December 26, 2004-January 7, 2005 Pattern Discussion

[donsutherland1]

Last week’s discussion raised a number of issues of what one might expect for the December 20-31 period. Before I get to those issues, there were a number of busts that were packed just in time for the Christmas holiday.

From two weeks ago, I had noted that I did not expect the mercury to reach 59° in New York City for the rest of December. At 11:38 am on December 23, the temperature did reach 59° in Central Park.

The second bust is a bigger one and it has had some ramifications for what lies ahead in the near-term. I had anticipated for several weeks that the NAO would go negative at least for a period of time starting around December 22 +/- 3 days. The NAO trended downward but never reached negative levels. Since then, it has begun to ascend.

As a result, coming shots of cold for the period covered (December 26-January 7) will probably not be as harsh as the outbreak that sent temperatures into the low teens from New York City southward and 6° in Boston (December 20 and 21).

As a result, the point that was made two weeks ago and again last week about the mean temperatures for the December 13-31 period may well have difficulty verifying. Without a negative NAO locking in the trough, the cold simply won’t be as sustained or even as severe as might otherwise have been the case. For reference, the point was as follows: “I believe that temperatures across a large part of the East should be running 3°-5° or more below normal on a regular basis this week onward, albeit with some modest warmups.”

For the 12/13-12/23 period, the following temperature anomalies have been recorded:

Boston: -1.8°
New York City: -1.5°
Washington, DC: -2.6°

Among the following additional points were made last week:

• I believe things still look good for December to end with all the major cities from Washington, DC to Boston having picked up at least some accumulation of snow and likely having seen the lowest minimum temperature in at least the upper teens.

In terms of lowest temperatures, this idea verified. The depth of the cold proved more substantial than the minimum criteria set forth. Lowest temperatures included:

Boston: 6° (December 20, 21)
New York City: 11° (December 20)
Philadelphia: 10° (December 20)
Washington, DC: 11° (December 20)

Snow accumulations were minimal to modest. They were as follows:
Boston: 0.6”
New York City: 0.6”
Philadelphia: 0.1”
Washington, DC: 0.1”

• the rest of the month will feature no prolonged sieges of bitter cold air, though there should be periodic pushes of cold-to-very cold air. As the month nears an end, assuming that the PNA goes negative, there is some danger that ridging might begin to retrograde toward the East.

Right now, this idea continues to look good with some modifications. There will be at least another shot of cold air later this weekend into the first part of next week, but it won’t rival the magnitude of the air mass that sent temperatures to their coldest levels of the season so far. In addition, moderation should occur as the month draws to a close.

• I’d have to argue that odds lean against any major or historic East Coast snowstorm this month… In fact, I am confident that there will be additional accumulations of snow after the upcoming event (12/19-20) and cities from Washington, DC through Boston should see additional accumulations.

There’s no question about this now. The only area that stands a chance at picking up perhaps a moderate or significant snowfall is easternmost New England as a clipper and offshore low attempt to phase this weekend. Downeast Maine and Cape Cod probably have the greatest possibilities of seeing at least an appreciable snowfall, but it is not out of the question that at least some snow backs into Boston, Providence, and even eastern Connecticut.

• In the Deep South, I believe opportunities remain for at least the threat of snow. Best prospects for that, in my view, lie across northern Alabama, northern Georgia, and northern Mississippi.

This threat has materialized to some extent and even southeast Texas, parts of Louisiana, and the Florida Panhandle have some chance at seeing minor snow or mixed precipitation today and tonight.

• there is increasing data that suggests that the PNA could turn negative beginning later this week and the Arctic Oscillation should remain generally positive for the remainder of this month.

The PNA turned negative on December 20 and continues to plunge. The ensembles continue to take it to near the bottom of the charts by early next week. Afterward, there is much uncertainty as to whether how negative it will hold for the remainder of the month and first days of January.

The Arctic Oscillation is strongly positive and there is strong ensemble support that it will remain that way through the end of December.

• The warmth in the West should peak this week [December 19-25] and then likely begin to fade.

