December 16/17 Winter Event

[Ji]

Euro at 00z has Leesburg below zero at surface, 925 and 850 . What gives?

[MillvilleWx]

Evening everyone. I know this storm is basically getting on everyone's last nerve in terms of tracking, so I'll keep this short and sweet. My current thoughts have not changed since my 12z post model analysis earlier this afternoon. This is a classic fall line storm with areas NW of the cities seeing incrementally more snow the further you are away from the urban corridor. Below is a copy of the Deterministic Heavy Snow and Icing Discussion from WPC. They produce these twice a day and will give you the scoop on what WPC is seeing since they ingest and dissect guidance on the daily, then collab with local offices, which then decisions in terms of Watches/Warnings/Advisories are made, as well as coordination with surrounding offices for precip totals on both QPF and snow, when applicable. Here's the discussion from this afternoon below. I cut off part of the discussion to omit the parts we don't care about.....

The NAM Nest this evening was basically my thoughts amplified with the core of 85H and 7H frontogen packing a punch on the initial thump as WAA screams north ahead of the trough, and under formidable diffluent flow will allow for a "hot and heavy" start to the precip for much of the sub-forum beginning Wednesday morning and carrying into the afternoon. The issue calls between 18z-21z as boundary layer easterlies become more aggressive and we see a lift of the R/S line to the north on the lead of the 50-60kt LLJ at 850mb. Expect cold temps at the surface to hold for much of the area north if I-70, but the I-95 corridor and low land areas below 500' will likely bump to at or above freezing for a time due to the depth of the WAA aloft mixing more efficiently to the surface, as well as physical latent heat release from precip falling through the column. Mix line will protrude west towards the Rt15 corridor, and perhaps even sneak past for a time towards the Catoctin front, but will likely hit a impass there as mountains shield the 81 corridor from the low level intrusion, which is classic for these types of setups.

By 01z Thu, guidance is consistent showing the deepest extension of the boundary layer warmth, and we begin to see the 5H and 7H troughs pivot overhead and potentially close off for a time, allowing the SLP along the Delmarva coast to become stacked and meander to the east. This will allow for a shifting dynamic from WAA to the generation of a CCB axis that will bisect much of PA into NNJ, and maybe extend down to the northern reaches of the sub-forum as shown by 7H Frontogenic progs on the 3km NAM Nest and the European. This will allow for cold air to rush in on the backside and we see a sharp response in 850mb temps and the lower boundary layer as temps go from as high as +2C to as low as -7C within just a few hrs. This is typical for a maturing deformation zone and anyone within the band will see the best ratios of the entire storm where snowfall can rack up quickly. 

Considering the mean SLP position, blend of Euro/NAM Nest/GFS 7H and 85H frontogenic forcing, the best chance for max snow will lie along the 81 corridor from the NE slopes of the BR in WV for areas like Paw Paw, up through HGR into C PA, pivoting back NE into NNJ. There's a secondary max that might be found from HGR east to Northern Baltimore Co, but the eastward extent is only if the deformation axis is a bit further east in development. More likely is HGR to Northern Carroll, but GFS keeps the door open on further eastward extent.

Here's my projected totals for snow/sleet:

East of I-95 near Baltimore: 2-4" with max to 6" if everything breaks right and boundary layer stays colder on initial WAA thump

East of I-95 near DC: 1-3" 

DCA: 1-3"

IAD: 4-8"

BWI: 2-5"

Eastern HoCo: 4-8"

Western HoCo: 6-10"

Southern MoCo: 2-5"

Northern MoCo: 4-9"

Loudon: 4-8" with local 10" in West Loudon

NoVA south of DC: T-2"

Southern Carroll: 6-10"

Northern Carroll (Westminster and north): 8-14" with local to 17"

Southern Frederick County: 6-10" 

Northern Frederick: 10-16" with local to 20"

Winchester: 10-16" with local to 18"

WV Panhandle: 10-16" with local to 18"

Southern Harford County: 5-10"

Northern Harford County: 7-12"

Southern Baltimore County: 3-7"

Northern Baltimore County: 6-12" with local to 15"

Southern PA from Chambersburg to Gettysburg: 12-18" with local to 22"

