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Met Winter 20-21: Pattern Drivers & Evolution


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Very interesting thread, explains what we are seeing with the stratosphere and PV as well as the evolution of the blocking over Greenland. Lots of interesting stuff to watch going forward, even if we don't get any more storms. 

 

 

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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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35 minutes ago, Oglem said:

Very interesting thread, explains what we are seeing with the stratosphere and PV as well as the evolution of the blocking over Greenland. Lots of interesting stuff to watch going forward, even if we don't get any more storms. 

 

 

Well, if we do have any more shots of snow, it will have to be after mid-March from the looks of the pattern.

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Anyone care to share their thoughts on the developing spring ahead of us?  Cold, warm, average, stormy?  What are the pattern drivers?

 

Not sure about the rest of you knuckleheads, but once the last snowflakes of the season stop flying, I'm ready for it to get warm.

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1 minute ago, Lisnowlover said:

Anyone care to share their thoughts on the developing spring ahead of us?  Cold, warm, average, stormy?  What are the pattern drivers?

 

Not sure about the rest of you knuckleheads, but once the last snowflakes of the season stop flying, I'm ready for it to get warm.

I don't usually do spring forecasts, because it isn't very consequential, but if I had to guess, it's mostly AOB normal until about mid-may, then switches abruptly to much above.

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A cold air mass is overspreading the region. Tomorrow will be fair but unseasonably cold. Moderation will quickly follow.

 

Overall, the first week of March will see variable temperatures, even as the week will very likely average cooler than normal. Another short but sharp cold shot is possible toward the end of the first week of March. Afterward, the ensembles are in good agreement that there will be a warming trend. The 3/1 12z EPS forecasts 500 mb height anomalies that are reasonably similar to those that prevailed during March 9-15, 2020 at 216 hours. That period saw much above normal temperatures in the Middle Atlantic and New England areas. Therefore, the potential exists that parts of the region could see their warmest temperatures so far during the second week of March.

 

Statistical guidance based on the state of the ENSO and forecast teleconnections implies that the first half of March could wind up generally 1°-3° above normal in the Middle Atlantic and southern New England regions. The latest dynamical guidance is suggests temperature anomalies toward the bottom of that range for the first half of March.

 

The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around February 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.60°C and the ENSO Region 3.4 anomaly has averaged -0.80°C. La Niña conditions will likely prevail at least through most of March.

 

The SOI was -8.47 today.

 

The preliminary Arctic Oscillation (AO) figure was +1.356 today.

 

On February 28 the MJO was in Phase 6 at an amplitude of 0.886 (RMM). The February 27-adjusted amplitude was 0.990.

 

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. Since January 1, New York City has picked up 28.1" snow.

 

Winters that saw December receive 10" or more snow, less than 10" in January, and then 10" or more in February in New York City, saw measurable snowfall in March or April in 83% of cases. Winter 2009-2010 was the exception where only a trace of snow was recorded. This group of winters saw 6" or more snow during the March-April period in 50% of the cases. All said, it is more likely than not that there will be measurable snowfall after February.  

 

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8 hours ago, Lisnowlover said:

Anyone care to share their thoughts on the developing spring ahead of us?  Cold, warm, average, stormy?  What are the pattern drivers?

 

Not sure about the rest of you knuckleheads, but once the last snowflakes of the season stop flying, I'm ready for it to get warm.

I would not  surprised to see a few cold days the first two weeks of April...a majority of analogs I looked at did have one last gasp before it really got warm to stay...as we saw last year it could get cold in May with snow...

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14 hours ago, uncle w said:

I would not  surprised to see a few cold days the first two weeks of April...a majority of analogs I looked at did have one last gasp before it really got warm to stay...as we saw last year it could get cold in May with snow...


West Based La Niña should be in full effect over Strat as the driver between now and around ~March 15th/20th. 
 

I would expect to see a few days of mid/uppers 40s and then a quick cool shot til the 20th. After that, i am becoming more convinced we begin to ramp up temp wise and that SE ridge expands due to La Niña re-emerging as the driver. Would not be shocked if we get a mid 60 Last week March /first week of April.

 

would also expect severe storms and flooding events around then too 

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The Arctic Oscillation (AO) is forecast to rise sharply over the next 7-10 days. It will very likely peak at or above +3.000 and several ensemble members suggest that it could top out at +4.000 or above. This outcome will help bring the warmest air so far this season into the Middle Atlantic and southern New England areas. Temperatures will likely reach the 60s in New York City during the height of the warmth. Philadelphia could see the temperature approach or even reach 70° if some of the guidance is correct.

 

This does not mean that New York City or Philadelphia have seen their last snowfall.  Since 1950, there have been three cases where the AO peaked at +4.000 or above during the first half of March. All of those cases subsequently saw additional measurable snow in both cities.

 

1956:
Maximum AO: +4.692, March 2
March 12-24: 21.1" snow in New York City (snowiest March 12-24 period on record)
March 12-24: 10.9" snow in Philadelphia (3rd snowiest March 12-24 period on record)
April 8: A storm brought measurable snow to New York City

 

Note: The snowy March period coincided with a return of AO blocking, which persisted through late April.

