2013 Fall Medium Range Discussion

[donsutherland1]

Don..great post as usual!

I have very little doubt that the pattern is reacting to such a sustained deeply negative Arctic Oscillation and I know the Pacific has been working against sustained colder wx in the east since the first of Dec.. but does it usually take this long for a deeply AO- to fully drive a colder pattern change down into the lower latitudes or is this a rather unusual case?

The AO has not been as severely negative as it was in December 2009 and December 2010. December 2009 had a monthly mean AO of -3.413. December 2010 had one of -2.631. The Pacific has played a role with regard to the slow progression. The PNA has now been negative for 41 consecutive days. Had the AO been as severely negative as it was in 2009 and 2010, it would likely have overwhelmed the pattern.

[donsutherland1]

Pattern Change Now Evolving as Panic of December '12 Rises...

The storm that brought record daily snowfall to Minneapolis-St. Paul commenced a sequence of events that is leading to a pattern change. That sequence of events will likely include several systems (one underway and one or two others in coming days) that will be noted more for wet than white in the East. Afterward, the last 10-14 days (14 days for the Plains States and 10 days for the East Coast) could see generally cooler than normal weather.

The rising panic that Winter 2012-13 is becoming a repeat of the non-Winter of 2011-12 has resulted for a large gap between the actual pattern change that is now imminent and expectations. The pattern change was likely to be slow with a fairly lengthy transition before sustained colder weather set in. Given the combination of an EPO+, PNA-, and persistent Arctic warmth, severe cold was not very likely for much or all of December. Expectations were for prolonged and deep cold to set in with the potential for excessive snows. That gap was unsustainable, hence the rising panic.

If one steps back to take a look at the non-Winter of 2011-12, one finds:

1. A powerful AO+ regime predominated in December.

2. The long-range guidance and analog cases were unrelenting with their warm idea.

3. The subtropical jet was quiet.

To date, one finds:

1. A persistent AO- regime.

The AO has now been negative for 22 consecutive days. It is likely to remain predominantly negative for the remainder of the month as per the ensemble guidance and also historic cases. Notable long-lived blocks that developed in the 11/20-12/10 timeframe have typically been long-lived. Put another way, the blockiness that was present in mid-Autumn reasserted itself during the winter.

Recent examples include the blocking regimes of 2009-10 and 2010-11. The following severe blocking episodes (minimum AO value of -3.000 or below) began in late November/early December (11/20-12/10) following a blocky October (monthly AO of -025 or below):

December 7, 1966-January 11, 1967: 36 days

December 7, 1981-January 12, 1982: 37 days

November 29, 2009-January 15, 2010: 48 days

December 3, 2010-January 15, 2011: 44 days

All four of those cases saw the January AO average < 0. KU snowstorms occurred during the winter in 1966-67, 2009-10, and 2010-11. A KU snowstorm occurred during the spring in 1981-82,

2. The long-range guidance has been anything like last winter. In fact, the latest CFSv2 guidance has trended toward widespread cold to begin January and a generally cold month across much of North America. With the PNA having been negative for 41 consecutive days, both historic cases and some ensemble members suggest that it could go positive near or during January. Once that happens, the dam that has kept some of the coldest air bottled up in Alaska and westward could break and a genuine prospect of at least an outbreak of severe cold could develop.

Below are the latest CFSv2 weekly (weeks 3 and 4) and monthly (January 2013) forecasts:

3. The SOI has recently gone negative. December 10-12 had values below -40. The 30-day moving average has gone negative and the 90-day moving average is near 0. Often such developments suggest a stronger subtropical jet. Hence, there is a possibility that the closing 10 days of December and perhaps the opening 10 days of January could be stormy.

In sum, the gradual pattern change is unfolding. At first, the cold will be a little more impressive than seasonal cold. Storminess could increase as well. The possibility of an outbreak of severe cold could increase after the start of January, as the PNA heads to more neutral values,and especially if it goes positive. All said, even as the first two weeks of December have been sufficiently warm to rekindle nightmares of the non-Winter of 2011-12, there are big differences that argue against a repeat.

