January 17th-18th Winter Storm Discussion

[phil882]

why? this is observed at 7am this morning.  Not even representative of whats going to happen later.

 

Exactly... KGSO is in a much different situation than some locations just lee of the escarpment because they are well removed from the higher terrain and will primarily be getting low level northeasterly flow, which is more parallel to the Apps. rather than orthogonal. Thus there shouldn't be any sort of terrain induced lift or sinking due to the low-level flow and thus dynamical processes can dominate.

 

KGSO's profile goes isothermal from the surface to 850 hPa at around 9pm per the RAP. I think the only thing that could prevent GSO from getting accumulating snow at this point is a substancial northward/southward deviation in the deformation band and that doesn't appear likely right now.

 

[calculus1]

Its really quite simple. As the northerly flow increases as the 850 hPa low intensifies, the downsloping off the Appalachian mountains will also increase resulting in adiabatic warming and weaker precipitation rates immediately in the lee of the mountains. This is the same process that resulted in a local minima in snowfall accumulation in the immediate lee of the higher elevations in the upper foothills of NC in the March 2009 event, and it could potentially play out in a similar manor in this event. In fact, the amount of cold 850 hPa air is actually less than the March 2009 I've been mentioning so the problem could potentially be more exaggerated for those with marginal themodynamics in the lee of the Appalachians. 

 

Phil, thanks so much for contributing your thoughts.  I wanted to get your opinion on this case study of the March 2009 storm.  Here the authors say that the minimum could not be attributed to downsloping.  In fact, they couldn't really determine what the cause of the minimum was.  Here's the quote I am referencing, and then the link is below:

 

The origin of the warmer air in the foothills was not clearly understood.  Wind direction in the vertical veered from northeast to south from the surface to 500 mb and above, so an obvious downslope wind component to produce warming by subsidence did not exist.  An untested hypothesis suggested that the predominant cooling in the cold air damming occurred farther to the east near the axis of the low-level jet in Fig. 10.  The cooling progressed slowly along the foothills and did not lower surface temperatures close to freezing until late in the precipitation event.

 

http://www.erh.noaa.gov/gsp/localdat/cases/2009/1-2March2009Snow/1-2MarchSnow.html

[burgertime]

  cause it's weenie time!

 

By the way 18z Hi Res model dramatically lower with QPF compared to 12z run. Actually has good totals for the upstate out to 5 hours. It could explode over the next few frames though.

 

And it does rebound. Actually looks pretty good. Snow changeover occurs at hour 8 on the Hi Res for CLT further west out towards Shelby hour 7. 

[msuwx]

wow, this sounding does not look good for GSO

 

 

That was from 12z and matches up well with what the NAM had forecast at that point.

[Wow]

Still 10C at 7AM is pretty warm. might be colder now though. 

 

It is if you look at current measurements.

[SN_Lover]

It is if you look at current measurements.

alright. did you see the dew point drop? it's dropped 10 degrees in 5 hours in mooresville. 

[jburns]

It is if you look at current measurements.

He's right though.  I definitely will not snow at 7am this morning because it didn't.  

[MarvelMountain]

The problem is for a few locations just in the lee of the mountains, this same northerly flow must descend from those higher peaks to the lower elevations immediately in the lee (Marion, Morgonton, Lenior).

This rap sounding at 00z shows everything you need to see taken just south of Marion. Notice how the profile goes unsaturated very close to the surface. This is that northerly flow descending off the mountains that acts as a warming and drying agent that prevents snowfall in these select unlucky locations. 

 

Thanks Phil. Very well written. I just happen to be a little south of Marion, so I won't get my hopes too high. I'm just fortunate that this area has gotten so much rain this month, and there's more to come.

[DaculaWeather]

Look at the deformation of the 850 right now

 

[DaculaWeather]

Looks like FFC is quietly adding some accumulation POPs to the north Metro zones. Dunwoody went from "little to no" to "up to half an inch" with the 2:00 update.

Yes, slowly increasing.

