December 16/17 Winter Event

[Scarlet Pimpernel]

1 minute ago, 40westwx said:

I want you all to be prepared for the greatest succession of model runs in Mid Atlantic snow storm history.. over the next 36 hours we are going to see a slow and steady shift to colder temperatures.. all of you all teetering on the brink will see you 1-3 turn in  to 2-4.. then to 6-8 and then.. the ever important 8-14.  

This shit is happening

@Jebman, is that you?? 

[WxUSAF]

For those who forecast by ensemble snow maps...just saw the 12z Eps probability of 6”+. I think MBY has been in the 50% contour on almost every run, maybe occasionally bumping up or down one contour. And today’s run? In the 60% contour. Biggest difference is the gradient has tightened which is what almost always happens as you get closer to start time. Howard county has just under 50% to over 90% across it.

[clskinsfan]

1 minute ago, Clueless said:

It’s a little early, no?  Only 3pm here.  

NAM is running now. And looks a little colder. 

[SnowGolfBro]

2 minutes ago, 40westwx said:

I want you all to be prepared for the greatest succession of model runs in Mid Atlantic snow storm history.. over the next 36 hours we are going to see a slow and steady shift to colder temperatures.. all of you all teetering on the brink will see you 1-3 turn in  to 2-4.. then to 6-8 and then.. the ever important 8-14.  

This shit is happening

I remember calling the weather hotline every 6 hours or so the 3 days leading up to the Blizzard of 96.  That was essentially the progression lol

[PhineasC]

6 minutes ago, T. August said:

You in bel air now?

I’m everywhere. I’m standing right behind you now. 

[MillvilleWx]

After about 4.5 hrs of sleep, I decided to be a human at 1230 PM CST and get up for a bit to look at models. After gleaning over the runs, here's my quick thoughts.

I mentioned overnight how I thought the NAM12km had overamp bias with the surface and had height rises too high out ahead of the s/w trough along the Atlantic coast. All the while, the GFS still had a flat bias and the storm was escaping to the east too quickly with focus on the eastern LP instead of the western tuck of the double barrel structure. The guidance is coming into alignment now with majority showing a coastal SC to mouth of Chesapeake to a coastal hug of the Delmarva before stacking near Cape May as the 5H trough axis pivots overhead and briefly closes off. Today was the day where we can officially bring the Nam Nest into picture since it's finally at range. I mentioned before the Nest is a great tool for mesoscale and short term synoptic trends as it handles the UL pattern much better than the parent with a limited overamp bias inside 36 hrs. 

One of the positives in comparing the 12z suite was there was a good deal of agreement on the placement of the SLP center at Wed 18z at the mouth of the bay, about 25-50 miles near ORF. Traditionally, this is where the western crew would benefit as it throws moisture plume would be aimed up the 81 corridor with expansion NE as we see a better low-level convergence signature towards the low center with 85H frontogenesis increasing intensity up the 95 corridor. There will be a quick shift from nothing to moderate precip for pretty much everyone and there won't be a wasted QPF time frame as dew point depressions remain within reasoning of column moistening, unlike what we see with a pure arctic airmass. 

Between 18-00z Thu is where there are some differences in guidance. The GFS has come on board with western low developing and becoming the principle SLP component of the double barrel structure, along with the rest of guidance. They all have similar SLP placement near Lewes, DE at 00z Thu, although CMC/RGEM combo is still the most progressive of the bunch with the primary SLP NE of the remainder of guidance, so I would hesitate using verbatim output on the model due to it's progressive bias. In any case, one of the issues we are seeing is the delay in closing off 85H and 7H until somewhere overhead, which leads to a persistent SE fetch off the Atlantic. This would allow for a protrusion of warmer boundary layer air to advect west of the Piedmont and shift ptype from snow at onset, to sleet/rain, especially those east of the fall line. This has been one of the reasons I was hesitant to give higher totals on prediction for the I-95 corridor until you are farther away with elevation as mixing potential was much greater within that area east of Rt15. Rt15 to I-81 has been consistently the sweet spot for this due to multiple facets of the forecast. One is of course further away from the screaming easterlies within the boundary layer, so the warm nose is limited. There's also a benefit of consistent 7H frontogen extension back to I-81 where lift can be maximized for longer periods of time, leading to a QPF max centered in a triangle from Front Royal to Hagerstown to the Pars Ridge line in NW MoCo. There's a secondary QPF max likely within the strongest, most persistent corridor of 85H frontogenesis to the east along the I-95 coastal plain, so when the low finally begins to stack and 850mb temps crash, there will likely be a secondary snow max (Albeit not as hefty as further west due to snow longevity) along and west of the frontogenic forcing. This places an area like Pars Ridge in Carroll and northern Baltimore Co at play for another tick in snow compared to the rest of the sub. The alignment and strength of the frontogenic forcing is still up in the air, but so far the consistent placement on the Euro and now NAM Nest lead me to believe we are starting to see those fine details coming into the picture. 

