12/14: Sunday funday? Will the south win again?

[yoda]

5 minutes ago, Eskimo Joe said:

Sterling alluded to a "low end warning event" in their late morning AFD update.

For the Alleghenies 

As the wave amplifies, most models show a jet steak developing
downstream, with an enhanced band of precipitation developing
in the equatorward entrance region of the jet streak. While
there`s still some uncertainty with respect to exactly where
this band winds up, most solutions have this enhanced band of
precipitation developing along the I-95 corridor Saturday
night. This could result in a relative minimum in precipitation
between the Blue Ridge and the Alleghenies, with higher totals
along the I-95 corridor (where the best synoptic forcing will
be) and in the Alleghenies (where there will be some additional
upslope snow as the system departs).

With such a narrow banded feature, there`s still a fair amount
of uncertainty with respect to how much precipitation will
ultimately fall. Precipitation could also potentially start as a
brief period of rain along the I-95 corridor before much colder
air rushes in later during the night behind an Arctic front. For
these reasons, a wide variety of potential solutions exists,
especially along the I-95 corridor. Further west, a high end-
advisory or low-end warning level snowfall appears likely.
Between the Allegheny Front and Blue Ridge lesser QPF amounts
are likely with all precipitation likely falling as snow. Most
solutions show a coating to two inches of snow in this area, but
as much as 4 inches could be possible in a high end scenario in
the Shenadoah Valley. Further east, around the I-95 corridor,
the widest range of potential solutions exists. If most of the
precipitation were to fall as rain, or the band of higher QPF
were to shift northward out of the area, as little as a coating
to an inch of snow could occur. Currently, we have 1-4 inches of
snow forecast as the most likely scenario to the east of the
Blue Ridge. In a high end scenario, as much as 6 inches of snow
could occur under the heaviest part of the band if the
precipitation stays all snow.

Aside from the threat for snow early in the day, winds will pick
up substantially behind this arctic front by Sunday afternoon.
Expect wind gusts out of the northwest up to 30 mph, with gusts
closer to 45 mph on the ridgetops out west. Wind headlines
cannot be ruled out for the ridges during this timeframe as a
result.

[Weather Will]

WB 18Z HRRR

[CAPE]

AFD from Mount Holly. Some weenie terminology in there lol

-Confidence continues to increase that a snow event that will impact the region Saturday night into Sunday morning. A clipper system will ride along the base of a closed upper low, moving across the Ohio River Valley during the day Saturday and into the Mid Atlantic states Saturday night before moving offshore Sunday. As this clipper system arrives across the region, the closed upper low will begin to reopen as an amplified trough, providing baroclinic forcing that will assist in the strengthening of a weak clipper system into more of a broad offshore low. As it strengthens, guidance shows a zone of strengthening 700-850mb frontogenesis (FGEN) developing across the southern half of the region as snow begins Saturday night into Sunday morning. Forecast soundings plentiful cold air through the column that is well saturated aloft with plentiful moisture within the dendritic growth region. All of this would point to a zone of potentially some increased snowfall intensity for a time early Sunday morning with snowfall rates potentially as high as 1" per hour at times. There still remains some potential on the southern fringe of the precipitation shield that the precipitation starts as some light rain or a mix of rain/snow before changing to all snow. Lows Saturday night will fall squarely into the 20s, supporting this all-snow event. The model consensus puts the axis of the maximum precipitation amounts very close to the I-95 corridor, favoring areas just south and east. Overall, a widespread 2-4 inches of snow are expected across the Highlands from northern NJ into southeastern PA, the I-95 corridor, and across the coastal plain into the central Delmarva Peninsula and the rest of southern NJ, including the Jersey Shore. Given the increasing potential for mesoscale FGEN snow bands, there is a potential for a concentrated are of 4-5 inches of snowfall somewhere near the I-95 corridor and immediately south and east with up to 20-30% chance for for a handful of reports over 5 inches in that specific area. At this time, we have issued a Winter Weather Advisory for much of the forecast area.

[bncho]

18z NAM won't cut it for DC

Edit: Another dumb post. Don't listen to me ever.

