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2/22-23 "There's no way..." Storm Part 2

Maestrobjwa

By Maestrobjwa,
in Mid Atlantic

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stormtracker
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MillvilleWx
MillvilleWx

Thanks man. I put a lot of effort into that one. A lot to go over. I’m hoping everything materializes and we all get some solid fun from this one. 

stormtracker
stormtracker

Couple of things: My pbp is shitty, but goddamn yall are fucking it up in here. Got to Houston to the airbnb and let me tell you...it's in a crack infested run down ass trenches ghetto.  Hey

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IronTy

IronTy

Posted
Posted

Question for mets and model gurus.  When data gets fed into a model (i.e., GFS), I understand in the satellite era how it's pretty easy to get temp data and precip/humidity.   But how do they capture atmospheric dynamics like the various vortices?  Clearly just utilizing weather station data and weather balloons wouldn't be near a high enough resolution to initialize a model accurately.  Do they do something fancy with satellites and refraction to measure Eddy currents in the atmosphere?  

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arlwx12

arlwx12

Posted
Posted

Snip of the 434 LWX AFD... 

Forecast details: Precipitation is expected to break out from
west to east across the region late tonight into early tomorrow
morning as large scale ascent ahead of the approaching upper
trough gradually overspreads the area. Precipitation should
begin as a mixture of light rain and snow for most, with all
snow above around 1500 feet. Surface temperatures will initially
be in the mid to upper 30s at lower elevations, and should hold
in the mid 30s through mid-afternoon. As a result, much of the
region will experience several hours of mixed rain and snow that
won`t accumulate and will largely be unimpactful other than
making the roads wet. However, snow will accumulate across the
higher elevations above 1500 feet throughout the day.

As we move into the late afternoon and evening, a combination of
factors will enable temperatures to start to fall. First, we will
start to lose solar insolation as the sun angle drops and the
sun eventually sets. Second, low-level cold advection will
increase as the upper trough approaches from the west and the
coastal low intensifies offshore, drawing colder air into the
region within northerly flow. Finally, increasing large scale
lift ahead of the upper trough and to northwest of the
developing coastal will act to dynamically cool the column. This
will result in a gradual changeover to all snow from higher to
lower elevations through the late afternoon and evening hours as
temperatures fall from the middle to lower 30s.

The heaviest precipitation locally is expected Sunday evening
through the first half of Sunday night as the coastal low tracks
off the Delmarva and the upper axis trough moves overhead. Two
locally enhanced areas of precipitation are expected within a
much broader precipitation shield that will encompass most of
the forecast area.

The first area of enhanced snowfall rates will be close to
Chesapeake Bay, where mid- level frontogenetic forcing to
northwest of the coastal low will be strongest. There is a bit
of uncertainty about how just far west this area of heavier snow
gets, but most solutions show it only impacting the counties
immediately adjacent to Chesapeake Bay in our forecast area (St.
Mary`s northward through Cecil). Snowfall rates could approach
an inch per hour at times in this area between roughly 6 PM and
2 AM.

The second area of enhanced snowfall rates will be along an
inverted trough axis (sometimes referred to as a Norlun trough)
that will extend north to south through north-central portions
of the forecast area. Dynamically, this will occur along a low-
level trough axis (in the 900-700 hPa layer) where northeasterly
winds in response to the developing coastal low offshore
converge with northwesterly winds advancing beneath the upper
trough. Model guidance is in very good agreement that such a
feature will occur, but there is still some uncertainty with
respect to the positioning. Such features typically are very,
very narrow in width (likely only 10-20 miles from west to
east), and are notorious for producing very heavy snowfall
rates. Most guidance shows hourly QPF values of around 0.1-0.2
inches, which would translate to 1-2 inches per hour of snow.
This feature will likely be either stationary or very slow
moving over several hours tomorrow evening into early tomorrow
night. A narrow band of 6-12 inches could occur as a result. Due
to position uncertainty, we spread this enhancement in
precipitation out over a slightly wider location than will
likely occur in reality. American model guidance (GFS, NAM,
HRRR, 3 km NAM, WRF-ARW, FV3, WRF-NSSL) have this feature
occurring roughly from Hancock, MD southward through Winchester
toward Front Royal, while most other guidance (Euro, Canadian,
ICON, most EPS members) have it occurring from near Hagerstown
southward into Loudoun County. Our current forecast hedges the
placement slightly more toward the eastern solution (Hagerstown
to Loudoun County), but has an enhancement over that broader
region. This is also why the Winter Storm Warning extends
southward and wraps around the DC Metro area.

