December 2020 General Discussions & Observations Thread

[MJO812]

18z GFS  Para is consistent  with a coastal. This run hits us. 

[NEG NAO]

The SSW is real the GFS is NOT !

[SnoSki14]

This December was a lot better than I expected so I'll take it as a win. 

I'm sure it'll snow again. 

[NEG NAO]

3 minutes ago, MJO812 said:

18z GFS  Para is consistent  with a coastal. This run hits us. 

Plenty of hints on various models of an east coast storm during the  1st week in January but its too far out for them to be consistent and accurate.............

[donsutherland1]

Despite bright sunshine, the temperature peaked in the lower 30s across the region. Meanwhile, additional record high temperatures were broken in parts of eastern Canada today.

Records included:

Amherst, NS: 59° (old record: 46°, 2003)
Bathurst, NB: 56° (old record: 39°, 2003)
Cap-Chat, QC: 60° (old record: 36°, 2014) ***2nd consecutive 60° day for first time on record in meteorological winter***
Caribou: 55° (old record: 53°, 1964)
Caribou, NS: 58° (old record: 48°, 2003)
Charlottetown, PE: 56° (old record: 52°, 1964)
Chéticamp, NS: 58° (old record: 46°, 2003)
Gaspé, QC: 54° (old record: 48°, 1977)
Goose Bay, NL: 49° (old record: 46°, 1964)
Grand Étang, NS: 53° (old record: 46°, 2005)
Halifax: 56° (old record: 52°, 1964)
Mary's Harbour, NL: 51° (old record: 37°, 2001)
Rivière-du-Loup, QC: 53° (old record: 37°, 2014)
Saint John, NB: 56° (old record: 55°, 1964)
Sept-Îles, QC: 45° (old record: 42°, 1964)
Yarmouth, NS: 59° (old record: 53°, 1964)

The likely continuation of Arctic blocking through at least the first 10 days of January would typically provide a higher than climatological probability for above normal snowfall. Ideally, an expansive block would be anchored across the Baffin Bay or Greenland, not south of the Davis Strait.

There is growing ensemble support for the latter outcome. The probability that the block will be anchored near Newfoundland and Labrador in the extended range can inhibit opportunities for snowfall. This can especially be the case should the block attempt to link up to the western Atlantic ridge. In coming days, it will become clearer whether the recent and still ongoing shift in the ensemble guidance toward that outcome will become the most likely scenario for the first half of January.

Nevertheless, there still exists some possibility for a storm during the January 3-5 period that could produce snow. There has been some support among ensemble members for such event.

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -0.9°C for the week centered around December 16. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.57°C and the ENSO Region 3.4 anomaly has averaged -1.17°C. La Niña conditions will likely prevail at least through the winter.

The SOI was +8.93 today.

Today, the preliminary Arctic Oscillation (AO) figure was +0.112.

On December 25 the MJO was in Phase 8 at an amplitude of 0.192 (RMM). The December 24-adjusted amplitude was 0.150.

Based on the latest guidance, the probability of a significant stratospheric warming event near or just after the start of January has continued to increase. The highest levels of the stratosphere will warm during the closing days of December. The warming will begin to descend during the opening week of January. In addition, the mean zonal winds at 1 mb and 10 mb will likely reverse while the mean zonal wind at 30 mb will likely slacken considerably.

There is the proverbial fly in the ointment. It appears that this warming event could produce a split in the polar vortex. Typically, when the polar vortex splits, Eurasia is favored for cold. Displacement of the polar vortex often favors North America.

The recent 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. For now, blocking appears likely to continue into the start of January.

Based on sensitivity analysis applied to the latest guidance, there is an implied 96% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 39.0°.

 

[eduggs]

5 hours ago, NEG NAO said:

In addition take a look at previous seasons when NYC received over 10 in. of snow in December and report back....

I don't think one December storm has much bearing on how the rest of the season will play out.  Places that are above average snowfall for this date probably have a better than 50% chance of finishing above average for the season.  But that's about all you can say.

