NYC/PHL January 7-9 Potential Part I

[tombo82685]

The wind killed the ratios last storm I believe, wind is not nearly as much of a factor with this storm, although you are right it will be a bit warmer in the lower layers

see thats what gets me, how do you determine ratios? The thing i read said its the temperature at which the snow is being made and through a certain part of the column. Other people i have heard it goes by surface temp to, so im not sure.

[psuhoffman]

These NORLUN toughs are crazy, have the potential to produce up to 2 feet in localized areas theyre almost like a lake effect snow band for coastal areas...either way if totals like that were to happen with this storm will probably be north of NYC based on current model runs and climo.

one of those set up down in MD in the 1940's in late March and dropped 22" of snow on Baltimore and 30" just NW of the city in one day.

[Isotherm]

i would rather have the base of the system sharpen up enough so we don't have to worry about placement of the inverted trough

Yeah, can't count on anything this far in advance with a norlun. They're basically nowcasting events. All we know right now is the corridor from PHL to BOS needs to be on the look-out for a light to moderate snowfall.

[_AR_]

Oh cmon guys you can't be serious with this "how much for xxxxx?!?" crap... What you need to realize is, unless something major changes, we are looking at a widespread 1-4", unless you get caught under that norlun trough setup, which the location of norluns do not get pinned down until, well, basically when it happens.

[Reale WX]

Oh cmon guys you can't be serious with this "how much for xxxxx?!?" crap... What you need to realize is, unless something major changes, we are looking at a widespread 1-4", unless you get caught under that norlun trough setup, which the location of norluns do not get pinned down until, well, basically when it happens.

Thank you.. and 1-4" might be a little generous but I like the thinking

[am19psu]

see thats what gets me, how do you determine ratios? The thing i read said its the temperature at which the snow is being made and through a certain part of the column. Other people i have heard it goes by surface temp to, so im not sure.

It depends on where the snow crystals are growing. When you hear about the max dendritic growth region, that means the strongest UVVs (and therefore highest supersaturations below) are around the -15C level, which creates dendrites and hence the highest ratios. You can't just easily look at a sounding or the 850 temps to get the ratios.

In the last blizzard, the winds broke the dendrites and that's why ratios were lower than you'd expect.

[_AR_]

see thats what gets me, how do you determine ratios? The thing i read said its the temperature at which the snow is being made and through a certain part of the column. Other people i have heard it goes by surface temp to, so im not sure.

I believe temperature is critical at all levels when it comes to ratios. You need certain temps where the snow forms to get good "growth", and you need cold enough temps throughout the column to the surface to keep the flakes from melting at all.

IMO unless you are getting snow in an arctic airmass, expect standard 10:1 ratios and you won't be disappointed.

[pasnownut]

Oh cmon guys you can't be serious with this "how much for xxxxx?!?" crap... What you need to realize is, unless something major changes, we are looking at a widespread 1-4", unless you get caught under that norlun trough setup, which the location of norluns do not get pinned down until, well, basically when it happens.

Not by the looks of NAM qpf grids....lots of dryslots showing up in 75% back in South Central into SE PA. Any further east solutions and I think it becomes a NYC special as well as points NE.

Nut

[_AR_]

Thank you.. and 1-4" might be a little generous but I like the thinking

It isn't that generous. I didn't think I needed to state that most people will be near the 1".

[tombo82685]

so can you determine this by a sounding, if so what do i look for. At what level do you need the -15c at, assuming no wind?

It depends on where the snow crystals are growing. When you hear about the max dendritic growth region, that means the strongest UVVs (and therefore highest supersaturations below) are around the -15C level, which creates dendrites and hence the highest ratios. You can't just easily look at a sounding or the 850 temps to get the ratios.

In the last blizzard, the winds broke the dendrites and that's why ratios were lower than you'd expect.

so what can i look at if you can't really use a sounding? At what level do you need the -15c at, assuming no wind?

