Winter 2013-14 medium range discussion

[donsutherland1]

Odds Growing of a Strong Cold Shot in the Pacific Northwest for December 3-6, 2013:

 

The PNA is forecast to fall below -1 in early December, even as the EPO remains strongly negative. Such a pattern can be conducive to strong cold shots for the Pacific Northwest.

 

The composite temperature anomalies for all December dates (1981-2010) when the PNA was -1 or lower is below:

 

 

 

The GFS ensembles indicate 850 mb temperatures that could run approximately 2 standard deviations below normal in parts of the Pacific Northwest. Charts showing the ensemble forecast, temperatures associated with such standardized departures, and daily record low maximum and minimum temperatures are below:

 

 

Finally, the 11/27/2013 0z run of the GFS forecasts some extreme cold for the Pacific Northwest with the lowest temperatures forecast as follows:

 

Portland: -10.7°C (13°F)

Seattle: -10.5°C (13°F)

Spokane: -14.0°C (7°F)

 

In sum, it appears likely that Seattle and Portland could see one or more low temperatures in the lower or middle 20s. One of those two cities could see a reading below 20°. Spokane will likely see one day with a high temperature in the upper teens or low 20s and a minimum temperature in the single digits.

[donsutherland1]

This morning, the Arctic Oscillation stood at +1.955. That follows a brief period of blocking in which the stage was set for what will be two significant intrusions of Arctic air in the eastern half of North America. The first was the 11/24-25 Arctic blast that set numerous daily low maximum records on the 24th, as well as some daily record minimum readings, particularly on the 25th. The next shot will be pushing into the east today and will produce another period of below normal to much below normal readings during the 11/28-30 period.

 

One of the scenarios discussed earlier in this thread was that if the AO goes positive and remains predominantly positive is that December 2008 provided a reasonable case for the outcome (#150). December 2008 featured some notable cold in the Pacific Northwest during a two-week period and such cold shows up on the operational and ensemble guidance (#181).  

 

With today's teleconnection data and ensemble forecasts, 2008 remains a leading case. In fact, the CFSv2 forecasts are remarkably similar both to the December 2008 monthly anomalies and the pattern progression, with only some minor timing differences. Below are the CFSv2 Week 2-4 forecasts and corresponding date in 2008 that seems to match quite well. Afterward, the December 2013 CFSv2 monthly forecast is compared with December 2008.

 

 

 

[skierinvermont]

2008 had more troughing in the western US (down into salt lake city). The CFS has a big SW ridge but it was a bit smaller on the Dec 26th run than the 25th run. I would gladly settle for 125% of average monthly snowfall in the Wasatch like December 2008 (120").

[The_Global_Warmer]

Last nights GFS ensemble mean has more spread with the the AO state going into the end of the first week of December than the last two updates have had.

 

The PNA continues to trend more negative in the medium range.

 

 

[HM]

Last nights GFS ensemble mean has more spread with the the AO state going into the end of the first week of December than the last two updates have had.

 

The PNA continues to trend more negative in the medium range.

 

 

 

The AO state will overall be positive through the medium range with a strong NAM state and PV. The reason the AO declines is from the breaking ridges over the EPO / N. Pac area. At their worst, they amplify into the pole, displace cold air down etc. causing the AO to decline for a while (like now). There is no sign of a dramatic PV-NAM weakening through December; however, brief poleward responses to PV-behavior both in the NAO domain and EPO-WPO domain will be possible. 

[donsutherland1]

Brief afternoon thoughts: Themes of 2008 abound...

 

1. The 12z GFS extended the cold period in the Pacific Northwest. In 2008, there was an approximately two-week long period of cold in that area (#165).In Seattle, 6 days had highs of 32° or less. The lowest high temperature was 26° on 12/20 (3rd coldest high for the date).

 

2. The December 3-6 period still looks unseasonably cold in the Pacific Northwest, but the cold lasts longer. Another shot of cold shows up on the GFS toward the end of its forecasting range.

 

3. The GFS ensembles now show cold anomalies of 2-3 standard deviations from normal (relevant table for the 12/1-10 period is shown in #181).