 

1990:
Maximum AO: +4.638, March 6
April 7: New York City: 0.6" snow; Philadelphia: 2.4” snow

 

Note: The AO never went negative again through April 7. The April 7 snowfall was largely a function of shortening wave lengths.

 

2015:
Maximum AO: +5.588, March 8
March 20-21: A storm brought measurable snow to such cities as Baltimore, Boston, New York City, Newark, and Philadelphia. New York City picked up 4.5” snow and Philadelphia received 3.9” snow.

 

Note: The snowstorm was preceded by a brief period of AO blocking.

 

The sample size is very small, so the only conclusion that is useful is that one should not write off the possibility of snowfall following the AO’s forecast peak.

 

Were the AO’s peak to occur near or after March 15, the prospect for additional measurable snowfall would be low. All four cases that saw the AO peak on or after March 15 saw no measurable snowfall following the AO’s peak. Those cases were 1968, 1978, 1986, and 2020.

 

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2 hours ago, RAllen964 said:


West Based La Niña should be in full effect over Strat as the driver between now and around ~March 15th/20th. 
 

I would expect to see a few days of mid/uppers 40s and then a quick cool shot til the 20th. After that, i am becoming more convinced we begin to ramp up temp wise and that SE ridge expands due to La Niña re-emerging as the driver. Would not be shocked if we get a mid 60 Last week March /first week of April.

 

would also expect severe storms and flooding events around then too 

the average max in March for NYC is around 70...I expect to see that by months end...Probably around mid month...

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1 hour ago, donsutherland1 said:

 

 

This does not mean that New York City or Philadelphia have seen their last snowfall.  Since 1950, there have been three cases where the AO peaked at +4.000 or above during the first half of March. All of those cases subsequently saw additional measurable snow in both cities

 

Here in the raritan valley over the last 40 years, 60% of the years have had accumulating snow in the 2nd half of March.... Averaging 2.1 inches. 20% of those years had a minimum of 5 inches of snow

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3 hours ago, RAllen964 said:


West Based La Niña should be in full effect over Strat as the driver between now and around ~March 15th/20th. 
 

I would expect to see a few days of mid/uppers 40s and then a quick cool shot til the 20th. After that, i am becoming more convinced we begin to ramp up temp wise and that SE ridge expands due to La Niña re-emerging as the driver. Would not be shocked if we get a mid 60 Last week March /first week of April.

 

would also expect severe storms and flooding events around then too 

I'm not sure if that's the case with the MJO in 8 going into 1. I would expect colder temps the 2nd half of March . Once the MJO  gets out of those phases, temps should skyrocket.

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Ol Man winter wants one more shot at winter come mid month for the Ides of March and the MJO going to Phase 8 then 1
GEFS
Long Range Discussions 21.0 - Page 14 Diagram_40days_forecast_GEFSBC_member
EURO
Long Range Discussions 21.0 - Page 14 ECMF_phase_51m_full
 
 
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1998 was going to break the record for the least amount of snow when 2-5" fell across the city from I think was a rear end storm...snow on the backside of a storm...another date in March that saw a good size snowstorm is March 22nd...some March 21st-23rd snowstorms in NYC...

3/21-22/64.....4.9"

3/21-22/67.....9.8"

3/22-23/92.....3.2"

3/21-22/98.....5.0"

3/21-22/18.....8.4"

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After a day characterized by unseasonably cold temperatures and wind chills more typical of mid-winter than early March, milder air will return for a short time. Under mainly sunny skies, temperatures will likely reach the upper 40s with some lower 50s in the northern Mid-Atlantic and southern New England areas tomorrow.

 

Overall, the first week of March will see variable temperatures, even as the week will very likely average cooler than normal. Another short but sharp cold shot is possible Friday through the weekend. Afterward, a strong warming trend should commence. Parts of the region will likely see their warmest temperatures so far during the second week of March. The 60° DT could extend into southern and perhaps even central New England during the height of the warmth. Central Park will very likely see its first 60° reading since December 25 and perhaps its highest temperatures since late November.

 

Statistical guidance based on the state of the ENSO and forecast teleconnections implies that the first half of March could wind up generally 1°-3° above normal in the Middle Atlantic and southern New England regions. The latest dynamical guidance is suggests temperature anomalies toward the bottom of that range for the first half of March.

 

The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around February 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.60°C and the ENSO Region 3.4 anomaly has averaged -0.80°C. La Niña conditions will likely prevail at least through most of March.

 

The SOI was -6.80 today. The SOI has now been negative for three consecutive days. The last time that occurred was October 25-29, 2020 when the SOI was negative for five consecutive days. This development could be an early indication that what has been a fairly stable La Niña regime throughout the winter could be moving closer to its end stages.

 

The preliminary Arctic Oscillation (AO) figure was +0.775 today.

 

On March 1 the MJO was in Phase 6 at an amplitude of 1.004 (RMM). The February 28-adjusted amplitude was 0.887 (RMM).