[TSSN+]

3 minutes ago, bncho said:

12z NAM won't cut it for DC

Shows like 2” for dc but sure lol

[bncho]

Just now, TSSN+ said:

Shows like 2” for dc but sure lol

LOL I was extrapolating it at hour 39

[T. August]

So close yet so far… 12k smokes south Jersey. 5-6”

[bncho]

[NorthArlington101]

Just now, bncho said:

That’s still okay. Now the 3k… no thanks lol. 

[baltosquid]

3k NAM is rougher with the rain-snow changeover and just takes longer to get going, especially for SW.

[Solution Man]

We sucking out here in the 66 corridor of NOVA

[Maestrobjwa]

5 minutes ago, bncho said:

LOL I was extrapolating it at hour 39

You might wanna avoid that kind of pbp posting--because if you're not sure you can kinda fall on your face, lol

[stormtracker]

11 minutes ago, bncho said:

18z NAM won't cut it for DC

Edit: Another dumb post. Don't listen to me ever.

sigh

[bncho]

pretend like I was talking about the 3k NAM

[TSSN+]

15 minutes ago, bncho said:

18z NAM won't cut it for DC

Edit: Another dumb post. Don't listen to me ever.

I don’t 

[bncho]

1 minute ago, TSSN+ said:

I don’t 

that's a very good decision 

[aldie 22]

I bet $5 this thing starts as rain 

[Paleocene]

1 minute ago, aldie 22 said:

I bet $5 this thing starts as rain 

rain in georgetown

[yoda]

Kinda late from LWX for their afternoon AFD

[Terpeast]

Just now, yoda said:

Kinda late from LWX for their afternoon AFD

Tough call for them. Take a little extra time to think it through 

[yoda]

1 minute ago, Terpeast said:

Tough call for them. Take a little extra time to think it through 

I'm figuring they would wait till after the 00z suite before issuing anything tbh

[NorthArlington101]

RGEM holds 

[yoda]

Its not heavy snow... but a good 6 to 8 hours of snow across most of the region on the 18z RGEM 

[yoda]

We all take

 

[yoda]

@NorthArlington101 do you have the closeup version?  This is the closest PW gets

 

[NorthArlington101]

Just now, yoda said:

@NorthArlington101 do you have the closeup version?  This is the closest PW gets

 

WxBell crawls for GEM maps so not yet. 
 

AFD is out btw - holding on advisories. I’ll let you copy paste 

[Imgoinhungry]

We all take

 

Make this come true, you must. In my best yoda voice.


.

[yoda]

Appalachians, precipitation will struggle to make progress to
the east of the Allegheny Front for several hours. As the wave
amplifies and approaches from the west, most models show a jet
steak developing downstream, with forcing for ascent increasing
within the equatorward entrance of the jet streak. Most
solutions show the jet entrance region lining up right along
I-95. Ascent within the jet entrance region may cause
precipitation to jump eastward and develop in-situ along the
I-95 corridor, largely skipping locations between the Allegheny
Front and Blue Ridge.

Precipitation within the jet entrance region to the east of the
Blue Ridge is expected to blossom during the mid-late evening
hours, and then slowly drift southeastward through the remainder
of the night. The precipitation may begin as a brief period of
rain or mixed rain and snow, especially along and southeast of the
I-95 corridor. This mix should be short-lived however, as much
colder air rushes in behind an Arctic front that will move
through over the course of the night. In terms of timing, some
light precipitation could begin as early as the mid-late evening
hours, but the bulk of the precipitation along the I-95
corridor is expected to occur between roughly 11 PM and 7 AM.

The band that will develop will be a relatively narrow feature,
and will feature moderate to heavy snow at times. Snowfall rates
within the band could near or potentially briefly exceed one
inch per hour at times late Saturday night. With a narrow
feature producing heavy precipitation, snow totals will be
heavily dependent on the ultimate placement of this band. This,
combined with the potential for a bit of mixing with rain at
onset makes for a challenging snowfall forecast.

