Let's Put To Bed That Colder Temps Always Mean Higher Ratios, Poster Event 1/28-1/29 Added.

[Rainshadow]

Thanks for all of your reports from the last winter storm.
 

With our recent winter storm, there was alot of discussion as to the fluff factor expected as temps were falling while it was snowing. This event ended surprisingly close to our climatological norm of snow to water equivalent. Its possible the wind, compaction, the 12-18hr duration, the small amount of time or lack of any time of omega in the snow growth area all contributed.

 

The lowest ratios were in the Poconos and Sussex County New Jersey.

 

Historically PHL has not had many large events (>/= 6") with SWE greater than 15:1.  Of the 56 events (6 inches or greater)  we have had since 1950 (I cant be sure how many were all snow), only 6 were greater than 15:1 (one was 15:1) and none were greater than 20:1.
 

These were taken from CoCoRaHS observations. Eastern Maryland there were not many reports. Counties  where some non snow fell are "*". If a county had less than four reports, they were combined with neighboring counties. It was a fairly uniform event across our CWA with 6-10" occurring.  I'm leaving out the ":1"
 

Talbot County*  11.0

Other Maryland Eastern Shore*  14.6
 

Sussex DE* 10.0
New Castle/Kent DE  11:5
 

Berks 12.5

Bucks 10.4

Carbon & Monroe 10.0

Chester 12.2

Lehigh & Northampton 10.2

Montgomery 10.8

Delaware & Philadelphia 9.6
 

Atlantic* 11.7

Burlington 13.0

Camden 12.4

Cape May* 12.5

Cumberland & Gloucester 11.8

Hunterdon 11.2

Mercer 13.1

Middlesex 11.4

Monmouth 11.1

Morris 10.7

Ocean 11.6

Salem 10.6

Somerset 11.9

Sussex 9.3

Warren 11.5

[Absolute Humidity]

It was pretty apparent just by shoveling the snow that the ratio's weren't special. This snow felt just as heavy as any other event.

[LMolineuxLM1]

It's like the end we had decent ratios for just a short amount of time but the under layers were crazy heavy here at least seemed a bit wet which became a brick of ice.

[uncle W]

I've experienced snowfalls at 32 33 degrees with high ratios...2/26/91 was such a storm...16/1 if I remember correctly with snow falling between 29 and 33 degrees...

[Rainshadow]

I've experienced snowfalls at 32 33 degrees with high ratios...2/26/91 was such a storm...16/1 if I remember correctly with snow falling between 29 and 33 degrees...

 

Uncle,

 

Yes. We can just go back to the previous snow band event in December here. The ratio was higher with that one (temps near 32F as it was snowing) than this one.

[Kevin Reilly]

Umm go no further than shoveling the snow here in Media it weighed a ton and compared to the event back in December this snow was much heavier pushing around.

[chubbs]

Umm go no further than shoveling the snow here in Media it weighed a ton and compared to the event back in December this snow was much heavier pushing around.

 Here it depended on location. In the driveway which is exposed to wind and drifted quite a bit it was dense. On the deck protected from the wind  it was unusually light for this area . 

[famartin]

 Here it depended on location. In the driveway which is exposed to wind and drifted quite a bit it was dense. On the deck protected from the wind  it was unusually light for this area . 

 

Decks are not representative locations for snow measurements.  See video.

[chubbs]

Decks are not representative locations for snow measurements.  See video.

 

 

Definately. My post was based on clearing the snow. Like shoveling feathers on the deck.

[famartin]

bump for those expecting 20:1 ratios in tomorrow's storm... might happen briefly but highly unlikely to be something that lasts the whole storm or even a lot of it.

[Patrick T]

But 15 to 20+ did verify for the entire last storm, no, Ray?

[famartin]

But 15 to 20+ did verify for the entire last storm, no, Ray?

No.  Might want to review the first post.

[Harbourton]

Regardless of the ratios, drifting may be a problem if this storm gets as deep as some models are predicting.

[phlwx]

Regardless of the ratios, drifting may be a problem if this storm gets as deep as some models are predicting.

 

Strictly based on QPF at 10-12:1, it'll be an issue at 6-8", yes....

[Absolute Humidity]

If anyone is interested in ratios what looked like for this event, at least in my area, I melted 14.3" of snow down to .60 LE. That's like what 23" to 1ish? Pretty amazing, however there is chance not all of the snow made it into the coco bucket. I compacted it down below the 7" line but some may have over spilled before I actually did that. I'll do a core comparison tomorrow. If any did spill over it couldn't have been more than an inch.

[famartin]

If anyone is interested in ratios what looked like for this event, at least in my area, I melted 14.3" of snow down to .60 LE. That's like what 23" to 1ish? Pretty amazing, however there is chance not all of the snow made it into the coco bucket. I compacted it down below the 7" line but some may have over spilled before I actually did that. I'll do a core comparison tomorrow. If any did spill over it couldn't have been more than an inch.