[cbmclean]

Don,

This may sound weird but I just want you to know that that last post was a pleasure to read from beginning to end. It was an excellent mixture of hard scientific data and entertaining prose. I particularly enjoyed "...to rekindle nightmares of the non-Winter of 2011-12." This produced an amusing image in my head of a winter-weather loving hobbyist tossing and turning inthe middle of the night in a puddle of his own sweat mumbling things like "no, no no historical +AO...no, no, no 3 sigma deviations for monthly average temperature...."

Keep up the good work.

[michsnowfreak]

Great post don!

[weathafella]

Wonderful writeup Don. Your reasoning is sound and hopefully it plays out this way. Thanks for your hard work at analyzing the pattern.

[Srain]

Don, the 00Z Op Euro and its ensembles have been flirting with the idea of a southern tracking Winter storm near Christmas ~vs~ a Lakes Cutter. We down here in the Southern Plains as well as the Southern Rockies have indeed seen a pattern change since December 9/10. Great analysis as always.

[HM]

Don, the 00Z Op Euro and its ensembles have been flirting with the idea of a southern tracking Winter storm near Christmas ~vs~ a Lakes Cutter. We down here in the Southern Plains as well as the Southern Rockies have indeed seen a pattern change since December 9/10. Great analysis as always.

That's because it was an actual pattern change and what amazes me is that there were mets at that time telling paying clients that "the pattern change is coming to cold, snow in the East."

What a ridiculous forecast to be made when the pattern is in the process of changing anyway. I guess a pattern that delivers in the western 2/3s doesn't make it newsworthy. You guys will rock it through the New Year.

[Met1985]

Great write up Don! As you said seems like this pattern change has been very slow but still changing. January should be interesting coming down the road.

[Srain]

That's because it was an actual pattern change and what amazes me is that there were mets at that time telling paying clients that "the pattern change is coming to cold, snow in the East."

What a ridiculous forecast to be made when the pattern is in the process of changing anyway. I guess a pattern that delivers in the western 2/3s doesn't make it newsworthy. You guys will rock it through the New Year.

It appears that way, HM. California, Arizona, New Mexico and Colorado have certainly benefited with the storm track and we have seen record cold in parts of Texas as well as a return of rainfall and general storminess that was absent for 2 month prior to when that pattern changed. The 00Z Euro does bode well for us down here and hopefully the pattern delivers for those that are hand wringing along the East Coast...

[HM]

As some of us suspected, this isn't a real MJO signal. Good evidence of that is when they move in the wrong direction, haha:

http://cawcr.gov.au/staff/mwheeler/maproom/RMM/phase.Last40days.gif

Gee I wonder what could be causing this?! lol...

Either way, active East-Asian-STJ jet will continue with -EPO coming up. It is a great recipe for you guys!

[easternsnowman]

Don S hit it on the nose last year, I feel he is correct here too!

[Srain]

EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD

1050 AM EST MON DEC 17 2012

VALID 12Z THU DEC 20 2012 - 12Z MON DEC 24 2012

HIGH LATITUDE BLOCKING OVER NORTHEASTERN CANADA WILL COMBINE WITH

REINFORCED RIDGING SOUTH OF THE ALEUTIANS TO KEEP AN ACTIVE

SOUTHERN STREAM THROUGH THE CONUS OVER THE NEXT WEEK. THESE

NORTHERN POSITIVE HEIGHT ANOMALIES CORRELATE WELL WITH EACH OTHER

THROUGH TELECONNECTIONS AND BOTH ACT TO SUPPORT ROBUST SYSTEMS.

THE SYNOPTIC DIFFERENCES AMONG THE GUIDANCE ARE RELATIVELY

SMALL... BUT THE DETAILS WILL BE IMPORTANT DOWN THE ROAD. IN

ADDITION... CONTINUITY REMAINS GOOD WITH FEW CHANGES FROM RECENT

HPC FORECASTS.

