East Tennessee Weather II

bigdaddy

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Damn, I got my days messed up but I don’t think it matters. I was looking at at euro model for Jan 4 ish. But even now that looks like a wash. I hate 40s and rain. Thanks for the update.
 

MetVol

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As for the severe threat, it will probably be confined to southeastern portions of East TN (Chattanooga, Cleveland, Athens, ect).
Yeah any severe risk on Friday would likely be limited to the southern TN valley. With such a strong LLJ, it won't take much to get some damaging winds to the surface. We'll have some heavy rain across SE TN and high winds across the mountains and foothills, too. Downslope flow across the mountains will limit overall rainfall amounts across the foothills.

Longer term, some interesting teleconnections to watch. ECMWF is showing a negative AO and negative NAO through the middle of January with a positive PNA pattern becoming more likely into the second week of January. This would favor cooler weather and the potential for some storminess and snowfall. At least some hope for snow lovers...
 

MetVol

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You are quickly becoming my favorite weather info source
now do Little Cottonwood canyon outside of Salt Lake City the last week of January
Glad to help! Near SLC you're dealing with elevations of 8-11k ft, so they should likely have some snowpack. However, if the hemispheric patterns setup as predicted (especially with the positive PNA pattern) then would have some warmer than average temperatures for the western US from mid to late January.
 
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MetVol

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Anyone see the Euro run for this Friday? 👀
I've been watching the evolution of this system for a few days. One caveat to the shared snow map is I'd be careful using 10:1 ratios with this system right now. Kuchera ratios (and the thermal profile in the ECMWF and GFS) would both support ratios lower than 10:1 (think between 6:1 or 8:1).

Looks like the ECMWF is coming into better agreement with the GFS. This storm track is favored based on the NAO, PNA, AO patterns I've referenced earlier. These patterns will probably be favorable for some snow chances during the next 2-3 weeks.

The big issue is low level cold air. At this point, the ECMWF, GFS, and Canadian are showing a lack of very cold low-level Arctic air. The key right now is how much dynamic cooling do you get beneath the upper low. Could easily wind up with some big snowflakes with surface temperatures around 34-35F. Still a lot of time between now and Thursday night, so we'll see how it trends over the coming days. FWIW, the GFS and ECMWF ensembles are still not excited about significant snow chances late this week just yet.
 
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headhunter15

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I've been watching the evolution of this system for a few days. One caveat to the shared snow map is I'd be careful using 10:1 ratios with this system right now. Kuchera ratios (and the thermal profile in the ECMWF and GFS) would both support ratios lower than 10:1 (think between 6:1 or 8:1).

Looks like the ECMWF is coming into better agreement with the GFS. This storm track is favored based on the NAO, PNA, AO patterns I've referenced earlier. These patterns will probably be favorable for some snow chances during the next 2-3 weeks.

The big issue is low level cold air. At this point, the ECMWF, GFS, and Canadian are showing a lack of very cold low-level Arctic air. The key right now is how much dynamic cooling do you get beneath the upper low. Could easily wind up with some big snowflakes with surface temperatures around 34-35F. Still a lot of time between now and Thursday night, so we'll see how it trends over the coming days. FWIW, the GFS and ECMWF ensembles are still not excited about significant snow chances late this week just yet.
Any ice chances?
 

headhunter15

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At this point, it doesn't look like any ice with this system for East TN. Really need a cold surface layer for that, and we're potentially dealing with the opposite: a warmer surface layer that needs to be cooled with strong ascent from very cold air aloft to get some wet snow.
Thanks! Looks like Friday morning could be interesting.
 

headhunter15

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A lot of uncertainty is my thoughts, especially for the valley and plateau. There's a really good chance for the mountains and far NE TN to see a good bit of snow accumulations. We'll know more about Thursday night into Friday sometime tomorrow.
WVLT in Knoxville had mentioned this morning that roads could be iffy on Friday morning and schools may want to pay attention, even in valley locations.
 

MetVol

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What is everyone thinking for Friday and potentially Monday?
Friday has so much boom/bust potential for East Tennessee. We'll get the southeast flow around the system which will lead to some warming across the valley and foothills of the mountains creating an opportunity for snow to mix with (or change to) rain. As the system moves away, winds turn toward the northeast allowing the dynamic cooling to kick in and mid-level temperatures drop by several degrees. This will change any leftover precip to snow Friday morning. Strong mid-level lapse rates may aid in some heavier snow rates developing (and I think that's what the NAM is picking up on).