 

There's actually a very high possibility of that.  CoCoRaHS gauges are only rated to 6" of snow. 

http://www.cocorahs.org/Content.aspx?page=measuresnow

"During heavy snow (6" or greater) the cylinder will fill to the top and overflow with snow. You will have to measure more often than once daily under heavy snow conditions."

[Absolute Humidity]

Haaa, then disregard, I'll do a core tomorrow.

[svh19044]

I posted in the other thread, but the storm total for Horsham PA was 8.7"  of snowfall from the core with a liquid equivalent of .57 giving a final ratio of 15:1. 

 

The whole story is that the first half of the storm at 4.4" of snow/.40 liquid equivalent was 11:1 ratio's while the second 4.3"/.17 liquid equivalent had a staggering ratio of around 25:1. 

[Absolute Humidity]

So

There's actually a very high possibility of that.  CoCoRaHS gauges are only rated to 6" of snow. 

http://www.cocorahs.org/Content.aspx?page=measuresnow

"During heavy snow (6" or greater) the cylinder will fill to the top and overflow with snow. You will have to measure more often than once daily under heavy snow conditions."

So I took a core sample, making sure all the snow at the base of board was added in and viola, the LE was larger. But only by an additional .05" make the total core LE of .65 or roughly 21 to 1 ratio.

[famartin]

So So I took a core sample, making sure all the snow at the base of board was added in and viola, the LE was larger. But only by an additional .05" make the total core LE of .65 or roughly 21 to 1 ratio.

Hmmm looking through the Monmouth reorts most had 0.7-0.8 (one reported over 1.0) LE for around a foot of snow

[RU848789]

Tony - great point about omega/vertical velocities.  For what it's worth, during the last storm I made a rather long-winded, but hopefully helpful post trying to explain my view on snow crystal nucleation and growth and how that is a function mostly of temps in the snow growth region, plus, the degree of supersaturation present in that region, as driven by omega.  Here it is, below.  Comments welcome...

 

"A few folks have asked about snow ratios and what affects snow ratios.  I'm not a meteorologist, but I am an expert in nucleation/crystallization phase changes (in the chemical/pharmaceutical industry, but the concepts apply almost exactly to snow). 

So, for those who are curious why our snow ratios will be so high (15-20:1, which means 0.5" of liquid gives 7.5-10" of snow, instead of the usual 5" of snow in a typical 10:1 ratio), conditions are expected to be very favorable for large, dry, fluffy snow crystals in the primary snow growth region (around 700 mb of pressure, several thousand feet up in the atmosphere).  Hope what follows helps. 

 

Specifically, as relatively warm, moist air saturated with water vapor is lifted into the 700 mb region, which will be very cold, relatively speaking vs. "typical" snowstorms, i.e., temps will be about -10 to -22C at that level, this will lead to that water vapor becoming highly superaturated, meaning the relative humidity of that parcel of air at that temperature actually well exceeds 100%, which denotes being supersaturated, i.e., beyond 100% saturation; thermodynamically, this situation cannot exist for long, as that supersaturated vapor wants to either condense into liquid or directly condense into frozen particles, depending on the temp (and pressure). 

 

This supersaturation leads to very fast snow crystal nucleation (the creation of snow crystals at those cold temps aloft), followed by good dendritic snow growth (via vapor phase deposition - the water vapor that remains supersaturated in the parcel essentially changes phases from vapor to ice, as it crystallizes and grows directly on the "starter crystals" that just nucleated) on those crystals, leading to dendrites and plates.  These dendtrites and plates "layer" better on the ground, such that there is more air present in the snow on the ground, resulting in a lower bulk density (low mass per unit volume) of that snow or a greater snow depth to liquid equivalent ratio.  Think of a pile of dry leaves vs. a pile of wet, aged leaves, in which the dry leaves contain ar less leaves and far more air per unit volume vs. wet leaves. 

 

To get powdery, fluffy, low bulk density snow, one needs both conditions, though: cold temps in the snow growth region, plus good vertical lift to drive the supersaturation - it's the vertical lift which carries warm, relatively moist air from the surface (or near the surface) up into the primary snow growth region around 700 mb (to be sure, supersaturation and nucleation/crystallization occur at more heights than 700 mb - it's just that the 700 mb region is the "standard" referred to), which leads to the supersaturation and at the right temps, the good plates/dendrites form and grow.  See the link for the pics of the crystals one typically gets at various temps in the snow growth region. 

 

Why -10 to -22C in the snow growth layer leads to plates and dendrites vs. rods or cubes is unclear to me.  Perhaps that's something I should look into..."

 

After this post, Loco Ako added a great graphic which helps show this..

 

[RU848789]

By the way, any explanations for why far SE NJ got so little precip/snow? 

[Absolute Humidity]

Hmmm looking through the Monmouth reorts most had 0.7-0.8 (one reported over 1.0) LE for around a foot of snow

Hmmm, I'm sure random variance would dictate some spots with more, others with less. .65 is not that different than .75 or .8 respectively. I know this wasn't Nevada desert snow in terms of ratios but nonetheless impressive.

[Absolute Humidity]

Just about all of the NYC stations are saying they got 8 - 11.5" from .25 - .45" LE.