[eduggs]

22 hours ago, donsutherland1 said:

The definition is qualitative, not quantitative. Measures such as the NAO and AO can provide related quantitative information.

https://glossary.ametsoc.org/wiki/Blocking

Exactly my point. If you want to make predictions regarding weather likelihoods based on climatological indices, you have to be precise about the locations of both the weather and the indices in question. A "blocky" pattern is a very broad statement that can have a wide range of implications for the northeast US.

[MJO812]

Last really warm Christmas was 2015 with 65 degrees.

That winter wasn't good except for the big blizzard in 2016. We did have 11 inches in December 2015.

I think we will get some snow next week and a big one at the end of Jan.

[NEG NAO]

39 minutes ago, eduggs said:

I don't think one December storm has much bearing on how the rest of the season will play out.  Places that are above average snowfall for this date probably have a better than 50% chance of finishing above average for the season.  But that's about all you can say.

calculate the percentage from this:

monthlyseasonalsnowfall.pdf (weather.gov)

[eduggs]

Just now, NEG NAO said:

calculate the percentage from this:

monthlyseasonalsnowfall.pdf (weather.gov)

That's a nice compilation of the past. But it doesn't tell us a whole lot about the future. We can try to make inferences to correlate, for example, December with the entire season, but we'd be on really shaky statistical ground.

[LibertyBell]

3 hours ago, NEG NAO said:

Plenty of hints on various models of an east coast storm during the  1st week in January but its too far out for them to be consistent and accurate.............

Yeah this is true, you cant hang on individual model runs.  1st ten days of January signal has been there consistently.

Also LOL if the NAO/AO weren't critical for 6"+ snowstorms then they wouldn't consistently be brought up in reference to them- and weather also moves south to north (especially during big storms) and north to south with reference to high pressure, saying weather always moves west to east is a vast oversimplification.

[LibertyBell]

4 minutes ago, eduggs said:

That's a nice compilation of the past. But it doesn't tell us a whole lot about the future. We can try to make inferences to correlate, for example, December with the entire season, but we'd be on really shaky statistical ground.

You dont buy the concept that a persistent snowcover from an early season snowstorm breeds more cold air and blocking resulting in a higher probability of more snowstorms in the next few weeks immediately after that initial storm?

 

[LibertyBell]

19 minutes ago, MJO812 said:

Last really warm Christmas was 2015 with 65 degrees.

That winter wasn't good except for the big blizzard in 2016. We did have 11 inches in December 2015.

I think we will get some snow next week and a big one at the end of Jan.

That winter also had a decent event in February that brought down a crane in Manhattan.  JFK had 40" and other parts of Long Island had 50"

And we were below zero for Valentine's Day!

Considering it started with the warmest December ever, that was a good winter (and Xmas Eve was actually 72 degrees!)

 

[eduggs]

2 minutes ago, LibertyBell said:

You dont buy the concept that a persistent snowcover from an early season snowstorm breeds more cold air and blocking resulting in a higher probability of more snowstorms in the next few weeks immediately after that initial storm?

 

No. I think any effect on synoptic level features is marginal. To the degree that snowcover affects large-scale patterns, it is hemispheric snow cover not regional snowcover that drives the influence.

[LibertyBell]

45 minutes ago, eduggs said:

No. I think any effect on synoptic level features is marginal. To the degree that snowcover affects large-scale patterns, it is hemispheric snow cover not regional snowcover that drives the influence.

It can actually be seen immediately after snowfalls when models start to correct to colder scenarios.  I distinctly remember this happening in 1993-94 and meteorologists talking about how snowcover was making airmasses colder than what the models had progged them to be before the snowstorm occurred.  It also affected the track of storms (they were tracking farther south than originally progged to) because of more than expected cold air pushing southward.

I wonder if the same might have been the case in 2010-11 which you might remember was forecast to be a mostly snowless winter, but it all turned on a dime on Boxing Day and then we had a very snowy stretch for about 5 weeks with long duration snowcover.  It makes me wonder if that completely unexpected snowstorm hadn't occurred, how the following 5 weeks would have turned out

 

 

[eduggs]

3 minutes ago, LibertyBell said:

It can actually be seen immediately after snowfalls when models start to correct to colder scenarios.  I distinctly remember this happening in 1993-94 and meteorologists talking about how snowcover was making airmasses colder than what the models had progged them to be before the snowstorm occurred.  It also affected the track of storms (they were tracking farther south than originally progged to) because of more than expected cold air pushing southward.

