122
FXUS65 KCYS 091739
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1139 AM MDT Tue Jul 9 2024

.KEY MESSAGES...

- Confidence is growing for a potentially significant heat wave
  to impact the region late in the week through the weekend.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 315 AM MDT Tue Jul 9 2024

Generally quiet and benign weather expected through the middle
of the week with a gradual warming trend. Models in good
agreement through Thursday...showing the dominant upper level
high, which has already brought record heat from Washington and
Oregon southward to Nevada and Arizona, slowly drifting eastward
into the Great Basin Region by Wednesday and then into Utah and
far southwest Wyoming by Thursday. Warm temperatures expected
today, but these temperatures will be close to seasonal
averages and generally in the 80s to near 90 for most locations.
Temperatures will really begin to heat up on Wednesday and
Thursday as this upper level high continues to push eastward,
with 700mb temperatures increasing between 16c to 20c Thursday
afternoon. Expect high temperatures on Thursday to already begin
pushing 100 degrees across portions of the area (generally for
elevations below 4500 feet) with widespread mid to upper 90s
elsewhere...even with the upper level high and associated ridge
axis still west of the I-25 corridor. Kept high temperatures
close to the previous forecast, which is near the NBM and GEFS
75th to 90th percentile. A few thunderstorms can not be ruled
out near the mountains, close to the Colorado border, due to the
natural upslope easterly winds across the high plains and the
light north to northwest winds west of I-25. However, have a
hard time believing much of this rainfall will reach the ground
due to inverted-V soundings and surface dewpoints in the 20s to
mid 30s. Kept POP around 10 percent for Laramie and Cheyenne
with 20 to 30 percent for the higher mountains each afternoon
and evening.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 228 AM MDT Tue Jul 9 2024

Much above average temperatures are expected in the medium range to
long term forecast. The potential for daytime highs to meet or
exceed 90 degrees for areas east of the Laramie Range for up to a
week in a row exists. An upper level ridge that has been semi-
stationary over the western CONUS will slowly propagate to the east
in the next several days. As this occurs, stagnant airflow from a
stacked upper level High, and a surface High will continue to impact
the Great Basin and Intermountain West with hot temperatures.
Deterministic output from model guidance has been consistent for
several days regarding the high likelihood of 90s/100s being the
forecast daytime highs for most locations east of the Laramie Range.
While this isn`t that particularly uncommon for summer across our
cwa, the persistent hot temperatures with little relief during the
overnight hours does cause concerns for possible heat advisory or
even excessive heat headlines beginning this weekend. Probabilistic
data suggests that Cheyenne may reach daytime highs in the upper 90s
to potentially even 100 degrees by Sunday and Monday of next week.
This would tie the all-time record high temperature for the city of
Cheyenne. However, one caveat is that model guidance is also being
consistent with the return of monsoon moisture toward the end of the
weekend into early next week. Unfortunately, the hot and dry
conditions are expected until we get relief via cloud cover and
light rain showers, which may create elevated to near critical fire
weather concerns. We will continue to monitor the trends regarding
the potential for the monsoon moisture to bring a wetting rainfall
greater than 0.10 inches to the area, as the very hot temperatures
will quickly dry the region out. By midweek, we see a gradual
decrease in the excessive heat for the area, but it will still be
quite warm.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1134 AM MDT Tue Jul 9 2024

VFR prevails. SCT/BKN coverage of low & mid-level cloud cover in
the range of 10k to 15k feet AGL, mainly for areas along/west of
the Laramie Range. Otherwise, SKC for most terminals. There will
be a small chance of a virga shower and locally gusty winds over
western areas, but overall would anticipate little or no impacts
to aviation interests.

&&

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

&&

$$

SHORT TERM...TJT
LONG TERM...BW
AVIATION...CLH