December 2020 General Discussions & Observations Thread

[snowman19]

2 minutes ago, bluewave said:

That’s why we have to wait for the individual short waves.  We will definitely need help from the PNA with such a strong PAC Jet and +EPO. But models won’t show those fine details until we get within about a week of the actual forecast period.

There in lies a big issue, the PAC jet. Over the last several winters, every attempt at sustained +PNA ends up falling apart because the juiced PAC jet crashes right into it and knocks it down as fast as it pops up

[CIK62]

The last 8 days of the month are averaging 40degs.(32/47).            Making it 35degs., or +2.0.

Month to date is 39.3[+0.7].             December should end between (38.2---39.5).

Models are snow less, but total rain through New Years Day is 5".      Measuring rain in inches during the winter doesn't sound nice.

The GEFS Extended which has been reading   Houdini's Magic Disappearing Acts,   has made the snow reappear instead for the Jan.6/7 (10"+) and again during Jan. 14-17(10"+).      Practice makes perfect so I am  trying it now.....................................................................................................................................................gone m i

48* (90%RH) here at 6am.       50* at 7am.      T rising steadily since 43* at Midnight.        52* by 10am.     53* by 10:30am.       54*, drizzle by 2pm.      55* at 3pm.       back to 53* at 4pm.

[donsutherland1]

Morning thoughts...

Clouds will increase today. Showers and then a steadier rain will arrive during the afternoon or evening. Overnight, heavy rain and high winds are likely. A general 1.00”-2.00” rainfall with locally higher amounts is likely. The wind will likely gust near 70 mph right along the coast and at or above 60 mph just inland. It will become exceptionally mild for the season. Temperatures will likely top out in the upper 50s and lower 60s across  most of the region. Likely high temperatures around the region include:

New York City (Central Park): 61°

Newark: 60°

Philadelphia: 62°

Tomorrow will begin with stormy and warm weather. Colder air will return later in the day and temperatures will plunge into the 30s.

[MJO812]

32 minutes ago, snowman19 said:

There in lies a big issue, the PAC jet. Over the last several winters, every attempt at sustained +PNA ends up falling apart because the juiced PAC jet crashes right into it and knocks it down as fast as it pops up

We have to be patient. This month is done for any winter weather. 

[Allsnow]

44 minutes ago, snowman19 said:

There in lies a big issue, the PAC jet. Over the last several winters, every attempt at sustained +PNA ends up falling apart because the juiced PAC jet crashes right into it and knocks it down as fast as it pops up

We had one for the 10 inch storm last week. It doesn’t need to be sustainable just has to spike briefly 

[Snowshack]

First signs of any breaks in the snowcover here as the temp spiked 15 degrees from around freezing between 4-6am.   Been a great week of snowcover.   Balmy 53f now.   Might as well cook down the remaining snow before the big rains.

[SACRUS]

Southeast winds and temps to 55.  Showers into PA going north. 

[SACRUS]

Looks back and forth bias/tilted warmer the next 7 - 10 days.  ECM has temps again pushing 60s new year eve/day before more cold with the brunt of the cold to the west GL and north as colder waves pulse through..

[bluewave]

1 hour ago, snowman19 said:

There in lies a big issue, the PAC jet. Over the last several winters, every attempt at sustained +PNA ends up falling apart because the juiced PAC jet crashes right into it and knocks it down as fast as it pops up

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO.

Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

[MJO812]

Anyone have the EPO ?A better pattern looks likely as we head into January .

[Isotherm]

Full snow cover maintained here through Christmas Eve. Will be gone later today, but a solid period for early winter (16th-24th).

[the_other_guy]

55F.

Complete breakdown this upcoming week of any cold weather.

Transient shots of cold with temps well AN beyond that.

Xmas in the 50s is the new normal sadly

[snowman19]

1 hour ago, bluewave said:

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO.

Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

Correct, we also have a +WPO, which is adding to the PAC driven mess. People need to be aware too, that the -NAO block may set up too far south....that needs to be kept in mind here. A too far south block hooking up with the WAR (no 50/50 low) is not good. That block needs to establish itself further north or you have big problems 

[LibertyBell]

3 hours ago, MJO812 said:

We have to be patient. This month is done for any winter weather. 

yeah what more do you want in December, we already had a double digit snowfall event, now it's January's turn.

