Jan. 12-13, 2018 winter storm Nowcast and Forecast

[AMZ8990]

If anyone's interested.  Here's the Thursday morning weather briefing from the NWS office out of Memphis.

[ShawnEastTN]

SREF plumes for snow ptype have improved for most locations from 3Z to 9Z although marginally for all but Nash and Crossville which went down.

MEM: Mean .27", Big Dog: 3.65"

Nash: Mean .69", Big Dog: 4.06"

Knox: Mean .26", Big Dog: 1.96"

Chatt: Mean .04", Big Dog: .55"

TRI: Mean .24", Big Dog: 2.4"

CSV: Mean .20, Big Dog: .86"

 

[ShawnEastTN]

Wow....  12Z NAM not looking very good.  If NAM is correct serious Ice Storm but very little snow.

[ShawnEastTN]

[ShawnEastTN]

If it is correct many will be without power possibly for days since it is going to be so cold behind this.  Up to and over an inch of ice in NW TN...  That about as serious as it gets for ice, really anything beyond .25" of ice is devastating especially without a rebound of temps afterward. 

[ShawnEastTN]

12Z RGEM is running now.  I generally trust the RGEM more than the NAM.

EDIT: SLP at hour 12 is about 50 to 100 miles SE of 0Z run of RGEM.

[Carvers Gap]

Check out the slp position on the HRRR.  I think the NAM is getting too amped.  The RGEM(I can see most of the run on WxBell now) shifts SE again.  As many have mentioned the ice situation from Nashville west is not good.  The RGEM now runs the spine of the Apps.  Those EPS slps which were east of the Apps may have some merit yet.  Pretty amazing to watch the temps crash in Memphis, northern MS, and northern AL.  The gradient on the RGEM at hour 30 was low 60s at TRI and upper teens in northern MS.  Those are some very strong dynamics in play and make forecasting a bear.  Too slow or too fast and either way is a bust.

For the eastern folks, here are the 0z EPS slp positions for hours 42 and 48...makes me think the models are not finished trending SE.  The RGEM is SE an 12z.

  

[AMZ8990]

RGEM totals.

[ShawnEastTN]

6 minutes ago, Carvers Gap said:

Check out the slp position on the HRRR.  I think the NAM is getting too amped.  The RGEM(I can see most of the run on WxBell now) shifts SE again.  As many have mentioned the ice situation from Nashville west is not good.  The RGEM now runs the spine of the Apps.  Those EPS slps which were east of the Apps may have some merit yet.  Pretty amazing to watch the temps crash in Memphis, northern MS, and northern AL.  The gradient on the RGEM at hour 30 was low 60s at TRI and upper teens in northern MS.  Those are some very strong dynamics in play and make forecasting a bear.  Too slow or too fast and either way is a bust.

For the eastern folks, here are the 0z EPS slp positions for hours 42 and 48...makes me think the models are not finished trending SE.  The RGEM is SE an 12z.

  

HRRR SLP in the gulf as of latest run, hadn't seen too much of that over the last day of runs usually as far south as Northern LA.

[ShawnEastTN]

12Z GFS straight up the spine of the Apps...  Such a tortured track.

[Carvers Gap]

The 12z GFS is negative tilt w/ the w the Memphis slp by hour 24.  That will really drive in the winter wx for west TN.  The snow axis continues to trend SE especially when you look at the axis pivot from KY lake over several runs.  The Plateau has appreciable amounts for this run.  Definitely want to see the Euro and EPS...normally I would not worry about the EPS within 24 hours, but is should tell us if the operational is done trending SE.

[Carvers Gap]

3 minutes ago, ShawnEastTN said:

12Z GFS straight up the spine of the Apps...  Such a tortured track.

Which is why I think the 0z EPS went east of the Apps.  The Apps runner rarely happens.  Usually we get a piece of the slp up west of the Apps and the warm nose and then the rest rounds the bend. At this moment, that would be my call.  But it is not out of the question that entire system(second wave) rounds the base of the Apps.  The trend lately is to bring the slp(second wave) to Chattanooga and then run the spine.  IF(stress) that trend continues, I would guess that it rounds the bend and goes up through western NC.  

