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Wintry Jan 15-16 Winter Storm Discussion & Obs

GaWx said:
Unless I’m missing something, I don’t see that much warmer for ATL area in general vs 18Z. Maybe 1C at most for warmest. Even so, that’s still only +5C, which is still very ZR friendly assuming there will be ample precip falling much of the night and strong wedging/east winds Sat night to get that low level cold air to ATL. And before that 850s still suggest IP to me.
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The 00z NAM never gets the dewpoint in KATL below 33. Its just an east wind, hardly any CAD really.

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metwannabe said:
Dang look how far N and NW the IP is, gonna be tons of pingers and snow lover hearts broken I'm afraid

View attachment 105755
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The primary going all the way into WVA just floods the mid levels with warm air. FV3 transfers quicker and you can see the ice signature go to more rain/snow. will be a good test of that new model against the NAM
 
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ForsythSnow said:
FV3 High res is south and colder lol. The wobbles are across the board.
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Yep. The FV3 took the 500Mb low essentially on the more southerly path that the 18zz NAM had. Only 50 miles difference or so, but that features placement and speed is that engine driving the train.
 
GaWx said:
I’m perplexed!
Does anyone else think the models showing ATL staying above 32 for the entire front part of the storm are wrong? I realize it may be above 32 for however many hours at the start with any rain that falls in the first part of the night, but the wedge will be then be strengthening overnight with increasingly strong E winds bringing in cold air. 850s never get above +4 C on any model.

History back to 1950 at ATL and other nearby areas (per examining old maps) says that when there is a strong wedge that holds combined with ample rainfall (in this case ~1”, which is plenty ample) and 850s don’t get above +5C, there will very likely be at least some ZR. But I’m seeing only down to 38ish on the Euro/GFS. Sorry, but that’s not going to happen imho as long as they actually get that ~1” of rain of course. If it does, that would be isothermal from 850 to the surface!! How can that possibly be with a wedge of colder air?? A wedge by definition has to be colder at the sfc than at 4K feet up (850 at ATL is 4K feet above ground, which is 5K feet elevation).

The next thing I wanted to eliminate is that the parent high isn’t that cold. I can eliminate that right now because highs in much of SE Canada were way down in the -0s. Lows this morning and tomorrow are in the -20s to some -30s!
Then I checked NYC and Philly, where the cold air is coming in. They’re expecting lows well down in the teens the next two nights with highs tomorrow only near low to mid 20s. There’s a strong (1040 mb) high that will move into the NE and will be slow to move out and weaken thanks to a 50/50 low.

By the way, with as cold as 850s are expected to be (only 0 to +2C through much of the night), that’s actually an indicator more for sleet than ZR per history. I see no mention of sleet in the FFC ATL forecast. I’m thinking that there could very well be several hours of sleet preceding a change to ZR. @dsaur even down your way there COULD be some sleet.

Side note: FFC has a high of 51 at KATL tomorrow. Maxar also does but has the coldest Sat/Sun low only down to 36. That’s going to bust!
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Larry, I'm actually holding more hope for a week out, and that band of sleet at the northen edge of the precip shield. That seems a very likely kind of set up...if it happens, lol. I'll take whatever this present storm dishes out, as I don't think the zr down here would be particularly heavy, the way things presently look. But if the cad stays reinforced such that it makes it down here in force, then things would change. Can it make it past the I 20 terror wall, beyond which monsters be? That sleet band a week out is another matter, if it happens like that...and Goofy has had it for several runs now. Everything is so iffy/on the edge down here, but suppressed with cold in place has often worked for me down here....and clipper/hybred whatis not so much....not like when I was in Atl, at any rate. What's your call for Sav?
 
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wow said:
A classic La Nina ice storm... memories of 1999
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Yep and it was lights out here for 30 hours. Temps never got above freezing until the precip was over. We may be about to do that again, this time with a lot of wind too.
 
Nashville Disco. Nobody wants to make a call.....

Area Forecast Discussion
National Weather Service Nashville TN
841 PM CST Fri Jan 14 2022

.UPDATE...
FOR EVENING DISCUSSION.

&&

.DISCUSSION...

