Dec 16-17 Snow/Ice potential storm

Frank_Wx wrote:The CMC, or Canadian model, is persistent and agrees with the short range models like the NAM that the ice threat will extend toward the coast. Again, I am not a believer in this scenario but would like to digest additional model runs later today and see if this holds any merit

sorry Frank missed ur earlier post. I think it's go be a fine line wether I see more than city. Mog that's horrid most over half a inch plus!! If that comes true nj and most of Westchester to lhv are go be without power.

Surface temps are at or above freezing for most folks now.  That is good.

Wet bulb temps still below freezing for most.  

What the HRDPS is showing would be like a once in 20 year ice storm. 3/4" - 1" range. I think more like .25" - .5" is possible 40 miles NW of 95.

few flakes flying in Western Suffolk County on Long Island

Great discussion here, just off from teaching my first round of classes. This going to be a serious issue for NNJ above I80 for sure. The ice maps are crazy and include sleet as well. Very complex and tough call here.

I see the meso's forming a LP off the SNJ coast and I listen to NSFXwx a very good pro met on twitch. He explained why the LP will op and strengthen - the EURO actually sees this but weaker than the mesos and the flow is CC - it doesn't need to be strong since teh cold air source over head is just that ..cold.
I am not rooting for this scenario just pointing this out - if the mesos are right then this storm becomes even more serious. Western BC through Sussex is in trouble .

From Mike Mostwill
The latest HREF depicting a potential mess overnight tonight into Tuesday early afternoon. The low level cold air is dense in nature & is illustrated well here, despite ML warmth. It takes more time to scour out, slower than the mid layers of the atmosphere.
https://twitter.com/MikeMostwill/status/1206611268418842624?s=20

Just a reminder Euro has had the same general solution, give or take intensity/mix line for about 4+ days... easily the most steady model during this storm. Every model is in step with the EURO, well maybe not every!!!

Mugs what I'm hearing from other Mets is that the atmosphere is cold from 900 millibars down and is more of a sleet signal and that the model algorithms are wrong showing freezing rain as they underestimate the cold aair the lower you get in the atmosphere not sure if this is true but that's what I'm hearing

I'm at 33 degrees with a dew point of 15 even if the dew point Rises to the low 20s as precipitation starts temps in my area probably drop to about 28 29 degrees. The wind direction on the models from what I'm hearing from other Mets is 60 to 70 degrees which is north to Northeast component at 5 to 10 miles per hour which is not going to do it as far as raising surface temperatures or scouring out the low-level cold air. That's why from the North Shore of Long Island through LaGuardia to about 80 in northern New Jersey anything north of there is going to be snow and sleet especially when the precipitation comes down heavy enough. We'll probably have a six to eight hour period of moderate too heavy precipitation then it'll start become more scattered and lighter in nature when it flips to freezing rain and maybe plain rain at the end. My call is 3 to 6 in from south to North for these areas. That's my experience with these type of systems very weak with a fresh shot of polar air and very weak wind flow at the surface.

850's and 925's temperatures haven't moved much.  I'm not seeing big upward bulges in the isotherms because the developing storm is weak and its trajectory.  A strong storm would plow right through that.  You can see the cold press even more exacerbated on the 1 PM reading.  Interesting.

@Al and Hee Haw great posts.
The ZR is sleet in the model configuration/algorithm which is ice but not nearly as damaging as ZR (ZR=Freezing Rain). That is good news if true.
HH that 925 map is telling - the storm isnt like you said gonna bully its way through this LLC since its not a coastal - SWFE event LP are weak in nature and my 30 years of following these the CAD usually wins out with a weak LP.

I heard Euro ticked a bit north. Can somebody post snow maps/ZR maps if possible?

amugs wrote:@Al and Hee Haw great posts.
The ZR is sleet in the model configuration/algorithm which is ice but not nearly as damaging as ZR (ZR=Freezing Rain). That is good news if true.
HH that 925 map is telling - the storm isnt like you said gonna bully its way through this LLC since its not a coastal - SWFE event LP are weak in nature and my 30 years of following these the CAD usually wins out with a weak LP.