[phil882]

Phil, thanks so much for contributing your thoughts.  I wanted to get your opinion on this case study of the March 2009 storm.  Here the authors say that the minimum could not be attributed to downsloping.  In fact, they couldn't really determine what the cause of the minimum was.  Here's the quote I am referencing, and then the link is below:

 

 

http://www.erh.noaa.gov/gsp/localdat/cases/2009/1-2March2009Snow/1-2MarchSnow.html

 

If the winds truly were northeasterly then I agree, its hard to get a downsloping component from that direction. However, if the winds were actually northerly or even a little west of north, then a downsloping component could be established. I think its pretty telling that the lack of snowfall perfectly mirrors the continental divide in McDowell County. The continental divide is essentially the sloping breaking point of the Appalachians and marks where water flows to the Mississippi River vs. Atlantic Ocean. For example the French broad river actually flows from south to north since it is on the west side of this divide. Thus is leaves the door open to suggest that some downsloping processes contributed towards the lack of snowfall in this county and others right along the edge of the divide. 

 

EDIT: In addition the NWS RAH office agrees with the downsloping assessment from their case study review of the March 2009 snowstorm.

 

 

A significant minimum in snow accumulation amounts was noted just east of the mountains where a considerable down slope flow and the associated subsidence resulted in reduced snow accumulations.

 

[Wow]

alright. did you see the dew point drop? it's dropped 10 degrees in 5 hours in mooresville. 

 

Yep, now down to near 40.

 

BTW, here is my snow accum. max map.  Northern NC mtns and SW VA going to get blasted.. already beginning there.  Then across the NC piedmont where the deformation band will set up.

 

[jburns]

Yep, now down to near 40.

 

BTW, here is my snow accum. max map.  Northern NC mtns and SW VA going to get blasted.. already beginning there.  Then across the NC piedmont where the deformation band will set up.

 

 

Temp 43, dew point 42.  I have a ways to go.

[WxKnurd]

Yep, now down to near 40.

 

BTW, here is my snow accum. max map.  Northern NC mtns and SW VA going to get blasted.. already beginning there.  Then across the NC piedmont where the deformation band will set up.

Going to be interesting seeing where the deformation band sets up as well as the training of any snow bands within in the deformation zone, looks like a reasonable map to me.  Hopefully a large portion of the I-85 and I-40 corridors can cash in tonight because of this, let the looking out the window begin!

[Wow]

Temp 43, dew point 42.  I have a ways to go.

Once the dynamics of this storm kick in you'll drop like a rock.

[SN_Lover]

if the trend continues changeover might be sooner? 

 

Mooresville, NC

[dsaur]

Yes, slowly increasing.

The sun was out again, but now it starting to drizzle.  Maybe my ride in the dry slots is ending.  Here's hoping.  You been getting any rain up there?  T

[strongwxnc]

Awesome insight Phil!

I assume my location in Rutherford County will see a good bit of downsloping but it does not apper to be the case from your assessment!

If the winds truly were northeasterly then I agree, its hard to get a downsloping component from that direction. However, if the winds were actually northerly or even a little west of north, then a downsloping component could be established. I think its pretty telling that the lack of snowfall perfectly mirrors the continental divide in McDowell County. The continental divide is essentially the sloping breaking point of the Appalachians and marks where water flows to the Mississippi River vs. Atlantic Ocean. For example the French broad river actually flows from south to north since it is on the west side of this divide. Thus is leaves the door open to suggest that some downsloping processes contributed towards the lack of snowfall in this county and others right along the edge of the divide. 

 

EDIT: In addition the NWS RAH office agrees with the downsloping assessment from their case study review of the March 2009 snowstorm.

 

Looks good John!

 

Yep, now down to near 40.

 

BTW, here is my snow accum. max map.  Northern NC mtns and SW VA going to get blasted.. already beginning there.  Then across the NC piedmont where the deformation band will set up.

 

[DaculaWeather]

Same here Tony, it got bright and the precip stopped except for some very light snow somethings around 3pm. It appears from radar it's about ready to begin again though. 

 

Temp 40.1 here with a dew point of 39 which is falling at the same rate as the temperature.  My wet-bulb is 39.6. 

 

Hmmm, I see my sig script isn't working...

[SnowGoose69]

Got a report of RASN in Villa Rica GA....my gut feeling is that band is gonna start dying right as it gets to the AL/GA border.