FOR THE FIRST PART OF THE FORECAST... THU-SAT/D3-5... THE

NORTHWEST AND NORTHEAST PORTION OF THE CONUS WILL BE THE MOST

ACTIVE. IN THE NORTHEAST PACIFIC... A DEVELOPING OMEGA BLOCK OVER

ALASKA WILL DROP AN UPPER LOW OUT OF THE GULF WHICH WILL PAUSE FOR

A FEW DAYS OFF THE PAC NW. THE CONTINUED ONSHORE FLOW WILL WRING

OUT SEVERAL INCHES OF PRECIPITATION ALONG THE COAST AND INTO THE

TERRAIN... INCLUDING UP TO SEVERAL FEET OF SNOW. DOWNSTREAM OVER

THE EAST... A DEEPENING CYCLONE WILL MOVE OUT OF THE MID-MS VALLEY

INTO THE GREAT LAKES AND THEN INTO NORTHERN NEW ENGLAND AS IT

SLOWS ITS EXIT AMID AMPLIFYING FLOW. THIS SHOULD SPREAD

INCREASINGLY HEAVY PRECIP... WITH SNOW ON THE NW SIDE... THROUGH

THE CENTRAL AND NORTHEASTERN STATES ESPECIALLY ON THURSDAY INTO

FRIDAY. THE GFS REMAINS A BIT QUICKER THAN THE GEFS MEAN WITH THE

PROGRESSION OF THIS SYSTEM... AND EACH ARE JUST AHEAD OF THE

ECMWF/ECENS MEAN. GIVEN THE GOOD CONTINUITY OF THE ECMWF AND A

SLOWER TREND IN THE GFS... BASED THE FIRST PART OF THE FORECAST ON

THE 00Z ECMWF.

BY SUN-MON/D6-7... THE 00Z ECMWF BECOMES QUITE SLOW TO EXIT THE

SYSTEM IN THE NORTHEAST COMPARED TO THE OTHER ECMWF/GEFS ENSEMBLE

MEMBERS AS A RESULT OF A VERY BLOCKY FORECAST BOTH OVER NORTHEAST

CANADA AND OVER THE CENTRAL CONUS. THE GFS REMAINS FLATTER WITH

THE FLOW FROM THE NORTHEAST PACIFIC INTO THE WEST COAST WHILE THE

ECMWF AND CANADIAN MAINTAIN A DEEPER UPPER LOW. THE GEFS AND ECMWF

ENSEMBLE MEANS FALL IN BETWEEN WITH THE FORMER A BIT FLATTER THAN

THE LATTER. GIVEN THE TENDENCY FOR THE GFS/GEFS TO UNDERAMPLIFY

THE FLOW... OPTED TO GRAVITATE TOWARD THE 00Z ECMWF ENSEMBLE MEAN

AS A HEDGED INTERMEDIATE POINT. THIS WILL SET UP A SYSTEM JUST

EAST OF THE SOUTHERN ROCKIES BY EARLY NEXT WEEK. THE PRECIPITATION

OVER THE WEST MAY NOT LET UP MUCH UNTIL THE VERY END OF THE MEDIUM

RANGE ONCE THE UPPER TROUGH MOVES INLAND.

FRACASSO

[blizzard1024]

Pattern Change Now Evolving as Panic of December '12 Rises...

The storm that brought record daily snowfall to Minneapolis-St. Paul commenced a sequence of events that is leading to a pattern change. That sequence of events will likely include several systems (one underway and one or two others in coming days) that will be noted more for wet than white in the East. Afterward, the last 10-14 days (14 days for the Plains States and 10 days for the East Coast) could see generally cooler than normal weather.

The rising panic that Winter 2012-13 is becoming a repeat of the non-Winter of 2011-12 has resulted for a large gap between the actual pattern change that is now imminent and expectations. The pattern change was likely to be slow with a fairly lengthy transition before sustained colder weather set in. Given the combination of an EPO+, PNA-, and persistent Arctic warmth, severe cold was not very likely for much or all of December. Expectations were for prolonged and deep cold to set in with the potential for excessive snows. That gap was unsustainable, hence the rising panic.

If one steps back to take a look at the non-Winter of 2011-12, one finds:

1. A powerful AO+ regime predominated in December.

2. The long-range guidance and analog cases were unrelenting with their warm idea.

3. The subtropical jet was quiet.

To date, one finds:

1. A persistent AO- regime.

The AO has now been negative for 22 consecutive days. It is likely to remain predominantly negative for the remainder of the month as per the ensemble guidance and also historic cases. Notable long-lived blocks that developed in the 11/20-12/10 timeframe have typically been long-lived. Put another way, the blockiness that was present in mid-Autumn reasserted itself during the winter.

