12/26-12/28 Potential Snow Threat

[nzucker]

Hope u are right..

You are probably too far southeast to benefit much from the front-end dump, though the 12z ECM gives you about 2" snowfall. The boundary layer warming is a serious issue for NYC and LI; even on the Euro, temperatures are approaching 40F there in the midst of the storm while Westchester/Rockland/NNJ are in the low-mid 30s. When I talk about the foreign models being colder, I'm mostly talking about 850s/mid levels, which is my major concern. Your major concern is the surface getting too toasty with east winds off the mild Atlantic.

0z NAM trended colder than 18z NAM, with the freezing line at 850mb about 30 miles south. It's still obscenely warm compared to other guidance, especially against the foreign models. Small amount of front-end snow for the NW suburbs but nothing significant..

[West Milford Highlander]

The RGEM is pretty similar to the Euro you know? It's only a touch colder...

People are underestimating this storm in here because the American guidance is warmer, and those are the maps that most posters look at. On the better foreign guidance such as the ECM/GGEM/RGEM, this is a cold storm for most of the NYC metro area with significant snowfall accumulations and potential icing.

A lot of people are going to be wrong if your right

[MJO812]

0z Nam clownmap still shows alot of snow just west of NYC. So close.

http://raleighwx.americanwx.com/models/nam/00znamsnow_NE030.gif

[nzucker]

A lot of people are going to be wrong if your right

NWS has definitely downplayed the storm...I find they tend to hug the GFS but I am just reading their forecast discussion now. However, I'm not forecasting massive accumulations or anything for NYC. I think the most Central Park gets is 2", and even that could be pushing it. The areas I'm concerned about are places with minor to moderate elevation in Northern New Jersey, and then Putnam/Westchester/Rockland/Orange...a lot of these places have mostly rain forecast and could see a pretty nasty storm.

[Jefflaw77]

You are probably too far southeast to benefit much from the front-end dump, though the 12z ECM gives you about 2" snowfall. The boundary layer warming is a serious issue for NYC and LI; even on the Euro, temperatures are approaching 40F there in the midst of the storm while Westchester/Rockland/NNJ are in the low-mid 30s. When I talk about the foreign models being colder, I'm mostly talking about 850s/mid levels, which is my major concern. Your major concern is the surface getting too toasty with east winds off the mild Atlantic.

0z NAM trended colder than 18z NAM, with the freezing line at 850mb about 30 miles south. It's still obscenely warm compared to other guidance, especially against the foreign models. Small amount of front-end snow for the NW suburbs but nothing significant..

Thanks for the personal update.. I've never been to confident w/ this storm.. I'm expecting maybe 1/2 hour of snow the rain and wind..

I'm hoping we cash in w/ this weekend's possible event and then maybe w/ the 1/3/13 threat..

[nzucker]

This is just LOL worthy to me from the forecast discussion...the models with the highest verification rate are the ECM and UKIE, but again the NWS simply hugs the American models because they come from their agency:

"A BLEND OF NAM AND GFS USED FOR FORECAST."

[PB GFI]

0z shows no frozen precip for NYC and immediate burbs. 24 hrs out. That's a pretty big diff between the US models and there foreign counterparts Still at this time.

[nzucker]

0z shows no frozen precip for NYC and immediate burbs. 24 hrs out. That's a pretty big diff between the US models and there foreign counterparts Still at this time.

Yes the American models are well warmer, but we've only seen the 0z NAM so far. We're still waiting on the GFS...I would imagine it trends a little colder so that it's more in line with the 12z ECM but slightly warmer.

[rgwp96]

This is just LOL worthy to me from the forecast discussion...the models with the highest verification rate are the ECM and UKIE, but again the NWS simply hugs the American models because they come from their agency:

"A BLEND OF NAM AND GFS USED FOR FORECAST."

and heres a quote from the nws "the nam 12hr fcst verified the poorest of the three gfs/euro/nam with the 00z soundings and surface low position."

[PB GFI]

Yes the American models are well warmer, but we've only seen the 0z NAM so far. We're still waiting on the GFS...I would imagine it trends a little colder so that it's more in line with the 12z ECM but slightly warmer.

I thnk the GFS will look similar to the NAM There's a chance the American models don't go to the oters until the secondary forms. Clearly one of the 850 interpretations r wrong

[allgame830]

That should say something...

and heres a quote from the nws "the nam 12hr fcst verified the poorest of the three gfs/euro/nam with the 00z soundings and surface low position."

[Snow_Miser]

0z shows no frozen precip for NYC and immediate burbs. 24 hrs out. That's a pretty big diff between the US models and there foreign counterparts Still at this time.

