Heavy Snow in Oklahoma, December 2 to 3, 2020

Area Forecast Discussion
National Weather Service Norman OK
1052 PM CST Tue Dec 1 2020

...New AVIATION...

.SHORT TERM...
(This evening through Wednesday night)
Issued at 305 PM CST Tue Dec 1 2020

Big weather story (and challenge) will be the storm system set to
impact the area as early as tomorrow morning and continuing
potentially into Thursday morning. Main forecast challenges are
determining where the deformation band sets up and also the low-
level thermal profile across the I-35 corridor by tomorrow
afternoon and evening.

The models have trended towards a stronger, slower, and slightly
further south system compared to where they were at yesterday. Just
taking a look at the synoptic pattern, the models depict the 500 mb
low center to track roughly near or along I-40, with the 700 and
850 mb low centers tracking somewhere across central and southern
Oklahoma respectively. With the deformation band historically
setting up to the to the north and west of the 700 mb track, this
would place it somewhere across west-central, central, into
northern Oklahoma. Models generally agree with this, with higher
QPF totals now shown into central and west-central Oklahoma.
Storm-total QPF is now expected to be greater than 0.5" across
much of central/west-central/northern Oklahoma.

The big question will be what is the low-level thermal-profile
within the deformation band, especially across central Oklahoma. The
global models (namely the ECM/GFS) show warmer air advecting in
from the south ahead of the system, keeping the profile warm
enough for just rain across much of central Oklahoma, including
the OKC metro. Meanwhile, the higher-res models show a quicker
northerly wind shift which allows the low-level profile to cool
quicker. Heavy precipitation rates will also be required to help
dynamically cool the near-surface temperatures enough for a switch
to snow for most areas outside northwest Oklahoma. Leaned closer
to the hi-res guidance as it typically outperforms the coarser
resolution global models in these scenarios, but a lot of
uncertainty exists with a tight temperature gradient likely
setting up near the I-35 corridor during the afternoon.

Putting all of this together leads to the rain-snow line likely
starting out about a county or two north/west of the I-44/I-35
corridors tomorrow morning. Precipitation rates will become heavier
by the afternoon and the low-level thermal profile will cool
allowing the transition zone to shift slowly eastward with time. By
tomorrow evening the profile will likely cool enough for snow into
the OKC metro but by this time models suggest deeper saturation will
likely be waning. However, there is at least some potential for a
few hour period of a moderate to heavy wet snow in the OKC metro
if temperatures can cool quickly enough by late afternoon/early
evening before the deformation band begins weakening later in the
evening. Snow totals are expected to be in the 4-8" range across
northwest into west-central Oklahoma where temperatures will be
coldest, tapering to a trace to up to two inches along and west of the
I-44/I-35 corridor, highest across north-central Oklahoma.
Potential exists for a small corridor of greater than 8" totals
across northwestern Oklahoma, depending on how long the heavier
precipitation band lingers into Wednesday evening, but uncertainty
precludes the explicit inclusion of this in the forecast at this
time. Given such marginal temperatures, accumulation will mostly
be on grassy and elevated surface outside periods of heavier
snowfall. A Winter Storm Warning was issued for the areas with
greatest confidence of seeing greater than 4" amounts
(northwestern/west-central Oklahoma), with a Winter Weather
Advisory issued for areas bordering the warning with the greatest
confidence of seeing 1-3" totals. Additional counties may be
needed to be added to the advisory along the south and/or eastern
fringe once greater confidence exists regarding temperatures.

Ware

&&

.LONG TERM...
(Thursday through next Monday)
Issued at 305 PM CST Tue Dec 1 2020

With most of the focus on the short term period, left the model
blend mostly as is for the long term. Light snow may linger
across northern Oklahoma into Thursday morning before shutting off
during the afternoon. Expect a cool but dry day elsewhere on
Thursday as the system exits and clouds clear from west to east.
The rest of the extended looks fairly quiet with our area
generally within dry northerly flow, caught between a large trough
over the eastern US and a cutoff low stalled well to our
southwest. Temperatures will moderate to near average by the
weekend into early next week.

Ware

&&

.AVIATION...
(06Z TAFS)
Issued at 1050 PM CST Tue Dec 1 2020

Expect to see VFR conditions lower into MVFR around 12Z and then
IFR by mid-morning with precip developing across much of the
area. Snow across the west with mainly rain farther east and
south. This will remain predominate conditions through much of the
forecast with some translation of snow into the I-35 corridor
Wednesday evening and overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK  37  39  32  39 /  10  70  40  10
Hobart OK         33  38  30  41 /  10  50  20  10
Wichita Falls TX  37  41  31  45 /  10  30  10  10
Gage OK           31  33  26  37 /  20  60  50  10
Ponca City OK     33  40  31  39 /  10  80  70  20
Durant OK         40  47  33  47 /  20  70  20  10

&&

.OUN WATCHES/WARNINGS/ADVISORIES...
OK...Winter Storm Warning from noon Wednesday to noon CST Thursday
     for OKZ004>007-009>012-014>017.

     Winter Weather Advisory from noon Wednesday to noon CST Thursday
     for OKZ018-022>024.

TX...None.
&&

SHORT TERM...08
LONG TERM....08
AVIATION...30

Hazardous Weather Outlook...UPDATED
National Weather Service Norman OK
1023 PM CST Tue Dec 1 2020

OKZ004>048-050>052-TXZ083>090-030430-
Harper-Woods-Alfalfa-Grant-Kay-Ellis-Woodward-Major-Garfield-
Noble-Roger Mills-Dewey-Custer-Blaine-Kingfisher-Logan-Payne-
Beckham-Washita-Caddo-Canadian-Oklahoma-Lincoln-Grady-McClain-
Cleveland-Pottawatomie-Seminole-Hughes-Harmon-Greer-Kiowa-Jackson-
Tillman-Comanche-Stephens-Garvin-Murray-Pontotoc-Coal-Cotton-
Jefferson-Carter-Johnston-Atoka-Love-Marshall-Bryan-Hardeman-
Foard-Wilbarger-Wichita-Knox-Baylor-Archer-Clay-
1023 PM CST Tue Dec 1 2020

This hazardous weather outlook is for portions of northern...
western...central...and southern Oklahoma...and western north
Texas.

.DAY ONE...Through tonight...

No hazardous weather is expected.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday...

.Winter Storm...
Periods of heavy snow are expected to begin across western parts
of Oklahoma after daybreak on Wednesday, then spread eastward and
northward through the day and Wednesday night. A majority of the
snow accumulations will be seen north of Interstate 40 and west of
Interstate 35. Hazardous travel conditions will be likely across
portions of northern and western Oklahoma, particularly Wednesday
afternoon and night. The highest snow totals are currently
expected across northwest Oklahoma, around the Alva, Woodward,
Fairview, and Camargo areas, where between five and ten inches
could be common.

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