487
FXUS65 KCYS 031143
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
543 AM MDT Fri May 3 2024

.KEY MESSAGES...

- A cold front will move through the region today with another
  round of shower activity in the mountains and isolated
  thunderstorms over the southern Nebraska Panhandle. Snow
  levels will remain above 6500 feet.

- Mainly dry and warmer conditions are anticipated for the weekend.

- Breezy to windy, and cooler weather expected for Monday
  through Wednesday, with isolated to scattered late day showers
  and thunderstorms.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 305 AM MDT Fri May 3 2024

Today...A progressive and positively tilted shortwave trough aloft
moves from western Wyoming this morning to central Wyoming by mid
afternoon and to eastern Wyoming by late afternoon. Its associated
fairly strong cold front moves quickly across our counties by late
afternoon with winds turning to the north and increasing. With ample
low and mid level moisture, and decent frontal lift along with
dynamic lift supported by 500-300 mb and 700-500 mb quasigeostrophic
lift, we anticipate scattered to numerous showers spreading from our
western counties this morning to our southern and eastern counties
this afternoon, along with isolated thunderstorms mainly east of I-
25. Snow will fall over the higher elevations of the Snowy and
Sierra Madre Ranges with amounts from 4 to 7 inches, however with
the snow falling during the daylight hours, there will likely be
some melting and compacting of the snow, thus no advisory issuance
seems necessary. With the strength of the cold front and the
blustery north winds, it will feel rather chilly for early May.

Tonight...Precipitation will end quickly this evening as the
shortwave trough aloft moves off to our east. Looks like a cold
overnight as surface high pressure builds southward across eastern
Wyoming and western Nebraska and skies become clear.

Saturday...Transitory shortwave ridging aloft will build overhead
and with plenty of sunshine and 700 mb temperatures near 2 Celsius,
maximum temperatures will reach the mid 50s to mid 60s, with
southeast low level winds limiting the warmup.

Saturday night...Decent moderation in temperatures will occur as
southwest flow aloft strengthens ahead of the approaching trough
aloft over the Great Basin states, inducing increasing south winds
and a thermal ridge over our counties, with low temperatures from
the mid 30s to lower 40s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 305 AM MDT Fri May 3 2024

Sunday will be the warmest day of the weekend as a shortwave ridge
axis moves just to the east ahead of a large scale upper level low
moving towards the central Rockies. 700mb temps will warm near 6-10C
with afternoon temperatures reaching the upper-60s and 70s ahead of
increasing cloud cover with the approaching upper level low. Areas
west of the Laramie Range, especially southwest Carbon Co and the
Sierra Madres will begin to see increasing moisture Sunday night
leading to accumulating snowfall above 7500 ft elevation. Based on
the upper level low track, the majority of wrap around moisture will
most likely develop farther north and east. However, lee troughing
across much of the WY Front Range will lead to increasing mslp
gradients and the potential for strong westerly winds across our
area starting Monday.

Latest NBM probabilities of 55+ mph wind gusts are quite high (>80%)
for most wind-prone areas across southeast WY with areas covered by
50% probabilities expanding outside of wind-prone locations onto
adjacent foothills and plains. Additionally, in-house guidance has
been showing high probabilities (60-80%) for high winds, however
there still remains run-to-run uncertainty with the duration and
timing of strongest winds. This should clear up as models continue
to get a better idea on the low track and evolution. Right now, the
timing for the strongest winds appears to be Monday afternoon with
700mb flow climbing over 60 kt across southeast WY and 850mb (700mb)
CAG-CPR height gradients exceed 70m (60m). Latest cluster analysis
shows ~45% of EC membership favors a slightly farther south track
that will lean towards stronger wind speeds aloft over our area.
Overall, there remains strong ensemble support for high winds early
next week with latest NAEFS and EC showing over climatological 99th
percentile 700mb winds.

This upper level low looks to stall out across the central CONUS
leaving southeast WY and western NE under a general troughing pattern
through the remainder of the week. This will lead to below average
temperatures for early May with additional chances for light
precipitation.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 536 AM MDT Fri May 3 2024

SCT-BKN mid-level clouds persist early this morning across the
region with VFR conditions as rain/snow showers approach from
the west per latest satellite and radar imagery. These showers
will likely reach KRWL over the next few hours with lowering
ceilings and visibilities through the morning. Additional shower
development is expected along a frontal boundary that will be
positioned from KLAR through KCDR by midday with gusty northerly
winds developing as the front continues to move to the south.
Cannot rule out a few rumbles of thunder near KSNY which could
see a stronger storm develop early this afternoon before the
frontal boundary clears the area. Skies will begin to clear
early this evening as precipitation continues to move off
towards the east.


&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.

&&

$$

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