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Holston_River_Rambler

December 8-10 Storm Discussion

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Good morning everyone! Big 12z runs of our favorite models (yes even the goofy GFS) are on the deck! I would consider the GFS an outlier on the low side with QPF and the RGEM on the high side. All models had remarkable consistency from the 0z to 6z runs. The GFS and ICON slightly bump up totals with each passing run. Huge test for the FV3-GFS since it will become the main GFS in a month. It has behaved so much differently from the GFS for the past several days.

I think we can finally lock down this storm and it’s totals after the 12z runs. This is the money run in my opinion.

Regardless of what happens the whole storm system has been modeled consistently for a whole week! It showed up 240 hours ago and here we still are tracking a similar scenario. No comparison between the two storms but we may be talking about the December 8-10 storm being seen a week in advance just like we talk about the 1993 storm was seen a week in advance.

Off topic: Noticed some intriguing marketing as Food City is advertising WCYB’s weather updates.

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I believe MRX is holding off until this afternoon to get a complete look at everything, the 850 (what brings the snow/ice) is still back in W TX...plenty of time to hold off. Any snow outside extreme NE TN today is a bonus, the "show" comes with how the 850 comes thru.

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The 12z NAM really deepening over the coastal areas of the Carolinas on this run.  At some intervals as it approaches Cape Hatteras from Cape Fear, it is 5-7 millibars lower than 6z.  It is tucked neatly against the coast.   That is the sign of a strengthening storm.  At 36 is goes to 999 mbs as it literally goes over Hatteras.  Quite the organized powerhouse at that time.  It drops 10-14" over NE TN/ SW VA.  Nice run and similar to 6z.  

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8 minutes ago, TellicoWx said:

12z 3K ups totals in central valley around knox

 

Ouch, looks great but for some reason warm air gets trapped in the clinch river valley and I never transition to full snow. Normally I would dismiss this but I've seen this supported run after run for an entire day.

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12 minutes ago, Holston_River_Rambler said:

That little band of precip brought 850 temps down quite a bit in the central valley. 850 0 degree Celsius line is into McMinn county now. 

Even the 925 0 degree Celsius line, which had been up near TRI, is now below Knox. 

Correct, I have noticed a very persistent NE wind that has actually picked up as the morning has evolved. The cold advection is winning per radar trends. 

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14 minutes ago, Kasper said:

Correct, I have noticed a very persistent NE wind that has actually picked up as the morning has evolved. The cold advection is winning per radar trends. 

I was wondering when you were gonna make an appearance, glad to see you posting @Kasper!

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There is a PWS up on the Cherohala Skyway near Indian Boundary Lake, I look at it to see the trends up in elevation. My temps here in the valley have been steady for past couple hours at 37. The station up on the mtn has began warming in the last hour and is now above my temp.

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25 minutes ago, BlunderStorm said:

Ouch, looks great but for some reason warm air gets trapped in the clinch river valley and I never transition to full snow. Normally I would dismiss this but I've seen this supported run after run for an entire day.

I think you do OK w that run.  Here is the map for the full run. (12z 3K NAM)

1861181560_ScreenShot2018-12-08at10_05_47AM.png.57767398e6a6b4abec9d1fdbb90ba2f8.png

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On the 12z NAM, the area between Knox and Monroe/McMinn Co is about 1° to warm at 850 or the snow output would mirror Knox roughly. On the 12z 3k, it's even greate as it blazes the 850s over this area. Starting late tonight the PWS will help tell which is more correct.

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1 minute ago, TellicoWx said:

On the 12z NAM, the area between Knox and Monroe/McMinn Co is about 1° to warm at 850 or the snow output would mirror Knox roughly. On the 12z 3k, it's even greate as it blazes the 850s over this area. Starting late tonight the PWS will help tell which is more correct.

How are the current surface maps verifying vs the first few hours of the 12z NAM?  Just wondering how the high pressure over the top, valley temps, and slp are verifying. That will tell us which models are likely handling this well.

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4 minutes ago, Carvers Gap said:

How are the current surface maps verifying vs the first few hours of the 12z NAM?  Just wondering how the high pressure over the top, valley temps, and slp are verifying. That will tell us which models are likely handling this well.

 

Latest SPC U S  Composite Map (1).png

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6 minutes ago, 1234snow said:

 


Carvers, I believe the 12z GFS is also in the kool-aid!

b20f200fdab9d1726ce0752639021ebb.jpg

9f6ec9759f548dba2ec22f03df7ba72f.jpg

 

And there is .6 of ZR in that somewhere four our back yards.   The GFS is a full blown, nasty winter storm for NE TN and now portions of the eastern areas Central Valley and the northern Plateau.

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I see MathMet lurking, hope you are doing well.  We all probably MBY focused on some level, but I’d like to know if you have an opinion of the mesoscale models showing the downslope this AM?  If your prior opinion still stands no worries about a response,  I know you have to be busy....lol

overall modeling seems to be converging on a heavy northeast (maybe much of east) TN snow.  It’s funny I’m almost obsessing about the trailing piece of energy as much as the main system.  I find that discrete feature fascinating!

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RAP model looking good for a heavy wet snow event in Northeast/Central E TN as to the hour it goes out as of now. Heaviest snow bands will set up just over the Rain/Snow line as relatively warmer but below freezing temps can house more moisture and therefor a heavier snowfall rate with this type of system.

8CAFB360-5794-4405-A453-E6A5E6DB106F.gif

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MRX morning late-morning update....

National Weather Service Morristown TN
1049 AM EST Sat Dec 8 2018

.DISCUSSION...

No notable adjustments for the morning update. Narrowed the
north-south gradient of rain chances through the afternoon hours to
account for current radar trends. Radar imagery shows a very tight
gradient between light precip in the south and nothing for the
central and northern parts of the forecast area. Suspect this
trend will continue. Didn`t make any drastic adjustments, just
narrowed the gradient on the northern half of the precip shield.

Otherwise, accounted for current temperature trends and
subsequently trimmed back mention of snowfall to mainly the higher
elevation spots in the mountain. Previous shift had some minor
accumulations, less than 2", in those higher elevation spots. Left
that in, but did knock them down by a few tenths. Better snowfall
potential will arrive later tonight and will address that time
period with the afternoon forecast package.

 

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31 minutes ago, tnweathernut said:

I see MathMet lurking, hope you are doing well.  We all probably MBY focused on some level, but I’d like to know if you have an opinion of the mesoscale models showing the downslope this AM?  If your prior opinion still stands no worries about a response,  I know you have to be busy....lol

overall modeling seems to be converging on a heavy northeast (maybe much of east) TN snow.  It’s funny I’m almost obsessing about the trailing piece of energy as much as the main system.  I find that discrete feature fascinating!

That trailing piece of energy is very fascinating. The RGEM shows it almost phasing with the backside of the departing low and keeps snow over most of E TN through Monday Morning!

 

 

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I cannot see how MRX can ignore the trends this morning. I really wish if they were just going with their gut on this they would tell us that and I would respect it. It’s better that way than leaving everyone scratching their heads wondering what they are looking at, especially the northern plateau areas which look almost as good as the NE valley.

 

 

.

 

 

 

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