[SACRUS]

SWCT is .75"-1"

NYC is .50"-75"

Hard to see on the map but the 0.50(+) looks just north of the city. looks like an i-80 north special per this run. The city looks on the 0.25 - 0.50 line and south of 78 looks 0.25 (-)

[tombo82685]

Hard to see on the map but the 0.50(+) looks just north of the city. looks like an i-80 north special per this run. The city looks on the 0.25 - 0.50 line and south of 78 looks 0.25 (-)

yea central park sounding is .46 with temps around freezing to start, then falling to upper 20s

http://68.226.77.253...km/NAM_Knyc.txt

[am19psu]

so can you determine this by a sounding, if so what do i look for. At what level do you need the -15c at, assuming no wind?

I think you can estimate using 700mb, since in winter storms, that's where the strongest UVV is because of the deformation zone/frontogenetic forcing, but that is far from precise. Maybe rainshadow or MGorse can chime in here, since I know that is something they work with on a more regular basis.

For me, along the East Coast, I go with the _AR_ method and just use 10:1. The areas that get better ratios are almost always on the mesoscale unless you are dealing with a true Arctic airmass, in which case the -15C isotherm is lower in the atmosphere.

[pasnownut]

so can you determine this by a sounding, if so what do i look for. At what level do you need the -15c at, assuming no wind?

My understanding is that it would need to be at all levels. I've seen many mets discuss how at 500 or 700 there is a warm layer that kicks the pants out of snow growth while all other layers are good for better ratios. That is the laymans version of what your looking for.

Nut

[hudsonvalley21]

yea central park sounding is .46 with temps around freezing to start, then falling to upper 20s

http://68.226.77.253...km/NAM_Knyc.txt

0.67 up this way.

http://68.226.77.253/text/NAM80km/NAM_Kswf.txt

[Reale WX]

so can you determine this by a sounding, if so what do i look for. At what level do you need the -15c at, assuming no wind?

so what can i look at if you can't really use a sounding? At what level do you need the -15c at, assuming no wind?

You need to find the region (in the sounding) where the strongest omegas coicide with cold, supersaturated air as other have stated. On bufkit there is a tool called snow growth. Where that lines up with the strongest omegas = best snow ratios, generally found around the 700 mb level. You can also look for CSI banding but thats alot more complicated

[Reale WX]

Can play around with this site too it equates the ratios for you I believe

http://sanders.math.uwm.edu/cgi-bin-snowratio/sr_map_main.pl

[MAG5035]

so can you determine this by a sounding, if so what do i look for. At what level do you need the -15c at, assuming no wind?

so what can i look at if you can't really use a sounding? At what level do you need the -15c at, assuming no wind?

Do believe you want that optimal -15ºC level to conincide with the region of best lift (omega), which is generally around that 700mb level that ampsu19 suggested as a good guesstimate. If it is very cold and that -15ºC level is below the region of best lift (colder than -15) than you won't get quite as good snow ratios. In cases of a thin warm layer intrusion as the snowflake falls thru the column, sometimes the flake will melt enough to rime up and be more like a snow pellet, and those are def not very good ratio wise (prolly more of a 7-10:1 type).

[SnowGoose69]

These NORLUN toughs are crazy, have the potential to produce up to 2 feet in localized areas theyre almost like a lake effect snow band for coastal areas...either way if totals like that were to happen with this storm will probably be north of NYC based on current model runs and climo.

The NAM's depiction of the inverted/norlun setup is a bit unrealistic...first off its extending it way too far inland, they normally do not have much of a lifeline once you get inland from the coastal areas by more than 50 miles or so...so the NAM's depiction over Monticello and Liberty NY at 72 hours of the snow from the trough is probably BS...other than that the NAM setup is perfect for a norlun/inverted trough to form, the 850 winds are light and we have PVA at a deep upper low or trough at 500mb...the GFS shows winds too strong at 850mb on most of its runs so far.

[am19psu]

Do believe you want that optimal -15ºC level to conincide with the region of best lift (omega), which is generally around that 700mb level that ampsu19 suggested as a good guesstimate. If it is very cold and that -15ºC level is below the region of best lift (colder than -15) than you won't get quite as good snow ratios. In cases of a thin warm layer intrusion as the snowflake falls thru the column, sometimes the flake will melt enough to rime up and be more like a snow pellet, and those are def not very good ratio wise (prolly more of a 7-10:1 type).

