Discussion-OBS Weekend Feb 8-9 Another mainly 12 hour snow-ice event possibly changing to rain before ending Sunday. NYC-LI-S of I78 on the edge?

[RU848789]

27 minutes ago, BoulderWX said:

Genuine question - the output on that map doesn’t look anything close to pivotal. I get different algorithms and sleet/snow being counted but the difference is huge. Any idea why?

See my post above.  TT counts sleet as 10:1 snow in their "snowfall" maps, meaning 2" of sleet would be about 6" of snow, so the NAM is spitting out about 2" of sleet and a little snow on TT.  But Pivotal doesn't count sleet toward the snow total at all, which is why their NAM maps are only showing 1-2" of pure snow for most, at least south of 80.  2" of sleet has the same mass as 6" of snow, so the impact on driving/removal is the same - there just aren't visibility issues and it's not as pretty.  It's above my pay grade to speculate on whether the NAM or the other models will be right, lol.  

[SnowGoose69]

The NAM idea made more sense last storm because it was truly much more disorganized.  It barely had an organized precip shield til it was almost overhead.  This system is a bit faster to get going.  I also don’t think 4-6 is realistic at all for NYC, I would only go 2-4 right now and closer to 2 than 4

[MJO812]

Rgem 3-6 for NYC

[psv88]

RGEM v NAM eh?

[SnowGoose69]

Just now, psv88 said:

RGEM v NAM eh?

To be honest I forecast for the entire eastern US and both have been bad this winter overall.  The Euro has more or less owned the show this year inside 36 hours.   

[sussexcountyobs]

I'm assuming Mt. Holly will put up a winter storm watch for my area on their next forecast update since Upton has had them up for Bergen and Passaic counties since 4am.

[BoulderWX]

13 minutes ago, RU848789 said:

See my post above.  TT counts sleet as 10:1 snow in their "snowfall" maps, meaning 2" of sleet would be about 6" of snow, so the NAM is spitting out about 2" of sleet and a little snow on TT.  But Pivotal doesn't count sleet toward the snow total at all, which is why their NAM maps are only showing 1-2" of pure snow for most, at least south of 80.  2" of sleet has the same mass as 6" of snow, so the impact on driving/removal is the same - there just aren't visibility issues and it's not as pretty.  It's above my pay grade to speculate on whether the NAM or the other models will be right, lol.  

Sorry, I had missed it. Appreciate the explanation. 

[tristateweatherFB]

4 minutes ago, sussexcountyobs said:

I'm assuming Mt. Holly will put up a winter storm watch for my area on their next forecast update since Upton has had them up for Bergen and Passaic counties since 4am.

Within 24 hrs of then event.  They will put up warnings and wwa around 3pm

[MJO812]

9 minutes ago, psv88 said:

RGEM v NAM eh?

Nam has spotty precip everywhere 

[psv88]

11 minutes ago, SnowGoose69 said:

To be honest I forecast for the entire eastern US and both have been bad this winter overall.  The Euro has more or less owned the show this year inside 36 hours.   

Agreed. 

[NEG NAO]

16 minutes ago, MJO812 said:

Rgem 3-6 for NYC

That west to east banding across central NJ reminds me of what happened last Feb 16 -17 storm......

[RU848789]

15 minutes ago, MJO812 said:

Nam has spotty precip everywhere 

Huh?  NAM has 0.5-0.7" QPF like most of the other models; it's just that most of it is sleet...

[mikem81]

36 minutes ago, MJO812 said:

Rgem 3-6 for NYC

MJO: please no 10;1 maps for a SWFE

[winterwarlock]

gfs really shafts western sections

 

[MJO812]

3 minutes ago, mikem81 said:

MJO: please no 10;1 maps for a SWFE

It still shows a few Inches. Get ready.

[MJO812]

Gfs 

[RU848789]

GFS also showing more sleet where the sleet amount = (TT "snow" (which includes 10:1 sleet) - Pivotal pure snow)/3; when they show the same amount of "snow" that means no sleet.  Would be nice to have a sleet map and a pure snow map, lol...

 

[NittanyWx]

Pretty clear warm nose around 750 on this GFS run.  That remains the chief concern, especially coast and jersey.  The globals tend to underdo these at this range.

 

As I mentioned a couple days ago, you hope you can hold off some of this with decent enough lift, but that's the push/pull of this storm.  

[ForestHillWx]

It’s the primary driving north to Buffalo before the transfer. Anytime that’s depicted, we ping. 

[the_other_guy]

I’m gonna take the under on this storm especially after this week with the models. I’m especially gonna take the under for the city.

if I walk away with close to 4 inches in Westchester, I’ll be pleasantly surprised. If I walk away with more than 4 inches I’m gonna be shocked.

[jm1220]

6 minutes ago, ForestHillWx said:

It’s the primary driving north to Buffalo before the transfer. Anytime that’s depicted, we ping. 

Also the mid level 850 low track. When that goes NW of you, S mid level winds are driving warm air in. With these kind of storms you hope a lot of overrunning precip can happen first before the warm air arrives. You want those to redevelop south of you to keep cold air in. 