I wonder if the same might have been the case in 2010-11 which you might remember was forecast to be a mostly snowless winter, but it all turned on a dime on Boxing Day and then we had a very snowy stretch for about 5 weeks with long duration snowcover.  It makes me wonder if that completely unexpected snowstorm hadn't occurred, how the following 5 weeks would have turned out

 

 

I don't buy this. Local snowcover definitely decreases surface temperatures, especially during clear, windless nights. So weather models, especially back in the early 90s, might have over-estimated temperatures when there was snowcover.  It might also shift marginal wintry situations slightly colder, although this is questionable. But I believe that any significant impact of regional snowcover on synoptic scale track/features is anecdotal and not scientifically well supported.

[LibertyBell]

30 minutes ago, eduggs said:

I don't buy this. Local snowcover definitely decreases surface temperatures, especially during clear, windless nights. So weather models, especially back in the early 90s, might have over-estimated temperatures when there was snowcover.  It might also shift marginal wintry situations slightly colder, although this is questionable. But I believe that any significant impact of regional snowcover on synoptic scale track/features is anecdotal and not scientifically well supported.

Yes it was a marginal improvement, nothing major, but just enough to slightly shift things (sometimes that's all it takes.)

This area almost always has a rain/snow/mix line within the region so something that could shift that line say 5-10 miles could make a big difference.

 

 

[wdrag]

Good Sunday morning everyone, While there is still opportunity for a short period warm-wet windy scenario for the NYC forum Jan 1, this large scale long duration complex event is trending colder icier for I84 and definitely heavy qpf-exacerbated flood potential, as the southern stream separation and northern stream deamplification short waves continues. Topic updates ~ 7AM. 

 

[CIK62]

The last 5 days of December are averaging 37degs.(31/43).         Making it 34degs., or +1.0.

Month to date is 39.6[+1.4].         December should end near 38.7(+1.0).

25*(64%RH) here at 6am.       30* by 11am.        36* by 1pm.      38* at 2pm.        40* at 3pm.

New Year's Day period has  about 4" of rain?      GFS just lowered this to 1"+, in agreement with the other models.       It also has 8! 50-Degree Days to bury chances of a BN January baring this great SSWE that might be a spilt on the wrong side of the N.P. for us anyway.     Uncorrected for the first 12 days of January, the GFS is averaging 44degs.(37/51), or +11.        Toward end of period s.e. Canada looks to be +40 to +50.       Finally, the latest  CFSv2 burns the whole North American Continent in January, somewhat of a flip.

[bluewave]

If the past is any guide, then NYC may have to wait until later January or February for its next 6”+ snowstorm. There have been 9 years with a 6”+ event in NYC between December 1st and the 20th since 1930. The good news is that all of the 9 years did get at least one follow up warning level event. We would have to go back to 1926-1927 for the most recent year with no further 6”+ events in the season.

NYC December 6”+ snowstorms before the solstice in December and the date of the next event

12-20-09......2-10-10

12-05-03.....1-27-04

12-5-02.......2-17-03

12-19-95.......1-7-96

12-11-60........1-19-61

12-3-57..........2-15-58

12-19-48.......2-28-49

12-19-45........2-20-46

12-18-32........2-11-33

 

 

[wdrag]

Now that we have a day or two of relative downtime, I've started a new topic in MET 101- a concern of mine is bleeding/muting the appropriate use of weather terminology.  We have by and large, my guess, is at least 80% routine weather days. Then there are the High Impact events.

One of these are arctic outbreaks.  It is my opinion, that we tend to apply the term arctic too frequently, reducing it's valued application in truly very cold, wind chill warning (not advisory) criteria situations.

If you're interested, it's all in MET 101. Have a day!

[donsutherland1]

Morning thoughts...

