066
FXUS65 KCYS 240840
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
240 AM MDT Tue Sep 24 2024

.KEY MESSAGES...

- Above average temperatures and dry conditions expected
  Wednesday onwards.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 230 AM MDT Tue Sep 24 2024

Latest GOES Nighttime Microphysics RGB shows mid-level cloud
cover across east-central WY through the NE panhandle associated
with the earlier shortwave passage to our northeast. This upper
level trough will continue to dig into the MS River valley,
while 500mb height rises climb across the central Rockies today.
As clouds continue to clear through this morning, dry conditions
will prevail with seasonable weather today. Afternoon highs will
be in the 70s for most.

Wednesday and Thursday will be quite warm across southeast
WY and western NE as the thermal ridge of 700mb temps 14-16C
move overhead. Latest NAEFS guidance places these 700mb temps
over the climatological 99th percentile value for late
September. Afternoon highs Wednesday will be in the 80s for
most while Thursday will temperatures climb into the upper 80s
and 90s, especially east of the Laramie Range. Latest NBM
probability of afternoon highs exceeding 90F degrees is 50-80%
for much of the NE panhandle. Would not be surprised to see
observed afternoon temperatures rival record highs for a few
sites. The current forecast high for Thursday in Chadron is 96F
degrees which would be the 4th latest 95+ degree day in their
climatological record.

In addition to Thursday`s warmth, near-critical fire weather
conditions are possible with the above normal temperatures and
westerly downsloping winds across the Laramie Range dropping
afternoon RHs below 15 percent. An upper level system passing
well to the north will lead to a weak frontal passage Thursday
afternoon supporting winds gusting 25-35 mph.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Issued at 230 AM MDT Tue Sep 24 2024

No major changes to the long term forecast, with the broad upper
level ridge pushing further southward as an upper level shortwave
passes to the north. Under this setup, zonal flow is expected to
take hold keeping the upper level high to the south across the Four
Corners and an upper level cutoff low cycling off across the
southeast CONUS. A decent warmup is expected to continue during this
time period, with 700mb temperatures hovering around +14c to +16c,
leading to prolonged warmer temperatures for late September. As a
result, will begin to see daytime highs in the low to mid 80s
through at least Sunday. Decided to keep temperatures close to the
NBM, with any model guidance still a bit too far out to make any
significant changes. However, will need to start considering
blending in higher NBM percentiles to the current blends for this
weekend, with the NAEFS mean 700mb temperatures in the
climatological 90th percentile for the majority of our areas in
southeast Wyoming and the Nebraska Panhandle.

In addition to the increased temperatures, dry forecast associated
with dry downsloping flow will inevitably raise fire weather
concerns as the minimum RH values drop to the mid to low-teens for
much of southeast Wyoming and the Nebraska Panhandle. Winds do not
appear to reach fire weather critical thresholds during the times of
critical level humidity values through Weekend. However, will need
to monitor the development of an upper level closed low that will
retrograde towards eastern Colorado by late weekend, which could
induce some stronger gradients for the CWA and some possible
shortwave disturbances to pulse across the zone on the back end of
the low. Otherwise, the upper level pattern begins to break down by
the beginning of the work week, with the upper level low finally
pushing towards the Eastern Seaboard, making way for shortwave to
dig across the zone and bringing colder temperatures both Monday and
Tuesday. Little moisture advection associated with this front,
keeping the region dry and on the colder side.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1017 PM MDT Mon Sep 23 2024

Expect mostly cloudy skies overnight east of the Laramie Range.
Ceilings will remain above MVFR range. An isolated sprinkle can
not be ruled out at AIA before sunrise. Expect VFR at all
terminals on Tuesday with mostly sunny skies and light northwest
winds.

&&

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

&&

$$

SHORT TERM...MB
LONG TERM...MRD
AVIATION...MAC