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BlunderStorm

11/12/19 Tennessee Valley Early Winter Event

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T

3 minutes ago, ShawnEastTN said:

I think the models are anticipating the cold air to advect faster than we normally see and catching up to the heavier precip before it's done not just the super light stuff that would normally just be sprinkles behind the front. What MRX is counting on is that the cold air doesn't advect fast which is typical climo for these.

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This is most likely the explanation.  I remember back in the 80's a similar setup when I lived in Cleveland.  MRX had us set to pick up their usual little or no accumulation.  The Arctic front roared in around midnight with high winds and 50 mph gusts. The cold air caught up with the remaining moisture.   Cleveland ended up with almost 4 inches of snow and Chattanooga got nothing. This is what makes it so hard to forecast snow totals around our area with so many micro climates.

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10 minutes ago, BlunderStorm said:

We're seeing support for significant moisture behind the front across the board when it comes to models (at least for eastern areas). Can it all be wrong? Maybe, climo is a force to be reckoned with.

Yup, Climo and microclimates makes this a tough call.  Gotta think somebody somewhere is in a sweet spot though

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5 minutes ago, BlunderStorm said:

We're seeing support for significant moisture behind the front across the board when it comes to models (at least for eastern areas). Can it all be wrong? Maybe, climo is a force to be reckoned with.

I think, to a degree, what is causing the models to anticipate such a fast changeover to snow, is the strength of the High Pressure that is driving the system. A 1049-1050 High entering the US, like we have right now is not your normal high pressure. Even for January standards, that is not your average high pressure system. Even by the time it gets down to TX, it’s still 1043-1044! I’m not sure if we had a high that strong all winter last year. Hopefully it will be strong enough to push the cold air in as fast as the models are advertising! Time will tell.

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I’m curious to see today if short range models back down on QPF after the changeover. It’s happened a few times before leading up to an event lol.

So far the 12z NAM holds serve. Solid 2-3 inches across entire area.

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I’m curious to see today if short range models back down on QPF after the changeover. It’s happened a few times before leading up to an event lol.

So far the 12z NAM holds serve. Solid 2-3 inches across entire area.

SREF actually jump from 2” to 3” mean from 03z to 09z this morning for TYS.


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Just got around to reading MRX overnight discussion and it grabs my attention that they point out that significant forcing lags behind the front with the jet overhead. That makes me feel better about the precip enhancement post frontal passage that the mods are seeing

 

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14 minutes ago, Daniel Boone said:

I remember years past, mainly 70's and 80s of this occurring with arctic frontal passages. Several inches would fall , even in the lower elevations. 

 

38 minutes ago, Jed33 said:

I think, to a degree, what is causing the models to anticipate such a fast changeover to snow, is the strength of the High Pressure that is driving the system. A 1049-1050 High entering the US, like we have right now is not your normal high pressure. Even for January standards, that is not your average high pressure system. Even by the time it gets down to TX, it’s still 1043-1044! I’m not sure if we had a high that strong all winter last year. Hopefully it will be strong enough to push the cold air in as fast as the models are advertising! Time will tell.

 

49 minutes ago, bearman said:

T

This is most likely the explanation.  I remember back in the 80's a similar setup when I lived in Cleveland.  MRX had us set to pick up their usual little or no accumulation.  The Arctic front roared in around midnight with high winds and 50 mph gusts. The cold air caught up with the remaining moisture.   Cleveland ended up with almost 4 inches of snow and Chattanooga got nothing. This is what makes it so hard to forecast snow totals around our area with so many micro climates.

 

1 minute ago, PowellVolz said:

Just got around to reading MRX overnight discussion and it grabs my attention that they point out that significant forcing lags behind the front with the jet overhead. That makes me feel better about the precip enhancement post frontal passage that the mods are seeing

To sum up my thoughts after yalls input:

So you're telling me there's a chance.gif

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To sum up my thoughts after yalls input:
1592848352_Soyouretellingmetheresachance.gif.17756fb1a65f39b81c5dbd56550c9f23.gif

Still a lot of “if and buts” we are working with. If the cold air is a couple hours late we are looking at a flurry or two.


