371
FXUS65 KCYS 181736
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1136 AM MDT Sat May 18 2024

.KEY MESSAGES...

- Warm & breezy conditions are expected again for today. Overall
  chances for showers are low, but an isolated storm cluster may
  develop during the late afternoon and/or early evening along
  and southeast of a line from Cheyenne to Alliance.

- The risk for showers and thunderstorms is expected to increase
  from Sunday afternoon through Monday as significant upper-
  level troughing deepens and digs into the 4 corners region.

- Widespread rain and high-elevation snow may be possible as
  early as Monday afternoon, courtesy of lee cyclogenesis over
  southeast Colorado with a sub-1000-mb surface low tracking to
  the northeast across Kansas and Nebraska.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 427 AM MDT Sat May 18 2024

A warm & breezy start to the weekend across southeast WY and the
western NE Panhandle as fast, quasi-zonal flow aloft persists in
association with an active northern stream jet. Despite the cold
frontal passage last evening, 700-mb temperatures should rebound
nicely this AM with the majority of models suggesting +6 to +8 C
over much of the area by 18-21z today. Most areas should see day
time highs in the 70s F. Greater precipitation chances should be
confined to the S and E across Colorado and central Nebraska for
today as weak short wave energy traverses the southern stream in
the next 12-18 hours, but there will be a chance for a couple of
showers or weak thunderstorms during the late afternoon into the
early evening, particularly to the southeast of a line from KCYS
to KAIA. A transition to a more unsettled weather pattern should
commence for Sunday and Monday as a stronger mid and upper-level
trough deepens over the Pacific NW, ending the persistent split-
flow pattern. As the trough deepens and digs into the 4 Corners,
lee cyclogenesis should occur by mid-day Monday w/ potential for
a more widespread wrap-around precipitation episode taking shape
by late in the period with the sfc low lifting into the southern
and central plains. As such, expect increasing daily chances for
showers and thunderstorms across much of the area for Sunday and
Monday.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Issued at 427 AM MDT Sat May 18 2024

No major changes for the long term forecast. An progressive pattern
will continue with daily chances for precipitation across the
region. On Tuesday, the upper-level trough associated with the cold
front on Monday will push through the region. A reinforcing shot of
cold air will funnel in behind the front, leading to much cooler
temperatures for Tuesday. Highs will be in the upper-40s to mid-50s
area wide. With the cooler temperatures and 700mb temperatures below
0C, snow showers cannot be ruled out across southeast Wyoming. As
the trough rotates out of the region throughout the day Tuesday,
brief zonal flow followed by a low amplitude ridge will move
overhead for Wednesday, leading to a quick warm up in temperatures
with highs in the upper-50s to upper-60s. Some energy will remain
overhead at 500mb cyclonic vorticity advection remains across the
region. Therefore, isolated to scattered showers are expected once
more.

Long range model agreement falls apart on Thursday, as the GFS
suggests a potent trough digging across the region while the ECMWF
favors a low amplitude trough that remains well north of the region.
Given the disagreement between models, kept PoPs in the 15-30% range
for much of the CWA, as some isolated precipitation may be likely
with the energy aloft. The trough in the GFS is progged to move out
of the region for Friday and Saturday, but disagreement still
remains between the models. Long range models suggest a longwave
trough developing over the western CONUS, but timing, strength, and
evolution are very different between models at this time. Kept low-
end PoPs in the forecast as some precipitation may be possible with
the energy aloft. Temperatures Friday and Saturday will be in the
mid-60s to mid-70s across the region.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1134 AM MDT Sat May 18 2024

VFR conditions expected through the forecast period. Mainly
quiet this afternoon with some breezy conditions in Wyoming. A
few isolated thunderstorms may develop between about 23z and
03z, mainly in the southern NE panhandle. A low level jet is
expected to bring gusty southerly winds at times to NE panhandle
terminals overnight and into Sunday morning.

&&

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

&&

$$

SHORT TERM...CLH
LONG TERM...AM
AVIATION...MN