Recent examples include the blocking regimes of 2009-10 and 2010-11. The following severe blocking episodes (minimum AO value of -3.000 or below) began in late November/early December (11/20-12/10) following a blocky October (monthly AO of -025 or below):

December 7, 1966-January 11, 1967: 36 days

December 7, 1981-January 12, 1982: 37 days

November 29, 2009-January 15, 2010: 48 days

December 3, 2010-January 15, 2011: 44 days

All four of those cases saw the January AO average < 0. KU snowstorms occurred during the winter in 1966-67, 2009-10, and 2010-11. A KU snowstorm occurred during the spring in 1981-82,

2. The long-range guidance has been anything like last winter. In fact, the latest CFSv2 guidance has trended toward widespread cold to begin January and a generally cold month across much of North America. With the PNA having been negative for 41 consecutive days, both historic cases and some ensemble members suggest that it could go positive near or during January. Once that happens, the dam that has kept some of the coldest air bottled up in Alaska and westward could break and a genuine prospect of at least an outbreak of severe cold could develop.

Below are the latest CFSv2 weekly (weeks 3 and 4) and monthly (January 2013) forecasts:

3. The SOI has recently gone negative. December 10-12 had values below -40. The 30-day moving average has gone negative and the 90-day moving average is near 0. Often such developments suggest a stronger subtropical jet. Hence, there is a possibility that the closing 10 days of December and perhaps the opening 10 days of January could be stormy.

In sum, the gradual pattern change is unfolding. At first, the cold will be a little more impressive than seasonal cold. Storminess could increase as well. The possibility of an outbreak of severe cold could increase after the start of January, as the PNA heads to more neutral values,and especially if it goes positive. All said, even as the first two weeks of December have been sufficiently warm to rekindle nightmares of the non-Winter of 2011-12, there are big differences that argue against a repeat.

Love it..."The panic of December 2012..." You are correct nobody should ever write a winter

off so early. But what has been frustrating is that it has been over 21 months since I have

seen a nice snowscape with at least 4 inches of snow on the ground. I live in upstate NY in a decent lake effect area. Last winter my greatest snow depth was a paltry 2 inches and even that was not widespread as it melted under the trees. Never in my whole life have I had to wait this long to see decent snow cover! I also am a skier and just was hoping for an early start to the winter which obviously in upstate NY has not happened. The past is the past...so like you I am very hopeful. The blocking regime which has been persistent looks legit and once the pacific jet slows down and if we can get into a positive PNA we could see a bonafide arctic outbreak. it is really damn cold in Alaska and northwestern canada. This air keeps getting colder and colder...

Of course after last winter, many are just plain pessimistic no matter what, because we had such great winters 2009-2010 and 2010-11 and then nothing last year. Plus the global warming folks are going nuts about summer loss of sea ice, record warm temperatures etc. a roller coaster ride for winter lovers. I still believe there has been some modest global warming but we still can easily see awesome cold, snowy winters. But this is for the climate change forum and that is all I am going to say here on this forum.

[blizzard1024]

Love it..."The panic of December 2012..." You are correct nobody should ever write a winter

off so early. But what has been frustrating is that it has been over 21 months since I have

seen a nice snowscape with at least 4 inches of snow on the ground. I live in upstate NY in a decent lake effect area. Last winter my greatest snow depth was a paltry 2 inches and even that was not widespread as it melted under the trees. Never in my whole life have I had to wait this long to see decent snow cover! I also am a skier and just was hoping for an early start to the winter which obviously in upstate NY has not happened. The past is the past...so like you I am very hopeful. The blocking regime which has been persistent looks legit and once the pacific jet slows down and if we can get into a positive PNA we could see a bonafide arctic outbreak. it is really damn cold in Alaska and northwestern canada. This air keeps getting colder and colder...

Of course after last winter, many are just plain pessimistic no matter what, because we had such great winters 2009-2010 and 2010-11 and then nothing last year. Plus the global warming folks are going nuts about summer loss of sea ice, record warm temperatures etc. a roller coaster ride for winter lovers. I still believe there has been some modest global warming but we still can easily see awesome cold, snowy winters. But this is for the climate change forum and that is all I am going to say here on this forum.

