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Jan 25th Winter Weather Discussion Thread


Marion_NC_WX

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Yes and yes on both counts. Battle of the NAM vs. everyone else...wonder who wins?  :whistle:

The GFS did come in a little wetter at 12Z; so you could say the American models Vs the Euro. I think we all know this is going to be a light event. But, these types of systems can over (..and under) perform more than the models depict. We're going to have to wait for the actual radar returns.  **if it under performs not much is lost

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welp, from our friend DT...don't shoot the messenger:

 

*** COMMENTS ON 12Z JAN 23 EURO ...FOR JAN 25 ***

12Z EURO HOLDS COURSE... shows two 6 hours periods of snow over OH WVA VA MD DEL northern NC ...southern PA and S NJ... the MODEL shows 0.10 to 0.25" in the 6 hour periods.... which is like 1-2 or maybe 1-3" of snow.

Over WVA and sw VA ... from ROA west the total liquid is 0.25 to 0.50" would be like 3-6 or 4-8"

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welp, from our friend DT...don't shoot the messenger:

 

*** COMMENTS ON 12Z JAN 23 EURO ...FOR JAN 25 ***

12Z EURO HOLDS COURSE... shows two 6 hours periods of snow over OH WVA VA MD DEL northern NC ...southern PA and S NJ... the MODEL shows 0.10 to 0.25" in the 6 hour periods.... which is like 1-2 or maybe 1-3" of snow.

Over WVA and sw VA ... from ROA west the total liquid is 0.25 to 0.50" would be like 3-6 or 4-8"

 

EURO saying 0.25'' to 0.50 for ROA? Gonna be another mountain special perhaps?

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What's your thoughts on the freezing rain end of this for the Mnts? It seems like CAD events have a hard time with zr once you get away from the escarpment.

 

Model soundings from both the NAM and GFS suggest the AVL valleys will be sub-freezing all day on Friday, rising to near 32F by 6pm.  We start cold and dry, and the CAD seems to want to supply a nice fetch of cold dry air, keeping the lower BL nice and cold.  Meanwhile, a pronounced warm nose develops between 850-700, so I believe we start as snow, then as the warm nose deepens, we transition to either sleet or freezing rain (depends just how deep that nose gets).  But, regardless of what happens at 850-700, the surface is below freezing the entire time.

 

This doesn't seem to be your typical escarpment-only event.  The temps aren't marginal like they usually are.  In fact, Thursday morning's quick cold frontal passage will usher in more cold and dry air on very brisk northwesterly winds.  This sets the stage for a frigid evening Thursday night and Friday morning areawide.

 

QPF amounts are light.  I believe the first half will be snow (maybe .25" liquid equivalent), and the rest (.10") is ZR or PL.

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The GFS and NAM throw us a bone and then the Doctor pulls back.  Meh.  The Doc still looks okay here, though, I suppose.

 

The JMA looks good.  :weenie:

 

I am a bit concerned being on the east side of the mountains for this one.  Though I'm not in the foothills, the western Piedmont can still get in on a little screw action here if we aren't careful.

 

Does anyone know what kind of snowfall ratios we should be expecting?

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I would not be surprised if we had a repeat of the half inch of snow that paralyzed Raleigh a couple of years back.

 

If this comes to fruition, I would bet the precip will be somewhat bandy and someone may get 0.25-0.3" of precip while someone 50 miles away gets hosed.

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I'm crying with you. We got shafted on last weeks storm too :(!!!

 

This is a different type of scenario IMO.

 

I see a better chance of a "massive" qpf shadow east of the mountains...the moisture will be hitting the mountains and the low levels will be extremely dry here.

 

Not your typical foothill shadow...more widespread.  

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This is a different type of scenario IMO.

 

I see a better chance of a "massive" qpf shadow east of the mountains...the moisture will be hitting the mountains and the low levels will be extremely dry here.

 

Not your typical foothill shadow...more widespread.  

 

It's not a QPF shadow...you ended up with more liquid with that last storm than most of it. The "shadow" was due to warmer air because of winds in your location. Do you even soak in anything you read? 

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Does anyone know what kind of snowfall ratios we should be expecting?

1-3 inches of snow and sleet. I'll take it!! figuring a little higher snow ratio than 10:1 of course...

 

My opinion, but I'd go with standard 10:1 here given that the mid levels are warming.  You like to see a very cold column to get the higher end ratios.

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When it says .15 to .25, does it mean less than 1/4 inch of snow (or whatever), like dusting?

