Math/Met

When it comes to downslope winds in East TN, I would never say never. There are so many possible ways for it to happens. I assume that areas along the mountains of SE TN would have a slightly better chance of that happening, due to the surface winds being SE on the other side of the mountains in that area. I think areas farther to the northeast would be pretty safe from downslope in this situation. Just to be clear since there is some discussion about this now, this isn't a significant inverted trough. It is very subtle (mainly seen in wind field), but it maybe just enough to help us out a little. Especially in eastern counties. And the northerly flow down the valley could help areas further south with temps, as Jeff mentioned.

In these cases, the inverted trough is induced by the terrain. The air flow is different on either side of the mountains, so you can basically get a "pinching" (not a very technical way of describing it) between the two flows. Neither side has to deal with much downslope because it creates rising air in the low levels. It is a fixed feature because the mountains are a permanent feature. Hope that makes sense.

I always try to looks at small details for any event in East TN. Mainly because the terrain can cause things to go unexpectedly wrong or sometimes in our favor. Looking at the NAM, the thing I like about this system is that low level winds over WNC are from a more easterly direction during the start of the system, while winds over the ETN valley are more northerly. This typically happens when we get an inverted trough induced along the mountains, which helps provide some low level lift and often produces more precip than modeled. This current situation is more subtle, but the characteristics are still there. It’s something to watch to see if precip trends upward as we go.

I’ll move this to the main discussion based on Carvers suggestion. Just wanted to say that the wind event potential has trended a little stronger in my opinion. I thought the MRX discussion was very good regarding this potential.The NAM has slightly shifted the 850mb wind to more of a southerly direction, and that could be just enough to increase the mountain wave enhancement. You don’t really need a southeasterly flow at 850mb because the cross barrier flow is determined at lower levels based on statistical analysis. We often have a southerly or even slightly SW flow over the valley during a mountain wave event. This current event is right on the threshold, so it could go either way in terms of significant MW enhancement. Everything else is favorable. Regardless of MW enhancement, the LLJ is strong enough to potentially cause some tree problems in the mountain and foothills due to saturated ground conditions.

Glad they did quality control and straightened that out. Are they saying 81mph was the peak gust today? Just wondering because it looked like there were legitimate gusts in the mid to upper 80's based on the plot. Not that it really matters at this point, just wondering if all recorded gusts were higher than actual winds.

I don’t want to post too much about the mountain wave event, but here is why I think the red data plots are incorrect. If you expand out to a 720 hour plot, you can see errors show up several times. The peak (green) is usually very accurate.

I haven't heard any major damage reports, but it looks like there are a lot of trees down in southern Greene County. WCYB Probably not the best idea to be standing there.

That’s unfortunate. It may end up being correct, but I would be VERY surprised. The near 90mph gusts seem legit. I have a full dataset for research purposes that goes back to 2008, and 123mph would be way above anything recorded there. I do think it’s possible for Camp Creek to gust over 100mph in mountain wave events. I’ve speculated that it was over 100mph in 2004, but there was no reliable data at that point.

https://oculus.atdd.noaa.gov/campcreek/

I think you are correct to ignore the red data on that chart. It is unreliable. The peak gust data (green) is probably accurate, so nearly 90mph.

About 30 minutes after posting that, Camp Creek switched to a SE wind and gusted to 53mph. It should continue to increase.

Everything still looks on track for a significant mountain wave wind event. It has taken awhile for conditions to become favorable. Even though VWP indicates 40kt SE winds at 4000ft, the cross barrier flow remains blocked. Camp Creek winds haven't really increased yet and aren't currently blowing from a SE direction. Conditions become much more favorable in the next few hours. HRRR is showing the enhancement right along the mountains and especially in the Camp Creek area by tomorrow morning. That's not the most reliable wind product, but it usually does a good job of showing areas of mountain wave enhancement (even if wind speed isn't accurate). The biggest question for me is how trees will hold up in areas with possible 75+ mph wind gusts and saturated soil.

Favorable conditions for mountain waves will be in place later tonight and especially tomorrow morning. MRX issued a High Wind Warning and mentioned the potential for downed trees due to saturated ground in the AFD. It could take a few hours for mountain waves to really get going tonight/tomorrow morning. Models show a very strong temperature inversion across the mountains later tonight and the 850mb flow has a bit for of an easterly component. So, it could take until early tomorrow morning to get the proper balance between cross barrier wind speed and stability (haven’t calculated the Froude number, just basing on past experience). The cross barrier flow could be partially blocked for part of the night and could prevent the downslope flow from being sustained. After the initial round of precip lifts north, the 850mb flow becomes more southerly and the temperature profile is more conducive. That’s when the conditions become very favorable for mountain waves. This could be a strong event, which will likely cause some problems with down trees along the mountains.

In addition to the flooding threat, there could also be a mountain wave event Tuesday night into Wednesday as a strong LLJ develops over the region with a favorable wind profile. With the saturated ground, these strong winds along the mountains could cause some problems as well.

JoMo, I don’t post here often, but it’s awesome to hear that you made it through the storm. It was apparent that the people on this board truly care, and we are all glad you’re safe.