[LibertyBell]

1 hour ago, bluewave said:

We only needed one storm this month for many areas to get to above normal snowfall. That was when the +PNA combined with the -AO-NAO. It really came down to that supercharged 50/50 low we got. Otherwise, the tucked in storm on the 16-17th would have been a warmer event. As it was my area only got 4” of snow due to the WAA aloft and quick flip to sleet. The month will end milder than models were expecting just several days ago. You mentioned the trade wind surge a few days ago. That may be related to why we are getting the Niña ridge showing up north of Hawaii. But this is still occurring with other more Niño-like features. We would definitely need more help from the PNA in January to counter the +EPO and fast Pacific Jet. But those short term details usually don’t show up on the longer range forecasts. Just a little +PNA can go a long way with -AO -NAO.

Slight Niña Ridge poking up north of Hawaii allowing more of a trough out West

Correct, that is the climatology for this region, you only need the pattern to be good for a couple of days each month, irrespective of what the overall "pattern" might be.

 

[uncle W]

1 hour ago, Isotherm said:

Full snow cover maintained here through Christmas Eve. Will be gone later today, but a solid period for early winter (16th-24th).

1955, 1964, 2008 all suffered the same faith...Christmas eve 1964 was one og the foggiest nights I can remember...the snow that was on the ground for 5 days melted before midnight...

[LibertyBell]

3 hours ago, Allsnow said:

We had one for the 10 inch storm last week. It doesn’t need to be sustainable just has to spike briefly 

and that's how our winters go (outside of the extreme outliers on either end), you typically get brief spikes and that's where the vast majority of our wintry weather comes from.

 

[LibertyBell]

1 minute ago, uncle W said:

1955, 1964, 2008 all suffered the same faith...Christmas eve 1964 was one og the foggiest nights I can remember...the snow that was on the ground for 5 days melted before midnight...

no one thought to cover it so it wouldn't melt?

 

[uncle W]

1 hour ago, MJO812 said:

Anyone have the EPO ?A better pattern looks likely as we head into January .

there is still one member in the ao forecast that goes against the grain...I doubt its right...

[LibertyBell]

11 hours ago, Stormlover74 said:

But it doesn't guarantee snow. Jan 2010 was not snowy. Jan. 85 was bitterly cold but not a ton of snow 

yeah neg nao in January is a misleading stat to use because it could be too strong and cause storms to be suppressed.

 

[LibertyBell]

3 hours ago, donsutherland1 said:

Morning thoughts...

Clouds will increase today. Showers and then a steadier rain will arrive during the afternoon or evening. Overnight, heavy rain and high winds are likely. A general 1.00”-2.00” rainfall with locally higher amounts is likely. The wind will likely gust near 70 mph right along the coast and at or above 60 mph just inland. It will become exceptionally mild for the season. Temperatures will likely top out in the upper 50s and lower 60s across  most of the region. Likely high temperatures around the region include:

New York City (Central Park): 61°

Newark: 60°

Philadelphia: 62°

Tomorrow will begin with stormy and warm weather. Colder air will return later in the day and temperatures will plunge into the 30s.

I want to see if any of our major stations will verify with hurricane force gusts....do you think that's likely, Don?

 

[eduggs]

The 500mb progression looks dreadful on all guidance out at least 7 days. Although I suppose the storm around NYE could correct more favorably. It looks a lot like tonight's event.

[bluewave]

19 minutes ago, snowman19 said:

Correct, we also have a +WPO, which is adding to the PAC driven mess. People need to be aware too, that the -NAO block may set up too far south....that needs to be kept in mind here. A too far south block hooking up with the WAR (no 50/50 low) is not good. That block needs to establish itself further north or you have big problems 

The south based blocking has been a theme this month. Notice the warmer than normal temperatures pushing down into the Northeast. This may be related to the record SSTs over the NW Atlantic and cold pool south of Iceland.

 

[SnowGoose69]

22 minutes ago, eduggs said:

The 500mb progression looks dreadful on all guidance out at least 7 days. Although I suppose the storm around NYE could correct more favorably. It looks a lot like tonight's event.

The Op GFS had another “glorious” run at 12Z.  It basically just continually repeats the same thing over and over Day 7-16 which is almost certainly wrong but it’s funny how many torch cutter Op runs it’s continued to have while the ensembles argue for something totally different 

[donsutherland1]

36 minutes ago, LibertyBell said:

I want to see if any of our major stations will verify with hurricane force gusts....do you think that's likely, Don?