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Still a lot of “if and buts” we are working with. If the cold air is a couple hours late we are looking at a flurry or two.


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But what if it's 2 hours early...

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17 hours ago, wxrjm said:

Our thoughts- some of the higher totals towards the higher elevations in the range. 

Not sold on the Euro, as I think we'll have near freezing temps BUT if we get a nice period of moderate snow, it could accumulate nicely in spots. 

Model Snow - Studio Earth.png

Good to see you on here again.  These Arctic fronts as they interact with the Plateau add a certain degree of difficulty.  Often, the cold takes it time draining in from the Plateau...but sometimes it does not.  The big high out West has me with one eye over my shoulder.  Either way, tracking in early November is all bonus!  

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 I’m anxious to see how the models do in northwestern ARkansas and southwestern MO, their under a winter wether advisory now.  Once they start to get affected we can have a better idea how this system is tracking towards us, and if certain models were/are correct.  

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27 minutes ago, AMZ8990 said:

 I’m anxious to see how the models do in northwestern ARkansas and southwestern MO, their under a winter wether advisory now.  Once they start to get affected we can have a better idea how this system is tracking towards us, and if certain models were/are correct.  

Snow is showing up already in extreme north western Arkansas and Thunder snow is being reported just along the Kanas and Arkansas border.

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Just now, bearman said:

Snow is showing up already in extreme north western Arkansas and Thunder snow is being reported just along the Kanas and Arkansas border.

Heavy sleet in Tulsa as well as per the OKL/TX/ARK thread.    Definitely interesting developments IMO.  

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12z suite looks pretty good so far for E TN...especially the foothills, Plateau, SW VA, and portions of NE TN.  That said, many of the models(global and short range) have upped their totals slightly.  Never want the trend to be going down at this range.  Not sure what is causing the system to max out over E TN, but several models depict a pretty decent precip max over the eastern valley with this.  The questions is whether the cold is going to move as quickly as modeled.  The big 1050+ high argues for that.  However, as I stated above...the Plateau can do strange things with systems like this.  It may give some good orographic lift or it may hold up the cold.  Either way, still an interesting early season system on tap.   I would not be surprised if some valley locations received and inch or two of snow.  Seems weird to state that as climatology really frowns upon snow this early...but it can happen and that high is no joke.  

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AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
1222 PM EST Mon Nov 11 2019

.UPDATE...
FOR 18Z AVIATION.

&&

.DISCUSSION...

No major changes will be made to the forecast for today, aside
from adjusting hourly temp grids to better align with obs. We will
have one last mild day to enjoy before a frigid air mass builds in
tomorrow morning, with highs today in the lower to mid 60s.

Regarding tonight`s frontal passage and potential snow
accumulations - the 12Z NAM does not appear significantly
different from its previous run. One slight difference appears to
be a slightly deeper warm nose in its sounding at CHA, suggesting
a period of sleet during the transition from rain to snow. Will
await additional data before making any changes to that period.

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12z suite looks pretty good so far for E TN...especially the foothills, Plateau, SW VA, and portions of NE TN.  That said, many of the models(global and short range) have upped their totals slightly.  Never want the trend to be going down at this range.  Not sure what is causing the system to max out over E TN, but several models depict a pretty decent precip max over the eastern valley with this.  The questions is whether the cold is going to move as quickly as modeled.  The big 1050+ high argues for that.  However, as I stated above...the Plateau can do strange things with systems like this.  It may give some good orographic lift or it may hold up the cold.  Either way, still an interesting early season system on tap.   I would not be surprised if some valley locations received and inch or two of snow.  Seems weird to state that as climatology really frowns upon snow this early...but it can happen and that high is no joke.  


1044 High pressure. Is that strong enough?





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20 hours ago, wxrjm said:

Our thoughts- some of the higher totals towards the higher elevations in the range. 