Gettysburg to York: 11-17" with local to 20"

Bullseye: Northern York County to Harrisburg to Eastern PA Coal Country: 16-24" with local to 28"

Ji's House: -7" (I'm gonna pay @leesburg 04 to steal his snow)

 

[thunderman]

[Cobalt]

the Euro was wayyy better with the rates of the WAA there. That's where I-95 and immediate points West get most of the snow there. Wondering if that'll be a prominent trend but that snowfall is more believable than the snow it was giving us on wraparound 

[psuhoffman]

@Ji trends. It was significantly worse then 18z. The bleeding hasn’t stopped. I’d like to see a suite of guidance where we’re not must grasping at things like “well that wasn’t as much worse as I feared”. 

[jayyy]

11 minutes ago, Cobalt said:

the Euro was wayyy better with the rates of the WAA there. That's where I-95 and immediate points West get most of the snow there. Wondering if that'll be a prominent trend but that snowfall is more believable than the snow it was giving us on wraparound 

100% Always bet on WAA snows from a Miller A over wraparound snows. If the CAD is even slightly underdone (very likely), we may see an area wide 3-6” before we even have to worry about the mix line. I think Baltimore sees 4-8” despite mixing issues at the height because of the initial dump.... unless the overall trend continues through  tomorrow 

[clskinsfan]

Pretty big drop in qpf this run. Still a great storm. I'm not complaining. And it is much more realistic now. Still feel good about my 8-12 from Harrisonburg to Front Royal. And 12-18 from Front Royal to Hagerstown. But I hope we don't see a trend in lower qpf throughout the day tomorrow. Good night all.

[psuhoffman]

4 minutes ago, clskinsfan said:

Pretty big drop in qpf this run. Still a great storm. I'm not complaining. And it is much more realistic now. Still feel good about my 8-12 from Harrisonburg to Front Royal. And 12-18 from Front Royal to Hagerstown. But I hope we don't see a trend in lower qpf throughout the day tomorrow. Good night all.

The QPF is lower because it tracks the storm up over CAPEs house and into southern NJ. That pushes the best forcing further NW towards state college PA. That’s the perfect track for them to get crushed but it’s getting inside where we can expect to get big totals. 

[jayyy]

14 minutes ago, clskinsfan said:

Pretty big drop in qpf this run. Still a great storm. I'm not complaining. And it is much more realistic now. Still feel good about my 8-12 from Harrisonburg to Front Royal. And 12-18 from Front Royal to Hagerstown. But I hope we don't see a trend in lower qpf throughout the day tomorrow. Good night all.

Don’t worry, 6z will do it’s usual QPF dump and put out 30”clown maps  

 

Night sir. 

[Cobalt]

25 minutes ago, Cobalt said:

the Euro was wayyy better with the rates of the WAA there. That's where I-95 and immediate points West get most of the snow there. Wondering if that'll be a prominent trend but that snowfall is more believable than the snow it was giving us on wraparound 

Can't tell if I'm seeing things but yeah the initial WAA looks way beefier

Through 0z (when DC and immediate NW changes over)

 

vs 18z at that exact time

Obviously grasping at straws, and it doesn't matter if that extra snow is washed away from a low that tracks up the bay, but I thought this was somewhat interesting to see so I thought I'd share. 

 

[Ruin]

So did they throw out that 40 inch nammer for south central PA?

[Mordecai]

06z 12k NAM

[Ruin]

what is that like a inch of frz rain 

 

[MillvilleWx]

NAM Nest came in super aggressive with the 850mb easterlies on the 06z run. That was actually wicked and reminded me a bit of March 2017 unfortunately. The scene will be seriously wintry across the northern half of the sub with 4-8" of snow, followed 1-2" of sleet and some ZR mixed prior to changing back to snow at the end. I was expecting some mixing as I mentioned in my forecast, but blasting out to the I-81 corridor is beyond my expectations. I hope it doesn't turn out like that. I can see LWX cutting totals back for part of the region because even I thought they might be too aggressive in spots, but damn. 7H fronto is stout, but it slings up into PA and never wraps back. That was disheartening to see. This is when the NAM Nest is going to have more weight added to forecasting too, especially the mesoscale. I'm sticking with my current forecast for now, but even I might have to trim if I see more aggressive 85H easterlies. 