 

Not necessarily. Depends on where you're located and it falls as rain or snow/ice. If 0.25" falls as snow, you're looking at maybe 2-3 inches if the ratios are high. If it's rain, then it's just what it says. (0.25")

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It's not a QPF shadow...you ended up with more liquid with that last storm than most of it. The "shadow" was due to warmer air because of winds in your location. Do you even soak in anything you read? 

 

I believe the mountains will actually do us harm in this type of scenario...in regards to precip. Different direction and much colder surface. 

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Anybody glanced at the 12z hi-res 4km NAM? 

Doesn't look good for northern GA with .5-.75" QPF and temps never get above freezing. 

And those of you throwing out the NAM: you do recall we threw it out last week until the GFS and eventually Euro came around. 

 

Yep we remember it well because it ended up looking more like the GFS and Euro by the time it was over with. 

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Model soundings from both the NAM and GFS suggest the AVL valleys will be sub-freezing all day on Friday, rising to near 32F by 6pm.  We start cold and dry, and the CAD seems to want to supply a nice fetch of cold dry air, keeping the lower BL nice and cold.  Meanwhile, a pronounced warm nose develops between 850-700, so I believe we start as snow, then as the warm nose deepens, we transition to either sleet or freezing rain (depends just how deep that nose gets).  But, regardless of what happens at 850-700, the surface is below freezing the entire time.

 

This doesn't seem to be your typical escarpment-only event.  The temps aren't marginal like they usually are.  In fact, Thursday morning's quick cold frontal passage will usher in more cold and dry air on very brisk northwesterly winds.  This sets the stage for a frigid evening Thursday night and Friday morning areawide.

 

QPF amounts are light.  I believe the first half will be snow (maybe .25" liquid equivalent), and the rest (.10") is ZR or PL.

 

I was just looking at the atmospheric profile for Asheville at hour 54 and was a bit surprised to see how large a warm nose was being shown on the GFS. I was figuring you guys would have more of a sleet profile like we may have along the escarpment. Anyway,  what the GFS shows definitely is a freezing rain scenario and with temps down in the mid to upper 20's at the onset, anything that falls will immediately stick.

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Anybody glanced at the 12z hi-res 4km NAM? 

Doesn't look good for northern GA with .5-.75" QPF and temps never get above freezing. 

And those of you throwing out the NAM: you do recall we threw it out last week until the GFS and eventually Euro came around. 

 

Yeah...following the NAM last week ultimately led to another Met and myself trying to make the best out of a bust by shouting bigfoot calls into Saluda.  It reminded me why I don't pay attention to it at this point of the game.

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If you are wondering why the Euro was just a tick further north, here's why. Look at the Plains vorts..... they are more separated....less interaction until later on the 0z run.

post-390-0-57285900-1358967503_thumb.png

 

The energy consolidates a bit soon on the 12z and thus everything end up a little farther north.

post-390-0-84424700-1358967511_thumb.png

 

As for these precip amounts, you have to be very careful in assigning 'trends' of this and that. We are quibbling over the differences in hundredths or at most tenths of an inch in most instances (I know it's more in some instances), and that is sort of within the 'noise' range of a 48 hour prog. 

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Product: Air Force Temp Drop (Dropsonde) Message (UZNT13 KNHC)
Transmitted: 23rd day of the month at 17:09Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 306)
Mission: Non-Tasked Mission, possibly not tropical (flight in the North Atlantic basin)
Mission Identifier: 130123154019306 (2 digit year/2 digit month/2 digit day/6 digit mission start time/Last 3 digits of aircraft tail number)
Date Mission Started: January 23rd in '13
Time Mission Started: 15:40:19Z
Observation Number: 04

Part A...

Date: Near the closest hour of 17Z on the 23rd day of the month
Highest Mandatory Level For Which Wind Was Reported: 400mb
Coordinates: 28.4N 86.9W
Location: 142 miles (229 km) to the S (172°) from Pensacola, FL, USA.
Marsden Square: 081 (About)

Level	Geo. Height	Air Temp.	Dew Point	Wind Direction	Wind Speed
1028mb (30.36 inHg)	Sea Level (Surface)	17.2°C (63.0°F)	Approximately 9°C (48°F)	45° (from the NE)	10 knots (12 mph)
1000mb	238m (781 ft)	14.8°C (58.6°F)	Approximately 8°C (46°F)	45° (from the NE)	13 knots (15 mph)
925mb	891m (2,923 ft)	9.2°C (48.6°F)	Approximately 4°C (39°F)	35° (from the NE)	13 knots (15 mph)
850mb	1,589m (5,213 ft)	7.0°C (44.6°F)	Approximately -8°C (18°F)	50° (from the NE)	10 knots (12 mph)
700mb	3,170m (10,400 ft)	2.0°C (35.6°F)	Approximately -27°C (-17°F)	310° (from the NW)	11 knots (13 mph)
500mb	5,810m (19,062 ft)	-13.7°C (7.3°F)	Approximately -45°C (-49°F)	305° (from the NW)	16 knots (18 mph)
400mb	7,460m (24,475 ft)	-26.7°C (-16.1°F)	Approximately -60°C (-76°F)	250° (from the WSW)	11 knots (13 mph)

Information About Radiosonde:
- Launch Time: 16:47Z
- About Sonde: A descending radiosonde tracked automatically by satellite navigation with no solar or infrared correction.

Remarks Section...

Location of Highest Altitude where wind was reported: 28.36N 86.86W
Time of Highest Altitude where wind was reported: 16:47:03Z

Location of Lowest Altitude where wind was reported: 28.34N 86.84W
Time of Lowest Altitude where wind was reported: 16:57:14Z

Mean Boundary Level Wind (mean wind in the lowest 500 geopotential meters of the sounding):
- Wind Direction: 45° (from the NE)
- Wind Speed: 11 knots (13 mph)

Deep Layer Mean Wind (average wind over the depth of the sounding):
- Wind Direction: 320° (from the NW)
- Wind Speed: 8 knots (9 mph)
- Depth of Sounding: From 398mb to 1028mb

Average Wind Over Lowest Available 150 geopotential meters (gpm) of the sounding:
- Lowest 150m: 159 gpm - 9 gpm (522 geo. feet - 30 geo. feet)
- Wind Direction: 50° (from the NE)
- Wind Speed: 11 knots (13 mph)

Sounding Software Version: AEV 07489

Part B: Data For Significant Levels...

Significant Temperature And Relative Humidity Levels...
Level	Air Temperature	Dew Point
1028mb (Surface)	17.2°C (63.0°F)	Approximately 9°C (48°F)
936mb	9.6°C (49.3°F)	6.6°C (43.9°F)
911mb	9.4°C (48.9°F)	Approximately -4°C (25°F)
895mb	8.8°C (47.8°F)	Approximately -8°C (18°F)
863mb	7.4°C (45.3°F)	Approximately -3°C (27°F)
850mb	7.0°C (44.6°F)	Approximately -8°C (18°F)
829mb	6.4°C (43.5°F)	Approximately -17°C (1°F)
756mb	5.4°C (41.7°F)	Approximately -29°C (-20°F)
677mb	0.4°C (32.7°F)	Approximately -20°C (-4°F)
599mb	-3.9°C (25.0°F)	Approximately -32°C (-26°F)
482mb	-15.7°C (3.7°F)	Approximately -51°C (-60°F)
398mb	-27.1°C (-16.8°F)	Approximately -59°C (-74°F)

Significant Wind Levels...
Level	Wind Direction	Wind Speed
1028mb (Surface)	45° (from the NE)	10 knots (12 mph)
1002mb	45° (from the NE)	13 knots (15 mph)
932mb	50° (from the NE)	8 knots (9 mph)
915mb	25° (from the NNE)	17 knots (20 mph)
899mb	35° (from the NE)	13 knots (15 mph)
872mb	35° (from the NE)	14 knots (16 mph)
850mb	50° (from the NE)	10 knots (12 mph)
763mb	250° (from the WSW)	1 knots (1 mph)
701mb	310° (from the NW)	10 knots (12 mph)
670mb	285° (from the WNW)	14 knots (16 mph)
601mb	305° (from the NW)	20 knots (23 mph)
570mb	285° (from the WNW)	20 knots (23 mph)
553mb	295° (from the WNW)	23 knots (26 mph)
447mb	295° (from the WNW)	12 knots (14 mph)
416mb	275° (from the W)	13 knots (15 mph)
398mb	245° (from the WSW)	11 knots (13 mph)

 

Radiosonde data from the Gulf of Mexico. They must be very interested in the weather out there right now.

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Euro not looking as good for much PL/ZR here- a bit warmer. Not that I was that excited about this anyway, I much prefer snow, a bit of sleet then cold rain- meh.

I don't know how the Euro does down there but its horrid in the NE with temps...always too warm at the surface with wintry events, especially onces that are marginal, its resolution may not pick up the CAD in NE GA.

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