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John1122

February 17-18th Winter Storm Thread.

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15 minutes ago, McMinnWx said:

How well has the HRRR done this winter vs. the NAM?  

The HRRR has been killing the NAM on snow systems.  The NAM has mostly been pretty bad this year but has been okay a couple of times. 

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The HRRR has been killing the NAM on snow systems.  The NAM has mostly been pretty bad this year but has been okay a couple of times. 

Will give the NAM credit for the Christmas Eve storm. Seems like it was the most steady mod and the most aggressive but at the same time all of the mods basically had the same forecast overall. Seems like the Euro was the last one to join in.


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1 minute ago, PowellVolz said:


Will give the NAM credit for the Christmas Eve storm. Seems like it was the most steady mod and the most aggressive but at the same time all of the mods basically had the same forecast overall. Seems like the Euro was the last one to join in.


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If I remember right the NAM was lost on that one and never did catch up. I'll have to go back and look and see. 

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If I remember right the NAM was lost on that one and never did catch up. I'll have to go back and look and see. 

Ok I’ll take your word over mine on this one. You remember this stuff much better than I do.


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8 minutes ago, PowellVolz said:


Ok I’ll take your word over mine on this one. You remember this stuff much better than I do. emoji23.png


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I said this at about 60hrs out about the NAM in that thread. I don't think it ever fully caught up even as the event was happening. 

"The NAM was just a blank for everyone that run, but the NAM beyond 48 hours leaves a lot to be desired. The RGEM didn't look too bad, but it's not likely all that reliable beyond 48 either."

The GFS actually nailed that system and didn't waiver. 

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1 minute ago, John1122 said:

I said this at about 60hrs out about the NAM in that thread. I don't think it ever fully caught up even as the event was happening. 

"The NAM was just a blank for everyone that run, but the NAM beyond 48 hours leaves a lot to be desired. The RGEM didn't look too bad, but it's not likely all that reliable beyond 48 either."

The GFS actually nailed that system and didn't waiver. 

Kind of been a strange year in that regard, the GFS has been fairly good

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I said this at about 60hrs out about the NAM in that thread. I don't think it ever fully caught up even as the event was happening. 
"The NAM was just a blank for everyone that run, but the NAM beyond 48 hours leaves a lot to be desired. The RGEM didn't look too bad, but it's not likely all that reliable beyond 48 either."
The GFS actually nailed that system and didn't waiver. 

You’re right... it was the GFS that was solid.


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AFD is up from MRX
Very good write up!!! Spot on with watching overnight lows tonight and how that translates tomorrow for highs and how models don't handle cold sticking around longer in the eastern valley than often modeled. One of MRX best write up in recent memory, they seem to be better in general in their write ups this season than prior seasons.

Sent from my SM-G965U using Tapatalk

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National Weather Service Nashville TN
300 PM CST Tue Feb 16 2021

.DISCUSSION...

Another bitterly cold day across the mid state. Current 2 PM
temps have only warmed to 13 to 16 across the entire mid state
area. Clouds have persisted, although a few peaks of sunshine have
occurred for those lucky few locations.

Next storm system has trended a little colder but is not quite as
moisture-laden as previous model runs. Nevertheless, it will still
pack a punch and a winter storm watch will be issued soon. It will
begin at 3pm Wednesday and continue until 6PM Thursday.

An overview of the mslp progs indicates more of a snow oriented
pattern whereby the sfc trough inversion is oriented more sw-ne and
is a little further to our southeast. isobars across the mid state
our more east west and rather flat. The 0C line at 850 mb now appears
to be at or below 0C at Nashvile through the entire event. There are
still a few outlying mini troughs to the northwest of the main
trough. This can be found through the lower levels of the
atmosphere. thus, some warming in the lower levels will reach
into our eastern and southern zones and may turn the precip over
to all rain for a brief time for that area.

