717
FXUS65 KCYS 012105
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
305 PM MDT Mon Jul 1 2024

.KEY MESSAGES...

- Strong to severe thunderstorms possible this afternoon and
  evening...mainly across the northern Nebraska Panhandle into
  Converse and Niobrara Counties in east central Wyoming.
  Thunderstorms will generally end by 6pm.

- Much drier air and warmer temperatures expected Tuesday into
  Wednesday when we could see critical fire weather conditions
  for some areas along and west of the Laramie Range.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 258 PM MDT Mon Jul 1 2024

Ongoing showers and thunderstorms will generally diminish in
intensity this evening as they move east toward more stable air in
the central NE panhandle given strong capping remaining in stable
cloud cover. Farther west, a broad trough axis will continue slowly
lumbering eastward through the northern Rockies. This feature and
associated weak lift/elevated instability will keep isolated
showers and possibly a few rumbles of thunder going overnight,
especially over the higher terrain and higher basins of southeast
Wyoming. The trough axis finally will pass east of southeast Wyoming
and Western Nebraska by mid-morning on Tuesday. Have opted to keep
low-chance PoPs in the forecast through Tuesday morning to cover the
threat given by this trough and any lingering instability aloft. By
18z Tuesday, dry westerly flow will overspread most of the CWA with
temperatures running near to slightly below seasonal averages on
Tuesday afternoon. The one exception will be in northern Converse
and Niobrara counties, possibly into Sioux and Dawes county NE where
colder air aloft over top of surface heating in the wake of the
trough will be enough to force a few afternoon showers in a post-
frontal regime. Cloud cover will generally clear in the southern
half of the CWA, with areas along and north of US26 remaining partly
to mostly cloudy through the day. By Tuesday night into Wednesday
morning, heights will steadily rise with zonal flow moving in over
the high plains. Expect a mainly clear night with dry air in place
on Tuesday night, leading to temperatures running around 5 degrees
below average, possibly even cooler in the southeast Wyoming
mountains. Forecast confidence is generally high throughout the
short-term with only minor adjustments done to PoP and QPF grids in
this forecast package.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Issued at 258 PM MDT Mon Jul 1 2024

Thursday... Deterministic and ensemble model guidance agree on the
next upper-level trough and associated jet digging into southeast
Wyoming by Thursday morning. The trough will send a cold front down
the eastern WY plains early in the period, resulting in slightly
cooler temperatures and highs in the mid to upper 70s, along with
breezy northwest winds. This feature will also bring the best
precipitation chances to east-central WY and northwest NE Thursday
morning and afternoon, ending during the evening. The best low-level
moisture will remain to the east, and shear weak, resulting in only
weak thunderstorms expected.

Friday-Saturday... Behind the aforementioned trough, models agree on
building a ridge over the western US, resulting in northwest flow
developing over WY and w NE. Weak disturbances in the flow may bring
an occasional weak shower or storm. Otherwise, as the ridge builds,
temperatures across the plains will rise from around 80 on Friday to
near 90 on Saturday.

Sunday - Monday... Models begin to diverge Sunday and Monday, the
agree on continued ridging across the western US with northwest flow
over WY. Ensembles and deterministics disagree on how amplified the
ridge becomes, with the Euro becoming more amplified than the GFS.
The GFS solution brings better shower and thunderstorm chances to
the region. High temps should remain in the mid to upper 80s by the
start of next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1143 AM MDT Mon Jul 1 2024

Forecast challenges today include the timing of showers and
thunderstorms, especially over the next 6 hours. LAR and CYS
will likely see precipitation by 19z however any category
reductions to below IFR are unlikely. MVFR vis is possible in
the heaviest brief downpours. By 20z, strong to severe
convection will likely affect CDR, with reductions to MVFR vis
likely along with stronger outflow winds. Showers and storms
have a much lower risk of lowering categories at AIA, BFF, and
SNY. Expect lingering cloud cover above MVFR thresholds at all
terminals east of I-25 this evening with mainly clear skies at
RWL and LAR tonight.

&&

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

&&

$$

SHORT TERM...MAC
LONG TERM...BL
AVIATION...MAC/BL