January 15th-17th 2024 Arctic Blast/Snow Event

[John1122]

Congrats 

3 minutes ago, *Flash* said:

I just want to cash out on the 18z Icon. Too good to be true, I know. 

It's literally been that exact same run from like 140 hours til now around 70.

[Carvers Gap]

3 minutes ago, Mrwolf1972 said:

Not bad

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Slight jog SE w/ the snow line once pace middle TN.

[John1122]

The RGEM precip field moved NW about as much as the NAMnest moved SE. 

[jaxjagman]

National Weather Service Nashville TN
207 PM CST Sat Jan 13 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(This afternoon through Sunday Night)
Issued at 200 PM CST Sat Jan 13 2024

Our main concerns continue to be the developing bitter cold and
snow. After temps fall below freezing tonight, they are not
expected to reach freezing again until Thursday. Cold wx
precautions should be implemented, and we encourage plans to make
warming shelters available throughout the next several days.
Significant snow accumulations are expected to begin Sunday
evening and continue through the day Monday and into Monday night.
Our forecast shows 3 to 4 inches for most of the area. Our
northwest counties may come in on the low side of that, while
some enhanced bands of snowfall could produce localized amounts of
5 to 6 inches in some spots along and south of I-40.

Before the big storm arrives, we will have a cold frontal passage
tonight that will reinforce the Arctic air. This front will be
accompanied by a brief band of snow flurries or showers. Areas
along and north of I-40 may see a dusting late tonight, especially
for areas along the KY border.

Sunday will be dry for most of the day and very cold. Highs will
not climb out of the 20s for most of us. Light snow will start to
spread into our far western counties after 3 PM.

Light snow will blossom across the area Sunday evening, then the
intensity will gradually increase late night. By daybreak Monday,
most areas will see the ground getting covered, and up to 1 inch
may accumulate for the west half.

&&

.LONG TERM...
(Monday through next Saturday)
Issued at 200 PM CST Sat Jan 13 2024

A Winter Storm Watch remains posted for Sunday evening into
Tuesday morning. Models have come into better agreement
confidently depicting widespread snowfall amounts in the 3 to 5
inch range. This will occur as a broad upper level disturbance
crosses the region with deep cold air already in place. Often we
deal with precipitation type changes in our winter forecasts, but
this one will be all snow. A 120KT upper level jet stream will set
up with Middle Tennessee located under the favorable right
entrance region throughout Monday. Moisture will be deep through
the atmosphere and forecast soundings show very favorable thermal
and moisture profiles for the growth of snowflakes. The area will
also be within a low to mid level frontal convergence zone. All
of this means high confidence in snow with potential for enhanced
bands of snow setting up, giving locally greater totals, perhaps 5
or 6 inches in some spots. It is hard to know exactly where the
bands will develop, but even the generalized totals of 3 to 5
inches will cause significant travel impacts. Also, with such
cold air in place, the snow will stick right away and it will
stick around as temps stay sub-freezing until Thursday.

The cold air with the snow and after the snowfall will not be
record-setting (most records are well below zero), but it will be
dangerous for vulnerable populations as wind chill values will
fall below zero. So, a wind chill advisory may ne needed,
especially early Tuesday morning and early Wednesday morning.

As if the early to mid-week wx festivities were not enough, we
are looking at another shot of accumulating snow later in the
week, perhaps 1 inch for late Thursday into Friday!

&&

[Vol Man]

Nice writeup by MRX

.LONG TERM... (Sunday night through next Saturday) Issued at 330 PM EST Sat Jan 13 2024 Key Messages: 1. Probability for an accumulating snow Monday into Tuesday is increasing. See Winter Storm Watch for additional details. Uncertainty regarding high temperatures especially in the southeastern part of Tennessee.

2. Very cold temperatures in the wake of the potential snow. Single digit temperatures and near or subzero wind chill possible Wednesday morning.