Temperature anomalies for December 19-23 include:

Los Angeles (Downtown): +1.6°
Portland: +1.8°
Seattle: Normal

With the PNA continuing to plunge and the latest model guidance, next week looks to be colder than the one that is now concluding.

At this point in time, one has seen the above normal to much above normal height anomalies over the Atlantic hold nearly stationary in the means over the past week. The trough that had blasted into the East beginning just after mid-month split with one piece over the Deep South (which is rewarding parts of that area with wintry weather) and another beginning a trek westward. The above normal height anomalies in the Gulf of Alaska has also retreated somewhat to the west.

However, the SOI has now crashed and stood at –30.80 on December 24. This suggests that the period of retrogression could be nearing its end. If so, look for the trough to back up to the Rockies before perhaps beginning to migrate eastward. What happens out in the Atlantic is still highly uncertain.

Right now, I believe the following assumptions are reasonable:

• The PNA tanks as shown on the ensembles and then after the New Year begins a slow but steady recovery. It probably won’t go positive until the latter part of the first week in January at the earliest.

• The NAO will hold at positive levels through the entire December 26-January 7 period.

• Retrogression ends and a more progressive pattern could begin to establish itself.

• ENSO remains fairly constant.

As a result, it would not be surprising if the middle of next week through the middle of the first week in January sees the East warm up with readings perhaps running somewhat above normal for that timeframe (approximately December 30-January 5). Afterward, readings could begin to cool. During the warmest period, it is possible that DCA-NYC and perhaps Boston might see one or two 50° or warmer days.

No significant snowfall is likely during this time across the East. Only eastern New England has a chance at seeing an appreciable/significant snowfall from the aforementioned situation where a clipper might attempt to phase with an offshore low.

The Pacific Northwest could see readings run below normal with perhaps the opportunity for at least a little snow. I believe the greatest opportunity for a big snowfall lies to the east of this region with perhaps the Rocky Mountain states seeing a significant snowfall at some point next week. Readings in the Pacific Northwest should begin to moderate after the New Year.

Southeast Texas will likely see above normal rainfall through at least the first week of January.

For the longer-range, the latest weekly ENSO regional profile (Regions 1+2, 3, 3.4, and 4) is most similar those of 1968, 1977, 1979, 1986, and 2003. Three of those winters ultimately proved memorable in much of the northern Mid-Atlantic and Northeast: 1968-69, 1977-78, and 2003-04. All saw either a major Mid-Atlantic or New England snowstorm.

Average snowfall for select cities came to:

Boston: 46.7”
New York City: 31.9”
Philadelphia: 28.6”
Washington, DC: 19.1”

With the exception of December 2003, which featured a significant northern Mid-Atlantic and New England snowstorm, December snowfall amounts in these cities were modest.

Consequently, even as December snowfall has proved disappointing in this region, it is far too soon for one to write off the snowfall prospects there for Winter 2004-05.

[sertorius]

donsutherland1:

Thanks so much again for the info!! The last week of December will be quite warm here in the Central Plains and looks like we could even see some big storms by Friday as a low tracks thru the Dakotas-a very spring like track. But, and this is where I wonder: if I am correct, and I'm prob. not-Latin teachers rarely are, the PNA will begin to rise from the minus 3 range beginning next week-this I think corresponds to the models solutions of this area heading back to seasonal norms by the 3rd or 4th of jan. and possibly a more active pattern. From what little research I've done, it seems that the PNA must be between 1 and neg. 1 for us to get winter weather. I do think we will have at least 5-8 days of hard winter weather this month in this area-for my area, that is really all you can expect as we are def. not a winter wonder land in Lawrence, Kansas-we only average 17 inches of snow with our coldest temp. at 39!!! Thanks again-I really appreciate your posts and have learned alot from them. Happy holidays to you!!

PS: My kids are already in bed and I have all the presents done just so you don't think I'm neglecting my family Some weather in the gulf coast huh!!???

