wncsnow

You know when Don Sutherland posts its about to get real..

4 minutes ago, HurricaneTracker said:

Hi all.  I hear some folks have asked for my take on the current winter storm.  Happy to help and participate here when I can and when I think my posts will be informative (rather than just banter or MBY endless posts).  So here goes.  AND do note - this is for the mountains of WNC only.  Sorry other readers.

I think most, if not all, of you have the general idea that a big winter storm is on tap.  That storm system is currently entering Southern California (which is a great thing for them!).  They are in serious drought out that way and every storm system helps.  The southern position of the upper level low moving onshore in associated with a strong subtropical jet are two very common characteristics of El Niño.  So you will see some folks in the main thread refer to this as an El Niño wave.  In El Niño years, the subtropical jet (STJ) flows fast from west to east from SoCal through southern Texas and into the Gulf Coast states.  That is exactly what we have here.   By Saturday, this jet buckles tremendously as our low gets carved out, with wind speeds greater than 180 knots (almost 200 mph)!  This is very intense and only seen with the biggest storm systems in the mid-latitudes.  The southeastern states will be under the right entrance region of the jet (a proxy for upward vertical motion).

Then we have the full wave at 500mb moving in across the ArkLaTex region at 18Z Saturday.  Meanwhile, a strong northern stream wave is forecast to be located over central North Dakota.  Over time, the GFS model does not ever phase (I.e., merge) these two waves into one.  Instead, the primary wave that comes into California scoots across the Deep South and induces a surface low pressure system near Houston, TX basically first thing Saturday morning.  This low draws upon rich and deep gulf moisture (characterized by precipitable water values in excess of 1.40” - incredibly deep for December and sourced from the STJ and eastern Pacific!  Wow!  By Saturday night and into Sunday morning, this deep moisture is pointed straight at the southern Apps, much like a fire hose but with deep tropical connections.  Meanwhile, as the surface cyclone moves into southern Georgia, we have southwest winds aloft but locally we have southeast winds circulating around our low.  This in turn brings in a secondary layer of moisture at the surface, combined with deep tropical moisture aloft.  I just cannot emphasize how big a deal this tropical fire hose is.  Even in spring this would be a big deal (for severe weather/flooding reasons).

The surface low however has other things to work with.  A seasonally-strong cold cP (continental-polar) airmass, will be building into the Midwest on Friday and Saturday.  In winter, anything over 1040mb is a very cold airmass.  This high pressure is basically squeezed east as the STJ buckles and mass evacuation (I.e., air parcels being ejected from the center of the low pressure in Texas), act to strengthen the squeeze (confluence) in the Midwest.  Let’s not forget this high will be moving over some snow cover, which acts like a refrigerator.  Some models handle the intensity of such highs differently.  Regardless, all models take the high into New England and then the cold oozes southwest, hugging the entire Apps Chain all the way to western NC.  Enter the wedge.  This wedge is sourced from cold air in New England.  Wedging is reinforced (I.e., positive feedback loop) by dynamical cooling from precipitation and ageostophic adjustment due to barrier winds.  We have all those ingredients here.   Southeast winds around the low act to also serve as an “upslope” mechanism, inducing upward vertical motion and enhancing any existing synoptic-scale vertical motions.  Oof.  

Score one for the NAM here.  GFS has been very bad so far this year with wedging air masses (too warm).  It has always played catch up while the CMC and RGEM greatly (and I do mean greatly!) overdoes the cold wedge.  NAM seems to be the sweet spot (did I just type that?).  It has a 1038mb high moving into position during the day Saturday. So, the question is, how cold?  Ignoring surface temperatures for the time being, the 850mb temperatures (~5000’) stay below freezing the entire time!  The cold is REINFORCED by precipitation and 35 knot southeasterly winds above the surface.  Surface temperatures are also below freezing, as a stready wind vector from the NE funnels cool and dry cP air into the storm system, and the forecast soundings (thermal profiles) remain ALL SNOW on the GFS model.

Take a moment and examine the thermal profile I shared here for 7pm Saturday night.  Note that very deep isothermal layer (layer of equal temperature...below freezing) from the surface to 700mb.  This is a classic WNC heavy duty, paper machete, snow sounding.  And I can tell you our thermal profiles stay this way for a while.  Oof.

So, let’s review. We have 1) cold high pressure wedging down...check.  2) source of upward vertical motion (double check).  3) moisture?  Oh heck yea.  CHECK.  And this is just the southern stream wave!  The northern stream eventually comes down to reinforce the growing trough over the east coast giving us our second punch in the gut.

OK.. now here is where I lay down my personal thoughts having digested and explained it all here.  <takes off the gloves>

I want to impart a few things on you guys.  Stop looking at the snow maps.  They are assuming 10:1 ratios....and just by looking at those soundings, you can absolutely tell it won’t be 10:1 (I am thinking 7:1, based solely on experience).  You should be looking at trends in the QPF.  And you should NOT look at the QPF from the GFS - why?  Because it has been wrong by a factor of 2, and even 3, most of the fall season in western North Carolina!  (Not saying it could be right elsewhere, but for now, WNC has been missed badly by the GFS).  Here the Euro and NAM models have performed very well in this department.  And you gotta think...BIG source of tropical moisture.  Plus Atlantic moisture.  Plus vertical motion.  Plus jet dynamics.  When the dynamics are there the moisture will find a way.  We are not lacking dynamics.  Euro was around 3.00” of liquid equivalent.  NAM isn’t out this far yet.  GFS was 1.40” (multiply by a factor of 2 and you get 2.80”).  Dang!  That’s a LOT of liquid.  Thermal profiles support snow, and maybe some sleet far southern escarpment as the warm nose tries to invade (briefly).