Not sold on the Euro, as I think we'll have near freezing temps BUT if we get a nice period of moderate snow, it could accumulate nicely in spots. 

Model Snow - Studio Earth.png

Awesome to have your insight.  Looking forward to watching the afternoon and evening modeling roll in and also seeing if this system has a trick or two up its sleeve tomorrow morning.

 

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Looking at PWS up stream it's acting like a double front, with the true arctic front lagging several hours behind the initial cold push. Energy/lift is riding between the two, more along the true arctic front. Looking at PWAT surging up the Apps (visible in the increase in moisture on the NC side of the TN/NC line as the arctic front is catching the lead push) and isobars backing down the front as it pulls in to the area, piece of energy is riding up the Apps enhancing the lift along east TN increasing the total.

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32 minutes ago, PowellVolz said:

 


1044 High pressure. Is that strong enough?

 

 

 

 

 

 


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Pretty much the Holy Grail of high pressures for November.  That is strong even during winter.  The 0z Euro had a high at 9h that was 1052.  The 12z that just ran has 6z at 1049.  Both of those forecast readings are on the east end of Yellowstone National Park near the Beartooths.  

The 12z Euro does appear to slightly back off its totals over E TN.  Looks like more of 1-2" of snow for E TN vs 2-4".  

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Just drove from Antioch to Dickson... dropped from 63 to 54. Rain has moved into Nashville area. According to nashvilleseverewx this rain is hours earlier than anticipated 

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14 minutes ago, Utvols235 said:

Just drove from Antioch to Dickson... dropped from 63 to 54. Rain has moved into Nashville area. According to nashvilleseverewx this rain is hours earlier than anticipated 

Intial cold push has entered NW TN, basically extends from Clarksville sw to Humboldt and just north of Memphis...should be a steady gradual drop behind it.

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Hot off the press:

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
307 PM EST Mon Nov 11 2019

.SHORT TERM...(Tonight and Tuesday)...

Radar over Middle TN shows quite a bit of precip falling but surface
obs that are reporting precip are rather sparse as the precip is
falling from midlevel clouds into a dry layer. Rain chances will
gradually rise as the dry layer moistens through the evening. A SW
low level flow ahead of the approaching cold front will maintain
mild temperatures, with most spots in the 50s until around midnight.

The cold front is expected to be at the Plateau around 04Z, and
sweep through the area by 10Z. A sharp drop of temperatures will
follow, and with much of the precip being post-frontal, rain will
transition to snow. The big question, as it has been over the past
few days, continues to be how long temps will be cold enough for
snowfall before drying aloft ends precip. The current forecast will
not make significant changes from the previous one, with the change
over expected to occur mainly between 07Z and 12Z.

During the changeover, forecast soundings show near-freezing
isothermal profiles, which means that only a degree or two difference
aloft can have a big effect on snow amounts. However there are
factors that suggest that model snow amounts are too high, mainly in
the Valley. The primary factor working against snow accumulation is
how warm the ground will be after today`s sunshine and 60s. Another
factor is the presence of a warm nose in model soundings, and the
NAM and GFS have trended toward a deeper above-freezing layer. This
will especially be a factor in the southern Valley where the warm
layer persists longer, and thus may have a mix of sleet in the
rain/snow transition.

The addition of a sleet mix for a few hours south of I-40 will be
the main change from the previous forecast. Forecast snow amounts
will not be changed significantly, with a dusting to a half inch
expected across the central and northern Valley, including
Knoxville and TRi-Cities. The lower elevations of the northern
Plateau and SW VA will have amounts in the half inch to one inch
range, with higher elevations between 1-3 inches. The TN mountains
will also be in the 1-3 inch range.

Rapid drying in the dendritic growth zone will end any potential for
snow accumulations in the 12-15Z time frame. After this time, there
will be a very shallow layer of moisture above steep lapse rates,
which may produce some scattered flurries in northern areas and the
mountains. High temps for the day may occur in the morning as strong
cold advection ensues through the day. Forecast highs in the lower
to mid 30s will be near or below record low max temperatures (see
Climate section below).

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