Update #3: Final Snow Map, Ice Accretion, Flash Freeze

A mighty winter storm is going to bring all kinds of weather to our area beginning late Sunday and continuing into mid-afternoon Monday. With cold air in place, most of us are likely to start as snow. The snow will be heavy at times with rates as high as 2" per hour. Different area of the Tri-state are going to experience a variety of precipitation types. Some will transition from snow-sleet-freezing rain-rain. Others maybe just snow to rain. And the list goes on. A lot of that is dependent on temps. in different layers of our atmosphere, such as 700mb, 850mb, 925mb, and surface.



The size of this storm impresses me. There are thunderstorms circulating around the low level center that are colliding with the cold air to the north. This is giving parts of the Midwest insane snowfall rates. I drew in the likely path this storm is likely to take. Once it cuts into western PA, that is going to warm temps. up along the east coast. However, there is a blocking High to our north. Once the primary feels the effects of the HP, it will transfer its energy to the coast and develop a secondary low pressure system which will pass to our east. This is where the process becomes convoluted and brings havoc to making a forecast. How far north the primary gets, when and where the transfer happens, and how strong this storm gets all play a role in how much snow will fall in specific areas.



In all honesty, this is going to be one of those storms where nowcasting will be essential. There are too many different scenarios in place here where someone could see an extended period of sleet or freezing rain, while area just 10-20 miles south could be in plain rain. What I do expect to happen is impressive snow to fall between the hours of 3am-6am for NYC Metro. Most guidance insists on impressive VV's during this time frame that could bring snowfall rates near 2" per hour. That is part of the reason why I went with 4-8" for NYC. I do think the low end of that scale is attainable. Isolated areas in the red will see snow amounts greater than 12". That is likely to be elevation based and also due to the higher snow ratios. What we have to look during the day on Monday is to see if any rain or freezing rain that is falling changes back over to snow once the secondary low takes over and track east of us. This is a plausible solution and shown on some guidance which could increase snowfall amounts along the immediate coast, including NYC.



I'm not very confident releasing ice maps but I felt one was in order here. The areas shaded in dark pink, note that I said "possible" meaning that it's not a sure thing. I do believe at least .10" of ice is likely in the lighter pink shaded regions. Once mid-layers warm up, the snow will gradually change to sleet/rain but surface is probably still below freezing. Once that liquid hits the ground it's going to ice over, or changeover to freezing rain just above the surface. Either way, not a pleasant situation and it does not get better.



Once this storm pulls away, it is going to drag down tremendously cold air into the region. Temps. will plummet into the single digits and near 0 degrees north and west of NYC. The consequence? Well, if your area got rain or freezing rain during the day the ground is now saturated. With temps. crashing below freezing, those saturated grounds are going to freeze over. Please be very conscience of this when your commute Tuesday morning. The storm is expected to end by mid-afternoon Monday, so some drying will occur, but it's still worth mentioning in my opinion. Just trying to give you the heads up.

In sum, this is a complex setup (surprise surprise) and one that I think will have to be monitored as the day goes on Monday. If need be, I will even make an emergency updated snow map early Monday if I see the storm trending differently. And to be clear, that would be for better or worse. We'll have to see how this all plays out. Have a great Superbowl Sunday. Please stay safe!

Frank

WINTER STORM WARNING now in effect for the 5 boroughs and surrounding areas, they've held off on upgrading Southern Nassau & Suffolk just yet. Northern parts of those counties under WSW as well.

Winter Storm Warning for Nassau and Suffolk.

Great write up Frank, thanks to you, and everyone else!, who makes this board fun and informational!

Just woke up see soul what did I tell ya. 4 to 8 and yikes 1/4 ice which was upped from.1 to .25 storm will be interesting for sure. Could get dangerous monday and again tues morning. Frank I know this is a crap shoot but that darker ice area or any of it for th as t fact is me if u were to guess will this effect travel.in the am monday or be during the day? Wil it be wise for me to travel to work Monday morning if I have to?

jmanley32 wrote:Just woke up see soul what did I tell ya. 4 to 8 and yikes 1/4 ice which was upped from.1 to .25 storm will be interesting for sure. Could get dangerous monday and again tues morning. Frank I know this is a crap shoot but that darker ice area or any of it for th as t fact is me if u were to guess will this effect travel.in the am monday or be during the day? Wil it be wise for me to travel to work Monday morning if I have to?

You sure did, buddy. I am just used to Watches going down to Advisories when north of here goes up to a Warning and we stay at a Watch haha.
At any rate, as much as I nay-say an ice storm here in the city, this map (Accretion, NAM 06z) is very disconcerting if it ever were to come to fruition.

