High Wind in Wyoming, February 18 to 19, 2021

Area Forecast Discussion
National Weather Service Cheyenne WY
426 PM MST Thu Feb 18 2021

.SHORT TERM...(Today through Friday night)
Issued at 316 AM MST Thu Feb 18 2021

A few light snow showers remain along the Colorado-Wyoming border,
along and just east of the I-25 corridor this morning. Should see
these snow showers tapper off in the next hour or two. Went ahead
and cancelled the Winter Headlines along the I-80 corridor between
Cheyenne and Laramie with the snow showers largely over. However,
behind the passing shortwave, areas of low clouds and fog, dense
at times, have developed across the central and southern
Panhandle, and along I-80 between Cheyenne and areas west to
Rawlins. A few areas are flirting with Dense Fog Advisory
thresholds, sop will monitor further development should the
headline need to be issued. Even still, model guidance indicates
that fog should diminish by midmorning.

The active weather continues in the short-term with many
forecasting challenges as southeast Wyoming and the western
Nebraska Panhandle sit under the influence of a northwesterly flow
aloft behind the exiting shortwave. Today will generally be quiet,
with some clearing, until this afternoon, as surface gradients
tighten along the Laramie Range and to the north of the Snowy
Mountains; this feature will combine with a 700-800 mb 60 kt jet,
strong subsidence and steep lapse rates for a strong wind event
for southeast Wyoming's wind-prone corridors with gusts to 70 mph,
while also brining widespread gusty winds to the remainder of the
region through Friday afternoon. Additionally, a mountain-top
inversion will then allow for a mountain wave break, Friday
morning through afternoon, expanding the area of High Winds to the
lee-side of the Snowy and Laramie Ranges. This is effect the
cities of Cheyenne, Laramie and Wheatland, especially Friday mid-
day with gusts to 60 mph. High Wind Warnings are in place for the
effected areas.

Gusty winds region-wide could cause nuisance driving conditions
this afternoon through Friday afternoon due to blowing and
drifting snow with a light surface snowpack still in place across
the High Plains and adjacent High Terrain. Blowing and drifting
snow will especially be an issue along the I-80 corridor between
Rawlins and Laramie, where additional light snowfall is expected
overnight tonight and tomorrow. Snow should be light, so don't
anticipate near-blizzard conditions, though that areas has a
propensity to overachieve so will have to keep an eye on the
area. Also expect isolated light snow showers along the I-80
corridor along and east of the Laramie Range under the
northwesterly flow.

Winds and hazardous conditions will tapper Friday night as upper
level winds become zonal ahead of the next trough.

.LONG TERM...(Saturday through Wednesday)
Issued at 316 AM MST Thu Feb 18 2021

Shortwave ridging will be...short-lived early Saturday as most
guidance is pretty set on a trough over the Great Basin approaching
our area delaying our warmup an few more days. This fairly
progressive system will bring chance for snowfall across much
portions of the CWA Saturday afternoon and evening. Moist upslope
flow will support most snow to fall in the Sierra Madre and Snowy
Ranges, while adjacent plains could see upwards of an inch or two.
Latest NBM guidance suggests QPF interquartile range of 0.08" to
0.32" for this event in the Sierra Madres with 15 to 17:1 ratios
likely. Currently, this is on the low end of Advisory criteria for
the mountains, but still may warrant headlines in the coming days.
Other area of concern will be the North Snowy Range Foothills as the
front passes through shifting wind directions more northwesterly
providing more upslope flow for the Arlington/Elk Mountain area
along Interstate 80. Hazardous travel conditions are a possibility
Saturday night for those traveling between Laramie and Rawlins.

