NYC CWA Feb 1-2 Storm Discussion

[IsentropicLift]

Upton taking their sweet time with the afternoon package. Probably trying to figure out if it's worth going with a WSW for the city and getting everyone excited when the main event for the city and points east are still in the second-third periods.

[simpsonsbuff]

based on the zone forecast, UPton should be going with a WSW for Manhattan on north and west... We'll see if that happens...

[NorthShoreWx]

Understand that John. But NAM has at least .50" of liquid when NYC is 25 degrees. That is ICE. When surface is 25 degrees, it freezes. 30-32, yes. But when its 25-29, freezing will be widespread.

True enough.

Water freezes on contact with surfaces less than 32. Ice doesn't stop accreting until 32. I said this before, but the same physical laws apply in NYC. They may think they are special, but not when it comes to physics.

If some posters are going to insist that it needs to be significantly colder than 32 for ice to form in NYC, at least clarify that is because a lot of the surfaces may still be warmer than the air. If the temperature in central park is 31.8F, the shrubs growing at the zoo will accrete ice. Some water will run off before freezing, but they will accrete ice. Likewise, the snowpack will accrete ice until the temperature reaches freezing.

There are too many old wives tales being repeated in this thread.

[LocoAko]

Some reading for people who want to learn more (I haven't read these, just stumbled upon them)

Urban Modification of Freezing-Rain Events

STANLEY A. CHANGNON

Changnon Climatologist, Mahomet, Illinois

26 September 2002 and 4 January 2003

ABSTRACT

A new national database for freezing-rain occurrences during the 1945–2000 period provided an opportunity

for a study of the potential urban effects on freezing-rain events. Numerous past studies of snowfall events in

urban areas have defined decreases of 10%–35% related to the urban heat island. The heat island, which acts

to elevate near-surface temperatures, could also keep some freezing-rain situations from occurring in the city.

The study involved four cities in the Midwest and Northeast for which the average annual number of days with

freezing rain are three or more, for which data from in-city stations existed, and for which data for several

surrounding rural stations existed. The two largest qualifying cities, New York City, New York, and Chicago,

Illinois, had sizable reductions in average and maximum annual freezing-rain-day frequencies, ranging from

16% to 43% less than values of surrounding rural stations, and their freezing-rain ‘‘seasons’’ were 1–2 months

shorter than those in surrounding rural areas. The ocean/lake influences at both cities, along with the heat island,

also helped to reduce the local incidence of freezing-rain events. Two qualifying smaller urban areas,Washington,

District of Columbia, and St. Louis, Missouri, had reductions in freezing-rain-day occurrences but had no shifts

in the length of their freezing-rain seasons. Results suggest that freezing-rain occurrences in large cities are

decreased between 10% and 30% by the heat island, which acts to keep rain from freezing to urban surfaces.

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0450%282003%29042%3C0863%3AUMOFE%3E2.0.CO%3B2

Local and Synoptic Environments Associated with Freezing Rain in the

Contiguous United States

CHRIS C. ROBBINS* AND JOHN V. CORTINAS JR.1

Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, Oklahoma

(Manuscript received 5 January 2001, in final form 31 July 2001)

ABSTRACT

Local and synoptic conditions associated with freezing-rain events in the continental United States, as well

as the temporal and spatial variability of these conditions, have been documented for the period 1976–90. It

had been postulated that the characteristics of the thermodynamic stratification observed during freezing rain

would be similar regardless of geographical location. However, through hypothesis testing, it was found that

some interregional variability exists in the magnitude of various sounding parameters that the authors felt

characterized the important aspects of the thermodynamic profile of freezing-rain environments. This variability

seems to be related not only to local effects resulting from terrain variations and nearby water sources, but also

from regional differences in synoptic-scale atmospheric environments favorable for freezing rain.