 

4. The MOS guidance, which runs only through 12/5 and factors in climatology, shows lowest temperatures for Seattle, Spokane, and Portland as 28°, 14°, and 28° respectively.  The 12z GFS shows lowest temperatures through 12/6 of 15° in Seattle, 7° in Spokane, and 15° in Portland.

 

All said, confidence that the Pacific Northwest is poised for a period of cold, possibly severe relative to climatology for a time, and possibly one that could last at least a week or longer is growing.

[The_Global_Warmer]

Wow. The GFS has like a Double Triple Decker Phaser event.  Good lord.  Not that the GEM is anymore reliable.  but the differences are well wild.

 

 

 

[The_Global_Warmer]

Todays 12z GFS handles the PNW closed upper low completely differently than 24 hours ago.

 

 

[It's Always Sunny]

Todays 12z GFS handles the PNW closed upper low completely differently than 24 hours ago.

That solution is still about a week out so I'm not too surprised. Today's ensembles have the ULL over the Intermountain West.

[donsutherland1]

December 8-14, 2013 Idea:

 

In terms of teleconnections, the same theme of an EPO-/AO+ that has dominated November seems likely to continue into at least the second week of December. Both the ensembles and teleconnection cases indicate that the cold will be focused primarily in the western half of the U.S. The strong shot of cold for the Pacific Northwest starting around 12/3 remains on target and will likely persist into at least the beginning of the second week of December. The same holds true for the Northern Plains. The outcome farther east will depend on some of the cold air coming eastward, possibly in pieces rather than all at once with a shifting trough.

 

The teleconnection cases and select ensemble charts are below:

 

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how do i print screen

 

I suspect that the ensembles might be rushing the cold to the east. I do believe there is a higher probability that the cold is able to bleed eastward across the northern tier. 2008 remains the leading teleconnection case at present, so I'm using it for some insight.

 

Overall, my thoughts are that the Pacific Northwest, Northern/Central/Southern Plains, Great Lakes area, and northern New England are likely to wind up colder than normal. The Middle Atlantic and southern New England regions will probably wind up near normal. The Southeast and Gulf Coast will probably be warmer than average. The Southwest will probably also be somewhat warmer than normal.

 

If the arrival of the cold air is delayed and if the area of warmth proves more expansive than what the ensembles are suggesting--and the ensembles have more expansive cold anomalies than my thinking--that could be an indication that the pattern is transitioning toward a milder winter in at least the eastern half of the U.S. Some of the other teleconnection cases that have begun showing up are December 1951, 1972, and 1990. Not all are good ENSO matches, but the combination of a strong EPO- and strong AO+ is fairly uncommon.

 

In the meantime, one should be thankful that the long-range is never locked in stone. Uncertainty can provide hope for a nicer outcome. Happy Thanksgiving to all and happy Hanukkah to all of AmericanWx's Jewish members.

[SnowGoose69]

The evolution of the slow transition to the trof into the East looks alot like when the pattern reversed last January last year, it took seemingly a week for the arctic air mass to make it from Kansas City to Raleigh.  I think the truth lies somewhere between the Euro/GFS in the 8-15 day period, the Euro southeast ridge is probably too strong because its cutting or attempting to overdig energy into the SW, I've noticed that its been progressively dampening the SE ridge as we get inside Day 8 and the next run its trying to show it again at Day 10 only to further beat it down in the ensuing 2 runs.  The GFS I'm sure is too cold too far SE as is almost always the case in the medium or long range. 

[Huffwx]

This adds nothing, but i love the phrase--Beating down as SE Ridge.

 

Good luck to those in the PAC NW-- enjoy some cold and winter!

 

 

Happy Thanksgiving to all!

[Wow]

The evolution of the slow transition to the trof into the East looks alot like when the pattern reversed last January last year, it took seemingly a week for the arctic air mass to make it from Kansas City to Raleigh.  I think the truth lies somewhere between the Euro/GFS in the 8-15 day period, the Euro southeast ridge is probably too strong because its cutting or attempting to overdig energy into the SW, I've noticed that its been progressively dampening the SE ridge as we get inside Day 8 and the next run its trying to show it again at Day 10 only to further beat it down in the ensuing 2 runs.  The GFS I'm sure is too cold too far SE as is almost always the case in the medium or long range. 