3. Additional wintry system possible Thursday night into Friday, details highly uncertain.

Discussion: Still on track for a significant winter storm for Eastern Tennessee and southwest Virginia. A 140 knot jet aloft will develop ahead of the upper trough dipping out of Canada. Closer to the surface low level convergence and strengthening isentropic lift will provide for a corridor of snow to develop. Expect snowfall to develop over eastern Tennessee Monday morning, with exact timing still a little unknown. Despite continued waffling in deterministic runs on exact track of the snow Monday into Tuesday, ensemble probabilities are increasing for not only accumulating snowfall, but several inches of snowfall. NBM probabilities and some guidance suggest localized higher amounts of snow, but there are some caveats. Biggest concern outside of exact track of the heaviest snow is temperatures on Monday. Guidance has a bifurcated solution set, with a multitude of members showing near or subfreezing temperatures as daytime highs, but some members, including the NAM, show temperatures getting above freezing on Monday in the southeastern portions of Tennessee. That could spell spoiler, at least in the southernmost counties and lower elevations of the foothills where those warmer temperatures reside. The northern portions of Tennessee and Virginia are likely to remain below freezing, allowing for quick accumulations. Beyond the snow, we`re in for a spell of absolutely frigid temperatures. Euro and GFS ensembles are keying on high probabilities of single digit temperatures Wednesday morning, with the best chances for temperatures 20 to 30 degrees below normal values in line with where the ensembles have snow accumulations. It is quite possible for many locations that once we slip below freezing Sunday evening, we will not get back above freezing until Thursday afternoon. After that we have another shortwave trough accompanied by a much larger upper trough digging into the Ohio River valley Thursday night into Friday that will bring with it another chance of wintry weather. Once the whole upper trough swings through, that will potentially bring another shot of significant cold to the region. Ensembles have very low probabilities of valley snow, but near 50% chance for an accumulating snow in the mountains, which is pretty good signal for the high elevations at the day 6 range. &&

[Mrwolf1972]

That would depend on where one lives.  

I'd take the icon 18z

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[tnweathernut]

18 minutes ago, nrgjeff said:

NAM seems a little off this setup. We got the gentle isentropic upglide we all been wishing for since 2015.

Energy for our system is just getting onshore in the Pac NW. Looks like the 18Z NAM is a little south (John, Carvers posts above) and the NAM will get more of the Pac NW wave on the 00Z run. Hopefully the NAM will settle in with the Globals.

I'm cautiously optimist about Chattanooga. Cold air should be in place. A brief mix is possible due to low level temps, but this feels like an all snow event. Energy sliding up from the Deep South with isentropic lift is hard for even KCHA to screw up. Fingers crossed

Little concern elsewhere. Looks like a gem coming for much of us!

I agree this is the setup where most should score with little harm from thermal layers off a setup we have waited for ...... for a LONG time.  It's not like we have a wrapped up negative tilt system coming at us.   What do you think about the modeling consistently showing a warm nose/downslope up the western side of the apps into NE TN?   I don't want to assume, but would guess you think this is overdone, solely based on the setup?

[Carvers Gap]

Here is the comparison map for the 18z RGEM (12z on right) and also 18z icing map.  Most significant winter storms have mixing issues weather NYC or Boston or here.  The entry point into the eastern valley is eastward.  TRI's numbers are up.  Overall,  a pretty steady run.  

 

[Carvers Gap]

8 minutes ago, Mrwolf1972 said:

I'd take the icon 18z

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Again, depends on where one lives.  Knoxville is likely gonna be good regardless.  TRI folks are on a bit of a snow drought.  So permit us a moment of hope.  (Chattanooga would be in worse shape in that regard.).  

[PowellVolz]

Here is the comparison map for the 18z RGEM (12z on right) and also 18z icing map.  Most significant winter storms have mixing issues weather NYC or Boston or here.  The entry point into the eastern valley is eastward.  TRI's numbers are up.  Overall,  a pretty steady run.  

 

If this stays as is I like where I’m located.




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[Carvers Gap]

44 minutes ago, tnweathernut said:

I thought the RGEM and Euro both popped a less side low in SW NC.  I figured this was the root cause of thermals getting screwed up in NE TN.

You may be right on that.  The NAM had weak SLP in north central Georgia off the top of my head.  A lee side would make sense.

[Carvers Gap]

1 minute ago, PowellVolz said:

If this stays as is I like where I’m located.




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I hear that.  LOL.  Ice w/ the cold which follows is not good!