FWIW....the 12Z GFS verifies your ideas Don. At 16 days it transitions to a very positive PNA and the east gets crushed with very very cold air. 1000-500 mb thicknesses drop below 500 dm to NYC-BWI and are in the upper 480s in northern NY. 850 mb temperatures drop to between -20 and -27 across much of the northeast. Of course this likely WON'T verify like this but it does verify the idea that if the PNA can go positive major sub zero temperatures would cover a lot of the northeast. Day 16 GFS is just an illustration on how easy it would be to get this arctic air down to the northeast. The potential is there....but when will it come and how cold will it be....that is the million dollar question. The GFS does tend to overdo these cold air outbreaks in the later periods...but again the idea and potential is there.

[Srain]

The 12Z operational GFS and Euro as well as the GEFS continue to advertise a rather strong Winter Storm ejecting from the Southern Rockies early next week taking a bit more southern storm track than the mid week system. In fact there are hints of wintry weather potential very far S into Oklahoma and Texas as well as Louisiana if the guidance should verify.

[donsutherland1]

Thanks all for the kind words.

Today's 12z guidance suggests that the ideas mentioned yesterday appear reasonable. There continues to be some support for the idea that the PNA could go neutral and possibly positive in the extended range helping dislodge some very cold air from Alaska/northwestern Canada. The Plains States into the Great Lakes region will likely experience a series of winter events over the next two weeks (Steve aka Srain has posted on this). Toward the end of that timeframe, the opportunity for snows farther east could increase as the subtropical jet remains active. The risk of an Arctic outbreak could increase after the start of January (Blizzard1024 observed such an outcome on today's 12z run of the GFS).

[Isotherm]

Thanks all for the kind words.

Today's 12z guidance suggests that the ideas mentioned yesterday appear reasonable. There continues to be some support for the idea that the PNA could go neutral and possibly positive in the extended range helping dislodge some very cold air from Alaska/northwestern Canada. The Plains States into the Great Lakes region will likely experience a series of winter events over the next two weeks (Steve aka Srain has posted on this). Toward the end of that timeframe, the opportunity for snows farther east could increase as the subtropical jet remains active. The risk of an Arctic outbreak could increase after the start of January (Blizzard1024 observed such an outcome on today's 12z run of the GFS).

I'm not as confident about the PNA modality change as I am w/ the EPO change, which should be occurring later this week. It's no coincidence that the colder temperatures seem to be arriving almost immediately after we see the EPO neutralize, w/ higher heights building up across Alaska. This initiates the cross polar flow, finally delivering some arctic air into southern Canada and northern tier of the US down the road.

Here's the signalling shift depicted in today's guidance. It's a pretty significant change, from +2SD to neutral/slightly negative after the 20th:

The PNA has been forecasted to go positive in the D10-15 range on many occasions over the past few weeks, but as that time frame approaches, the data tends to back off the idea. I think it's possible we see a neutral or maybe if we're lucky a transient PNA burst, but I believe it's probably more likely that the slightly negative PNA regime will continue.

Current guidance:

With that being said, while the PNA hasn't helped us over the past 2 weeks, I think the EPO signal is much more important. If we can get higher heights to remain over AK/NW Canada, it's ok if we've got a bit of a trough along the West Coast. What's not ok is when there's a large low height field over AK and the Arctic as that cuts-off our Siberian source air.

I agree with your conclusions and it appears today's guidance is becoming more persistent with colder air getting into the picture for Dec 20th-30th. Given the major NPAC change, that idea makes sense. The AO / NAO remain negative and will continue to be so IMO through the month of January. However, it's obvious the EPO has been dominating this particular month so far given the torch across the CONUS. If we can continue w/ a negative EPO into early January, the prospects of getting some of the severe NW Canadian cold into the US increases as well.

[CoastalWx]

The pattern is still cutter prone even with that storm just after Christmas. It may still work out for areas further north into New England, but there isn't a big block or confluence to really force this off the Delmarva for example. We still have time so it isn't set in stone, just something I'm seeing.

[GaWx]

***Fwiw***, the new Euro weeklies look pretty chilly and wet for the Midwest, Mid-Atlantic, and SE in general with near to above avg. precip. and near to below avg. temp.'s after a warm 12/17-23. So, fwiw, 12/24-1/13 look fairly good if these are to be believed.

Patternwise at 500 mb, the good news is that they have a nearly continuous E Canada/SW Greenland block and a somewhat -AO on avg. The bad news for the SE and Mid-Atlantic is that the pesky -PNA doesn't seem to go away.

