Feb 18-19 long duration manageable snow and ice event

[wdrag]

554A/17: Topic headlines adjusted from the original late last week to the snowier wintry solution. A burst of moderate to briefly heavy snow Thursday, begins lightly between midnight and 6AM (OBS-NOWCAST thread will be started this evening)  Thursday much of the area, though it may delay a bit to the daylight hours north of I84. QPF etc has decreased since originally threaded. Modeling allows sleet/freezing rain to get involved near the Thursday evening rush hour and eventually back to manageable, possibly intermittent snow on Friday.  Some modeling has a decent burst of snow Friday.  ~Half a foot or more seems likely for much of the area with sleet/freezing rain (even maybe eventually even a bit of rain e LI) limiting the risk of 6" south of I78 and possibly LI as well. Graphics added are WPC 09z ensemble chance of 8"+, chance of .01 freezing rain for the periods indicated (note ensemble chance of 8+ has higher chances southwest of Harrisburg but that includes time not shown in this depiction) and the NWS regional snow forecast. 

 

517A/16: A nice solution coming (overall colder and snowier than what modeling was generally offering Friday the 12th) with a range of accumulations of 1" to possibly as much as a foot in the upper high end scenario. Thursday's evenings commute should be snowy for much of the area and see delays,  as it readies for a possible change to ice Near I78-LI (rain far south part of the subforum)  and then ends Friday, most of it done by sunrise Friday (but with early morning delays/cancels). Too early for me to be sure for the NYC/LI/NNJ membership but plenty of modeling close to half a foot.  A watch/warnable snow-ice event seems to be coming for a portion of NYC subforum,. IFFFFF NYC were to report half a foot, that would place NYC in the top 5 snowiest February's. 

This coming snow-sleet, whatever, should rejuvenate snow depth , and maybe allow half a foot or more for much of the area into Monday Feb 22. 

One WPC graphic added: the 24 hour prob of 2" of snow by 7P Thursday. 

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625A/15:  Adding the ~5z/15 NWS prob of 3+" snow graphic. Otherwise, variable modeling with it appears to me a slightly colder trend, but still any snow should change to sleet/freezing rain for a time, and maybe just rain LI s of I78. Very uncertain but NWS probs are very high just north and west of NYC for 3"+.  We'll see how it works out. 

 

525AM Sunday the 14th- Valentines Day!  This event still looks interesting for snow lovers, despite the warm GFS OP. This is a prelim update for an event 5 days away. Definitely Advisory minimum potential, especially interior and possible Watch-Warning material interior part of the forum north of I78. Early guess on modeling...a range of 1/2-5" of snow-sleet Thursday before a change to ice North of I78 and just rain LI and south of I78 Thursday evening with rain most of the area for a short time Friday morning. Snow and ice ne PA/nw NJ se NYS/n CT. How much of each phase unknown. May add another graphic or two by the 915AM full update of this topic.  Here's the NWS ensemble prob of 3+" of snow Thursday...that light blue is 70% up there by I84. 

 

520PM Saturday: EPS drifting north for Friday morning so front end snow/ice goes to rain, possibly north of I84 Fri AM? Still... with all the modeled qpf, the 806AM water snow equivalent weight concerns, and definitely gutter ice water damming/roof leakage possibilities.  Five to 6 days away.

 

806AM Saturday the 13th update:  Ensembles differ (GEFS far northwest with a primary into the e Great Lakes), while the 00z/13 EPS further southeast with a coastal and therefore colder. NAEFS is in the middle and says snow or ice to start the 18th, changing to rain before ending on the 19th.  I won't add many graphics since its similar to yesterday. My concern is another ice storm for the I84 high terrain corridor and snow pack water equivalent weight increasing as well as jammed snow and ice laden gutters. 00z/13 EPS-EC not to worry so much as it likes less qpf and more snow down at least to I84.   What I think we all know... delays and cancels coming for Thursday, at least the region close to the nw side of I95 and northward.  I added the Thursday-Friday 12/8-19 total qpf graphic generated by the NWS early this morning. It might be a bit heavy and too far north but uncertainty. 

