Discussion-OBS Noon Wed Feb 5-Noon Thu Feb 6 Snow-ice changing to rain Thu morning except ice may linger through Noon parts of I84 corridor.

[Allsnow]

Just now, jm1220 said:

Agree, no idea why people at this latitude root them on. You have the rare 2/22/08 or 11/14/18 where the snowy front end actually happens but 5/6 of them or more are crap south of I-84. They’re good for New England and UNY. 

I’d prefer this over some torch pattern in February. 

[LibertyBell]

Just now, jm1220 said:

I don’t know, I think the New England forum started it and it makes sense because they’re warm mid level overrunning events on SW flow so it caught on. 

if one tracks far enough to our south that it never changes to rain would it still get the same name? Like if it didn't get north of the Delmarva for example?

 

[snowman19]

31 minutes ago, Stormlover74 said:

When it shows snow and thickness >545 it's best to plan on sleet

^This. With those soundings, it’s going to be sleet not all snow like the RGEM is showing, not with those midlevel temps and thicknesses. No way in hell would it be all snow. Plus, when there’s a strong warm nose event like this one is going to be, the models always underestimate the midlevel warmth at this range. Wouldn’t surprise me if this is a quick transition to sleet after a quick 1/2 inch to an inch of snow

[RU848789]

Still a thump on 12z GFS...

[eduggs]

16 minutes ago, jm1220 said:

I don’t know, I think the New England forum started it and it makes sense because they’re warm mid level overrunning events on SW flow so it caught on. 

Most of our wintry precipitation events exhibit southwest mid-level flow - particularly upper mid-levels (500mb). Actually our prevailing flow is SW. Only when there is a well defined mid/ULL will the flow wrap around to the NE. SWFE generally refer to the lower mid-levels or high lower levels - 700mb-850mb level plus/minus reflecting e.g., the 850mb low going west of us.  SNE typically has more buffer to hold off the encroaching warm layers since 850mb lows cutting into WNY/PA tend to redevelop south of LI due to the land-ocean boundary and frictional effects.

[EastonSN+]

GFS snow sleet to dry slot.

[eduggs]

23 minutes ago, LibertyBell said:

if one tracks far enough to our south that it never changes to rain would it still get the same name? Like if it didn't get north of the Delmarva for example?

 

It is not a precise scientific term.

[winterwx21]

Good to see some of the models showing a bit of a thump. Hopefully HRRR and GFS have a clue and we can get a couple inches before sleet, but I know there's the risk of it ending up more sleet. Very close call that we probably won't have a better idea on until late tomorrow. Even if it ends up being mostly sleet, that certainly beats freezing rain or rain. Glad this is looking like a decent winter weather threat. 

[snowman19]

8 minutes ago, EastonSN+ said:

GFS snow sleet to dry slot.

The GFS is making the same mistake as the RGEM with the midlevel warm nose. Look at the GFS soundings, those thicknesses and midlevel temps = sleet, not snow. It’s showing all snow when it should be showing sleet. So the 10:1 snow ratio maps are getting inflated. It has a sleet sounding, yet it’s showing all snow. And using the HRRR at this range is definitely not advisable at all. It’s nowhere near its accurate range 

[BxEngine]

Post the gfs sounding. Cant compare a gfs map to a hrrr sounding and claim 1 is correct. Doesnt work like that. 

[snowman19]

5 minutes ago, BxEngine said:

Post the gfs sounding. Cant compare a gfs map to a nam sounding and claim 1 is correct. Doesnt work like that. 

I’m talking about the GFS sounding in that post, not the NAM’s or the RGEM’s. Just click on the GFS precip type map at the time it’s showing snow and the sounding comes right up on Pivotalweather. Its own sounding doesn’t support the precip type it’s showing. The RGEM did the same, the sounding at the same time doesn’t support its own precip map, showing snow, they are sleet soundings not snow soundings 

[NorthShoreWx]

16 minutes ago, snowman19 said:

^This. With those soundings, it’s going to be sleet not all snow like the RGEM is showing, not with those midlevel temps and thicknesses. No way in hell would it be all snow. Plus, when there’s a strong warm nose event like this one is going to be, the models always underestimate the midlevel warmth at this range. Wouldn’t surprise me if this is a quick transition to sleet after a quick 1/2 inch to an inch of snow

That is a snow sounding.  Those mid-level temps and thicknesses support snow.

