12/15 - 12/16 Coastal/Winter Storm & Observations

[HeadInTheClouds]

18z GFS won't back down with colder solution and higher snow amounts. 

 

[Tatamy]

15 hours ago, Tatamy said:

Models continue with the theme of the significant snows being north and west of I287 and I80 and west of the Hudson River.  Snow during the day Thursday mixes with other forms of frozen/freezing precip later in the day and into the night.  I am thinking 3-6” primarily at places over 1000’ with higher amounts up towards the Catskills.  

I am sticking with my thoughts from earlier.  Lower elevations primarily get 1-3”.  Most places south of I84 will be mainly rain tomorrow night.

[Nibor]

Wish I had the time to head up to the Catskills for this one. 

[donsutherland1]

Tomorrow, a complex storm will bring a cold rain to coastal regions into Friday. Some of the rain could be heavy. A general 0.50"-1.50" is likely. Interior sections could see accumulating snow before a changeover. The potential exists for a moderate to perhaps significant snowfall from central Pennsylvania across central New York State.

The latest EPS weeklies continue to suggest that near normal to below normal temperatures could prevail during the December 19-26 and December 27-January 2 periods. No severe cold is likely through at least the first three weeks of December. Afterward, as the PNA goes neutral, the prospect for snowfall and more significant cold could increase. Reflecting the rising probability of snowfall, about 50% of the 12z EPS ensemble members currently show 1" or more snowfall for New York City during the December 23-24 period.

The AO fell reached -4.000 on December 10th. Since 1950, there were 11 cases that saw the AO reach -4.000 or below during December. Mean snowfall for those cases was 9.0" (Median: 9.1"). 64% of such cases saw 6" or more of snowfall in December while 45% of such cases saw 10.0" or more snow. In contrast, during all other December cases, mean December snowfall was 3.5" (Median: 2.5"). 91% of those cases also saw a colder than normal December in the northern Middle Atlantic region. In terms of seasonal snowfall, 64% of those seasons saw 30" or more snowfall in New York City with 45% having 40" or more. Just 18% of such cases had less than 20" seasonal snowfall, both of which had less than 10" for the December-January period.

The ENSO Region 1+2 anomaly was -0.7°C and the Region 3.4 anomaly was -1.0°C for the week centered around December 7. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -1.23°C and the ENSO Region 3.4 anomaly has averaged -0.95°C. La Niña conditions will likely persist through mid-winter.

The SOI was +1.61 today.

The preliminary Arctic Oscillation (AO) was -3.136 today.

On December 12 the MJO was in Phase 4 at an amplitude of 1.066 (RMM). The December 11-adjusted amplitude was 1.307 (RMM).

Based on sensitivity analysis applied to the latest guidance, there is an implied 62% probability that New York City will have a colder than normal December (1991-2020 normal). December will likely finish with a mean temperature near 38.3° (0.8° below normal).

 

[HeadInTheClouds]

Dacks just got named 

 

[RU848789]

4 hours ago, HeadInTheClouds said:

18z GFS won't back down with colder solution and higher snow amounts. 

 

0Z NAM is even colder/snowier with regard to the southern extent of significant snow (except for the weird snow hole over Scranton).  If either of these were to verify or even be close, there are going to be a lot of surprised people.  

[HeadInTheClouds]

3 minutes ago, RU848789 said:

0Z NAM is even colder/snowier with regard to the southern extent of significant snow (except for the weird snow hole over Scranton).  If either of these were to verify or even be close, there are going to be a lot of surprised people.  

I think a lot will be determined by precip intensity at lower elevations. If it's heavy it could snow and when it is moderate or light it will rain. I still think Nam numbers are overdone at lower elevations. It will be interesting to see how things turn out. 

[Blizzwalker]

What happened to the NAM's seeing the warm layer for the 84 corridor and points south ?

I know that 10:1 maps are giving inflated numbers  on the southern edge, given this setup, but same models were predicting much less in Orange co several runs ago.  As others have mentioned,there seems to be a modest trend.