 

As of this starter thread it appears the region along and south of I80 including LI-NYC would have mostly rain but possibly a front end burst of snow or ice. Presuming the cold source over New England remains intact at the time of  late next weeks arrival of this large amplitude central USA trough, there exists potential of around 1/4" of glaze or more, for at least the I84 corridor high terrain (especially northeast-east slopes),  IF there is only  a little sleet or snow to start.  Longer duration of any snow or sleet (ice pellets) at the start, would reduce the risk of advisory or even warnable amounts of icing. There is even some modeling suggesting enough cooling toward the departure of storm that precip might end as snow. Finally the long shot (low probability-wishcast?) this far in advance is that this system comes out in two pieces, one ~the 18th...colder and bit snowier,  and a second delayed piece of energy late 19-20, possibly redeveloping a little further south than now modeled with a colder solution.  For now,  it looks like a period or two of heavy rain LI/NJ coast and a period or two of mixed heavy precipitation nw of I-95, especially the I-84 corridor.

EPS modeling of snowfall has been emphasizing PA-NYS central-northern New England for heavy snowfall (or ice) with the gradient edge in our NYC subforum meaning greater chances of snowfall  ice accumulation error.

This could become a major storm of one sort or another for our subforum. 

It will be of interest to monitor the water equivalent in the remaining snowpack the morning of the Feb 20.  If that snowpack is with 4" of water equivalent on some widespan flat roofs and or ice/snow clogged gutters, we might be seeing some associated damage developing?  No science from myself on this. 

[jm1220]

Thanks Walt! We might be heading back to a pattern where the SE ridge is asserting itself again and blocking might relax, meaning we go back to warmer storm tracks. Hopefully we can make one more run with a cold system but down here on the coast it’s always tougher as it is. And it might be a big story as you say with the sleet/ice this weekend being absorbed into an already thick snowpack. 

[eduggs]

GFS rains to Quebec City, but the CMC starts colder with snow to ice and then rain. Either way, to me this has a lot of the hallmarks of a big ice storm. Cold antecedent airmass. Deep snow pack. High pressure over Quebec province. Gulf-origin low that heads inland to western PA.

[HVSnowLover]

11 minutes ago, eduggs said:

GFS rains to Quebec City, but the CMC starts colder with snow to ice and then rain. Either way, to me this has a lot of the hallmarks of a big ice storm. Cold antecedent airmass. Deep snow pack. High pressure over Quebec province. Gulf-origin low that heads inland to western PA.

Yea this storm may be more favorable for snow/ice than the early week storm as the separation and the highs may allow for some nice cooling and CAD 

[eduggs]

2 minutes ago, HVSnowLover said:

Yea this storm may be more favorable for snow/ice than the early week storm as the separation and the highs may allow for some nice cooling and CAD 

I agree especially for a possible burst of snow at the onset. But personally I favor ice or rain for this setup because of the forecasted trof axis (it's really far west) and the high 500mb heights.

[wdrag]

806-810AM Saturday the 13th update:  Ensembles differ (GEFS far northwest with a primary into the e Great Lakes), while the 00z/13 EPS further southeast with a coastal and therefore colder. NAEFS is in the middle and says snow or ice to start the 18th, changing to rain before ending on the 19th.  I won't add many graphics since its similar to yesterday. My concern is another ice storm for the I84 high terrain corridor and snow pack water equivalent weight increasing as well as jammed snow and ice laden gutters. 00z/13 EPS-EC not to worry so much as it likes less qpf and more snow down at least to I84.   What I think we all know... delays and cancels coming for Thursday, at least the region close to the nw side of I95 and northward.  I added the Thursday-Friday 12/8-19 total qpf graphic generated by the NWS early this morning. It might be a bit heavy and too far north but uncertainty. 

One thought: Trof axis so far west Thursday morning that snow can fall in 1000-500 thickness warmer than 540 because of marginal temps- ie the 18th. Eventually as the trough closes in, the WAA overwhelms closer to the surface and further north, with secondary development key to CAD and ice instead of rain. 

[NEG NAO]

12Z Euro

[eduggs]

The EC goes to sleet in and around the City pretty quickly. Several hours of snow well to the north. Overall a much colder solution than the GFS or even the CMC. I would lean towards a warmer solution, but this is still good to see at this stage.

