406
FXUS65 KCYS 100002
AFDCYS

Area Forecast Discussion
National Weather Service Cheyenne WY
602 PM MDT Sat May 9 2026

.KEY MESSAGES...

- Numerous rain showers and widely scattered thunderstorms
  expected on Saturday. A few strong thunderstorms or an
  isolated severe storm possible.

- Mostly dry and warmer weather will prevail for Sunday through
  Wednesday, with thunderstorms possibly returning late in the
  week.

&&

.SHORT TERM /THROUGH MONDAY NIGHT/...
Issued at 152 PM MDT Sat May 9 2026

Scattered showers and some weak thunderstorms are noted on radar
across the area as of this afternoon primarily for our northern
zones with much stronger activity seen to the northwest moving
into Central Wyoming. At the surface, a cold front is currently
draped across portion of the northern Nebraska Panhandle and up
into northeastern Wyoming, while aloft an upper level shortwave
is making its way across Wyoming and into Nebraska through the
day. Current expectation for the rest of today is in line with
the morning forecast package, and expecting scattered
thunderstorms with widely scattered strong to possibly severe
activity today.

High resolution guidance remains largely in agreement on this
continuing over the next several hours, with a few thunderstorms
possible but remaining largely sub-severe. Then as the front
drops across the area, we should see an uptick in thunderstorm
activity along this boundary across the I-25 and I-80 corridors,
with an increase in severe parameters fueling stronger to
possibly severe activity. Along this area should be increasing
CAPE values with pockets of 800-1200 J/kg, 0-6 KM shear values
of 40-60 knots but isolated peaking at around 70-80 knots noted
as well on the HRRR, and steepening low and mid level lapse
rates. Storms will likely be clustered in nature with limited
potential for individual supercells, though cannot rule out at
least one to occur early on. By the later part of this
timeframe, most CAMs agree that activity will congeal into more
linear fragments as they move into Nebraska with intensity
waning as the sun sets. Greatest threats will be gusty winds and
isolated large hail with activity being higher based in nature.

Overnight temperatures should actually chill notably behind the
cold front in tandem with clearing skies fueling radiational
cooling, with widespread lows in the 30`s expected Sunday
morning. A building ridge will then control the weather across
the area for the remainder of the short term as we see
temperatures rebounding into the 60`s and 70`s on Sunday, and
then significant warmth on Monday as highs skyrocket into the
80`s and 90`s. This will be knocking on the door of record highs
for most of our forecast area with highs 20 degrees above
normal. Alongside this record warmth brings the return of
critical fire weather conditions as our RH values bottom out in
the low teens to near single digits on Monday with some breezy
winds possible along the I-25 corridor and along the base of the
Laramie Range. Will have to take a deeper dive into fire fuels
as we move into Sunday and determine if Red Flag products will
be necessary or not.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Issued at 152 PM MDT Sat May 9 2026

The general pattern going into Tuesday is one of upper level
ridging. A rather large high pressure system will be building over
the Four Corners Region with an axis of it passing through. This
should allow temperatures to reach the mid 70s to low 80s. We do
have fire weather conditions showing up in the interior mountains
near Rawlins this day. Humidities appear very low, possibly getting
into the low teens with gusty conditions. Elsewhere, dry conditions
may favor some elevated concerns. These conditons should persist
into Wednesday where some spots in valleys east of the Laramie Range
could reach the 90s and near daily record temperatures. Humidities
plummet given the favorable environment for deep layer mixing.
Relative humidities reaching the mid and low teens are a
possibility. Attention to conditions these few days should be
maintained for fire weather interests. Thursday a plume of monsoonal
like moisture makes its way north from the Eastern Pacific into our
area. The ridge gets pushed southeast into Texas allowing increasing
chance of isolated to scattered showers and storms. PoPs are low at
this time, and surface layer mixing will still be high creating dry
conditions at the surface. So, the most likely outcome Thursday are
the continued fire weather risk, but maybe throw in a few dry and
windy thunderstorms. About this time a compact, but high amplitude
trough will be passing over the northwestern Pacific Coast. Global
models differ on the speed and strength of this feature. The GFS is
much more aggressive with this trough and is a bit slower/south with
the progression as it reaches our area Friday. ECMWF is a bit more
progressive, weaker and northward with its trajectory. Both have the
general negative tilt form to the trough which tend to be more
dynamic than positive and flatter systems. The timing is somewhat
important from a severe weather angle, a slower and more southward
system may allow for the favorable left exit region of the jet to
the south of the trough to be in phase with the better daytime
heating. At the moment the models make this a more north and
eastward event. A dry slot on the south side of the system will
create sinking air and may tighten pressure gradients in the 700
mbar enough to create strong winds. Indeed our machine learning
models highlight an elevated risk Friday morning and afternoon
(~40%) for west to east mountain gap flow locations. Conditions area
wide continue to by dry and warm, so fire weather is likely to
continue, even going into Saturday. Fuels in our Nebraska Panhandle
zones are not in good shape with little green up reported. The
snowfall received on the eastern slopes and ridges of the Laramie
Range has caused some greenup with vegetation. The periods of recent
rain may stave off more critical fire concerns going into this
period.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 541 PM MDT Sat May 9 2026

The bulk of the storm activity is beginning to depart into
Colorado currently with KSNY being impacted by nearby storms.
Wide areas of light stratiform rain is lingering behind these
storms and generally lower ceilings of around 5000 feet at the
Nebraska terminals. Some storms and rain showers may develop
during the overnight hours until around 10z. The atmosphere has
been overturned by this afternoons convection and latest high
resolution guidance is suggesting less storm coverage than it
was predicting earlier. Therefore, higher storm chances have
been taken out of the 00z TAFs. Ceilings lower at all terminals
overnight, possibly to MVFR or IFR conditions at KRWL, KLAR, and
KCYS. Fog may develop near daybreak at all terminals, but
certainty remains low. KLAR will have the greatest chance of fog
if it does occur at 30%, elsewhere around 20%. Will monitor for
changes in guidance to introduce fog probabilities at the 06z
TAFs. Tomorrow clouds thin out and lift with more persistent for
the Nebraska Terminals, but are expected to be in VFR.

&&

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

&&

$$

SHORT TERM...CG
LONG TERM...RV
AVIATION...RV