Probabilistically speaking, 12z guidance has focused in on the
I-95 corridor from DC northeastward, and then eastward along
US-50 toward the Chesapeake, with northeast Maryland southward
toward Annapolis having the greatest probabilities for higher
totals. As of this moment, a broad 1-4 inches from the vicinity
of the I-95 corridor eastward appears like the most likely
scenario, with embedded maxes of 4-7 inches possible where the
band resides for the longest time period. Since there will be
very sharp snowfall gradients on the edges of this band, and
there`s still a bit of uncertainty with respect to where this
band will be, we`ve decided to hold off on issuing headlines to
the east of the Blue Ridge for the time being. Headlines will
almost certainly be needed eventually, and we`ll continue to
assess trends and refine the forecast through the remainder of
the day. Snow will end from northwest to southeast a few hours
either side of daybreak, with the back edge of the snow clearing
southern Maryland by around mid-morning.

Strong cold air advection is expected behind the Arctic front
through the day Sunday, with 850 hPa temperatures crashing to
around -15 to -20 C by peak heating. This will cause
temperatures to drop through the 20s over the course of the day.
Northwesterly wind gusts to around 35 mph will make it feel even
colder, pushing wind chills into the single digits and teens.
After the snow moves out, dry conditions are expected to the
east of the mountains. Upslope snow showers will linger in the
Alleghenies over the course of the day. Cold and windy
conditions will continue through Sunday night, with cold weather
headlines likely being needed for portions of the area.

&&

[Interstate]

It just gets started a little too late... just like most of our transfers 

[Eskimo Joe]

8 minutes ago, yoda said:

Appalachians, precipitation will struggle to make progress to
the east of the Allegheny Front for several hours. As the wave
amplifies and approaches from the west, most models show a jet
steak developing downstream, with forcing for ascent increasing
within the equatorward entrance of the jet streak. Most
solutions show the jet entrance region lining up right along
I-95. Ascent within the jet entrance region may cause
precipitation to jump eastward and develop in-situ along the
I-95 corridor, largely skipping locations between the Allegheny
Front and Blue Ridge.

Precipitation within the jet entrance region to the east of the
Blue Ridge is expected to blossom during the mid-late evening
hours, and then slowly drift southeastward through the remainder
of the night. The precipitation may begin as a brief period of
rain or mixed rain and snow, especially along and southeast of the
I-95 corridor. This mix should be short-lived however, as much
colder air rushes in behind an Arctic front that will move
through over the course of the night. In terms of timing, some
light precipitation could begin as early as the mid-late evening
hours, but the bulk of the precipitation along the I-95
corridor is expected to occur between roughly 11 PM and 7 AM.

The band that will develop will be a relatively narrow feature,
and will feature moderate to heavy snow at times. Snowfall rates
within the band could near or potentially briefly exceed one
inch per hour at times late Saturday night. With a narrow
feature producing heavy precipitation, snow totals will be
heavily dependent on the ultimate placement of this band. This,
combined with the potential for a bit of mixing with rain at
onset makes for a challenging snowfall forecast.

Probabilistically speaking, 12z guidance has focused in on the
I-95 corridor from DC northeastward, and then eastward along
US-50 toward the Chesapeake, with northeast Maryland southward
toward Annapolis having the greatest probabilities for higher
totals. As of this moment, a broad 1-4 inches from the vicinity
of the I-95 corridor eastward appears like the most likely
scenario, with embedded maxes of 4-7 inches possible where the
band resides for the longest time period. Since there will be
very sharp snowfall gradients on the edges of this band, and
there`s still a bit of uncertainty with respect to where this
band will be, we`ve decided to hold off on issuing headlines to
the east of the Blue Ridge for the time being. Headlines will
almost certainly be needed eventually, and we`ll continue to
assess trends and refine the forecast through the remainder of
the day. Snow will end from northwest to southeast a few hours
either side of daybreak, with the back edge of the snow clearing
southern Maryland by around mid-morning.

Strong cold air advection is expected behind the Arctic front
through the day Sunday, with 850 hPa temperatures crashing to
around -15 to -20 C by peak heating. This will cause
temperatures to drop through the 20s over the course of the day.
Northwesterly wind gusts to around 35 mph will make it feel even
colder, pushing wind chills into the single digits and teens.
After the snow moves out, dry conditions are expected to the
east of the mountains. Upslope snow showers will linger in the
Alleghenies over the course of the day. Cold and windy
conditions will continue through Sunday night, with cold weather
headlines likely being needed for portions of the area.

&&

The LWX AFD effectively highlights the strong dynamics at work. It would not surprise me to see someone between Baltimore and Philly/S Jersey get half a foot of snow from this.