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Met Winter 20-21: Pattern Drivers & Evolution


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A relatively quiet weather pattern remains in place. The dry weather could last through much of this week before a storm impacts the region late Friday or Saturday.

 

The first 15 days of January are well on track toward finishing generally warmer than normal across the northeastern United States, Quebec, and much of eastern Canada overall.

During the second half of January, there will be some potential for snow events in the Middle Atlantic and southern New England regions. Afterward, the evolution of the AO will determine whether such potential continues into February. Uncertainty about the long-range has increased. There had been emerging ensemble guidance showing that the AO could go positive in the closing week of January, but more recent guidance shows a continuation of Arctic blocking.

 

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.1°C for the week centered around December 30. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.77°C and the ENSO Region 3.4 anomaly has averaged -1.07°C. La Niña conditions will likely prevail at least through the winter.

 

The SOI was +23.79 today.

 

Today, the preliminary Arctic Oscillation (AO) figure was -0.728.

 

On January 12 the MJO was in Phase 3 at an amplitude of 1.259 (RMM). The January 11-adjusted amplitude was 1.242.

 

Following a significant stratospheric warming event, the stratosphere is now cooling. The mean zonal winds have reversed at 1 mb and 10 mb. They could still reverse at 30 mb. In the wake of this warming event, the polar vortex will likely split. The dominant piece will, as is typical with such events, migrate to Eurasia.

 

The significant December 16-17 snowstorm during what has been a blocky December suggests that seasonal snowfall prospects have increased especially from north of Philadelphia into southern New England. At New York City, there is a high probability based on historic cases that an additional 20" or more snow will accumulate after December. Were blocking to disappear, snowfall prospects would diminish. Blocking appears likely to continue into at least the last week of January.

 

Based on sensitivity analysis applied to the latest guidance, there is an implied 84% probability that New York City will have a warmer than normal January. January will likely finish with a mean temperature near 35.7°.

 

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While there's reasonable agreement on a -AO and -NAO persisting into early January, there is some uncertainty WRT whether or not the Pacific side offers any help or not. The EPS develops a +EPO into e

I'm starting to get a little more excited for early-mid December. It looks like the Pacific jet will retract significantly, which is the real reason for the retrograding Alaskan LP. Upper level diverg

I think that we are going to see a pretty impeccable 500mb pattern after January 10th.    The -NAO originally forced by wave breaking (which is occurring in the very near future) will become

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On 1/11/2021 at 3:16 PM, PB GFI said:

 

I like how the POS gets squeezed back over the AO domain, your mean air flow comes out of Siberia and now you`re connecting the trough to the one E of Hawaii here. 

I would like that to dive off more, so I get a transient PNA spike.

The teleconnection pressure differences don`t see that yet. 

 

But that`s a beautiful connection into Europe and should slow some stuff down. 

 

 

1611662400-TIo4okJYto0.png

 

 

That SE ride is retrograding as well and that would your PNA if that W piece continues to dive off the WC 

 

image.png.683e5d92622ced28007704c9ac9cfa4a.png

 

image.png.7360c6a6442f48b7c6a9e7a12f79c82a.png

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So we obviously want to keep that negative from centering over Anchorage again.

The good news is it didn't dive into the SW.

 

But the models have been you showing the continuous retrogression in the means the height field has moved E to W.

 

Screenshot_20210114-033424_Chrome.jpg.fd05019294a0ad5356ef137d24fa133f.jpg

 

The once SE ridge is now over the 4 corners and the negative is leaking off the W/C and is already interacting with the trough NE of Hawaii

It's allowing the negative to stay centered just off the EC and leaving the trough in the NE.

But look at how stout that block is 15 days out, that's such a strong signal. 

 

So where " could this go "  when you zoom in this helps a bit.

 

Screenshot_20210114-033527_Chrome.jpg.0d787bdd183fd78834c23786a528ca1d.jpg

 

The trough axis is already leaning back off the WC and there are actual height rises all the way into W Canada.

 

So the goal would be to connect the PNA with the block if you like cold.

 

 

 

 

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6 minutes ago, Snowy Hibbo said:

MHO. Just begging the question that the Pacific wasn’t as good as I thought it would be this month, got sucked into the hype train I guess :) 

 

Yep , there was a lot of hype.

 

Latest NAM states look to go positive. Vortex also looking to get better organized late month on stratobserve. 

 

 

 

 

gfs_nh-namindex_20210113.png

 

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10 minutes ago, OceanSnow said:

 

Yep , there was a lot of hype.

 

Latest NAM states look to go positive. Vortex also looking to get better organized late month on stratobserve. 

 

 

 

 

gfs_nh-namindex_20210113.png

 

 

If that plot ends up being true, then it's lights out for the rest of winter.

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7 minutes ago, OceanSnow said:

 

Yep , there was a lot of hype.

 

Latest NAM states look to go positive. Vortex also looking to get better organized late month on stratobserve. 

 

 

 

 

gfs_nh-namindex_20210113.png

 

The start of February could be ugly if we get another +EAMT extension with unfavorable mjo. Will be important to keep blocking around for February. Perhaps the pac improves towards mid February if the mjo goes into p8-1-2 

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6 minutes ago, Jake302 said:

 

If that plot ends up being true, then it's lights out for the rest of winter.