 

This was the case for November.  A few weeks ago the SE ridge was in full agreement across all the model suites in the long range.  Just look how that verified.  I'd be very cautious to buy into a western trough/SE ridge pattern digging in and holding on.. at leas until we see some substantial blocking in place to slow things down.

[donsutherland1]

Brief afternoon thoughts...

 

1. Partial teleconnection cases continue to highlight December 2008.

 

2. PAC NW cold shot for 12/3-10 (details for the 12/3-6 period in #181) continues to look fairly impressive (2σ-3σ anomalies). Some daily record low maximum readings and possibly even daily record low temperatures could be set in parts of the region during that period.

 

3. Some cold air will likely bleed eastward, but a gradient could set up somewhere between the Middle Atlantic region and New England sometime toward mid-month. The placement of the gradient could determine who receives snowfall and who receives rainfall as systems come eastward. For illustrative purposes, December 19-20, 2008 featured a storm that brought a cold rain to Philadelphia, 4.5" snow to New York City, 6.3" to Islip, 12.5" to Boston and 14.1" to Worcester.

 

4. The possibility exists that near or just after mid-month, there could be a more expansive cold shot in the East, possibly preceded by some storminess. The possibility of storminess shows up on the GFS ensembles in the extended range.

[donsutherland1]

Upcoming Cold Period in the Pacific Northwest…

 

The cold period is likely to run from 12/3 through 12/10, as the guidance has extended the period. That outcome is consistent with some of the teleconnection cases and larger pool of PNA- cases that closely resemble the current pattern and possible evolution of such patterns in the past. Among the teleconnection cases showing up have been 1956, 1972, and 2008 (also in the objective analogs). All of those years featured some impressive cold in the Pacific Northwest. 

 

The latest GFS ensemble guidance shows cold anomalies reaching 2-3 standard deviations at times.

 

 

The surface temperatures consistent with such anomalies for the December 1-10 period (1981-2010 climate reference period) are:

 

 

The daily low maximum and low minimum records for Portland, Seattle, and Spokane are below:

 

 

The last time the temperature fell below 25° in Seattle ws January 13, 2013 (24°) and the last time the temperature fell below 20° was February 26, 2011 (19°). The last time the temperature fell below 25° in Portland was just recently on November 22, 2013 (24°, 3rd lowest reading for 11/24) and the last time it fell below 20° was February 26, 2011 (18°). The last day with a high temperature of 32° or below in Seattle was January 19, 2012 (30°). In Portland, it occurred on November 24, 2010 (32°).

[Srain]

The composite analogs in the Day 8+ range have been remarkably stable for the past 3 to 4 cycles for the Central/Western Region. There are some memorable dates via those analogs if the pattern does in fact develop across the Western 2/3rds of North America.

[donsutherland1]

December 16-31: What if the EPO Shifts to Predominantly Positive?

 

Although the second half of December is still well into the future and the EPO has been negative for 21 consecutive days, one cannot automatically assume that the EPO will remain predominantly negative throughout December. In fact, historical experience argues that the EPO would likely go positive by mid-December +/- one week. The longest stretch during which the EPO remained negative that commenced in November was 45 days. The second longest stretch was 33 consecutive days (2 occasions). The third longest stretch was 32 consecutive days.

 

With the AO likely to remain predominantly positive, that raises the question as to what the outcome might be should the EPO flip to positive.

 

Below are the composite charts for all cases December 16-31, 1981-2010 when the EPO ranged between -3 and -1 and the AO between +1 and +3 (EPO-/AO+) and when the EPO ranged between +1 and +3 and the AO between +1 and +3 (EPO+/AO+).

 

 

 

The composite anomalies reflect all dates, but there is some variability. If one takes a look at the four most recent years during which the EPO-/AO+ conditions were predominantly met, one finds a lot of variability.

 

 

If, however, one looks at the four most recent years during which the EPO+/AO+ criteria were predominantly met, one finds less variability.

 

 

In sum, should the EPO flip to positive and then remain predominantly positive for much or all of the second half of December, a much milder pattern could set in. For now, the ensembles are not yet suggesting such an outcome. However, historical experience argues that it is something that has to be considered and that it probably is more likely than not.

