February/March 2021 - Frigid or Flop? Pattern/Longterm Forecast Thread.

[Carvers Gap]

2 hours ago, tnweathernut said:

Just once, I'd like to see a clean surface and 850 low pass.  Seems almost impossible to not send energy into east TN that wrecks the thermals.  I appreciate @Carvers Gap for trying to will a winter threat to our area over the last couple of days.  lol

Man...the 18z RGEM ice total.  Man.   

[TellicoWx]

18z GFS...keep working that mojo Carvers lol

[Stovepipe]

So another sloppy dusting maybe.

[Dsty2001]

8 minutes ago, TellicoWx said:

18z GFS...keep working that mojo Carvers lol

Just to note how wild that would be, at my house would be close to 8", a 15 min drive down the road would turn into 3

 

[edit]

 

With little to no change in elevation at that

[fountainguy97]

Rgem with the 1” ZR amounts across NE TN. We will pass on that.

[TellicoWx]

5 minutes ago, Dsty2001 said:

Just to note how wild that would be, at my house would be close to 8", a 15 min drive down the road would turn into 3

 

[edit]

 

With little to no change in elevation at that

Think the GFS is trying to pickup all the valley locations, but doesn't have a low enough resolution. It's trying to show the cold becoming entrenched but the algorithm is spitting out snow...that's an ice look.

[John1122]

MRX acknowledged the possibility of frozen on the front end for the first time in their AFD. I can't blame them for being reluctant to do much with it, the NAM actually seems to have done pretty well with this event and it isn't onboard yet. 

[fountainguy97]

Nice trend here on gfs.  NAM is long range still and on an island. It likes to over amp these type of events and push them too far NW. 

[Holston_River_Rambler]

18z Euro still got da thump:

 

 

[Holston_River_Rambler]

Interesting obs of the energy:

the main piece (at least it seems to me) is the first circle. The second one seems to come on a kick it enough to suppress it and keep it from cutting so much. Also still interested to see what the 3rd piece might do as it dives in and rounds the base of the trough. 

[dwagner88]

At this point I’m honestly so sick of the glancing blows and near misses, I’m just ready for 70’s and sun. 

[Shocker0]

33 minutes ago, Holston_River_Rambler said:

18z Euro still got da thump:

 

 

Ok where can we lock in these totals?

[Olhausen]

Will the 4 inches of snow and sleet here and more for areas north west and north help keep this next system more snow? Basically how much influence could it have?

[Carvers Gap]

The 18z GEFS mean is roughly 2-6" of snow from SE TN to NE TN and increasing as you go NE.  Just have to run accumulations through Saturday in order to pick-up wrap around snow as well.   

[CG2]

The 18z GEFS compared to the 0z GEFs for the same time frame and ending Saturday.  E TN amounts are all Weds/Thurs on this.  18z EPS(which is an off-run so beware) has increased totals 1-2" as well compared to this time yesterday. Again, this is NOT a forecast but just discussion and trying to hone-in on what seems probable.  For those new here, please understand we are just sorting through model runs right now.  18z on left and 0z on right...both from 2.15.21.  The trend is for bigger totals...we will see if that holds.

[Carvers Gap]

From MRX's Hazardous Wx Outlook just so folks don't thing we are cooking up something unsubstantiated in regards to model support.  It could trend better or it could trend worse, but I feel like this is a good description....

An intense storm system will affect the region Wednesday night
and Thursday. Strong southerly winds will affect the East Tennessee
mountains and foothills Wednesday night and Thursday morning.
Precipitation could start as a mix of snow, sleet, and freezing
rain Wednesday night into early Thursday morning across parts of
the Plateau, northern Tennessee Valley, and southwest Virginia
before changing to all rain. Periods of heavy rainfall Thursday
may cause some localized flooding. Rain will change to light snow
Thursday night with light accumulations possible.

 

[John1122]

1 hour ago, Olhausen said:

Will the 4 inches of snow and sleet here and more for areas north west and north help keep this next system more snow? Basically how much influence could it have?

Basically little or none in my experience. The upper levels torch and you change to rain regardless of snow on the ground. 

[Carvers Gap]

1 hour ago, Olhausen said:

Will the 4 inches of snow and sleet here and more for areas north west and north help keep this next system more snow? Basically how much influence could it have?

I guess hypothetically it could allow for the cold to feed into your area longer.  I do wonder if the reason we are seeing modeling in the east change to a mixed bag at onset Thursday is due to:

1.  This current system seems a little quicker than modeled, and has changed spacing between it and the second system.

2.  The snow on the ground to my west is allowing the cold to work eastward more easily.  

Tough to say though on a microscale how much of a difference it makes.  On a large scale, a nice snowpack can definitely speed a supply or resupply of cold.  Keep us updated.  Will be an interesting test.    I do wonder if the second system is a bit flatter on modeling today due to HP being able to "push" a bit more.  We will see if those trends hold.

