December Forecast Discussion

[SnowGoose69]

It seems like the pattern is getting more favorable on the guidance and then it begins to back off. For example todays run of the ECM at day 10 shows a cutter again. To me it seems as if the core of the cold is going to be set up in the west and central part of the US. 

 

The Euro has constantly been doing this beyond Day 7, look at what it showed 3 days ago at Day 10 and what it shows now at Day 7....it over digs energy into the SW so it tends to be too mild in the ERN US with ridging, you can take that system it shows at Day 10 now and shove it about 500-100 miles SE most likely.

[doncat]

The Euro has constantly been doing this beyond Day 7, look at what it showed 3 days ago at Day 10 and what it shows now at Day 7....it over digs energy into the SW so it tends to be too mild in the ERN US with ridging, you can take that system it shows at Day 10 now and shove it about 500-100 miles SE most likely.

Agree, posted before how its been popping that eastern  ridge in the long range since August.

[BlizzardWarning]

The event on December 30-31 does not look like a good opportunity for snow.  Models indicate that the storm will develop well to the SW of the NYC Area as this is where the best pressure falls occur.  Before the storms arrival a southernly return flow sets up as the high pressure scoots off to the east, just south of the area.  This southerly flow exists for 36 hours before precipitation falls.  At this time, 500 Millibar on the GFS and EURO seem to suggest that placement of the storm should be somewhere over the Ohio River Valley and trek toward the Western New York State.  Given the Orientation of the Ridge and Trough, this makes sense.

[SnoSki14]

The Euro has constantly been doing this beyond Day 7, look at what it showed 3 days ago at Day 10 and what it shows now at Day 7....it over digs energy into the SW so it tends to be too mild in the ERN US with ridging, you can take that system it shows at Day 10 now and shove it about 500-100 miles SE most likely.

Or it could be correct. It seems like it's accuracy would go up the closer we get. If the SE ridge exists and there's no NAO then the threat of more cutters seems fairly possible.

[SnowGoose69]

The event on December 30-31 does not look like a good opportunity for snow.  Models indicate that the storm will develop well to the SW of the NYC Area as this is where the best pressure falls occur.  Before the storms arrival a southernly return flow sets up as the high pressure scoots off to the east, just south of the area.  This southerly flow exists for 36 hours before precipitation falls.  At this time, 500 Millibar on the GFS and EURO seem to suggest that placement of the storm should be somewhere over the Ohio River Valley and trek toward the Western New York State.  Given the Orientation of the Ridge and Trough, this makes sense.

 

Impossible to really know yet...we sort of need to see what the event on the 29th the Euro has does first...I'm not buying that event at all because I think the push of arctic air from the west and the general progressive nature of the pattern is not going to allow it to occur...that event though influences the next one.

[Isotherm]

Some hope for the hopeless as we approach Christmas...

 

 

November 2014's PDO value of +1.72 was one of only 7 years since 1950 in which the November PDO value was > +1.0, indicative of a pattern than tends to feature troughiness in the Aleutians and ridging in the US West Coast.

 

Those years were as follows:

 

1959

1976

1983

1986

1987

1993

2002

 

-100% of the ensuing winters were colder than normal nationwide; 1959-60 was the only year that featured slightly warmer than normal temps in the Northeast, and this was actually due to a strong -NAO pattern that particular winter.

 

 

-6/7 (86%) of the winters featured a -AO overall for DJF. Only 1983-84 had a +NAO/AO couplet, but the winter was still quite chilly in the Eastern US.

 

-The mean 500mb pattern was such that high latitude blocking dominated, with ridging in the west and large scale troughing in the East; a clear -EPO/-AO/-NAO regime on average

 

500mb composite of the PDO analog years:

 

 

 

The one milder exception in the Northeast US. Strong -NAO still dominated.

 

 

 

 

USA temperature departures for the years:

 

 

 

Point being, based upon the strongly positive PDO at the onset of this meteorological winter, the statistics since 1950 suggest a 0% chance for a torch / warm winter nationwide, and a 17% chance for a warmer than normal winter in the Northeast.

 

While the sample size is obviously small, the type of pattern we had/have for late autumn 2014 was one of only several years w/ strongly positive PDO regimes. If this winter turns out warm nationwide, which it shouldn't, it will be the only event to do so since 1950 within a PDO of > +1.0.

 

This encouraging statistic coupled with the fact that -AO regimes have historically coincided with strongly positive +PDOs, should provide some comfort going forward.