The immediate DC Metro will likely fall within a relative min
between these two areas of precipitation enhancement, but will
still experience several hours of accumulating snow tomorrow
evening into tomorrow night. Another localized minimum will be
between the inverted trough and the Allegheny Front. Very little
in the way of snow may end up falling in the shadow of the
mountains just to the east of the Allegheny Front and also in
the Central Shenandoah Valley.

Across the entire forecast area, snow totals will be heavily
elevation and snow rate dependent. With such marginal
temperatures in place, a lot of the snow will be lost to melting
at lower elevations with surface temperatures above freezing,
while higher elevations have lower temperatures and accumulate
more efficiently. The aforementioned heavier snowfall rate areas
(closer to the low and near the inverted trough) will help to
drive dynamic cooling through strong lifting in the column,
thereby bringing cooler temperatures down to lower elevations,
and making snowfall accumulate more efficiently.

In terms of specific accumulation amounts, a general 2-4 inches
is expected in the DC Metro, although there could be locally
lower totals at the lowest elevations if warmer temperatures
and lighter precipitation rates verify. 4-6 inches is expected
along the Bay shore from St. Mary`s northward through Baltimore
City, with higher totals of 6-12" from Carroll eastward toward
Cecil. Higher totals of 8-16 inches are expected in the
Catoctins, where snow will accumulate more efficiently
throughout the event. Snow will also accumulate efficiently
southward along the Blue Ridge, where a general 6-10 inches of
snow is expected. To the west of the Blue Ridge, snow totals
will be heavily elevation dependent, with 3-6 inches expected at
higher elevations between the Allegheny Front and Blue Ridge,
while lower elevations in the Central Shenandoah Valley and
Potomac Highlands see little in the way of accumulation. A
general 1-3 inches is expected at lower elevations along the
I-70 corridor to the west of the Blue Ridge, with the exception
of near Hagerstown, where they could receive significantly more
snow under the inverted trough. For now, that inverted trough
area which extends southward from near Hagerstown into Frederick
and Loudoun is forecast to receive around 3-6", but as
mentioned before, the gradient will likely be tighter than
depicted, and the max there will likely be between 6 and 12
inches. In the Alleghenies Winter Storm Warnings are in effect.
Snow will linger much longer there through the day Monday within
upslope flow behind the departing low. Snowfall accumulations
there are expected to reach 6-12 inches by Monday evening.
Elsewhere, snow should wind down late tomorrow night through
mid-morning Monday.
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Chris78

Chris78

Posted
Posted
4 minutes ago, arlwx12 said:

Snip of the 434 LWX AFD... 

Forecast details: Precipitation is expected to break out from
west to east across the region late tonight into early tomorrow
morning as large scale ascent ahead of the approaching upper
trough gradually overspreads the area. Precipitation should
begin as a mixture of light rain and snow for most, with all
snow above around 1500 feet. Surface temperatures will initially
be in the mid to upper 30s at lower elevations, and should hold
in the mid 30s through mid-afternoon. As a result, much of the
region will experience several hours of mixed rain and snow that
won`t accumulate and will largely be unimpactful other than
making the roads wet. However, snow will accumulate across the
higher elevations above 1500 feet throughout the day.

As we move into the late afternoon and evening, a combination of
factors will enable temperatures to start to fall. First, we will
start to lose solar insolation as the sun angle drops and the
sun eventually sets. Second, low-level cold advection will
increase as the upper trough approaches from the west and the
coastal low intensifies offshore, drawing colder air into the
region within northerly flow. Finally, increasing large scale
lift ahead of the upper trough and to northwest of the
developing coastal will act to dynamically cool the column. This
will result in a gradual changeover to all snow from higher to
lower elevations through the late afternoon and evening hours as
temperatures fall from the middle to lower 30s.

The heaviest precipitation locally is expected Sunday evening
through the first half of Sunday night as the coastal low tracks
off the Delmarva and the upper axis trough moves overhead. Two
locally enhanced areas of precipitation are expected within a
much broader precipitation shield that will encompass most of
the forecast area.

The first area of enhanced snowfall rates will be close to
Chesapeake Bay, where mid- level frontogenetic forcing to
northwest of the coastal low will be strongest. There is a bit
of uncertainty about how just far west this area of heavier snow
gets, but most solutions show it only impacting the counties
immediately adjacent to Chesapeake Bay in our forecast area (St.
Mary`s northward through Cecil). Snowfall rates could approach
an inch per hour at times in this area between roughly 6 PM and
2 AM.