[Dave C]

The forecasters here have mentioned an unusual trough setting up over eastern New England Sunday with localized heavy snowfall. We also will have some ocean enhancement and the clipper system swinging through. Cape Cod up through Boston and coastal NH and Maine are in line for heaviest amounts...... Here's our latest NWS discussion
http://www.erh.noaa.gov/box/fcsts/BOSAFDBOX.html

[donsutherland1]

On Friday, I noted: The only area that stands a chance at picking up perhaps a moderate or significant snowfall is easternmost New England as a clipper and offshore low attempt to phase this weekend. Downeast Maine and Cape Cod probably have the greatest possibilities of seeing at least an appreciable snowfall, but it is not out of the question that at least some snow backs into Boston, Providence, and even eastern Connecticut.

Happily, there have been some changes whereby even the Boston and Providence areas should see an appreciable and maybe significant snowfall. Overall, the models have trended where the qpf has been increased over the past few days.

However, for those in New York City and Philadelphia, one probably won't expect much more than a light snowfall.

My estimated accumulations are as follows:

Boston: 3"-6" locally 8"
Bridgeport: 1"-2"
Cape Cod: 4"-8" locally 10"
Montauk Point: 2"-5"
Nantucket: 4"-8" locally 10"
New Haven: 2"-4"
New York City: Around 1"
Newark: Coating to 1"
Philadelphia: Coating to 1"
Providence: 3"-6"
White Plains: Around 1"

[donsutherland1]

There is now good model support for the idea of a warmup in the East. As noted previously, "[I]t would not be surprising if the middle of next week through the middle of the first week in January sees the East warm up with readings perhaps running somewhat above normal for that timeframe (approximately December 30-January 5)... During the warmest period, it is possible that DCA-NYC and perhaps Boston might see one or two 50° or warmer days."

The 12/26 0z run of the ECMWF suggests that such a scenario is quite realistic. The following are the projected 850 mb temperatures (°C) for 1/1 0z and 1/2 0z on that run:

Code: Select all

City   1/1 0z   1/2 0z
BOS    2.5     -0.6
DCA    6.9      7.4
NYC    4.9      4.1
PHL    6.3      6.6
PVD    3.2      1.1
RIC    8.5      8.1


Key:
BOS: Boston
DCA: Washington, DC
NYC: New York City
PHL: Philadelphia
PVD: Providence
RIC: Richmond

At this point in time, these figures just through 1/2 0z suggest a high temperature of at or above 50° looks realistic at least from NYC and south. Moreover, this is just for the early part of the period highlighted for possible above normal readings, so one cannot rule out a 50° or above high even to Boston before the milder pattern begins to break down.

[Stephanie]

We are forecasted to be in the 50's by the end of the week.

[Chris the Weather Man]

Reminds me of Last year... Got so warm last week of Dec and into the 6th of Jan.... Then....... Winter came with a huge punch....

[wxguy25]

Don, Great work as always.

I did some research on the NAO cycle to see what if any correlation exists between the DEC NAO value and that of the JAN-MAR period. The condition was that I ONLY looked at El Nino winters (regardless of the intensity of the EN event)

In the EL NINO years where the NAO averaged positive in DEC (shown in the dataset below) there was only ONE WINTER (1972-73) which saw a +NAO throughout on a monthly scale. The rest all had at least one or more months which saw a –NAO develop. 1957-58 was the extreme of what it could get to. The MAR NAO in 1958 was -3.1!!!

Even 1982-83 (the powerful EL NINO year) had a –NAO in FEB, and the 1991-92 winter had a
–NAO in JAN.

it is the three years which had a –NAO in ALL THREE of the following months which saw the best conditions in the east AFTER DEC. those years were 1957-58 (FEB blizzard in NYC, end of the winter storm MAR 1958 – over 20” from MD into PA) , and 1965-66 (the Blizzard of JAN 30-31 1966 which developed as the PV split in response to the retrograding block, one piece became the 50-50 low and the other dropped over the lakes and phased w/ some STJ energy creating the major event)

