156
FXUS65 KCYS 281011
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
411 AM MDT Tue May 28 2024

.KEY MESSAGES...

- Potential for isolated dry thunderstorms capable of producing
  strong, erratic wind gusts across the I-80 corridor late
  Tuesday afternoon.

- Strong to severe thunderstorms mainly along and east of I-25
  into the Nebraska Panhandle Wednesday afternoon with large
  hail and strong winds.

- Active weather pattern continues Thursday into the weekend
  with daily chances for showers and thunderstorms.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 330 AM MDT Tue May 28 2024

Looking at another nice and warm day across much of southeast
WY and western NE for Tuesday with afternoon highs in the 70s
for most as the upper level ridge axis slides overhead. A weak
shortwave passage over the central Rockies could lead to
scattered showers and an isolated thunderstorm to develop over
the higher terrain near the CO/WY border late this afternoon.
Forecast soundings show very dry lower levels supportive of
gusty outflow winds with and in the vicinity of any storms that
develop. There is the possibility for these storms to spread
east of the Laramie Range along the I-80 corridor early this
evening with enhanced convergence along the inverted trough
extending northward from eastern CO, but again expecting little
to no precipitation along with gusty winds as LCLs extend well
above the freezing level.

Latest GOES WV imagery shows an upper level low approaching the
PacNW coast that will continue to move eastward across the northwest
CONUS headed into Wednesday. Strong southerly flow Wednesday morning
ahead of the low will begin to advect higher dew points across much
of eastern WY and the NE panhandle. This enhanced low-level moisture
may even lead to a few areas of patchy fog to develop briefly before
eroding with daytime heating. This will begin to prime the
environment for storms in areas east of the Laramie Range Wednesday
afternoon where even 10th percentile SBCAPE values are exceeding
1200 J/kg over the NE panhandle per the latest HREF with 30-35 kt
of shear.

SPC recently upgraded the Day 2 (Wednesday) Severe Weather Outlook
to a Slight Risk for Severe Thunderstorms with large hail and strong
winds possible east of I-25 into the NE panhandle. Will continue to
monitor potential timing of storms, but as of right now hi-res
guidance is suggesting initiation over the higher terrain around
midday with storms moving east towards better moisture east of a
boundary near the NE/WY border with notable CAPE values in the hail
growth zone (>700 J/kg between -10C and -30C). The most likely
timing for strong to severe storms will be late in the afternoon
into early in the evening as an enhancing LLJ potentially supporting
upscale growth into a convective line with strong outflow winds.
Lingering showers and storms will be possible Wednesday night before
the cold frontal passage.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Issued at 330 AM MDT Tue May 28 2024

A more summer-like weather pattern will dominate the week ahead
with mild temperatures and near daily chances for showers and
thunderstorms expected.

A broad trough located over the Canadian Rockies will be the main
weather maker for the end of this week. An initial shortwave
ejecting underneath this feature will push a surface trough through
the area by Thursday morning, leading to the dryline surging
eastward and low level winds turning westerly across much of the
area. Low level moisture and decent directional shear may hold on in
the far eastern counties of the forecast area, but further west the
isolated thunderstorms that develop will probably struggle to have
rain reach the ground, ending more as wind producers in the drier
low levels. Overall storm coverage should be lower on Thursday
compared to Wednesday. Thursday`s highs are also expected to be a
little cooler than Wednesday in the post frontal airmass. Most
guidance then shows a surface high sliding down the east side of the
Rockies late on Thursday, pushing the dryline back to the west and
putting better moisture in place for Friday. A secondary lobe of
vorticity rotating around the trough aloft on Friday should also
give a slight boost to lift, although this feature doesn`t look too
impressive. Look for greater storm coverage on Friday, with the
possibility for strong to severe storms also potentially returning.

Forecast confidence starts to break down heading into the weekend
and beyond, with subtle differences in the overall synoptic pattern
resulting in divergent outcomes for local surface weather. Most
model guidance shows the flow aloft becoming more zonal with some
weak shortwaves possibly passing through. The exact location of
these shortwaves will determine each day`s temperatures and
thunderstorm chances, but overall we are looking at a gradual
warming trend into early next week. Saturday should maintain
isolated to scattered afternoon thunderstorms, but expect things to
trend drier Sunday into early next week as more ensemble guidance
shows westerly low level flow and lower surface dewpoints.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1009 PM MDT Mon May 27 2024

Northwest flow aloft will continue overnight while a ridge aloft
moves overhead by Tuesday evening. Clear skies will prevail,
with ceilings near 8000 feet developing at Laramie and Cheyenne
after 00Z. Winds will gust to 20 knots at Cheyenne from 15Z to
00Z, and at Laramie from 18Z to 00Z.

&&

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

&&

$$

SHORT TERM...MB
LONG TERM...MN
AVIATION...RUBIN