Math/Met

13 minutes ago, fountainguy97 said:

35 with full sun and biscuits falling.  Probably .75-1" an hour rates blowing over the upslope mountains.  
 

Stunning. 

That's a really interesting report. It sounds like the snow equivalent to what I've seen at Camp Creek a few time during mountain wave events. Just a few clouds, but you can get bursts of huge rain drops. 

1 hour ago, fountainguy97 said:

It's not just temps either. Massive dryslot runs right up the gut of Eastern TN as the transfer occurs.  Deform band crushes to the west. So the way I see it not only are we fighting temps but also the unavoidable downsloping that will probably show up even more pronounced on high res. 
 

For Eastern TN I wouldn't be hopeful for much action at all this weekend unless we get a decent track shift.

The way it is modeled right now, the southeast flow at 850mb is really going to be difficult for us for awhile. In these CAD situation in WNC, it usually takes a really long time for the flow to become more favorable for us. A lot working against us at the moment. 

4 hours ago, Wurbus said:

Would have been perfect if that pesky warm nose would stay out of the valley! Would be nice to have 1 system to not worry about the warm nose.

The 06z GFS would be a good way to avoid most of that. It wasn’t perfect for the valley, but it had a lot of nice features.  The low stayed far enough south to keep the 850mb flow more east verses southeast, and there was an inverted trough extending up the mountains (provides lift and helps maintain a down valley flow). The 12z GFS changed the 850mb flow to a SE direction. That would cause a lot of downslope problems for many in East TN. Too early to worry about the details though.

23 minutes ago, Holston_River_Rambler said:

I think part of what the models see is some downsloping off of the Frozen Head mts. Makes sense with a NE or NNE wind. 

 

 

Agree. There are some subtle hints of sinking air in that area at the lower levels. It’s not very significant, but it could have a slight effect on temperatures in those areas.  Hopefully the overall dynamics of the system will overcome it, but it's hard to ignore when models pick up on it (speaking from experience with my area).

1 minute ago, PowellVolz said:

Oh so you can see it?


.

I can see it. Great picture.

Greeneville hail from earlier today. Taken about 30 minutes after the storm.

6 hours ago, Carvers Gap said:

Had yet another day running in the snow.  I have never seen so many days of snow with so few inches of it!   LOL.  

What is your seasonal total so far? Just wondering. 

1.75 at my house. No complaints considering that these types of systems (with a downslope component) usually don't work out well for most of Greene County.

That actually takes my seasonal total to 15 inches, so I'm happy so far.

23 minutes ago, fountainguy97 said:

3 consecutive minutes gusting to 29mph here.again a very sheltered station. Could be 35-40mph. Driving rain/snow mix.  Was not expecting this type of wind event. 

Thanks for the wind obs. That's basically what I was referring to in my post from earlier today with the sounding showing a wind profile matching what you'd normally expect from a downslope event.  

I just looked at the 925mb winds (correlation with downslope winds), and the RAP starts to diminish the SE flow at that level after 06z. 

Thank you!

Anyone have the 18z Euro snow map. I changed subscriptions and no longer have it.

I thought this was interesting in terms of seeing how it plays out tonight. GFS sounding near Greene County. The sounding suggests snow, but the wind profile is more consistent with a downslope event. An unusual situation. I have a hard time believing that would actually be snow in my area at that time with that wind profile, but that's what it shows. After that, the wind shifts and downslope stops being an issue. 

I'm not a fan of the GFS increasing downslope flow over the mountains. At least for my area.

Carver,  Just wanted to say that you do a great job with these pattern discussions. It always makes for a good read.

3 minutes ago, Stovepipe said:

It's just swirling around Greeneville too.

I haven't gone outside to measure lately, but probably around 3 inches here.

I’m currently getting some of the heaviest snow so far. Flakes are bigger here too.

Feeling pretty good about this event in Greene County. Currently at 1.25 inches. With the RAP showing some support at 700mb and the coldest 850mb temperatures still being advected into the area, there should be continued development/enhancement as it interacts with the terrain.

29 minutes ago, fountainguy97 said:

can see the flow starting to pull more toward our classic NW direction as the ULL is sweeping through. Full on NW regime will begin over the next few hours!

I agree. The direction and temperatures at 850mb should continue to improve this afternoon/evening for the NW flow areas.

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.

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.

The mountain wave event has started at Camp Creek. Wind gusts currently around 70mph. 

Mrx has issued a High Wind Watch for the mountain wave event this weekend. This looks like the best setup so far this season. It checks most of the boxes in terms of various parameters for Camp Creek (and other foothill locations) to get very strong gusts Saturday night and Sunday. 

34 minutes ago, Daniel Boone said:

Currently 35 here. Noticed Bristols 40. Downsloping appears greater there for now. Hrrr didn't do well here for Christmas storm. Of course, different setup but, it as with the Nam 3k does tend to overdo Downsloping here in Lee County.  Although, in the current situation with the wind trajectory, unfortunately it may be close to being right. 

How much downsloping effects the event will be a close call. Just after I posted that, the 03z run came in with an improvement in NE TN…with a slightly more easterly component (rather than perpendicular) over the mountains near Greene and Unicoi Co for example.  

31 minutes ago, Stovepipe said:

FWIW at TYS according to meteograms:

18z NAM: 7 inches with a Cobb of 4.5

00z NAM: 3.8 inches with a Cobb of 0.2

HRRR and RAP still showing zero frozen precip.

00z RGEM: a dusting

The HRRR in particular is showing a persistent SE flow at 850mb over the mountains. That would make it very difficult for temperatures to cooperate in many parts of the valley in a marginal situation. I hope that changes.

I'm not suggestion that the RAP will be correct, but it has a more defined inverted trough centered over the mountains in the early part of that loop. There are many factors to consider, but that's what caught my attention. If that happens, then that could be a major help for some areas.

It's great!