[Carvers Gap]

The 14z HRRR has southeast Missouri at 33F and northeast Missouri at -1F at hour 18.

At hour 7, Memphis is at 64...by hour 18, they are at 34.

[nrgjeff]

Some of that nasty ice QPF will fall as sleet, so I think even the NAM does not spell total disaster. Also the NAM hints at a dry slot which might bring freezing drizzle over sleet, but that is very light. So the NAM offers two ways out of bad freezing rain. GFS wants to steepen/quicken the cold front which would cut off the freezing rain in favor of at least sleet if not snow faster. 

Next for the Tri Cities I have a good snow feeling in my gut despite what models show*. Carvers points out the HRRR. The HRRR EXP/PARA is juicier with the comma head in Mid-Tenn. Also a little south at the end of the run. I could see that brushing and/or redeveloping toward the Tri Cities. 

* Euro was with me before it was against me before it was with me again.

Otherwise I agree with all the NWS discussions at the national and local level. Ice could disappoint by cutting down snow, but I do not see a bad ice storm in the cards. Kentucky could get locally 5-6 inches of snow within their 1-4 inches. Maybe we can reel in some thunder sleet for Nashville?

And for Chattanooga, I'm ready for rain and thundershowers ending as cold drizzle and 34F. Rooting for everybody's snow north and west. Get TROWAL'ed!

[weathertree4u]

20 minutes ago, Carvers Gap said:

The 14z HRRR has southeast Missouri at 33F and northeast Missouri at -1F at hour 18.

At hour 7, Memphis is at 64...by hour 18, they are at 34.

Still seeing lot of ice projected for middle tn and wondering why the entire area not under winter storm warning 

[BullCityWx]

4 minutes ago, nrgjeff said:

Some of that nasty ice QPF will fall as sleet, so I think even the NAM does not spell total disaster. Also the NAM hints at a dry slot which might bring freezing drizzle over sleet, but that is very light. So the NAM offers to ways out of bad freezing rain. GFS wants to steepen/quicken the cold front which would cut off the freezing rain in favor of at least sleet if not snow faster. 

Next for the Tri Cities I have a good snow feeling in my gut despite what models show. Carvers points out the HRRR. The HRRR EXP/PARA is juicier with the comma head in Mid-Tenn. Also a little south at the end of the run. I could see that brushing and/or redeveloping toward the Tri Cities. 

Otherwise I agree with all the NWS discussions at the national and local level. Ice could disappoint by cutting down snow, but I do not see a bad ice storm in the cards. Kentucky could get locally 5-6 inches of snow within their 1-4 inches. Maybe we can reel in some thunder sleet for Nashville?

And for Chattanooga, I'm ready for rain and thundershowers ending as cold drizzle and 34F. Rooting for everybody's snow north and west. Get TROWAL'ed!

http://68.226.77.253/text/NAMSFC/NAM_KBNA.txt

 

extracted NAM data does show TSPL for them.

[Carvers Gap]

11 minutes ago, weathertree4u said:

Still seeing lot of ice projected for middle tn and wondering why the entire area not under winter storm warning 

Probably waiting on the 12z Euro and EPS.  It is what I would do.  I think Memphis had to hoist theirs last night due to time and proximity of the actual system.  This afternoon a SPS or advisory or WSW might go up for Nashville area.  But this is increasingly tricky from Nashville eastward.  With the models trending some to the SE(after the slp passes Memphis), where is the slp placement?  If it rounds the base of the southern Apps, that opens up a big can of worms.  I would wait until this evening and for the EPS/Euro combo.  I would not issue anything for TRI until tomorrow AM if at all.  Might put up a special weather statement about incoming cold and potential for snow showers or discuss in the hazardous weather statement.  Still so much uncertainty.  Jeff's comments above do a great job summing this up as usual.  **edit**

[ShawnEastTN]

12Z Euro SLP NE GA and sub 1000.