The strongest mid-level frontogen will lift into PA, but there is a curve back towards the NW tier of the sub as the 5H and 7H trough axis pivots and closes north of our lat. That will be when the deformation axis begins to develop and we see more SW/NE banding alignment take shape. All guidance has a bulk of the CCB into PA now due to the northern close off, so the max snow potential will reside into PA with the central PA corridor as the best spot for lolli's to 2'. I still think a general 8-14" with local to 16" is possible from Emmitsburg to Mappy with the highest totals further west. 10-16" with local to 20" is possible along the 81 corridor out into WV and SoPA from the Rt99 to US15 extension (Ala @Ellinwood map). The I-95 coastal plain will unfortunately take the brunt of this shift with lowest totals around 1-3" to the east of the corridor, but incremental increases further to the NW, especially once west of the fall line. From there, 3-6" at the beginning of the fall line, with 5-10" 20 miles after that down thru western HoCo, western MoCo, and Loudon in VA. The Catoctins are probably the odd ball in the bunch given elevation, so I would place them in the 10-16" range for this one. Precip should come to an end between 06-12z everywhere with snow lasting the longest over the northern tier of the sub. 

It sucks not being able to be back home to enjoy it, but I love forecasting and this was fun to track and look at the meteorology unfolding from afar with no skin in the game. I hope it trends a bit further SE and everyone can cash a bit more. There's still time for a small tick, but I think the markings are set right now. 

[Yeoman]

4 minutes ago, 40westwx said:

I want you all to be prepared for the greatest succession of model runs in Mid Atlantic snow storm history.. over the next 36 hours we are going to see a slow and steady shift to colder temperatures.. all of you all teetering on the brink will see you 1-3 turn in  to 2-4.. then to 6-8 and then.. the ever important 8-14.  

This shit is happening

You got some khalifa Kush in that pipe?

[baltosquid]

HRRR with its first digital snow for Baltimore for this one. Looks very cold overall. But it's also at 48 hours so... just fun for now.

[Yeoman]

1 minute ago, PhineasC said:

I’m everywhere. I’m standing right behind you now. 

Hopefully with your mask on

[deer]

6 minutes ago, 40westwx said:

I want you all to be prepared for the greatest succession of model runs in Mid Atlantic snow storm history.. over the next 36 hours we are going to see a slow and steady shift to colder temperatures.. all of you all teetering on the brink will see you 1-3 turn in  to 2-4.. then to 6-8 and then.. the ever important 8-14.  

This shit is happening

This science seems solid

[Fozz]

22 minutes ago, WxUSAF said:

NWS forecast looks a lot like 12z euro. More N-S gradient in MD due to how much snow falls after the flip back to snow. I like the NWS map although it’s maybe a little bullish on the 12-18” area size.

That’s what I was thinking as well. Simply based on climo and the most recent guidance, I’m thinking more like 6-12” (or perhaps 5-10” per MillvilleWx) for the nearby north and west Baltimore suburbs such as Cockeysville, Owings Mills, and probably also Reisterstown, with the 12”+ totals north and west of a line from Hereford to Mt Airy.
 

I think @Ellinwood’s map is a better guess.