The 00z NAM was a good bit colder for the northern portion of the storm into NE PA than the 18z was. Still a warm solution here, but not a bad trend.

[Irishmick9]

Winter Storm Warning just posted for Sussex...4 to 8 inches... 2 to 4 tenths ice

[SnowGoose69]

Watch for the CT valley advection effect tonight. Thats when you get a clear night up in SNE ahead of a storm and they radiate into the teens with very low DPs getting advected down into the NYC region on the NE wind. This is what caused the forecasts to get blown on the first round of the 12/5/03 storm. Still think we won't see any snow on LI or even JFK but I'd watch everywhere from northern Queens and Bklyn northwest closely.

[MJO812]

0z rgem still has a 2 hour period of light snow for NYC but then quickly changes to rain. Inland areas look really nice.

http://collaboration.cmc.ec.gc.ca/cmc/cmdn/pcpn_type/pcpn_type_gem_reg.html

[NYCSuburbs]

0z rgem still has a 2 hour period of light snow for NYC but then quickly changes to rain. Inland areas look really nice.

http://collaboration...pe_gem_reg.html

Still might be a bit too cold but it's still warmer than the 12z run and a step IMO towards a more reasonable solution. With the 12z run almost all of N NJ was safely in the snow zone during the bulk of the storm, this one has the rain/snow line a little more north with a primarily mix event for eastern NE NJ.

[MJO812]

Still might be a bit too cold but it's still warmer than the 12z run and a step IMO towards a more reasonable solution. With the 12z run almost all of N NJ was safely in the snow zone during the bulk of the storm, this one has the rain/snow line a little more north with a primarily mix event for eastern NE NJ.

It is still much colder than the Nam. It is far away from snow even down to the coast.

[Zelocita Weather]

Gfs coming in a little better...nice front end thump depicted...

[nycsnow]

Really worried for the costal flooding on wind for us costal peeps, stay safe

[IntenseBlizzard2014]

The RGEM is incredibly close for Southern Westchester County to have Heavy Snow for at least 75% of the event.

[nzucker]

Gfs coming in a little better...nice front end thump depicted...

The 850 line looks about 15-20 miles south on 0z GFS compared to 18z GFS. At 24 hours it is just south of JFK whereas the 18z at 30 hours had the freezing line bisecting Long Island. Decent run for the NW suburbs but still significantly warmer than foreign guidance, and with a lot of rain after the initial snow. RGEM and Euro limit the amount of time places like Westchester and NNJ deal with rain, whereas the GFS has heavy plain rain after the front-end thump.

[isnice]

Clear skies and low dew points. Here's to hoping for some evaporational cooling!

[NYCSuburbs]

According to the HPC diagnostics discussion the 0z NAM has initialization errors:

INITIALLY, THE 00Z NAM APPEARS TO BE 2-3C TOO WARM WITH ITS 850

HPA FREEZING LINE ACROSS VIRGINIA/MARYLAND AND THE UPPER OHIO

VALLEY, WHICH HAS POSSIBLE IMPLICATIONS FOR ITS FORECAST WINTER

WEATHER PRECIPITATION TYPES EARLY ON.

DURING THE SHORT RANGE PERIOD, THE 00Z NAM BECOMES A SLOWER THAN

THE REMAINDER OF THE GUIDANCE WITH THE SYSTEM MOVING THROUGH THE

NORTHEAST FROM LATE THURSDAY ONWARD, AND LIES NEAR THE SOUTHWEST

CORNER OF THE 12Z GLOBAL ENSEMBLE SPREAD WITH ITS ASSOCIATED

SURFACE LOW POSITION FRIDAY MORNING.

[snywx]

LOL @ the snow map for the 0z NAM..

[Isotherm]

Couple of things to keep an eye on obserbation wise over the next 24 hours, as I believe we might be looking at a nowcasting event here.

1) Surface wind direction

Right now most of us are advecting very nicely on northerly/NNE winds of 0-10 degrees with dew points falling into the low/mid 20s. Surface high pressure of 1032mb is situating itself near the southern tip of Hudson's Bay, initiating the infamous cold air damming process east of the Appalachains. Wind direction should remain dominate out of the N/NE throughout the next 12-15 hours, but monitor it closely as the onset of heavier precipitation arrives. The tightly packed isobars with their SE-NW orientation at H85 would lead one to believe that we'll be screaming easterly/ESE winds by tomorrow afternoon. However, a strong surface high attempts to resist that rush of marine air with the NELY surface winds. If your wind direction is still 0 to 50 degrees or so late tomorrow afternoon, you'll probably stay frozen longer thab progged. If you've already gone to 80-90 degrees with due easterlies, the CAD didn't hold well at all, and your boundary layer will be torching.

