637
FXUS65 KCYS 141201
AFDCYS
Area Forecast Discussion
National Weather Service Cheyenne WY
600 AM MDT Wed Oct 14 2026
.KEY MESSAGES...
- Cool temperatures will prevail for the rest of the week with
widespread showers this evening through Thursday morning.
- Accumulating snow will develop in the higher peaks, and then
spread to areas above about 6500 ft in elevation Wednesday evening
into Thursday morning. Snowlevels may lower down to 5500 to 6000
feet briefly before precipitation ends later Thursday morning.
- Near freezing temperatures are possible (20 to 40% chance east of
I-25) Wednesday night. A growing-season-ending freeze is expected
Thursday night into Friday morning across the entire area.
- Drier and milder weather expected this weekend.
&&
.SHORT TERM /THROUGH THURSDAY/...
Issued at 217 AM MDT Wed Oct 14 2026
Widespread shower activity is occurring as the Pacific upper
level system advances. A plume of deep layer moisture created
by early convection near the Four Corners area is being advected
northward ahead of the upper level low. As a result periods of
light to moderate rain (snow for mountain peaks) should continue
through about mid morning. Upslope flow along the Southern
Laramie Ranges with this moisture is causing another round of
fog. Already mesonet stations along I-80 and the Summit are
detecting reduced visibilities to less than a quarter mile. This
area stays socked in throughout most of the day as depicted in
high resolution model visibility fields. Outside the fog and
precipitation, thick cloud coverage can be expected. These
clouds should keep daytime highs on the cool side with most
spots peaking out in the low 40s to low 50s. Honestly, perfect
cozy vibe weather if you ask me. About mid morning the plume of
moisture will have moved north and west around the upper level
system with a dry slot wrapping in behind it. This reduction in
moisture should put a limit to the shower activity over a good
chunk of the area, except for western parts of Carbon County.
In the later parts of the afternoon the upper level system
begins to take on a more negative tilt with a rather amplified
southern axis swinging in from the southwest. A cold front will
be colocated with this axis and act to ramp up strong
isentropic lift. A nice conveyor belt of showers and isolated
thunderstorms along this front in the southern and eastern parts
of our area is being depicted in high resolution guidance. t
about the same time the front pushes through, the system starts
the process of occlusion, beginning the process of developing a
TROWAL on the northwestern side of the systems circulation. The
initial band location is in relatively good agreement among
models to start in Natrona and Carbon Counties. As the event
progresses, several new bands develop further east and south.
The locations of these bands are different in each model
solution. The second most confident location of a TROWAL band
could be from near Wheatland and southwest to Laramie.
Additional banding are dependent of mesoscale forcing inside the
circulation where small vorticity maximums could spur bands
further south. The potential for heavier rain or snow amounts
from these bands, at the upper end of solutions, are around a
foot of snow along the ranges. Interest in travel along I-80
from Arlington to Cheyenne should monitor conditions and changes
to the forecast as the event unfolds and if higher amounts are
realized. Totals between 3 to 12 inches are more confident for
interior mountain basins and ranges. As a result Winter Weather
Advisories are in effect through Thursday evening.
Mountains: Snow should be falling at peaks above 10,000 feet.
The northeastern face of the Snowy Range being the most
favorable for snowfall in the short term given northeasterly
flow. Expected 24 hour snow totals through 6 PM tonight are
between 3 to 7 inches. As the upper level system moves east,
the cooler side of the low pressure should begin to drop snow
level from west to east. The expected lowest snow level while
precipitation is occurring is about 6,000 feet. If a heavy snow
band does end up over one of the three main ranges in
southeastern Wyoming, lower snow elevations are possible. In
this phase of the system the Snowy Range is anticipated to
receive at least a foot of snow. The biggest unknown at this
time is for the Laramie Ranges where the widest range of
solutions exist. The forecasted 3 to 6 inches of snow is on the
conservative side, with amounts of over a foot being shown in a
few high resolution models. The probability of seeing this
amount is between 10 to 30% across the entire range. I should
mention that the SPC REFS has a local maximum where the TROWAL
sets up (mentioned above) and where low spread in the ensemble
depicts a 60% chance of occurrence. This seems too
under dispersed as the entire range from Glendo to the WY/CO
border may be where the TROWAL band sets up.
Cheyenne and Laramie: The confidence that snow falls at Laramie
is increasing compared to previous forecast periods. The
anticipated amounts for Laramie through Arlington are between 1
and 4 inches, Laramie specifically being just under 3 inches.
