455
FXUS65 KCYS 060958
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
358 AM MDT Mon May 6 2024

.KEY MESSAGES...

- Strong winds today for southeast Wyoming and western Nebraska
  with a prolonged period of elevated winds continuing through
  midweek. Wind gusts of 70-80 mph are possible for wind-prone
  locations Monday.

- Cool and unsettled weather continues for Wednesday through
  Friday with a chance of late day showers and thunderstorms.

&&

.SHORT TERM /THROUGH TUESDAY/...
Issued at 320 AM MDT Mon May 6 2024

Latest GOES WV imagery shows a negatively tilted upper level low
approaching the western CWA border with a stream of moisture
across western and central NE under southerly flow ahead of the
trough axis. Radar imagery though the night has shown increasing
echos across Carbon and Albany Co, however the better low-level
moisture is positioned east of the Laramie Range with dew points
this morning in the upper-40s and 50s. KDWX in southwest Carbon
Co has been reporting snow with 1 SM since midnight, however
SNOTELs in the Sierra Madres has been limited with the reported
SWE so far tonight.

Winds across the NE panhandle have been gusting 35 to 45
mph most of the night with the Pine Ridge and Chadron being the
strongest. Numerous 60 mph gusts have been recorded up that way
with strong southerly flow with the nocturnal LLJ that should
continue until daybreak as the front approaches turning winds
more westerly. Remaining High Wind Warnings across the NE
panhandle have been cancelled early with the exception of Scotts
Bluff, Banner, and Kimball Co. Strong subsidence in the wake of
this passing upper level low looks to spread east into portions
of the NE panhandle late this afternoon and tonight. This could
support westerly winds gusting 50 to 60 mph. Therefore, High
Wind Warnings for these areas have been extended until Tuesday
morning.

Remaining High Wind Warnings look to be on track across much of
southeast WY. NAEFS continues to show maximum climatological
700mb winds for this unusual early May high wind event. Latest
GFS shows 700mb flow climbing around 70 to 80 kt across the
Laramie Range. Despite being on the high side of the GEFS
distribution, 25th percentile GEFS winds are still plenty for
strong winds and mountain wave activity across our region. In-
house random forest guidance continues to show a strong signal
for high winds extending outside of the wind-prone locations
today. While latest observations have not show an uptick in
winds just yet, wind directions have begun to change to more
westerly across Carbon Co as the upper level trough axis begins
to move through the CWA. Should see a quick increase in wind
gust as this system passes through this morning. Initially, will
see mountain wave activity with strong mountain top inversions
noted in forecast soundings and eventually transition to
afternoon mixing of vertical momentum with steeping low-level
lapse rates. This is when we expected winds to move off the
Laramie Range and Foothills and spread across the adjacent
plains through Monday evening.

This expected low track will bring wrap around moisture and
precipitation in east-central WY later this morning and
continuing into the afternoon. Could even see rain showers
develop over the North Laramie Range around daybreak Monday with
a few rumbles of thunder as they track off to the northeast.
Latest RAP analysis has analyzed nonzero elevated instability
across Converse and Niobrara Co. With colder air and more
widespread precipitation developing on the backside of the low,
higher elevations of the North Laramie Range could see around 6
inches of snowfall. Accumulating snowfall along with the
potential for strong winds will lead to visibility reductions in
blowing snow. Therefore, a Winter Weather Advisory has been
issued through tonight. Lower elevations will likely remain all
rain, however short range guidance like the HRRR has been
lowering snow levels in recent runs allowing ptype to switch
over to snowfall around midday. This is also reflected in the
NBM ptype probabilities as snow has jumped from 20% to 60% in
these areas. With the QPF expected, this has the potential for
notable snowfall accumulation in western Converse Co, so will
need to continue to monitor trends and observations as this
system evolves as this is not reflected in the current forecast
package.

Looking ahead to Tuesday, a strong mountain wave signature will
persist. Monday`s negatively tilted upper level low will begin
to stall out and even retrograde westward across eastern MT as
it becomes vertically stacked. Underneath this nearly
stationary low will be the passage of a secondary shortwave that
support strong winds again at least of the wind-prone locations
with occasional gusts up to 60 mph across adjacent foothills
and plains off the Laramie Range in southeast WY. Precipitation
chances will return to south- central WY with accumulating
snowfall possible for the higher terrain in the Sierra Madre and
Snowys, however this still appears to be below advisory levels.
One thing to consider will be blowing snow that could lead to
significant reductions to visibility.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Issued at 320 AM MDT Mon May 6 2024

Tuesday night/Wednesday...Another shortwave trough aloft pivots
around the primary upper trough producing scattered showers for
our forecast area, with the least coverage across far southeast
Wyoming and the southern Nebraska panhandle due to downslope
winds. Continued windy due to low level pressure gradients and
winds, with 700 mb temperatures near -2 Celsius yielding high
temperatures from the upper 40s to upper 50s.

Thursday...Continued cool with 700 mb temperatures near -4 Celsius
yielding maximum temperatures from the upper 40s to upper 50s. Low
and mid level moisture looks plentiful enough for scattered to
numerous showers and isolated thunderstorms.

Friday...Although dynamics look rather limited, it appears there
will be enough low and mid level moisture for scattered showers and
isolated thunderstorms. 700 mb temperatures rise slightly from
Thursday, thus temperatures will be slightly warmer.

Saturday...Cyclonic northwest flow aloft prevails with enough low
and mid level moisture to aid in developing isolated to widely
scattered afternoon and evening showers and thunderstorms primarily
south of a Rawlins to Scottsbluff line.

Sunday...The flow aloft becomes northerly for our forecast
area around the upper trough over the Central Plains states. The
cyclonic flow aloft will combine with adequate low and mid level
moisture to produce isolated to scattered late day showers and
thunderstorms, most numerous near the Colorado state line.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1024 PM MDT Sun May 5 2024

Winds will be the primary concern at all aviation sites over the
next 24 hours. Expect wind shear at all terminals overnight
tonight with extremely strong southwest flow aloft switching to
westerly on Monday. MVFR cigs are likely at SNY AIA and CDR
however they should not drop to IFR given dry near surface
layers. Expect mainly dry weather except for a few showers at
RWL which should not lower VIS.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 6 AM this morning to 9 PM MDT
     this evening for WYZ103.
     High Wind Warning from 8 AM this morning to 9 PM MDT Tuesday
     for WYZ103>105-107>109-115-117>119.
     High Wind Warning until 6 PM MDT Wednesday for WYZ106-110-116.
     Winter Storm Warning until 6 PM MDT this evening for WYZ112.
     Winter Weather Advisory until 6 PM MDT this evening for WYZ114.
NE...High Wind Warning until 6 AM MDT early this morning for NEZ002.
     High Wind Warning until 6 AM MDT Tuesday for NEZ019-020-054.

&&

$$

SHORT TERM...MB
LONG TERM...RUBIN
AVIATION...MAC