-- Discussion containing changed information from previous version are highlighted. --
554
FXUS65 KCYS 251130
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
530 AM MDT Wed Sep 25 2024

.KEY MESSAGES...

- Elevated to critical fire weather conditions possible through
  late week. Fire Weather Watch in effect from Thursday morning
  through Thursday evening for central Platte and southwest
  Goshen county.

- Above average temperatures and dry conditions expected
  Wednesday onwards.

&&

.SHORT TERM /THROUGH FRIDAY/...
Issued at 324 AM MDT Wed Sep 25 2024

Latest surface analysis has continued to show high pressure building
from the Western Seaboard through to the Intermountain West, with
the fast moving cold front that dug through our region days prior
now across the Great Lakes. Overnight observations have been
relatively mild with temperatures in the high-40s, light winds,
and clear overhead skies for both southeast Wyoming and the
Nebraska Panhandle.

Upper level ridge axis has continued tracking across the
Intermountain West yesterday afternoon, with further progression
expected eastward into the High Plains by late week. As a
result, a decent warmup is expected, with models remaining
consistent over the last few days, keeping 700mb temperatures to
around +16c through Thursday. As a result, will begin to see
daytime in the low to high 80s today, and up to the high-80s for
southeast Wyoming and high 90s for the Nebraska Panhandle on
Thursday. Ultimately, due to the model consistency over the
last several days, began blending in higher NBM percentiles into
the short term forecast, primarily on Thursday, with the NAEFS
mean 700mb temperatures in the climatological 90th percentile
for the I-25 corridor and into the 99th percentile for the
majority of areas in the Nebraska Panhandle.

Main concerns in the forecast focus on the prolonged dry conditions,
combined with the much warmer temperatures on Thursday, which will
inevitably raise fire weather conditions as the minimum RH values
drop to the mid to low-teens for much of southeast Wyoming and the
Nebraska Panhandle. Wind speeds will remain the main uncertainty and
if they are able to reach critical thresholds. As it currently
stands, HiRes model guidance has continued to increase the westerly
downsloping component to the wind, with several shortwave
disturbances propagating within the flow, kicking up wind speeds to
near-critical and critical levels. As a result, went ahead and
issued a Fire Weather Watch for central Platte and southwest Goshen
county Thursday morning through Thursday afternoon where local in
house model guidance has been trending up wind speeds up to 35
mph possible. Will need to monitor both Converse and Niobrara
county to include both areas into the fire weather headlines
with the HREF probabilities of reaching critical fire weather
conditions around 20% to 30% from 18z to 21z Thursday.
Otherwise, some humidity recovery is expected Thursday night
into Friday.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Issued at 324 AM MDT Wed Sep 25 2024

Above average temperatures and dry conditions expected through this
weekend with the upper level ridge reamplifying over the central
Rockies. Afternoon highs will be in the 80s to low-90s, especially
over the NE panhandle, as 700mb temps return to 12-14C which is over
the climatological 99th percentile value per the latest NAEFS.
However, yet another upper level trough will traverse the Canadian
border Sunday night into Monday. While this trough will not make a
big dent into the upper level ridge over the southwest CONUS, 500mb
heights across our area will lower leading to cooler weather
starting Monday, but still remaining close to normal for late
September/early October. Latest NBM has afternoon highs in the upper
60s to 70s Monday through the middle of next week. However, quite a
bit of uncertainty exists as noted by MaxT standard deviations,
especially east of the Laramie Range into western NE. This is tied
to the amplitude of the passing wave along the Canadian border as
~20% of the grand ensemble digs the upper level low deeper into the
central CONUS on the eastern periphery of the ridge bringing cooler
temps aloft and the next chance for frost/freeze concerns.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
-- Changed Discussion --
Issued at 525 AM MDT Wed Sep 25 2024

VFR conditions expected across area terminals through the
forecast period. Gusty afternoon winds to 25 kt expected near
KRWL out of the southwest. Terminals east of the Laramie Range
into the NE panhandle will primarily be out of the
south/southeast.
-- End Changed Discussion --

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Fire Weather Watch from Thursday morning through Thursday
     evening for WYZ432.
NE...None.

&&

$$

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