[John1122]

12z cut snow totals dramatically for the western areas again. It's odd, the 00z brings the snow an the 12z takes it away.  Memphis gets about .2 ice and 1 inch of snow that run although some of the .2 precip that falls as ice may be sleet.

[ShawnEastTN]

11 minutes ago, John1122 said:

12z cut snow totals dramatically for the western areas again. It's odd, the 00z brings the snow an the 12z takes it away.  Memphis gets about .2 ice and 1 inch of snow that run although some of the .2 precip that falls as ice may be sleet.

Yeah I'm a little perplexed by that run, a stronger SLP even, would have thought totals would have been higher.

[John1122]

Euro has a max of 3 inches of snow in Tennessee near Clarksville. 1-2 inch totals are confined to the border counties with Kentucky, mostly from my area, west to Dyersburg although some of that area is under 1 inch verbatim on the map. But the general idea is that most snow will be in Kentucky this run where 3-5 inches are fairly common. Especially a couple counties north of the border.

[Kentucky]

 

All too familiar with this look, I like the trend tho

[Carvers Gap]

31 minutes ago, ShawnEastTN said:

12Z Euro SLP NE GA and sub 1000.

Shawn, do you have the slp placement immediately after that one?

[John1122]

The heaviest precip seem to fall just before places make the changeover to ice. But it still appears that a good portion of West Tennessee and Middle Tennessee from Nashville west get a heavy ice event. Though if you get sleet it may not be as much. Generally appears that .25-.5 fell as frozen that run in those areas.

[ShawnEastTN]

Yes its in your backyard.  Literally crosses the Apps highest peaks from south to north that run.

 

[John1122]

3 minutes ago, Carvers Gap said:

Shawn, do you have the slp placement immediately after that one?

It's about 10 miles from Johnson City 3 hours later.

[John1122]

We had a storm a few years ago that ran the spine of the Smokies, I'd never seen that before. I can't recall seeing one cross the Smokies like that but it probably has happened.

[John1122]

It's ripping snow in Kentucky by that point, but the precip shield is ragged and falling apart in Tennessee. The 32 degree line runs down the Plateau from NE Claiborne Co to Chattanooga by that hour.

[Carvers Gap]

12 minutes ago, John1122 said:

We had a storm a few years ago that ran the spine of the Smokies, I'd never seen that before. I can't recall seeing one cross the Smokies like that but it probably has happened.

I remember that.  We all swore up and down that it would not do it...and it did.  Very interested to see the EPS slp placements for that time frame.  Might be a very slight jog northwest on that operational run.  Not sure if that is a hiccup of slp placement as it looks very similar to 0z...or if that is the end of the SE trend and now it comes back NW.

edit...the slp placement back across the Smokies just looks like a nuance.  In other words, it had slightly lower pressure than the east side, so it plopped the slp there.  Likely, the majority of the surface low went east of the Apps.  That weather.us site has some nice graphics that you can toggle.

[ShawnEastTN]

13 minutes ago, *Flash* said:

A few things...

1) This system has some Feb 2015 to it in the sense KY hogs all the snow and it's mostly ice south of the border. :/ Still...that storm was a memorable winter wx event with the precip 'triple threat'.

2) Could be wrong but seems the HRRR is slowly but surely strengthening that low...so hopefully that will mean more snow when all is said and done.

3) Lastly, random amateur question...but is what WRF-NMM is to the WRF-ARW similar to what NAM3 is to the NAM12? Hard to tell if I'm looking at dry air intrusion or lack of resolution on the WRF-ARW. Like what the WRF-NMM is showing.

Edit: Maybe it is a resolution issue since the WRF-ARW2 shows high snow amounts though the bottom end of the precip shield looks like it's falling apart.

I could be wrong but I believe they are essentially the same with different variants on the numerical side of the model (Could almost think of them like ensemble members under the same operational), I don't believe there is resolution difference.  I generally like looking at the NMM for eye candy.  Seems to me its usually bullish on qpf.