1/19 - The Weekend Roulette Wheel Thing

[DDweatherman]

Rgem is a little better with the rain snow line on 6z. Slightly more SE and totals not quite as outrageous, but still a big storm NW of the fall line. 

[Interstate]

I will say this. The RGEM has pretty much been locked in. 

[Ji]

Sw looks stronger on gfs thru 42

[stormtracker]

GFS better, wetter

[wxmvpete]

My heavy snow discussion tonight went into some of the model differences, the synoptic/mesoscale setup, and how the probabilistic snowfall totals and impact guidance looked as of tonight. 

...Mid Atlantic and Northeast...
Day 3...

...Confidence is increasing in a disruptive winter storm from the
Mid-Atlantic to the Northeast with locally heavy snowfall possible
along the I-95 corridor...

Model diagnostics: Over the past 24-36 hours, guidance has come
into better agreement on a deepening 500mb trough over the Ohio
Valley and higher height rises in the Atlantic south of Bermuda.
AI-based guidance (ECMWF-AIFS and GFS GraphCast) have been showing
this increasing potential over this time span while ensembles
(ECMWF-EPS, GEFS, GEPS) have all gradually trended snowier as
well. While this is the case, deterministic guidance still shows
the lingering uncertainties with the 500mb trough's amplitude and
position 12Z Sunday. The 00Z GFS is slightly deeper vs the 00Z
ECMWF. The 00Z CMC is similar to the ECMWF 500mb disturbance's
strength, but with less confluence over the Northeast, allowing
for a more storm track on the northern side of the track
distribution. The UKMET also has a similar look to the Canadian,
albeit with a colder boundary layer setup given stronger confluence
over the Northeast. Overall, the AI-based guidance and the trends
in the ensembles provide an increased confidence in a synoptic-
scale setup that is boosting confidence in a winter storm from the
Mid-Atlantic to the Northeast, but more specific details on storm
track still need to be ironed out over the next 24-36 hours.

Synoptic & mesoscale analysis: The approaching upper-level trough
Saturday night will amplify over the Ohio Valley and place a
strengthening 250-500mb layer-averaged jet streak over the Mid-
Atlantic by Sunday morning. NAEFS shows 200mb and 500mb winds over
the Southeast U.S. are above the 90th climatological percentile
and foster healthy upper level divergence aloft on Sunday. At
lower levels, a cold front Saturday night will stall out along the
Mid-Atlantic coast and into southern Virginia. The front, residing
beneath the synoptically-favorable jet stream setup, will spawn an
area of low pressure Sunday morning in the Carolinas and gradually
strengthen as it heads for the Mid-Atlantic coast Sunday
afternoon. The heaviest banding of snow is likely to reside north
of 850mb frontogenesis, which will become more and more pronounced
as the 850mb low forms somewhere along the Jersey Coast and tracks
northeast towards Long Island and the MA Capes Sunday evening. The
storm is a progressive one, but given the sufficient synoptic and
mesoscale processes, the deformation zone of heavy snow would be
more than capable of generating ~1"/hr snowfall rates, especially
for areas from the Delaware Valley on north and east through the
Tri-State area and into southern New England where they are more
likely to have better mesoscale forcing as the 850mb low deepens
Sunday night.

Timing & snowfall/impact probabilities: As mentioned before, this
is a quick hitting system that is all but gone by midday Monday as
it races toward the Canadian Maritimes by Monday afternoon. Snow
is forecast to be at its heaviest Sunday morning and afternoon for
the DC/Baltimore metros, the Philly/NYC metros Sunday afternoon
and evening, then across southern New England Sunday night into
early Monday morning. Latest WPC probabilities show moderate-to-
high chances (50-70%) for snowfall totals >4" from the Delaware
Valley on north through the Lower Hudson Valley and across southern
New England. Low-to-moderate chances (30-50%) for >4" extend as
far north and east as Downeast Maine. WPC probabilities even show
some spotty low chance probabilities (10-20%) for snowfall totals
>8" in parts of southern New England. The DC/Baltimore metro areas
sport low chance probabilities (10-30%) for >4" of snowfall at the
moment, while the Philly and NYC metros are in the moderate range
(40-60%) for >4" of snow. While exact amounts remain unclear, the
WSSI-P Minor probabilities are >60% for the full length of I-95
from DC to Boston, indicating the heightened potential for
hazardous travel conditions Sunday into Monday. WPC has initiated Key
Messages for this event and can be viewed at the bottom of this
discussion.