[yoda]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
409 AM EST Tue Dec 15 2020

MDZ003>006-501-502-507-VAZ028-030-031-WVZ050>053-055-503-504-
152145-
/O.UPG.KLWX.WS.A.0002.201216T1200Z-201217T0900Z/
/O.NEW.KLWX.WS.W.0003.201216T1200Z-201217T0900Z/
Washington-Frederick MD-Carroll-Northern Baltimore-
Extreme Western Allegany-Central and Eastern Allegany-
Northwest Harford-Frederick VA-Warren-Clarke-Hampshire-Morgan-
Berkeley-Jefferson-Hardy-Western Mineral-Eastern Mineral-
409 AM EST Tue Dec 15 2020

...WINTER STORM WARNING IN EFFECT FROM 7 AM WEDNESDAY TO 4 AM EST
THURSDAY...

* WHAT...Heavy snow expected. Total snow accumulations of 12 to
  18 inches.

* WHERE...Portions of northern and western Maryland, northwest
  Virginia and eastern West Virginia.

* WHEN...From 7 AM Wednesday to 4 AM EST Thursday. Snow will
  overspread the region Wednesday morning, become heavy at times
  during the afternoon and evening, taper off late Wednesday
  night.

* IMPACTS...Travel will be very difficult to impossible.
  Potential impacts include significant travel delays and
  closures. Plan ahead to minimize impact on you and your family.

[yoda]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
409 AM EST Tue Dec 15 2020

MDZ001-VAZ026-027-029-040-501-505-507-WVZ501-502-505-506-152145-
/O.UPG.KLWX.WS.A.0002.201216T1200Z-201217T0900Z/
/O.NEW.KLWX.WS.W.0003.201216T1200Z-201217T0900Z/
Garrett-Rockingham-Shenandoah-Page-Rappahannock-Northern Fauquier-
Western Loudoun-Northern Virginia Blue Ridge-Western Grant-
Eastern Grant-Western Pendleton-Eastern Pendleton-
409 AM EST Tue Dec 15 2020

...WINTER STORM WARNING IN EFFECT FROM 7 AM WEDNESDAY TO 4 AM EST
THURSDAY...

* WHAT...Heavy snow expected. Total snow accumulations of 8 to
  12 inches.

* WHERE...Portions of western Maryland, northern and western
  Virginia and eastern West Virginia.

* WHEN...From 7 AM Wednesday to 4 AM EST Thursday. Snow will
  overspread the region Wednesday morning, become heavy at times
  during the afternoon and evening, taper off late Wednesday
  night.

* IMPACTS...Travel will be very difficult to impossible.
  Potential impacts include significant travel delays and
  closures. Plan ahead to minimize impact on you and your family.

[yoda]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
409 AM EST Tue Dec 15 2020

MDZ008-011-503-505-506-508-VAZ506-152145-
/O.CON.KLWX.WS.A.0002.201216T1200Z-201217T0900Z/
Cecil-Southern Baltimore-Northwest Montgomery-Northwest Howard-
Central and Southeast Howard-Southeast Harford-Eastern Loudoun-
409 AM EST Tue Dec 15 2020

...WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY MORNING
THROUGH LATE WEDNESDAY NIGHT...

* WHAT...Heavy mixed precipitation possible. Total snow
  accumulations of 4 to 8 inches and ice accumulations of around
  one tenth of an inch possible. Winds could gust as high as 35
  mph.

* WHERE...Portions of central, northeast and northern Maryland
  and northern Virginia.

* WHEN...From Wednesday morning through late Wednesday night. Snow
  will overspread the region Wednesday morning, mix with sleet and
  freezing rain during the afternoon and evening, then change back
  to snow before ending late Wednesday night.

* IMPACTS...Travel could be very difficult to impossible.
  Potential impacts include significant travel delays and
  closures. Plan ahead to minimize impact on you and your family.