[PowellVolz]

Nice writeup by MRX
.LONG TERM... (Sunday night through next Saturday) Issued at 330 PM EST Sat Jan 13 2024 Key Messages: 1. Probability for an accumulating snow Monday into Tuesday is increasing. See Winter Storm Watch for additional details. Uncertainty regarding high temperatures especially in the southeastern part of Tennessee.
2. Very cold temperatures in the wake of the potential snow. Single digit temperatures and near or subzero wind chill possible Wednesday morning.
3. Additional wintry system possible Thursday night into Friday, details highly uncertain.
Discussion: Still on track for a significant winter storm for Eastern Tennessee and southwest Virginia. A 140 knot jet aloft will develop ahead of the upper trough dipping out of Canada. Closer to the surface low level convergence and strengthening isentropic lift will provide for a corridor of snow to develop. Expect snowfall to develop over eastern Tennessee Monday morning, with exact timing still a little unknown. Despite continued waffling in deterministic runs on exact track of the snow Monday into Tuesday, ensemble probabilities are increasing for not only accumulating snowfall, but several inches of snowfall. NBM probabilities and some guidance suggest localized higher amounts of snow, but there are some caveats. Biggest concern outside of exact track of the heaviest snow is temperatures on Monday. Guidance has a bifurcated solution set, with a multitude of members showing near or subfreezing temperatures as daytime highs, but some members, including the NAM, show temperatures getting above freezing on Monday in the southeastern portions of Tennessee. That could spell spoiler, at least in the southernmost counties and lower elevations of the foothills where those warmer temperatures reside. The northern portions of Tennessee and Virginia are likely to remain below freezing, allowing for quick accumulations. Beyond the snow, we`re in for a spell of absolutely frigid temperatures. Euro and GFS ensembles are keying on high probabilities of single digit temperatures Wednesday morning, with the best chances for temperatures 20 to 30 degrees below normal values in line with where the ensembles have snow accumulations. It is quite possible for many locations that once we slip below freezing Sunday evening, we will not get back above freezing until Thursday afternoon. After that we have another shortwave trough accompanied by a much larger upper trough digging into the Ohio River valley Thursday night into Friday that will bring with it another chance of wintry weather. Once the whole upper trough swings through, that will potentially bring another shot of significant cold to the region. Ensembles have very low probabilities of valley snow, but near 50% chance for an accumulating snow in the mountains, which is pretty good signal for the high elevations at the day 6 range. &&

I’m I reading this correctly that MRX isn’t really all that concerned with PType issues outside of the lowest elevations of the southern valley?


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[codgator]

25 minutes ago, *Flash* said:

I just want to cash out on the 18z Icon. Too good to be true, I know. 

Yeah I agree that would be A+

[Uncle Nasty]

There's too many damn models to choose from. I was on another forum earlier, and people were arguing about which model was the best. The model that showed the most snow for their area was the best.

With that said, models are just tools used for guidance. We'll either get very little or get a great southern snow. Models are just an educated guess. Let's see what old Mama Nature has in store for us regarding a blanket of white on the ground for everyone.

I appreciate all the PBP and write-ups from all you knowledgeable folks!

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[ShawnEastTN]

I’m I reading this correctly that MRX isn’t really all that concerned with PType issues outside of the lowest elevations of the southern valley?


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Yeah I read that as literally the Georgia border area as their only thermal concerns since they specifically say southernmost counties.

[John1122]

1 minute ago, Uncle Nasty said:

There's too many damn models to choose from. I was on another forum earlier, and people were arguing about which model was the best. The model that showed the most snow for their area was the best.

With that said, models are just tools used for guidance. We'll either get very little or get a great southern snow. Models are just an educated guess. Let's see what old Mama Nature has in store for us regarding a blanket of white on the ground for everyone.

I appreciate all the PBP and write-ups from all you knowledgeable folks!

Sent from my SM-S916U using Tapatalk
 

With how it goes around here, the actual worst one is usually the one that shows the most snow!

[bearman]

3 minutes ago, PowellVolz said:

 

I’m I reading this correctly that MRX isn’t really all that concerned with PType issues outside of the lowest elevations of the southern valley?


.

 

I think you are reading it right and neither is @energyJeff worried about mixing and I have a lot of confidence in his thoughts.

[Carvers Gap]

Models once inside of 36 hours which I normally use in this order for E TN....RGEM, HRRR, 3k NAM.  I do watch trends on deterministic models, and ensembles still have a place.  NBM of models is good until it can't keep up with trends.

[TellicoWx]

Looking at the RGEM soundings, the wind direction this doesn't appear to be a downsloping issue. More like what is seen on every front rolling off the plateau, it slowed the front just a smidge more. Doing so causes less time for the Arctic air to wash the warmer air out of the valley, as it gets pushed against the Smokies. It's like a quasi warm nose in a way...rates, speed, and several other factors can quickly erase this problem, but won't be ironed out until closer to the event.

[Carvers Gap]

7 minutes ago, PowellVolz said:

 

I’m I reading this correctly that MRX isn’t really all that concerned with PType issues outside of the lowest elevations of the southern valley?


.

