342
FXUS65 KCYS 171008
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
408 AM MDT Thu Jul 17 2025

.KEY MESSAGES...

- Critical fire weather conditions are expected this afternoon
  for portions of Carbon county.

- Warmer temperatures and daily chances for PM showers and
  thunderstorms will continue into early next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 400 AM MDT Thu Jul 17 2025

GOES water vapor imagery shows drier air progressing across the
forecast area from west to east this morning as largely zonal flow
takes over across the northern half of the CONUS. Monsoonal moisture
is visible over the Four Corners states, but is getting suppressed
south of the WY/CO state line behind a modest vort-max. Low-level
moisture, however, remains plentiful thanks to the surface high over
the northern plains remaining pushed up against the mountains.
Dewpoints in the 50s continue across most of the area with the
exception of Carbon county. Combined with low-level upslope flow,
this is producing areas of low clouds and fog over most areas east
of the Laramie range this morning. This will kick off Thursday with
cool and moist conditions, but expect this to burn off from west to
east through the morning and into the early afternoon hours. Much
drier air will work into Carbon county as the moisture retreats to
the east. Combined with gusty west winds underneath the zonal flow
aloft, critical fire weather conditions are expected this afternoon.
Thunderstorm activity will be more limited today as a result of very
dry air in the middle to upper atmosphere, but this will improve
through the afternoon as the monsoon moisture tries to push back
across the state line. Expect to see some diurnal cumulus along and
south of I-80 with a few radar echoes showing up into the early
evening hours. This activity may produce gusty winds.

Moisture availability will have the opposite problem on Friday. A
weak trough dipping into the Pacific NW will help give the flow
aloft a southerly component, and pump good mid to upper level
moisture back into the area. However, the amplifying ridge will also
push the surface trough and associated dryline well to the east,
leading to poor boundary layer moisture for all except areas
north/east of Lusk to Chadron to Sidney (roughly). A vort-max
ejecting out of the monsoon region will pass through the area late
Friday afternoon into the evening hours, providing sufficient
forcing to kick off scattered showers and thunderstorms. Most of
this activity will be high-based with little rainfall potential, but
these storms will encounter a more favorable environment once then
hit the dryline. A few isolated strong to severe thunderstorms may
be possible, mainly along the US-20 and US-385 corridors. The late
arrival of the trough axis may keep shower and thunderstorm activity
over the area well into the night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 400 AM MDT Thu Jul 17 2025

A fairly stagnant weather pattern will take hold Saturday and
continue through the middle part of next week. This will be
characterized by a broad trough over the Northwest and a broad ridge
over the central/southern Plains. Modest southwest flow will
continue over our area for much of this period, with a slow but
general warming trend each day through at least Tuesday. Surface
moisture will recover somewhat Saturday up to the Laramie range,
supporting widely scattered showers and thunderstorms with potential
for an isolated strong to severe storm once again. Ensembles
generally position the surface dryline further east on Sunday
through Tuesday. Despite decent mid to upper level moisture
continuing to flow out of the monsoon region, the boundary layer is
expected to remain dry and thus limit rainfall potential. Still,
isolated to scattered PM showers and thunderstorms can still be
expected each day with some gusty wind potential likely.
Temperatures will be above average for this period, in the upper 80s
to lower 100s for most, but since this is the climatological hottest
time of the year, record highs are not very probable. Another cool
down and return of moisture is possible around Wednesday of next
week, but confidence is fairly low at this lead time.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1127 PM MDT Wed Jul 16 2025

Plentiful moisture and upslope flow is producing another round
of low CIGs over the High Plains tonight through Thursday
morning. Confidence in IFR is high for KCYS and KSNY and moderate
at KLAR, KAIA, and KBFF. Confidence in IFR was too low to add to
the TAF for KCDR. In addition, periods of fog may occur through
Thursday morning, particularly at KCYS and KSNY. Expect
aviation conditions to gradually improve Thursday morning.
Thursday afternoon`s thunderstorm threats will be more limited
compared to the last several days.

&&

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

&&

$$

SHORT TERM...MN
LONG TERM...MN
AVIATION...MN