[deltadog03]

My forecast ideas look pretty good IMO.  However I need to probably lower Asheville's amounts I think.  I am going to lower there's and there's only (not the higher terrain around there) to 1-2".  Looks like AL has got around 2-3" *from what reports I have seen* and ATL metro should still be around T-1" with 1-3" North of there.  The upstate is still a tough call for me, but I do think they will see 1-3" potentially.  

[superjames1992]

LOL, weenies jumping off a cliff now right before you get snowed in.  Obsessing over 7 AM observations. 

 

I'm feeling good in KGSO.  It would take a complete bust for KGSO to miss out on some decent snowfall at this point.  Of course, I'm sitting here hoping for the big one, but it should be a decent shot in any case.

 

One thing is for sure.  It is cold, windy, and rainy out there now.  We've had a lot of rain this morning/afternoon and I'd have to think flooding could be a problem at some point, especially once the wet snow starts to melt away tomorrow.

 

NWS' point-to-point forecast has 3-7" for GSO now, for what it's worth (not much).

[DueUCMe]

Fox8 in High Point is getting reports of rain mixing with snow in Mount Airy, NC in Surry County already.

[DaculaWeather]

My forecast ideas look pretty good IMO.  However I need to probably lower Asheville's amounts I think.  I am going to lower there's and there's only (not the higher terrain around there) to 1-2".  Looks like AL has got around 2-3" *from what reports I have seen* and ATL metro should still be around T-1" with 1-3" North of there.  The upstate is still a tough call for me, but I do think they will see 1-3" potentially.  

Chris, I'm thinking the same thing. I'm thinking for the north metro counties maybe 1-3"

[Wow]

Thanks, but I have had two full cardiac arrests.  Next time would you mind using different terminology?  

 

 

 

LOL.. man is that rain whipping around rightnow.

[calculus1]

If the winds truly were northeasterly then I agree, its hard to get a downsloping component from that direction. However, if the winds were actually northerly or even a little west of north, then a downsloping component could be established. I think its pretty telling that the lack of snowfall perfectly mirrors the continental divide in McDowell County. The continental divide is essentially the sloping breaking point of the Appalachians and marks where water flows to the Mississippi River vs. Atlantic Ocean. For example the French broad river actually flows from south to north since it is on the west side of this divide. Thus is leaves the door open to suggest that some downsloping processes contributed towards the lack of snowfall in this county and others right along the edge of the divide. 

 

 

EDIT: In addition the NWS RAH office agrees with the downsloping assessment from their case study review of the March 2009 snowstorm.

 

Thank you, sir.  I hated that effect living in Lenoir at that time.  It was a heart-breaker.  I now like in Hickory, which seemed to be far enough away (at least for that particular storm) from the mountains to avoid the disaster of no snow.

[wncsnow]

New GSP snow map very similar to the previous map

[phil882]

Awesome insight Phil!

I assume my location in Rutherford County will see a good bit of downsloping but it does not apper to be the case from your assessment!

 

While I do think there will be some downsloping where people experience northerly or northwesterly flow on the lee slopes... I don't want to overstate it either. The area that will be directly impacted should be pretty small and will be further negated by the strong dynamical cooling of melting snowfall in the same region. So the question still comes down to where will the deformation band go. However, I think it adds an extra element to the puzzle that might hurt folks in the immediate lee of the Appalachians if the deformation band does not set up directly over that region, allowing downsloping to play a larger role in limiting CAA and precipitation rates. 

[strongwxnc]

Thanks for the lesson on this today Phil. For those of us that live in the lee, it becomes a constant questions. Thanks for clearing that up for us!

 

 

While I do think there will be some downsloping where people experience northerly or northwesterly flow on the lee slopes... I don't want to overstate it either. The area that will be directly impacted should be pretty small and will be further negated by the strong dynamical cooling of melting snowfall in the same region. So the question still comes down to where will the deformation band go. However, I think it adds an extra element to the puzzle that might hurt folks in the immediate lee of the Appalachians if the deformation band does not set up directly over that region, allowing downsloping to play a larger role in limiting CAA and precipitation rates. 

Upped my total yet again. However, we are only taking .5

New GSP snow map very similar to the previous map

[superjames1992]

I'm having a hard time seeing AVL seeing as little snow as GSP is forecasting.