Sunday looks to be slightly cooler with the cold frontal passage
with highs mostly in the upper-20s and 30s, but the warm up begins
Monday along with the return of strong winds. Highs will reach the
mid-40s Monday and Tuesday, possibly even reach 50 in the southern
Nebraska Panhandle as 700mb temperatures climb to around -5C to 0C.
With these warmer temperatures, also returns stronger winds.
Pressure gradients along the Laramie Range look to tighten back up
as 700mb CAG-CPR height gradients rise to 65-70m around midnight
Monday and continue through early Tuesday as the area remains in the
right exit of a 250mb jet. Local guidance is favoring high wind
potential at this time, but will need to continue to monitor these
trends heading into the weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 421 PM MST Thu Feb 18 2021

Wyoming TAFS...VFR, with occasional IFR at Rawlins until 04Z.
Wind gusts to 30 knots at Rawlins until 13Z Friday, then gusts to
42 knots. Wind gusts to 26 knots at Laramie and Cheyenne until
03Z, then gusts to 40 knots after 15Z Friday.

Nebraska TAFS...VFR.

&&

.FIRE WEATHER...
Issued at 316 AM MST Thu Feb 18 2021

Cold temperatures and light snowfall will continue a period of
low fire concerns. Temperatures will rise back up to
near normal this weekend and slightly above normal early next
week with strong winds over southeast Wyoming.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 5 AM Friday to 5 AM MST Sunday for
     WYZ112-114.

     High Wind Warning until 5 PM MST Friday for WYZ106-110-116-117.

     Winter Weather Advisory until 5 PM MST Friday for WYZ110.

     High Wind Warning from 9 AM to 5 PM MST Friday for WYZ107-115-
     118.

NE...None.
&&

SHORT TERM...AB
LONG TERM...MB
AVIATION...RUBIN
FIRE WEATHER...AB

Hazardous Weather Outlook
National Weather Service Cheyenne WY
507 AM MST Thu Feb 18 2021

WYZ106-107-110-115>118-191215-
Central Laramie Range and Southwest Platte County-
East Platte County-North Snowy Range Foothills-Laramie Valley-
South Laramie Range-South Laramie Range Foothills-
Central Laramie County-
507 AM MST Thu Feb 18 2021

This hazardous weather outlook is for portions of south central
Wyoming and southeast Wyoming.

.DAY ONE...TODAY AND TONIGHT

Foggy conditions this morning will lift by mid-morning. Strong
winds begin this afternoon across the wind-prone corridors of
southeast Wyoming, mainly impacting high-profile vehicles.
Winds will cause blowing and drifting snow, leading to slick road
conditions.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Snow showers overnight and tomorrow will lead to reduced
visibilities, less than a mile at times, generally west of the
I-25 corridor. High Winds continue for the wind-prone areas of
southeast Wyoming; wind gusts to 60 mph will spill into the
Laramie Valley and the High Plains Friday morning through
afternoon. Blowing and drifting snow impacts will continue, as
well as blowover risk. Next wind event begins Sunday.

.Spotter information statement...

Spotter activation will not be necessary.

NEZ002-003-019>021-054-055-095-096-WYZ101>105-108-109-111>114-119-
191215-
Dawes-Box Butte-Scotts Bluff County-Banner County-Morrill-
Kimball County-Cheyenne-North Sioux-South Sioux-
Converse County Lower Elevations-Niobrara County-
North Laramie Range-Ferris/Seminoe/Shirley Mountains-
Shirley Basin-Goshen County-Central Carbon County-
Southwest Carbon County-Sierra Madre Range-
Upper North Platte River Basin-Snowy Range-East Laramie County-
507 AM MST Thu Feb 18 2021

This hazardous weather outlook is for portions of panhandle
Nebraska...western Nebraska...east central Wyoming...south
central Wyoming and southeast Wyoming.

.DAY ONE...TODAY AND TONIGHT

Foggy conditions, dense at times, will lift by mid-morning. Winds
will cause blowing and drifting snow west of the I-25 corridor,
leading to slick road conditions.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

Winds will cause blowing and drifting snow region-wide, leading
to slick road conditions Friday. Warming expected this weekend and
next week.

.Spotter information statement...

Spotter activation will not be necessary.