Winter 2020-2021 Outlook

[40/70 Benchmark]

https://easternmassweather.blogspot.com/2020/11/winter-outlook-2020-2021-mixed-type-la.html

 

Here is my winter outlook, if you are looking for something to pass the time, while a team of molasses molecules counts the NV ballots.

The abridged version is linked....there are also options for more technical discussion of the telconnections if so desired.

Most wintery period looks to be December, and potentially another bout in March, but it may very well just result in a cold spring...as last season did.

[40/70 Benchmark]

Please let me know if you guys like the new format, as it seemed the other way was just too tedious and time consuming for both myself as well as the reader.

[cleetussnow]

Still reading but this is a great write up.

[40/70 Benchmark]

[dmillz25]

15 minutes ago, 40/70 Benchmark said:

I would take 11-21” inches of snow after last year’s debacle. Excellent read

[USCAPEWEATHERAF]

I am not liking the 15-25" snowfall amounts forecasted for Hyannis

[Sey-Mour Snow]

Interesting that you think average snowfall for Hartford with a torch through peak snow climo. 

[40/70 Benchmark]

7 minutes ago, Sey-Mour Snow said:

Interesting that you think average snowfall for Hartford with a torch through peak snow climo. 

Peak snow climo is such for a reason...its near the coldest time of the year, and thus positive temp anomalies are not as prohibitive to snowfall. Throw in an active first and last third, and bang....climo seasonal snowfall.

Retention is another story....well below normal.

[stadiumwave]

On 11/5/2020 at 12:25 PM, 40/70 Benchmark said:

https://easternmassweather.blogspot.com/2020/11/winter-outlook-2020-2021-mixed-type-la.html

 

Here is my winter outlook, if you are looking for something to pass the time, while a team of molasses molecules counts the NV ballots.

The abridged version is linked....there are also options for more technical discussion of the telconnections if so desired.

Most wintery period looks to be December, and potentially another bout in March, but it may very well just result in a cold spring...as last season did.

 

Great job!!

[Isotherm]

Ray - saw your comment on my thread. Just had a read of your forecast - great work and write up as per usual; well reasoned. As you noted, we are essentially harmonious on the bigger picture and overall season, but mostly differ on timing. I had initially thought early winter/Dec would be favored about a month ago, but as some of the mid autumn data emerged, it drove me toward the January-focused potential more and more. Re March, agree, lower confidence expressed here, though at this juncture I think it will be fairly hostile for the Eastern US. Here's my analogs z500 composite for March, if you're interested. Will be fascinating to see how this winter evolves, and certainly from a more local perspective, whether we can exceed snowfall totals of the past two winter seasons.

 

[JB_Wchstr]

20 minutes ago, 40/70 Benchmark said:

I probably should have gone 12/15 to 1/15 for the best stretch, but I don't think that will sink my outlook.

If we only get a month, which is generous these days, might as well be through the holidays and into the coldest part of winter. 

[RUNNAWAYICEBERG]

4 week winter, buckle up weenies. 

[JB_Wchstr]

49 minutes ago, RUNNAWAYICEBERG said:

4 week winter, buckle up weenies. 

Don’t forget step-down in, transition out and the obligatory reset.  Did you feel that chill in the air? That was it 

[leo2000]

Wall to wall to winter. Kidding of course whatever happened to those winters anyways?.

[40/70 Benchmark]

On 11/11/2020 at 11:41 AM, Isotherm said:

Ray - saw your comment on my thread. Just had a read of your forecast - great work and write up as per usual; well reasoned. As you noted, we are essentially harmonious on the bigger picture and overall season, but mostly differ on timing. I had initially thought early winter/Dec would be favored about a month ago, but as some of the mid autumn data emerged, it drove me toward the January-focused potential more and more. Re March, agree, lower confidence expressed here, though at this juncture I think it will be fairly hostile for the Eastern US. Here's my analogs z500 composite for March, if you're interested. Will be fascinating to see how this winter evolves, and certainly from a more local perspective, whether we can exceed snowfall totals of the past two winter seasons.

