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December 8-10 Storm Discussion

Holston_River_Rambler

By Holston_River_Rambler,
in Tennessee Valley

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Carvers Gap

Carvers Gap

Posted
Posted
3 minutes ago, jaxjagman said:

Is the some feed back problem,that OBS looks like it might be to warm in NE TN?

Manage Blocking.png

I think most places already have precip to our west.  No precip here yet.  I have 42 degrees in Kingsport.  Might be a small downslope w that number on the grid.  Winds are out of the NNE.  Man, it feels cold though.  Last I checked, our humidity was pretty low.  I think once it starts, that number drops pretty quickly.  

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MissyB

MissyB

Posted
Posted

Long time lurker, first time poster. Enjoying all the discussion about this storm. I understand MRX tends to be conservative with their predictions/advisories but do you think will they add additional counties to the WWA? I'm in Blount Co just across the river from Knox. 

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Holston_River_Rambler

Holston_River_Rambler

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Really interesting to watch the radar and temps from Look Rock back to Knoxville

Maybe 37 on top of Look Rock, layer of dense fog (that was in the process of raising) as I went down the mountain. About 1/3 of the way down the temp bottomed out at around 35 and then started back up. Low 40s or so in Knoxville and it looked like it hadn't even rained. 

Looking at NEXRAD radar it looks like the precip. is actually slowly backing away from Knoxville for now (don't take that to mean I think it's going away) Just interesting set up from foothills to valley today. 

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Blue Ridge

Blue Ridge

Posted
Posted
Really interesting to watch the radar and temps from Look Rock back to Knoxville
Maybe 37 on top of Look Rock, layer of dense fog (that was in the process of raising) as I went down the mountain. About 1/3 of the way down the temp bottomed out at around 35 and then started back up. Low 40s or so in Knoxville and it looked like it hadn't even rained. 
Looking at NEXRAD radar it looks like the precip. is actually slowly backing away from Knoxville for now (don't take that to mean I think it's going away) Just interesting set up from foothills to valley today. 

It seems to have floated north and then back south off and on today. FWIW, the HRRR shows it retreat south for a couple of hours before the primary shield builds in.
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Carvers Gap

Carvers Gap

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Posted

This is the final run of the 18z GFS for NE TN folks before the event begins.  Seven runs ago it had virtually nothing and has trended steadily to this....that is quite a difference.  I did notice that the 18z RGEM finally stopped its consistent and probably unrealistic rocket trajectory of snowfall totals.  It backed down just a hair, but very respectable totals.

952175590_ScreenShot2018-12-08at4_48_09PM.png.ae8b370855466170484f6ea5b7549419.png

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Windspeed

Windspeed

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16 minutes ago, Carvers Gap said:
This is the final run of the 18z GFS for NE TN folks before the event begins.  Seven runs ago it had virtually nothing and has trended steadily to this....that is quite a difference.  I did notice that the 18z RGEM finally stopped its consistent and probably unrealistic rocket trajectory of snowfall totals.  It backed down just a hair, but very respectable totals.952175590_ScreenShot2018-12-08at4_48_09PM.png.ae8b370855466170484f6ea5b7549419.png

Not only has it caved, look at how much better it resolves the vort at 850mb. The past few days it didn't even resolve 145dm. We essentially have stronger lift in the weakness over the Southern/Central Apps. That, and also the precip column should be a classic dynamic cooling event for heavy wet snow.beeba6bd12f5513daa3c3f7bc61d49a4.gif

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Carvers Gap

Carvers Gap

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Posted

Now, the 18z RGEM would be a total mess and this would strain the power grid.  We want no part of this.  We need to pull for the Euro temp profile to verify.  Otherwise, .5-.75 ZR/6-12" snow/with a sprinkling of pingers.  Last run of the RGEM before it begins is a formidable winter storm.  Snow totals are liquid equivalent for those new to this type of map.  

1032782166_ScreenShot2018-12-08at5_06_13PM.png.08b7adc2a128d29f5bb07650d6f8ae03.png

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TellicoWx

TellicoWx

Posted
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3 minutes ago, Carvers Gap said:

Looks like we have some snow in NW TN/SW KY/AR.  Who do we have out there?  Tag them if you know them.... @Will (little rock), you seeing anything yet?