[HeadInTheClouds]

00Z RGEM - a lot less and nearly nothing east of Hudson and it has been consistent with this. 

 

[Tatamy]

21 minutes ago, RU848789 said:

0Z NAM is even colder/snowier with regard to the southern extent of significant snow (except for the weird snow hole over Scranton).  If either of these were to verify or even be close, there are going to be a lot of surprised people.  

What you see near Scranton is the same orographic effect that you see in the Hudson River valley.  The easterly flow near the surface experiences downsloping as it descends from the mountainous terrain to the east of these locations.  This has the effect of drying out the atmosphere.  The terrain just east of Scranton is up to 2000’ above MSL while the city itself is in a much lower valley location.

[Tatamy]

16 minutes ago, Blizzwalker said:

What happened to the NAM's seeing the warm layer for the 84 corridor and points south ?

I know that 10:1 maps are giving inflated numbers  on the southern edge, given this setup, but same models were predicting much less in Orange co several runs ago.  As others have mentioned,there seems to be a modest trend.

The model is seeing strong lift in the atmosphere which is producing heavier precip.  This in turn is bringing colder air down from aloft and changing the precip to snow.

[snywx]

0z GFS wow 

It continues to print out a huge event for these parts 

[HeadInTheClouds]

Big difference between GFS and CMC especially in HV. 

 

[snywx]

1 minute ago, HeadInTheClouds said:

Big difference between GFS and CMC especially in HV. 

 

W of the Hudson looks locked in on most guidance. You can see some evidence of potential downsloping along & E of the river

[HeadInTheClouds]

2 minutes ago, snywx said:

W of the Hudson looks locked in on most guidance. You can see some evidence of potential downsloping along & E of the river

Yup. CMC/RGEM have been very consistent with downsloping/shadowing. American models not so much. It's a huge difference with only 24 hours before game time. 

[eduggs]

As long as mid-levels don't torch, snow vs rain in NNJ, SENY, and NW CT will likely come down to localized mesoscale effects. Precipitation intensity will play a role. I'd also be interested to know how different the topographical maps input into the models are for the GFS, NAM, and CMC. I wonder if small differences in the discretized topography could be affecting the slight downsloping and upsloping leading to the critical 1 or 2 degree differences. This is a very marginal snow situation so there could be significant differences with elevation and location.

[CoolMikeWx]

It'll be interesting to see the 10 mile difference, if any at all, between my home in Middletown, five minutes north of Walmart and my business in the village of Florida with this kind of disagreement in models. Really gunning for all snow but of course that might still be a long shot.

It's rather amazing how the GFS has almost not changed at all in how many runs??

Sent from my SM-S908U using Tapatalk

[LibertyBell]

7 hours ago, HeadInTheClouds said:

Dacks just got named 

 

Dacks gonna get WHACKED

[LibertyBell]

6 hours ago, Tatamy said:

What you see near Scranton is the same orographic effect that you see in the Hudson River valley.  The easterly flow near the surface experiences downsloping as it descends from the mountainous terrain to the east of these locations.  This has the effect of drying out the atmosphere.  The terrain just east of Scranton is up to 2000’ above MSL while the city itself is in a much lower valley location.

My house in the mountains south of Scranton will see a lot more snow than Scranton will, Scranton is a snowhole.

 

[LibertyBell]

5 hours ago, eduggs said:

As long as mid-levels don't torch, snow vs rain in NNJ, SENY, and NW CT will likely come down to localized mesoscale effects. Precipitation intensity will play a role. I'd also be interested to know how different the topographical maps input into the models are for the GFS, NAM, and CMC. I wonder if small differences in the discretized topography could be affecting the slight downsloping and upsloping leading to the critical 1 or 2 degree differences. This is a very marginal snow situation so there could be significant differences with elevation and location.

This is very much like an early spring kind of storm

 

[wdrag]

Good Thursday morning everyone. Dec 15. 

