-- Discussion containing changed information from previous version are highlighted. --
913
FXUS61 KPBZ 190200 AAA
AFDPBZ

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
900 PM EST Sat Jan 18 2025

.SYNOPSIS...
Impactful snow possible for northern West Virginia and the ridges
of southwest Pennsylvania tonight through Sunday, followed by an
extreme cold outbreak Monday through Wednesday.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
-- Changed Discussion --
KEY MESSAGES:

- A cold front completes its passage this evening
- Temperatures fall into the teens and 20s behind the front
- Snow showers possible in the ridges along and immediately
  behind the front with only minor accumulations expected.
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A cold front continues to cross SW PA and northern WV this
evening. A band of rain developed earlier this evening ahead of
the front, with a brief changeover to light snow after FROPA.
Areas across the higher terrain will stay predominantly snow,
with generally an inch of less of accumulation.

The steady precipitation is ending as the colder air moves in.
This should limit accumulation for most areas to a few tenths of
an inch or less. Temperatures will fall into the teens and lower
20s overnight in cold advection, which could cause some standing
water from the earlier rainfall to freeze. Issued a Special
Weather Statement to highlight this potential.

Snow chances will begin to increase again late tonight south of
I 70 ahead of the next approaching shortwave trough.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Snow expected Sunday and Sunday night, with the heaviest
  accumulations expected in the ridges and areas south and east
  of Pittsburgh.
- Winter Storm Warnings and Winter Weather Advisories go into
  effect for ridges and adjacent lowlands.
- Temperatures continue to fall, with wind chills eventually
  dropping below zero Sunday night.

--------------------------------------------------------------------

There has been increasing confidence in an impactful winter
system for the West Virginia ridges as another cyclone develops
and moves up the front, shoveling moisture back into the cold
sector of the low for the high terrain. The Winter Storm Warning
has been expanded to include all WV ridges in Preston, Tucker,
and eastern Monongalia counties. A Winter Weather Advisory has
been issued for adjacent lowlands in Marion and Monongalia
counties in WV, and for all of Fayette and the ridges of
Westmoreland counties in PA.

The latest model updates suggest that the low track will still
be such to impact primarily the WV ridges, where a Winter Storm
Warning remains in effect. Some minor impacts are looking more
possible in the PA ridges and lowland areas of northern WV as
well, where 13z NBM probabilities for at least 3 inches now
exceed 50% and Winter Weather Advisory has been issued. It is
important to note that even this close to the onset of snow,
there is still a rather large amount of uncertainty regarding
the high-end potential snowfall amounts, particularly for areas
south and east of Pittsburgh. Spreads between the 25th and 75th
percentiles are as much as 6 inches (8+ inches for the
10th/90th spread), making headline decisions difficult as the
floor for this event may be less than 2 inches and the ceiling
is as high as a foot in some places. Hopefully guidance narrows
in on a common solution and forecast confidence increases over
the next 12 hours, but as of now it is possible that additional
last-minute upgrades/expansions of headlines may be needed.

Upslope flow will support lingering snow showers along the
ridges through Sunday night as the colder air continues to
advect into the region and increasing snow ratios, though the
period of heaviest snow still appears to align with 12Z to 18Z
Sunday. With temperatures continuing to drop Sunday night, wind
chills are expected to dip below zero by early Monday morning.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
KEY MESSAGES:

- Arctic outbreak with dangerously cold temperatures and wind
  chills likely next week.
- There will be some warming by the end of the week.

--------------------------------------------------------------------

     EXTREME COLD MONDAY THROUGH WEDNESDAY...

Confidence has increased enough on dangerous cold with significant
impacts to issue an Extreme Cold Watch. Extremely low temperatures
and wind chill temperatures are expected to impact the region Monday
through Wednesday. Arctic air will dip down out of far northern
Canada across the eastern United States beginning Sunday night. The
cold impacts through at least Wednesday morning remain high
confidence. There is high agreement among ensemble clusters of the
500mb height and temperature trends of deep troughing across the
eastern CONUS, dipping temperatures as low as 35 degrees below
normal.

Confidence has increased that the coldest daytime high of the period
may be Monday (middle single digits to 10 degrees Fahrenheit) with
the initial intrusion of arctic air, but clear skies and the
potential for decoupling and cold air drainage overnight mean that
the coldest morning may be Tuesday and Wednesday morning.

Given the complex terrain and micro-meteorological cold air drainage
processes, low temperatures will likely be variable across the area
with the coldest pockets in sheltered valleys. Exposed ridge tops
may be a bit warmer, but also exposed to the wind. All in all, low
temperatures in the high negative single digits and low negative
teens with wind chills as low as -25F for the lowlands and -30F for
the ridges.

Forecast confidence decreases Wednesday, with GEFS dominated
ensembles showing a brief bout of shortwave rejoining bringing
temperatures up to the high 10s, while the Euro and Canadian
ensembles hold on to the cold with continued highs in the single
digits. On Thursday morning under the surface high, efficient
radiative cooling with light wind is expected to drop wind chill
temperatures close to advisory criteria, however, cloud cover will
prevent those temperatures from getting too cold. Even with the
bimodal solution, the watch extends through 15Z to account for one
mode and also the cumulative impacts of the extreme cold to this
point.

We recommend beginning to prepare for this cold conditions now.
Unprotected pipes can freeze and burst. Prolonged exposure to the
cold may lead to hypothermia. Frostbite can occur in as little as 30
minutes for exposed skin. It is encouraged to bring movable plants
indoors. Extreme care is encouraged for the protection of pets and
animals. Rescheduling any events, especially outdoor events, is
encouraged.