 

Maybe on Long Island.

[EastonSN+]

34 minutes ago, SnowGoose69 said:

The Op GFS had another “glorious” run at 12Z.  It basically just continually repeats the same thing over and over Day 7-16 which is almost certainly wrong but it’s funny how many torch cutter Op runs it’s continued to have while the ensembles argue for something totally different 

CMC looks like it's cooking something at the end of the run. A little like the EC but a little colder air in front.

[bluewave]

1 hour ago, LibertyBell said:

Correct, that is the climatology for this region, you only need the pattern to be good for a couple of days each month, irrespective of what the overall "pattern" might be.

 

The oddity this month for NYC is how mild it has been for a December with a 10”+ snowstorm. Most other Decembers were much colder. But warm and snowy has been a new theme that has emerged since the mid 2000’s.

2020...39.3...so far

2010...32.8

2009...35.9

2003...37.6

2000...31.1

1960...30.9

1948...38.3

1947...34.0

1933....32.7

1916....34.0

1912....39.3

1872....26.7

[qg_omega]

1 minute ago, bluewave said:

The oddity this month for NYC is how mild it has been for a December with a 10”+ snowstorm. Most other Decembers were much cooler. But warm and snowy has been a new theme that has emerged since the mid 2000’s.

2020...39.3...so far

2010...32.8

2009...35.9

2003...37.6

2000...31.1

1960...30.9

1948...38.3

1947...34.0

1933....32.7

1916....34.0

1912....39.3

odd its been so warm, we had like 8 days of full snow cover on a 10 inch storm, seems very impressive to me in December.

[bluewave]

14 minutes ago, qg_omega said:

odd its been so warm, we had like 8 days of full snow cover on a 10 inch storm, seems very impressive to me in December.

It helped having the 4 coldest days of the month follow the snowstorm. 

[donsutherland1]

A strong storm will pass to the west of the region tonight bringing a general storm total 1.00"-2.00" rainfall with locally higher amounts. The storm will also bring high winds with gusts of 60 mph to many parts of the region and 70 mph to coastal areas. After a warm start with readings in the upper 50s and lower 60s, temperatures will fall tomorrow as colder air returns.

Caribou, which saw its first-ever 60° December temperature earlier this month will very likely set a daily record high temperature tomorrow. The existing daily temperature record is 48°, which was set in 2014.  

In the wake of that storm, the unseasonably warm air will be driven into Atlantic Canada where record high temperatures are likely tomorrow through Sunday. Unseasonably cold air will push into Florida. Record low temperatures are possible in some parts of the state, especially along the Gulf Coast and southern portions of the Florida Peninsula, tomorrow and especially Saturday.

The likely continuation of Arctic blocking through at least the first week of January will provide a higher than climatological probability for above normal snowfall for the December 21-January 10 period, with the focus on the January 1-10 period. There is some clustering of support among the EPS ensemble members for January 3-5. The AO- is particularly important for moderate or significant snowfalls in the New York City and Philadelphia areas.

For the December 15-January 15, 1950-2020 period, the following percentages of select snowstorms have occurred when the AO was negative:

New York City:
4" or more: 66%
6" or more: 80%
10" or more: 86%

Philadelphia:
4" or more: 81%
6" or more: 85%
10" or more: 100%

Further, an AO-/PNA+ pattern is especially favorable for moderate or significant snowstorms during the first half of January. For the January 1-15, 1950-2020 period, daily snowfall reached or exceeded 4" on 1.7% of days in New York City and 1.2% of days in Philadelphia. During AO-/PNA+ patterns, those respective frequencies were 2.3% and 1.7%. In short, moderate or significant snowfalls were 37% more common in New York City and 42% more common in Philadelphia during AO-/PNA+ patterns.

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 +4.88 today.

Today, the preliminary Arctic Oscillation (AO) figure was -0.921.

On December 23 the MJO was in Phase 6 at an amplitude of 0.366 (RMM). The December 22-adjusted amplitude was 0.901.

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 wind at 1 mb will likely reverse while the mean zonal winds at 10 mb and 30 mb slacken considerably.

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 82% probability that New York City will have a warmer than normal December. December will likely finish with a mean temperature near 38.8°.