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Long Range Pattern Drivers & Evolution Thread


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The 33andFive...Day Outlook -- Monitor here

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Hey Tom. I did not favor a warm Nov or Dec. I thought the effects of the NPO-induced cold would first start out West in December; and when the NAO eventually relaxes for a time, we would get some warm

The shifted west tropical forcing from traditional Niño, or even Modoki, has created a stronger Subtropical High in western Pacific / Hadley. This has promoted the return of the "Kamchatka Low" which

Back on December 26, composite date for MJO passage at high amplitude in Phase 4 and historic data associated with strong AO+ patterns in combination with a positive EPO implied that the GEFS was miss

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Larry Cosgrove still holding fairly strong that there won't be much change to a colder and possibly snowier pattern in his longer term outlook until the end of January. Although he did say there could be a colder period early in the new month. All is not lost but his reason for keeping the east coast on the warmer side is the ridging over Cuba and Hispaniola. Also when the pattern does become more favorable for snow in late January he once again mentions the snow chances will increase between the Continental Divide and the Appalachian Mountains but did not mention the east coast. So take it for what it is.

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11 minutes ago, Rtd208 said:

Larry Cosgrove still holding fairly strong that there won't be much change to a colder and possibly snowier pattern in his longer term outlook until the end of January. Although he did say there could be a colder period early in the new month. All is not lost but his reason for keeping the east coast on the warmer side is the ridging over Cuba and Hispaniola. Also when the pattern does become more favorable for snow in late January he once again mentions the snow chances will increase between the Continental Divide and the Appalachian Mountains but did not mention the east coast. So take it for what it is.

I tend to agree that any sustained pattern change (if any) will happen after mid month.  There is a window for something 1/5-1/10 so hopefully we cash in on that.

 

The EPS have consistently been showing the dreaded SE ridge day 12+.  That can sometimes work if you’re on the right side of the gradient but unfortunately we’d need some Atlantic help that is not currently modeled to help suppress heights in the East.  The long range is so volatile so no point in getting worked up on any particular run past day 10.  Hopefully the 5th-10th works out.

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Here's why I have a hard time believing this ridge in the east isn't transient.

Here was the old day 10 to 15.

ecmwf-ensemble-avg-namer-t850_anom_5day-8441600.png.1d3ccf6904b758a07fd2ebe2bd89b62d-1.png.bab9e2f8e2749be05ea5daf90536602c.png

 

Notice the TPV is over Alaska and the Positive is really sitting well SW of the Aleutians.

And still it corrected to this, 

ecmwf-ensemble-avg-namer-t850_anom_5day-8441600.png.e47d1bfd9aad3a4a34261fe33303f693.png

 

And then 2 days later we are here, ecmwf-ensemble-avg-namer-t850_anom_5day-8657600.png.a581f423e3f32d5f6e24afaeaa934d23.png

 

So when I see this in the new day 10 to 15 , 

ecmwf-ensemble-avg-namer-t850_anom_5day-8916800.png.eef2f8927043d0a51d023b3703712407.png

 

The ridge is displaced much further east,  you have a negative EPO and the TPV is sitting over the Canadian prairies so with that EPO the mean flow should be SE.

 

 

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2 minutes ago, 33andrain said:

CFS not backing down on cold look even in its shorter long range. 

It has been keying in on 1/8 for a big change to cold weather past couple runs. Shows a highly anomalous ridge south of Alaska allowing for what appears to be cross polar flow. *400hr forecast caveats applyCapture.PNG.4f6c5bbd2ca99558dda6a42c3e03dec5.PNG

 

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The long-modeled sharp increase in the Arctic Oscillation (AO) is now underway. Over the past 2 days, the AO has risen 2.5 sigma. Over the past 3 days, it has risen more than 2.8 sigma. Since 1950, there were seven prior years when the AO rose 2.5 sigma or more over a two-day period during December 20-31. During the 2010s, there has been a cluster of such events: 2014, 2015, 2016, and now 2019. Four of the prior cases saw monthly snowfall in excess of 10" in New York City during the following January: 1963-64, 1977-78, 2014-15, and 2015-16. Two had less than 4" snowfall in January: 1967-68 and 1972-73.

 

Widespread 0.50"-1.50" precipitation is likely in the region tonight into tomorrow. As a result, Allentown will very likely reach 60" precipitation for a record second consecutive year and Scranton could reach 50" for a record second consecutive year. 2019 will also rank among the 30 wettest years on record for New York City.

 

Through December 28, monthly anomalies for select cities were:

 

Baltimore: +2.0°, Boston: +1.6°, Islip: +0.6°, New York City: +0.2°, Newark: +0.3°, Philadelphia: +0.5°, and Washington, DC: +1.2°.

