February 4th-6th Storm Threat Discussion

[TWCCraig]

Most of the heavy falling precip should be done by noon. This is a morning event.

 

Exactly. When the precip begins to shut off, thats when the 4km moves the CF north. Going to have to watch this tomorrow but for now I think it stays south through the morning hours.

[dbc]

So if upton is calling for 4-6" snow and 0.34" ice, that means they are assuming the entire event is frozen

Thinking the 4-6 includes sleet. This is the NAM at 24 I believe and should help clarify things as far as the NAM 18z output is concerned:

[winterwarlock]

Mt holly has reduced my snowfall to zilch..

[Rjay]

It usually happens. The CF signature on the 4km NAM is expected to stay south of LI through the morning hours, it cuts through the center of the island eventually around noon, at that time the north shore will definitely be colder than the south shore. But before that the difference is minimal.

It eventually happens though. 95% of the time in these type of events. Having a snow pack is nice and all but if the only way I could keep it is if I received freezing rain instead of rain, I'd choose rain every time.

[NorthShoreWx]

The impacts of the freezing rain will ultimately come down to the wind direction and whether your area can stay more than 1 degree below freezing. There's more to ZR than just the model showing it. The worst impacts come when you're a few degrees below and it's raining moderately. This allows for significant ice accretion.

 

ZR is a delicate balance requiring a continued source of low level cold air.  The latent heat release from heavy freezing rain is considerable and without a source of fresh low level cold, the zr sows the seeds of it's own destruction. 

 

The problem with 32 is that it is a balance point between freezing and melting and a lot of water runs off harmlessly.  On the other hand, 31 can sometimes do the trick. 

 

PS, John, I know you knew this.

[Metsfan]

Most of the heavy falling precip should be done by noon. This is a morning event.

right that's why I think Upton is going for more ice now then rain.

[Zir0b]

NAM is showing over 1" qpf as pure freezing rain for most of Central NJ. Wow. 

[Rjay]

Exactly. When the precip begins to shut off, thats when the 4km moves the CF north. Going to have to watch this tomorrow but for now I think it stays south through the morning hours.

Definitely a close call. I'm kind of torn forecasting-wise. Climo says we rain. I can see the 4k NAM being right as well though. I think we stay frozen longer than the most models show but we end as rain on the south shore. North Shore stays all frozen.

[Heavy Snow Warning]

Thinking the 4-6 includes sleet. This is the NAM at 24 I believe and should help clarify things as far as the NAM 18z output is concerned:

I just don't buy that Orange and Rockland will see that little snow.  I think it's a 3-6 inch storm up there with a good amount of sleet ending as FRZ drizzle.

[Stormlover74]

So verbatim, the NAM could be 2-3" sleet? Wow

Just going by 2007 ewr got 5" of sleet from a little over an inch of liquid.. Might have been a bit of snow mixed in too

[TWCCraig]

Definitely a close call. I'm kind of torn forecasting-wise. Climo says we rain. I can see the 4k NAM being right as well though. I think we stay frozen longer than the most models show but we end as rain on the south shore. North Shore stays all frozen.

 

Yeah, we will go above freezing eventually and the north shore will stay pretty frozen, but by the time the CF moves through most precip would have fallen already. Going to be a major event regardless.

[BlueSkiesFading]

I think the ZR is being a little too played up on here. In my opinion, I think most areas see way more sleet then ZR. If I had to guess if say 2-4" of snow across NYC metro with 4-6" for the northern burbs. Then I think we get a a half inch of liquid falling as sleet across areas north of 78 in NJ and away from the south shore of LI. Then maybe 0.10-0.25" of ZR in a similar area. I'm sure there will be a strip of heavier ZR somewhere across N-C NJ, but I doubt it will be as widespread as some are making it out to be.

[IsentropicLift]

How are you going to get 3-6" of snow when ratios are 4:1 or maybe 6:1 at best while the snow is falling?

[Rjay]

ZR is a delicate balance requiring a continued source of low level cold air. The latent heat release from heavy freezing rain is considerable and without a source of fresh low level cold, the zr sows the seeds of it's own destruction.

The problem with 32 is that it is a balance point between freezing and melting and a lot of water runs off harmlessly. On the other hand, 31 can sometimes do the trick.

PS, John, I know you knew this.