These results suggest that freezing-rain forecast techniques, which rely on critical parameters derived for

specific geographical locations, may not be applicable if applied elsewhere. Therefore, forecasters evaluating

the possibility of freezing rain over synoptic-scale areas should not expect one variable that characterizes a

sounding to be an accurate indicator of freezing rain across the entire region. Algorithms that evaluate the entire

thermodynamic profile and consider the effect of this profile on frozen and freezing precipitation may provide

forecasters with a quick and more accurate method of evaluating the potential for freezing rain than traditional

forecast techniques, such as partial thickness.

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0434%282002%29017%3C0047%3ALASEAW%3E2.0.CO%3B2

From the second article:

More recently, case studies have utilized rawinsonde

observations (Young 1978; Bocchieri 1980; Zerr 1997;

Bernstein 2000) and remote sensing techniques, such as

wind profilers and Doppler radar (Martner et al. 1993;

Ramsey 1995; Thoreson 1995; Zerr 1997), to view the

atmosphere’s vertical structure during freezing-rain

events. Bernstein (2000) used data at six rawinsonde

sites to identify important regional and local influences

on freezing precipitation in the United States. He found

that warm advection was the primary forcing associated

with freezing-rain events. In addition, he determined

that the thermodynamic profile during freezing rain usually

had an elevated warm layer with a depth of up to

2800 m, and a maximum temperature within the layer

that ranged from 1C to 10C. Below the warm layer, was

a subfreezing layer, which had a depth of up to 1400

m, and a minimum temperature within the layer that

ranged from -1C to -7C. Cortinas (2000) found similar

results for freezing-rain events in the Great Lakes

region of North America.

[IsentropicLift]

I can tell you one thing, ice may not be a problem for trees and powerlines with marginal temps and mod QPF but the untreated roads and surfaces will still accumulate up to 32. I'm sorry but if it's 25 degrees out and raining, the concequences will be tremendous.

[NJwinter23]

True enough.

Water freezes on contact with surfaces less than 32. Ice doesn't stop accreting until 32. I said this before, but the same physical laws apply in NYC. They may think they are special, but not when it comes to physics.

If some posters are going to insist that it needs to be significantly colder than 32 for ice to form in NYC, at least clarify that is because a lot of the surfaces may still be warmer than the air. If the temperature in central park is 31.8F, the shrubs growing at the zoo will accrete ice. Some water will run off before freezing, but they will accrete ice. Likewise, the snowpack will accrete ice until the temperature reaches freezing.

There are too many old wives tales being repeated in this thread.

The debate here is how much of the liquid being predicted to fall while surface temps <=32 will actually accumulate on surfaces given the the thermal profiles and other factoirs such as heavy precip rates leading to runoff. We're not trying to re-define the laws of physics in NYC

[Sundog]

True enough.

Water freezes on contact with surfaces less than 32. Ice doesn't stop accreting until 32. I said this before, but the same physical laws apply in NYC. They may think they are special, but not when it comes to physics.

If some posters are going to insist that it needs to be significantly colder than 32 for ice to form in NYC, at least clarify that is because a lot of the surfaces may still be warmer than the air. If the temperature in central park is 31.8F, the shrubs growing at the zoo will accrete ice. Some water will run off before freezing, but they will accrete ice. Likewise, the snowpack will accrete ice until the temperature reaches freezing.

There are too many old wives tales being repeated in this thread.

I think what we are really debating here is the efficiency of the rain freezing. Of course freezing rain will accrue much better at temps in the mid 20's. If temps are in the low 30's, some freezing rain will still accrue but not as easily as with temps in the 20's. The sun also platys a factor in borderline situations. Two weeks ago when we had a period of freezing rain, the trees on the south facing side of my house had the ice melting off while the shrubs on the north facing side were still covered in ice. Temps were right around freezing.

[Wild Turkey]

True enough.

Water freezes on contact with surfaces less than 32. Ice doesn't stop accreting until 32. I said this before, but the same physical laws apply in NYC. They may think they are special, but not when it comes to physics.

If some posters are going to insist that it needs to be significantly colder than 32 for ice to form in NYC, at least clarify that is because a lot of the surfaces may still be warmer than the air. If the temperature in central park is 31.8F, the shrubs growing at the zoo will accrete ice. Some water will run off before freezing, but they will accrete ice.