 

Despite losing climo, I feel like you have more margin for error with respect to scoring in an unfavorable pattern in March due to the changing wavelengths. All it takes is one well placed bowling ball....

[Go Kart Mozart]

3.4 and 4 rallying?

[40/70 Benchmark]

10 hours ago, Go Kart Mozart said:

3.4 and 4 rallying?

That was expected. I said in the outlook that the western flank shouldn't cool too much more..

[RUNNAWAYICEBERG]

On 11/11/2020 at 2:29 PM, leo2000 said:

Wall to wall to winter. Kidding of course whatever happened to those winters anyways?.

He gone. 

[Typhoon Tip]

On 11/11/2020 at 2:29 PM, leo2000 said:

Wall to wall to winter. Kidding of course whatever happened to those winters anyways?.

The Industrial Revolution 

[40/70 Benchmark]

https://easternmassweather.blogspot.com/2020/12/will-real-nao-please-stand-up.html

 Will the Real NAO Please Stand Up

January 2021 Positions to Deliver the Blow That Latter December 2020 Did Not

Generalizations: The Cardinal Sin of Sociology and Meteorology

One of the most fundamental traits inherent of all human beings is that we love to be appreciated for all of our unique and innate abilities. Indeed, to generalize any individual as part of an indistinguishable larger group is to gloss over the qualities and abilities that define us as human beings, and provide us with our own sense of identity. Suffice to say, generalizations make it exceedingly difficult if not impossible to adequately characterize any human being, or anything else for that matter. We  must treat the atmosphere the same way. Generalizations breed contempt, indifference, laziness and complacency. A generalization is an antonym of exhaustive, which is a term that should describe any forecaster worth reading. This is because in forecasting it is the aforementioned, minute idiosyncrasies that often differentiate between a mundane rainstorm and a paralyzing blizzard. Thus a forecasting approach fraught with generalizations can blind any prospective forecaster to the atmospheric nuances that are responsible for such tremendous variation in resultant sensible weather. This is the essence of why these generalizations are so inimical to making friends. Not only are those around you insulted, but they are ill prepared for the weather due to a shitty and tremendously flawed forecast that did not accurately and exhaustively assess all of the data at hand. This is a principle that Eastern Mass Weather warned against prior to the severe la nina winter of 2017-2018, as well as prior to the current season. The consensus was very mild in both instances due to a generalization of the respective la nina events, which is silly because one was east based and one mixed type. Central-based events are usually most mild and benign across the eastern US. Many of us are guilty of committing the same cardinal sin with respect to the characterization of teleconnections, and namely the NAO.

 

Much like ENSO Events, Location Crucial for Blocks

The month of December was not quite as active in terms of winter weather across the area as implied, in large part because the large Christmas event this past week was entirely rainfall across the region. The easy first guess would be because the NAO was not predominately negative, as expected, but this is not true.

 

A more exhaustive review of the data reveals why.

Latter December has been characterized by a "thumb ridge" of higher heights across the north atlantic to the south of Greenland, as opposed to a true block over Greenland.

 

Although technically registering as a negative NAO due to higher heights in the southern periphery of the NAO domain, this is not a block because it does nothing to "block" a storm from cutting inland. This was evidenced by the inland track of the Christmas low, and this same regime looks to plague the next event.

 

New Year's Storm Potential

Note that as a deep trough carves out in the center of the county later this week, we have yet to establish the block over Greenland.

 

While the initial instinct if to forecast a repeat of the Christmas storm, remember that it is important to consider each and every subtle nuance to the pattern.

 

Note that a subtle RNA signature briefly emerges:

 

 

 

Which is evidenced by the lower heights in the Pacific North West:

 

 

 

 

The lower heights in the PNW act to mute the amplification of the downstream trough due to the development of higher heights in the SE US.

