537
FXUS65 KCYS 081959
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1259 PM MST Fri Nov 8 2024

.KEY MESSAGES...

- Light to moderate snow will affect southeast Wyoming and the
  far southwest NE panhandle this afternoon through Saturday.
  The greatest impacts will be tonight after dark into Saturday
  morning where some snow may stick to highways and local
  roadways.

- An occasionally windy and mostly dry period will occur for
  Sunday through Friday, with near normal temperatures for
  Sunday through Wednesday, and above normal temperatures for
  Thursday and Friday.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 1242 PM MST Fri Nov 8 2024

An early-season winter storm remains ongoing this afternoon over
southeast Wyoming and western Nebraska. A plume of subtropical
moisture tied to an upper-level low-pressure system over the
southwestern CONUS is providing some of the necessary
ingredients for light to moderate snow today. While surface
temperatures remain rather mild and snow levels hovering
near/slightly above the surface the farther east you go in
Wyoming into western NE, forecast guidance suggests a more
favorable dynamic setup developing over the high plains over the
next several hours into the evening/overnight period. This can
already be seen in the numerous convective plumes of
precipitation developing over the central and southern high
plains and translating north-northwestward through the KS/CO
high plains. Short-term high-resolution guidance has steadily
fallen into line showing good ensemble agreement in a period of
moderate to possibly heavy precipitation over southwest Nebraska
into southeast Wyoming generally toward/just after sunset
tonight. Despite meager boundary layer temperatures, if the
higher-end snow rates can be realized at this time, it is
possible for the current snow forecast to run on the lower-end
of the possible outcomes. This has been reflected in a general
increase in snow totals of around 1-2 inches along the Advisory
area. The biggest question mark will along the eastern fringes
of the current snow forecast where greater snow rates and
boundary layer cooling may lead to quite a bit more snow than
expected. However, if the current dry-slot and lower snow rates
remain, the current forecast will remain on track. The other
tricky spot in the forecast will be along the I-80 summit in the
south Laramie range. Cooler temperatures may end up increasing
snow ratios this evening and overnight, resulting in slightly
higher snow totals than what is currently shown. Have opted to
keep the current Winter Weather Advisory in effect given the
downturn in radar trends this afternoon. However, once again if
higher snow rates/better dynamics can be realized overnight, a
Winter Storm Warning upgrade may be needed in the I-80 Laramie
Range summit location.

The developing surface low pressure system over the high plains
should slowly lift northeastward during the morning and
afternoon hours on Saturday. PoP chances have been increased
with additional QPF farther west in this forecast package for
the southeast Wyoming/western NE area on Saturday given the
latest westward shift in guidance. It will be a cold and
blustery day on the west side of this storm system as surface
flow generally turns more northwesterly by the afternoon and
lingering light snow comes to an end. Overall, forecast
confidence is fairly high with this storm system. The main
questions remain snow rates this evening and tonight - if
heavier precipitation can develop expect higher snow totals in
the Sidney-Kimball area as well as along the I-80 summit. If
precipitation remains light, totals will run near our current
official forecast if not slightly less.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 1242 PM MST Fri Nov 8 2024

Saturday night/Sunday...As the pesky upper low moves further to the
east of our counties Saturday night, the flow aloft will back from
northerly to westerly with a developing surface lee trough. On
Sunday, a progressive and low amplitude shortwave trough aloft
passes overhead, with strengthening surface and low level gradients
as seen on our local wind models, which indicate a decent chance for
high winds to possibly develop for our Wyoming wind prone locations
and possibly even for other nearby locations. The downslope chinook
winds will aid in a warming trend with maximums in the mid to upper
40s west of I-25, and 50s to lower 60s east of I-25.

Monday...The fast moving zonal flow aloft continues with decent
surface lee troughing, helping to produce another breezy to windy
day. Continued mild with 700 mb temperatures near 4 Celsius.

Tuesday...As a broad low amplitude trough aloft develops, the low
and mid level gradients strengthen significantly, possibly
portending another high wind event for our Wyoming wind prone
locations, as also seen on our high wind models. Temperatures will
be slightly cooler for most locations.

Wednesday...Colder temperatures develop in the wake of a cold
frontal passage and with northwest flow aloft developing. With 700
mb temperatures near -2 Celsius, maximum temperatures will only be
in the upper 30s to lower 40s west of I-25, and upper 40s to mid 50s
east of I-25. Continued breezy to windy based on the projected low
and mid level gradients.

Thursday...Heights aloft rise slightly at 500 mb with the flow aloft
backing to more westerly, inducing another surface lee trough
development, and with 700 mb temperatures rising to near 4 Celsius,
highs will warm to the upper 40s to mid 50s west of I-25, with upper
50s to lower 60s east of I-25. Continued breezy to windy based on
the low and mid level gradients.

Friday...As another shortwave trough aloft moves into the Great
Basin states, our flow aloft turns west southwest with 500 mb
heights falling about 100 meters, thus slightly cooler temperatures
expected with low and mid level gradients suggesting another windy
day, especially for our Wyoming wind prone locations such as
Arlington, Bordeaux, Vedauwoo and the I-80 Summit.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1042 AM MST Fri Nov 8 2024

Latest radar loop was showing the snowfall mostly in northern
Colorado, but there have some bands of snow that have been
crossing the I-80 corridor at times. These bands of snow have
reduced the visibility to near a mile or less at times and
reduced the ceilings to the MVFR category. This trend should
continue during the next two to three hours with more widespread
and heavier snowfall moving into the higher elevations above
5kft agl after 22Z. This includes areas between KIBM and KLAR.
LIFR ceilings and vsby are likely this evening and overnight.
Meanwhile, the lower elevations will experience mostly rain with
better visibility, but the ceilings will still most likely be in
the IFR category. KLAR may actually get shadowed by this event
due to northeast flow through much of the day into the evening.
The wind is expected to switch to the north at KLAR after 09Z
which may reduce the visibility and lower ceilings.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 11 AM MST Saturday for
     WYZ116>119.
NE...Winter Weather Advisory until 11 AM MST Saturday for NEZ054.

&&

$$

SHORT TERM...MAC
LONG TERM...RUBIN
AVIATION...REC