Cool and cloudy at update time. Pretty quiet out there. We`ll take
it because the next couple of days are going to be hectic. I`m not
going to go into a bunch of in-depth analysis here, mainly because
the 00Z model suite hasn`t come in yet. I`ll leave that to the
overnight crew. What I will say is that several places in Middle
TN look like they`re going to get more snow than they bargained
for Saturday night and Sunday. Yes, models are all over the place
as far as positioning where the heaviest snow is going to fall,
but if there`s anything they agree on, someone (or a large swath
of someones) is gonna get hammered. Of note, the 00Z HRRR has
finally started to show heavy snow accumulation. I mention this,
because arguably, the HRRR did the best with the last two snow
events across the mid-state. That said, I have also seen evidence
of forecast soundings showing strong Omega signs in the dendritic
growth layer across a good swath of I-40 and south. How`s that
for scientific? Basically, it means heavy snow for a period of
time.

All of this is leading to potentially 4-8 inches of snow across a
good portion of the area and I wouldn`t be surprised to see a
couple of spots see more and even a few spots (probably our far
northwest counties) see something closer to an inch.

I think the bottom line is: be prepared. Many places are going to
get a bunch of snow and everyone knows how even an inch of snow
can cripple TN when it comes to travel and traffic. Be prepared
for major travel impacts by late Sunday morning, lasting through
the night and probably even worse Monday morning in the aftermath
as temperatures in the morning should bottom out in the 20s,
freezing over anything liquid on the roads. Afternoon
temperatures Monday will try to inch towards 40 but I`m seeing a
lot of clouds Monday, so the sun may not be out to help melt
anything on area roadways. Hopefully by Tuesday, we can start
getting things back towards normal.
 
GaWx said:
Unless I’m missing something, I don’t see that much warmer for ATL area in general vs 18Z. Maybe 1C at most for warmest. Even so, that’s still only +5C, which is still very ZR friendly assuming there will be ample precip falling much of the night and strong wedging/east winds Sat night to get that low level cold air to ATL. And before that 850s still suggest IP to me.
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Larry I’ve read your posts for a long time. I trust your gut if you feel like this has the potential to be a bigger deal. You know Atlanta and GA Climo like no one else. I was actually thinking of some of your old posts from past storms regarding 850’s of 0 to +2 in Atlanta having a lot of sleet. I’m willing to bet we see a few surprises tomorrow night.
 
Myfrotho704_ said:
But the 3km is kinda bearish around CLT with the band, that trend north with everything including the 850 low isn’t very ideal View attachment 105745
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Watching the sleet snow line on correlation coefficient is going to be a hassle. I have a feeling it will not be a very definitive line like we’re used to
 
Wild Weather Monger said:
Yep. The FV3 took the 500Mb low essentially on the more southerly path that the 18zz NAM had. Only 50 miles difference or so, but that features placement and speed is that engine driving the train.
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I mean it would make sense for it to transfer much further south… this isn’t a weak little in-situ CAD… this is a true classical CAD set up.
 

FV3 Convective-Allowing Forecast System - Environmental Modeling Center - Virtual Lab

vlab.noaa.gov vlab.noaa.gov

"FV3 is designed to efficiently scale to the available resources on any supercomputer for faster, higher resolution images. The current GFS, developed before the age of high speed computers, is not able to provide such highly detailed informations. Even if it ran on a computer with more processing power, it would not work faster"

"NAM development was frozen after the March 2017 upgrade, and RAP/HRRR development with the WRF-ARW model will cease after the RAPv5/HRRRv4 upgrade in 2020. However, operational execution of these modeling and associated DA systems will continue until comparable FV3-based systems are able to give similar performance."

snku_acc.us_ma.png


FY2019-FY2020 : HRRR v4 implementation and FV3-LAM development
  • Development of the FV3-based limited-area (FV3-LAM) to bring its capabilities and performance up to that of the current CAM systems
  • Finalize and implement RAPv5/HRRRv4
  • Add the extended HRRR forecasts to HREF, replace NMMB members in HREF with SAR-FV3 members
  • Preliminary ensemble DA testing with FV3-LAM

FY2020-FY2021 : FV3-LAM development/testing for Meso/CAM
  • Finalize porting of HRRR physics into CCPP for use in FV3-LAM
  • Finalize FV3-based RAP
  • Continue evaluation of FV3 SAR against existing systems
  • Continue development and testing of DA capabilities with FV3-LAM
  • Continue evaluation in NOAA testbeds

FY2021-FY2023 : Evolution to a FV3-based single core Rapidly Refreshed Forecast System (RRFS) : FV3 CAM ensemble with DA
  • Ensemble analysis and forecast system development with FV3_LAM and JEDI
  • Development of stochastic physics for single core
  • Continue evaluation in NOAA testbeds
  • Pursuant to favorable evaluation, implement RRFS v1.0 [2023]
 
This must be the worst model of all FV3?
1642420800-MgBUPefBqDg.png
 
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