 

This creates a delicate balance between how much the SW can retain its integrity, which will promote a more inland track, and how much it is attenuated by the fast flow of a compressed geopotential medium due to the fleeting SE ridge. The latter promotes a more seaward track and albeit a weaker system, a possible colder solution.

 

 

 

Whatever happens later this week, the plot then thickens by the second week of January.

Major Potential Looms Toward Mid January Due to Stratospheric Evolution

Currently, the stratosphere remains fairly weak, which creates the opportunity for cold to escape into the mid latitudes. However, that does not necessarily mean that it will escape into north America. In fact, currently the vast majority of the cold is focused in Asia.

Remember not to generalize all weakening PV episodes.

 

 

 

However there is now growing confidence that the balance of cold will begin to shift toward North America as we enter the new year.

 

 

 

 

 

 

 

 

 

 

This sets the stage for what currently looks to be a classic pattern for a major east coast snow storm during the second week of January.

 

While a true Sudden Stratospheric Warming is unlikely for reasons specified in the winter outlook, there does exist strong multi cluster support among ensemble guidance for such a a pattern to materialize.

GFS Ensemble agree with the aforementioned ECMWF mean:

 

Canadien Ensemble also concurs:

 

 

 

 

 

Should this fail to materialize, then there will not be a major east coast winter storm. While it may be overstated to a degree, which is often the case with respect to extended ensemble projections, there was some support for west-based NAO blocking during the first half of January in the analog composite.

 

 

 

 

 

 

 

Said blocking should begin to abate in latter January, potentially setting the stage for a significant late winter reprieve.

[raindancewx]

Looks like my analog blend had Boston snowfall at 19.8 inches through 12/28, compared to the 17.3 inches observed through 12/28. Will be curious to see how the season finishes. The weighting was 2007-08 (x5), 2012-13 (x2), with the others at x1. This is Boston snow totals from xmACIS through 12/28.

1995-12-28

28.2

2003-12-28

21.5

2007-12-28

26.9

2012-12-28

1.2

2019-12-28

11.5

[40/70 Benchmark]

1 hour ago, raindancewx said:

Looks like my analog blend had Boston snowfall at 19.8 inches through 12/28, compared to the 17.3 inches observed through 12/28. Will be curious to see how the season finishes. The weighting was 2007-08 (x5), 2012-13 (x2), with the others at x1. This is Boston snow totals from xmACIS through 12/28.

1995-12-28

28.2

2003-12-28

21.5

2007-12-28

26.9

2012-12-28

1.2

2019-12-28

11.5

Yea, looks on the right track....though Dec 2020 was def not as snowy as Dec 2007 across most of CNE and NNE.

[raindancewx]

I agree with that. It was never really supposed to be a carbon copy of 2007-08 though. 2012-13 is a hell of a lot warmer than 2007-08 in December in your area if my memory is right, that was one of the things I liked about it. I gave 2012 the next highest weight after 2007-08 because I never really bought the La Nina being able to keep pace with 2007-08, and I wanted a lot of super low-sea ice years with a cold ENSO. So 2012-13 fixed the sea ice and ENSO strength. 2003 and 1995 and 2019 were in there for more complicated reasons.

[40/70 Benchmark]

2 minutes ago, 40/70 Benchmark said:

I was pretty happy with the December forecast locally, but nationally that PNA really flipped the script on the forecast. For once the polar domain was not the issue.

December 2020 Verification & January 2020 Preview 

December 2020 Verification & January 2020 Preview

Well Behaved Arctic; Problematic PNA

The main premise of the December portion of the 2020-2021 Winter Outlook was the re emergence of high latitude blocking as a prominent winter feature.

 

The following is an excerpt from the actual Winter Outlook released in early November.

 

"There has only been one winter (DM) month, March 2018, that has averaged a negative NAO since February and March 2013. It is postulated that there is a high likelihood that we will add to that list this season. Most likely in December, but possibly March or even both. "

-Eastern Mass Weather 11-5-20

 

This was an especially bold call considering the state of long range guidance at the time, which was suggesting the development of a rather formidable polar vortex once again. 