[Rainshadow]

Just about all of the NYC stations are saying they got 8 - 11.5" from .25 - .45" LE.

 

I hope you are not basing this on airport obs. I was an observer at all of the three NYC area airports and they all stunk during snow. The snow fell sideways and not in the buckets.  Suffolk County CoCoRAHS ratio was 17:1. 

[Rainshadow]

Anyway here is the latest event:

 

We had a great textbook case here, where the higher ratios were with the frontogenetic band and snow growth/omega cross hairs along I95.  I've attached an MPE map, but I think these pcpn estimates are on the high side.  Maybe because people worked today, the CoCoRaHS collection was less than average, so I had to do a bit more combining of counties than last time to get at least 5 or more in most of them.  As my math professors would say, as the student can readily see, lower ratios occurred with colder temperatures northwest of the band.  Beside above, the lighter intensity probably helped cause more settling.  Rain contamination(*) I think was limited to Sussex and Cape May. Here goes:

Maryland Eastern Shore...15:1
Kent and New Castle........18:1
Sussex DE*.....................13:1

Poconos.........................14:1
Berks..............................12:1
Lehigh Valley....................13:1
Chester............................19:1
Montgomery.....................17:1

Bucks/De/PHL..................18:1

Sussex NJ........................13:1
Warren..............................17:1
Morris...............................14:1
Hunterdon.........................16:1
Somerset..........................18:1
Middlesex.........................17:1
Monmouth.........................17:1
Mercer...............................18:1
Burlington...........................17:1
Ocean...............................12:1
Camden.............................18:1
Gloucester..........................17:1
Cumberland & Salem...........12:1
Atlantic...............................11:1
Cape May*..........................10:1

 

[Rainshadow]

By the way, any explanations for why far SE NJ got so little precip/snow? 

 

It almost looked like they spent too much time in the "dry slot".  They were stuck between the fgen banding and lack of pva until the evening.  By then the jet aloft was offshore.

[JERSEYSNOWROB]

Anyway here is the latest event:

 

We had a great textbook case here, where the higher ratios were with the frontogenetic band and snow growth/omega cross hairs along I95.  I've attached an MPE map, but I think these pcpn estimates are on the high side.  Maybe because people worked today, the CoCoRaHS collection was less than average, so I had to do a bit more combining of counties than last time to get at least 5 or more in most of them.  As my math professors would say, as the student can readily see, lower ratios occurred with colder temperatures northwest of the band.  Beside above, the lighter intensity probably helped cause more settling.  Rain contamination(*) I think was limited to Sussex and Cape May. Here goes:

Maryland Eastern Shore...15:1

Kent and New Castle........18:1

Sussex DE*.....................13:1

Poconos.........................14:1

Berks..............................12:1

Lehigh Valley....................13:1

Chester............................19:1

Montgomery.....................17:1

Bucks/De/PHL..................18:1

Sussex NJ........................13:1

Warren..............................17:1

Morris...............................14:1

Hunterdon.........................16:1

Somerset..........................18:1

Middlesex.........................17:1

Monmouth.........................17:1

Mercer...............................18:1

Burlington...........................17:1

Ocean...............................12:1

Camden.............................18:1

Gloucester..........................17:1

Cumberland & Salem...........12:1

Atlantic...............................11:1

Cape May*..........................10:1

 

24hr-20140122.12z.png

Wow interesting stuff! Thanks! Great job with the storm too BTW!

[Rainshadow]

Wow interesting stuff! Thanks! Great job with the storm too BTW!

 

Thank-you!

[Absolute Humidity]

Anyway here is the latest event:

 

We had a great textbook case here, where the higher ratios were with the frontogenetic band and snow growth/omega cross hairs along I95.  I've attached an MPE map, but I think these pcpn estimates are on the high side.  Maybe because people worked today, the CoCoRaHS collection was less than average, so I had to do a bit more combining of counties than last time to get at least 5 or more in most of them.  As my math professors would say, as the student can readily see, lower ratios occurred with colder temperatures northwest of the band.  Beside above, the lighter intensity probably helped cause more settling.  Rain contamination(*) I think was limited to Sussex and Cape May. Here goes:

Maryland Eastern Shore...15:1

Kent and New Castle........18:1

Sussex DE*.....................13:1

Poconos.........................14:1

Berks..............................12:1

Lehigh Valley....................13:1

Chester............................19:1

Montgomery.....................17:1

Bucks/De/PHL..................18:1

Sussex NJ........................13:1

Warren..............................17:1

Morris...............................14:1

Hunterdon.........................16:1

Somerset..........................18:1

Middlesex.........................17:1

Monmouth.........................17:1

Mercer...............................18:1

Burlington...........................17:1

Ocean...............................12:1

Camden.............................18:1

Gloucester..........................17:1

Cumberland & Salem...........12:1

Atlantic...............................11:1

Cape May*..........................10:1

 

24hr-20140122.12z.png

Nice map. That actually looks really good to me. I did another core melt from a different location and found .78 LE so take a few hundreds off for sublimation and 17:1 is right in line.