Snow amount confidence is below average for the I84 corridor because of mixed snow-sleet-rain, and temperatures marginal for sticking. Attempted details follow, along with 3 maps inclusive of the 3AM NWS snow amount forecast. Note there is very little cold air to draw into this storm with temperatures already above freezing from Boston all along the east coast and Worcester is sitting only at about freezing. This combined with the rather warm 1000-500MB thicknesses poses a challenge for 4" amounts occurring nw NJ (FWN) to POU. Power outages seem to be a potential problem Poconos-Berkshires in 32-33F heavy wet snow of 6+" tonight and gusty winds 25-35 MPH. 

mPing: Anyone notice its posting delays for businesses now.

I still think models selecting precip types and assigning snowfall in each time period is questionable.  00z/15 EC is down.  In my opinion: temps at 1PM here in nw NJ will decide how much sticks. If it's 35, the warmer models prevail. If its 32F the colder models prevail.  

Later Thursday through Friday Dec 22-23: A potentially stronger storm with heavier snowfall but also a possible change to rain-ice? Wind may gust 50-60 MPH everywhere in the northeast USA for a short period of time. 

Christmas (24th-27th): Blustery with the coldest temperatures so far this winter, for a couple of days. 

Maps attached: The NWS deterministic forecast that went into this mornings forecasts. An ensemble map of snowfall by sunrise Friday and an impact severity map. Please click the maps for greater clarity, using the color bar for your area of interest and see a little explanation of each one. Use the color bar for the experimental winter severity index,  the SPC HREF only through 7A. Friday, and the NWS deterministic forecast for their 4AM forecasts of this morning. 

[IrishRob17]

@wdrag I noticed that with mPING this morning too. 

[Tatamy]

Precip in the form of snow and sleet now starting to break out in the Reading area of PA and areas south of there.

[wdrag]

Just letting you know that 11z HRRR temps seem absurdly warm at midday into western NJ... not sure what the problem is.  If they are that warm... there won't be much accumulation in SC.  That temp of 34 at KORH is bothersomely warm at 7AM.  

Lots of uncertainty in Sussex County NJ and probably up to POU in the modeled Kuchera snow gradient.  

[snywx]

1 minute ago, wdrag said:

Just letting you know that 11z HRRR temps seem absurdly warm at midday into western NJ... not sure what the problem is.  If they are that warm... there won't be much accumulation in SC.  That temp of 34 at KORH is bothersomely warm at 7AM.  

Lots of uncertainty in Sussex County NJ and probably up to POU in the modeled Kuchera snow gradient.  

24/21 here. 
 

looks like upton is finally acknowledging the potential for a tight snow gradient here in Orange County

[Tatamy]

22 minutes ago, wdrag said:

Just letting you know that 11z HRRR temps seem absurdly warm at midday into western NJ... not sure what the problem is.  If they are that warm... there won't be much accumulation in SC.  That temp of 34 at KORH is bothersomely warm at 7AM.  

Lots of uncertainty in Sussex County NJ and probably up to POU in the modeled Kuchera snow gradient.  

Models are really struggling with the snowfall gradient across NW NJ and the Lehigh Valley of PA.  Compare the 0z and the 6z Euro.  The 6z HRRR and the 12z HRRR are another pair to look at.

[Tatamy]

Snow is breaking out on the west side of Allentown currently.  Looks to be coming down moderately as shown on radar / webcams to the west of there.

[snywx]

11 minutes ago, Tatamy said:

Models are really struggling with the snowfall gradient across NW NJ and the Lehigh Valley of PA.  Compare the 0z and the 6z Euro.  The 6z HRRR and the 12z HRRR are another pair to look at.

What did the 6z Euro show snowfall wise. I’m hearing it ticked cooler

[Brasiluvsnow]

I am surprised that this thread is not getting more action as it is literally game time. Like many of you I am curious to see if the colder modeled solutions come to fruition or was the GFS always on crack ?

[Tatamy]

1 minute ago, Brasiluvsnow said:

I am surprised that this thread is not getting more action as it is literally game time. Like many of you I am curious to see if the colder modeled solutions come to fruition or was the GFS always on crack ?

It’s to be determined.