High Wind in Wyoming, February 19 to 21, 2023

Area Forecast Discussion
National Weather Service Cheyenne WY
505 AM MST Sun Feb 19 2023

.SHORT TERM...(Today through Wednesday)
Issued at 504 AM MST Sun Feb 19 2023

...WIDESPREAD HIGH WIND EVENT AND MOUNTAIN SNOWFALL BEGINS TODAY.
WINTER STORM TO IMPACT THE REGION MONDAY THROUGH WEDNESDAY...

Multiple weather threats to impact SE Wyoming beginning today and
continuing through Wednesday. The first hazard will be a
prolonged high wind event that will first impact SE Wyoming today
and persist into Tuesday. The strongest winds will be confined
across the wind prone areas, but across portions of Carbon County,
the south Laramie Range Foothills, and the I-25 corridor will see
high winds develop throughout the day today and wind gusts across
these areas could approach 75 mph. It is possible wind gusts could
exceed 80 mph across the wind prone areas multiple times during
this long duration wind event.

.HIGH WIND EVENT...With high confidence for a significant high
wind event today, all High Wind Watches were upgraded to High Wind
Warnings with the addition of the wind prones and I-80 summit.
Model parameters and in-house guidance continue to show strong
signals for a prolonged high wind event to impact much of SE
Wyoming. Winds will first increase over the wind prone areas this
morning then ramp up across Carbon County. These high winds will
gradually spread into the SE Wyoming valleys toward the afternoon.
The best window for the first surge of significant wind gusts for
this event will occur Sunday night through early Monday morning.
During this timeframe, both the 850 and 700 mb Craig to Casper
height gradients rapidly increase to +80 meters at both height
levels and max out at 88/84 meters late tonight. 700mb winds
during this timeframe are between 70-75 knots with adequate
downward omega maxima aligned along the spine of the Laramie
Range. Sustained winds at this time could be in the 40 to 50 mph
range with gusts ranging from 70 mph (valleys) to 80 mph (wind
prones/summit). High winds for the wind prone areas and I-80
summit should remain consistent with periods of high wind gusts
mixed in with periods of lighter winds.

Wind gusts could briefly drop below High Wind criteria across
Carbon County and the I-25 corridor for a few hours Monday
morning, but a an approaching strong shortwave and associated
surface frontal boundary will quickly tighten the pressure
gradient across the region and usher in a band of 60+ knot 700mb
winds. Wind gusts will quickly increase with high wind criteria
gusts expected. The second surge of stronger wind gusts with this
event should occur late Monday night into Tuesday morning. Once
again CAG-CPR gradients climb above 80 meters. In-house data shows
a 3hr window where the 850 and 700mb CAG-CPR gradients max out at
97/85 meters respectively. This last pulse of high winds will
should occur pre FROPA as the front approaches from the north.
This frontal passage will also signal the end of the high wind
event as, as the front will shift the flow aloft quickly ending
the high wind event.

.SNOWFALL...The forecast remains on track with respect to the
short term and medium range guidance. Northwest flow aloft will
persist as the shortwave moves through the region today. Light to
moderate intensity snow showers are expected to persist through
the late afternoon hours. The winter weather advisory appears to
be the best choice for a headline, despite a slight uptick in
forecast snowfall totals for the NamNest and HRRR. Visibility
reductions will also be a concern due to the strong winds today.
With the highest wind gusts up to 70-80mph in the wind prone/gap
areas, blowing snow could create near blizzard conditions in the
Sierra Madre and Snowy Range mountains. We will see a general
swath of 4-10 inches of snowfall the remainder of today in the
aforementioned mountains. Localized areas above 9500 feet could
see up to a foot of additional snowfall. The remainder of the
forecast area will remain dry, as near to above average
temperatures are forecast today. A temporary lull is expected for
the snow shower activity in the higher elevations and mountain
terrain from Sunday night into early Monday. Another shortwave
disturbance is progged to arrive by midday Monday afternoon into
midday Tuesday, bringing another round of snow activity to the
higher terrain and mountain ranges. This will be the second round
of several occurrences for snowfall accumulations for the
mountains. Have continued the snow forecast with updated QPF
totals on Monday into Tuesday. Short-term guidance has hinted at
slightly more amounts of QPF, thus have gone with a slight bump in
the overall liquid melted equivalent for snowfall to water
content. The NamNest was too aggressive with QPF, so went with a
blend of the previous forecast amounts and other high resolution
model data.

