tnweathernut

This will be a nowcast situation, as several thought all along. These lows tend to be very hit or miss, just the nature of how they evolve as they move west to east. The only place I feel good about an accumulating snow are the mountains along the east TN border, and especially western NC.

3k 12z NAM far less enthused for northeast TN outside the mountains, but hits the Knoxville area and points WSW to just northwest of Chattanooga hard with a widespread area of 5-7”

Low res 12z NAM snow totals. ........ a couple of posts down. lol

3k 0z NAM is generous to many in northeast TN and still gives hope for some around Chattanooga and other parts of southern TN. .

Looking at the animation, it appears the explosive precip never makes it back over the mountains like on previous model runs. Starts in western NC and pivots there before pulling away to the east.

Looks like the 12z. I think 18z lost its mojo, except for the mountains and western NC. Biggest lollipops are in Grundy County, Scott and Campbell Counties. Outside of the mountains there's a bunch of less than 1/2" amounts scattered across Tennessee It does show a couple of inches in Chattanooga, so there's that!

Excellent discussion by the Morristown peeps: AREA FORECAST DISCUSSION National Weather Service Morristown TN 348 PM EST Wed Jan 6 2021 LONG TERM...(Thursday night through Wednesday)... The main story for the long term period is the chance for widespread snowfall Thursday night into Friday, with several inches expected in the east TN mountains and a chance for some accumulating snow down into the valley floor. Will be focusing the discussion on this system as a result. Thursday evening a deep southern stream upper trough will cutoff over the Arklatex region, shifting east across northern Mississippi and Alabama through the night and into the Carolinas on Friday. There remains some disagreement with the placement of the upper low as it traverses the TN/MS/AL border Thursday night, which has implications on precip type and amounts. This lends itself to a still-low confidence forecast for the lower elevations of the TN valley. Elsewhere, especially in the east TN mountains along the NC border, confidence is much higher in precip type and reasonably high with regards to amounts. Precip looks to spread into the southern counties during the evening hours tomorrow, working north through the central valley by midnight or so, and finally up into the northern zones by daybreak Friday morning. This seems to be pretty well agreed on in the numerical guidance. BUFR soundings from various models do not support any snow reaching the lower elevations until after midnight, but between evaporative and dynamic cooling and the baseline thermal profile, expect that at minimum a rain/snow mix will be seen fairly early on at elevations above 2,000 ft or so. Snow levels will work their way lower through the night though, and expect to see a rain/snow mix down to the valley floor during during the very early morning hours on Friday. Let me go ahead and address the elephant in the room here and say that it doesn`t appear that this will be a very impactful snow event for the TN valley south of roughly Morristown or maybe even a little further north than that. Looking upstream, there is no source of frigid, dry arctic air that will surge south into the TN valley to support prolonged periods of snow at low elevations. Model soundings show a weak warm nose induced by southeasterly flow across the mountains, or perhaps a deep isothermal layer near the freezing line, through the time period where snow will exist. Given forecast surface temperatures, the driving factor in any accumulating snow will be precip rates and frankly they don`t look outstanding outside of the Appalachians where orographic lift will help enhance rates there. Have a tenth or two of accumulation from the southern valley up to around the Morristown area in the forecast. Now, moving on to the plateau, mountains, and other locales. The best window of heavier precipitation rates looks to be from roughly midnight Thu night through daybreak Fri morning. This is when the best low and mid level frontogenetic forcing transits the area. More susbtantial deep ascent will stay east of the forecast area into the Carolinas. Likewise, a persistent TROWAL feature is absent across our CWA, so this will be a quick hitting system in large part. Still, given the low freezing levels to start, expect that the mountains could pick up a quick 4-6" of snow late Thursday night as this system passes by. Some northwest flow snow showers will likely linger into Friday evening, but the best accumulating snowfall will be done by late Fri morning most likely. On the plateau, the same situation applies. Being further removed from the best forcing, expect snow amounts in the 1-3" range there. Having said all of that, decided to hoist up a Winter Storm Watch for the east TN mountains and far western NC from 8pm EST Thu through 8pm EST Fri. Confidence seems high enough to warrant that at this time. If trends continue, will likely need an advisory for the plateau. However, there`s enough uncertainty there, as well as the far northern TN valley and southwest Virginia (both of which will be furthest from the best moisture and lift) to hold off on any headlines now. Have snowfall accumulations in the 1-3" range in those locales as well but would not be surprised if those change (up or down) in future forecast packages. Otherwise, for the remainder of the long term period, cool and dry conditions continue through the weekend. There is a chance another southern stream system could bring chances for widespread wintry precip again on Monday night into Tuesday, but uncertainty is very high right now and it not worth going into detail on that system just yet.