However it worked out reasonably well, as the NAO averaged at least modestly negative.

 

 

And the polar vortex underwent consistent assaults, as evidenced by the extremely negative AO.

 

 

Guidance ultimately adjusted, and the consensus then scrambled to follow suite.

Although the forecast worked out fairly well locally, there was some limitations with respect to the Pacific pattern that were of a much larger detriment to the national forecast.

 

Here if the forecast temperature anomaly map from early November:

 

 

"The month of December should average 1-2 degrees below normal for northern New England, near normal to a degree above normal for central southern New England, and 1-2 degrees above normal from north to south near New York City points southward into the mid atlantic. Cold will dump over the high plains and bleed eastward".

-Eastern Mass Weather 11-5-20

 

The temperature forecast verified locally across southern New England and the Boston area.

 

 

(Courtesy of Eric Fisher via Twitter)

 

But there was a significant RNA pattern forecast that is quite typical of significant la nina, but what actually verified was a formidably PNA that is more representative of an el nino. This wreaked havoc with the national temperature pattern. 

 

 

 

 

Note that while the forecast was for cold centered in the northern plains, and the anomalies generally configured in a cool north, warmer south gradient typical of la nina, the opposite actually verified. Due to the PNA pattern that materialized, cooler anomalies verified to the south with warmer anomalies to the north, which is observed more frequently during el nino events. This variation in the pattern ultimately had important ramifications on the anticipated forms of cyclogenesis.

 

December Snowfall

The forecast was for month was for the developments of storms of fairly moderate intensity, since the forecast higher heights in the southeast would work in concert with the expected negative NAO shear amplifying shortwaves. 

 

"It should be an active period marked by above average precipitation, especially for points north of Washington, DC. Primary modes of cyclogenesis include Alberta clippers, southwest flow events, and Miller B redevelopers, the latter of which especially prevalent during periods of negative NAO. New England should be favored for snowfall, especially central and northern parts of the region. The mid atlantic will need breaks in the RNA to coincide with negative NAO flex for significant snowfall, which is not exceedingly likely, but possible. A White Christmas is more probably than climatology would suggest this season. While the month is likely to average a negative NAO in the mean, this is not meant to imply that excessive blocking will reside for the entirety of the month".

-Eastern Mass Weather 11-5-20

 

 

 

 

 

 

Since the anticipated southeast ridge never materialized, one major event did in fact impact the northeast US near mid month, which is when the pattern was expected to become more active.

 

 

                                    (Courtesy Eric Fisher via twitter)
 

 

Although this system deposited over 12" of snowfall over a relatively large area just one week prior to the holiday, much of the area was denied a white Christmas, nonetheless. This was due in large part to some idiosyncrasies regarding the positioning of the higher heights in the NAO domain.

 

Much like ENSO Events, Location Crucial for Blocks

The month of December was not quite as active in terms of winter weather across the area as implied, in large part because the large Christmas event this past week was entirely rainfall across the region. The easy first guess would be because the NAO was not predominately negative, as expected, but this is not true as previously discussed.

 

 

A more exhaustive review of the data reveals why.

Latter December has been characterized by a "thumb ridge" of higher heights across the north atlantic to the south of Greenland, as opposed to a true block over Greenland.

 

Although technically registering as a negative NAO due to higher heights in the southern periphery of the NAO domain, this is not a block because it does nothing to "block" a storm from cutting inland. This was evidenced by the inland track of the Christmas low, however, long range guidance suggests that this will change heading into the month of January as NAO becomes more ideal.

 

 

January 2021 Preview

Here is the original forecast release from early November:

 

January Forecast Temperature Composite:

"Temperatures should be near normal to 1 degree above across northern New England, 1-3 degrees above normal in central and southern New England, and 2-3 degrees above in the mid atlantic. Any storm activity will entail large precipitation type issues near the coast, with the most snow reserved for northern New England. The RNA pattern should only strengthen, as overall storm activity wanes".