[HVSnowLover]

1 hour ago, eduggs said:

The EC goes to sleet in and around the City pretty quickly. Several hours of snow well to the north. Overall a much colder solution than the GFS or even the CMC. I would lean towards a warmer solution, but this is still good to see at this stage.

Unfortunately we know the mid levels love to torch fast so might be mainly a sleetfest before the eventual change to rain. 

[NEG NAO]

0Z Canadian

 

[NEG NAO]

0Z GFSv16

[MJO812]

Nice thump of snow on the Euro for NYC 

Colder run but eventually turns to rain

[wdrag]

525AM Sunday the 14th- Valentines Day!  This event still looks interesting for snow lovers, despite the warm GFS OP. This is a prelim update for an event 5 days away. Definitely Advisory minimum potential, especially interior and possible Watch-Warning material interior part of the forum north of I78. Early guess on modeling...a range of 1/2-5" of snow-sleet Thursday before a change to ice North of I78 and just rain LI and south of I78 Thursday evening with rain most of the area for a short time Friday morning. Snow and ice ne PA/nw NJ se NYS/n CT. How much of each phase unknown. May add another graphic or two by the 915AM full update of this topic.  Here's the NWS ensemble prob of 3+" of snow Thursday...that light blue is 70% up there by I84. 

[Northof78]

Almost all models now, have a nice thump of snow at least to start

[NEG NAO]

36 minutes ago, Northof78 said:

Almost all models now, have a nice thump of snow at least to start

Upton keeps it all mainly snow and sleet especially west of the Hudson majority of the event. The  location and strength of the HP to the north through the entire event is the key player in this setup IMO..............

[EastonSN+]

9 hours ago, NEG NAO said:

0Z GFSv16

Watch the v.16 be way more consistent run to run than any other model. Even took EURO to the woodshed during the blizzard

[NEG NAO]

46 minutes ago, EastonSN+ said:

Watch the v.16 be way more consistent run to run than any other model. Even took EURO to the woodshed during the blizzard

latest clown map from the v16 GFS

[MJO812]

Gfs going towards the euro with a front end thump for Thursday 

[Northof78]

Gfs looks 4-8" thump...

[NEG NAO]

9 minutes ago, Northof78 said:

Gfs looks 4-8" thump...

[MJO812]

6z GFS vs 12z GFS

 

Less amped and high ticked west up north

 

[hudsonvalley21]

Just now, NEG NAO said:

Constantly changing model runs for the last few days. Forecasting is basically going down to now casting, or at least it appears that way.

[eduggs]

21 minutes ago, NEG NAO said:

Subtract 3 or 4" for sleet liquid equivalent. Looks like 4-7" of snowfall for our area on the 12z GFS. 

[MJO812]

Cmc is also trending less amped with a transfer

[HVSnowLover]

This is becoming less of a front end thump to windswept rain (cutter) and more of a front end thump to light mix scenario, hopefully the models will continue to force the transfer quicker and further south. 

[steve5728]

How much snow for NYC metro?

[eduggs]

Big differences on the CMC compared to the GFS. The CMC has a much stronger 2nd and weaker primary. As a result it holds onto freezing or frozen precipitation longer with less rain. I think it has the right idea overall with a weak surface coastal reflection and northerly drain. But I think the GFS will be partly right showing a primary strong enough to keep snowfall below warning criteria, warm mid-levels for significant ip/zr, and eventually shift most areas to rain. 

[NEG NAO]

4 minutes ago, Brett said:

This is the GFS version that gets replaced next month right? I went on pivotal weather and the GFS 16 seems to be showing much less snow 

its actually pushing the snow further south on 12Z compared to 6Z

[eduggs]

2 minutes ago, Brett said:

Just looked at the Canadian model on Pivotal the Kuchera snow map doesn’t give that much snow at all may be that it is sleet and freezing rain ?

The GFS has a stronger primary which leads to stronger WAA, a bigger snow thump, and more QPF overall. But it also warms faster as a result and has a shorter duration of ip/zr and more rain.

[NEG NAO]

1 hour ago, eduggs said:

 

12Z Euro