The winter storm watch will involve 2 segments. segment 1 will
include roughly the northwestern two thirds of the mid state, and
segment 2 will include the southeastern third. For our
northwestern two thirds, we are looking at 1-4 inches of snow
with around one tenth inch of ice. For the southeastern third, we
have 1 inch of snow and one tenth of an inch of ice. Note that impact
based decisions are in support of the southeastern third`s
prognosticated snow and ice totals.

For the forecast, we will begin to see light snow move in early
Wednesday morning across the west. The precipitation will pick up
in intensity Wednesday night and we will see mostly snow across
the northwest half and then snow, freezing rain and some rain
southeast. The precip intensity will decrease but will be all
light snow on Thursday night. After a few morning flurries on
Friday morning, the precip will then end.

For the near term temps, very cold again tonight with steady or
slightly falling temps and lows of 10-17. Highs will rebound some
and into the 30s by Wednesday afternoon. Looks like 25 to 33 for
your low temps Wednesday night. Temps will remain nearly steady on
Thursday.

For the ext fcst, improving conditions expected with warmer temps.
Highs will reach near 50 for Sunday and Monday along with a chance
of rain. Mid 50s for Tuesday after the system exits.
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3 minutes ago, John1122 said:

Honestly the wide variety in modeling that MRX is talking about seems to be the NAM family vs basically every other model. 

And what is crazy... the 18z NAM is really icy in NE TN.   Up to .65" of ice accumulation for all of the TRI.  Not sure folks are even aware of the threat here..........

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2 minutes ago, CG2 said:

And what is crazy... the 18z NAM is really icy in NE TN.   Up to .5" of ice accumulation for all of the TRI.  Not sure folks are even aware of the threat here..........

The NAM doesn't even agree with itself. The 12k blanks me on ice and snow and the 3k gives me 1-2 inches of snow and .10 ice. Which is the exact forecast MRX put out for my area.  So I suspect they may he rolling 3k heavy in their forecasts.  

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3 minutes ago, John1122 said:

Honestly the wide variety in modeling that MRX is talking about seems to be the NAM family vs basically every other model. 

They do seem to hug the warmest solutions and it does play out well for them often but their term wide seems more of a bias rather than an honest statement.

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4 minutes ago, John1122 said:

The NAM doesn't even agree with itself. The 12k blanks me on ice and snow and the 3k gives me 1-2 inches of snow and .10 ice. Which is the exact forecast MRX put out for my area.  So I suspect they may he rolling 3k heavy in their forecasts.  

Gutsy call to ride the 3K NAM.  It rarely has precip amounts for changeover correct IMBY.  But...it has been a while since I have had an ice set-up.  I almost go back to your comment the other day where they referenced ice as a rarity here.  I agree with you...it is actually common, but just not heavy IMBY.  We get lots of small icing events here.  When I was in high school, we used to get 2-4" storms often followed by warm nose drizzle and rain.  Set-up looks similar.  Interesting for sure.  I wasn't expecting anything to track 48 hours ago, so I can really complain!!!  LOL.

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1 minute ago, bearman said:

They do seem to hug the warmest solutions and it does play out well for them often but their term wide seems more of a bias rather than an honest statement.

This year like every year, has been tough on mets in our forum area. Elevation differences means you have people getting significant winter weather and 10 miles away people getting nothing.  So one group or another is mad that the forecast was wrong. 

They've missed under twice with advisories when I got warning level snow here.  There was warning level ice here but not down in town with the event just passed so people down there didn't understand the WSW we just had.  

I think we had one busted advisory this winter where not much happened. 

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I'm glad we have a potential event to track. About 48 hours ago it looked like we'd all be mid to upper 40s for both days, or higher. Maybe the cold spilled over the Plateau finally and will help everything perform better snow wise.

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Just now, CG2 said:

Gutsy call to ride the 3K NAM.  It rarely has precip amounts for changeover correct IMBY.  But...it has been a while since I have had an ice set-up.  I almost go back to your comment the other day where they referenced ice as a rarity here.  I agree with you...it is actually common, but just not heavy IMBY.  We get lots of small icing events here.  When I was in high school, we used to get 2-4" storms often followed by warm nose drizzle and rain.  Set-up looks similar.  Interesting for sure.  I wasn't expecting anything to track 48 hours ago, so I can really complain!!!  LOL.