This is one of the clues I recall on the night before VD 2007. Wind direction did not exceed about 50-55 degrees.

2) Dew points / wet bulb temperature

The advection of drier air will persist overnight and by tomorrow at 7am, the forecast guidance suggests dew points around 20F for most of the region. Keep an eye on those. If you wake up tomorrow morning with dew points in the 15-20F range, it probably means drier than forecast air got advected down, and thus there's a higher chance of wetbulbing to freezing upon pcpn onset, in turn snow sticking more efficiently. The guidance has higher dew point air rushing in by 4pm as winds pick up from the east, but again, the dew point rise ties into the wind direction as well.

What will happen? In times of model divergence I think synoptics usually win out. I could be wrong, but I think the synoptic features point toward the solution painted by foreign models and less likely to see the NAM verify. With a strong sfc high and pretty good initial dewpoint depression, I would expect the freezing level at 850 to collapse southward into the hvy pcpn shield as depicted by most guidance. We'll see how it plays out but should be interesting.

[Dosh]

Couple of things to keep an eye on obserbation wise over the next 24 hours, as I believe we might be looking at a nowcasting event here.

1) Surface wind direction

Right now most of us are advecting very nicely on northerly/NNE winds of 0-10 degrees with dew points falling into the low/mid 20s. Surface high pressure of 1032mb is situating itself near the southern tip of Hudson's Bay, initiating the infamous cold air damming process east of the Appalachains. Wind direction should remain dominate out of the N/NE throughout the next 12-15 hours, but monitor it closely as the onset of heavier precipitation arrives. The tightly packed isobars with their SE-NW orientation at H85 would lead one to believe that we'll be screaming easterly/ESE winds by tomorrow afternoon. However, a strong surface high attempts to resist that rush of marine air with the NELY surface winds. If your wind direction is still 0 to 50 degrees or so late tomorrow afternoon, you'll probably stay frozen longer thab progged. If you've already gone to 80-90 degrees with due easterlies, the CAD didn't hold well at all, and your boundary layer will be torching.

This is one of the clues I recall on the night before VD 2007. Wind direction did not exceed about 50-55 degrees.

2) Dew points / wet bulb temperature

The advection of drier air will persist overnight and by tomorrow at 7am, the forecast guidance suggests dew points around 20F for most of the region. Keep an eye on those. If you wake up tomorrow morning with dew points in the 15-20F range, it probably means drier than forecast air got advected down, and thus there's a higher chance of wetbulbing to freezing upon pcpn onset, in turn snow sticking more efficiently. The guidance has higher dew point air rushing in by 4pm as winds pick up from the east, but again, the dew point rise ties into the wind direction as well.

What will happen? In times of model divergence I think synoptics usually win out. I could be wrong, but I think the synoptic features point toward the solution painted by foreign models and less likely to see the NAM verify. With a strong sfc high and pretty good initial dewpoint depression, I would expect the freezing level at 850 to collapse southward into the hvy pcpn shield as depicted by most guidance. We'll see how it plays out but should be interesting.

I'm gonna go back to this when it's 34F and raining tomorrow night I hate it when we get our hopes up before a slopfest.

[SnoSki14]

This could be a case where we see a very heavy thumping snow for a few hours, possibly accumulating a couple inches and then turning into a heavy wind driven rain with temps in the low to mid 40s.

And it's something I loathe because it's like getting the chair pulled under you. At least it'll be interesting with the winds, seeing snow, and then having something else to track right after.

[isnice]

Whatever happens, someone's gonna bust big tomorrow, be it the foreigns or the American models. 12/26/10 comes to mind in terms of the bust potential here.

[Isotherm]

I'm gonna go back to this when it's 34F and raining tomorrow night I hate it when we get our hopes up before a slopfest.

Oh you'll be raining tomorrow night, I'm not arguing that. I'm talking the first several hours of the storm as there's a huge discrepancy between the NAM and most other guidance. Does NYC go essentially right over to rain or can they get some accum before the changeover? We'll see.

[MJO812]

0z Ukie has a 989 low on Eastern LI. Colder than the GFS and Nam.

http://meteocentre.com/models/explorateur.php?lang=en&map=na&run=00&mod=ukmet&stn=PNM&comp=1&run2=00&mod2=ukmet&stn2=PNM&hh2=030&fixhh=1&hh=036