OTOH, in those situations, you can get better ratios outside of the mesoscale banding areas, since the strongest UVVs are farther down in the atmosphere.

[Reale WX]

The NAM's depiction of the inverted/norlun setup is a bit unrealistic...first off its extending it way too far inland, they normally do not have much of a lifeline once you get inland from the coastal areas by more than 50 miles or so...so the NAM's depiction over Monticello and Liberty NY at 72 hours of the snow from the trough is probably BS...other than that the NAM setup is perfect for a norlun/inverted trough to form, the 850 winds are light and we have PVA at a deep upper low or trough at 500mb...the GFS shows winds too strong at 850mb on most of its runs so far.

"they normally do not have much of a lifeline once you get inland from the coastal areas by more than 50 miles or so" - at least according to past history, who knows (sort of joking here, sort of not lol)... on the other hand it is fairly rare for this too occur so far south to begin with.

18z gfs 850 winds initially support some snow over NYC and are parellel to the sfc trough on a NW to SE axis.. then really relax well north of us where everything looks favorable

[tombo82685]

Do believe you want that optimal -15ºC level to conincide with the region of best lift (omega), which is generally around that 700mb level that ampsu19 suggested as a good guesstimate. If it is very cold and that -15ºC level is below the region of best lift (colder than -15) than you won't get quite as good snow ratios. In cases of a thin warm layer intrusion as the snowflake falls thru the column, sometimes the flake will melt enough to rime up and be more like a snow pellet, and those are def not very good ratio wise (prolly more of a 7-10:1 type).

where do you find where the best omega is? Do you just use the 700mb charts on the models for best uv's, then go to a sounding and see what temperature is at that level.

[jm1220]

I can't remember the last time we had significant snow from a norlun anywhere near here. Those are typically for eastern New England, but again this winter is anything but typical.

Also, temps spike out on LI before the heavy snow comes in this NAM run on the east wind. The ocean is cold enough now that any east wind isn't an automatic death sentence like it is in December, but it still wouldn't surprise me if raindrops were mixed in at least to start (IF this Nam run is correct which is a big stretch more than 24hr out)

[hazwoper]

Reale - PHL saw 8" in Feb 2007 from an inverted trough.

[Allsnow]

Reale - PHL saw 8" in Feb 2007 from an inverted trough.

2009

[am19psu]

Here is a ppt that Wes made for HPC. Might be of use re: all of the ratio discussion.

http://www.hpc.ncep.noaa.gov/research/snowfcst/snow.pdf

[tmagan]

I can't remember the last time we had significant snow from a norlun anywhere near here. Those are typically for eastern New England, but again this winter is anything but typical.

Also, temps spike out on LI before the heavy snow comes in this NAM run on the east wind. The ocean is cold enough now that any east wind isn't an automatic death sentence like it is in December, but it still wouldn't surprise me if raindrops were mixed in at least to start (IF this Nam run is correct which is a big stretch more than 24hr out)

December 1988

[hazwoper]

OOPS, yes I meant 2009

[Thunder Road]

last norlun was Feb 4, 2009

PHL saw 8.4"; Woodbury, NJ saw 10"; IMBY there was 4.5"

I remember one run of either the NAM or the NMM-WRF printing out 15" for Reading. In the end, they saw like an inch or two, but they were along the axis of heaviest snow, just a little too far north.

Everyone's 1-3" call busted badly for that storm. I was smart enough to 2-5", which just barely covered my ass but not the rest of Philly LOL

[jm1220]

The other thing about an inverted trough/norlun is that obviously the party is 50-75 miles wide and little outside of that. A lot of people are going to be mighty unhappy unless this storm somehow spins up closer to shore. My money is on a general few inches from the upper low and the inverted trough being weaker than modelled. The chances for a more organized storm are very low unless the upper air low consolidates significantly and dives SE. The strung out nature to it produces a lot of snow showers and maybe this norlun, that's it.