525
FXUS65 KCYS 162345
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
545 PM MDT Sat Aug 16 2025

.KEY MESSAGES...

- A marginal risk (1 of 5) for severe weather is expected today,
  primarily for our northern fringes of the WY/NE border region,
  with general thunderstorms expected elsewhere.

- Precipitation chances begin to lessen to end the weekend and
  begin next week, with mostly hot and dry conditions expected
  for the front half of the week.

- A cold front late in the week should bring back rainfall while
  also helping to temper highs across the region for next week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 300 PM MDT Sat Aug 16 2025

Southwest flow continues aloft this afternoon, with a fairly potent
upper level shortwave trough axis moving over the area. Showers and
thunderstorms have developed over the northern Colorado Front Range
and are now moving northeast across Laramie County, kicked off by
the shortwave aloft. Expect this to grow upscale as it moves to
the northeast through the rest of the afternoon and evening
hours. For the most part, today`s activity is expected to be
sub-severe. Instability is mostly unimpressive, around 500 to
1000 J/kg SBCAPE in Wyoming, and a touch higher in Nebraska,
with modest lapse rates and weak vertical wind shear. The
exception is the northern Nebraska panhandle & Niobrara county
where 0-6km shear is around 30 knots and the atmosphere is a
little more unstable. Once storm activity reaches this area, we
may see isolated storms become strong to severe. Elsewhere, look
for mainly brief heavy rainfall (with ample moisture, these
storms should be fairly efficient rainfall producers), small
hail, and winds gusting to around 40 mph. Most of the
thunderstorm activity is expected to conclude by around 9PM, but
a few showers and isolated rumbles of thunder may continue
through much of the night. Skies will gradually clear towards
Sunday morning with near average low temperatures expected.

Much drier air will begin to move in aloft heading into Sunday.
Forecast soundings show a very dry atmosphere above about 400-mb by
Sunday afternoon after today`s shortwave nudges the lingering
monsoon moisture off to the east and ushers in a drier airmass
behind. The boundary layer will also dry out a bit, though decent
moisture remains mainly between about 400 and 600-mb. Look for high
temperatures just a touch higher than today, remain several degrees
warmer than average for this time of year. A shallow layer of
instability should still be enough to kick off widely scattered
showers and thunderstorms, but moisture will be more limited,
leading to lower chances for wetting rainfall with tomorrow`s
thunderstorm activity. The sames areas of Niobrara county into the
northern Nebraska panhandle should hold on to better low level
moisture, so expect to see a better chance for down pours and
perhaps some isolated once storms reach this area.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 300 PM MDT Sat Aug 16 2025

Starting Sunday the Intermountain West starts to dry out as an upper
level ridge becomes centered on the four corners region of the
United States. Monday, the Intermountain west will be in a southern
flow helping to advect in some moisture for some possible isolated
thunderstorms in the afternoon and evening. There are a couple vort
maxes that pass through the region that may help with the synoptic
lift to help sustain any shower or thunderstorm development but
stronger forcing will be needed to help anything severe develop. SPC
does have a marginal risk for Monday, given the model soundings of
the dry layer near the surface wind does seem like the most likely
threat. The main question will be if there is enough shear for
updraft and downdraft separation to sustain any potential for severe
development. Tuesday through Thursday morning, the upper level ridge
becomes rooted into the four corners region making us hot and dry
for potential fire weather concerns. 700mb temps returns to that 20C
threshold allowing for surface temperatures to reach 90 to 100F in
the lower elevations while the higher elevations will be in the 80
to 90F range. Thursday currently appears to the hottest day however
there is a cold front that may prevent some of those higher
temperatures depending on timing. The cold front does have some
uncertainty as the global models have different timings for the
arrival of the cold front. This cold front also may be the start of
our precipitation chances for the week as a large low pressure
system is progged to move across/along the Canadian border and
flattening our ridge.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 544 PM MDT Sat Aug 16 2025

There are showers to the southwest of KBFF that may still
impact it so Prob30 was left in the TAF. Still expecting showers
to affect the Nebraska terminals but for the most part the
Wyoming terminals may be done for the night. However, there is
some showers developing near KRWL that may send a temporary
strong wind gusts but not enough confidence to place in the TAF.

&&

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

&&

$$

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