As mentioned previously, if we get a band of heavier
precipitation set up either location, wet bulbing could push the
marginally freezing surface temperatures to below freezing. The
vertical profile is primed otherwise with a deep saturated
layer with ample negative omega in the DGZ to promote efficient
snow production. At Cheyenne, some accumulation of snow is
likely in the morning hours Thursday. The current thinking is
that with the marginal temperatures during the event that road
and pavement surface stay largely clear. The expected total
accumulations here are below an inch of snow, but there is a
30-50% chance that totals meet one inch. This again depends on
where small scale banding decides to occur, if at all.
Areas to the east and north of the foothills and mountain ranges
may experience periods of mixed precipitation, but otherwise
accumulation of snow is not likely. The QPF of rain is generally
between an inch to an inch and a half. QPF at locations from
Douglas north and near Rawlins are about half an inch.
The Pacific upper level system begins to depart our area to the
east. The chances of rain and snow drop off by Thursday night.
&&
.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Issued at 217 AM MDT Wed Oct 14 2026
Once the potent Pacific storm exits the area to the east and
accelerates into the Great Lakes Region, primary forecast concern
will shift to a hard freeze and frost Thursday night into Friday
morning as clouds dissipate and skies clear for the night. Becoming
increasing confident that a growing-season ending hard freeze is
certain for most of the area as even the 90th percentile (warm-side)
NBM and Grand Ensemble lows are in the mid to upper 20s for a large
bulk of the forecast area. Freeze headlines are expected soon with
low temperatures forecast to range from the mid teens to mid 20s,
but want to handle the storm system impacting the area today and
Thursday first. Otherwise, it will start to warm up on Friday as the
eastern Pacific ridge axis translates east into the Intermountain
West. Northwest flow will continue over the forecast area though, so
highs will be seasonably cool and generally in the 50s to low 60s
across the region.
For the weekend, medium to long Range models continue to be in good
agreement, showing the broad upper level ridge axis translating
eastward into the Front Range. Expect drier weather with pleasant
daytime temperatures for mid October with highs in the 60s to low
70s...and some mid 70s for western Nebraska. Low temperatures will
be seasonable and generally in the 30s to low 40s into next Monday
morning. Saturday morning will be the coldest morning with lows
generally in the mid 20s to mid 30s with some frost possible. A weak
cold front will brush by the area Saturday night, resulting in
temperatures a few degrees cooler than Saturday and gusty westerly
winds on Saturday shifting into the north on Sunday.
Further out, all models show the upper level ridge axis shifting
east into the central and eastern portion of the United States as
another Pacific system moves near the west coast by late Monday and
Tuesday. Tuesday afternoon will likely be the warmest day of next
week with highs in the mid 60s to mid 70s due to south to southwest
flow at the surface and aloft. Models show this storm system slowly
tracking eastward over the western United States with increasing
chances of light rain and cooler temperatures by next Wednesday and
through the end of next week.
&&
.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 600 AM MDT Wed Oct 14 2026
Potent Pacific storm system will continue to accelerate eastward today
and tonight. A brief break in the rainfall is expected with low CIGS
and some fog remaining over the area, possibly into this afternoon.
Rain will increase in coverage and intensity this evening while
spreading northward. Rain may change to snow for KRWL, KLAR, and
possibly KCYS later in the forecast period.
HAZARDS/WEATHER TRENDS: IFR to LIFR conditions are most likely at KCYS
through the day and into tonight with persistent easterly flow. Western
Nebraska terminals will continue to see MVFR CIGS, briefly increasing
to VFR by this afternoon. Conditions will deteriorate between 00z and
06z Thursday as moderate rainfall develops over the area with IFR or
near IFR conditions through tonight. KRWL will be tricky since it will
be on the fringe of the IFR conditions and not totally confident KRWL
will switch over to snow before the precipitation ends late tonight.
KLAR will see intervals of MVFR conditions today with RA or +RA
developing around 03z, with a good chance (80%) of precipitation
changing to all snow with LIFR conditions. Kept snow out of KCYS for
now due to limited confidence in timing.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Weather Advisory from 6 PM this evening to noon MDT
Thursday for WYZ110-112-116.
Winter Weather Advisory until noon MDT Thursday for WYZ114.
NE...None.
&&
$$
SHORT TERM...RV
LONG TERM...TJT
AVIATION...TJT
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