Fabulous February Arctic Outbreak

[tnweathernut]

The 12z ukmet is a north central TN crush job, over 9", a ton of qpf for the entire state (1+), but likely mixing issues southeast and parts of east TN

[Stovepipe]

12z Ukie snow:

 

[tnweathernut]

Wow, just wow at the 2m temperature spread at hour 84 on the 12z ukie.  It's 53 just south of the south central TN border and in the low 20's on the TN/KY border due north.

[Stovepipe]

12z Euro ensemble mean looks like op, control does too but even more snow, especially for north GA (like 6+).  This is just through Wed, it keeps adding more as time goes on.

[LithiaWx]

Awesomesauce

 

 

[John1122]

I really hope this one works out. I seriously can't see that tiny a precip shield with the 12z GFS track/strength and it was a big shift north from 06z. After that large a shift, I'm not sure it won't shift way further north at this rate.

[John1122]

MRX had one of it's best forecast discos ever this afternoon. Kudos, Also they are riding with the Euro/NAM as of now. Say the GFS has been too erratic to trust at this point.

[ladyjmayo]

MRX had one of it's best forecast discos ever this afternoon. Kudos, Also they are riding with the Euro/NAM as of now. Say the GFS has been too erratic to trust at this point.

 

Agreed!  They seem to have hit a good balance with this one:

 

Area forecast discussion

National Weather Service Morristown Tennessee

307 PM EST Friday Feb 13 2015

Short term...(tonight through Saturday night)...high pressure over

the area shift east tonight and early Saturday. An Arctic front

will move through late in the day Saturday...followed by a surge of

bitter cold air. Precipitation will move in Saturday

afternoon...especially north...and will likely start as some light

rain showers in valley areas before transitioning to snow showers by

Saturday night. However...freezing levels will be low enough for

most of the precipitation to fall as snow in the higher elevations...and

some light snow accumulation is expected there. Winds will increase

ahead of the front and will continue as winds shift to the northwest

behind the front. Winds will be stronger in the higher elevations

of the east Tennessee mountains...and will issue a Wind Advisory for the

mountains from Monroe north. The very cold air will combine with

the winds to produce wind chill values that reach warning criteria

in these same mountain areas...so will issue a wind chill watch as

well for Saturday night. May end up needing a Wind Chill Advisory

for some other parts of the area as well...especially the plateau

and SW Virginia...but will let later shifts evaluate this. Will issue an

Special Weather Statement highlighting the snow and cold potential.

Long term...(sunday through friday)... very interesting forecast

in the extended period...with a possible significant winter weather

event occurring on late Sunday night and Monday. However...this is

still an uncertain forecast given the fluctuations between forecast

models regarding the timing of the system and the amount of quantitative precipitation forecast

that will occur. Currently...my feeling is that the European model (ecmwf) /and its

emsembles/ has been more consistent in showing timing/track and quantitative precipitation forecast

for this event. To a lesser extent...the NAM is on board with this

European model (ecmwf) wetter solution...though its timing is earlier by around 12

hours. Combined with the sunfreezing air...this would support

widespread snowfall across the region during this time period. The

GFS also shows a snow solution...but is much weaker with quantitative precipitation forecast

amounts. Given its very erratic run to run track record of

late...have opted to weigh the European model (ecmwf)/NAM solutions more heavily for

this forecast package. At any rate...all model guidance suggests

that some snowfall /possibility significant/ will occur across the

Tennessee Valley and southern appalachian region from 06z Monday to

06z Tuesday.

The primary factor for generating this snowfall will be the very

cold temperatures in place at the surface and aloft Sunday night...

with lows /even with some cloud cover/ bottoming out in the teens

across the nearly the entire Tennessee Valley. Lift will also

enhanced by a fairly Stout 700 mb jet rotating over the region. The

main questions will be much moisture will be available to work with

and the timing of the precipitation. As mentioned...the NAM is

earlier with its timing and shows the heaviest precipitation moving

through the area faster...during a 06-18z Monday time period. The

European model (ecmwf)/Canadian shows a slower solution during the day and more of a

12z Monday to 00-06z Tuesday time frame. In each case though...quantitative precipitation forecast

amounts are high which would generate a good measurable snowfall

areawide. As a result...have introduced snowfall amounts for this

time period...though as mentioned timing is still a big question.

At this time...have favored the European model (ecmwf) solution more and show accumulation

occuring toward the late morning and afternoon on Monday. Although

it will most definitely be possible to see higher amounts should the

forecast continue to trend this way...have gone a little

conservative in snowfall amounts for now give the model flucuation.

This will allow for some flexibility and fine-tuning as more model

runs come...and confidence increases one way or the other. As

mentioned...models have wavered with this system quite a bit...so

exact totals/timing are still uncertain at this time. However...confidence

is high for some valley and mountain snowfall accumulations on

Monday. As such...have added a broad 1-2 inches in the grids across

the entire forecast area...with very slightly higher amounts across

the southern valley/plateau and mountains. The potential for a

widespread heavier snow event is possible for Monday...but do want

to see a couple more model runs before having enough confidence to

place this in the forecast.

Thereafter...the forecast remains somewhat in question...though the

favored European model (ecmwf) shows a drier period for Tuesday into Wednesday as the

base of the trough rotates across the region. Other than some light

snow showers across the mountains Tuesday night...the secondary low

that will form on the leeside of the mountains will track further

east and thus keep any additional precipitation to the east of the

mountains. The GFS shows some moisture working in on Tuesday...but

given its aforementioned back and forth track record have been

cautious with trusting this for now. Models do hint at the potential

for another round of precipitation moving southeast into the

Tennessee Valley early Thursday...though the magnitude and track are

still uncertain this far out. Overall...this upcoming week will be

very cold and much below normal for this time of year. Some relief

may occur by Friday into the weekend as southerly winds and perhaps

some weak ridging start to return.

 

Although, I am not sure about the Saturday snow.  I have not heard much about that...

[Jed33]

Wow a great discussion by MRX don't think I've seen one by them that good in a long long time. It was so well thought out and well written regarding this potential which is still up for grabs.

[jaxjagman]

 

Didnt leave yet after all

[John1122]

Comparing former storm tracks to the current GFS track. January 28-30th 2010 had a track that ran west to east around 50 miles north of the current GFS track with similar strength. That was pretty much a Valley wide event. I personally got 13 inches from it. It's precip shield was up to around Cincinnati at it's northernmost. Everyone South of 64 in Kentucky got significant wintery weather.

[John1122]

Can you do Crossville Jax? They generally are about the closest reflection of my weather.

[tnweathernut]

The 12z Euro gives the look that we could do this again around day 8/9.  

 

just looking at low locations and the general setup.

[Carvers Gap]

I have finally been able to sit down and digest the 12z model suite this afternoon.  I still think this event is far from settled, but seems a little more in focus....

 

1.  The GFS is either going to score a coup or end-up being wrong for four straight runs.  It is a little erratic, but is consistant w/ a more southern track which was somewhat verified w/ this afternoon's model runs.  Just because we don't like it, doesn't mean it gets thrown out.  But...it is on its own now in blanking the state.  However, it needs to be watched because it has been pretty decent this winter.  The track of that low would be impressive and would be a two event system.  First, moisture would stream in ahead of the main low.  Then the low would ride through south GA.  Not a bad track, and I wouldn't rule out a solution w/ a much bigger precipitations shield.

2.  Euro/UKMET/Canadian Southern slider along the Arctic boundary.  Looks like that is indeed the plan. I would say if this develops, it will look very much like a blend of those models.  They have held consistently to that track and have barely moved.  Looks like the low tries to jump to the coast and the far eastern Valley could lose snow totals due to that.

3.  Now the question, how much?  Nobody knows.  So, I will venture a only a guess...but is preliminary in nature only.  I would guess that the models shift a tad north as this almost has a clipper feel to it.  Now, this will ride the Arctic boundary.  I would guess the heaviest amounts 6-10" will fall on the northern Plateau.  Current guidance is south of that, but I am putting my money on a shift northward of 100-150 miles.  I think Nashville finally cashes in w/ 2-4".  I think TRI would roll w/ 5-6."  Knoxville 4-5."  Chatt is the wild card.  Might be go big or go home.  Could be 2" of slop or 6-7" as the models really have centered on that spot.  Memphis looks to be money w/ 5-6."

4.  Wild cards...still a lot in play here.  Where does the boundary set-up?  Does that piece of energy in the southwest get caught and pulled into the feature?  Does it weaken even more tomorrow and just become a glorified clipper?  Is it one or two waves?  If a second wave is "real," does it turn the corner and create a bigger storm? 

5.  Finally, at least we have something to track...I hope it hits somebody in the Valley mainy because I have been banging the climo drum all winter and want to show it is far more reliable than the SAI.  Norms do matter.  The Pacific does matter.  The Atlantic does matter.  The activity level of the sun does matter.  And again I will add, I hate Nino winters.  They have a habit of being late, and are feast or famine once they arrive. 

[Carvers Gap]

The 12z Euro gives the look that we could do this again around day 8/9.  

 

just looking at low locations and the general setup.

 

I agree, but the PNA is forecast by CPC to go strongly negative.  A positive NAO and AO are in place.  One would think we are about to get very warm followed by more cold.

[jaxjagman]

Can you do Crossville Jax? They generally are about the closest reflection of my weather.

 

think thats cross,if not let me know

[Carvers Gap]

[John1122]

It is, thank you!

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think thats cross,if not let me know

[John1122]

I have finally been able to sit down and digest the 12z model suite this afternoon.  I still think this event is far from settled, but seems a little more in focus....

 

1.  The GFS is either going to score a coup or end-up being wrong for four straight runs.  It is a little erratic, but is consistant w/ a more southern track which was somewhat verified w/ this afternoon's model runs.  Just because we don't like it, doesn't mean it gets thrown out.  But...it is on its own now in blanking the state.  However, it needs to be watched because it has been pretty decent this winter.  The track of that low would be impressive and would be a two event system.  First, moisture would stream in ahead of the main low.  Then the low would ride through south GA.  Not a bad track, and I wouldn't rule out a solution w/ a much bigger precipitations shield.

2.  Euro/UKMET/Canadian Southern slider along the Arctic boundary.  Looks like that is indeed the plan. I would say if this develops, it will look very much like a blend of those models.  They have held consistently to that track and have barely moved.  Looks like the low tries to jump to the coast and the far eastern Valley could lose snow totals due to that.

3.  Now the question, how much?  Nobody knows.  So, I will venture a only a guess...but is preliminary in nature only.  I would guess that the models shift a tad north as this almost has a clipper feel to it.  Now, this will ride the Arctic boundary.  I would guess the heaviest amounts 6-10" will fall on the northern Plateau.  Current guidance is south of that, but I am putting my money on a shift northward of 100-150 miles.  I think Nashville finally cashes in w/ 2-4".  I think TRI would roll w/ 5-6."  Knoxville 4-5."  Chatt is the wild card.  Might be go big or go home.  Could be 2" of slop or 6-7" as the models really have centered on that spot.  Memphis looks to be money w/ 5-6."

4.  Wild cards...still a lot in play here.  Where does the boundary set-up?  Does that piece of energy in the southwest get caught and pulled into the feature?  Does it weaken even more tomorrow and just become a glorified clipper?  Is it one or two waves?  If a second wave is "real," does it turn the corner and create a bigger storm? 

5.  Finally, at least we have something to track...I hope it hits somebody in the Valley mainy because I have been banging the climo drum all winter and want to show it is far more reliable than the SAI.  Norms do matter.  The Pacific does matter.  The Atlantic does matter.  The activity level of the sun does matter.  And again I will add, I hate Nino winters.  They have a habit of being late, and are feast or famine once they arrive. 

 

Excellent thoughts, the GFS isn't actually the furthest south track on the 12z. I think the Canadian is further south. It just has a much more expansive QPF field than the GFS. I have no idea why the GFS shows such small precip fields. Looking back at past storms of similar strength/track shows the GFS 12z precip shield 400 miles further south than what actually verified.

[tnweathernut]

18z GFS came north, keyed on the second piece of energy and dampened out the first.  Hammers east TN, not so much west.  Also gives a good snow to our friends in northern MS and northern AL.

 

very ukie like, sending the low into northern GA.

[John1122]

WPC discussion on the GFS precip shield. 

 

 

 

SHORT WAVE ENERGY TRACKING FROM THE NORTHERN ROCKIES CARVES OUT A
POSITIVELY TITLED LONG WAVE TROUGH ACROSS THE SOUTHWEST STATES AND
SOUTHERN PLAINS ON DAYS 2 AND 3. WHILE THERE WAS GENERALLY DECENT
AGREEMENT ON THE PLACEMENT OF THE LONG WAVE TROUGH...THERE WAS
SPREAD ON THE TRACK OF THE SURFACE LOW AND THE AMOUNTS OF MOISTURE
DRAWN NORTH FROM THE GULF OF MEXICO. THESE FACTORS INFLUENCE THE
NORTHERN EXTENT OF THE PRECIPITATION SHIELD AND PRECIPITATION
TYPE. AT THIS POINT...THE 12Z NAM/00Z ECMWF/ECMWF ENSEMBLE MEAN
BLEND APPEARS TO HANDLE THE MOISTURE FOR DAYS 2 AND 3 (THE 12Z GFS
SEEMS TOO SUPPRESSED WITH THE MOISTURE)..

[John1122]

GFS will have this running the apps at 00z. It's shifted 200 miles north in the last 3 runs. 

18z GFS came north, keyed on the second piece of energy and dampened out the first.  Hammers east TN, not so much west.  Also gives a good snow to our friends in northern MS and northern AL.

 

very ukie like, sending the low into northern GA.

[ShawnEastTN]

GFS just wow!!!  Hammer on plateau and east!  Long duration event!

[ShawnEastTN]

After seeing that, I agree Carver, Chatty has the potential to get buried!  Right on the edge of the precip types.

[Windspeed]

Well 72 hours out and I'm now officially on the hype train. Chooo Chooooooo!!!

[John1122]

GFS is 2-5 from Memphis NW to the highland rim, then 8-12 Plateau and East.

[John1122]

The GFS gets pretty cold too,

 

[ShawnEastTN]

The GFS gets pretty cold too,

 

Whats really awesome about that is this will be one of those rare snows where every flake that falls sticks.  Ground will be rock hard already.

[Jed33]

Lol look at 12z Friday AM if you want cold good grief

That kind of cold for so many days will not verify?!? GFS have you lost it? Below zero just about every morning from wed on to Saturday? I don't think so. Haha would be cool to experience it but man it would come with a hefty price!

[ShawnEastTN]

If the GFS is right and that bad boy cranks up the coast rather than just slides east, we get a pretty good pressure gradient.  Dare I say blowing snow...  Drifts...  What?!? Gusts to 30, 8-12"...  Not impossible.