February/March 2020 Winter's Last Chance Thread

[tnweathernut]

There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)

Does anyone else remember this event?

[ShawnEastTN]

There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)
Does anyone else remember this event?

I think I remember a handful of those over the years, those are the ones that I remember Morristown having to continually up their forecast snow totals for during the actual events.

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[PowellVolz]

There was a scenario several years back where modeling was not enthused at all about precip into Tennessee.  I remember Robert @ WxSouth ended up picking up on the inverted trough and in the end there was a decent snow from it.  I can't remember the year, but my recollection tells me the basics were familiar... (i.e. overrunning, inverted trough, no defined low, etc.)
Does anyone else remember this event?

It was 2014 I believe. We were in between two systems. About a week before we had a snow/sleet/RZ system that dumped 3-6 inches across the valley before changing to sleet. The inverted trough happened on a Wednesday afternoon and the NWS didn’t start talking about it till the night before. I ended up with 4-5”. A week later we had another overrunning event that was snow to ice to rain. School was out for two weeks.


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[PowellVolz]

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.

Absolutely. What I was thinking is if the boundary was in the valley, the SE flow over the mountains might down slop before it was lifted back up. I very well could be overthinking this and cramming to much into a small space.


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[John1122]

This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 

 

.A STRONG UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE TENNESSEE

RIVER VALLEY ON WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT...PULLING

MOISTURE WESTWARD FROM A LOW PRESSURE SYSTEM ALONG THE CAROLINA

COAST. THIS SYSTEM WILL BRING THE POSSIBILITY OF SIGNIFICANT

SNOWFALL ACCUMULATIONS OVER MUCH OF EAST TENNESSEE...SOUTHWEST

VIRGINIA...AND EXTREME SOUTHWEST NORTH CAROLINA BY EARLY THURSDAY

[PowellVolz]

This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 
 

.A STRONG UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE TENNESSEE

RIVER VALLEY ON WEDNESDAY AFTERNOON AND WEDNESDAY NIGHT...PULLING

MOISTURE WESTWARD FROM A LOW PRESSURE SYSTEM ALONG THE CAROLINA

COAST. THIS SYSTEM WILL BRING THE POSSIBILITY OF SIGNIFICANT

SNOWFALL ACCUMULATIONS OVER MUCH OF EAST TENNESSEE...SOUTHWEST

VIRGINIA...AND EXTREME SOUTHWEST NORTH CAROLINA BY EARLY THURSDAY

I’m just about 100% positive that’s the inverted trough snow we got. I remembered it was on a Wednesday and was pretty sure it was in 14’


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[Holston_River_Rambler]

Here's the radar loop from the storm(s) I think y'all are talking about. 

[Math/Met]

15 minutes ago, PowellVolz said:

 

Absolutely. What I was thinking is if the boundary was in the valley, the SE flow over the mountains might down slop before it was lifted back up. I very well could be overthinking this and cramming to much into a small space.


.

 

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.

[tnweathernut]

5 minutes ago, John1122 said:

This is the MRX discussion from when Robert made the call about enhanced snow over East Tennessee in 2014. I don't quite think it is the same set up as here. 

 

 

 

Yep, totally different from the first few words..... lol

nice find........You always amaze me with your records and recollections.  You are a great asset to our group!!

[John1122]

15 minutes ago, PowellVolz said:

 

I’m just about 100% positive that’s the inverted trough snow we got. I remembered it was on a Wednesday and was pretty sure it was in 14’


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It was a Tuesday-Wedneday timeframe. Around Feb 11th and 12th I think. 

[John1122]

MRX rolling with the Euro based on their snow map. Can't really blame them. 

[Math/Met]

I believe this snowfall output was from a weak inverted trough event. Totals increased at the last minute if I remember correctly.

[ShawnEastTN]

Morristown's first guess.

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[Save the itchy algae!]

Well Morristown originally thought I wouldn’t get any snow two weekends ago and I ended up with over two inches.  By linear thought progression that means I should get over 4” this time in Farragut.

[Holston_River_Rambler]

18z Euro. Finally figured out how to make these on my phone: 

https://giphy.com/gifs/VeZ269fobmDUjSeJQL

 

 

 

[TellicoWx]

Haven't got to look at the 18z Euro, but from Webbs reaction sounds good.

[Wurbus]

Very nice increase in the plumes for Knoxville. Went from 1/2 inch mean to 1 inch mean, including one big dog and several more showing more than the 15z

[Vol4Life]

3 minutes ago, Wurbus said:

Very nice increase in the plumes for Knoxville. Went from 1/2 inch mean to 1 inch mean, including one big dog and several more showing more than the 15z

Remind me...what model are those plumes based off of?

[TellicoWx]

8 minutes ago, Vol4Life said:

Remind me...what model are those plumes based off of?

SREF..kind of like the ensemble of the NAM. Ran in between the NAM runs, usually a good indicator of where the next upcoming NAM run may go.

 

 Currently, the Weather Research and Forecasting Non-hydrostatic Mesoscale Model (WRF-NMM) model is run as the NAM, thus, three names (NAM, WRF, or NMM) typically refer to the same model output. The WRF replaced the Eta model on June 13, 2006.^[1] The model is run four times a day (00, 06, 12, 18 UTC) out to 84 hours. It is currently run with 12 km horizontal resolution and with three-hour temporal resolution, providing finer detail than other operational forecast models. The NAM ensemble is known as the Short Range Ensemble Forecast (SREF) and runs out 87 hours.

[TellicoWx]

Looking at the meteograms for the 18z Euro, while the qpf output went up, the surface temps in the eastern valley are a mess...35-40 during the duration of the precip.

[Icy Hot]

NE TN will be below freezing Wednesday night, so ground temps should accommodate any snow that does fall.

[TellicoWx]

00z NAM with basically same track with the energy...stronger returns along the southern TN border vs 18z.

[Vol4Life]

I know the NAM has a tendency to over amplify systems, but does it handle thermal profiles pretty well?

[BNAwx]

1 minute ago, TellicoWx said:

00z NAM with basically same track with the energy...stronger returns along the southern TN border vs 18z.

That map is a throat punch to Nashville...

[TellicoWx]

2 minutes ago, Vol4Life said:

I know the NAM has a tendency to over amplify systems, but does it handle thermal profiles pretty well?

With the last system it handled the temp profile the best..showed the problems on the road for Chatt vs the other modeling.

[TellicoWx]

1 minute ago, BNAwx said:

That map is a throat punch to Nashville...

Yeah it is..the 925 was a tick further south (but by just 10 mi or so. If NAM is to be believed..10 mi could make a big difference on the cutoff.

[Holston_River_Rambler]

3km NAM, while not a throat punch to the northern plateau, is at least a wicked jab.

 

[John1122]

If the Euro jumps on board tonight I'm going to hope for an inch. If not I'll expect snow showers with no accumulations and hope I'm wrong. 

It's amazing how many times I've been too far north the last few years. 

[TellicoWx]

00z NAM sounding is almost a mirror image of the sounding last week...would be some nice big wet flakes.

[Vol4Life]

It appears that the NW expansion of the precipitation shield that we were seeing in runs yesterday and earlier today has ceased.  Hoping that trend will start back up so that our friends to the north and west get in on the action.