 

Eastern Mass Weather 11-5-20

 

 

 

January Forecast Precipitation Composite:

A lull in winter for the northeast, especially below the latitude of northern New England and east of New York state, should develop during the month, as storms becomes less frequent and the predominate track shifts inland. Some seasonal cold bouts should be sufficient for some mountain snow, and perhaps some "front end" wintery precipitation further to the south.

 

The original forecast called for a recovery of the PV in the latter portion of the month. However, that looks as though it may be delayed by disruptions to the PV that may potentially be more severe than originally forecast. This in large part due to intense warming in the polar stratosphere. The implication of this is that we are currently more than likely in the midst of the "lull" in the winter pattern, which began with the shift of the NAO block to the south and the attendant "Grinch Storm" in latter December, and will likely persist through the first week of the  new year.   The month may also average closer to normal than expected, and colder further to the south across the eastern US.

This "lull" period also consisted of the light rain event last night, and what will be a primarily rain event tomorrow night, although it is likely to begin as a brief period of snow and ice across the interior

 

 

It is after one final mix to rain event this weekend that the plot may being to thicken. Although Sudden Stratospheric Warming events are relatively infrequent during la nina events and westerly QBO seasons, the emergent el nino like tendencies continue to imply that this may be a viable option beyond the first week of the month.

 

Currently, the stratosphere remains fairly weak, which creates the opportunity for cold to escape into the mid latitudes. However, that does not necessarily mean that it will escape into north America. In fact, currently the vast majority of the cold is focused in Asia.

Remember not to generalize all weakening PV episodes.

 

 

 

However there is now growing confidence that the balance of cold will begin to shift toward North America as we enter the new year.

 

 

 

 

 

 

 

 

 

 

This sets the stage for what currently looks to be a classic pattern for a major east coast snow storm during the second week of January.

 

While a true Sudden Stratospheric Warming is remains somewhat dubious for reasons specified in the winter outlook, there does exist strong multi cluster support among ensemble guidance for such a a pattern to materialize.

Guidance continues to emphatically suggest the development of a west-based NAO beyond the first week of the month.

 

 

 

There maybe additional system worth watching early next week for wintery implications before the true fever pitch for the second week of 20201 and beyond.

 

 

 

[raindancewx]

Looks like Boston's December high went from an average of 41.7F in 1981-2010 to 42.5F in 1991-2020. A year like December 2020 is now about average.

[40/70 Benchmark]

January Review and February Preview

January 2020 Recap

What Went Wrong

There were two major flaws with the January forecast.

1) The Pacific pattern was again rather poorly forecast, as the residual + PNA pattern of December carried over through roughly the first 2/3 of the month of January.

 

 

 

This obvious wreaked havoc with the national temperature composite in much the same manner as it in December in that the gradient was inverse of what was forecast. While the anomalies in New England were fairly accurate across at leas the souther portion of the region, it was cooler to the south, and warmer the north, which was opposite of the forecast.

 

"Temperatures should be near normal to 1 degree above across northern New England, 1-3 degrees above normal in central and southern New England, and 2-3 degrees above in the mid atlantic. Any storm activity will entail large precipitation type issues near the coast, with the most snow reserved for northern New England. The RNA pattern should only strengthen, as overall storm activity wanes".

 

-Eastern Mass Weather 11-5-20

 

Here is the forecast temperature anomaly composite:

vs the the actual:

 

Note that while locally the forecast managed to succeed, it suffered suffered nationally as it did in December, due to the poorly forecasted December PNA that lingered throughout the first 2/3 of January.

 

2) The second main issue with the January portion of the outlook was that high latitude blocking has shown no signs of abating, as forecast. This has likely been protracted by the early January Sudden Stratospheric Warming event.

