658
FXUS65 KCYS 292336
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
536 PM MDT Mon Apr 29 2024

.KEY MESSAGES...

- Increasing precipitation chances tonight into early Tuesday
  with a cold frontal passage. Accumulating snowfall possible
  for the Sierra Madre and Snowy Ranges, especially above 8000
  feet elevation.

- Strong winds likely with and behind the front across the
  Laramie Range Tuesday morning. Gusts up to 60 mph possible.
  Additionally, dry downsloping winds could result in critical
  fire weather conditions Tuesday afternoon for portions of the
  North Platte River Valley.

- Active extended forecast period with multiple rounds of rain
  and snow showers with occasional thunder possible daily
  through the rest of the week.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 233 PM MDT Mon Apr 29 2024

Latest GOES WV imagery an upper level trough over the PacNW
that will continue to move towards our CWA bringing chances for
precipitation and strong winds. Overall seeing a warm day across
southeast WY and western NE with temperatures so far reaching
the upper-50s to mid-60s east of the Laramie Range and mid-50s
farther west. However, gusty west winds and SCT to BKN cloud
cover will continue through the afternoon as the shortwave ridge
axis shifts to the east today. Hi-res guidance shows showers
beginning to increase across Carbon Co early this evening, but
will increase in coverage closer to midnight as the cold front
currently analyzed over eastern ID near the WY border begins to
move through the CWA. Most of the area will likely see ptype
remain as rainfall, however elevations above 8000 feet could see
accumulated snowfall. This will most likely be confined to the
Sierra Madre and Snowy Ranges that could see up to 6 inches
overnight. Precipitation will continue into early Tuesday
morning before quickly moving off to the east with the frontal
boundary that will be in play for potential severe thunderstorms
in eastern NE in the afternoon.

Additionally, strong winds appear likely with and immediately behind
the frontal passage Tuesday morning. Downward omega fields still
look to be strong across the Laramie Range. Westerly 700mb flow
aloft increases to 40-45 kt, but has been on a slight downward trend
over the last 24 hours with the GFS with hi-res guidance mostly
showing sub-warning level gusts. In-house guidance has also been
showing this slight downward trend in high wind probabilities and
gust estimates for wind-prone locations. NBM probabilities of
exceeding 55 mph still remains over 50% for most of the wind-prone
locations across southeast WY, especially across the Central Laramie
Range. Regardless, this bora wind setup could still lead to brief
periods of localized wind gusts near 60 mph so have decided to keep
the High Wind Warnings/Watches going across the area.

With these westerly downsloping winds, dry conditions are likely
across the adjacent foothills and plains into portions of the NE
panhandle. However, there is uncertainty on if the post-frontal
temperatures will be warm enough for a prolonged period of critical
fire weather conditions with 700mb temps changing the most across
east-central WY and the northern NE panhandle. Fire Weather Watches
remain in effect for areas near Torrington and Scottsbluff.
Temperatures Tuesday afternoon look to be 5-10F degrees cooler than
Monday, but still reaching the low-60s east of the Laramie
Range.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 233 PM MDT Mon Apr 29 2024

An active pattern in the long term with multiple disturbances
ejecting through the forecast area, resulting in near daily
chances of precipitation and near-normal temperatures. The long
term period starts with an upper-level low sweeping east across
the northern Rockies and into the Northern Plains between
Wednesday and Thursday. Due to the low being north of the
forecast area, our main impacts will likely be gusty winds and
cooler temperatures with low precipitation chances. The
mountains have the best chance at accumulating snowfall, but
rain becoming snow cannot be ruled out at lower elevations,
especially along and west of the I-25 corridor Wednesday night.
This low is quickly followed by a shortwave entering the
forecast area Friday, increasing precipitation chances once
again. Precipitation type is still somewhat uncertain, but it
will more than likely be snow in the mountains and rain at lower
elevations with possible thunderstorms in the High Plains.
Saturday finally brings a ridge of high pressure that will
increase high temperatures back to above-normal through Sunday.
The ridge will also keep conditions dry through the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 536 PM MDT Mon Apr 29 2024

A cold front moving across the region overnight will bring showers
and low clouds to terminals in the area. Most terminals will see
rain showers, however, snow could mix in to terminals west of the
Laramie Range. Visibility drops will be possible in light to
moderate rain. A brief period of IFR to MVFR CIGs will be possible
for KRWL and KLAR later tonight. This front is progressive, so
clouds will clear out by Tuesday morning. Expect windy
conditions behind the front during the day Tuesday. Wind gusts
over 40 kts will be possible.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for WYZ433.
     High Wind Warning from 6 AM to 6 PM MDT Tuesday for WYZ106-107-
     116-117.
     High Wind Warning from 3 AM to 6 PM MDT Tuesday for WYZ110.
     High Wind Watch from Tuesday morning through Tuesday afternoon
     for WYZ118.
NE...Fire Weather Watch from Tuesday afternoon through Tuesday
     evening for NEZ435-436.

&&

$$

SHORT TERM...MB
LONG TERM...LEG
AVIATION...SF