With a slightly warmer sounding there would be sleet.

[BxEngine]

2 minutes ago, snowman19 said:

I’m talking about the GFS sounding in that post, not the NAM’s or the RGEM’s. Just click on the GFS precip type map at the time it’s showing snow and the sounding comes right up on Pivotalweather. Its own sounding doesn’t support the precip type it’s showing. The RGEM did the same, the sounding at the same time doesn’t support its own precip map, showing snow, they are sleet soundings not snow soundings 

Post it. I know how to do it. If youre going to compare, post the shot too. The initial discussion was about the hrrr sounding. The gfs sounding is different, and different areas of our subforum have pretty significant differences over a short distance especially in the later morning hours.

[eduggs]

Ptype and dynamics of snow falling through a melting layer are more complicated that you would think: https://journals.ametsoc.org/view/journals/atsc/78/6/JAS-D-20-0353.1.xml

Snowflakes don't instantaneously melt if the temperature is above freezing and the melting process cools the air, making it self-inhibiting. The NAM used to model these processes better than other guidance including the GFS. I assume it still does. But ptype involves meso- or micro-scale dynamics that aren't always accurately modeled at current model grid sizes.

[winterwx21]

8 minutes ago, NorthShoreWx said:

That is a snow sounding.  Those mid-level temps and thicknesses support snow.

With a slightly warmer sounding there would be sleet.

Yeah they're showing snow now, but it's so close that we shouldn't be too optimistic yet. Tomorrow's model runs are the ones that will tell the story. Could go either way as far as getting a couple inches of snow or mostly sleet before it eventually changes to rain. 

[eduggs]

Thickness values are a useful tool for approximating ptype but are imprecise.

[BxEngine]

5 minutes ago, winterwx21 said:

Yeah they're showing snow now, but it's so close that we shouldn't be too optimistic yet. Tomorrow's model runs are the ones that will tell the story. Could go either way as far as getting a couple inches of snow or mostly sleet before it eventually changes to rain. 

That was more forkys point, that it being that close it is oftentimes leaves temps underdone. But you cant compare a sounding from one model and compare it to a model output from a different model. The gfs model as of now is cooler at that level than the hrrr, at least in the places i looked. 

[kat5hurricane]

1 hour ago, psv88 said:

SWFEs are the fucking worst 

The worst and the models always underestimate the warm layer. This is a typical 1-2 inch slopfest that will get washed away deal at the coast as opposed to these cold 1-2 inch snows that we've been getting this winter prior that have stuck around for the most part. These are NYC suburb and New England events generally.

[SnowGoose69]

The Euro seems out to lunch on this one, I am still wary of totally discounting it, maybe the 06z run was a blip but its evolution overall is just different than any other model right now.

[BxEngine]

5 minutes ago, BxEngine said:

That was more forkys point, that it being that close it is oftentimes leaves temps underdone. But you cant compare a sounding from one model and compare it to a model output from a different model. The gfs model as of now is cooler at that level than the hrrr, at least in the places i looked. 

That being said, i def agree that in these setups the sleet often moves in earlier than modeled, especially if the models are known to be too cold at that levels. But thats a different debate. 

[EastonSN+]

FWIW the CMC is colder and mostly sleet now as opposed to rain. Almost never gets to rain fully, mostly sleet to dry slot. 

[SnowGoose69]

2 minutes ago, EastonSN+ said:

FWIW the CMC is colder and mostly sleet now as opposed to rain. Almost never gets to rain fully, mostly sleet to dry slot. 

Its very possible places from N Queens on W-NW never go to rain on this event, while there is ESE flow, its light, the event is very fast moving and short duration and there may be too much wet bulbing initially to push temps over 32 til the precip is almost over.  LGA is roughly 32/21 at the start, if they fall to 28 I really doubt an 8-10kts wind from 090-110 blowing across a large area of sleet/snow on the ground is going to get them over freezing before the event exits.   I still think there is mostly sleet though after maybe 2 hours of snow at the start.