 

 

 

 

 

 

 

It is evident in the forecast composite that while some blocking was forecast to persist into the new year:

 

It has clearly been more prevalent than forecast, as evidenced by the actual monthly composite:

 

While this portion of the season outlook was certainly flawed, it was not without its strengths.

 

What Went Right

The month of January was forecast to see lower heights build into the Alaskan region as part of a positive East Pacific Oscillation, and as illustrated in the verification composite above, this was indeed the case. The Aleutian ridge relocated to the southeast, away from Alaska, as forecast. This led to an active Pacific jet, which made it very difficult to time phasing well enough for any major northeast storms, as is often the same in moderate to strong la nina events. In fact, thus mid winter lull was very well forecast.

"A lull in winter for the northeast, especially below the latitude of northern New England and east of New York state, should develop during the month, as storms becomes less frequent and the predominate track shifts inland. Some seasonal cold bouts should be sufficient for some mountain snow, and perhaps some "front end" wintery precipitation further to the south".

 

-Eastern Mass Weather 11-5-20

 

Here was the forecast temperature composite, which depicted a dearth of precipitation along the east coast:

vs reality:

 

 

Note that both the active Pacific jet across the Pacific northwest, as well as the fairly quiet conditions along the east coast were both well forecast. The storm track did indeed feature multiple mixed precipitation events and rain events in the area during what was a well below normal month snowfall wise with most location measuring single digit monthly totals. However, the tide has quickly turned to begin what was expected to be a very mild month of February.

 

High Latitude Blocking Likely to Delay February  Forecast Warm up

A major premise of the seasonal forecast was that while the polar vortex would be prone to assaults early on in the season, it would ultimately recover, however, the major Sudden Stratospheric Warming event that occurred in early January proved that particular supposition incorrect. 

 

Note how diffuse and nearly indiscernible the polar vortex remains at present, as the polar stratosphere remains infiltrated with warmth.

 

 

Clearly the polar domain is still reeling from last months Sudden Stratospheric Warming, which means that, an end to the current high latitude blocking regime is not imminent. While this is in conflict with the timing of the progression laid out in the Winter Outlook, the current data is indisputable and overwhelming. However, as was the case with the development of the RNA, it may be a case of delayed, but not denied.

 

Note the recovery to at least near neutral with respect to the polar fields, as forecasted by the EPS:

 

Recovery of Polar domain and consolidation of polar vortex forecast later in February.

 

Likewise, a realignment of the Pacific is also expected to take place toward mid month, as lower heights work in tandem with RNA to induce an active Pacific jet.

 

 

 

Active Pacific Jet Expected for Especially Second Half of February

 

This evolution is well supported by the European weekly product.

 

Depicted below is the major negative NAO and EPO blocks that are expected to persist throughout the early portion of the month:

 

 

 

Note by mid month, the NAO block has weakened, and the EPO block as retrograded towards a more classic la nina position, in the vicinity of the Aleutians. The latter of which continues lower heights in the west.

 

 

 

Finally, by the final week of the month, there is a vortex in the vicinity of Alaska, which would flood the CONUS with milder Pacific air, and at least theoretically, make sustaining any residual high latitude blocking more difficult.

 

 

This is congruent with a the longer range forecast for a more consolidated polar vortex, which is more fixed near the pole.

 

 

In summary, while the month of February is certain to feature more high latitude blocking than forecast due in large part to the early January Sudden Stratospheric Warming, there remains ample opportunity for the original forecast monthly departure of +2 to +4F to verify due to anticipated second half warming. Regardless, the month does not appear to be void of opportunities for winter storms, nor was it ever anticipated to.

[40/70 Benchmark]

February Review & March Preview

February Recap

Arctic & Atlantic

The supposition going into the season was that any major disruption of the polar vortex would occur in latter February or March, after a very mild February. However, said disruption occurred in early January, which significantly altered the February landscape from what was forecast. What was forecast to be a rather benign and very mild month

 

Eastern Mass Weather February 2021 Forecast Temp Departures

 

 began with the capstone event of the winter on the first of the month, which set the tone for what was an average month temperature wise with above average snowfall. Thus the residual impact of the January Sudden Stratospheric Warming (SSW) continued the theme of both delaying and muting the anticipated warm up during the second half of the winter season. The anticipated positive AO during the month of February obviously did not work out, although it has finally since recovered. The steep decline centered around mid month coincides with the arctic plunge into the deep south.