 

 

A rather dramatic change the last couple days in that NAM plot. Going towards the ERA5 mean in the GEFS 35 day run.  

 

Still too early to make assumptions.  Also, the - AO and - NAO have failed to deliver a SECS to the Mid Atlantic once they set in , which may indicate at this time the Pac is the driver.  

  Ensemble plume

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In actuality it's the warmer ideas in the east on the EPS that are being  scaling back.

Here was the old run

 

Screenshot_20210114-064940_Chrome.jpg.bf268876970479c4cf44a7514523548b.jpg

 

Here is the new run for the same time. 

 

Screenshot_20210114-065105_Chrome.jpg.dd8548d3054790b05bb6caf1331e8a4a.jpg

 

The coldest  anomalies were never forecast before the 20th and that looks on target. 

 

You can clearly see below how the 7 day EPS continues to cool

 

As I posted above here is the 22-29 from a warm biased LR model.  

 

 

Mid Jan to Mid Feb still looks good and it looks to start here 

 

 

image.png.db55a035b522b7b83c94b6324cef81ae.png

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17 minutes ago, OceanSnow said:

 

 

A rather dramatic change the last couple days in that NAM plot. Going towards the ERA5 mean in the GEFS 35 day run.  

 

Still too early to make assumptions.  Also, the - AO and - NAO have failed to deliver a SECS to the Mid Atlantic once they set in , which may indicate at this time the Pac is the driver.  

  Ensemble plume

Cfs is definitely a better look. The vortex will recover just need it to stay normal or below 

08894891-508E-4F49-AF73-2DC5B85A6B52.png

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If the Euro is right and you're blocking for another 45 days and you get into February with shortening wavelengths and you get a lucky rotation into 8 and 1 then you will extend what really is just beginning to take shape.

 

I would not can winter off 1 plot.

 

The SSW already took place and it's reversal doesn't mean its effects are gone in a week. 

The damage is done. 

 

I would take a measured approach and look for the cold to seed the pattern 1st during the actual forecast.

 

If it was suppose to BN after the 20th and the models are now showing that then I see no reason to worry about what comes after.

 

 

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25 minutes ago, Allsnow said:

The start of February could be ugly if we get another +EAMT extension with unfavorable mjo. Will be important to keep blocking around for February. Perhaps the pac improves towards mid February if the mjo goes into p8-1-2 

Frictional Torque is positive, so a jet extension in the Pacific is possible. 
Doubt the MJO is going to do that for a while.

 

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5 minutes ago, Snowy Hibbo said:

Frictional Torque is positive, so a jet extension in the Pacific is possible. 
Doubt the MJO is going to do that for a while.

 

Agree. I don’t see any favorable phases for a while. The current wave will gain strength in the Niña phases. My hope is it’s strong enough to get into 8-1-2 with a weakening Niña. But at that point it’s the end of February and who really cares lol.

 

I agree, we need to capitalize on the blocking sooner then later. My feeling is we get something around 25/26th and then the pattern breaks down 

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2 minutes ago, Allsnow said:

Agree. I don’t see any favorable phases for a while. The current wave will gain strength in the Niña phases. My hope is it’s strong enough to get into 8-1-2 with a weakening Niña. But at that point it’s the end of February and who really cares lol.

 

I agree, we need to capitalize on the blocking sooner then later. My feeling is we get something around 25/26th and then the pattern breaks down 

 

Paul has been really good with this. Basically I would not hold out any hope on a coherent favorable MJO signal for the East.  However cold may slide East in time. Certainly not severe cold by any means. But, hopefully cold enough for a window near the end of the month.     

 

 

 

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9 minutes ago, Allsnow said:

Agree. I don’t see any favorable phases for a while. The current wave will gain strength in the Niña phases. My hope is it’s strong enough to get into 8-1-2 with a weakening Niña. But at that point it’s the end of February and who really cares lol.

 

I agree, we need to capitalize on the blocking sooner then later. My feeling is we get something around 25/26th and then the pattern breaks down 

 

The cycling though the evolution of the may have implications for March 

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5 minutes ago, OceanSnow said:

 

Paul has been really good with this. Basically I would not hold out any hope on a coherent favorable MJO signal for the East.  However cold may slide East in time. Certainly not severe cold by any means. But, hopefully cold enough for a window near the end of the month.     

 

 

 

Yeah, I believe when the -epo pukes we will see some cold come our way. It will get trapped under the block once it slips East. Artic cold from ssw? That will dump only the west with the -pna

 

The ensembles are showing a small ridge towards the end of the month out west. Not enough to overcome the trough but enough to give us a chance at a snowstorm 

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1 minute ago, OceanSnow said:

 

The cycling though the evolution of the pattern, AO and Pac, etc., may deliver what DT  alluded to in his seasonal forecast and update, that the potential is there for March in some degree. 

 

 

It’s funny you say that, the chart I posted yesterday with blocking lingering into March had the best look out west lol

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