[Jonger]

So +EPO and +AO is just about as big of a disaster as possible.

 

Thanks for the helpful information Don.

 

What does a +EPO and a -AO bring?

[donsutherland1]

So +EPO and +AO is just about as big of a disaster as possible.

 

Thanks for the helpful information Don.

 

What does a +EPO and a -AO bring?

 

Hopefully, when the EPO goes positive, it will only be for a brief time.

 

As for EPO+/AO-, the composite is warm nationwide, but there is variability. December 16-31, 1995 featured cold in the eastern 1/2 of the CONUS, including very cold conditions around the Great Lakes. In contrast, December 16-31, 2002 was very close to the composite.

 

[QcSevereWx]

We are right now in the most negative state of the EPO for the 2013-2014 winter.

2013 10 25 -100.402013 10 26 -163.842013 10 27 -170.982013 10 28 -101.832013 10 29  -20.892013 10 30   47.692013 10 31   55.422013 11 01    4.102013 11 02  -14.102013 11 03   -5.722013 11 04    8.272013 11 05   -1.182013 11 06   -9.092013 11 07   17.862013 11 08    3.682013 11 09  -77.792013 11 10 -110.792013 11 11 -174.312013 11 12 -234.392013 11 13 -254.582013 11 14 -248.572013 11 15 -216.572013 11 16 -185.432013 11 17 -136.342013 11 18  -95.952013 11 19  -58.372013 11 20  -44.782013 11 21  -70.822013 11 22  -62.682013 11 23  -51.762013 11 24 -125.672013 11 25 -178.142013 11 26 -211.102013 11 27 -221.95

can't last much longer, but who knows. We can be in a once in a hundred year event.

[The_Global_Warmer]

With the OPI so far looking good.  We better hope the EPO pulls it off or...

 

 

Sadly it's not winter for 2 more days. 

 

And technically 23 more. 

 

This negative EPO has been completely wasted.

[Ed Lizard]

Red Tagger  'Its Always Sunny' added this link to a Met 101 thread.  I'd not heard of the EPO before this season... 

 

http://www.crh.noaa.gov/dtx/winter_2002-03_outlook_review.php#eponao

[Ginx snewx]

We are right now in the most negative state of the EPO for the 2013-2014 winter.

2013 10 25 -100.402013 10 26 -163.842013 10 27 -170.982013 10 28 -101.832013 10 29  -20.892013 10 30   47.692013 10 31   55.422013 11 01    4.102013 11 02  -14.102013 11 03   -5.722013 11 04    8.272013 11 05   -1.182013 11 06   -9.092013 11 07   17.862013 11 08    3.682013 11 09  -77.792013 11 10 -110.792013 11 11 -174.312013 11 12 -234.392013 11 13 -254.582013 11 14 -248.572013 11 15 -216.572013 11 16 -185.432013 11 17 -136.342013 11 18  -95.952013 11 19  -58.372013 11 20  -44.782013 11 21  -70.822013 11 22  -62.682013 11 23  -51.762013 11 24 -125.672013 11 25 -178.142013 11 26 -211.102013 11 27 -221.95

can't last much longer, but who knows. We can be in a once

in a hundred year event.

Or we can have a 1955/56 type EPO where transient positives show up. Not unusual at all for transient features to appear and then the pattern reverts. The problem with using monthly correlations is individual days are blended . 