 

Accordingly, the NAO was also slower to recover than anticipated, but did manage to average slightly positive for the month. In fact, the NAO was actually neutral at the time of the mid month arctic outbreak, which combined with the arctic and pacific pattern to focus the severe mid month arctic outbreak in the nation's mid section. While the impact of the polar vortex disruption significantly impacted the forecast for the arctic region, the Pacific was much better forecast, which is a reversal from the first half of the season. 

Pacific

The month overall in the mean featured a modest positive PNA, which was actually well forecast. And as can be noted in the annotation below, the peak of the monthly positive PNA spike coincided with the arctic plunge mid month.

 

 

Thus the higher heights over the western US worked in conjunction with the relative dearth of a vehicle to drive the cold east, given the neutral NAO, to focus the wrath of this outbreak over the nation's mid section. This is very evident in the monthly temperature departure chart, which is obviously quite a bit different from the forecast from last fall, posted above. This is due to the misdiagnosis of the arctic region attributable to the major mid season SSW.

 

 

Actual February 2021 Monthly Temp Departures

There was also an active Pacific forecast during the month of February, as evidenced by the positive precipitation anomaly over the pacific northwest in the forecast anomaly chart from last fall, pictured below.

 

This active Pacific jet was well forecast:

 

 

Eastern Mass Weather Forecast February 2021 Monthly Precipitation Anomaly Chart 

However the high latitude blocking in conjunction with the well forecast modest + PNA resulted in a storm track that was more suppressed than anticipated, which focused snowfall more across southern New England and the northern mid atlantic, rather than northern New England, as expected.

 

 

 

Actual February 2021 Monthly Precipitation Departure

 

Conclusions

 

The implications of the disparity between the how this season has evolved and the outlook issued in November will be discussed more extensively in the post season analysis issued this spring. In the meantime, what has become apparent this February is that the hemispheric forcing regime accompanying this particular cold ENSO event has been more redolent of the EP la nina seasons included in the mixed-type la nina composite, as opposed to the modoki type. Nothing illustrates this more than the vertical velocity chart for the month of February:

February 2021 Vertical Velocities (Forcing)

This depicts the vast majority of the atmospheric forcing pinned to the west of the dateline, as was the case with respect to the EP composite examined last fall.

 

 

EP La Nina Vertical Velocity (Forcing) Composite

 

Note that the warmer anomalies near the dateline ensure that forcing remains over the central and western Pacific, similar to a modoki el nino, which creates this DM H5 composite. Also evident is that the Aleutian ridge focuses more to the northwest relative to the modoki, cp event, which will be evident when that particular composite is reviewed. This often entails a protrusion of said ridge into the polar region at times, which likely contributes to the lower heights over the mid latitudes:

 

 

 

EP La Nina Composite

 

Here is the H5 composite for February 2021, with the high latitude blocking and accompanying aleutian ridge clearly displaced to the northwest, as cited in the above EP composite.

 

Actual February 2021 H5 Composite

 

Versus the forecast composite for the month, which was biased more towards the center of the EP/CP continuum and thus a relative death of high latitude blocking and an Aleutian ridge displaced more to the southeast.

 

Forecast February 2021 H5 Composite

 

More this in May, but March comes first.

March Preview

Last fall, the prevailing though for March was that a degree of high latitude blocking (lesser magnitude than what is indicated in the composite) may become reestablished at some point in the month, as the Pacific jet remained active and heights on the west coast elevated, somewhat.

