December 8-10 Storm Discussion

[AMZ8990]

The differences in snow totals between the pivotal fv3 and the tropical tidbits fv3 is pretty insane.  Not too mention there is some heavy pockets of freezing rain in Arkansas, South Carolina, and Georgia that showed up that run.  Scary amounts of ice if it planned out.  Definitely need to keep an eye on the ice totals with this storm.

[AMZ8990]

1 minute ago, John1122 said:

Well, I'm back in the yard stick game on the FV3. That's about as good a run across our region as you'll ever see. 12 plus across so much of the state. 

Right!!  We dream of that all year.

[Carvers Gap]

2 hours ago, Blue Ridge said:

Curious why such a hole over Unicoi, Carter, Johnson, and Washington Counties exists. Mixing or downslope?

I agree w blunder storm...looks like downslope.  We get it here in Kingsport w northwest flow events often.  Sinking air.  You can kind of see it where Jeff said the Plateau acts as a snow shadow when precip comes in from the east there, in this case the west sides of mountain areas gets less.  

[John1122]

Ratio'd FV3 map. This is going to be powerline breaking paste. 

[Blue Ridge]

I agree w blunder storm...looks like downslope.  We get it here in Kingsport w northwest flow events often.  Sinking air.  You can kind of see it where Jeff said the Plateau acts as a snow shadow when precip comes in from the east there, in this case the west side of it.

That was my guess as well but usually that isn’t quite so apparent in guidance at this stage. Cuts totals over those counties from previous runs while increasing the surrounding areas. Interesting solution.

[Carvers Gap]

6 minutes ago, Blue Ridge said:

That was my guess as well but usually that isn’t quite so apparent in guidance at this stage. Cuts totals over those counties down while increasing the surrounding areas. Interesting solution.

You know I haven't even look at winds with this.  Winds aloft must be humming to produce those solutions.  The Euro is less sensitive to it.  Hopefully it will be a good test as to weather the GFS is a bit too sensitive to it.  It has been such a long time since we have had this type of system, I am going to have to brush up on the bias with these.  @Math/Met, you are the expert on winds in the mountains in Greeneville.  Is the downslope overly pronounced on that run or legit.  I am not sure.

[John1122]

I remember a downslope situation for the Tri area guys a few years ago.  Moisture was coming over the Smokies and riding almost NNW. I was downstream of snow that would happen in Maryville. At some point I remember it cutting off towards the Tri-Cities.

[Carvers Gap]

3 minutes ago, John1122 said:

I remember a downslope situation for the Tri area guys a few years ago.  Moisture was coming over the Smokies and riding almost NNW. I was downstream of snow that would happen in Maryville. At some point I remember it cutting off towards the Tri-Cities.

Kingsport usually does OK w these types of evens (famous last words...I probably guaranteed myself a steady rain w that comment), because we are not as close to the Apps, and we get some lift as it(east to west wind) pushes over the Plateau.  The other crazy thing is that temps rise in the Apps foothills with the downslope as the air compresses ever so slightly.    

[John1122]

Just now, Carvers Gap said:

Kingsport usually does OK w these types of evens (famous last words...I probably guaranteed myself a steady rain w that comment), because we are not as close to the Apps, and we get some lift as it(east to west wind) pushes over the Plateau.  The other crazy thing is that temps rise in the foothills with the downslope as the air compresses ever so slightly.    

I remember one of the guys shooting up to like 35-40 degrees during the event. It's in one of the obs threads. 

[tnweathernut]

1 hour ago, Carvers Gap said:

That is full blown maximus right there.

I had an event where downsloping took me from 32 to 47 with breaks in the overcast while 10 miles northwest had mixed precip and 33

[Carvers Gap]

10 minutes ago, John1122 said:

I remember one of the guys shooting up to like 35-40 degrees during the event. It's in one of the obs threads. 

Oh, yeah.  Very true.  @tnweathernut, just mentioned it.  It is crazy business as the winds rush down those mountains.  With opposite winds, I get it when we get northwest flow events.  I have had evenings where JC is getting hammered, and I can see the moon at night.  The craziest is when we we had ice on this side of the valley as the cold banked against the Plateau, and the foothills of the Apps were like fifteen degrees warmer.  It was like a mini-Cad.  I think Jeff mentioned it a few days ago.  