1957 1.2 -0.1 -1.8 0.7 -0.9 -1.2 -1.5 -0.4 -1.7 1.9 -0.4 0.3
1958 -0.7 -1.7 -3.1 0.6 -0.7 -2.0 -1.5 -1.8 0.3 0.4 0.6 -0.6
1965 0.0 -1.2 -1.4 0.9 -0.9 1.1 -1.5 -0.5 0.2 0.5 -2.3 1.1
1966 -1.3 -1.2 0.0 -0.7 0.5 1.3 -0.1 -1.5 -0.8 -0.8 0.1 1.1
1972 0.1 -0.1 0.1 -0.2 0.3 1.3 0.6 0.9 -0.2 1.0 0.0 0.6
1973 0.1 1.7 0.5 -1.3 -0.1 0.4 0.1 0.7 -0.2 -0.6 -1.2 0.4
1982 -0.7 0.1 0.8 0.3 0.2 -1.6 1.0 -0.1 1.0 -0.5 1.4 1.7
1983 0.9 -0.5 -0.1 -1.4 -0.8 1.3 0.9 1.7 -0.2 0.6 -1.3 0.3
1986 1.6 -1.0 2.3 -0.6 0.5 0.6 -0.2 -1.2 -1.2 2.3 1.6 0.7
1987 -0.8 -0.8 -0.4 1.3 0.8 -1.9 0.3 -1.3 -0.3 0.3 0.5 -1.4
1991 0.5 1.2 -0.6 0.6 1.7 -0.7 0.1 1.7 0.0 -0.1 0.7 0.2
1992 -0.4 0.6 0.8 0.4 2.6 -0.3 0.8 0.1 0.3 -1.5 0.9 0.3

Now this correlation while impressive is only going to be relevant IF the Atlantic SSTA profile changes. Currently we have warm water in the central ATL feeding the ridge, so you get the enhanced Atlantic jet and stronger Icelandic low (+NAO).

In order for the NAO to go negative we MUST see the warm pool disperse and weaken (which it has been doing somewhat--probably in response to the North Atlantic jet blasting across) and an SSTA tripole to develop w/ a warm North Atlantic and warm subtropical Atlantic (which we have already), w/ the cool pool in the center.

Looking at the MEAN SSTA across the north Atlantic for Decembers w/ a –NAO the aforecited SSTA tripole is clearly evident.

http://wxguy.storm2k.org/nao_ssta.JPG

IMO assuming that the SSTA reversal takes place, I see NO reason why (given the correlations between El Nino years and the JAN-MAR NAO) the NAO would NOT average negative for the JAN –MAR period (or perhaps JUST FEB and MAR given the fact that the NAO will be positive for at least the first two weeks of JAN based on the looks of the ECMWF for the past several runs and the GFS ensembles—it should go negative in the JAN 15-20 timeframe through).

In the meantime w/ a +NAO and RNA pattern setting in, I cannot deny that the potential exists for a MAJOR Midwest snowstorm. How big and where will come w/ time but w/ that trough centered near 120W the storm track is from the SW (California/northern BAJA Mexico) to the western lakes problems for Des Moines, MSP, and Omaha? I think so.

[wxguy25]

Another thing lending credence to my ideas regarding a Midwest snowstorm is the EPO trending negative. The D 10 ECMWF says that the jet undercuts the omega ridge that develops out near 150 W and results in MASSIVE cutoff high/rex block formation over the N PAC.

Bear in mind the OP GFS, ECMWF, ensembles and virtually all of the modeling indicates this developing.

The GFS ensembles actually retrograde the feature toward the Bering Strait and Kamchatka peninsula which takes it OIUT of the –EPO position and into a –WPO position however the result is basically the same.

Thusly the block develops near 150 W forcing the trough down at 120-130 W (along or just inland from the west coast). Here is where the problem develops though WRT to the mean storm track as long as the block is present. IF the NAO was negative I would be concerned about a MILLER B situation developing since an s/w ejecting out of that region would NOT be able to go into the lakes and instead be forced to cut eastward, but since it is not, and we will have MEAN SE ridge development w/ NO block or 50-50 – a s/w ejecting out of the SW US would probably be allowed to run into the WRN lakes unabated. This is the reason why I believe the Midwest (further west of the areas which just received the heavy snow in OH, IL, KY) may be in the running for a MAJOR snowstorm in this pattern.