 

A week ago, those anomalies were:

 

Baltimore: +0.3°, Boston: -0.8°, Islip: -1.4°, New York City: -2.7°, Newark: -2.1°, Philadelphia: -1.3°, and Washington, DC: -0.4°.

 

A short-duration cold shot is possible late in the first week of January into the second week of January. Nevertheless, there is a growing risk that New York City and Newark could have an average temperature near or even above 40° for the first week of January. A tendency for ridging could develop during the latter part of the second week of the month. The predominant state of the EPO will likely be crucial to the persistence of any colder patterns.

 

Based on the forecast strongly positive AO to start January, the probability of a significant (6" or greater snowstorm) for the major cities of the Middle Atlantic region during the first week of January is low. Since 1950, the biggest snowfall for that region when the AO was +2.000 or above during the January 1-15 period occurred during January 14-15, 1954 when Philadelphia received 3.0" snow and New York City picked up 2.0". Boston has had numerous 6" or greater snowstorms during such cases, including one 10" or greater snowstorm. Therefore, the risk of significant snow would likely be greatest over New England assuming this relationship holds (no significant offsetting variables).

 

Some of the newer AO forecasts keep the AO at +2.000 or above through January 10. If so, that development could adversely impact Mid-Atlantic significant snowfall prospects beyond the first week of January.

 

Despite the development of a sustained colder than normal temperature regime, Utqiagvik (formerly Barrow) is nearing the end of its warmest year on record. 2019 will likely conclude with a mean temperature of 20.9°. The existing record is 18.9°, which was set in 2016. Currently, 2017 ranks as the second warmest year and 2018 ranks as the fourth warmest year.

 

The ENSO Region 1+2 anomaly was +0.4°C and the Region 3.4 anomaly was +0.6°C for the week centered around December 18. For the past six weeks, the ENSO Region 1+2 anomaly has averaged +0.12°C and the ENSO Region 3.4 anomaly has averaged +0.56°C. The remainder of winter 2019-2020 will likely feature neutral-warm to weak El Niño conditions.

 

The SOI was -0.94 today.

 

Today, the preliminary Arctic Oscillation (AO) figure was +0.120.

 

No significant stratospheric warming event appears likely through January 7, but warming will likely develop in the upper stratosphere and approach or reach 5 mb toward the end of the first week of January. Wave 2 activity will remain relatively muted at 30 mb through most of the first week of January, but a moderate Wave 2 hit could occur at or above 10 mb leading to the upper stratospheric warming. Overall, most of the stratosphere is forecast to remain cold through the first week of January on the EPS. However, the upper stratospheric warming will need to be watched for downward propagation.

 

On December 28, the MJO was in Phase 7 at an amplitude of 1.233 (RMM). The December 27-adjusted amplitude was 1.511.

 

Since 1974, there were five cases when the MJO was in Phase 6 at an amplitude of 1.500 or above during the December 20-31 period, as has been the case this year. The temperature anomalies were closely tied to how much time the MJO spent in Phase 8 during that timeframe. The mean temperature for cases with more than 5 such days was 29.0° in New York City. The mean temperature for those with 5 or fewer such days was 36.1°. The overall 1981-2019 mean temperature for January 1-15 is 33.8°.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied >99% probability that December will wind up warmer than normal in New York City with a monthly mean temperature near 38.5°.

 

At present, a warmer than normal January appears likely in the region.

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19 minutes ago, Snowy Hibbo said:

I don’t really see anything exciting.

 

There is probably something in there during that 6th-9th Jan period. 
 

Then you get a -EAMT > Aleutian ridging > Western troughing > Eastern ridging for a  week after that.

 

The pattern is up and down, some threats here and there, but it’s largely more of the same, except maybe for that 6th-9th period.

 

The problem is that there’s still IOD forcing, and there’s also some tropical forcing in the MJO domain that may be more conducive to Eastern cold. So you have two competing signals.

 

We have GWO Phase 5, but that will head to Phase 8 in the next week, and then go for another orbit in the neutral/negative phases in the first two weeks of January. This will help make the 6th-9th a reality, but then force Aleutian ridging on a synoptic scale to make for a poor pattern. 
 

The stratosphere is pretty neutral, and the best chances of a SSW are further down the road.

 

Then you have to wait for the next orbit of the GWO probably later in January and early February.

As I’ve said previously, the base state is going to change slowly, it’s not going to flip all the sudden.

 

Appreciate you sharing your thoughts Zac. 

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Sounds to me like the January 5th-9th potential "could" be an appetizer to what "may" happen later next month and into February. IF things work out then we "could" have a 4-6 week period with cold temps and multiple chances for wintry weather which I think would be OK with most on here. It appears our streak of another backloaded winter may continue with this one being a bit earlier then the last couple of years. Obviously the verdict is still out on what will happen later next month.

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