All in all, I liked what I saw. However, the fwiw of the weeklies can't be overemphasized and I would have preferred to have seen a higher PNA for the East Coast. The Midwest may not really be hurt by the -PNA I suppose.

[GaWx]

***Fwiw***, the new Euro weeklies look pretty chilly and wet for the Midwest, Mid-Atlantic, and SE in general with near to above avg. precip. and near to below avg. temp.'s after a warm 12/17-23. So, fwiw, 12/24-1/13 look fairly good if these are to be believed.

Patternwise at 500 mb, the good news is that they have a nearly continuous E Canada/SW Greenland block and a somewhat -AO on avg. The bad news for the SE and Mid-Atlantic is that the pesky -PNA doesn't seem to go away.

All in all, I liked what I saw. However, the fwiw of the weeklies can't be overemphasized and I would have preferred to have seen a higher PNA for the East Coast. The Midwest may not really be hurt by the -PNA I suppose.

After further analysis, I admittedly like what I see on the new Euro weeklies even a bit more. Here's why:

1) Both the NAO and AO are more negative (stronger blocking) than the Euro weekly run from four days ago, which covered the same exact four weeks.

2) After a slightly warmer week #1 in the E US (no surprise after the warm adjustments of the last few days), the 2 meter temp.'s for the subsequent three weeks in the E 1/2 of the US are overall significantly colder vs. the Euro weekly run from four days ago, which as I mentioned covers the same exact four weeks (through 1/13). Weeks 2 and 4 are much colder than that from the prior run whereas week 3 is a little colder. As a matter of fact, weeks 2-4 actually have colder than normal covering most of the country from coast to coast.

I, of course, do take these with a big grain of salt. However, so that the reader doesn't just think that I'm a nonobjective cynic, I will point out two encouraging things about the weeklies that may mean there's some credibility:

1) This is the coldest week 2-4 run two meter anomalywise for the US as a whole by a good margin since at least early Sep. (as far as I went back). That covers 31 Euro weekly runs. Actually, I saw no other run having all of weeks 2-4 with such widespread below normal U.S. temp.'s

2) The runs in late Nov. for Dec. were largely warm. The 11/29 run had a torch for four weeks.

[Srain]

The pattern is still cutter prone even with that storm just after Christmas. It may still work out for areas further north into New England, but there isn't a big block or confluence to really force this off the Delmarva for example. We still have time so it isn't set in stone, just something I'm seeing.

[blizzard1024]

I'm not as confident about the PNA modality change as I am w/ the EPO change, which should be occurring later this week. It's no coincidence that the colder temperatures seem to be arriving almost immediately after we see the EPO neutralize, w/ higher heights building up across Alaska. This initiates the cross polar flow, finally delivering some arctic air into southern Canada and northern tier of the US down the road.

Here's the signalling shift depicted in today's guidance. It's a pretty significant change, from +2SD to neutral/slightly negative after the 20th:

The PNA has been forecasted to go positive in the D10-15 range on many occasions over the past few weeks, but as that time frame approaches, the data tends to back off the idea. I think it's possible we see a neutral or maybe if we're lucky a transient PNA burst, but I believe it's probably more likely that the slightly negative PNA regime will continue.

Current guidance:

With that being said, while the PNA hasn't helped us over the past 2 weeks, I think the EPO signal is much more important. If we can get higher heights to remain over AK/NW Canada, it's ok if we've got a bit of a trough along the West Coast. What's not ok is when there's a large low height field over AK and the Arctic as that cuts-off our Siberian source air.

I agree with your conclusions and it appears today's guidance is becoming more persistent with colder air getting into the picture for Dec 20th-30th. Given the major NPAC change, that idea makes sense. The AO / NAO remain negative and will continue to be so IMO through the month of January. However, it's obvious the EPO has been dominating this particular month so far given the torch across the CONUS. If we can continue w/ a negative EPO into early January, the prospects of getting some of the severe NW Canadian cold into the US increases as well.

I concur. The Pacific has been killing us so far this December. Shut it down...then we can tap into a cold and stormy pattern that come with high latitude blocking regimes.

It would be nice for a positive PNA but sometimes that just delivers cold with fast flow and just clippers/LES...so in some ways maybe neutral PNA is good for bigger snowstorms.

