Re: Observations/ Final Discussion Thread 1/2 - 1/3, 2014 Snowstorm

[Frank_Wx]

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
LOW WAS BEGINNING TO DEEPEN MORE RAPIDLY ALONG THE OUTER BANKS OF
NORTH CAROLINA TO EAST OF THE DELMARVA. MORE RAPID DEEPENING IS
EXPECTED THROUGH THE OVERNIGHT AS THE UPPER TROUGH MOVES TOWARD
THE EAST COAST.

LIGHT TO MODERATE SNOW ACROSS THE CWA. HEAVIER SNOW BAND WAS TO
THE SOUTH OF LONG LAND AND LIKELY AFFECTS COASTAL CONNECTICUT AND
LONG ISLAND AFTER 05Z WITH COMMA HEAD/DEFORMATION PRECIPITATION
AREA EXTENDING ON THE NW SIDE OF THIS LOW IMPACTING MUCH OF THE
AREA LATER TONIGHT...

[Quietace]

Looking at the radar. The back edge has pretty much stalled. Or slowed down extremely.

[oldtimer]

Wow Wow Nice Frank lol

[Frank_Wx]

Looking at the radar. The back edge has pretty much stalled. Or slowed down extremely.

Yup

and temperatures are beginning to plummet.

Current temps everyone???

[Frank_Wx]

According to my station, 18 degrees

Find your station

http://www.wunderground.com/weather-forecast/US/NJ/Cranford.html

[aiannone]

17* now. Dropped 6 degrees in 2 hours

[oldtimer]

17*

[Quietace]

26 here.

[essexcountypete]

17*
We were at 23 when I checked around 6pm

[docstox12]

14 degrees Mahwah NJ

[aiannone]

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE NEW YORK NY
1054 PM EST THU JAN 2 2014

NYZ078>081-177-179-030600-
NORTHWESTERN SUFFOLK-NORTHEASTERN SUFFOLK-SOUTHWESTERN SUFFOLK-
SOUTHEASTERN SUFFOLK-NORTHERN NASSAU-SOUTHERN NASSAU-
1054 PM EST THU JAN 2 2014

...BAND OF HEAVY SNOW MOVING INTO LONG ISLAND...

AT 1045 PM NATIONAL WEATHER SERVICE DOPPLER RADAR SHOWED A BAND OF
HEAVY SNOW MOVING OFF THE CENTRAL NEW JERSEY COAST AND HEADED FOR
NASSAU AND SUFFOLK COUNTIES. THE BAND SHOULD REACH THE SOUTH SHORE
OF LONG ISLAND BY 1130 AM AND OVERSPREAD MAINLY SOUTHERN NASSAU
AND MOST OF SUFFOLK COUNTY THROUGH 1 AM. SNOWFALL RATES OF 1 TO 2
INCHES PER HOUR ARE EXPECTED WITH THIS BAND. WITH LOCALLY HIGHER
AMOUNTS POSSIBLE IN THE CORE OF THE BAND. NEAR WHITE CONDITIONS
ARE LIKELY AT TIMES WITH THIS BAND. PERSONS ARE URGED TO STAY
HOME AND AVOID TRAVEL DURING THIS TIME.

[sabamfa]

12.1*
http://www.wunderground.com/cgi-bin/findweather/getForecast?query=07470

[bloc1357]

16.8° here. Temps are dropping like rocks!!!

[Frank_Wx]

So temps basically in the teens for most besides Ryan, who will get there eventually.

Ratios are still 15:1 but once they get between 10-13 degrees it will be more like 17:1 then if we reach single digits, 20:1

[SNOW MAN]

24.4* Whiting NJ

[aiannone]

frank, ratios are 20:1 when you are 19 or below
http://www.erh.noaa.gov/box/tables/snowfall-meltwater.html

[mako460]

Amy Freeze still sticking with ABC's map from this morning. She gets to stay inside and Jeff is wearing a funky hat, LOL.

[Noreaster]

Ace good idea not joining them....Posted a current 500 mb map on americanwx and got yelled at for saying the trough is going negative lol.   I'm "wishcasting"...anyeay its clearly slightly negative so we'll see what this mean for our sensible weather.

[HectorO]

End by 7am? If it doesn't pick up, the city will look foolish for shutting things down.