[Carvers Gap]

You all love those northwest flow events...I just roll my eyes.  I stare at the radar, and SE KY just eats all of those returns.  I keep hoping a band will sneak over the mountains.   Sometimes, like today, we see decent northwest flow...but it has to be at the correct angle.  

[John1122]

3 minutes ago, Carvers Gap said:

Oh, yeah.  Very true.  @tnweathernut, just mentioned it.  It is crazy business as the winds rush down those mountains.  With opposite winds, I get it when we get northwest flow events.  I have had evenings where JC is getting hammered, and I can see the moon at night.  The craziest is when we we had ice on this side of the valley as the cold banked against the Plateau, and the foothills of the Apps were like fifteen degrees warmer.  It was like a mini-Cad.  I think Jeff mentioned it a few days ago.  

East Tennessee may be one of the hardest areas to forecast there with the volume of microclimates. 5900 feet in elevation difference in the MRX area. Three major landforms that cause various levels of downslope, upslope and damming. 

[Carvers Gap]

Something else to consider as this comes ashore in California.  (Someone feel free to grab Griteater's sat pic or just link it.)  I wonder if the positive trends this afternoon and evening are because this is getting sampled better at the surface.  I do know it is a bit of a myth that they are poorly sampled, because satellites do pretty well with systems in the Pac now.  But surfaces obs certainly help.  I think we will get a very good picture of things over the next two model suites as this comes ashore.  

[Carvers Gap]

1 minute ago, John1122 said:

East Tennessee may be one of the hardest areas to forecast there with the volume of microclimates. 5900 feet in elevation difference in the MRX area. Three major landforms that cause various levels of downslope, upslope and damming. 

No doubt!  Yeah, I don't know how forecasters do it.  We are in relatively close proximity to three bodies of water...Great Lakes, GOM, and Atlantic.  And the Pacific is where many of our storms have their origin.  We have plenty of flat continent to our north and west, so cold just roars in here.  This area is at the intersection of many influences....lots of hands in the cookie jar so to speak.  A good microclimate example is that Johnson City gets significant flash flooding from time to time as storms stall over Buffalo Mountains and just rain themselves out.  The Methodist Camp up there was washed out a few year ago.  

[John1122]

4 minutes ago, Carvers Gap said:

Something else to consider as this comes ashore in California.  (Someone feel free to grab Griteater's sat pic or just link it.)  I wonder if the positive trends this afternoon and evening are because this is getting sampled better at the surface.  I do know it is a bit of a myth that they are poorly sampled, because satellites do pretty well with systems in the Pac now.  But surfaces obs certainly help.  I think we will get a very good picture of things over the next two model suites as this comes ashore.  

I believe the sampling comes more into play with the northern stream energy from what I've read from the WPC meta. 

[Holston_River_Rambler]

Here is the latest GOES 17: 

[Carvers Gap]

2 minutes ago, John1122 said:

I believe the sampling comes more into play with the northern stream energy from what I've read from the WPC meta. 

Ah, thanks.  Good to know.  I am assuming it is in like the NWT as of now....

[Carvers Gap]

2 minutes ago, Holston_River_Rambler said:

Here is the latest GOES 17: 

Great latitude for a storm to arrive in western NA if you like EC storms.  Thanks for the pic.

[Holston_River_Rambler]

Here is a quote from earlier today from ORH_wxman (Met) in the NE forum on the sampling: 

"That 2md shortwave diving in at 108-120 hours up in Quebec is the real key to keeping this south. It is there on the GGEM too which eventually shoves the storm east as it reaches NJ...that shortwave is currently on the Siberian side of the Arctic Ocean. It is in the southern route of the northwest passage by 00z Saturday and still only at the southern shore of Hudson Bay by 00z Sunday. That is an important piece that probably won't have good sampling even by satellites for a few days." 

[BlunderStorm]

20 minutes ago, Carvers Gap said:

You all love those northwest flow events...I just roll my eyes.  I stare at the radar, and SE KY just eats all of those returns.  I keep hoping a band will sneak over the mountains.   Sometimes, like today, we see decent northwest flow...but it has to be at the correct angle.  