Omg over a inch jesus that's more than concerning but all ate saying a quarter which is bad enough a half inch or more and my area would b a disaster.

jmanley32 wrote:Omg over a inch jesus that's more than concerning but all ate saying a quarter which is bad enough a half inch or more and my area would b a disaster.

I will say, after being thru two of the worst New England ice storms in history, once you crest .25 accretion, the s____ starts to hit the fan QUICK. Anything about that is just too much weight for tree limbs and lines, etc.

If this trend continues we could be looking at one if not the biggest snow and ice storms for the area. The snow fine and 4 to 8 I'll take but that much ice I cannot even imagine what that would b like forget getting into your car!

06z came so far north its all rain for nyc and into westchester wow, that throws a wrench in everyones forecast, lp goes right over nyc and across ct dang, i hope thats wrong.

NWS agrees completely with Frank's map up here, 8 to 16.Some mix tomorrow morning then back to snow.Only .1 of ice which is good.

Totally nowcast as NWS mentions mid LI could be an area where temps get up into the 40's east.A lot less snow for coastal areas as rain will wash it away.Big question there is back end snow from the secondary low.They mention the flash freeze when temps crash as the low moves away.Tuesday morning will be terrible in those mix areas.

Jogs 10-20 miles N or S will have consequences.We'll see.

jmanley32 wrote:06z came so far north its all rain for nyc and into westchester wow, that throws a wrench in everyones forecast, lp goes right over nyc and across ct dang, i hope thats wrong.

NWS mentioned this as a possibility and forecast then would have to be "drastically altered". They are hedging.

on the 4km nam its almost a allout ice barrage for a large area jeeze, still models disagree, nws and frank do agree which is cool, but they may change things after todays runs if these things hold, such a nowcast coming.

Since there will be accumulating snow before the ice, does that lessen the imapact of the ice accretion ? Versus an all ice event ?

Not an expert, but I would say it somewhat does.Easier to shovel walks and driveways with a little snow under the ice.Otherwise, pure ice means you will be chopping it off.Trees and wires are different as the snow usually blows off those spots and the ice accumulates.

Final Snow Map: The Gray and Dark Blue zones are going to be the most difficult to get right. The widest part of LI is about 22miles. If the track of this storm shifts north or south by that margin as you can see it could mean a big difference in snow totals. The biggest concern for the Gray and Dark Blue zones, and possibly the southern portions of the purple is going to be the accumulation of ice. The Monday morning commute will be dangerous for that reason.
[img][/img]

Wow, Doc, from tip of NE Jersey down to near Asbury park, a lot can happen in that N or S shift.LI is crazy.

Nowcast will be a blast on this one.

You guys are doing a great job tracking this, but remember the last storm jogged East 50 miles the last minute and really through havoc into everyone's totals. This storm is oriented a little different in that it's coming from the west and possibly transferring it's energy to the coast. Could such a jog north or south happen with this storm? As S rock was saying A jog of 15 or 20 miles will have huge impact if it was 30 or 40 Miles north or South like the last storm It would really create havoc one way or the other for snow totals. As always we're at the mercy of the storm and we sit and wait to see what it decides to do.

Notice the Highs to the north in southern Canada. Still just a 1008 surface low. Key will be how east it gets before it cuts.

You can see the polar air pressing down on the storm

http://tempest.aos.wisc.edu/radar/us3compjs.html

Meaning if it gets further east before it cuts because the polar high supresses it more then we wouldnt see as much warm air being brought into the system?

lglickman1 wrote:Meaning if it gets further east before it cuts because the polar high supresses it  more then we wouldnt see as much warm air being brought into the system?

Correct

That's just it CP.  Typically with such a strong arctic air mass to the north with confluence in the Canadian maritime and a nice block into Greenland this storm should not get past 40*N lat.  In Theory.  The problem is how strong the system looks to be as it trys to cut west into the block.  The question is this:  What happens when an unstoppable force meets an immovable object?   Are the models correctly depicting how these two forces are going to interact?  Now cast will tell the story.  It is def going to be interesting

Here you can see the PV is currently situated over the NE Hudson Bay.  Ideally it should be a little further S.  You can see the trough digging into the nations heart land with the pink on the back side indicating it will deepen.  Nice block into Greenland with the confluence in the Canadian Maritime.  Personally I would like to see the area to our NE over Novia Scotia close off.  
http://earth.nullschool.net/#current/wind/isobaric/500hPa/orthographic=-92.07,44.84,1024

Here you can see our Primary LP forming.  
http://earth.nullschool.net/#current/wind/surface/level/overlay=mean_sea_level_pressure/orthographic=-92.07,44.84,1024

so no way to tell which way it will go until it actually happens on the maps