There are too many old wives tales being repeated in this thread.

Isn't the issue really that you can't just say "the surface is below freezing on the models so ice will accrete"? Roadways get above freezing due to traffic and salt can prevent freezing even if the surface air temp is below 32. Rain that falls at 36 degrees and hits a 31.8 degree bush probably isn't going to accrete enough ice for it to matter. You might as well call it plain rain at that point. So yes, in general, if the *surface* is less than 32 (unless we're talking treated roadways), you'll get the rain freezing on contact. But the air temp being 31.8 doesn't necessarily tell you anything.

[Stormlover74]

I agree but since afternoon packages/zone forecasts already went out don't think we'll see warnings until late tonight. Which is interesting because it is starting in less than 12 hours but we don't get the warning criteria precip until tomorrow night so I guess maybe thats why they are holding off.

based on the zone forecast, UPton should be going with a WSW for Manhattan on north and west... We'll see if that happens...

[NorthShoreWx]

Good post John, but I'm just curiouis why you think this wouldn't accrete? Temperatures in the mid-to-near-upper-20s should let it freeze, especially if there is snow on surfaces to help the ZR stick to. I don't know much about it admittedly, but I assume the intensity and related latent heat release would only become an issue once you get to the 31/32F range. No?

Agree.

[armadillo]

I don't know how many of you have lived through real ice storms. I grew up in a rural town in southern Missouri and ice storms were the norm rather than the exception. You can debate the physics all you want, but if we get a half inch of ice, it doesn't matter if it melts on the road, because you still can't drive over the tree limbs.

[EasternLI]

I agree but since afternoon packages/zone forecasts already went out don't think we'll see warnings until late tonight. Which is interesting because it is starting in less than 12 hours but we don't get the warning criteria precip until tomorrow night so I guess maybe thats why they are holding off.

I wouldn't be suprised if some of the area remained under a watch, seems like there's still a lot of uncertainty as to how things ultimately play out.

[Stormlover74]

They just are not very common in this part of the country and in urban areas in general. Not to say it can't or won't happen but the only rather severe icestorm I remember was 1/7/94 and that even had temps in the 19-24 range for most of the storm. usually we get sleet or warm up enough to change to plain rain

I don't know how many of you have lived through real ice storms. I grew up in a rural town in southern Missouri and ice storms were the norm rather than the exception. You can debate the physics all you want, but if we get a half inch of ice, it doesn't matter if it melts on the road, because you still can't drive over the tree limbs.

[Kaner587]

GFS looks cold so far...too lazy to look at 12z but the surface is pretty cold. 1035 high in canada...

[armadillo]

They just are not very common in this part of the country and in urban areas in general. Not to say it can't or won't happen but the only rather severe icestorm I remember was 1/7/94 and that even had temps in the 19-24 range for most of the storm. usually we get sleet or warm up enough to change to plain rain

Agreed. I have lived here 10 years and can't remember anything I would call an ice storm. My hometown had a really bad one about 2 years ago that was devastating. Power out for up to 3 weeks, millions of trees down, shut down everything for days. I was in SC right after Hugo and the aftermath of that ice storm was way worse.

[ag3]

GFS more agressive with tonight's first event then NAM. .25"-.50" of snow and sleet.

Then stays frozen for NYC thru hour 42 for .25" of ice.

After that its all rain. About .75" of it.

[Kaner587]

They just are not very common in this part of the country and in urban areas in general. Not to say it can't or won't happen but the only rather severe icestorm I remember was 1/7/94 and that even had temps in the 19-24 range for most of the storm. usually we get sleet or warm up enough to change to plain rain

I agree they aren't very common, but the poster who grew up with many ice-storms, you make an excellent point, and that actual makes sense based on what I remember from mid-western ice-storms of the past. The blacktop is often completely wet but the problems never arise from ice accretion on the blacktop, it almost always has to do with the accretion and power lines and trees, which is almost an absolute if temps are in the mid to upper 20's. I think some people may be dismissing this based on climatic history for the area, but the truth is, that even if we only manage to accrete 0.3 in of ice on trees and powerlines, that could easily create problems, (for NYC metro at least). In my location, and for the surrounding areas, I am a little nervous as the potential impacts up here could be huge.