[Carvers Gap]

From the MRX evening disco...Time to put the bat signal up for @Math/Met.  Good set-up? 

 

The aforementioned S Plains mid/upper shortwave will eject ENE
across the MS Valley into the TN and OH Valleys during this period
while becoming slightly negatively tilted. This along with a 150+ kt
upper jet will deepen the surface low as it lifts through the
vicinity of the Appalachians and eastern OH Valley. Forcing from the
strong upper jet will lead to a strong, southerly low-level jet Wed
night that will pump strong moisture transport into the S
Appalachians region. This strong moisture transport, isentropic
upglide, and additional dynamic forcing as the surface low
approaches will lead to widespread precip developing north of an
advancing warm front Wed night. Deterministic and ensemble guidance
still differ regarding the exact track of the low and resultant
thermal fields (as is usually the case in the winter), so precip
type at the onset Wed night is low confidence. The GFS is the
coldest solution, the NAM is the warmest, and the GEFS/Euro/CMC
ensemble means are in the middle. Leaned heavily on the ensemble
means and NBM for temps and precip type Wed night into Thurs morning
which suggests a period of snow, sleet, and freezing rain possible
from the Plateau through the N Valley into SW VA, so generally N of
I-40 and W of I-81. Forecast soundings support this idea with a
gradually descending warm nose as the warm front lifts N, but as
mentioned, precip type and location confidence is low. This will be
fine tuned as new guidance arrives over the next 48 hours. One thing
that is certain is that a high end mountain wave will occur across
the E TN mountains and foothills Wed night through Thurs morning
since the low-level jet will be favorably oriented perpendicular to
the terrain, it will be a very strong low-level jet of 60-80 kts,
and an inversion will be in place below 850 mb leading to ducting
values over 20. This will likely lead to 80+ mph gusts downsloping
into the foothills such as Camp Creek. As the mid/upper shortwave
and surface low lift NE Thurs, a strong cold front will cross the
region. We could see a dry slot part of the morning, but expect
precip to quickly return as the strong upper jet maintains strong
frontogenetic forcing ahead of the cold front with continued strong
low-level moisture transport ahead of the boundary. PWATS will be
above the 90th percentile with some elevated instability, so periods
of heavy rain are possible. Warmer air advecting in ahead of the
front will allow any mixed precip in northern areas Thurs morning to
quickly change to rain for the afternoon.

[Bigbald]

25 minutes ago, Carvers Gap said:

From the MRX evening disco...Time to put the bat signal up for @Math/Met.  Good set-up? 

 

The aforementioned S Plains mid/upper shortwave will eject ENE
across the MS Valley into the TN and OH Valleys during this period
while becoming slightly negatively tilted. This along with a 150+ kt
upper jet will deepen the surface low as it lifts through the
vicinity of the Appalachians and eastern OH Valley. Forcing from the
strong upper jet will lead to a strong, southerly low-level jet Wed
night that will pump strong moisture transport into the S
Appalachians region. This strong moisture transport, isentropic
upglide, and additional dynamic forcing as the surface low
approaches will lead to widespread precip developing north of an
advancing warm front Wed night. Deterministic and ensemble guidance
still differ regarding the exact track of the low and resultant
thermal fields (as is usually the case in the winter), so precip
type at the onset Wed night is low confidence. The GFS is the
coldest solution, the NAM is the warmest, and the GEFS/Euro/CMC
ensemble means are in the middle. Leaned heavily on the ensemble
means and NBM for temps and precip type Wed night into Thurs morning
which suggests a period of snow, sleet, and freezing rain possible
from the Plateau through the N Valley into SW VA, so generally N of
I-40 and W of I-81. Forecast soundings support this idea with a
gradually descending warm nose as the warm front lifts N, but as
mentioned, precip type and location confidence is low. This will be
fine tuned as new guidance arrives over the next 48 hours. One thing
that is certain is that a high end mountain wave will occur across
the E TN mountains and foothills Wed night through Thurs morning
since the low-level jet will be favorably oriented perpendicular to
the terrain, it will be a very strong low-level jet of 60-80 kts,
and an inversion will be in place below 850 mb leading to ducting
values over 20. This will likely lead to 80+ mph gusts downsloping
into the foothills such as Camp Creek. As the mid/upper shortwave
and surface low lift NE Thurs, a strong cold front will cross the
region. We could see a dry slot part of the morning, but expect
precip to quickly return as the strong upper jet maintains strong
frontogenetic forcing ahead of the cold front with continued strong
low-level moisture transport ahead of the boundary. PWATS will be
above the 90th percentile with some elevated instability, so periods
of heavy rain are possible. Warmer air advecting in ahead of the
front will allow any mixed precip in northern areas Thurs morning to
quickly change to rain for the afternoon.

