February 11 -12 Winter Storm Threat

[RU848789]

12Z Euro is a solid 3-4" of actual snow for most of CNJ/NYC, overall.  It then looks like both areas get about 1" of sleet and then rain.  Transition times are 2-3 hours earlier for me in the Edison area vs. Manhattan, but the end result looks similar.  Changeover to rain looks to be around 4-5 pm for me and maybe 6-7 pm for CPK.  Euro shows 4-6" of snow well NW of 95 (like NW of a line from Allentown to Newburgh).  About 1.4" of total precip for CNJ/NYC with about half of that falling as rain with temps in the mid/upper 30s, so it would likely be mostly absorbed by the slushpack.  As modeled.   

[TJW014]

1 minute ago, RU848789 said:

12Z Euro is a solid 3-4" of actual snow for most of CNJ/NYC, overall.  It then looks like both areas get about 1" of sleet and then rain.  Transition times are 2-3 hours earlier for me in the Edison area vs. Manhattan, but the end result looks similar.  Changeover to rain looks to be around 4-5 pm for me and maybe 6-7 pm for CPK.  Euro shows 4-6" of snow well NW of 95 (like NW of a line from Allentown to Newburgh).  About 1.4" of total precip for CNJ/NYC with about half of that falling as rain with temps in the mid/upper 30s, so it would likely be mostly absorbed by the slushpack.  As modeled.   

That's good news. There's still some wiggle room to improve a little more as well. 1-2" of snow, followed by up to an inch of sleet, changing to freezing rain, to rain.

I'm about 30 miles to your south, so I expect the changeover to occur between 1 and 2 pm

 

[MJO812]

36 minutes ago, yankeex777 said:

Without seeing any maps that sounds like an improvement.

Alot of sleet and some snow

[Ericjcrash]

3 minutes ago, Snow88 said:

Alot of sleet and some snow

Music to my ears. When does NYC go above freezing?

[Juliancolton]

This is perhaps more germane to the interior, but worth keeping in mind that the p-type maps will often show sleet or mix if there's a +0.2C layer somewhere, even though it would clearly still be snowing in reality.

[SnowGoose69]

2 minutes ago, Juliancolton said:

This is perhaps more germane to the interior, but worth keeping in mind that the p-type maps will often show sleet or mix if there's a +0.2C layer somewhere, even though it would clearly still be snowing in reality.

With that sort of strong SW flow though that layer might verify a solid degree warmer or more  

[hudsonvalley21]

1 minute ago, SnowGoose69 said:

With that sort of strong SW flow though that layer might verify a solid degree warmer or more  

With that possible strong SW flow at that layer. Would that be enough to scour out the CAD at the surface or would that increase the possibility of having a longer period of ZR on this sounding?

[Juliancolton]

10 minutes ago, SnowGoose69 said:

With that sort of strong SW flow though that layer might verify a solid degree warmer or more  

I agree that is something to watch out for, though in this particular case it seems like WAA on the SW flow will have shut off by that time frame. Isohypses parallel to isotherms, etc...

[HVSnowLover]

NAM is straight out nasty especially for anyone even just north of the city, lots of sleet followed by some ZR

[RU848789]

17 minutes ago, Juliancolton said:

This is perhaps more germane to the interior, but worth keeping in mind that the p-type maps will often show sleet or mix if there's a +0.2C layer somewhere, even though it would clearly still be snowing in reality.

Always wondered about that.  This is similar to the kind of heat transfer calculations/modeling I've in the past on chemical reactors with phase changes and I assume is done via algorithms now that hopefully are correct, but I could see that in borderline situations like this one how an algorithm might say sleet, when the reality is snow.  We're talking having to model the heat input, over time with variable column temp, during a flake's transit down about 7000+ feet at about 10-15 mph, iirc, so it takes about an hour to traverse that distance and I simply don't know what the delta above 32F needs to be over X time to achieve flake melting (especially when that delta isn't a constant). 