[Isotherm]

Those analog years snowfall wise: No year under 25" of snow at New Brunswick; 25.5" (1959), 28.1" (1976) , 47.3" (1986),  37.7" (1983) , 51.1" (1993), 51.3" (2002), 25.3" (1987).

[BlizzardWarning]

Impossible to really know yet...we sort of need to see what the event on the 29th the Euro has does first...I'm not buying that event at all because I think the push of arctic air from the west and the general progressive nature of the pattern is not going to allow it to occur...that event though influences the next one.

 

My bad.  I'm confused regarding timing. Yeah that second event is probably not going to happen given all the confluence.  The first event will most likely cut west.  Is it impossible to know for sure?  Yes, but the western solution is more likely at this point and my gut is pointing in that direction.  

 

Why do I believe this? There isn't any mechanism holding the cold air in place.  The NAO will be positive, the trough will likely be oriented over the west, and the trough will not dig too far south because the Pacific Ridge is oriented too far Northwest as a result of the PNA being slightly positive.  Also, the AO looks to be slight negative which doesn't bode well for the durability of that cold air push.  

[mattinpa]

My bad. I'm confused regarding timing. Yeah that second event is probably not going to happen given all the confluence. The first event will most likely cut west. Is it impossible to know for sure? Yes, but the western solution is more likely at this point and my gut is pointing in that direction.

Why do I believe this? There isn't any mechanism holding the cold air in place. The NAO will be positive, the trough will likely be oriented over the west, and the trough will not dig too far south because the Pacific Ridge is oriented too far Northwest as a result of the PNA being slightly positive. Also, the AO looks to be slight negative which doesn't bode well for the durability of that cold air push.

I think SnowGoose is right here. Let's see what the first storm does because it could have big impact on the trough.

[SnoSki14]

The AO and EPO definitely override the NAO and are the main factors to always keep in mind. I'm not really worried about the NAO but certainly the lack of a negative AO and the unfavorable MJO is not a good sign.

And yes even though we will have a -EPO it will be nowhere near to the extent of last winters EPO so we're going to need additional help from the other indices particularly the AO.

[Drz1111]

Dude, the AO and the NAO are not independent variables! You need to take a class or something before you post again.

[bluewave]

The 216 hr Euro ensembles really underestimated the SE Ridge this week as it is going

to verify much stronger. It has been backing off the strength of the -AO drop this week.

 

old run

 

 

new run

 

[SnowGoose69]

The Euro has really been underestimating the strength of the SE Ridge recently.

Look how much stronger it will verify this week at 120 compared to the previous

240.

 

old run

 

ecmwf-ens_z500a_nhem_10.png

 

new run

 

ecmwf-ens_z500a_nhem_6.png

 

That may be more a product of the model being too fast with the pattern change...notice how it was too quick building the big ridge by Alaska.

[uncle W]

 

Those analog years snowfall wise: No year under 25" of snow at New Brunswick; 25.5" (1959), 28.1" (1976) , 47.3" (1986),  37.7" (1983) , 51.1" (1993), 51.3" (2002), 25.3" (1987).

 

right now 1986-87 is the best analog of the bunch...It didn't get going until the second half of January...it had a three or four week period of snow and cold...

[PB GFI]

I just jumped back on and really have no idea what some of you are looking at in regards to the 28th storm .

5 days ago i said that the xmas storm and the SW after would cut then you had to watch the backside for development .

That's the 28th storm.

You have a pressing cold front as the front comes through the area an area of LP will as per the 12z euro rides from OBX to CC . This has a very similar look to the post SB storm. The source region of this air is arctic. The outcome will be different than in November.

The 28th storm doesn't cut. If it doesn't snow or will be because the system slides east.

[bluewave]

That may be more a product of the model being too fast with the pattern change...notice how it was too quick building the big ridge by Alaska.

 

I also think that the lack of the strong phase this week won't be enough to really pump the heights near Greenland

to the extent that the model was showing. So any -AO drop will be transient before we rebound to more positive

levels to start January.

[bluewave]

I just jumped back on and really have no idea what some of you are looking at in regards to the 28th storm .

5 days ago i said that the xmas storm and the SW after would cut then you had to watch the backside for development .

That's the 28th storm.

You have a pressing cold front as the front comes through the area an area of LP will as per the 12z euro rides from OBX to CC . This has a very similar look to the post SB storm. The source region of this air is arctic. The outcome will be different than in November.

The 28th storm doesn't cut. If it doesn't snow or will be because the system slides east.

 

The Euro ensemble mean looks very meh Dec 28-31. The -EPO shift keeps things more progressive.