Mullinax

[yoda]

426am AFD from LWX 

A relative lull is expected Saturday late afternoon and evening
as the initial Arctic front pushes to the east and a wave of
surface low pressure goes with it, at least outside of the
mountains, where snow looks to continue. A second wave of low
pressure will take shape over the TN Valley, which will become
our Sunday winter storm.

Precipitation chances continue to increase on Sunday with
guidance trending towards a snowier solution areawide. At least
a light accumulating snowfall is becoming increasingly likely
across most of the forecast area as a fast-moving, yet potent,
low pressure system slides by to our south. The arctic front
Saturday will have ushered in sub-freezing air to much of the
region by the time of precipitation onset. There may be some
thermal issues towards southern MD and the VA Piedmont, but for
the most part, looks like an all snow event for many.

Initial forecast amounts are in the 1 to 3 inch range in those
areas where thermal issues may exist at the onset, with 3 to 4
inches seems most likely along and north of I-66/US-50. The
upslope areas will of course see substantially more, and over a
bit of a longer timeframe. For most, this system will be very
quick-moving, lasting around 6 to 12 hours or so.

[Ji]

Snow 7am

[stormtracker]

4-8 across the forum, except 2-4 south of Charles County

[Ji]

Mix line closer to cape…low more tucked in

[MillvilleWx]

1 minute ago, wxmvpete said:

My heavy snow discussion tonight went into some of the model differences, the synoptic/mesoscale setup, and how the probabilistic snowfall totals and impact guidance looked as of tonight. 

...Mid Atlantic and Northeast...
Day 3...

...Confidence is increasing in a disruptive winter storm from the
Mid-Atlantic to the Northeast with locally heavy snowfall possible
along the I-95 corridor...

Model diagnostics: Over the past 24-36 hours, guidance has come
into better agreement on a deepening 500mb trough over the Ohio
Valley and higher height rises in the Atlantic south of Bermuda.
AI-based guidance (ECMWF-AIFS and GFS GraphCast) have been showing
this increasing potential over this time span while ensembles
(ECMWF-EPS, GEFS, GEPS) have all gradually trended snowier as
well. While this is the case, deterministic guidance still shows
the lingering uncertainties with the 500mb trough's amplitude and
position 12Z Sunday. The 00Z GFS is slightly deeper vs the 00Z
ECMWF. The 00Z CMC is similar to the ECMWF 500mb disturbance's
strength, but with less confluence over the Northeast, allowing
for a more storm track on the northern side of the track
distribution. The UKMET also has a similar look to the Canadian,
albeit with a colder boundary layer setup given stronger confluence
over the Northeast. Overall, the AI-based guidance and the trends
in the ensembles provide an increased confidence in a synoptic-
scale setup that is boosting confidence in a winter storm from the
Mid-Atlantic to the Northeast, but more specific details on storm
track still need to be ironed out over the next 24-36 hours.

Synoptic & mesoscale analysis: The approaching upper-level trough
Saturday night will amplify over the Ohio Valley and place a
strengthening 250-500mb layer-averaged jet streak over the Mid-
Atlantic by Sunday morning. NAEFS shows 200mb and 500mb winds over
the Southeast U.S. are above the 90th climatological percentile
and foster healthy upper level divergence aloft on Sunday. At
lower levels, a cold front Saturday night will stall out along the
Mid-Atlantic coast and into southern Virginia. The front, residing
beneath the synoptically-favorable jet stream setup, will spawn an
area of low pressure Sunday morning in the Carolinas and gradually
strengthen as it heads for the Mid-Atlantic coast Sunday
afternoon. The heaviest banding of snow is likely to reside north
of 850mb frontogenesis, which will become more and more pronounced
as the 850mb low forms somewhere along the Jersey Coast and tracks
northeast towards Long Island and the MA Capes Sunday evening. The
storm is a progressive one, but given the sufficient synoptic and
mesoscale processes, the deformation zone of heavy snow would be
more than capable of generating ~1"/hr snowfall rates, especially
for areas from the Delaware Valley on north and east through the
Tri-State area and into southern New England where they are more
likely to have better mesoscale forcing as the 850mb low deepens
Sunday night.