Wow, 80 mph gusts.  Those suckers aren't the easiest things to chase since they can come in on the cusp of bad weather.  I tried chasing the last one up camp creek bald, only to encounter snow and ice, and than I worried getting off the mtn without tree debree killing me.  Have decided it's best to hunker down in place in an area without trees.  I've just not prepped enough to ride one out, but on the bucket list

[Stovepipe]

23 minutes ago, Carvers Gap said:

From the MRX evening disco...Time to put the bat signal up for @Math/Met.  Good set-up? 

 

The aforementioned S Plains mid/upper shortwave will eject ENE
across the MS Valley into the TN and OH Valleys during this period
while becoming slightly negatively tilted. This along with a 150+ kt
upper jet will deepen the surface low as it lifts through the
vicinity of the Appalachians and eastern OH Valley. Forcing from the
strong upper jet will lead to a strong, southerly low-level jet Wed
night that will pump strong moisture transport into the S
Appalachians region. This strong moisture transport, isentropic
upglide, and additional dynamic forcing as the surface low
approaches will lead to widespread precip developing north of an
advancing warm front Wed night. Deterministic and ensemble guidance
still differ regarding the exact track of the low and resultant
thermal fields (as is usually the case in the winter), so precip
type at the onset Wed night is low confidence. The GFS is the
coldest solution, the NAM is the warmest, and the GEFS/Euro/CMC
ensemble means are in the middle. Leaned heavily on the ensemble
means and NBM for temps and precip type Wed night into Thurs morning
which suggests a period of snow, sleet, and freezing rain possible
from the Plateau through the N Valley into SW VA, so generally N of
I-40 and W of I-81. Forecast soundings support this idea with a
gradually descending warm nose as the warm front lifts N, but as
mentioned, precip type and location confidence is low. This will be
fine tuned as new guidance arrives over the next 48 hours. One thing
that is certain is that a high end mountain wave will occur across
the E TN mountains and foothills Wed night through Thurs morning
since the low-level jet will be favorably oriented perpendicular to
the terrain, it will be a very strong low-level jet of 60-80 kts,
and an inversion will be in place below 850 mb leading to ducting
values over 20. This will likely lead to 80+ mph gusts downsloping
into the foothills such as Camp Creek. As the mid/upper shortwave
and surface low lift NE Thurs, a strong cold front will cross the
region. We could see a dry slot part of the morning, but expect
precip to quickly return as the strong upper jet maintains strong
frontogenetic forcing ahead of the cold front with continued strong
low-level moisture transport ahead of the boundary. PWATS will be
above the 90th percentile with some elevated instability, so periods
of heavy rain are possible. Warmer air advecting in ahead of the
front will allow any mixed precip in northern areas Thurs morning to
quickly change to rain for the afternoon.

[TellicoWx]

0z NAM starting to step toward the other models...brings ice into the eastern valley

[John1122]

23 minutes ago, TellicoWx said:

0z NAM starting to step toward the other models...brings ice into the eastern valley

It was actually warmer than 18z but got precip into the area earlier. It has a massive warm nose around 750 that no other modeling has. 

[John1122]

I know my sounding is wrong on the RGEM. It has my temp at 31 and my dewpoint at 32 at hour 57.  The warm nose showed up on it too but less pronounced than the NAM. 

[Carvers Gap]

The 0z RGEM is yet again flatter and colder than its previous run.

[Carvers Gap]

Interesting feature on the 0z RGEM  (which the 18z NAM had) was a secondary wave showing up along the front.  Not implausible, and something to watch.  The 0z RGEM is just as nasty as its 18z counterpart, BUT it has about 1/3 less overall precip.  I think this is because the system is being forced to slide along a bit vs just roaring up the valley.  This fits a recent trend(will it continue) of the SLP being forced further east and less of its energy not being allowed to force its way up west of the Apps.  Looks like modeling is feeling the cold high to the north and west of the eastern valley on this run.

[Matthew70]

2 hours ago, dwagner88 said:

At this point I’m honestly so sick of the glancing blows and near misses, I’m just ready for 70’s and sun. 

Yes!  This all day! 

[John1122]

V16 just crushing parts of the area. 

It was early with losing the major freezing rain here. Hopefully it's onto something here too. 

[John1122]

The regular GFS was more blotchy and IMO unrealistic compared to it just on the fact that it has weird dollops of heavy snow with nothing north or south of it and it wasn't driven by elevation or anything else. 

[Daniel Boone]

Most of the weather forecast media outlets are all going with the strong WAA warm nose Thursday with possibly a light mix early quickly changing to heavy rain. 

       It's as if they never saw any of the snowy runs.

     Granted,with the way this system done, it does make it hard to believe those solutions but, not totally discount especially when there's players on the field that could cause those solutions.