By the end of next week (Thursday, Friday, Saturday), there is
still high confidence that ridging builds in and warms high
temperatures into the low 30s and upper 20s with lows in the low
20s to upper 10s, which is still a hare below average.

&&

.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
A crossing cold front is driving an area of light rain ahead of
it, with precipitation possibly changing to snow before becoming
intermittent/sparse for much of the evening and overnight hours,
with precipitation overnight most likely tied to the higher
terrain. MVFR/IFR ceilings will trend towards MVFR areawide as
the front crosses and exits the region.

The next shortwave and surface low will approach from the
southwest early Sunday morning and slowly spread snow into the
region by 15z. Variance in positioning of the heaviest snow
bands remains large, which will impact snowfall rates/intensity
as well degree of restrictions. Initially on the wetter side,
the heaviest snow (with rates that could approach 1"/hr) is
favored SE of KPIT with a general axis from KMGW to KLBE (and
areas SE of that line). This is also the area where 1-2 mile
visibility is most likely for several hours, perhaps briefly
dipping below that 1 mile threshold. By the end of the TAF
period, a trend towards more showery snow will be seen, with
lake enhancement and upslope flow being the driving factors.


Outlook...
Dry, cold advection in the wake of the departing surface low
will improve restrictions through Monday morning, though
localized lake enhanced snow showers may persist.

Arctic temperatures arrive Sunday night and remain in place
through Wednesday behind this exiting system. Expect a return of
VFR conditions, but periods of gusty wind and prolonged sub-
freezing temperature that includes many hours with negative wind
chills. There is a low probability for a weak system to pass
Tuesday evening that may foster areas of light snow and cig/vis
restrictions.

&&

.CLIMATE...
A period of anomalously cold weather is expected to pass Monday
through Wednesday that will challenge many standing January
temperature records. Attached below are the standing
climatology for local sites. Pittsburgh has a full record,
while other sites are partial records and may not be fully
reflective of historical temperatures:

January 20th:         High Minimum       Low Minimum
Pittsburgh, PA         1F  (1985)        -18F (1985)
Wheeling, WV           13F (1940)        -1F  (1940)
Morgantown, WV         3F  (1985)        -17F (1985)
New Philadelphia, OH  -3F  (1994)        -22F (1994)
Zanesville, OH        -2F  (1985)        -17F (1985)
DuBois, PA            -2F  (1985)        -19F (1985)

January 21st:         High Minimum       Low Minimum
Pittsburgh, PA         5F  (1984)        -18F (1985)
Wheeling, WV           12F (2000)        -2F  (1924)
Morgantown, WV         2F  (1985)        -18F (1985)
New Philadelphia, OH  -8F  (1985)        -19F (1985)
Zanesville, OH         7F  (1985)        -22F (1984)
DuBois, PA             0F  (1985)        -22F (1985)

January 22nd:         High Minimum       Low Minimum
Pittsburgh, PA         10F (1961)        -14F (1936)
Wheeling, WV           11F (2014)        -4F  (2014)
Morgantown, WV         11F (2014)        -5F  (1984)
New Philadelphia, OH   5F  (1984)        -15F (1994)
Zanesville, OH         13F (2014)        -11F (2011)
DuBois, PA             8F  (2013)        -11F (1984)

Below is the lowest daily high and daily low temperatures of the
21st century. This encompasses all days of all months running
from January 2000 to present:

                      High Minimum       Low Minimum
Pittsburgh, PA         4F  (01/07/2014)  -10F (01/17/2009)
                                              (02/20/2015)

Wheeling, WV           5F  (01/07/2014)  -10F (01/07/2014)

Morgantown, WV         7F  (01/07/2014)  -9F  (01/28/2014)
                           (01/28/2014)       (01/29/2014)

New Philadelphia, OH   6F  (01/16/2009)  -18F (01/28/2014)
                           (01/28/2014)
                           (02/15/2015)

Zanesville, OH         6F  (01/28/2014)  -20F (01/29/2014)

DuBois, PA             0F  (01/07/2014)  -17F (02/16/2015)

In addition, Pittsburgh has not seen a daytime high below 4F
since January of 1994. Pittsburgh has also has not seen 2
consecutive days of high temperatures less than 10F since
January of 1997. If you extend this statistic to 3 days, you
would have to go back to February 1899.

The last time Pittsburgh`s minimum temperature was less than or
equal to -5F was December 2022. Last time it was below or equal
to -10F was February 2015. For 2 consecutive days of lows less
than or equal -10F, you would have to go back to January of
1994.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Extreme Cold Watch from late Sunday night through Thursday
     morning for PAZ007>009-013>016-020>022-029-031-073>078.
     Winter Weather Advisory from 1 AM Sunday to 9 AM EST Monday
     for PAZ074>076.
OH...Extreme Cold Watch from late Sunday night through Thursday
     morning for OHZ039>041-048>050-057>059-068-069.
WV...Extreme Cold Watch from late Sunday night through Thursday
     morning for WVZ001>004-012-021-509>514.
     Winter Weather Advisory from 1 AM Sunday to 9 AM EST Monday
     for WVZ021-509.
     Winter Storm Warning from 1 AM Sunday to 9 AM EST Monday for
     WVZ510>514.

&&

$$

SYNOPSIS...Cermak/WM/Milcarek
NEAR TERM...WM
SHORT TERM...Cermak/Milcarek/Shallenberger
LONG TERM...Lupo
AVIATION...Frazier/CL
CLIMATE...Milcarek