[Dark Star]

1 hour ago, MJO812 said:

Rgem 3-6 for NYC

But wasn't the subsidence area projected right where the 6.1" bullseye over NE Jersey and NYC is shown?

[Northof78]

Looks like NWS New York right on with general 3-6" around the metro so far with some sleet as well given all morning guidance. 

[RU848789]

Finally found this, which really shows well the amounts of snow, sleet, freezing rain and rain for the 12Z NAM for selected locations. For Newark, it has 0.54" total precip, which includes 1.7" of snow (assumes 10:1 ratio), about 1.1" of sleet (from 0.37" of sleet as liquid and using a 3:1 ratio) and no freezing rain or plain rain.

For Philly, it has 0.69" total precip, which includes 1.4" of snow, about 0.3" of sleet (from 0.11" of sleet as liquid and using a 3:1 ratio), but it also shows 0.42" of freezing rain (and no plain rain), which would be just terrible. Rule of thumb is maybe 1/2 to 2/3 of freezing rain precip actually accretes on sub-32F surfaces (some runs off, especially if precip is moderate to heavy; drizzle accumulates much better), meaning maybe 0.25" of ice accretion, which is close to the 0.17" of accumulated freezing rain from the NWS forecast.

Biggest take home message is no plain rain, so this will be quite impactful even for areas south of 78 which might get a lot less pure snow, as sleet and freezing rain are as bad or worse. Even AC is only showing half of the 0.6" of total precip as plain rain. Of course, this is just the NAM model verbatim and the actual outcome might be much different as per the NWS with more snow and less sleet/freezing rain for most.

https://coolwx.com/cgi-bin/getbufr.cgi?region=NJ&stn=KACY&model=nam&time=current&field=prec

 

[SnowGoose69]

4 minutes ago, RU848789 said:

Finally found this, which really shows well the amounts of snow, sleet, freezing rain and rain for the 12Z NAM for selected locations. For Newark, it has 0.54" total precip, which includes 1.7" of snow (assumes 10:1 ratio), about 1.1" of sleet (from 0.37" of sleet as liquid and using a 3:1 ratio) and no freezing rain or plain rain.

For Philly, it has 0.69" total precip, which includes 1.4" of snow, about 0.3" of sleet (from 0.11" of sleet as liquid and using a 3:1 ratio), but it also shows 0.42" of freezing rain (and no plain rain), which would be just terrible. Rule of thumb is maybe 1/2 to 2/3 of freezing rain precip actually accretes on sub-32F surfaces (some runs off, especially if precip is moderate to heavy; drizzle accumulates much better), meaning maybe 0.25" of ice accretion, which is close to the 0.17" of accumulated freezing rain from the NWS forecast.

Biggest take home message is no plain rain, so this will be quite impactful even for areas south of 78 which might get a lot less pure snow, as sleet and freezing rain are as bad or worse. Even AC is only showing half of the 0.6" of total precip as plain rain. Of course, this is just the NAM model verbatim and the actual outcome might be much different as per the NWS with more snow and less sleet/freezing rain for most.

https://coolwx.com/cgi-bin/getbufr.cgi?region=NJ&stn=KACY&model=nam&time=current&field=prec

 

Yeah, in order to get over 2 places like EWR need the period from 23-02Z to be pretty snowy, if its very light they'll end up primarily sleet from 03-07z when the best precip rates are.  Unlike last storm due to the transfer the winds will likely back to 030-050, we could see LGA/EWR possibly get to 33-34 for a time and then drop back to 30-32.

[winterwx21]

1 hour ago, SnowGoose69 said:

To be honest I forecast for the entire eastern US and both have been bad this winter overall.  The Euro has more or less owned the show this year inside 36 hours.   

We anxiously wait to see the Euro in a little while then. Hopefully we can at least get a 2 to 4 inch event from this. 

[MJO812]

6 minutes ago, winterwx21 said:

We anxiously wait to see the Euro in a little while then. Hopefully we can at least get a 2 to 4 inch event from this. 

That looks likely

[snowman19]

58 minutes ago, NittanyWx said:

Pretty clear warm nose around 750 on this GFS run.  That remains the chief concern, especially coast and jersey.  The globals tend to underdo these at this range.

 

As I mentioned a couple days ago, you hope you can hold off some of this with decent enough lift, but that's the push/pull of this storm.  

The CMC is even seeing a pronounced warm nose now, it turned it to sleet all the way up to High Point State Park on this latest run. Considering that the globals are very likely underdoing it, can we completely discount models like the high res NAM-NEST? I normally ignore the NAM suite but in special situations like this with a warm nose, it can sometimes actually score a rare coup. FWIW, the extended HRRR and the SREFs are similar to the NAM-NEST as well

 

Link to the NAM-NEST in case anyone wants to look: https://weather.cod.edu/forecast/legacy/

 

@SnowGoose69

[MJO812]

The Weather Channel

[donsutherland1]

The 12z HREF: