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January 17th-18th Winter Storm Discussion


BullCityWx

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From The NWS - Raleigh for the Piedmont Triad of NC

 

EXPECT RAIN TO CHANGEOVER TO HEAVY WET SNOW IN THE TRIAD REGIONBETWEEN 6 AND 8 PM. THIS TRANSITION WILL SHIFT EWD WITH TIME AS MIDLEVEL LOW TRAVERSES THE REGION. THIS TRANSITION  SHOULD REACH THETHE TRIANGLE AREA AND THE NORTHERN-CENTRAL COASTAL PLAIN BETWEEN 9AND MIDNIGHT. THE TRACK OF THE 700MB CYCLONE SUGGEST A GOODPOTENTIAL FOR A SNOW BAND TO OCCUR OVER SECTIONS OF THEPIEDMONT...POSSIBLY NEAR OF JUST WEST OF THE TRIANGLE. INADDITION...WOULD NOT BE SURPRISED TO HAVE SOME LIGHTING OCCURWITHIN THE HEAVY SNOW BANDS.SNOWFALL RATES OF 1-2 INCHES PER HOUR NOT OUT OF THE QUESTION. THISWILL LEAD TO SNOW AMOUNTS OF 2-4 INCHES IN A SHORT PERIOD OF TIME. AWARM TOP SOIL...WARM PAVEMENT AND HEAVY RAIN OCCURRING PRIOR TOCHANGEOVER TO SNOW WILL INITIALLY LIMIT SNOW ACCUMULATION.STILL...EXPECT 2-4 INCHES OVER PARTS OF THE PIEDMONT MAINLY INGRASSY AREAS WITH 1-2 INCHES OF SLUSH DEVELOPING ON ROADWAYS. WITHTEMPS EXPECTED TO FALL PRIOR TO DAYBREAK TO NEAR OR SLIGHTLY BELOWFREEZING...DRIVING MAY QUICKLY BECOME TREACHEROUS/DANGEROUSOVERNIGHT INTO FRIDAY MORNING.AGAIN...THE THING THAT BOTHERS ME THE MOST IS THE LACK OF COLD AIRIN PLACE PRIOR TO STORM ARRIVAL. A DELAY OF CHANGEOVER BY ONE-TWOHOURS WILL CUT INTO EXPECTED SNOW AMOUNTS. IF THIS DELAYOCCURS...FINAL SNOW AMOUNTS MAY BE AT LEAST HALF OF WHAT ISCURRENTLY FORECAST (IF NOT MORE).

 

I don't like that last part. How likely is a delay based on what we are seeing now?

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From The NWS - Raleigh for the Piedmont Triad of NC

 

EXPECT RAIN TO CHANGEOVER TO HEAVY WET SNOW IN THE TRIAD REGIONBETWEEN 6 AND 8 PM. THIS TRANSITION WILL SHIFT EWD WITH TIME AS MIDLEVEL LOW TRAVERSES THE REGION. THIS TRANSITION  SHOULD REACH THETHE TRIANGLE AREA AND THE NORTHERN-CENTRAL COASTAL PLAIN BETWEEN 9AND MIDNIGHT. THE TRACK OF THE 700MB CYCLONE SUGGEST A GOODPOTENTIAL FOR A SNOW BAND TO OCCUR OVER SECTIONS OF THEPIEDMONT...POSSIBLY NEAR OF JUST WEST OF THE TRIANGLE. INADDITION...WOULD NOT BE SURPRISED TO HAVE SOME LIGHTING OCCURWITHIN THE HEAVY SNOW BANDS.SNOWFALL RATES OF 1-2 INCHES PER HOUR NOT OUT OF THE QUESTION. THISWILL LEAD TO SNOW AMOUNTS OF 2-4 INCHES IN A SHORT PERIOD OF TIME. AWARM TOP SOIL...WARM PAVEMENT AND HEAVY RAIN OCCURRING PRIOR TOCHANGEOVER TO SNOW WILL INITIALLY LIMIT SNOW ACCUMULATION.STILL...EXPECT 2-4 INCHES OVER PARTS OF THE PIEDMONT MAINLY INGRASSY AREAS WITH 1-2 INCHES OF SLUSH DEVELOPING ON ROADWAYS. WITHTEMPS EXPECTED TO FALL PRIOR TO DAYBREAK TO NEAR OR SLIGHTLY BELOWFREEZING...DRIVING MAY QUICKLY BECOME TREACHEROUS/DANGEROUSOVERNIGHT INTO FRIDAY MORNING.AGAIN...THE THING THAT BOTHERS ME THE MOST IS THE LACK OF COLD AIRIN PLACE PRIOR TO STORM ARRIVAL. A DELAY OF CHANGEOVER BY ONE-TWOHOURS WILL CUT INTO EXPECTED SNOW AMOUNTS. IF THIS DELAYOCCURS...FINAL SNOW AMOUNTS MAY BE AT LEAST HALF OF WHAT ISCURRENTLY FORECAST (IF NOT MORE).

 

Ugghhh...that's the biggest problem, if the changeover occurs at midnight RDU might see an inch, if it's a 10pm 2-4" looks great.  I still think GSO is the sweetspot up through Roxboro.

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A composite water vapor image , and animation

http://www.ssd.noaa.gov/goes/comp/nhem/flash-wv.html

 

The Pacific and Atlantic dynamics involved may be possible to watch.  Will the low(s) disconnect from the large moist air in the Pacific to which the past week's east coast weather system has been attached, or draw more greatly from it?

 

Hoping everyone will be safe through this!  It will not be a wind event at lower elevations and hopefully it will also stay as subdued as possible in the mountains.

post-8089-0-40950800-1358436832_thumb.jp

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Looks like the RAP just stuck a knife in the backs of east Tennesseans (again).  Thanks for posting that though! 

 

I think it will be an interesting case study for someone with a lot more knowledge than me, but for the models to change course and cut precip totals in half this close to the event (less than 24 hours) it makes you look for reasons why. 

 

My theory (if this actually happens) is that the interaction of the northern jet for a period actually disrupts flow into our area of east TN, cutting precip totals back quite a bit for us here.  This interaction is bad for us, but good for NC as I think it's also responsible for the increased totals for you guys.  Just a theory, and I am certainly NOT a professional........................would love to hear a met chime in with regards to this.

 

Cold core lows can do some crazy things, so you guys south and west of me..................GET YOU SOME DEFORM!

Models don't support much snow now and the radar does not either. I am going to be eating some crow with my friends on this one. Seems in NETN we almost have to have arctic air diving into a system from the GOM or cold air must already be in place.

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Huntsville update: http://www.daculaweather.com/4_afd_hun.php

 

.UPDATE...
FOR ADDING COUNTIES TO THE WINTER STORM WARNING.
&&

.DISCUSSION...
THE POWERFUL UPPER LOW CENTER IS NOW TRACKING INTO CENTRAL AL PER
RADAR/SATELLITE LOOPS. A PRONOUNCED SHEARED/DEFORMATION ZONE WITH
PL/SN WAS CROSSED MS INTO NWRN AL. A "FEEDER" BAND OF MORE CONVECTIVE
PRECIP OVER CULLMAN INTO MORGAN COUNTIES WAS A MIX OF -RA/PL. THE
COMPLICATING FACTOR IS LOW LEVEL NORTHERLY FLOW IN REPSPONSE TO THE
DEEPENING SFC LOW IN GA HAS ADVECTED DRIER AIR INTO SRN TN/NRN AL.
THIS HAS LOWERED DEW POINTS 5-7 DEGREES INTO THE 20S OVER THE PAST
FEW HOURS WHERE PRECIP WAS NOT FALLING AS OF YET. CONSEQUENTLY...THIS
HAS LIKELY SET THE STAGE FOR MORE RAPID COOLING OF THE ATMO AS PRECIP
FALLS...AND MAY ALLOW TEMPS TO REACH FREEZING FOR A BRIEF PERIOD
DURING THE SNOWFALL. ACCUMULATIONS OF SNOW ARE MORE LIKELY TO OCCUR
AS A RESULT. TO NO SURPRISE...THE QG AND DEFORMATION FORCING IS QUITE
STRONG AS THIS LOW MOVES NEWD...AND THE 12Z NAM QPF AND UPSTREAM
REPORTS OF 3-4 INCHES OF SNOW IN MS LENDS CONFIDENCE TO THE CURRENT
WARNING. WE HAVE RAISED ACCUMS BY ABOUT AN INCH...WITH LOCALLY HIGHER
AMTS SUGGESTED BY THE NAM...MAINLY IN HIGHER ELEVATIONS WHERE COLDER
TEMPS ARE ANTICIPATED. WE HAVE ALSO ADDED A ROW OF COUNTIES TO THE
WARNING. GUSTY NORTHERLY FLOW OF 15-25KT WILL LOWER VSBYS FURTHER AS
THE SNOW FALLS. BLACK ICE WILL LIKELY BECOME A PROBLEM THIS EVENING.

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Here is where I'm confused.. If this low is suppose to explode with more moisture as the day goes on and it comes down heavy in places like Birmingham, I don't understand why the ATL area won't see the same.. weird.. What am I missing??

For one, it's warmer here. 

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Just talked to Robert he said latest RAP lines up well with the NAM and just slams 85. I'm sure he'll have more at www.wxsouth.com

Yep, and Hi Res NAM like last night is showing some incredible 6 hour precip panels. Assuming that Gastonia and Shelby and points west turn to snow at 7 PM, which is about the time frame probably, it has 1.75" liquid equivalent most of that region in the southwest piedmont and extreme northern Upstate and some areas of 2.0" liquid equivalent falling AFTER 7 pm.  I questioned this last night, but it still has it. Pretty much most of western NC west of I-77 has 1.5" or so liquid equivalent going back to mountains, just in that 6 hour span from 7 PM to 1 AM.  Some parts of the escarpment, maybe Lake Lure had a 2.5" amount in just 6 hours, so if they have gone to snow, and if that is right, this will be a loaded snowstorm.  Probably eclipsing the March 2009 deal in western NC some areas, but then again I don't know if it's right, as I normall follow it more in severe weather season. The snow will be loaded with water content, so ratios are low of course, but tha will be a lot of weight for sure.  I think the model sees the deformation band better, and really lines the heart and soul of it from the northern Upstate to most of western NC for quite a while, then pivots eastward during the night and speeds up. I don't want to sound IMBY post, but the way it's lining up it sure looks to maximize lift, and rates somewhere in this area. I'm definitely NOT wanting a repeat of that terrible March 2009 night.

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Great water vapor loop as it rolls across the south. The loop does require Java but the images obviously do not so....

Go here http://www.daculaweather.com/4_sat_se_us.php and click on Water Vapor Loop, it loads a lot of images so it's a little slow.... AFTER it loads, click on "faster" about 7 times.

 

Smaller Flash loops here for those with Java disabled. http://www.daculaweather.com/4_imagery.php

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Updated Atlanta AFD: http://www.daculaweather.com/4_afd_ffc.php

 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
1047 AM EST THU JAN 17 2013


.UPDATE...
BIG FORECAST CONCERN REMAINS TO BE THE WINTER PRECIPITATION
EXPECTED THIS AFTERNOON AND EVENING.

FIRST WAVE OF PRECIP ALREADY THROUGH WESTERN GEORGIA AND
PROGRESSING INTO THE CAROLINAS AS THE LOW PRESSURE SYSTEM PUSHES
THROUGH MS/AL. WATER VAPOR IMAGERY SHOWS DRY SLOT MOVING INTO
WESTERN GEORGIA THIS MORNING...AHEAD OF THE NEXT AREA OF
PRECIPITATION...AND HAVE MADE SIGNIFICANT ADJUSTMENTS TO HOURLY
POP AND WX GRIDS AS A RESULT.

AS THE UPPER LOW PUSHES INTO EASTERN AL AND INTO GEORGIA...THE
NEXT AREA OF PRECIPITATION WILL MOVE INTO WESTERN GEORGIA. WITH
THE ORIENTATION OF THE DRY SLOT AS IT PUSHES ACROSS THE STATE...AS
THE PRECIP MOVES INTO THE STATE INTO THE AFTERNOON...COULD SEE
TRANSITION TO RAIN-SNOW MIX FIRST ACROSS WESTERN CENTRAL GEORGIA
BEFORE NORTHWEST GEORGIA. STILL ANTICIPATE HEAVIEST ACCUMULATIONS
TO BE IN THE FAR NORTH GEORGIA REGION AS THE UPPER LOW MOVES OVER
THE STATE AND CONVECTIVE NATURE OF THE PRECIPITATION OVERCOMES THE
WARM SURFACE TEMPERATURES.

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Here's the vertical velocities for Charlotte on the NAM (upward motion in negative values)...shows a burst of impressive values (-32+) in the 520 to 660mb range in the early evening with the deformation band.  2nd chart shows a coincident quick crash of the temperatures through the column...with saturation with respect to ice still present on RH profiles...all supports a burst of snow if the NAM is right.

 

 

cltvv.png
 
 

namtemps.png
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But, from everything I've read we're probably looking at 5:1 ratios. Still great, but I would think 5" will be the top snow totals coming out of this storm.

 

Given the setup, banding, very heavy rates/heavy precip totals, and decently cold enough temps aloft...I expect better than that in localized areas. That's not to say everyone will see that but I think 7 to 10 inches on grassy surfaces is a decent possibility wherever the heaviest banding occurs. RDU shows saturation all the way up to 450mb for a while which is pretty impressive.

 

As noted though by rdu, the very wet ground will hurt accumulations. I remember a snowstorm a while back where I got a few inches of rain and although it snowed like crazy the very wet ground, puddling of water, etc kept acculuations way down fronm what they would have been. It was funny seeing no snow in some areas and 4 to 6 inches(?) in others(?)..grassy surfaces.

 

I think robert (foothillsnc) has discussed all of this this pretty well imo. One thing is for sure, this will be a very beautiful snowfall for the nc folks, regardless of where you are at. At the very least a good 3 to 6 inches should be expected for many areas.

 

This is assuming 10:1 ratios though, right?

 

I wonder what it would put on the map if it took the death band into account.

 

Those of us that have been around a while know that these snowfall maps from the gfs/nam should be taken with a HUGE grain of salt.In fact they are worthless a lot of the times. I've seen these maps give me several inches when it was CLEAR that was impossible given the boundary layer temps and in fact I only got rain. Other times, I/others have gotten a lot more than what was shown on those maps.

 

They leave a lot to be desired to say the least. So folks, don't take these snowfall maps seriously.

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Models don't support much snow now and the radar does not either. I am going to be eating some crow with my friends on this one. Seems in NETN we almost have to have arctic air diving into a system from the GOM or cold air must already be in place.

 

I'm generally on the same page as you but on the plus side the RAP is showing some rather good reflectivity for us for a decent period.  No clue what that translates into as far as accums, but bodes well for heavy snow falling.

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Great minds fueled by Waffle House octane anyway.  I should probably clarify my thoughts though:

 

For SC - if you look at a map and follow I-85 from border to border, I am tempering my initial thoughts the closer you edge west toward GA.  I think Spartanburg and Cherokee counties from I-85 north still look game ready, but Greenville west will see less playing time (with the exception being the highlands of GVL, OCN and PIK counties).

 

Eastern Spartanburg county may see some action south of I-85.

That gets the snow very close to me if that turns out to be right since I'm in NW Union county about 7 miles SE of Pacolet. I am hoping to at least see some snow falling later this evening.

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12z gfs looks like the changeover is slower and the precip quicker to move out.

Tw

 

Yeah, peaked at that, I am sure the MA folks love that run, but at this point I would give the edge to the NAM/RAP.  But kudos to the GFS because it did fairly well with the overall setup of this storm the best from 4-5 days out, IMO.

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Yep, and Hi Res NAM like last night is showing some incredible 6 hour precip panels. Assuming that Gastonia and Shelby and points west turn to snow at 7 PM, which is about the time frame probably, it has 1.75" liquid equivalent most of that region in the southwest piedmont and extreme northern Upstate and some areas of 2.0" liquid equivalent falling AFTER 7 pm.  I questioned this last night, but it still has it. Pretty much most of western NC west of I-77 has 1.5" or so liquid equivalent going back to mountains, just in that 6 hour span from 7 PM to 1 AM.  Some parts of the escarpment, maybe Lake Lure had a 2.5" amount in just 6 hours, so if they have gone to snow, and if that is right, this will be a loaded snowstorm.  Probably eclipsing the March 2009 deal in western NC some areas, but then again I don't know if it's right, as I normall follow it more in severe weather season. The snow will be loaded with water content, so ratios are low of course, but tha will be a lot of weight for sure.  I think the model sees the deformation band better, and really lines the heart and soul of it from the northern Upstate to most of western NC for quite a while, then pivots eastward during the night and speeds up. I don't want to sound IMBY post, but the way it's lining up it sure looks to maximize lift, and rates somewhere in this area. I'm definitely NOT wanting a repeat of that terrible March 2009 night.

Robert hate to be a IMBY'r but looking at the latest Hi Res NAM and RAP snowfall maps it looks like most of the upstate are probably going to see mostly liquid with a small amount of change over to snow at the end.  Last night you seemed pretty confident that the upstate get see significant impact from this and that the models never handle these ULL correctly. I am a little confused here.  Were you saying that even though no model is showing signifcant snow for the upstate that you felt it would snow here based on your understanding and past experience with these systems  OR are you saying you are in agreement with what the Hi Res NAM and RAP is showing and that only the northern most portions of the upstate would see snow but that they would get slammed.  It looks like Spartanburg Co (which is in the upstate) stands a far better chance of snow than Greenville and Pickens county.  Is that correct or do you feel like central Greenville and Pickens are still in for a surprise.  Thanks and again sorry for the IMBY tone here.

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I'm generally on the same page as you but on the plus side the RAP is showing some rather good reflectivity for us for a decent period. No clue what that translates into as far as accums, but bodes well for heavy snow falling.

Still thinking warning-criteria snows are a lock for the mountains, though. Tri-Cities aren't completely out of it yet, especially Johnson City. Even 2" is much better than anything seen in the past two years.

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btw, this is a note worthy portion of rdu's discussion. It's going to be close in some areas as far as how much actually accumulates since there is a very sharp cutoff in terms of cold/warm air. A few tens of miles and 2 hours worth with regard to changeover can make a world of difference.

 

AGAIN...THE THING THAT BOTHERS ME THE MOST IS THE LACK OF COLD AIRIN PLACE PRIOR TO STORM ARRIVAL. A DELAY OF CHANGEOVER BY ONE-TWOHOURS WILL CUT INTO EXPECTED SNOW AMOUNTS. IF THIS DELAYOCCURS...FINAL SNOW AMOUNTS MAY BE AT LEAST HALF OF WHAT ISCURRENTLY FORECAST (IF NOT MORE).
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No two storms are alike, but this looks very similar to the 02/15/04 storm, but with higher totals in the mtns, and the overall amounts shifted slightly south.  

 

I think Charlotte pretty much gets fringed...dusting to an inch (GSP is going with 2-4 inches).  In central NC, I like the highest amounts on the counties bordering NC/VA.

 

Indeed, some notable similarities there.  Lest we forget what happened 11 days later... :weenie:

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Those of us that have been around a while know that these snowfall maps from the gfs/nam should be taken with a HUGE grain of salt.In fact they are worthless a lot of the times. I've seen these maps give me several inches when it was CLEAR that was impossible given the boundary layer temps and in fact I only got rain. Other times, I/others have gotten a lot more than what was shown on those maps.

 

They leave a lot to be desired to say the least. So folks, don't take these snowfall maps seriously.

 

Right. That's kind of why I asked; they're generally overdone, and then you mentioned they might be underdone. Thanks for the reply!

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btw, this is a note worthy portion of rdu's discussion. It's going to be close in some areas as far as how much actually accumulates since there is a very sharp cutoff in terms of cold/warm air. A few tens of miles, if that can make a world of difference.

 

AGAIN...THE THING THAT BOTHERS ME THE MOST IS THE LACK OF COLD AIRIN PLACE PRIOR TO STORM ARRIVAL. A DELAY OF CHANGEOVER BY ONE-TWOHOURS WILL CUT INTO EXPECTED SNOW AMOUNTS. IF THIS DELAYOCCURS...FINAL SNOW AMOUNTS MAY BE AT LEAST HALF OF WHAT ISCURRENTLY FORECAST (IF NOT MORE).

 

I am worried about that, too, but someone mentioned the RAP keeps showing the changeover not being delayed.

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Given the setup, banding, very heavy rates/heavy precip totals, and decently cold enough temps aloft...I expect better than that in localized areas. That's not to say everyone will see that but I think 7 to 10 inches on grassy surfaces is a decent possibility wherever the heaviest banding occurs. RDU shows saturation all the way up to 450mb for a while which is pretty impressive.

 

As noted though by rdu, the very wet ground will hurt accumulations. I remember a snowstorm a while back where I got a few inches of rain and although it snowed like crazy the very wet ground, puddling of water, etc kept acculuations way down fronm what they would have been. It was funny seeing no snow in some areas and 4 to 6 inches(?) in others(?)..grassy surfaces.

 

I think robert (foothillsnc) has discussed all of this this pretty well imo. One thing is for sure, this will be a very beautiful snowfall for the nc folks, regardless of where you are at. At the very least a good 3 to 6 inches should be expected for many areas.

 

 

Those of us that have been around a while know that these snowfall maps from the gfs/nam should be taken with a HUGE grain of salt.In fact they are worthless a lot of the times. I've seen these maps give me several inches when it was CLEAR that was impossible given the boundary layer temps and in fact I only got rain. Other times, I/others have gotten a lot more than what was shown on those maps.

 

They leave a lot to be desired to say the least. So folks, don't take these snowfall maps seriously.

 

Btw, about that 7 to 10 inches i mentioned, I'm not saying it will happen, there is just a chance it will in a localized area. It might not be but a few tens of miles wide if it happens. I don't want folks to think I'm actually calling for that amount, just it's possible.

 

Could be one of those cases where 7 to 10 inches actually falls..but due to wet ground it won't accumulate to that much...much like that storm I had several years back..where I did have that much fall but had much less accumulation. I remember it making me sick LOL..and it also involved an upper low

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