440
FXUS65 KCYS 070548
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
1148 PM MDT Tue May 6 2025

.KEY MESSAGES...

- Fog likely persisting through the overnight hours into
  tomorrow for Central Laramie County through the Laramie
  Summit, with patchy fog elsewhere.

- A slow-moving spring storm system will continue chances for
  showers and isolated thunderstorms through Wednesday.

- A warming trend will begin Thursday and last through the
  weekend with an isolated chance for afternoon showers and
  storms each day.

&&

.SHORT TERM /THROUGH WEDNESDAY NIGHT/...
Issued at 232 PM MDT Tue May 6 2025

Overcast and gloomy conditions has persisted through the day
thanks to a combination of northerly to northeasterly surface
flow alongside moist easterly flow aloft. With this flow pattern
expected to continue through the afternoon and evening, it`s
unlikely we`ll see significant breaks in this, particularly in
the foggy mess currently occurring from the Laramie Summit
eastwards into Central Laramie County. The occasional heavier
shower moving across could briefly lift visibilities and scour
out some of the fog, but conditions will remain conducive for
low clouds and fog until tomorrow morning. Because of this, have
extended the dense fog advisory through tomorrow morning, with
the expectation that breaks will occur at times but otherwise
impacted visibilities will persist until that time. Meanwhile, a
few thunderstorms have been noted just across the border in
Colorado as well as in the Nebraska Panhandle and moving across
into Wyoming, but the environment quickly weakens further to the
north and west causing these storms to fall apart thereafter.
With a meager environment for thunderstorms, a few stronger
cells with gusty winds as well as small hail could be possible,
but stronger to near severe activity is unlikely.

Moving into Wednesday showery activity should begin to wane
around sunrise as drier air begins to overspread the region,
which should also help alleviate the foggy conditions as well.
But easterly flow should at least fuel another round of showers
and storms on Wednesday during the afternoon, though this
activity will likely be more isolated to widely scattered in
nature. Light MUCAPE once again averaging under or just around
500 J/kg could support a stronger storm or two across southeastern
Wyoming and the southern Nebraska Panhandle including the
potential for brief gusty winds or some small hail, but severe
weather once again remains unlikely. By the evening and
overnight into Thursday, precipitation and skies will be
clearing as we start a warming trend moving into the long term.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 232 PM MDT Tue May 6 2025

An upper level ridge starts to push into the
Intermountain West as the Omega block and corresponding southern low
pressure system pushes east. On the heels of the block on the front
edge of the ridge is a shortwave that looks to develop some showers
in the afternoon Thursday. Given that we are in southerly flow as
the shortwave pushes east, the showers have a decent chance for
development due to the moisture advection . The most likely areas at
this time for the showers look to be in the mountain and mountain
adjacent areas. However, westerly flow takes over after the
shortwave passes leading to drier air in the lower levels to
possibly prevent some moisture from reaching the ground.
Temperatures for Thursday looks to be in the 60/70s with the
overnight temperatures in the 40`s. Friday, will be widespread 70`s
for the high temperatures. Given the dewpoints will be in the 20`s
and 30`s there is a chance for some pop up showers in the afternoon
sparked by daytime heating. The dynamics for Friday are pretty
marginal meaning the atmosphere is not that great for any severe
weather. The shear is 15 knots or less under this ridge leading to
any isolated thunderstorm development will collapse on itself
shortly after forming. CAPE values peak at 500 j/kg in the afternoon
along the I-80 corridor where the warmer temperatures are expected
(mainly in the Nebraska Panhandle).

This weekend looks pretty dry even with a shortwave passing through
to give extra lift to any lingering moisture. There is some weak
vort-maxes associated with this shortwave to give a slight chance
for afternoon showers but the moisture looks very limited as
dewpoints are in the low 20`s Saturday. Sunday`s shower potential
depends on the timing of the low pressure system pushing into the
Pacific Northwest. There is some decent vorticity to help shower
development in the afternoon and evening but the global models
aren`t too thrilled with the dynamics but its currently a ways out
for any high-res models to resolve the finer details for the
weekend`s shower potential.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1145 PM MDT Tue May 6 2025

A soggy storm system is continuing to produce difficult
aviation conditions tonight. IFR is most likely at Wyoming
terminals with low clouds pushing up against the mountains.
Persistent LIFR is expected to continue into Wednesday morning
at KCYS. In Nebraska, on and off showers and a few thunderstorms
will produce brief MVFR to IFR conditions until they begin to
decrease in coverage after about 10z. Expect some partial
lifting/clearing late morning into the early afternoon before
another round of showers and thunderstorms develops mid
afternoon, mainly impacting KAIA, KBFF, and KSNY.

&&

.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory until 6 AM MDT Wednesday for WYZ114.
     Dense Fog Advisory until 9 AM MDT Wednesday for WYZ116>118.
NE...None.

&&

$$

SHORT TERM...CG
LONG TERM...MM
AVIATION...MN