1955 10 28   -0.94
1955 10 29  -83.09
1955 10 30 -160.96
1955 10 31 -188.83
1955 11 01 -161.53
1955 11 02 -132.56
1955 11 03 -117.06
1955 11 04  -68.10
1955 11 05  -51.70
1955 11 06  -75.02
1955 11 07  -48.53
1955 11 08  -12.08
1955 11 09  -43.77
1955 11 10  -59.98
1955 11 11  -80.08
1955 11 12  -89.36
1955 11 13 -120.19
1955 11 14  -88.05
1955 11 15  -17.35
1955 11 16   -4.27
1955 11 17  -12.21
1955 11 18  -29.88
1955 11 19  -44.85
1955 11 20  -39.71
1955 11 21  -10.33
1955 11 22  -22.73
1955 11 23  -33.20
1955 11 24   -1.14
1955 11 25  -16.10
1955 11 26  -81.21
1955 11 27 -124.27
1955 11 28 -115.70
1955 11 29  -66.97
1955 11 30  -50.58
1955 12 01  -72.88
1955 12 02  -80.77
1955 12 03  -38.86
1955 12 04   -8.09
1955 12 05   31.45
1955 12 06   64.19
1955 12 07   47.59
1955 12 08   41.64
1955 12 09   50.92
1955 12 10   23.60
1955 12 11    5.73
1955 12 12  -31.42
1955 12 13 -160.88
1955 12 14 -293.89
1955 12 15 -348.93
1955 12 16 -355.80
1955 12 17 -329.59
1955 12 18 -321.42
1955 12 19 -318.69
1955 12 20 -312.11
1955 12 21 -336.00
1955 12 22 -261.75
1955 12 23 -152.72
1955 12 24 -104.66
1955 12 25  -83.11
1955 12 26  -23.93
1955 12 27    9.66
1955 12 28  -18.90
1955 12 29  -63.75
1955 12 30  -63.52
1955 12 31  -17.07
1956 01 01  -35.88
1956 01 02  -89.85
1956 01 03 -108.18
1956 01 04  -99.98
1956 01 05 -108.79
1956 01 06 -120.59
1956 01 07  -98.63
1956 01 08 -137.90
1956 01 09 -202.07
1956 01 10 -266.26
1956 01 11 -279.88
1956 01 12 -280.25
1956 01 13 -284.72
1956 01 14 -293.05
1956 01 15 -286.40
1956 01 16 -218.81
1956 01 17 -127.40
1956 01 18  -68.86
1956 01 19   -0.14
1956 01 20   67.78
1956 01 21   92.13
1956 01 22  126.25
1956 01 23  115.43
1956 01 24   46.11
1956 01 25  -17.43
1956 01 26  -51.34
1956 01 27  -10.97
1956 01 28    9.35
1956 01 29  -26.94
1956 01 30  -89.65
1956 01 31 -147.36
1956 02 01 -137.97
1956 02 02  -83.02
1956 02 03  -57.76
1956 02 04   -8.87
1956 02 05    0.43
1956 02 06  -33.84
1956 02 07  -34.47
1956 02 08   10.70
1956 02 09  -24.37
1956 02 10  -55.65
1956 02 11  -42.11
1956 02 12  -23.88
1956 02 13  -24.75
1956 02 14  -24.00
1956 02 15  -10.25
1956 02 16   26.16
1956 02 17    0.80
1956 02 18  -43.35
1956 02 19  -79.24
1956 02 20 -107.57
1956 02 21 -133.62
1956 02 22  -93.11
1956 02 23  -19.89

[donsutherland1]

December 2013 Idea (Revised):

 

It is rare that I wind up revising my monthly thoughts, but in this case it is necessary given the consistency of the data and now clear picture with respect to the Arctic Oscillation.

 

Hence, my initial December idea (#131) is not likely to verify. The partial teleconnection cases and exceptional consistency in which 2008 was highlighted as the leading teleconnection analog for December since that time argue strongly for a revision.

 

The final December map based on those partial cases is as follows:

 

 

 

 

Those anomalies likey reasonably represent the outcome. The notable cold coming to the Northern Plains and Pacific Northwest for the December 3-10 period should produce cold anomalies that won't be erased. At the same time, some pieces of the cold air mass will likely bleed eastward with perhaps a strong cold shot toward mid-month. But then, as the EPO likely rises, what has been the beginning of the end of the transitional period leading to winter will likely yield to more persistent mild weather in parts of the CONUS.

 

In sum, Canada, the Northern and Central Plains and Pacific Northwest are likely to be colder than normal for December. The Southeast into the Middle Atlantic region will likely be warmer than normal. New England could be near normal with some below normal anomalies in northern New England. The Southwest and Southern Plains should also be warmer than normal.