The main weather story is the winter storm that is forecast to
impact the region from late Tuesday afternoon through early Thursday
morning. The strong cold front with bitter cold temperatures is
anticipated to sweep across the region overnight Tuesday.
Temperatures will drop quickly behind this strong cold front, and
the difference between daytime highs on Tuesday afternoon, and
temperatures late Wednesday afternoon is forecast to be on the order
of potentially 40-50 degrees colder in the high plains and lower
terrain. This anomalous cold air mass will be amplified by winter
weather impacts as a Colorado surface low develops via lee-side
cyclogenesis. At this time of inspection, areas east of the Laramie
Range will see temperatures above freezing Tuesday evening thanks in
part to WAA across the area. This will likely cause a precipitation
type transitioning from light rain showers to snow showers as the
column cools adiabatically to below freezing for the wet-bulb
temperatures. This may impact overall snowfall totals as the
gradient for potential heavier snow accumulation will be sharp
across the Northern Colorado to WY/NE state line. The expectation is
that there will be a narrow timeline of warm surface temperatures
aloft as a melting layer between approximately 0Z-6Z erodes quickly
thanks to the strong cold front passage. Snow showers should spread
across the area quickly by midnight for most locations. Heavy
snowfall rates greater than 1 inch per hour may be possible in
localized areas. Confidence in the timing of snowfall and overall
snowfall totals are coming into better alignment the past 24-36
hours as model guidance samples better data closer to the onset of
the event. Have held off on any additional Winter Storm Watch
headlines for the area for now, since the event is still greater
than 48 hours away for areas not in a mountain zone west of the
Laramie Range.

Highest confidence for significant levels of snowfall accumulation
remains in the Sierra Madre and Snowy Range from Monday into the
latter portion of this week. The mountain zones will locally have 1
to 3+ inches of QPF once the main event is complete by early
Thursday morning, when including the early Monday morning onset of
additional snowfall. If we include the snowfall that occurs during
this weekend into the near-end of the extended forecast period,
localized areas above 8500 foot elevations could easily see 2 to 4
feet of snowfall. Due to this higher amount of confidence, this will
be the most likely areas to be upgraded to a new winter headline in
the coming 12-24 hours.

.LONG TERM...(Thursday through next Sunday)
Issued at 504 AM MST Sun Feb 19 2023

Arctic airmass remains in place on Thursday and temperatures will
again be well below normal across the region. Forecast uncertainty
increases considerably beyond Thursday, but most models continue
to trend in the direction of hanging a piece of the upper level
low over California and resuming moist WSW flow aloft that may
keep mountain snow going Friday. The extreme cold should moderate,
but remain below average.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 420 AM MST Sun Feb 19 2023

Areas of light -SN are observed across central Wyoming and will
approach the KRWL terminal this morning. Confidence is low for
this -SN to directly impact the terminal and reduce flight
categories so VCSH will continue to be the prevailing condition.
Across the rest of the Wyoming terminals, LLWS and strong wind
gusts will be the main aviation concerns for the valid TAF period.
Strong westerly winds will develop across the Wyoming terminals by
17z. Expect wind gusts to gust up to 50 knots with isolated higher
gusts possible. Lighter winds and VFR conditions are expected
across the Nebraska terminals.

&&

.FIRE WEATHER...
Issued at 504 AM MST Sun Feb 19 2023

No fire weather concerns will be present as continued cool and dry
conditions are expected for most locations. Recent snowfall and cool
temperatures has assisted with keeping fuels out of elevated or
critical thresholds.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...High Wind Warning from 5 PM this afternoon to 8 AM MST Tuesday
     for WYZ101-107-108-118-119.

     High Wind Warning from 2 PM this afternoon to 2 PM MST Tuesday
     for WYZ104-109-117.

     High Wind Warning from 11 AM this morning to 2 PM MST Tuesday
     for WYZ106-110-116.

     Winter Weather Advisory until 5 PM MST this afternoon for WYZ112-
     114.

     Winter Storm Watch from late tonight through late Wednesday
     night for WYZ112-114.

NE...None.
&&

SHORT TERM...BW/AW
LONG TERM...AW
AVIATION...BW
FIRE WEATHER...BW

Special Weather Statement
National Weather Service Cheyenne WY
513 AM MST Sun Feb 19 2023

WYZ110-191800-
North Snowy Range Foothills-
Including the cities of Arlington and Elk Mountain
513 AM MST Sun Feb 19 2023

Light snow showers will combine with gusty winds this morning to
create reduced visibilities. Visibility reductions to less than 1
mile are possible at times this morning as light snow showers
occur. Wind gusts in excess of 40-50mph will be possible at times
as well before strong winds overtake the region by this afternoon.

BW