Cool problem to ponder.  I do know that once sleet forms in the lower 2000-3000 feet of the atmosphere, that it'll take more than 1F delta to melt that ice pellet, as ice pellets will melt much more slowly than snowflakes, due to the far smaller exposed surface area per unit mass of a pellet vs. a flake.  The reason I bring this up, is most of the models, right now, have soundings where the flakes melt at 5000-7000 feet up, then freeze into ice pellets during their fall through the final 2000-3000 or so feet of sub-32F air and then the surface temp is creeping up faster than those bottom 2000-3000 feet, such that the surface is reaching >32F before the layer above it and I'd say that seeing a surface temp at 33-34 F is unlikely to melt the pellets.  

[mikem81]

3 minutes ago, HVSnowLover said:

NAM is straight out nasty especially for anyone even just north of the city, lots of sleet followed by some ZR

It cut precip in half through 7pm tommorrow. 

[qg_omega]

4 minutes ago, HVSnowLover said:

NAM is straight out nasty especially for anyone even just north of the city, lots of sleet followed by some ZR

On 2/10/2019 at 12:31 PM, qg_omega said:

Guys it's sleet to rain, stop with the snow maps.  Less than an inch of snow for NYC then sleet and rain.  It's a nothing burger

NAM is a nothing burger, precip is delayed and when it hits its some sleet to rain, little to no snow.  My thoughts remain the same, Upton looking to bust hard once again.

[CPcantmeasuresnow]

3 hours ago, Juliancolton said:

Come on, man. Anything less than a foot after settling isn't a "pack", it's just coverage. Don't compromise!

It's really just semantics but I get your point. And yes I am compromising, but the winter of 18/19 is all about compromising ones values and core beliefs.

This winter however 5 inches of snow followed by 3 inches of sleet qualifies as a snow pack. It would probably compress to a six inch slab of ice area wide, and barring a constant barrage of GLC's should last at least a couple of weeks. At least one would hope.

 

[495weatherguy]

1 minute ago, CPcantmeasuresnow said:

It's really just semantics but I get your point. And yes I am compromising, but the winter of 18/19 is all about compromising ones values and core beliefs.

This winter however 5 inches of snow followed by 3 inches of sleet qualifies as a snow pack. It would probably compress to a six inch slab of ice area wide, and barring a constant barrage of GLC's should last at least a couple of weeks. At least one would hope.

 

Friday and sat are forecasted to be fairly warm.  Near 50.   Do you think any “pack” could survive that?

[RU848789]

18Z NAM takes a large step warmer/wetter vs. 12Z, unfortunately, especially for the 95 corridor from Philly through NYC.  NYC, for example, now has 0.5-0.6" LE as frozen snow/sleet, while 12Z NAM had 0.9-1.0" LE as frozen.  Hope this isn't a sign of things to come...

 

[HVSnowLover]

8 minutes ago, qg_omega said:

NAM is a nothing burger, precip is delayed and when it hits its some sleet to rain, little to no snow.  My thoughts remain the same, Upton looking to bust hard once again.

People can underestimate all they want, this will be an impact event tomorrow morning and at least through early afternoon. The CAD signal is there, we can get caught up in details but I would be very surprised if this isn't at least 5-6 hours of frozen precip for the metro area tomorrow and as I said areas even just immediately NW of the city may be in for a lot more.

[Doorman]

Standard NAM  snow prog......where did I see this trend before?????  

Nam Nest for good measure

 

[Juliancolton]

10 minutes ago, RU848789 said:

Always wondered about that.  This is similar to the kind of heat transfer calculations/modeling I've in the past on chemical reactors with phase changes and I assume is done via algorithms now that hopefully are correct, but I could see that in borderline situations like this one how an algorithm might say sleet, when the reality is snow.  We're talking having to model the heat input, over time with variable column temp, during a flake's transit down about 7000+ feet at about 10-15 mph, iirc, so it takes about an hour to traverse that distance and I simply don't know what the delta above 32F needs to be over X time to achieve flake melting (especially when that delta isn't a constant). 