[yoda]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Baltimore MD/Washington DC
409 AM EST Tue Dec 15 2020

MDZ504-VAZ036>039-050>053-502-152145-
/O.CON.KLWX.WS.A.0002.201216T1200Z-201217T0900Z/
Central and Southeast Montgomery-Nelson-Albemarle-Greene-Madison-
Orange-Culpeper-Prince William/Manassas/Manassas Park-Fairfax-
Southern Fauquier-
409 AM EST Tue Dec 15 2020

...WINTER STORM WATCH REMAINS IN EFFECT FROM WEDNESDAY MORNING
THROUGH LATE WEDNESDAY NIGHT...

* WHAT...Heavy mixed precipitation possible. Total snow
  accumulations of 3 to 7 inches and ice accumulations of around
  two tenths of an inch possible.

* WHERE...Portions of central Maryland and central, northern and
  northwest Virginia.

* WHEN...From Wednesday morning through late Wednesday night. Snow
  will overspread the region Wednesday morning, mix with sleet and
  freezing rain during the afternoon and evening, then change back
  to snow before ending late Wednesday night.

* IMPACTS...Travel could be very difficult. Potential impacts
  include significant travel delays and closures. Plan ahead to
  minimize impact on you and your family.

[Ruin]

is the latest run a good one or a bad one?

[midatlanticweather]

6 minutes ago, Ruin said:

is the latest run a good one or a bad one?

Every 6z I am looking at look worse 

[yoda]

URGENT - WINTER WEATHER MESSAGE
National Weather Service Wakefield VA
452 AM EST Tue Dec 15 2020

VAZ048-509-151800-
/O.NEW.KAKQ.WW.Y.0003.201216T0900Z-201217T0500Z/
Fluvanna-Western Louisa-
Including the cities of Bybee, Central Plains, Cunningham,
Lake Monticello, Nahor, Palmyra, Troy, and Louisa
452 AM EST Tue Dec 15 2020

...WINTER WEATHER ADVISORY IN EFFECT FROM 4 AM WEDNESDAY TO
MIDNIGHT EST WEDNESDAY NIGHT...

* WHAT...Mixed precipitation expected. Total snow accumulations of
  up to two inches and ice accumulations of up to one tenth of an
  inch.

* WHERE...Fluvanna and Western Louisa Counties.

* WHEN...From 4 AM Wednesday to midnight EST Wednesday night.

* IMPACTS...Plan on slippery road conditions. The hazardous
  conditions could impact the morning or evening commute.

[BristowWx]

11 minutes ago, midatlanticweather said:

Every 6z I am looking at look worse 

I am starting to rethink my first flakes hopes after seeing 6z.  Might go straight from rain to rain

[Siberian-Snowcover-Myth]

33 minutes ago, Ruin said:

is the latest run a good one or a bad one?

 

[jayyy]

8-12 for Baltimore in NWS’s newest map - doesn’t line up with its own WSW. Seems silly

[MillvilleWx]

1 minute ago, jayyy said:

8-12 for Baltimore in NWS’s newest map - doesn’t line up with its own WSW. Seems silly

I'm a little perplexed at that too actually. 

[midatlanticweather]

2 minutes ago, jayyy said:

8-12 for Baltimore in NWS’s newest map - doesn’t line up with its own WSW. Seems silly

Everything east of the Blue Ridge I would cut in half of the lowest number for Virginia. An dc 

[MillvilleWx]

Heavy Snow and Icing Disco from WPC

[jayyy]

3 minutes ago, MillvilleWx said:

I'm a little perplexed at that too actually. 

It’s plausible if you believe the 12k nam’s thermals... tough model to hug however. Gotta see something big change today for me to believe this map comes to fruition.  

[clueless]

It’s almost showtime. Let’s keep this to model discussion only.  If you want to complain do it in banter. 

[MillvilleWx]

1 minute ago, jayyy said:

It’s plausible if you believe the 12k nam’s thermals... tough model to hug however. Gotta see something big change today for me to believe this map comes to fruition.  

Reading the WPC Heavy Snow and Icing Disco and then seeing that map was a little interesting. Maybe they are gonna see what the 12z runs come up with since the 00z north shift was so sudden compared to the last set of runs. I mean, we went front prime fronto over southern PA and the northern tier to central and northern PA. They still have time to adjust totals since the storm is over 24 hrs out