What did they shut down? 9 am is when models have it ending. But we always know that they get that wrong, so I said 7-9 am

Looking at the 500 mb again, the trough is actually negative right now.

Transit systems in parts of NJ are in County/State of emergency, and some trains and busses from NYC are getting done early.

[CPcantmeasuresnow]

4.6 degrees, moderate snow 2.7 inches so far. To far north it seems to get in the heavy bands, i"ll have to hope extreme ratios get me to 10 inches.

[Noreaster]

frank, ratios are 20:1 when you are 19 or below
http://www.erh.noaa.gov/box/tables/snowfall-meltwater.html

I had a whole bunch of posts earlier in the thread about ratios.  Its a very good read .  Its not really based on surface temps.

[Noreaster]

from earlier tonight

by Noreaster Today at 7:41 pm
From a poster at americanwx regarding ratios..its good info and stuff some of us know but he put it pretty simply which is helpful.

"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..."





http://stream2.cma.gov.cn/pub/comet/MountainMeteorology/SnowpackandItsAssessment/comet/afwa/snowpack/media/graphics/habits.jpg

[Noreaster]

you can see if the upper level temps are too cold ratios go back down

click on the chart to enlarge....i had to google it lol

ps these are most likely temps at 700mbs



https://www.google.com/search?q=snowflake+type+chart&client=firefox-a&hs=VuZ&rls=org.mozilla:en-US:official&channel=fflb&tbm=isch&source=iu&imgil=-nGIkejKwjNZGM%253A%253Bhttps%253A%252F%252Fencrypted-tbn0.gstatic.com%252Fimages%253Fq%253Dtbn%253AANd9GcTJPy_2p7rptxE7SI7tfZw3-SJx-X-KyZ1nU4igOcAnSfD7raBYrQ%253B400%253B305%253B8aQ35lhPskotRM%253Bhttp%25253A%25252F%25252Fwww.newschoolers.com%25252Fns%25252Fforums%25252Freadthread%25252Fthread_id%25252F401888%25252F&sa=X&ei=GwnGUvGuFaTksASd94CgDQ&ved=0CDwQ9QEwBA&biw=1341&bih=883#facrc=_&imgdii=_&imgrc=-nGIkejKwjNZGM%3A%3B8aQ35lhPskotRM%3Bhttp%253A%252F%252Fthumbs.newschoolers.com%252Findex.php%253Fsrc%253Dhttp%253A%252F%252Fwww.newscientist.com%252Fdata%252Fgalleries%252Fdn16170-snowflakes%252Fmorphologydiagram.jpg%2526size%253D400x1000%3Bhttp%253A%252F%252Fwww.newschoolers.com%252Fns%252Fforums%252Freadthread%252Fthread_id%252F401888%252F%3B400%3B305

[CPcantmeasuresnow]

frank, ratios are 20:1 when you are 19 or below
http://www.erh.noaa.gov/box/tables/snowfall-meltwater.html

I had a whole bunch of posts earlier in the thread about ratios.  Its a very good read .  Its not really based on surface temps.

Any idea what page it's on. I'd like to read it.

[RJB8525]

16 here feels like 7 according to weather underground

[Frank_Wx]

2.3 inches of snow Cranford, NJ

[aiannone]

Eastern PA Weather Authority
11pm update: The coastal low is taking shape, just east of Norfolk, VA. It has a minimum pressure of 1000mb, but is in the process of strengthening. As it moves to the ENE as shown on this image, it will continue to strengthen. As it does so, it will throw back more moisture into NJ, DE, and eastern PA. There are two red lines which separates the light snows expected the rest of the night, the moderate snows in the middle, and heaviest bands to the east of that line into New Jersey. Ratios are very high... in some cases greater than 20:1. So you don't need a lot of precipitation/liquid equivalent to get snow to accumulate in a hurry. I have been sitting under between 15-20dbz on radar in south Allentown for several hours, yet still adding about 3/4" every hour for a total so far of 4.5" ... so although the radar looks unimpressive in some areas, it is piling up faster than you would think due to the high ratios. Snow will continue through the night at similar intensity, and as the low pressure moves to the 2nd position (996mb) the radar will increase in intensity all the way back to the moderate areas we have indicated, and then as the system pulls away, snow will end from west to east from between 4am (far west) to as late as 10am (far eastern NJ) ...

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