[BL03]

Great post and research wxguy!

Things have been a little different than planed with a +NAO thru DEC and 2 significant storms missing the urban I-95 (except BOS) and a big OV snowstorm.........I thought the PHL-BOS area would get a nice snowstorm during X-MAS DEC 23-26 this from 2 months ago but it just missed......The reason is I thought there would be a nice -NAO this week but that of course that never happened. Most if not all Kocin SECS, MECS storms for the I-95 PHL-NYC area happen during a period of -NAO before the storm.......that doesn't mean it can't happen in a +avg NA0 but that there has to be a period of -NAO before the storm..........I was impressed at the facts in the PK book about this..........

Of the 30 significant snowstorm cases, 22 occured during periods when the NAO was clearly in its negative phase. FIVE cases occured during periods when the NAO was clearly positive. Of these 22, cases 10 occured during a period when the negative phase of the NAO was weakening or becoming positive, similar to the signals shown for the three examples during January 2000, December 2000, and March 2001..............Of 30 near-miss cases 16 happen during -NAO.........only 9 during positive!

During the very mild 1999/2000, both Jan and Feb exhibited a positive value of the NAO. However, when the daily NAO records are applied, it becomes clear that the period between 12 and 29 Jan was characterized by the negative phase of the NAO During this period, cold weather and significant snow affected the EUS, including a major snowstorm on 24-25 Jan
Some -NAO's to weak -NAO or towards pos...........
FEB 2003, JAN 2000, DEC 2000, MAR 93, JAN 87

The +NAO's in the near-miss cases most likely helped them be near misses. So like you have said WE MUST get the SST's to ones that support a -NAO which it has not done! They look better than they have in the past few months and hopefully we can get going by Mid Jan and Feb at latest.........If we saw a -NAO and a favorable Pac SST then the 2 miss storms would of been much closer calls! Folks dont lose hope......because I am not.......ITS NOT 2001-2002........we got the STJ (EL nino).....got cold in CAN.......but NO -NAO and inversed Pac SST's mean a lot and people in the NE are feeling it like me! I have a feeling FEB will be my month........its the best month anyways.......

[wxguy25]

Great post and research wxguy!

Things have been a little different than planed with a +NAO thru DEC and 2 significant storms missing the urban I-95 (except BOS) and a big OV snowstorm.........I thought the PHL-BOS area would get a nice snowstorm during X-MAS DEC 23-26 this from 2 months ago but it just missed......The reason is I thought there would be a nice -NAO this week but that of course that never happened. Most if not all Kocin SECS, MECS storms for the I-95 PHL-NYC area happen during a period of -NAO before the storm.......that doesn't mean it can't happen in a +avg NA0 but that there has to be a period of -NAO before the storm..........I was impressed at the facts in the PK book about this..........

Of the 30 significant snowstorm cases, 22 occured during periods when the NAO was clearly in its negative phase. FIVE cases occured during periods when the NAO was clearly positive. Of these 22, cases 10 occured during a period when the negative phase of the NAO was weakening or becoming positive, similar to the signals shown for the three examples during January 2000, December 2000, and March 2001..............Of 30 near-miss cases 16 happen during -NAO.........only 9 during positive!

During the very mild 1999/2000, both Jan and Feb exhibited a positive value of the NAO. However, when the daily NAO records are applied, it becomes clear that the period between 12 and 29 Jan was characterized by the negative phase of the NAO During this period, cold weather and significant snow affected the EUS, including a major snowstorm on 24-25 Jan
Some -NAO's to weak -NAO or towards pos...........
FEB 2003, JAN 2000, DEC 2000, MAR 93, JAN 87

The +NAO's in the near-miss cases most likely helped them be near misses. So like you have said WE MUST get the SST's to ones that support a -NAO which it has not done! They look better than they have in the past few months and hopefully we can get going by Mid Jan and Feb at latest.........If we saw a -NAO and a favorable Pac SST then the 2 miss storms would of been much closer calls! Folks dont lose hope......because I am not.......ITS NOT 2001-2002........we got the STJ (EL nino).....got cold in CAN.......but NO -NAO and inversed Pac SST's mean a lot and people in the NE are feeling it like me! I have a feeling FEB will be my month........its the best month anyways.......