I think most who have a clue know at least your second paragraph. That's why I'm not too worried (yet) in my location (unless the 4k nam is right).

[Rjay]

Yeah, we will go above freezing eventually and the north shore will stay pretty frozen, but by the time the CF moves through most precip would have fallen already. Going to be a major event regardless.

Might not be major for you and I. We'll see.

[TWCCraig]

Might not be major for you and I. We'll see.

 

1/4" of ice, some sleet and 2-4" of snow is major imo, major enough to cause a big disruption on the roads (not main roads).

[IsentropicLift]

Guys in the Mt. Holly CWA check your point and clicks, they have all just been updated.

 

For my zip code it says now 2-4" total of SN/IP and 0.25-0.50" total ice. Fits the graphic perfectly.

[TWCCraig]

Valid 9z on HRRR coastal front outlined in blue

 

[ILoveWinter]

Regarding the NWS (just asking and not criticizing): how do the mets here justify the 4-6  they are predicting in Manhattan?

 

1) Is it because they (NWS) believe the front end thump will be heavier than the models are forecasting?

2) Is it because they believe the 850s are slower to warm than modeled?

3) Is a lot of the 4-6 simply sleet?

 

Thanks.

 

Edit:

 

or 4) Something else entirely

[+SNfreak21]

HRRR is now on E-wall, good timing 

[Keith O]

Guys in the Mt. Holly CWA check your point and clicks, they have all just been updated.

 

For my zip code it says now 2-4" total of SN/IP and 0.25-0.50" total ice. Fits the graphic perfectly.

 

Add in the fact that temps are not forecast to go above freezing for the next 6 days and whatever falls tomorrow is sticking around for awhile for sure.  Think I'll be able to walk on top of my snowpack!

[Rjay]

1/4" of ice, some sleet and 2-4" of snow is major imo, major enough to cause a big disruption on the roads (not main roads).

I don't think we see 2-4" of snow. Maybe 1 or 2". I also don't know if we really see 1/4 of ice. 0z hi res models hopefully come to some sort of conclusion.

[Weathergun]

The 18z NAM has 80kt jet 700mb-800mb over the NYC area tomorrow morning. That's helping push warm wedge in the mid-levels. The NAM though has been overdone with low-mid-level flow,  with other storms this season:

 

 

[TWCCraig]

I don't think we see 2-4" of snow. Maybe 1 or 2". I also don't know if we really see 1/4 of ice. 0z hi res models hopefully come to some sort of conclusion.

 

1-2" and less than 0.25" of ice doesn't seem to add up to how much qpf we see from this storm. Are you expecting mostly rain here? Hi-res models are extremely accurate with low level cold, RGEM ticking south and colder now. I think we see at most 0.25" of plain rain, and that's mostly in the afternoon. I expect about 0.75" frozen, 0.2"-0.4" LE snow, 0.1" LE sleet, and 0.25" of ZR.

[WE GOT HIM]

HRRR is now on E-wall, good timing 

Do you have a link 2 the page I was looking for it before but couldn't find it

[+SNfreak21]

Do you have a link 2 the page I was looking for it before but couldn't find it

http://www.meteo.psu.edu/~fxg1/HRRRNE_CUR/comploop.html

[Rjay]

1-2" and less than 0.25" of ice doesn't seem to add up to how much qpf we see from this storm. Are you expecting mostly rain here? Hi-res models are extremely accurate with low level cold, RGEM ticking south and colder now. I think we see at most 0.25" of plain rain, and that's mostly in the afternoon. I expect about 0.75" frozen, 0.2"-0.4" LE snow, 0.1" LE sleet, and 0.25" of ZR.

As of now I'm leaning towards climo (mostly rain) but I cant rule out models underestimating low level cold air. Like I've been saying, it's a tough call for you, JM , LBsurfer and I.

[donsutherland1]

Do you have a link 2 the page I was looking for it before but couldn't find it

http://www.meteo.psu.edu/ewall/HRRRNE_CUR/comploop.html

[jm1220]

The prior snowcover may help preserve some cold air as well, to make it just the 1 or 2 degrees colder needed to accumulate ice. Tomorrow morning is going to be one hellish commute for most.

[Sn0waddict]

The total snow on the HRRR is miniscule, not sure why it's getting much attention.

 

That's only up until the last frame, which has the snow just starting in the area.