Northwest flow snow is geographical positioning and luck above all else. Elevation doesn't always get the job done for these things. It may help but it won't save the day in elevated valleys. Big A causes downsloping like clockwork for every NWF event. I see the snow showers come charging in and virtually hit a wall at the county line. Had that snow squall not slid in just right I'd have been reporting a glorified dusting of 0.2 in like yesterday. You know it's a good day to be a weather lover when snow is coming down hard as you mark observations and your looking at the modeling for a potentially much bigger event in a few days.

[Holston_River_Rambler]

Griteater in the SE forum says the 18z Euro is south of 12z. Not sure what its EPS mean will say (last night they apparently had different solutions). 

Apparently the surface freezing line is near Atlanta at hour 90. 

[Silas Lang]

31 minutes ago, tnweathernut said:

I had an event where downsloping took me from 32 to 47 with breaks in the overcast while 10 miles northwest had mixed precip and 33

I remember an event like this a few years ago when I lived in JC. 2013 or 2014? Snowing to my north, south, east, and west. It was mid 40s and overcast. 

[John1122]

I'm still searching for the 18z Euro.  I'd heard that it was going to run 4x a day. 

[John1122]

9 minutes ago, Silas Lang said:

I remember an event like this a few years ago when I lived in JC. 2013 or 2014? Snowing to my north, south, east, and west. It was mid 40s and overcast. 

That may be the one I'm referring to as well. 

[John1122]

14 minutes ago, Holston_River_Rambler said:

Griteater in the SE forum says the 18z Euro is south of 12z. Not sure what its EPS mean will say (last night they apparently had different solutions). 

Apparently the surface freezing line is near Atlanta at hour 90. 

I've not read that, but normally when those guys are talking about that in that way they are referencing CAD backing all the way to Atlanta. 

[Holston_River_Rambler]

True and fair enough. Sometimes when they say south, it may mean the CAD, not necessarily the features we are wanting to be south. 

EDITed the above. Earlier version was not how I meant it to sound. 

[Bango]

Prolly shouldnt read too much into Roberts facebook post tonight, but he doesn't seem too crazy about most of tennessee, and doesn't include east tn in his write up....(could just be an oversight)

[tnweathernut]

6 minutes ago, Bango said:

Prolly shouldnt read too much into Roberts facebook post tonight, but he doesn't seem too crazy about most of tennessee, and doesn't include east tn in his write up....(could just be an oversight)

I doubt it, he is normally very thorough....may just not be feeling it for Tennesseans.  A LOT of modeling says there’s a good chance TN can escape heavy snow and there’s been a massive warm nose on most modeling.

 

edit:  just went and read it.  He mentioned I-40N and not trusting precip types, likely referencing there will be more snow in those areas.  I’m sure his blog for paid subscribers is chocked full of useful information!  He’s one of the best around the SE..

[Math/Met]

1 hour ago, Carvers Gap said:

You know I haven't even look at winds with this.  Winds aloft must be humming to produce those solutions.  The Euro is less sensitive to it.  Hopefully it will be a good test as to weather the GFS is a bit too sensitive to it.  It has been such a long time since we have had this type of system, I am going to have to brush up on the bias with these.  @Math/Met, you are the expert on winds in the mountains in Greeneville.  Is the downslope overly pronounced on that run or legit.  I am not sure.

The 850mb winds turn from E to SE at around 96 hours. That’s what the FV3 seems to be depicting in that area. It shows up on the 850mb Vertical Velocity products.

I certainly can’t dismiss that output, but I think it could be overdone.  Based on that track, it’s really not a situation that I would normally worry too much about true downslope winds (when temperatures skyrocket along the foothills). The 925mb winds aren’t orthogonal to the mountains and winds near the surface are from the northeast.  In my opinion the GFS has a tendency to go overboard with downward vertical velocities in that area as well. It tends to paint a bullseye of downward velocities in that exact location. I’ve seen it on several occasions.  I’m not sure if it is correct or not, but I’ve seen unusual VV outputs in that area with southeast winds at that level.

I know that doesn’t answer the question, but that’s about all I can tell you at this point.