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TIMS model verification, December 31, 2021 - January 3, 2022


Holston_River_Rambler
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37 minutes ago, Blue Moon said:

Careful: the warm nose was missed by the HRRR for our area.

Between three separate rain shadows, and downsloping winds...we know the drill in Kingsport.  LOL. Not too mention we have easily the state's largest micro-heat island.  Not so much a warm nose here as it is warm air that just won't scour out or that we make our own warm air.  We also deal with downlsoping winds.  Once that slp swings to our SE, the warm nose stops.  What I saw with that 23z run of the HRRR was the slp was 1-2mb deeper over Upstate SC which has caused much more moisture to be on that model run.  Last Christmas, took a while for the warm air to leave and for cold to flood-in from the Plateau.  Our biggest advantage here is that we are have higher elevation than most cities....JC and Bristol are I think 100-200 feet higher than us.   We will see...thermal profile will be threading the needle.  Usually is.

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35 minutes ago, TellicoWx said:

 

Areas affected...parts of the southern Appalachians and Southeast Concerning...Heavy snow Valid 030019Z - 030515Z SUMMARY...Periods of moderate to heavy snow will likely develop through this evening as temperatures begin to drop and forcing for ascent strengthens markedly. Snow rates of 0.5-1 in/hour will be possible with the strongest bands. Brief periods of mixed precipitation including sleet and freezing rain may also develop. DISCUSSION...As of 0015 UTC, a potent mid-level shortwave trough was analyzed via WV imagery across the eastern ARKLATEX. To the south, a 90-100 kt jet streak was beginning to round the base of the positively tilted trough moving onshore across southwestern LA. A broad area of low pressure at the surface was centered across western GA with an expanding precipitation shield noted to the northwest of the low and ongoing convection. Recent surface observations across southwestern TN and northern MS have shown an increase in the occurrence of snow and mixed precipitation types over the last few hours with diurnal cooling taking place. Strong height falls from the approaching trough are forecast to advect eastward over the next few hours as the trough becomes negatively tilted, augmenting surface mass response and deepening the aforementioned surface low. Low-level cold advection should follow suit, accelerating the change over, first to mixed precipitation, and then quickly to snow of parts of the expanding precipitation field. While temperatures remain mild, the rain/snow line should move eastward with time concurrent with increasing precipitation rates from strengthening 850-700 frontogenesis and the development of convective bands owing to subtle buoyancy aloft. Regional soundings show favorable profiles for periods of moderate and occasional heavy snow expanding northeastward with time from northern AL into eastern/central TN along the western slopes of the southern Appalachians. Snow rates of 0.5 to 0.75 in/hr will be possible for several hours resulting in reduced visibility and potential travel issues. Localized 1+ in/hr rates may also be possible beneath the heavier convective elements or near local topography favorable for orographic enhancement. Snow may linger for a few hours overnight before forcing and dry air to the west shift precipitation northeastward.

mcd0023.gif

When was that released, Tellico?

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3 minutes ago, Carvers Gap said:

Between three separate rain shadows, and downsloping winds...we know the drill in Kingsport.  LOL. Not too mention we have easily the state's largest micro-heat island.  Not so much a warm nose here as it is warm air that just won't scour out or that we make our own warm air.  We also deal with downlsoping winds.  Once that slp swings to our SE, the warm nose stops.  What I saw with that 23z run of the HRRR was the slp was 1-2mb deeper over Upstate SC which has caused much more moisture to be on that model run.  Last Christmas, took a while for the warm air to leave and for cold to flood-in from the Plateau.  Our biggest advantage here is that we are have higher elevation than most cities....JC and Bristol are I think 100-200 feet higher than us.   We will see...thermal profile will be threading the needle.  Usually is.

tbh I think the snow just tries to avoid the stink from Kingston lol

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1 hour ago, Holston_River_Rambler said:

I could be 100% wrong about this, but it looks like as the energy is starting to close off and tilt more neutral, the TROWAL feature is starting to develop in West TN:

giphy.gif?cid=790b7611c882aa948881e04193

I think it is that small area of precip. starting to build back barely west of main moisture, just south of Jackson, TN.

 

You can also see the back edge of the lift the shortwave is producing (colder cloud tops/ darker purples over the same area of west TN) turning almost south to north on satellite (and maybe ever so slightly SSE to NNW):

giphy.gif?cid=790b7611e7eb7c97802d9ac9c2

 

 

Definitely agree it's starting to tilt, which helps middle TN warm nose problem. MS/AL border has already switched to all snow

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32 minutes ago, 1234snow said:

When is the last time that the SPC has issued a mesoscale discussion for tornadoes/severe weather and then for heavy snow the very next day?

Within 24 hours, many areas have gone from all-time record highs to accumulating snows.  No doubt, that is wild stuff.  Some modeling nailed this time from 3+ weeks ago and the rainfall that came right prior to today.  Truly amazing that computer modeling can do that now.  

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SPC Mesoscale discussion does not account for the Great Valley. I don't expect a micro-scale map, but that broad brush is pretty bad to be honest. Chattanooga in the heart of the heavy sticking snow? Um, no.

That aside, SPC seems to be with the local WFOs. They see the trough pivoting negative. That will indeed cool the column in a hurry. Lower Great Valley won't benefit much due to typical downslope and oh my it's still warm! Still SPC makes good points about the rest of the system. 

More than Feb. 2020 it reminds me of an event back in Kansas during October. Don't ask how long ago, haha. Tight low came in while temps were above freezing. Low pivoted negative and dumped 1-2 inches per hour snow.

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We are now casting at this stage.  The models are just making a guess and the short range models change every hour. One blip may mean something big then be gone next run.  

I'll say what I always say in these situations, know your backyard climo and it's probably going to work out for you as well as any model at this point.  

We are having some thunder here. 

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4 minutes ago, John1122 said:

We are now casting at this stage.  The models are just making a guess and the short range models change every hour. One blip may mean something big then be gone next run.  

I'll say what I always say in these situations, know your backyard climo and it's probably going to work out for you as well as any model at this point.  

We are having some thunder here. 

1000% agree....good example is the 01z HRRR, apparently inhaled some of the crack fumes from the 0z NAM for mby

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