[Stormlover74]

Much colder, Surface temps in the upper 20s by Wednesday 12z and .75" already fallen, all frozen. also the 850 line is right on top of us wednesday morning. Still warms to mid 30s by 18z wednesday however.

GFS looks cold so far...too lazy to look at 12z but the surface is pretty cold. 1035 high in canada...

[NorthShoreWx]

Isn't the issue really that you can't just say "the surface is below freezing on the models so ice will accrete"? Roadways get above freezing due to traffic and salt can prevent freezing even if the surface air temp is below 32. Rain that falls at 36 degrees and hits a 31.8 degree bush probably isn't going to accrete enough ice for it to matter. You might as well call it plain rain at that point. So yes, in general, if the *surface* is less than 32 (unless we're talking treated roadways), you'll get the rain freezing on contact. But the air temp being 31.8 doesn't necessarily tell you anything.

It tells you that ice will form faster than it melts on unheated surfaces. Its all kind of moot at that temperature unless there is a continuing feed of new cold air because with any decent rate of precipitation, latent heat release will quickly bring the temperature to equilibrium (between melting and freezing) at 32.0.

So, I don't really have an argument with several of the responses to my earlier post...I just want to caution about the wording used so that we don't have to read a thousand incorrect weenie posts during the next ice threat (there are impressionable posters lurking).

[earthlight]

A good bit colder than the 12z run

[Kaner587]

GFS more agressive with tonight's first event then NAM. .25"-.50" of snow and sleet.

Then stays frozen for NYC thru hour 42 for .25" of ice.

After that its all rain. About .75" of it.

Looks like it warms above freezing at about the same time as the NAM or about hr 45. So maybe a little less falls as rain, like 0.5. Either way there looks to be some messy conditions in the area Wed morning.

also this model consensus we have means there will likely be little if any flooding with temps at its highest point in the mid 30's.

[earthlight]

Here's a better image

[IsentropicLift]

For your FYI, Upton went with warnings for all of NJ Except Essex and Hudson Counties and all of SE NY and CT except kept watches from extreme E NJ all the way through E LI

[EasternLI]

Looks like it warms above freezing at about the same time as the NAM or about hr 45. So maybe a little less falls as rain, like 0.5. Either way there looks to be some messy conditions in the area Wed morning.

I'm not so sure we're done seeing things shifting around....Every set of models is treating the canadian HP a little differently.

[bluewave]

The 18z GFS has the offshore low a little stronger so the low level cold air drains further south around 36 hr than 12z.

[earthlight]

For your FYI, Upton went with warnings for all of NJ Except Essex and Hudson Counties and all of SE NY and CT except kept watches from extreme E NJ all the way through E LI

They went with warnings for Western Union and Western Essex..basically west of the GSP.

[psv88]

Here's a better image

damn long island looks small on that map...does this look like an event where the north shore and south shore have vastly different conditions? Or an event where the 32 line pretty much excludes long island from the continental us...gotta love those.

[nzucker]

Looks like it warms above freezing at about the same time as the NAM or about hr 45. So maybe a little less falls as rain, like 0.5. Either way there looks to be some messy conditions in the area Wed morning.

It looks as if we see about 4" of snow tonight on the GFS, with some freezing rain tomorrow.

There's also a bit of CAA behind the initial overrunning wave, which allows some parts of the NYC metro to start as snow in the main SW flow event before transitioning over to ZR/PL. Really a very interesting and potentially dangerous storm here, especially in Westchester where surface conditions are going to be colder. The secondary tries to squeeze out south of us, allowing more of the NE flow from the high to remain over the CWA. Another nowcast event with a very close call between heavy snow, devastating ice, and plain rain.