The second area of enhanced snowfall rates will be along an
inverted trough axis (sometimes referred to as a Norlun trough)
that will extend north to south through north-central portions
of the forecast area. Dynamically, this will occur along a low-
level trough axis (in the 900-700 hPa layer) where northeasterly
winds in response to the developing coastal low offshore
converge with northwesterly winds advancing beneath the upper
trough. Model guidance is in very good agreement that such a
feature will occur, but there is still some uncertainty with
respect to the positioning. Such features typically are very,
very narrow in width (likely only 10-20 miles from west to
east), and are notorious for producing very heavy snowfall
rates. Most guidance shows hourly QPF values of around 0.1-0.2
inches, which would translate to 1-2 inches per hour of snow.
This feature will likely be either stationary or very slow
moving over several hours tomorrow evening into early tomorrow
night. A narrow band of 6-12 inches could occur as a result. Due
to position uncertainty, we spread this enhancement in
precipitation out over a slightly wider location than will
likely occur in reality. American model guidance (GFS, NAM,
HRRR, 3 km NAM, WRF-ARW, FV3, WRF-NSSL) have this feature
occurring roughly from Hancock, MD southward through Winchester
toward Front Royal, while most other guidance (Euro, Canadian,
ICON, most EPS members) have it occurring from near Hagerstown
southward into Loudoun County. Our current forecast hedges the
placement slightly more toward the eastern solution (Hagerstown
to Loudoun County), but has an enhancement over that broader
region. This is also why the Winter Storm Warning extends
southward and wraps around the DC Metro area.

The immediate DC Metro will likely fall within a relative min
between these two areas of precipitation enhancement, but will
still experience several hours of accumulating snow tomorrow
evening into tomorrow night. Another localized minimum will be
between the inverted trough and the Allegheny Front. Very little
in the way of snow may end up falling in the shadow of the
mountains just to the east of the Allegheny Front and also in
the Central Shenandoah Valley.

Across the entire forecast area, snow totals will be heavily
elevation and snow rate dependent. With such marginal
temperatures in place, a lot of the snow will be lost to melting
at lower elevations with surface temperatures above freezing,
while higher elevations have lower temperatures and accumulate
more efficiently. The aforementioned heavier snowfall rate areas
(closer to the low and near the inverted trough) will help to
drive dynamic cooling through strong lifting in the column,
thereby bringing cooler temperatures down to lower elevations,
and making snowfall accumulate more efficiently.

In terms of specific accumulation amounts, a general 2-4 inches
is expected in the DC Metro, although there could be locally
lower totals at the lowest elevations if warmer temperatures
and lighter precipitation rates verify. 4-6 inches is expected
along the Bay shore from St. Mary`s northward through Baltimore
City, with higher totals of 6-12" from Carroll eastward toward
Cecil. Higher totals of 8-16 inches are expected in the
Catoctins, where snow will accumulate more efficiently
throughout the event. Snow will also accumulate efficiently
southward along the Blue Ridge, where a general 6-10 inches of
snow is expected. To the west of the Blue Ridge, snow totals
will be heavily elevation dependent, with 3-6 inches expected at
higher elevations between the Allegheny Front and Blue Ridge,
while lower elevations in the Central Shenandoah Valley and
Potomac Highlands see little in the way of accumulation. A
general 1-3 inches is expected at lower elevations along the
I-70 corridor to the west of the Blue Ridge, with the exception
of near Hagerstown, where they could receive significantly more
snow under the inverted trough. For now, that inverted trough
area which extends southward from near Hagerstown into Frederick
and Loudoun is forecast to receive around 3-6", but as
mentioned before, the gradient will likely be tighter than
depicted, and the max there will likely be between 6 and 12
inches. In the Alleghenies Winter Storm Warnings are in effect.
Snow will linger much longer there through the day Monday within
upslope flow behind the departing low. Snowfall accumulations
there are expected to reach 6-12 inches by Monday evening.
Elsewhere, snow should wind down late tomorrow night through
mid-morning Monday.

Wow. What a headache for @MillvilleWx

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LeesburgWx

LeesburgWx

Posted
Posted
2 minutes ago, clskinsfan said:

GFS is an absolute beatdown out here. Every single model has us getting the inverted trough goods now. Looks amazing. 

NWS write up is leaning more east from Hagerstown to Loudoun. Hoping we both can get some goods

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clskinsfan

clskinsfan

Posted
Posted
Just now, LeesburgWx said:

NWS write up is leaning more east from Hagerstown to Loudoun. Hoping we both can get some goods

Even if it sets up put here, which is what the models are showing, it will swing through there as well on the way out. I feel a lot better about all of us getting at least 5 inches now. 

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