Well the PAC signal is not that bad or at least NOT as bad as it was in OCT. We’ve got the warm pool near/east of 150 W and cold pool to the west of it which is a SIGNIFICANT dipole favoring a Western ridge and Aleutian low, but the problem is that its NOT as strong as 2002-03 or 1986-87 (and 1993-94). It does favor a weak +PNA in the means but MAY favor more of a –EPO as I just discussed until the warm pool Is CLEARLY up against the western coast of North America like NOV-DEC 2002.

WRT the NAO we just need to get a littlie more separation in the SSTA pools—once we have that expect the NAO to go negative.

BTW the –NAO during JAN 2000 was NOT a classic –NAO WRT the position of the positive height anomaly. It was displaced east near Ireland and England which still technically qualifies as a –NAO but like I said it’s NOT the classic blocking position and there was NO 50-50 low.

The three factors which are MOST important to major east coast snowstorm are

1 the phase of the NAO

2 50-50 low (is there one or not?)

3 PV position and intensity (is it strong?, displaced to the south?, weak and diffuse, in climo position and intensity?)

These are all factors you have to consider and questions you must ask yourself when forecasting a major east coast snowstorm or anticipating ones development.

[Wnghs2007]

Not to sound stupid or anything but what does WRT mean. Just wondering. Thanks Wxguy25 .

Also could you list a site where I can find current SSTA's, I have not been able to find any. And they would be really helpful.

[BL03]

Not to sound stupid or anything but what does WRT mean. Just wondering. Thanks Wxguy25 .

Also could you list a site where I can find current SSTA's, I have not been able to find any. And they would be really helpful.

https://www.fnmoc.navy.mil/PUBLIC/

With Respect To.........I believe

[wxguy25]

Not to sound stupid or anything but what does WRT mean. Just wondering. Thanks Wxguy25 .

Also could you list a site where I can find current SSTA's, I have not been able to find any. And they would be really helpful.

With Respect To.........I believe

Yep.

[Wnghs2007]

Not to sound stupid or anything but what does WRT mean. Just wondering. Thanks Wxguy25 .

Also could you list a site where I can find current SSTA's, I have not been able to find any. And they would be really helpful.

https://www.fnmoc.navy.mil/PUBLIC/

With Respect To.........I believe

Thanks

[Wnghs2007]

Heres a little photobucket i made of what I thought I heard wxguy25 say. LOL...




Is that right wxguy25? Does the area in Blue have to get cooler?

[Anonymous]

Excellent discussion, Don.

[wxguy25]

Heres a little photobucket i made of what I thought I heard wxguy25 say. LOL...




Is that right wxguy25? Does the area in Blue have to get cooler?

Close enough. Here is what a GREAT SSTA set-up looks like (from DEC 2002) I have highlighted specific features which are Important.

http://www.wxguy.storm2k.org/2002_ssta.JPG

[donsutherland1]

Great research, Wxguy25.


It will be interesting to see how the NAO unfolds later in January and February. At this point in time, I'm not yet ready to give up the idea that the NAO will flip to predominantly negative at some time in January and remain predominantly negative in February and perhaps March.

[wxguy25]

Great research, Wxguy25.


It will be interesting to see how the NAO unfolds later in January and February. At this point in time, I'm not yet ready to give up the idea that the NAO will flip to predominantly negative at some time in January and remain predominantly negative in February and perhaps March.

Thanks. I'm expecting the NAO to turn negative in the JAN 20-25 timeframe. I'll explain why in greater detail my JAN outlook which will be online tomorrow afternoon.