[meteorjosh]

OK folks, it is nowcast time from my perspective. The first parameter I want to point out is that there will be little radiational cooling tonight, even last night Newburgh bottomed out at 1f while Manhattan was in the low-20s with radiational cooling. So clearly the snowpack is really not going to be a great help to us in the city in cooling surface temps unless we have a nice NE gradient. Second, temps are currently running around 30f in the city, sure there will be some evaporative cooling with the onset of precip, but not 10 degrees worth.

That's my take, regardless of what the models are or are not showing.

[dbc]

If this verifies it can change to rain all it likes, it will do nothing to the snowpack and flooding will be of no concern.

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE NEW YORK NY

457 PM EST MON JAN 31 2011

...A SIGNIFICANT WINTER STORM WILL IMPACT THE AREA TUESDAY

THROUGH WEDNESDAY...

CTZ008>010-NJZ004-103>105-107-NYZ071-011100-

/O.UPG.KOKX.WS.A.0005.110201T1100Z-110203T0000Z/

/O.NEW.KOKX.WS.W.0005.110201T1100Z-110203T0000Z/

NORTHERN NEW LONDON-SOUTHERN FAIRFIELD-SOUTHERN NEW HAVEN-

EASTERN PASSAIC-WESTERN BERGEN-EASTERN BERGEN-WESTERN ESSEX-

WESTERN UNION-SOUTHERN WESTCHESTER-

457 PM EST MON JAN 31 2011

...WINTER STORM WARNING IN EFFECT FROM 6 AM TUESDAY TO 7 PM EST

WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN UPTON HAS ISSUED A WINTER STORM

WARNING FOR HEAVY SNOW...SLEET AND FREEZING RAIN...WHICH IS IN

EFFECT FROM 6 AM TUESDAY TO 7 PM EST WEDNESDAY. THE WINTER STORM

WATCH IS NO LONGER IN EFFECT.

* LOCATIONS...PORTIONS OF THE LOWER HUDSON VALLEY...NORTHEAST NEW

JERSEY...AND SOUTHERN CONNECTICUT.

* HAZARDS...HEAVY SNOW...SLEET AND FREEZING RAIN.

* ACCUMULATIONS...6 TO 9 INCHES OF SNOW ACCUMULATION...AND UP TO A

HALF AN INCH OF ICE ACCUMULATION BY LATE WEDNESDAY.

* TIMING...SNOW BEGINS AFTER MIDNIGHT TONIGHT...TRANSITIONING TO A

WINTRY MIX OF SLEET...SNOW AND FREEZING RAIN LATE TUESDAY

MORNING INTO TUESDAY AFTERNOON...BEFORE BECOMING INTERMITTENT

TUESDAY EVENING. THEN A MIX OF HEAVY SNOW...SLEET AND FREEZING

RAIN DEVELOPS LATE TUESDAY NIGHT...TRANSITIONING TO MAINLY

FREEZING RAIN LATE WEDNESDAY MORNING INTO EARLY WEDNESDAY

AFTERNOON BEFORE TAPERING OF LATE WEDNESDAY.

* IMPACTS...TRAVEL WILL BE IMPACTED TUESDAY THROUGH AT LEAST INTO

WEDNESDAY EVENING. SNOW AND ICE ACCUMULATIONS WILL MAKE FOR

DANGEROUS TRAVEL. ICE ACCUMULATIONS WILL LIKELY KNOCK DOWN SOME

TREE LIMBS AND POWER LINES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING FOR HEAVY SNOW MEANS SEVERE WINTER WEATHER

CONDITIONS ARE EXPECTED OR OCCURRING. SIGNIFICANT AMOUNTS OF SNOW

ARE FORECAST THAT WILL MAKE TRAVEL DANGEROUS. ONLY TRAVEL IN AN

EMERGENCY. IF YOU MUST TRAVEL...KEEP AN EXTRA FLASHLIGHT...FOOD...

AND WATER IN YOUR VEHICLE IN CASE OF AN EMERGENCY