Really hard for me to believe this is a rain system for Tennesseans early next week..... .

Seems like the afternoon AFD from the NWS in Morristown is late today. Maybe they are wanting to look at 18z before issuing? I thought they normally had something out by 2:30 EST? At the very least I think a special weather statement is warranted. Going to be interesting to see how they handle.

From what 500 looked at around day 3 I would have thought this was going to play out MUCH better than it did. I am guessing there will be numerous 12z euro individual ensembles that get the job done.

This edition of PBP was interrupted by an uninvited guest at just the wrong time. Remove that weird vort dance at 500mb between 108-126 and the surface would have likely been snowing/mixing in much of Tennessee too. Side note. My PBP's might go back into hibernation after that attempt. lol

There is an interaction with the main vort and a secondary vort at 500, around hour 108-120, that causes the trough to go negative and ends up raining on most of Tennessee 138-150 (though parts of TN may start as snow or mix). There is yet another vort that enters the picture, also in the northern stream between 138 and 144, further complicating an already complicated picture. Long story short, the system looks to be there............. but how the northern stream interacts/disrupts is likely going to lead to much wailing and gnashing of teeth amongst meteorologists and hobbyists alike. This could break bad or good and forecasts beyond 3-4 days should be taken with a boulder of salt.

System scooting east in the northern gulf and by 126 snow is falling in most of Arkansas. Euro shows light rains in most of Mississippi and Alabama. By 132 the low is in southern Alabama with snow/mix in northwest MS and snow/mix in or near Memphis. Still snowing in much of Arkansas at this time.

By 120, most of northern Louisiana is snowing and the light snows are streaking toward and just outside of Memphis

Surface responds between 96 and 108 with precip blossoming over Texas and the gulf coast, spawning a surface low in the northwest gulf. Snow breaking out in most of east Texas and western Louisiana at this time.

12z Euro is looking really good at 500 with a healthy wave entering west Texas at hour 96. Not a lot showing at that time that would mess with it (i.e. crush it) as it swings east. Should produce a decent system

My thoughts exactly..............

Just don't start the sentence by telling everyone you know MathMet says a foot is coming....

At this point, modeling seems to indicate an opportunity for snow winners, but keeps moving the goal posts around from model to model and from run to run. My guess is (outside of the mountains) we will just end up having to nowcast this one to determine where the lollipops of snow will end up falling. There's a reason they say, upper level low......... weather man's woe.

Lots of moving pieces at 500 and no way to nail this down for several more days. One small piece of energy in the right or wrong place can make the difference between something minor or something much more widespread. I think the overall pattern strongly suggests opportunity as we head into next week.

GFS Para shows the perils with an ULL and razor thin thermal profiles. We are pretty much rolling the dice. .

Now that this system is working into the short range and on multiple models, we probably should start a thread for it. Anyone feeling lucky?

Jeff will tell you that's not a likely solution. lol

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After taking a look at modeling this AM (OP & Ensembles) it appears the pattern we have all waited for (board wide) is still very much on track to produce numerous systems taking the low road, each with potentially colder air as we go through the next 2-3 weeks, perhaps ending with a truly cold airmass making its way into the lower 48 toward the end of this 2-3 week period. Lots of large scale features seemingly moving in good directions with several systems to track. About all you can ask for, not to mention we are getting this during peak climo ...... and not chasing it, hoping it materializes in mid March.