 

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. Since January 1, New York City has picked up 28.1" snow.

 

Winters that saw December receive 10" or more snow, less than 10" in January, and then 10" or more in February in New York City, saw measurable snowfall in March or April in 83% of cases. Winter 2009-2010 was the exception where only a trace of snow was recorded. This group of winters saw 6" or more snow during the March-April period in 50% of the cases. All said, it is more likely than not that there will be measurable snowfall after February.  

 

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1 hour ago, Snowman11 said:

A slight chance of wintry weather in the 2nd half of the month 

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I see the MJO is now making it just into 2 before it dives into the COD. Wasn't it killing it off just in 1, if not 8, just a few days ago?

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Under brilliant sunshine, temperatures soared into the 50s across most of the region today. Tomorrow will be fair but cooler.

 

Overall, the first week of March will see variable temperatures, even as the week will very likely average cooler than normal. Another short but sharp cold shot is possible Friday through the weekend. Afterward, a strong warming trend should commence. Parts of the region will likely see their warmest temperatures so far during the second week of March. The 60° DT could extend into southern and perhaps even central New England during the height of the warmth. Central Park will very likely see its first 60° reading since December 25 and perhaps its highest temperatures since late November.

 

Statistical guidance based on the state of the ENSO and forecast teleconnections implies that the first half of March could wind up generally 1°-3° above normal in the Middle Atlantic and southern New England regions. The latest dynamical guidance is suggests temperature anomalies toward or just below the bottom of that range for the first half of March.

 

The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around February 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.60°C and the ENSO Region 3.4 anomaly has averaged -0.80°C. La Niña conditions will likely prevail at least through most of March.

 

The SOI was -6.08 today. The SOI has now been negative for four consecutive days. The last time that occurred was October 25-29, 2020 when the SOI was negative for five consecutive days. This development could be an early indication that what has been a fairly stable La Niña regime throughout the winter could be moving closer to its end stages.

 

The preliminary Arctic Oscillation (AO) figure was -0.300 today.

 

On March 2 the MJO was in Phase 7 at an amplitude of 1.046 (RMM). The March 1-adjusted amplitude was 1.007 (RMM).

 

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. Since January 1, New York City has picked up 28.1" snow.

 

Winters that saw December receive 10" or more snow, less than 10" in January, and then 10" or more in February in New York City, saw measurable snowfall in March or April in 83% of cases. Winter 2009-2010 was the exception where only a trace of snow was recorded. This group of winters saw 6" or more snow during the March-April period in 50% of the cases. All said, it is more likely than not that there will be measurable snowfall after February.  

 

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9 hours ago, showmethesnow said:

I see the MJO is now making it just into 2 before it dives into the COD. Wasn't it killing it off just in 1, if not 8, just a few days ago?

Yes

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Cooler air is again overspreading the region. Tomorrow and Saturday will be fair but unseasonably cold.

 

Overall, the first week of March will see variable temperatures, even as the week will very likely average cooler than normal. Another short but sharp cold shot is possible Friday through the weekend. Afterward, a strong warming trend should commence. Parts of the region will likely see their warmest temperatures so far during the second week of March. The 60° DT could extend into southern and perhaps even central New England during the height of the warmth. Central Park will very likely see its first 60° reading since December 25 and perhaps its highest temperatures since late November.

 

Toward the latter part of the second week of the month, temperatures could begin to cool as the AO falls sharply from its forecast peak.

 

The ENSO Region 1+2 anomaly was -1.1°C and the Region 3.4 anomaly was -1.2°C for the week centered around February 24. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.60°C and the ENSO Region 3.4 anomaly has averaged -0.80°C. La Niña conditions will likely prevail at least through most of March.

 

The SOI was -8.47 today. The SOI has now been negative for five consecutive days. The last time that occurred was October 25-29, 2020 when the SOI was negative for five consecutive days. This development could be an early indication that what has been a fairly stable La Niña regime throughout the winter could be moving closer to its end stages.

 

The preliminary Arctic Oscillation (AO) figure was -0.957 today.

 

On March 3 the MJO was in Phase 7 at an amplitude of 0.718 (RMM). The March 2-adjusted amplitude was 1.051 (RMM).

 

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. Since January 1, New York City has picked up 28.1" snow.

 

Winters that saw December receive 10" or more snow, less than 10" in January, and then 10" or more in February in New York City, saw measurable snowfall in March or April in 83% of cases. Winter 2009-2010 was the exception where only a trace of snow was recorded. This group of winters saw 6" or more snow during the March-April period in 50% of the cases. All said, it is more likely than not that there will be measurable snowfall after February.  

 

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On 2/26/2021 at 5:06 PM, Allsnow said:

Agree. With the effects of the ssw done the mjo will be ruling the roost. I believe the second half of the month will be cold 

B08369F7-0C11-4B3C-93AE-12586576A907.png

546FC4AC-9749-413C-9B7F-F6D18AAD950C.png

Don’t really see any reason to back away from the thoughts in this post. Enjoy whatever warm temps we get next week 

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