And while I certainly wouldn't lock onto the absolute totals on this map, the hrrr has consistently run after run (it runs every hour) trended colder and colder throughout the day

6Z run

0Z run

amugs wrote:

Very close to the GFS ice map. Models are pretty locked in. Man if these ice projections are correct it's going to be downright horrific for some places.

@Scott - the HRRR could be onto something with a quick burst of snow that happens around Midnight for NYC Metro before changing to rain. But the changeover to mix/rain will be fairly quick.

Here is what the RGEM shows as snow before changing over. 1-2"

It's going to be impossible to measure the storm if you get two inches of snow and then an inch of sleet. Look for Central Park to under measure this storm which is nothing unusual

Frank_Wx wrote:

amugs wrote:

Very close to the GFS ice map. Models are pretty locked in. Man if these ice projections are correct it's going to be downright horrific for some places.

@Scott - the HRRR could be onto something with a quick burst of snow that happens around Midnight for NYC Metro before changing to rain. But the changeover to mix/rain will be fairly quick.

That has my area at .25". Meso's like NAM and HRDPS are 3x that for EPA. Order of magnitude difference in effect. I'm hoping globals handle the ice better, but skeptical that it'll be more.

heehaw453 wrote:

Frank_Wx wrote:

amugs wrote:

Very close to the GFS ice map. Models are pretty locked in. Man if these ice projections are correct it's going to be downright horrific for some places.

@Scott - the HRRR could be onto something with a quick burst of snow that happens around Midnight for NYC Metro before changing to rain. But the changeover to mix/rain will be fairly quick.

That has my area at .25".  Meso's like NAM and HRDPS are 3x that for EPA.  Order of magnitude difference in effect.  I'm hoping globals handle the ice better, but skeptical that it'll be more.

pushed north a bit I was in the ice on earlier models. This is all a nowcast I think. Will be interesting for sure.

18z NAM ice and snow maps

Frank_Wx wrote:18z NAM ice and snow maps

That ice had better be sleet and not all freezing rain. The half inch by me would be bad enough, but an incha nd a quarter plus? That would be historic.

Here is the warmest frame of 850mb temps on the 18z NAM



Here is the warmest frame of 925mb temps on the 18z NAM



Total freezing rain accum:

Frank_Wx wrote:18z NAM ice and snow maps

The ice trend is not good. The NAM brought significant icing more s/e. I'd be surprised in NWS doesn't sound the ice storm warning with afternoon package.

Use the dotted white line in the maps above as the freezing line.

If the white line is N&W of you on both maps you are raining. If 925mb is cold but 850mb is warm there is either sleet or freezing rain falling. One has to look and really understand soundings to know for sure the precip type

Upton's ice forecast is not nearly as prolific as what NAM is showing

This would be freezing rain for me.  Some sleet initially when the heavy stuff moves in, but the warm nose is too far south for much ice. Is it right though? Much better chance in NNJ i think.

heehaw453 wrote:

Frank_Wx wrote:18z NAM ice and snow maps

The ice trend is not good.  The NAM brought significant icing more s/e.  I'd be surprised in NWS doesn't sound the ice storm warning with afternoon package.

I's borderline, remember ice storm warning criteria differs in NYS and New England vs CNJ and Pennsylvania south. It's 1/2 inch of ice in all of NY State, NNJ and all of New England, anywhere south of there it's a 1/4 inch.

CPcantmeasuresnow wrote:

heehaw453 wrote:

Frank_Wx wrote:18z NAM ice and snow maps

The ice trend is not good.  The NAM brought significant icing more s/e.  I'd be surprised in NWS doesn't sound the ice storm warning with afternoon package.

I's borderline, remember ice storm warning criteria differs in NYS and New England vs CNJ and Pennsylvania south. It's 1/2 inch of ice in all of NY State, NNJ and all of New England, anywhere south of there it's a 1/4 inch.

I think Sussex, Passaic and Morris County in NJ you really got to pull that trigger now. Sounding suggest heavy freezing rain 30-31 degree surface temperature. This would easily exceed 1/2".