10:1 ratio gives you 28-30” of snow.  Bwa ha ha ha.  I can’t do it.  Just can’t do it.  What did GSP say, “generational” event?  You bet.

7:1 ratio still gives 15-18” of cement snow.  Oof.  Who in their right mind feels good about issuing a forecast like that around here?  It’s unheard of.  Can it happen?  It could.  Would I go with these values at day 4 (looking at you WYFF)....no.  Why not?  Because the atmosphere is always in motion.  Things flow like saltwater taffy being pulled from two ends.

And we still have time to watch this.  BUT BUT BUT...we have been watching this since Saturday, Dec 1.  It is equally mind-boggling to me to think that the large scale pattern and such has been so incredibly consistent for so long!  The Weather Prediction Center now has the mountains 70-90% chance of a major winter storm at DAY 4!  Wow. 

The Euro has a 96% chance of 6” or more from this system.  The GEFS mean is creeping up (on QPF...more snow, less sleet/ZR as the wedge is better reflected).

Oh and start time?  BANK ON EARLIER rather than later.  I have seen this time and time again.  These systems break out precipitation along the warm fronts and into the cold dome earlier than most systems.  GFS might have this right.  Another trend to watch next 2-3 days.

Alright, enough rambling.  Hope it’s helpful.  TL;DR - get ready.  Prepare now for a big snow event with potential for prolonged power outages. This is as big a deal since December 2009.  if you live anywhere in the cold air damming favored areas of WNC (sorry Franklin), this storm has your number.

 

 

 

Great post. Thanks

Just now, BretWheatley said:

Have a feeling this is an old image... 

Yes doesn't seem right...

8 minutes ago, lilj4425 said:

GSP’s forecast map: 

VERY bullish for them. Especially for southern areas 

LEssprecip into my area looks colder and good for you CNC and WNC peeps 

Let's have some fun! We are now 3.5 to 4 days out or less from what appears to be a significant winter storm for much of NC/SC and VA. Lets see who comes closest to verifying on snowfall total amounts. There will be 15 cities total and the contest will open up at 6 p.m. tonight and close at midnight. This will help test the accuracy of 3-4 day forecasts from Euro/GFS, etc. 

Cities:

Asheville

Boone

Charlotte

Danville, VA

Durham

Hickory

Jefferson

Greensboro

GSP

Lynchburg, VA

Mt. Mitchell State Park 

Raleigh

Roanoke

Statesville

Wilkesboro

We should do a snowfall amount contest for this one. Will be interesting.

1 minute ago, CentralNC said:

Yes, obviously going to be a huge storm but everyone has to keep in mind there WILL be some aspect of the storm not modeled correctly. Cold air, timing, track, phase.   Something will throw curveballs.  I think we all have learned to cast a weary eye at the clowns.  Not trying to damper but we have seen it so often.

I can see some gulf coast convection robbing moisture with this setup but QPF doesn't look like an issue 

nice CAD signature 

Compared to this at 6 Z

on the FV3 at least the heaviest snow amounts are trending north

Site freezing for anyone else? I imagine the server is getting hit pretty hard 

1 minute ago, griteater said:

It's Miller B hybrid basically...the advantage with this storm is having the damming high out front.  We haven't had that in some recent winter storms.  So, upstate to Charlotte to Raleigh, you just hope to get smacked with the early heavy overrunning portion of the storm before the warming aloft moves in....and make no mistake about it, it will move in with this setup.  Of course, things will change on the models over the next 3 days...that's almost a certainty.

Looking a lot like the Jan 2016 storm IMO

1 minute ago, DopplerWx said:

fv3 looks very similar to the gfs at 96hr.

Low looks a little further N to me

Other than Mt Mitchell/Blue Ridge areas, Statesville/Iredell was the jackpot that run 25-27 inches lol

Still snowing some in Eastern areas but..

Best GFS run in a while for Central NC in a while. Showed lower dps, slightly stronger CAD 

1 minute ago, Blue_Ridge_Escarpment said:

GFS and it’s ensembles came south at 6Z. It’s all noise right now. 

If euro looks similar or further north at 12z it definitely is trending..

The Euro has it changing to rain Sunday evening even up here in Danville,VA and staying rain until the backside swings through Monday evening. It has 6 to 8 on the front end then rain then another 3 to 5 with the deform band/pivot. 

The typical shifts north are happening now, I expect more shifts north the next few days. Roanoke to Lexington VA is in a great spot. DC will likely get more snow than places lile Greensboro. We are losing the conflunce..

So it begins.. we really need that confluence to trend stronger over the NE or the cold air will be outta here 

Yea that was the worst run in days for Central NC, and even less snow in WNC compared to past runs

This one is going to hammer the Mid Atlantic. Must be right..

12 minutes ago, AirNelson39 said:

I’d say that’s one bad thing about having such a huge Social Media Presence with so many followers and fans. You make a bold prediction and it fails you risk angry mobs lol

Oh I get it but you would think his weather weenie would show every now and then.. He missed last January snow incredibly bad... called for 2-3 day before storm and we ended up with 6-9 area wide. 

2 minutes ago, AirNelson39 said:

Hmm, Brad P on FB Live just now said even mtns will possibly change to rain at some point?? And def foothills and piedmont

Lol he busts more than participants at the WSOP. Seriously I don't think I can ever remember him making a bold forecast. He even told me once he hates making forecasts past 2 days and usually doesnt. That's not even forecasting..