They were referring heavily to the Central and southern valley with that statement and I was so confused because they get warm nose induced icing all the time in Knoxville and points south. Especially with Arctic air already in place rather than trying to move into the area. It was just a couple years ago when I drove from heavy snow here to an ice apocalypse in the Central valley. That AFD made it sound like something that happened every 20 or 30 years there.  

You guys tend to not quite get the warm nose as often and tend to be more likely to stay snow northeast of Mo Town but I know you get ice every few years at worst. 

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6 minutes ago, John1122 said:

They were referring heavily to the Central and southern valley with that statement and I was so confused because they get warm nose induced icing all the time in Knoxville and points south. Especially with Arctic air already in place rather than trying to move into the area. It was just a couple years ago when I drove from heavy snow here to an ice apocalypse in the Central valley. That AFD made it sound like something that happened every 20 or 30 years there.  

You guys tend to not quite get the warm nose as often and tend to be more likely to stay snow northeast of Mo Town but I know you get ice every few years at worst. 

Thanks for the clarification there.  This is a crazy forecast for them.  I have seen the warm nose bull out really entrenched, cold air.  However, I have seen the cold stubbornly hold from say Greeneville to Morristown.  Total crapshoot and modeling reflects that with the wide variety of solutions.

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Honestly, I can see a scenario where it sleets and then changes to rain after a brief opening of snow for TRI...or I can see a scenario where the boundary stubbornly holds and doesn't change until the every end of the storm.  

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The HRRR never changes mby to rain during the night Wednesday. The NAM is the only model that does that so far. 

3/4ths inch of QPF is predicted to the south of me a few miles in the non WSW zone. My forecast says up to 1 inch of snow and little or no ice with a low of 29. What happens to the QPF imby? 

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At HR48 the HRRR is steadily moving snow back across the state. The zr edge has moved from near Nashville to the Plateau over the preceeding 2 or 3 hours. Probably a little back end thump if that trend continues. 

 

HRRRMA_prec_ptype_048.png

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I remember several years back (would have to look back through the threads here, but it’s here somewhere)  where a front end thump was looking to change to rain but it just never did in the eastern valley. In the foothills and mtns it warmed up to nearly 50 degrees, however it stayed in the 20’s to around 30 in the valley and stayed snow the whole time! Ended up with 5.5in at the house and I know some places just north had over a foot! That was about as strange of a situation we could ever expect around here. The thinking was that somehow there was a cold pool aloft over the valley and that the warm nose hit the mtns and just never was able to penetrate back to the west. Extremely rare system indeed. 

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In regards to temps tomorrow based on lows tonight, some areas are already at their predicted low. Crossville is predicted for 14 and that's been their high today. It's 18 here with 12 predicted. Knox is predicted to get to 20 and it's only 26 there now. 

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3 minutes ago, Jed33 said:

I remember several years back (would have to look back through the threads here, but it’s here somewhere)  where a front end thump was looking to change to rain but it just never did in the eastern valley. In the foothills and mtns it warmed up to nearly 50 degrees, however it stayed in the 20’s to around 30 in the valley and stayed snow the whole time! Ended up with 5.5in at the house and I know some places just north had over a foot! That was about as strange of a situation we could ever expect around here. The thinking was that somehow there was a cold pool aloft over the valley and that the warm nose hit the mtns and just never was able to penetrate back to the west. Extremely rare system indeed. 

I think I remember that. I was in JC and it was like 50 degrees but up near Kingsport they had snow. It was like a super heated line up the spine of the Apps and the foothills immediate to them. My parents in Anderson county had a few inches and Knox saw snow. It was almost like a mini cad event in the valley. Cold air banked up against the plateau. It was a odd storm. I remember it vividly because I was pissed at getting blanked. LOL 

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