[RickinBaltimore]

4-6 here is a win for me. If the storm nudges a bit to the S/SE I'll take the boost in totals. Either way I just don't want cold white rain. (And Mappy enjoy your big time hit!)

[Eskimo Joe]

LWX expanding the watch into the counties bordering DC.

EDIT: @H2O gets a watch

[Maestrobjwa]

7 minutes ago, baltosquid said:

HRRR with its first digital snow for Baltimore for this one. Looks very cold overall. But it's also at 48 hours so... just fun for now.

We're gonna be livin' on the age, lol I can't quite tell with all the DC/snowbelt posts here...but are lookin at 2-4" or 3-6"?

[40westwx]

10 minutes ago, Deer Whisperer said:

This science seems solid

I am using the @Jebman algorithm 

[H2O]

7 minutes ago, Eskimo Joe said:

LWX expanding the watch into the counties bordering DC.

EDIT: @H2O gets a watch

Feels like a participation trophy for being picked last on the kickball team

[clskinsfan]

NAM has first flakes in the area around 9AM. At 48 has snow for everyone north of Charlottesville. 51 is crushing west of town. But I cant see where the 850 line is for sure. 

[jaydreb]

7 minutes ago, Maestrobjwa said:

We're gonna be livin' on the age, lol I can't quite tell with all the DC/snowbelt posts here...but are lookin at 2-4" or 3-6"?

Yes, that’s the latest LWX forecast depending on where exactly you are within the beltway.  

[LeesburgWx]

Where is the LP on the NAM? Blacksburg?

[SnowGolfBro]

The winter storm watch is prudent even close in to the cities.  The models don’t have to be “wrong” for Montclair to get 6-12 inches of snow.  Add a touch more cold air and a bit more of an easy track and presto snowstorm!

[MN Transplant]

NAM comes in hot and heavy.  18z R/S line is about DCA and then it blows north by 21z.  In that period, however, there is ~0.5” precip.  The longer that the transition holds off, the better we can do on the front end.  

[mattie g]

I can't believe I'm doing this, but the NAM at 51...

1. Is definitely colder
2. Has the LP probably 70 miles south and *just* a hair west of the last few runs 

[clskinsfan]

It flips me out here even at 54. Then back to snow at 57.

[Buddy1987]

Just now, clskinsfan said:

It flips me out here even at 54. Then back to snow at 57.

I bet you 3k looks better than 12k here shortly 

[RDM]

NWS just moved the WSW boundary S &E by about one county along much of the previous cut-off from central VA up through MD

 

[osfan24]

3 minutes ago, mattie g said:

I can't believe I'm doing this, but the NAM at 51...

1. Is definitely colder
2. Has the LP probably 70 miles south and *just* a hair west of the last few runs 

Do you mean east? It looks to me like, after it jumped a bit east at 12z, it's now jumped considerably east again at 18z. It's now off of OC and not just off either. Much better. Surprised the thermals look as bad as they do.

[Eskimo Joe]

To my eyes, the NAM looks east by a decent chunk (50 miles?).

[MN Transplant]

5 minutes ago, MN Transplant said:

NAM comes in hot and heavy.  18z R/S line is about DCA and then it blows north by 21z.  In that period, however, there is ~0.5” precip.  The longer that the transition holds off, the better we can do on the front end.  

This does not hold for the 3km.  

[Buddy1987]

Just now, Eskimo Joe said:

To my eyes, the NAM looks east by a decent chunk (50 miles?).

3k at 38 has much better moisture transport or at least looks more juicy as well. I really need front end to overproduce down this way because I don’t get ccb like a lot of folks farther to my north and east 

[mattie g]

4 minutes ago, osfan24 said:

Do you mean east? It looks to me like, after it jumped a bit east at 12z, it's now jumped considerably east again at 18z. It's now off of OC and not just off either. Much better. Surprised the thermals look as bad as they do.

I was referring to where it was at 51. It does scoot east after that.

We all know the NAM is bad, especially at range, so I'm not worrying about too many details - just some generalities I noticed during a pretty important period.