The key is: how much moisture is left and what is your main forcing mechanism? The recent 12z and 0z NAM is the most bullish placing significant wet snow across parts of the valley and mountains Friday morning between 6 AM and Noon. The GFS and ECMWF have been more tame (although the 18z ECMWF is putting out some significant snow like the NAM). This will be interesting to watch in terms of the evolution over the next couple days. You could literally range from nothing to nearly 8 inches in parts of the area. SREF plumes are all over the place. Talk about some high uncertainty! I can say with more certainty that we're looking at the potential for a wetter snow with ratios less than 10:1 (more 7:1 or 8:1). With this being a wet snow, slush on roads would be an issue, but even more so, you'd likely have many downed trees and power outages.

For fun, here is the 0z NAM forecast snow depth. It's counting on most of the accumulating snow melting as it falls with temperatures between 33-35F. This solution is still currently a higher outlier although the 18z ECMWF lined up similarly to this solution.
 

bigdaddy

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Friday has so much boom/bust potential for East Tennessee. We'll get the southeast flow around the system which will lead to some warming across the valley and foothills of the mountains creating an opportunity for snow to mix with (or change to) rain. As the system moves away, winds turn toward the northeast allowing the dynamic cooling to kick in and mid-level temperatures drop by several degrees. This will change any leftover precip to snow Friday morning. Strong mid-level lapse rates may aid in some heavier snow rates developing (and I think that's what the NAM is picking up on).

The key is: how much moisture is left and what is your main forcing mechanism? The recent 12z and 0z NAM is the most bullish placing significant wet snow across parts of the valley and mountains Friday morning between 6 AM and Noon. The GFS and ECMWF have been more tame (although the 18z ECMWF is putting out some significant snow like the NAM). This will be interesting to watch in terms of the evolution over the next couple days. You could literally range from nothing to nearly 8 inches in parts of the area. SREF plumes are all over the place. Talk about some high uncertainty! I can say with more certainty that we're looking at the potential for a wetter snow with ratios less than 10:1 (more 7:1 or 8:1). With this being a wet snow, slush on roads would be an issue, but even more so, you'd likely have many downed trees and power outages.

For fun, here is the 0z NAM forecast snow depth. It's counting on most of the accumulating snow melting as it falls with temperatures between 33-35F. This solution is still currently a higher outlier although the 18z ECMWF lined up similarly to this solution.
So since I’m just an avid follower of this thread during the winter and not a “weather guy” can you explain the ratios to me? I guess I could google it but you know.......I’m lazy and you sound like you know what you are talking about
 

Vol knight

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So since I’m just an avid follower of this thread during the winter and not a “weather guy” can you explain the ratios to me? I guess I could google it but you know.......I’m lazy and you sound like you know what you are talking about
The ratios are inches of rain to inches of snow. For example, 1:10 ratio is 1 inch of rain equals 10 inches of snow.
 

RDU VOL#14

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Anyone see the Euro run for this Friday? 👀
I’m not in East Tennessee, but central NC. There seems to be a lot of uncertainty here between the DFS and Euro for Monday and now maybe turning into Tuesday. We almost always get our snow here when the system goes underneath the Appalachians and comes from the Gulf. Not sure what Friday is looking like here either.
 

MetVol

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The ratios are inches of rain to inches of snow. For example, 1:10 ratio is 1 inch of rain equals 10 inches of snow.
To add to this, generally a colder temperature profile results in higher ratios greater than 10:1 (maybe 15:1 or 20:1) and warmer temperature profiles lead to ratios lower than 10:1 (like 7:1 or 8:1). Climatologically, most of our snows are usually around 10:1 or 12:1 in this area but can vary by a small amount. All depends on the temperature profile of the atmosphere.
 
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hUTch2002

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To add to this, generally a colder temperature profile results in higher ratios greater than 10:1 (maybe 15:1 or 20:1) and warmer temperature profiles lead to ratios lower than 10:1 (like 7:1 or 8:1). Climatologically, most of our snows are usually around 10:1 or 12:1 in this area but can vary by a small amount. All depends on the temperature profile of the atmosphere.
I’m in West Knoxville, Hardin Valley area. What are you thinking for this area? When I look at Weatherbug it shows little to no accumulation in Knoxville but up to 3 inches in Oak Ridge and we’re in between. The lows are only around 36-37 in Knoxville so I lean towards nothing happening. What do you see?
 

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