 

In addition, I read that they are concerned about precip issues along the length of the foothills as well is how I read it.

[nrgjeff]

26 minutes ago, tnweathernut said:

I agree this is the setup where most should score with little harm from thermal layers off a setup we have waited for ...... for a LONG time.  It's not like we have a wrapped up negative tilt system coming at us.   What do you think about the modeling consistently showing a warm nose/downslope up the western side of the apps into NE TN?   I don't want to assume, but would guess you think this is overdone, solely based on the setup?

Some downslope warming is possible on the front side of the system. However I don't think it'd be a deal killer. Maybe cut rates for a couple hours. If it even happens, start snowing, ease up, then get back at it second half. Kind of like Tennessee basketball, ha!
Otherwise, box to wire snow.

[Carvers Gap]

Just now, TellicoWx said:

Looking at the RGEM soundings, the wind direction this doesn't appear to be a downsloping issue. More like what is seen on every front rolling off the plateau, it slowed the front just a smidge more. Doing so causes less time for the Arctic air to wash the warmer air out of the valley, as it gets pushed against the Smokies. It's like a quasi warm nose in a way...rates, speed, and several other factors can quickly erase this problem, but won't be ironed out until closer to the event.

So it banks the warmer air against the Apps?  That is pretty rare.  Good catch.

[Silas Lang]

Just now, Carvers Gap said:

So it banks the warmer air against the Apps?  That is pretty rare.  Good catch.

I have seen similar situations pan out when living in Johnson City. Sorry @tnweathernut

[Carvers Gap]

Just now, Silas Lang said:

I have seen similar situations pan out when living in Johnson City. Sorry @tnweathernut

What Tellico is mentioning is different IMO.  I lived in JC for five years as well - love the upslope events!  It isn't really a downslope.  It is banking warm air up against the Apps as it gets pushed across the valley.  Amazing modeling can even model that TBH.  

[ShawnEastTN]

Looking at the RGEM soundings, the wind direction this doesn't appear to be a downsloping issue. More like what is seen on every front rolling off the plateau, it slowed the front just a smidge more. Doing so causes less time for the Arctic air to wash the warmer air out of the valley, as it gets pushed against the Smokies. It's like a quasi warm nose in a way...rates, speed, and several other factors can quickly erase this problem, but won't be ironed out until closer to the event.

This makes sense! I've always noticed in storms with strong downsloping along the mountains, before mixing occurs the warm air against the mountains pushes a cool pocket in the valley up against the eastern escarpment of the plateau. Almost like a bathtub sloshing. What you are describing is similar but in the other direction cold coming off the plateau displacing and pushing the relative warm pool toward the mountains. All of this before it all mixes and normalizes.

[tnweathernut]

7 minutes ago, Carvers Gap said:

Models once inside of 36 hours which I normally use in this order for E TN....RGEM, HRRR, 3k NAM.  I do watch trends on deterministic models, and ensembles still have a place.  NBM of models is good until it can't keep up with trends.

We haven't discussed this much, but where does the FV3 fit into the equation?   I honestly have NO clue.  

[TellicoWx]

2 minutes ago, Carvers Gap said:

So it banks the warmer air against the Apps?  That is pretty rare.  Good catch.

I wouldn't even call it warmer lol..small Zone of 33-34 temps between the 925-850 layer..dps are really low, so could be end up as virga until it saturates (which the wet bulb is 99.5% below freezing). Valley is like a tub..cold faucet needs turned on for a minute to push the warm out or saturate it long enough to turn cold.

[tnweathernut]

7 minutes ago, nrgjeff said:

Some downslope warming is possible on the front side of the system. However I don't think it'd be a deal killer. Maybe cut rates for a couple hours. If it even happens, start snowing, ease up, then get back at it second half. Kind of like Tennessee basketball, ha!
Otherwise, box to wire snow.

Thanks, that makes sense.  Good to see your Jayhawks get the train back on the tracks today.

[PowellVolz]

I can’t remember the date of this storm but (maybe 2017-2019) it feels like this outcome could be a similar situation. It was a snow/rain/snow forecast for the valley, heavy snow on the plateau with mostly rain in the foothills because of downsloping. The warm nose made it to I-40 in Knoxville up against the mountains but did not make it any further NW. I ended up with over 8”. The thought was we had a little CAD up against the eastern slopes of the Plateau that backed up into the valley. John got blasted that event. I remember watching the temps rise as the day went on. Gatlinburg was low 40’s, Knoxville made it to 35° but I stayed below 30. One of those rare times when the cold air won out in the valley.


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