 

March 2021 Forecast H5 Composite Form Last Fall

 

This was though to result in a near average monthly composite for much of the region:

 

 

March Forecast Monthly Temperature Departures Issued Last Fall

 

Normal to below average snowfall was implied, which still looks to the case, as the primary difference relative to the forecast from last fall is that more of an RNA looks to persist in conjunction with the modest high latitude blocking, mainly in the NAO region. 

 

Forecast NAO

 

The notion of at least modest blocking is supported by the passage of the MJO through phases 7 and 8 this month.

 

 

 

Forecast AO
 

 

This is a change from February in that the bulk of the blocking was in the AO region, however, should the RNA develop and prominent Pacific jet persist as expected, then the bulk of cold shots would continue to be focused to the west and any wintery events should be marginal and favor higher terrain.

 

 

Forecast RNA

 

 

Forecast EPO

Currently, the only major storm opportunity, which coincides with the encircled area of modularity on each respective index chart above,  looks destined for failure late next weekend. It looks to pass harmlessly put to sea, as the extension of a polar vortex lobe to the north acts to ensure its fate.

 

 

The risk should this overall monthly pattern materialize is slightly warmer than originally expected, which was near normal. Here is the forecast monthly mean pattern form the European guidance:

 

 

 

 

Canadien:

 

 

 

 

AND CFS:

 

 

 

Consensus is fairly strong on the guidance above, however, time will ultimately tell, as dynamical guidance is but half the equation.

[40/70 Benchmark]

Just now, 40/70 Benchmark said:

March was pretty well forecast....I was all over the blocking head fake from the composite, which I fell for last year. Not this year....I knew it would hold off until April.

March 2021 Review

Teleconnections

Following the deviation from the forecast in February, owed to the mid winter Sudden Stratospheric Warming protracting the blocking from the first half of the season, March has gone essentially according to plan. Any residual high latitude blocking relinquished its grip by mid February, paving the way for a very benign and unremarkable weather pattern across the region. The supposition from the winter outlook was that the reemergence of blocking during the month of March, which was implied by the forecast composite, would materialize more slowly than forecast and likely be delayed until April, much like last season. This assertion was based on both the +QBO, as well as the proclivity for moderate or stronger la nina events to truncate the winter season.

This forecast assertion as proved correct, as the polar domain remain relatively hostile to sustained winter weather for the vast majority of the month. 

 

 

As evidenced in the annotation above, some degree of blocking does look to reestablish itself during the month of April. This likely would have happened sooner had the la nina remained weaker, and/or the QBO were less resistant to high latitude blocking. Another implication of la nina remaining at moderate intensity into March is that the RNA pattern did not relinquish its grip as much as it could have if the cool ENSO event had either remained weak, or weakened at a faster rate.

 

Although the largely hostile polar domain and the lingering la nina did lead to relatively mild and quiet month of March with a great dearth of snowfall, it was not exotically warm in the mean, given that Aleutian ridge did indeed extend more poleward this month, as forecast.

 

Composite Verification

Here is the H5 composite for the month of March 2021:

 

 

Actual March 2021 H5 Composite

 

Note that while lower heights were prevalent both across the higher latitudes, as well as the western CONUS,  the Aleutian ridge did extend more to the NW and poleward, as forecast.

 

 

Eastern Mass Weather March 2021 Forecast H5 Composite

 

This acted to partially negate the modifying influence of the lower heights across higher latitudes and the the western US, which resulted in approximately a +1F monthly departure from the mean across the region.

Actual March 2021 Temp Anomalies

 

This was near the higher end of the forecast range for near normal monthly departures.

 

 

 

Eastern Mass Weather Forecast March 2021 Temp Departures

 

Finally, the month features below average precipitation, which worked in concert with the slightly above average temps to leave the region essentially void of monthly snowfall.

 

Actual March 2021 Precip Anomalies

 

These dry conditions were also congruent with the forecast expectations from last November for month of March.

 

Eastern Mass Weather March 2021 Forecast Precip Anomalies

 

 

 

The complete forecast review for the entirety of the winter 2020-2021 season will be issued in May.