NE AR has switched over to all snow, been following that area today to see how things play out. They did a special 18z balloon launch and found a warm nose at 850 still over Little Rock.

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Blue Ridge

Blue Ridge

Posted
Posted

Quick discussion w/r/t temps this afternoon:

KGCY (Greeneville) topped out at 41, while KTRI topped out at 43. Both had a light NE breeze much of the afternoon.

Meanwhile, K0A9 (Elizabethton) topped out at 45, with an even lighter occasional breeze from the SW - indicative of minor warming from downsloping.

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Carvers Gap

Carvers Gap

Posted
Posted

Great write-up this afternoon/evening by MRX.  Normally, I only post excerpts.  However, the entire discussion about the storm is worth a read...

The main concern is exactly how much snow will be seen, and
specifically for the central and northern parts of the forecast
area. The gist of that story is that we`ve bumped up snowfall
amounts enough to warrant an expansion of the winter storm warning
to include the northern plateau, TN valley, and also the
southwestern Virginia counties. Additionally we`ve also added new
counties to an advisory, to include the Knoxville metro as well as
areas around Cherokee county NC.

The parent upper trough responsible for the impending winter storm
is just now beginning to cross into Louisiana this afternoon.
Surface low pressure associated with this trough was situated just
east of the New Orleans area along the Gulf Coast. Regional radar
imagery shows widespread rain stretching across the Gulf states,
Tennessee, Georgia and even into the Carolinas this afternoon. This
will all rotate east and northward through the night as the upper
trough draws near, yielding a prolonged period of precipitation over
the southern Appalachians. Two main questions arise from this
scenario and those are 1) when/where will precipitation change to
all snow, and 2) how much will any given location get.

Despite a 1030-1035mb surface high being anchored to our north
during this event, only a modest amount of dry air influx will be
seen. Instead the driving force for snowfall will be dynamic
cooling, driven by strong vertical motions moving over the area from
just before daybreak through mid/late morning. This is evident in
rapidly cooling 850mb temperatures despite a neutral temperature
advection regime at that level. In any case, the resulting high
precip rates will help to put accumulating snow down to lower
elevations despite surface temperatures being around or perhaps
slightly above the freezing mark at the onset.

So what has changed then? Well, for starters we have upped snowfall
amounts across the TN mountains, northern plateau/valley areas, and
southwestern Virginia. Current model trends suggest that for the
central/northern half of the forecast area a changeover to all snow
should occur between 06z-10z, with a rain/snow mix likely expanding
into the southern valley by late morning. However, accumulations are
not expected to amount to much south of the Knoxville metro area.
For the central/northern valley, current thoughts are that 2-5
inches of snow will be seen beginning during the early morning hours
Sunday. This will include the Oak Ridge, Knoxville Metro, Jefferson
City, and Morristown areas. In the mountains, the ptype regime is
roughly the same as what was forecast by previous shifts, but made
upward adjustments to snowfall totals in the southwest Virginia per
the latest guidance, resulting in the previous advisory for the
northern plateau, southwest Virginia, and northern TN valley
counties being upgraded to a winter storm warning.

There are some uncertainties regarding how long precip will hang on
later Sunday. Current warnings/advisories extend to noon on Monday.
We will begin to lose upper level saturation by late afternoon/early
evening on Sunday, which would yield drizzle or maybe freezing
drizzle depending on the temperature profile. Perhaps some light
flurries could be seen, but we`re splitting hairs. In any case, the
end times of the warnings/advisories may need to be adjusted but
that will fall to the day shift tomorrow once the event is ongoing
and a better handle on the wind down of the system comes into view.
 

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AMZ8990

AMZ8990

Posted
Posted

Heard from the central and western states forum that southwest Oklahoma was seeing snow about 2 hours ago.  Not huge totals but the roads were snow packed from what was said, also said the flakes were huge in OKL.   Another guy in the northwest corner of Arkansas said he’s not seeing anything but just about the whole rest of the state is seeing some combination of rain or snow.

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