Cool problem to ponder.  I do know that once sleet forms in the lower 2000-3000 feet of the atmosphere, that it'll take more than 1F delta to melt that ice pellet, as ice pellets will melt much more slowly than snowflakes, due to the far smaller exposed surface area per unit mass of a pellet vs. a flake.  The reason I bring this up, is most of the models, right now, have soundings where the flakes melt at 5000-7000 feet up, then freeze into ice pellets during their fall through the final 2000-3000 or so feet of sub-32F air and then the surface temp is creeping up faster than those bottom 2000-3000 feet, such that the surface is reaching >32F before the layer above it and I'd say that seeing a surface temp at 33-34 F is unlikely to melt the pellets.  

There are a few very good COMET MetEd courses that introduce some of these topics. Elevated warm layer depth and maximum temperature have an almost linear relationship (I think something like r = 0.9), so snow falling through a <+1C layer usually will not have time to melt. Obviously there are myriad other factors to consider, but my main takeaway from that has always simply been not to assume a >0C layer is inherently a melting layer.

[ILoveWinter]

5 minutes ago, Doorman said:

Standard NAM  snow prog......where did I see this trend before?????  

NAM could very well be right but why are you only focused on this model?

[HVSnowLover]

Just now, ILoveWinter said:

NAM could very well be right but why are you only focused on this model?

Such a hard forecast in terms of initial snow vs mainly sleet. But I am confident it starts frozen and rips frozen for at least a few hours.    

[Doorman]

1 minute ago, ILoveWinter said:

NAM could very well be right but why are you only focused on this model?

ILW

not focused on the nam...just sharing guidance to back up some of my  older posts

how bout the rgem??

 

[Rtd208]

Mt.Holly continues the Winter Weather Advisory here which is in effect until 6 pm tomorrow for 2-4" of snow but has increased ice accumulation to one tenth of an inch

[Ericjcrash]

28 minutes ago, RU848789 said:

18Z NAM takes a large step warmer/wetter vs. 12Z, unfortunately, especially for the 95 corridor from Philly through NYC.  NYC, for example, now has 0.5-0.6" LE as frozen snow/sleet, while 12Z NAM had 0.9-1.0" LE as frozen.  Hope this isn't a sign of things to come...

 

It's no warmer, just a whole lot drier.

[SEC]

Sullivan County under a Winter Storm WARNING now. Gonna be a mess (and dangerous) on the roads tomorrow with snow and ICE.

 

[SnowGoose69]

5 minutes ago, Ericjcrash said:

It's no warmer, just a whole lot drier.

The margin for error on when precip arrives with this event is massive.  You can see on almost all guidance it teases for hours across EPA and WRN NJ before advancing in.  If that’s off by 4-5 hours there will be significantly more snow 

[RU848789]

11 minutes ago, Ericjcrash said:

It's no warmer, just a whole lot drier.

QPF is only down 0.2" (at EWR, per the graphic), but sleet is way down (from 0.8 to 0.5" LE) and rain is way up vs. 12Z (from 0.2 to 0.4"), so there's some warmth in there somewhere.  And it starts after the morning rush hour for anyone NE of Trenton.  As modeled, a disaster if you like wintry weather. At the same time Mt. Holly ups the ante on warnings across much of their area.  Like I said, let's hope it's a blip.  

[Ericjcrash]

2 minutes ago, SnowGoose69 said:

The margin for error on when precip arrives with this event is massive.  You can see on almost all guidance it teases for hours across EPA and WRN NJ before advancing in.  If that’s off by 4-5 hours there will be significantly more snow 

Yeah, wouldn't be surprised if it comes in an hour or two ahead of guidance. Seems to happen pretty often in SWFE.

[Doorman]

I will let the more skilled posters have a crack at this setup.... 

 

[Ericjcrash]

1 minute ago, RU848789 said:

QPF is only down 0.2" (at EWR, per the graphic), but sleet is way down (from 0.8 to 0.5" LE) and rain is way up vs. 12Z (from 0.2 top 0.4"), so there's some warmth in there somewhere.  And it starts after the morning rush hour for anyone NE of Trenton.  As modeled, a disaster if you like wintry weather. At the same time Mt. Holly ups the ante on warnings across much of their area.  Like I said, let's hope it's a blip.  

Let me clarify, its drier when temps support frozen precip. That chart shows it perfectly. Not good regardless. 

[sussexcountyobs]

Winter Storm Warning now up for Sussex County NJ. 4-7" snow and sleet, up to .2" ice.