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NYC/PHL Jan 17-19 Forecast Discussion


am19psu

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Looks nasty for Scranton.

It does look nasty, but in situations like this I remember the Pocono Plateau staying ice much longer than the surrounding valleys--to answer a previous poster's question about elevation. I think scranton-wilkes goes above freezing rather quickly tomorrow. I could be wrong, or wishcasting because I know i have to drive into work at 9am...

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Still big qpf though. 1 inch over N NJ on the GFS and 1.5 inches on the NAM. Either way, it better get above freezing.

These are always such tricky forecast situations. Timing temp advection is difficult and when it means getting above freezing or not to avoid significant snow or ice it is even more delicate. I would think if the higher qpf values are realized it could mean one of two things. Stronger warm air advection and quicker rise above freezing at all levels expect for perhaps parts of Warren Sussex, NW Morris & NW Passaic counties. If could also mean a dynamically cooled atmosphere and prolonged heavy wet snow or sleet. Pressed to give numbers for our area I would say 3-5" locally 6" N&W part of area with ~0.2-0.4" ice with 0.5" N&W areas again. But again it is as always a hour by hour forecast as we watch the freezing line progress or perhaps not progress. Regardless much of NNJ and eastern PA will be messy in the morning. How far into midday and afternoon is another question.

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Since the next viable snow threat for NYC/LI is the Thursday night/ Friday timeframe, I'll take any scenario for tonight/tomorrow's storm which least impedes our snowpack and leaves us with a solid foundation in which to add to later on this week.

If we can stay in the mid 30s or so, we probably keep a good amount of it. If we get above 40, we probably lose most of it. Very cold rain is usually absorbed into the snow and doesn't cause it to melt.

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Watched Jeff Smith on Ch 7 before and He has Wintry Precip starting by Midnight and staying Frozen until at least 9 Am in My area and Noon a little further North.. That is 9 to 12 hrs of Frozen Precip yet He has only 1 to 3 in Accumulation. The only way that happens is if it changes to Freezing Rain fairy Quickly which a 6 hr period of Freezing Rain will cause Major Problems.. I think this storm still has a few Surprises in store..24 degrees at 6:30 will be interesting to see if Temp drops much more before onset of Precip..

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If we can stay in the mid 30s or so, we probably keep a good amount of it. If we get above 40, we probably lose most of it. Very cold rain is usually absorbed into the snow and doesn't cause it to melt.

I'll take mid 30's as long as JFK doesn't all of a sudden shoot up to 51 degrees with that snow eating fog .

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Watched Jeff Smith on Ch 7 before and He has Wintry Precip starting by Midnight and staying Frozen until at least 9 Am in My area and Noon a little further North.. That is 9 to 12 hrs of Frozen Precip yet He has only 1 to 3 in Accumulation. The only way that happens is if it changes to Freezing Rain fairy Quickly which a 6 hr period of Freezing Rain will cause Major Problems.. I think this storm still has a few Surprises in store..24 degrees at 6:30 will be interesting to see if Temp drops much more before onset of Precip..

I've seen Brooklyn in the past go from high single digits to upper 30's in a 12 hour period, amazing what a warm flow off the ocean can do.

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Hello all

Here is the 18z run of the Wxsim module with the NAM/GFS incorporated. Still very consistent with a little more snow forecast then NWS but similar timings and impact overall...here is the rundown

Light Snow by 11pm Temp at 22.7

Mod Snow by midnight Temp at 23.1

Heavy Snow at 3am Temp at 24.9

Snow to IP mix around 5am (Total Snow accumulation 4 to 5" before changeover)

Heavy IP/ZR mix at 6am Temp 27.2

ZR thru 12noon - temp at 32.0 at noon (Total ZR 0.65")

Currently here

22.0

DP 12.1

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Hello all

Here is the 18z run of the Wxsim module with the NAM/GFS incorporated. Still very consistent with a little more snow forecast then NWS but similar timings and impact overall...here is the rundown

Light Snow by 11pm Temp at 22.7

Mod Snow by midnight Temp at 23.1

Heavy Snow at 3am Temp at 24.9

Snow to IP mix around 5am (Total Snow accumulation 4 to 5" before changeover)

Heavy IP/ZR mix at 6am Temp 27.2

ZR thru 12noon - temp at 32.0 at noon (Total ZR 0.65")

Currently here

22.0

DP 12.1

If that much ZR occurred, wow...

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Hello all

Here is the 18z run of the Wxsim module with the NAM/GFS incorporated. Still very consistent with a little more snow forecast then NWS but similar timings and impact overall...here is the rundown

Light Snow by 11pm Temp at 22.7

Mod Snow by midnight Temp at 23.1

Heavy Snow at 3am Temp at 24.9

Snow to IP mix around 5am (Total Snow accumulation 4 to 5" before changeover)

Heavy IP/ZR mix at 6am Temp 27.2

ZR thru 12noon - temp at 32.0 at noon (Total ZR 0.65")

Currently here

22.0

DP 12.1

is that only for your area? Can you run it for KHPN?

Thanks in advance

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If we can stay in the mid 30s or so, we probably keep a good amount of it. If we get above 40, we probably lose most of it. Very cold rain is usually absorbed into the snow and doesn't cause it to melt.

The snowpack here is about 14-15" , which is 11" of relatively soft snow over 3 or 4 inches of ice. The main question in my mind is how many inches of ice (i.e., hard snow...not frozen rain) are left on the ground when it eventually freezes up after the storm.

This might be a little frustrating for you because you may survive the rain tomorrow only to see the pack decimated while waiting for the cold air to seep in on Wednesday. The areas that can get back to freezing for a few hours Wednesday night will do much better than the areas that don't (NYC probably wont...parts of LI may or may not and inland is looking good).

Tomorrow may pull some surprises (the definition of surprise for this part of LI tomorow being anything better than a light snowfall followed by a day of pounding rain and 38 - 40). If there is a surprise, I think it would be in the form of more sleet than anyone is expecting (maybe even a few wet snowflakes mixed with the rain when you least expect it). This is for the north shore but it's a fairly low probability.

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Some things where pondering here tonight, Temp / dew pt spread is 15 degrees here, so that's a lot of dry air still in place and wet bulbs are in the lower 20s. LAMP numbers don't put newark above freezing until about 17Z on Tuesday, our thinking here is a coating to an inch or so in newark metro then sleet and freezing rain before going over to non freezing rain by 1pm tomorrow afternoon. Things many are trying to warm things up much too fast in the AM.

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I'm noticing that the RUC and HRRR are warming up the mid-levels earlier but holding onto the cold at the surface. That means less snow and more ice, which would be a pretty big disaster especially in the Poconos.

In the latest radar loops. The eastern NC area is filling in and the movment is due north (b-line to the Poccnos).

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For all you snow pack freaks, you can stop worrying because anyone north of the M/D line will have a glacier come Thursday AM.

Yeah I think there will certainly be some refreezing. Jeez, these kids get 2 big storms and they think the snow will last forever...

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Yeah I think there will certainly be some refreezing. Jeez, these kids get 2 big storms and they think the snow will last forever...

The snow is going to last a long time this winter...I still have a foot on the ground, am expecting 2-4" then icing tomorrow, and then there's the overrunning event Thursday night that may bring 6-10" to NYC metro. I've rarely seen such a persistent snowpack here but this is indeed an unusual winter.

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