[tacoman25]

FWIW....the 12Z GFS verifies your ideas Don. At 16 days it transitions to a very positive PNA and the east gets crushed with very very cold air. 1000-500 mb thicknesses drop below 500 dm to NYC-BWI and are in the upper 480s in northern NY. 850 mb temperatures drop to between -20 and -27 across much of the northeast. Of course this likely WON'T verify like this but it does verify the idea that if the PNA can go positive major sub zero temperatures would cover a lot of the northeast. Day 16 GFS is just an illustration on how easy it would be to get this arctic air down to the northeast. The potential is there....but when will it come and how cold will it be....that is the million dollar question. The GFS does tend to overdo these cold air outbreaks in the later periods...but again the idea and potential is there.

Though +PNA would definitely benefit the eastern half of the nation, of course you don't need it to get a cold pattern there. -EPO (which we haven't really seen at all this month) combined with -NAO (which we have seen to an extent and should continue to see for a while) almost always delivers very cold air to the eastern half of the nation.

So to me, the most important factor to get cold air for the country as a whole is the EPO. We gotta kick that cold troughing out of Alaska asap.

EDIT: I see Isotherm already made a lot of the same points, along with emphasizing that any hope for real +PNA in the forseeable future is not likely.

[Ottawa Blizzard]

Brett Anderson of accuweather sees no sustained cold over eastern North America for at least the next 10 days due to troughiness in the west. Mind you, as another member of this forum said, Anderson is the heat miser to JBs cold miser.

[Ottawa Blizzard]

Environment Canada's winter forecast is looking good so far. Cold in the west, mild in the east.

http://www.cbc.ca/news/canada/story/2011/12/01/weather-forecast-canada.html

[GaWx]

Brett Anderson of accuweather sees no sustained cold over eastern North America for at least the next 10 days due to troughiness in the west. Mind you, as another member of this forum said, Anderson is the heat miser to JBs cold miser.

However, IF the brand new Euro weeklies happen to be onto something, there could be a widespread and longlasting cold pattern over much of the U.S. for the subsequent 3+ weeks. I take with a grain of salt, but am admittedly paying attention. Stay tuned.

[Ottawa Blizzard]

However, IF the brand new Euro weeklies happen to be onto something, there could be a widespread and longlasting cold pattern over much of the U.S. for the subsequent 3+ weeks. I take with a grain of salt, but am admittedly paying attention. Stay tuned.

Hopefully it's right, the euro that is.

[GaWx]

Hopefully it's right, the euro that is.

Interestingly, the Euro weeklies are making it cold throughout the US despite a -PNA dominated pattern remaining. They are making it cold via strong and persistent blocking (a very strong west based -NAO and a decent though not as strong -AO) finally taking control from the not so good Pacific. Keep in mind that this is the coldest weeklies run for weeks 2-4 for the US in at least 3.5 months of runs and that it did well in advance of the torched December with mainly warm runs. That's why I'm not ignoring it.

[Ottawa Blizzard]

Interestingly, the Euro weeklies are making it cold throughout the US despite a -PNA dominated pattern remaining. They are making it cold via strong and persistent blocking (a very strong west based -NAO and a decent though not as strong -AO) finally taking control from the not so good Pacific. Keep in mind that this is the coldest weeklies run for weeks 2-4 for the US in at least 3.5 months of runs and that it did well in advance of the torched December with mainly warm runs. That's why I'm not ignoring it.

As a matter of interest I recall someone on this board saying once that the Pacific was unfavourable in 1993-94, but that the blocking brought us a super cold winter. Is this true? Could omething similar happen this year, bearing in mind that December 1993 was a torch up until the solstice. January 1994 was the coldest January of the twentieth century in Ottawa and the coldest since 1920 in Toronto.

[Isotherm]

As a matter of interest I recall someone on this board saying once that the Pacific was unfavourable in 1993-94, but that the blocking brought us a super cold winter. Is this true? Could omething similar happen this year, bearing in mind that December 1993 was a torch up until the solstice. January 1994 was the coldest January of the twentieth century in Ottawa and the coldest since 1920 in Toronto.

The PNA was near neutral with no real sustained ridging in the Western US, the NAO was positive, but the EPO and AO were both negative. This is why the AK region is so important: