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East TN, SWVA, E KY, and Plateau NW flow obs. Feb 1 - 2


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I'll open this one up with a MRX discussion:

Upper low over the Ohio river valley today will dig southeast as
shortwave dives southwest from the central plains into the deep south
and helps establish longwave trough over the Appalachian chain by
late tonight. This trough shifts to eastern seaboard by Monday
afternoon but does not pull away from the east coast until Canadian
shortwave drops into upstream side of trough and helps kick it off
to the east Wed night. This will set the stage for a prolonged
period of northwest flow over the forecast area, and subsequent
significant snowfall event over the east TN mountains.

Light snow will be ongoing over the mountains by Monday morning but
inbound vort lobe associated with upper low will kick off a 12 to
18hr period of moderate to heavy snow, at times, across the area.
Temps at H85 drop to -8C to -10C during this time and should help to
boost snowfall ratios into the mid teens most likely. This is
especially true given that saturation will extend well into/above
the DGZ, which is not typical of your average NW flow snowfall
event. Successive periods of 0.15 to 0.25" should therefore yield
some 7-10" snowfall amounts in the Smokies and adjacent TN mountain
zones Monday through Monday evening. Snowfall rates will taper off
tomorrow night into Tuesday morning, but an additional 2-4" would
certainly not be out of the question during that time. Moisture
thins out during the day Tuesday but one last vort lobe moving
through Tuesday evening may help snow showers continue, especially
in southwest VA and the far northeastern TN mountains, through
Tuesday night and early Wed morning. Storm total amounts of 10-12"
in the Smokies seem very reasonable, and may even be a bit
underdone, with 7-9" possible south of there into Monroe county and
also north of the Smokies into Unicoi county. It should be noted
here that these values will be for areas above 2,500 ft in
elevation. Below that, totals will likely be 40-50 percent lower.

Elsewhere, uncertainty in snowfall totals is a little higher. The
northern plateau, higher terrain of southwest Virginia, and the far
northeast TN mountains will all see accumulating snowfall. How much
is less certain than the mountains. At this point the forecast calls
for 1-3" in the plateau and southwest Virginia, and mountains of
Carter and Johnson counties in TN. In general this seems reasonable
for now. Accumulating snowfall in the TN valley is certainly
possible, north of the Knoxville metro area, but will be largely
dependent on precipitation rates I believe. In other words, suspect
there will be plenty of snow in the air, but unless there are bursts
of heavier precip rates I`m not sure there will be much chance for
it to stick during the day Monday. And as moisture thins out Monday
night into Tuesday, more typical NW flow snow shower activity will
limit how much QPF and thus the amount of snowfall, there is to be
had in the valley.

 

 

giphy.gif

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Thanks for starting this.  No doubt some of our mountain chain is going to get white smoked....

It’s funny MRX downplays the valley areas northeast of Knoxville.  While I don’t disagree the moisture thins out.......  this type of storm evolution with energy left over the apps is notorious for light to occasional moderate snow bands making their way across the area, valleys included.  Combine this with temps in the 20s overnight Monday and into Tuesday morning and I almost expect travel issues and school changes here on Tuesday.

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1 hour ago, Holston_River_Rambler said:

NAM 3km is keeping expectations realistic for Le Conte <read with heavy sarcasm>.

yz0mmTf.png

 

 

Insane haha 

the amount of energy aloft is very high. I’ve only been here for two winters but this is by far the most vigorous NW flow I’ve seen predicted. 
 

the DGZ zone (-10 to -17) starts at 850mb and there is ample moisture and upslope to produce a very significant event. I wouldn’t be surprised to see 18+ on our best NW peaks.2348B7B3-14FD-4E02-876E-24078AF4E286.png.e18872916636301d37fa4b350d748db8.png

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Finding it strange that NWS Nashville has only given our area (Crossville/Monterey) a "Special Weather Statement" so far and no WWA. This area does really well in these events and the models all seem to support 2+ inches so it's odd to me. TWC even shows 3-7" here by Tuesday morning. Someone will be way off one way or the other.

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2 hours ago, fountainguy97 said:

The DGZ zone (-10 to -17) starts at 850mb and there is ample moisture and upslope to produce a very significant event. I wouldn’t be surprised to see 18+ on our best NW peaks.2348B7B3-14FD-4E02-876E-24078AF4E286.png.e18872916636301d37fa4b350d748db8.png

I think the 850mb vertical velocity chart is one of the most useful tools for our area. I don't see it posted often, but I always look at those. Especially when the DGZ gets close to mountain top levels.

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19 minutes ago, Math/Met said:

I think the 850mb vertical velocity chart is one of the most useful tools for our area. I don't see it posted often, but I always look at those. Especially when the DGZ gets close to mountain top levels.

It’s a very cool depiction of those up-slope enhancements.  The first thing I noticed was just how hard that down-slope side actually is in Western NC. 
 

not sure how strong 10+ (bars per second?) is but considering the velocity up by our main low pressure is abt the same I’d say that must be some pretty strong lift.

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9 minutes ago, Dsty2001 said:

Would anybody like to explain to me what exactly an NW event is?  I've heard of them in the past and kind of understand a little, but it'd be cool to get a detailed explanation!

In layman’s terms it’s pretty much explained in its title. “NorthWest Snow” low level winds from the northwest  pass up and over the mountains. Those NW facing slopes get enhanced lift during these times and that’s why they can get a ton of snow. 

Wind from the northwest hits the mountains and is forced up. Creating lift and snow along those areas. 

It can be feast or famine as the NW slopes get dumped on but slopes not facing the exact perfect way get much less snow. 
 

here are a couple links. One has pictures which I like. The other is pretty In depth. But a good read! Google is my best friend for terms I don’t know lol. 

https://www.weather.gov/media/gsp/localdat/NWFS_discussion_group/Additional Links/Northwest Flow Snow_Dec05.pdf
 

http://appstate.edu/~perrylb/Research/Publications/Misc/Perry_2006_Diss.pdf

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32 minutes ago, John1122 said:

Point forecasts in these situations always crack me up. It's like "rain before 1 am, then rain and snow between 2 and 3 am, then snow between 4 and 5 am, then rain between 7-8 am, then snow between 9-11 am."

Agree. They're about laughable. Imo, an embarrasment to modern Meteorology.

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Monday and Tuesday snow event is going to be very interesting, even just vicariously through Plateau and northeast reports. Mountains gonna get hammered.  

Snowfall map above respects the terrain because this is a classic NWFS event. Stiff NW wind will leverage upslope areas but downslope shadows will be sharp. JC will do a lot better than Kingsport. Maybe next synoptic system? I'd still have some sticking in Knoxville, even if not accumulating much. Oak Ridge is unfortunately a little more in the Plateau lee snow shadow, but should see flakes. Don't ask about Chattanooga, please lol!

The forecast soundings really intriguing to me. Deep cold nearly saturated air is forecast low levels and mid-levels through Monday, much of it a prime DGZ too. In fact up to 500 mph is moist early Monday. Moisture is less deep Monday night, but that's plenty for the mountains to get pounded and Plateau / Virginia to keep snowing. The DGZ is a little lower than typical in the sounding, which is actually favorable in this orographic event. Could it beat Christmas some areas?

Like storm chasers talk about ground scraping mesos, looks like a ground scraping DGZ is forecast. Have fun!

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Just now, nrgjeff said:

Monday and Tuesday snow event is going to be very interesting, even just vicariously through Plateau and northeast reports. Mountains gonna get hammered.  

Snowfall map above respects the terrain because this is a classic NWFS event. Stiff NW wind will leverage upslope areas but downslope shadows will be sharp. JC will do a lot better than Kingsport. Maybe next synoptic system? I'd still have some sticking in Knoxville, even if not accumulating much. Oak Ridge is unfortunately a little more in the Plateau lee snow shadow.

The forecast soundings are really intriguing to me. Deep cold nearly saturated air is forecast low levels and mid-levels through Monday, much of it a prime DGZ too. In fact up to 500 mph is moist enough early Monday. Moisture is less deep Monday night, but plenty for the mountains to get pounded and Plateau / Virginia to keep going. The DGZ is a little lower than typical in the sounding, which is actually favorable in this orographic event. 

Like storm chasers talk about ground scraping mesos, looks like a ground scraping DGZ is forecast. Have fun!

Moisture is less deep Monday night, but if the valleys can find some snow bands tomorrow evening and into early Tuesday...................  with temps projected in the mid 20s it might look more snowy Tuesday morning than at any point tomorrow with temps tomorrow in the 33-35 range.  I almost expect more road problems Tuesday morning vs tomorrow for the valley areas in the WWA.

As you say, the mountains are going to get smoked, regardless of what happens below 2500!

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1 hour ago, PowellVolz said:

MRX is starting to expand their snow maps some to include the valley north of 40.
 

 

 


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Something interesting, my area (Tellico) usually does very poorly in NWSF events (Skyway is completely different story) due to the topography here (town almost sits in a bowl). MRX very rarely puts more than .5" on their maps for here due to this. So for them to go with 1"-2", it tells me they are currently expecting an unusually higher end NWSF event.

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Good point. I ask if as much snow as the Christmas event. Due to temps this should be more impactful either way. 

2 minutes ago, tnweathernut said:

Moisture is less deep Monday night, but if the valleys can find some snow bands tomorrow evening and into early Tuesday...................  with temps projected in the mid 20s it might look more snowy Tuesday morning than at any point tomorrow with temps tomorrow in the 33-35 range.  I almost expect more road problems Tuesday morning vs tomorrow for the valley areas in the WWA.

As you say, the mountains are going to get smoked, regardless of what happens below 2500!

Plus it's not a holiday. Cancel school! Wait it's already at home. Still this is going to be more trouble due to the cold temps.

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