Timing & snowfall/impact probabilities: As mentioned before, this
is a quick hitting system that is all but gone by midday Monday as
it races toward the Canadian Maritimes by Monday afternoon. Snow
is forecast to be at its heaviest Sunday morning and afternoon for
the DC/Baltimore metros, the Philly/NYC metros Sunday afternoon
and evening, then across southern New England Sunday night into
early Monday morning. Latest WPC probabilities show moderate-to-
high chances (50-70%) for snowfall totals >4" from the Delaware
Valley on north through the Lower Hudson Valley and across southern
New England. Low-to-moderate chances (30-50%) for >4" extend as
far north and east as Downeast Maine. WPC probabilities even show
some spotty low chance probabilities (10-20%) for snowfall totals
>8" in parts of southern New England. The DC/Baltimore metro areas
sport low chance probabilities (10-30%) for >4" of snowfall at the
moment, while the Philly and NYC metros are in the moderate range
(40-60%) for >4" of snow. While exact amounts remain unclear, the
WSSI-P Minor probabilities are >60% for the full length of I-95
from DC to Boston, indicating the heightened potential for
hazardous travel conditions Sunday into Monday. WPC has initiated Key
Messages for this event and can be viewed at the bottom of this
discussion.

Mullinax

Great write-up as always! Looks like we are seeing the proverbial “goal posts” among the deterministic and can assess the finer details likely either this afternoon, or by tonight. Ensemble spread is muted compared to yesterday. Looks like a beautiful day of snow and football this Sunday. Couldn’t be more stoked for that. I’ll try my best to follow what you volleyball set to me today 

[Ji]

4-8 across the forum, except 2-4 south of Charles County

Concerned about a nw trend?

[stormtracker]

1 minute ago, Ji said:

Mix line closer to cape…low more tucked in

It's a hit dude. lol..look back a page

[stormtracker]

Just now, Ji said:

Concerned about a nw trend?

I mean, with the RGEM being north/west a little?  But Euro/GFS/Ukie are where we want it...so I'm fine for now

[Ji]

I mean, with the RGEM being north/west a little?  But Euro/GFS/Ukie are where we want it...so I'm fine for now

[Ji]

6-10? lol

[yoda]

 

 

[stormtracker]

1 minute ago, Ji said:

6-10? lol

Let's not get greedy.  Still having a hard time believing we'll get about 4 where I am

[aldie 22]

2 minutes ago, Ji said:

Looks ok

[CAPE]

9 minutes ago, Ji said:

Mix line closer to cape…low more tucked in

It's not really even a mix line. Hideous dry slot. Some light precip as the low pulls north. That track isn't good for over here but more like the CMC, which has been pretty consistent.

[CAPE]

SBY gets .05" total qpf on that run lol

[Ji]

Looks ok

Sw Loudoun special

[winter_warlock]

 Most guidance is looking  good  for a 4 to 7 inch  snowstorm for alot if us!!.. 

 But if the CRAS don't  show it I'm not a beleiver!!  Lol

[mitchnick]

I don't see it posted, so here's 0z EuroAI qpf.

[mitchnick]

A bit of good news for the non-NW folks. 6z GGEM has shifted south some. Here's the link to qpf that falls as snow. Remember to multiply mm times .4 to get qpf in inches. Don't forget to move the decimal point!!!

https://meteocentre.com/numerical-weather-prediction/precipitation-accumulation.php?lang=en&map=qc&run=06&mod=cmc_gdps&hi=000&hf=120&type=SN&mode=latest&yyyy=latest&mm=latest&dd=latest&capa_verif=off

[snowfan]

7 hours ago, Ji said:

Ugh it’s slipping away

 

[mappy]

QPF totals for each model IMBY

06z GFS .3   00z Euro AI .55   06z Euro .29   00z GEM .97   06z Icon .27   06z Ukie .39   06z NAM .08

Hoping those Canadians have the right idea 

[mitchnick]

6z Euro filling in the gaps at least. 

[snowfan]

[mappy]

FWIW - NWS Blend QPF for the area 

[snowfan]