Today will be mostly sunny and cool. Temperatures will likely top out in the upper 30s across most of the region. Likely high temperatures around the region include:

New York City (Central Park): 38°

Newark: 39°

Philadelphia: 38°

Tomorrow will be fair and noticeably milder.

[uncle W]

1 hour ago, bluewave said:

If the past is any guide, then NYC may have to wait until later January or February for its next 6”+ snowstorm. There have been 9 years with a 6”+ event in NYC between December 1st and the 20th since 1930. The good news is that all of the 9 years did get at least one follow up warning level event. We would have to go back to 1926-1927 for the most recent year with no further 6”+ events in the season.

NYC December 6”+ snowstorms before the solstice in December and the date of the next event

12-20-09......2-10-10

12-05-03.....1-27-04

12-5-02.......2-17-03

12-19-95.......1-7-96

12-11-60........1-19-61

12-3-57..........2-15-58

12-19-48.......2-28-49

12-19-45........2-20-46

12-18-32........2-11-33

 

 

some years had a 4" storm before the next big one...1898 had a big storm of 10 " in November and the next big one came in Feb...1899 had snow before the next big one...The winter is going the way that 1973-74 did...warm in the means but a snowstorm mixed in...73 had more ice...if it continues on that page the first part of January had some snow...arctic blast the third week...big thaw the end of January...

[NEG NAO]

58 minutes ago, uncle W said:

some years had a 4" storm before the next big one...1898 had a big storm of 10 " in November and the next big one came in Feb...1899 had snow before the next big one...The winter is going the way that 1973-74 did...warm in the means but a snowstorm mixed in...73 had more ice...if it continues on that page the first part of January had some snow...arctic blast the third week...big thaw the end of January...

did the 73-74 winter season have a SSW event ? IMO this advertised SSW event soon is going to be the wild card this winter - it will probably change the current  storm tracks we have been experiencing and also if there is a split in the PV that just makes things more uncertain and complex.*Stratosphere warming watch* Strong signals now emerge for a disruptive stratospheric warming event in early January, possibly impacting the course of Winter (severe-weather.eu)

[donsutherland1]

41 minutes ago, NEG NAO said:

did the 73-74 winter season have a SSW event ? IMO this advertised SSW event soon is going is the wild card this winter - it will probably change the current  storm tracks we have been experiencing and also if there is a split in the PV that just makes things more uncertain and complex.*Stratosphere warming watch* Strong signals now emerge for a disruptive stratospheric warming event in early January, possibly impacting the course of Winter (severe-weather.eu)

No. January 1973 had a SSW event, but winter 1973-74 did not.

[Rjay]

18 hours ago, snowman19 said:

^This. I think some people forget that weather moves west to east in the Northern Hemisphere sometimes. If the PAC absolutely sucks, you are f-ed (excuse my language). I don’t care what the Atlantic and arctic are doing. The PAC trumps the NAO and AO.  All -NAO and -AO does when the PAC sucks, is trap PAC garbage air under the block. That, and the fact that the depicted -NAO block is way too far south and is hooking itself up with the WAR is another problem in itself. As far as the “SSW” and “SPV split” hype going on right now on social media, please spare us. We’ve seen this movie before and we know how it ends. It’s the same cast of weenie characters hyping the same SSW’s and SPV splits winter after winter, after winter, with no understanding of how they actually work or happen

 

Yup to all of it.    Good post.  

[bluewave]

Pretty consistent pattern with the North American snow cover since October. Notice the big drops following the spikes back in October and mid-December. This tells us that it’s been a struggle to maintain the cold for more than brief periods. 
 

[NEG NAO]

44 minutes ago, donsutherland1 said:

No. January 1973 had a SSW event, but winter 1973-74 did not.

and the SSW event in January 1973 did NOT lead to any significant increase in snowfall the rest of the winter as 72-73 ended up with 2.8 inches in NYC

[uncle W]

1 hour ago, NEG NAO said:

and the SSW event in January 1973 did NOT lead to any significant increase in snowfall the rest of the winter as 72-73 ended up with 2.8 inches in NYC

it did get colder in Feb...it remains to be seen what and if a SSW event does to our sensible weather...

[MJO812]

12z gfs para still has the early January threat