[Stormlover74]

1 minute ago, SnowGoose69 said:

Its very possible places from N Queens on W-NW never go to rain on this event, while there is ESE flow, its light, the event is very fast moving and short duration and there may be too much wet bulbing initially to push temps over 32 til the precip is almost over.   I still think there is mostly sleet though after maybe 2 hours of snow at the start.

Seems most reasonable 

[MANDA]

1 minute ago, Stormlover74 said:

Seems most reasonable 

Message from modeling last 24 hours is that any frozen accumulations (snow, sleet) will be light, on the order of 1 -2" for most locations.  That is not to say it won't be a sloppy and slippery mess Thursday morning.  Not going to do much to increase the snow totals for the season to date for anyone, especially the snow starved crowd.  To sum it up.....Next.

[BoulderWX]

11 minutes ago, MANDA said:

Message from modeling last 24 hours is that any frozen accumulations (snow, sleet) will be light, on the order of 1 -2" for most locations.  That is not to say it won't be a sloppy and slippery mess Thursday morning.  Not going to do much to increase the snow totals for the season to date for anyone, especially the snow starved crowd.  To sum it up.....Next.

See ya on the next one. Some of us are quite happy with another couple of inches. 

[weatherpruf]

43 minutes ago, kat5hurricane said:

The worst and the models always underestimate the warm layer. This is a typical 1-2 inch slopfest that will get washed away deal at the coast as opposed to these cold 1-2 inch snows that we've been getting this winter prior that have stuck around for the most part. These are NYC suburb and New England events generally.

The immediate suburbs usually turn pretty quickly too. Rather sleet than slop, but nothing to be done about it. If it ain't a decent snow my only other concern is my loved ones who have to drive; sleet is deceptive.

[weatherpruf]

15 minutes ago, BoulderWX said:

See ya on the next one. Some of us are quite happy with another couple of inches. 

I'm actually loving this recent warmup. It's been so cold my skin is like sandpaper and my sump pump is still frozen, probably will be till June. This morning's walk was nice. Felt springlike. 

[Allsnow]

The primary is getting pretty far nw on most of the models. I just don’t see this as snowy thump outcome but I’ll be happy to be wrong.

 

I think Saturday night has the best shot for a thump 

[RU848789]

1 hour ago, eduggs said:

Ptype and dynamics of snow falling through a melting layer are more complicated that you would think: https://journals.ametsoc.org/view/journals/atsc/78/6/JAS-D-20-0353.1.xml

Snowflakes don't instantaneously melt if the temperature is above freezing and the melting process cools the air, making it self-inhibiting. The NAM used to model these processes better than other guidance including the GFS. I assume it still does. But ptype involves meso- or micro-scale dynamics that aren't always accurately modeled at current model grid sizes.

All true, but the bottom line is that it's a close call on most model soundings and will likely be a close call in reality, plus no model in the world can get the entire column thermal profile exactly right at each time step, so this will be more of a radar and observational event than most.  Would love all snow/ sleet with minimal ZR and rain...

[LibertyBell]

1 hour ago, eduggs said:

Most of our wintry precipitation events exhibit southwest mid-level flow - particularly upper mid-levels (500mb). Actually our prevailing flow is SW. Only when there is a well defined mid/ULL will the flow wrap around to the NE. SWFE generally refer to the lower mid-levels or high lower levels - 700mb-850mb level plus/minus reflecting e.g., the 850mb low going west of us.  SNE typically has more buffer to hold off the encroaching warm layers since 850mb lows cutting into WNY/PA tend to redevelop south of LI due to the land-ocean boundary and frictional effects.

Even the parts of SNE that are east of us? We've seen a few examples where, for example, the cape and other extreme coastal parts of New England change to rain before we do.

So if the storm and the 850mb low both go south of us, it's simply a bowling ball storm and not an SWFE?