411
FXUS65 KCYS 142126
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
326 PM MDT Sat Sep 14 2024

.KEY MESSAGES...

- Critical fire weather conditions continue this afternoon,
  mainly in Carbon, Albany, and Converse counties. A Red Flag
  Warning is in effect.

- Chances for showers and thunderstorms will return Sunday
  through Tuesday, followed by another chance for precipitation
  and cooler temperatures late in the week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 305 PM MDT Sat Sep 14 2024

Latest GOES WV imagery showers primarily zonal flow across the
area in the wake of the vort max passing through earlier this
morning. A mid-level jet will continue to traverse central WY
today with elevated winds downsloping off the North Laramie
Range contributing to critical fire weather conditions today
(see fire weather discussion below for more details). Otherwise,
mostly clear skies across the CWA. With the earlier timing of
the vort max passage this morning, the dryline has quickly
passed into the NE panhandle through Chadron, but Alliance and
Sidney remain with winds out of the south and dew points in the
mid-50s. The latest HRRR and NAMNest now does initiate a storm
or two in Morrill/Cheyenne Co where latest GOES imagery shows
ongoing cumulus development. Will need to continue to monitor
observational trends through this afternoon for possible storm
development, but decided to continue with 15-20% PoPs in the
southern NE panhandle.

The dryline will begin to retreat westward overnight towards the
I-25 corridor as an upper level low begins to build into the
western CONUS. Moist southerly flow into the NE panhandle could
support patchy fog early Sunday morning. As larger scale lift
arrives with a leading shortwave passage in southwest flow,
showers and thunderstorms will be possible Sunday afternoon.
CI will be most likely between the dryline position and the
Laramie Range. Additional diurnal circulations (Chugwater
Cyclone) may lead to additional areas of convective initiation
around Platte/Goshen Co Sunday afternoon before storms begin to
propagate eastward. Large instability profiles for this time of
the year (~1500 J/kg MLCAPE) will support the possibility of
hail, but shear will be marginal limiting organization to
multicellular structures. A capping inversion will be in place
farther east that will likely limit any deep convection until
early in the evening across the NE panhandle. SPC has included
eastern portions of our CWA into a Marginal Risk for Sunday
afternoon.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 305 PM MDT Sat Sep 14 2024

The long term will feature a switch to a more active, wetter
pattern. With a first taste of more fall-like temperatures towards
the end of next week.

Next week will start off mild with the CWA sandwiched between a deep
trough coming on shore of the west coast, and a broad ridge over
much of eastern CONUS. This puts the CWA in south to southwest flow
which will advect both warmer air and Pacific moisture into the
region. This will lead to temperatures on Monday that are above
average, especially east of the Laramie Range. Expect highs east of
the Laramie Range to be in the 80s and 90s, and highs out west to be
in the 70s. With the increased moisture advection Monday, showers
and storms will likely develop. Models seem fairly consistent with
keeping the better mid-level moisture west of the Laramie Range, so
this area will be the most likely location of any precipitation that
develops. Showers and storms could develop by late afternoon and
continue into Monday night.

Good agreement between the GFS and ECMWF with bringing the west
coast trough into Wyoming by Tuesday afternoon. Moist southerly flow
ahead of the trough and lift from the trough will provide the set-up
for another, more widespread precipitation event Tuesday afternoon.
Showers and storms will linger into Tuesday night, but will quickly
clear out by Wednesday morning as the trough passes north of the
CWA. Wednesday will be dry, but cooler, as more seasonable 700 mb
air sits overhead.

Headed into the end of the work week, expect even more precipitation
chances and cooler temperatures. The GFS and ECMWF remain in good
agreement, bringing a potent positively tilted trough into the
Rockies by Thursday night. Mid-level moisture and frontogenesis from
a strong cold front will likely produce widespread precipitation
across the area. This cold front will also likely lead to some light
mountain snow accumulations in the Sierra Madre and Snowy Ranges.
While temperatures are not expected to be cold enough to snow in the
lower elevations and plains, expect chilly low temperatures Saturday
morning, followed by what will likely be seasonable to below average
temperatures during the day.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1140 AM MDT Sat Sep 14 2024

Expect VFR conditions through the day and into the evening hours.
Occasional gusts of 20 to 25 kts will be possible throughout the
afternoon. Weak southeast flow early Sunday morning could lead to
the development of patchy fog in the southern Nebraska panhandle and
North Platte River Valley. Low status may also be possible in this
area which could lead to MVFR conditions Sunday morning.

&&

.FIRE WEATHER...
Issued at 305 PM MDT Sat Sep 14 2024

Critical fire weather conditions continue this afternoon across
much of south-central Wyoming northeast through east-central
Wyoming, as a mid-level jet traverses the North Laramie Range.
Afternoon RHs have dropped near 10 percent with gusts up to 35
mph. Did have to expand the Red Flag Warning to FWZs 417, 423, and
425 based on observational trends early this afternoon. Expect
conditions to persist into early this evening before winds begin
to calm overnight, but could still see gusts around 15 mph around
the higher terrain. Additionally, poor recoveries up to 35 percent
are likely west of the dryline tonight. Chances for precipitation
return Sunday afternoon with thunderstorms possible along and
east of the Laramie Range into the Nebraska panhandle. Farther
west, dry conditions will lead to elevated fire weather concerns
with afternoon RHs around 10-15 percent, but winds are expected to
remain below critical thresholds. Active weather pattern with
chances for precipitation continue into early next week.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Red Flag Warning until 8 PM MDT this evening for WYZ417>423-
     425-427.
NE...None.

&&

$$

SHORT TERM...MB
LONG TERM...SF
AVIATION...SF
FIRE WEATHER...MB