 55°; Record: 58°, 1950
Vancouver: Unofficial High: 12°C (53.6°F)--New Daily Record; Old record: 11.7°C (53.1°F), 1950

With highs in Seattle likely to reach 57°-60° and 12.8°C-14.4°C (55°F-58°F) in Vancouver tomorrow, records could be challenged or broken. High temperature records for 12/24 are as follows:

Seattle: 57°, 1947
Vancouver: 13.3°C (55.9°F), 1963

[donsutherland1]

Evening thoughts...

This morning, I wrote, "I also believe at least part of the East Coast will see some snowfall in the closing days of the month. New England will likely be the prime candidate for the 12/25-26 system. Another system might spark coastal development off the Delmarva and bring at least the threat of some snow to the northern Mid-Atlantic and New England in the 12/28-29 period. There is ensemble support for both systems. The latter system has the potential to bring 0.50” of precipitation, particularly to eastern New England, according to a significant cluster of ensemble members. The 12/23 6z ensembles have a much larger area of 0.50” than the 0z run."

The 12/25-26 system might better be described as a 12/25-27 system. There is some support for secondary development that would throw some light precipitation back into New England into the morning of 12/27.

In terms of snowfall, while much of the model guidance is warm, interior New England has a reasonable chance at seeing some measurable snowfall. Snow showers could occur in such cities as Providence and Boston and they might leave a small accumulation. The 12/24 0z NAM offers some support for at least a changeover to light snow or flurries (probably < 0.5") at the tail end of the system for Providence, Boston, and Portland.

Unfortunately for the greater New York City area and nearby suburbs, at least in my view, it appears that the moisture would be gone by the atmosphere could support snow.

So, overall, this appears to be a limited event and largely one that would be confined to interior and northern New England as far as snowfall is concerned.

In terms of the latter event, the latest (12/23 12z and 18z) GFS and NCEP ensemble guidance continues to suggest that a strengthening clipper-type system will likely track northeastward after reaching the Virginia Capes/Delmarva to a position east of Cape Cod. The 12/29-30 period appears more likely now. The larger area of 0.50" precipitation that showed up on the 6z ensembles has been retained.

It's really too soon to get into precipitation-type. Suffice it to say that while milder air will be a real concern, there could be sufficient dynamic cooling for at least some accumulating snow. The 12/23 12z ECMWF is particularly promising for the Mid-Atlantic. However, it seems to be an outlier relative to the other guidance (models and ensembles). Nonetheless, let's see if a trend toward that more extreme solution begins to develop.

ECMWF 850 mb temperatures/850 mb RHU/700 mb RHU for 12/30 12z:
Baltimore: -3.3C/100%/88%
Boston: +2.3C/98%/95%
New York City: -0.8C/97%/71%
Philadelphia: -1.2C/100%/68%
Richmond: -3.2C/100%/92%
Washington, DC: DCA: -3.5C/100%/92%; IAD: -4.5C/100%/98%

In the end, the first system will probably offer only very limited snowfall opportunities. The latter one holds greater potential for a more widespread accumulating snowfall, even as warmer air could intrude.

In any case, I do not expect either storm to be a candidate as a "Kocin-Uccellini" snowstorm. Only 1/4 (25%) of such December snowstorms occurred during a negative PDO. In the absence of strong blocking, I just don't see prospects for such a storm to be very encouraging this month. That does not mean that some location cannot see a significant accumulation. It does mean that such accumulations would not be sufficiently widespread in the major population centers of the East Coast so as to merit the storm's fitting the criteria employed by Kocin and Uccellini in highlighting East Coast snowstorms.

[invisible]

I dont understand why the Pacific Northwest will stay warm for the next two weeks with the negative PDO. I think its not normal for our region with that below normal level. Why does this stuff happen ??

The NAO and PNA are netural right now. They create a zonal flow. It often lead to cold spells for the Pac Northwest. I think its a sign that the pattern in the NW will shift before the middle of January.

[donsutherland1]

Invisible,

Had the PDO been positive, perhaps it would have been even warmer. The PDO- has helped keep the PNA from reaching sharply positive levels. Still, at least through the rest of this month and into the first days of January, the PNA will probably remain mostly positive, though not sharply positive.

I believe that the sharply negative Arctic Oscillation (now again < -2.00) helped fight off the PDO-. If the PDO- has weakened in December--and I'll wait for the actual figure on that--could be a critical piece in determining how Winter 2005-06 will evolve.

In terms of the temperatures, the current warmth peaked today. Seattle and Vancouver set record highs yet again.

Seattle: 62°
Vancouver: 14.0°C (57.2°F)--Unofficial

Previous record highs for 12/24:
Seattle: 57°, 1947
Vancouver: 13.3°C (55.9°F), 1963

Through the rest of this month, it appears that the mean trough will remain offshore from Oregon/Washington/British Columbia. At the same time the East will remain under moderate conditions even as the mean trough there retreats to the southeast and shrinks.

There remains a chance of an important pattern amplification during the middle/latter part of the first week in January. Whether or not this would lead to a regime change where the trof goes to the West remains to be seen. The Arctic Oscillation is progged to be going severely negative at that time. Furthermore, in cases where the AO has averaged -1.5 or below in December, which appears ever more likely, one has typically seen a warm January in the Pac NW.

Hopefully, by the middle of next week, I'll have more confidence in how things will evolve through the first half of January.

[donsutherland1]

Verification:

For Texas:

The cold is coming. It appears that based on the pattern with good support on the computer guidance and ensembles, the period after mid-month should turn colder to possibly much colder than normal. That cold could persist toward the Christmas/Hanukkah holidays before it fades.

With an active southern jet, some parts of Texas will probably see some snow and, if the timing is right, even eastern Texas might have a shot at some frozen precipitation but that is not the most likely scenario. Probably the best chance for accumulating snow would be in such cities as Dallas in the December 17-19 timeframe.

12/15-22 Anomalies:

Dallas: -1.8°; last colder than normal day: 12/20; Lowest temperature: 31°, 12/16
Houston: -6.8°; last colder than normal day: 12/22; Lowest temperature: 34°, 12/22

No snow was reported in Dallas.

[Brian_from_bellingham]

This December has been interesting ( tempereature wise, though not snow wise) for the NW. Seattle had about 37 days in a row with below normal temperatures starting in November (a lot of the national guys thought it was much warmer then it actually was, since it was dry, but when it is clear here, it cools off a lot at night, and fog can prevent temps from warming up much). Now we have gone to the other extreme, much warmer and wetter. This is consistent with neutral or slightly negative SST's. These kinds of winters can also feature bigger cold and snow events. This is certainly different then last year.

[VoodooCadillac]

Interesting Brian - much the same can be said for here. Long period (much of December) with below normal temperatures (but nothing extreme). But it's warmed up significantly the last few days. I cycled to elevations above 5000 feet today on the Blue Ridge Parkway - something I wouldn't normally be able to do at this time of the year. But the Parkway is closed (to vehicles) at high elevations due to tree and wind damage from a recent ice storm.

The local weather guys seem to think it's going to stay warm for the foreseeable future. Lots of showers in the forecast as well.

We're getting ready to vacation in Steamboat Springs. They claim (the Resort) to have had more snow in November 2005 than any other November in record. It's still snowing almost everyday. So..........we've seen little snow here, but I'll see lots of snow soon.