[SnowGoose69]

I just jumped back on and really have no idea what some of you are looking at in regards to the 28th storm .

5 days ago i said that the xmas storm and the SW after would cut then you had to watch the backside for development .

That's the 28th storm.

You have a pressing cold front as the front comes through the area an area of LP will as per the 12z euro rides from OBX to CC . This has a very similar look to the post SB storm. The source region of this air is arctic. The outcome will be different than in November.

The 28th storm doesn't cut. If it doesn't snow or will be because the system slides east.

 

Yeah, the 28th-29th event cannot cut, my guess is it will be a miss due to the pattern out west...if you look back at the SB event or other similar wave formation events like this they usually only impact areas east of a line from Harrisburg up to about NW NJ and usually occur when a big ridge is already established out west.  The reason the Euro shows the event and the GFS less is because the GFS still sees the 26th-27th system as being stronger, likely because its a NRN Stream event, the 28th-29th event is a SRN stream thing more so and thats why the Euro sees it...but the GFS blowing up the 26-27th event more so than the Euro also means the 28-29th one cannot really happen if the first one does.

[PB GFI]

Yeah, the 28th-29th event cannot cut, my guess is it will be a miss due to the pattern out west...if you look back at the SB event or other similar wave formation events like this they usually only impact areas east of a line from Harrisburg up to about NW NJ and usually occur when a big ridge is already established out west.  The reason the Euro shows the event and the GFS less is because the GFS still sees the 26th-27th system as being stronger, likely because its a NRN Stream event, the 28th-29th event is a SRN stream thing more so and thats why the Euro sees it...but the GFS blowing up the 26-27th event more so than the Euro also means the 28-29th one cannot really happen if the first one does.

I like the press of the trough here  . Not the greatest set up but all I am looking for is to get KNYC to 4 inches for the month of Dec so we can still lean on the better analogs .

[SnoSki14]

The Euro ensemble mean looks very meh Dec 28-31. The -EPO shift keeps things more progressive.

What analog are you leaning toward this winter.

[bluewave]

What analog are you leaning toward this winter.

 

 

El Nino Decembers since 1980 when there was no strong -AO December signal

and the NYC seasonal snowfall.

 

82-83.........27.2

86-87.........23.1

87-88.........19.1

91-92.........12.6

94-95..........11.8

97-98..........5.5

04-05..........41.0

06-07..........12.4

 

 

 

[SnoSki14]

What happens when you couple those stats along with the very positive PDO years Isotherm showed?

[PB GFI]

18z Para is a day or 2 behind the euro . But both like a system on EC before new years.

Let's see if we can get it to stick on the models as we get closer to next weekend

[Superstorm93]

The 18z GFS para for Dec 30th would be amazing...

[SnoSki14]

The gfs still looks nice post 27th. Remember for those who say cold and dry that once we get closer you'll often see systems start popping up especially in a year with an active subtropical jet.

That end of December early January period is one of our best shots at snow thus far.

[Yanksfan]

The gfs still looks nice post 27th. Remember for those who say cold and dry that once we get closer you'll often see systems start popping up especially in a year with an active subtropical jet.

That end of December early January period is one of our best shots at snow thus far.

I don't think we need to worry about many dry periods this winter. That subtropical jet means business. Our concern will be how much cold air we have to work with, along with proper trough alignment.

[bluewave]

What happens when you couple those stats along with the very positive PDO years Isotherm showed?

 

The +PDO December composite was much different from this December. Neither the October

-AO analogs nor the November +PDO analogs worked out for December. 

 

 

[Doorman]

http://mag.ncep.noaa.gov/model-guidance-model-area.php

 

http://www.tropicaltidbits.com/analysis/models/

 

 

Dec 30

guidance trends

 

GEFS -spag

GFS -18Z run

Gem -18Zrun

Fast and Flat

 

more than just one look

and I won't bite the hook

 

 

   dm

[PB GFI]

http://mag.ncep.noaa.gov/model-guidance-model-area.php

 

http://www.tropicaltidbits.com/analysis/models/

 

dec-30.gif

 

Dec 30

guidance trends

 

GEFS -spag

GFS -18Z run

Gem -18Zrun

Fast and Flat

 

more than just one look

and I won't bite the hook

 

 

   dm

Cherry picking are we ? So No euro ? No Para ? Don't look at the CPC for Dec 28 thru jan 4.

Will make u sad.

[NYCSNOWMAN2020]

In my humble opinion once the rain event on Dec 24 is done with I think we shall have more clarity on upcoming pattern.