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FXUS65 KCYS 220452
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1052 PM MDT Sat May 21 2022

.SHORT TERM...(This evening through Monday)
Issued at 300 PM MDT Sat May 21 2022

The main challenges of the short term forecast involve continued
near record low temperatures, followed by the possibility for
showers and some storms Sunday night into Monday.

Currently, the broad upper level trough has become entrenched over
the Rockies behind the last system. A subtle 500-mb vorticity
maximum moving down from the northwest over the eastern part of
the CWA is providing some increased lift over some very slight
instability. GOES satellite imagery shows some small cumulus
clouds bubbling up over snow-free ground cover with cloud bases
around 5-8 kft. A few have gotten deep enough to produce some
very light rain and snow showers reaching the ground, but very dry
air aloft is inhibiting significant precipitation. As the
afternoon progresses, dry mid-level air will work in and suppress
this weak convection.

Skies clear tonight with the push of drier air. With weak winds
expected, another night of strong radiative cooling will lead to
near record low temperatures once again. While tonight probably
won`t be as cold as last night, many records will be easier to
match tonight than last. For example, the forecast lows at
Cheyenne, Laramie, Rawlins, and Chadron are all below the daily
record lows for May 22nd. NBM probabilities show high
probabilities of freezing temperatures across nearly all of the
area. Thus, decided to upgrade all current Freeze Watches to
Freeze Warnings. Confidence is high everywhere except in the
lowest elevations of the North Platte river valley and near
Chadron.

Another more vigorous shortwave currently moving into the Pacific
northwest will dive across Idaho tonight. Surface pressure falls
are expected to begin near the Four Corners on Sunday and expand
southeasterly flow for locations east of the Laramie range. This
will significantly increase moisture advection and boost
precipitable water values to over 0.5" for these areas by roughly
00z Monday. Positive vorticity advection and weak isentropic
upglide ahead of the developing midlevel low will provide some
lift late Monday evening into the overnight hours leading to
development of showers. Continued cold air aloft will support some
snow showers mixing in above about 7500 ft, although accumulations
should be light and confined to the mountains. Instability is
limited, so we could see some isolated thunder but severe weather
is still not expected. The trough axis crosses our area by midday
Monday ushering in drier air aloft, but some low level wraparound
moisture remains in place with weak surface based instability,
leading to isolated to scattered showers continuing through the
afternoon on Monday.

.LONG TERM...(Monday night through Saturday)
Issued at 300 PM MDT Sat May 21 2022

Long Range models in good agreement for most of next week, showing
a continuation of the unsettled and cool weather pattern Tuesday
and Tuesday night. Models continue to be consistent with the
warming trend beginning on Wednesday and lasting through Friday of
next week.

For Tuesday, models show the next Pacific upper level trough
digging southeast into the Cowboy State. Expect another round of
rain showers through most of the day and into Tuesday evening with
ample instability during the day. Snowlevels will range between
7000 to 8500 feet so can`t rule out some snow across the high
valleys, but confidence is low at this time with limited amount of
cold air associated with the trough. Increased POP between 50 to
70 percent Tuesday afternoon with some low level convergence and
low to midlevel instability present. It should be cool enough
during the day where strong or severe thunderstorms are highly
unlikely across the area. High temperatures will struggle to reach
the low to mid 50s, with maybe highs around 60 across the lower
elevations of the western Nebraska panhandle.

As we head into the middle of the week, models all show a broad
upper level ridge axis amplifying over the western United States
and drifting east into the Front Range by Thursday. A warmer and
drier weather pattern is expected Wednesday through Friday before
the next weak cool front moves towards the region later in the
week. With most models and ensembles showing 700mb temperatures
between 10c to 15c by Friday, high temperatures in the mid 70s to
mid 80s are expected with some low 90s over western Nebraska
Friday afternoon.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1052 PM MDT Sat May 21 2022

VFR conditions possible through tomorrow afternoon before the
next round of precipitation moves from west to east across the
region. Latest HiRes guidance indicates shower and thunderstorm
activity increasing in coverage after 00z tomorrow, before moving
out of our region shortly before midnight. In addition to the
shower activity, additional concerns over the next 24 hours exist
with gusty winds, with wind gusts upwards to 25 to 30 knots and
the potential for patchy fog across the Nebraska Panhandle.
Current HiRes models have been consistent over the last few runs
bringing in some moisture in the boundary layer, clearing skies,
and light winds.

&&

.FIRE WEATHER...
Issued at 300 PM MDT Sat May 21 2022

Fire weather concerns remain low over the next several days with
cool temperatures and precipitation chances continuing through
midweek. Scattered showers and thunderstorms are possible Sunday
and Monday with continued below average temperatures and breezy
conditions developing. Drier air works in on Wednesday as a
warming trend begins. Dry weather and above normal temperatures
are expected for Thursday and Friday.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Freeze Warning until 9 AM MDT Sunday for WYZ101-102-107-108-118-
     119.

     Freeze Warning until 9 AM MDT Sunday for WYZ104>106-109>111-113-
     115>117.

NE...Freeze Warning until 9 AM MDT Sunday for NEZ002-003-019>021-054-
     055-095-096.

&&

$$

SHORT TERM...MN
LONG TERM...TJT
AVIATION...MRD
FIRE WEATHER...MN