[usedtobe]

December 2013 Idea (Revised):

 

It is rare that I wind up revising my monthly thoughts, but in this case it is necessary given the consistency of the data and now clear picture with respect to the Arctic Oscillation.

 

Hence, my initial December idea (#131) is not likely to verify. The partial teleconnection cases and exceptional consistency in which 2008 was highlighted as the leading teleconnection analog for December since that time argue strongly for a revision.

 

The final December map based on those partial cases is as follows:

 

 

 

 

Those anomalies likey reasonably represent the outcome. The notable cold coming to the Northern Plains and Pacific Northwest for the December 3-10 period should produce cold anomalies that won't be erased. At the same time, some pieces of the cold air mass will likely bleed eastward with perhaps a strong cold shot toward mid-month. But then, as the EPO likely rises, what has been the beginning of the end of the transitional period leading to winter will likely yield to more persistent mild weather in parts of the CONUS.

 

In sum, Canada, the Northern and Central Plains and Pacific Northwest are likely to be colder than normal for December. The Southeast into the Middle Atlantic region will likely be warmer than normal. New England could be near normal with some below normal anomalies in northern New England. The Southwest and Southern Plains should also be warmer than normal.

Don,  I don't know whether you're right or wrong but I like that you are willing to modify your forecast and think you always do a good job presenting the data.   LIke you, I am worried about the EPO going positive as the AK ridge retrogrades.  I think that is still somewhat up in the air though it does look like the ens means are heading that way. 

[Srain]

Don and Wes, we here in the Central/Western Region are carefully monitoring the developments that we are seeing in the Medium/Longer Range depicted by the various ensembles. The latest Day 11+ composites tend to raise an eyebrow as we tied the earliest snow fall in SE Texas dating back to 1944 with a surprise snow event on the night of December 10, 2008. That earliest snowfall record for Houston was broken the next December in 2009. It will be interesting to monitor the guidance over the next several days to see how this pattern develops across the Western 2/3rds of North America.

 

 

[Amped]

GFS VS EURO with the block over  south of Iceland

 

[JamieOber]

Don,

 

That was a fairly close to normal Dec for temps in northern Appalachians with several ice events. This includes a significant ice storm on Christmas Eve. Interesting that such storms are showing up on the models.

[donsutherland1]

Don,  I don't know whether you're right or wrong but I like that you are willing to modify your forecast and think you always do a good job presenting the data.   LIke you, I am worried about the EPO going positive as the AK ridge retrogrades.  I think that is still somewhat up in the air though it does look like the ens means are heading that way. 

Thanks Wes. Monthly ideas are sort of like throwing a long bomb. The risk of error is always great. I don't think there's any merit in standing with an idea when the data seems to have turned overwhelmingly unsupportive. In fact, doing so would probably be more foolish than anything, as the idea would depend strictly on the hope that something changes rather than any concrete premise.

 

Even as the EPO is difficult to forecast and it is tempting to go with persistence, the idea that the EPO- will be approaching historical benchmarks by mid-December argues for some relaxation/retrogression of the Alaska ridge. That could be all that's needed for the AO+ to exert a larger influence than it has to date.

 

Also, the magnitude of cold likely to impact the Pacific Northwest and Northern Plains in the near- and medium-term tends to support the composite maps that come up with the recent data. Unfortunately, it also strengthens my overall winter idea of a milder winter in much of the East.

[donsutherland1]

Don and Wes, we here in the Central/Western Region are carefully monitoring the developments that we are seeing in the Medium/Longer Range depicted by the various ensembles. The latest Day 11+ composites tend to raise an eyebrow as we tied the earliest snow fall in SE Texas dating back to 1944 with a surprise snow event on the night of December 10, 2008. That earliest snowfall record for Houston was broken the next December in 2009. It will be interesting to monitor the guidance over the next several days to see how this pattern develops across the Western 2/3rds of North America.

 

11292013 Gay 11+ Composite Anaologs 814analog_off.gif

 

11302013 06Z GEFS gfs-ens_T2ma_namer_37.png

 

For the West, the upcoming pattern evolution is quite exciting. There are certainly a number of really appetizing dates in the mix.

 

Interestingly enough, the leading date on both the 8-day and 11-day composite analogs is from December 2008.