Greybull, Wyoming Weather Forecast Discussion

170
FXUS65 KRIW 262342
AFDRIW
Area Forecast Discussion
National Weather Service Riverton WY
542 PM MDT Fri Sep 26 2025
.KEY MESSAGES...
- Gusty north winds 20 to 25 mph behind a cold front will
  continue through the afternoon, decreasing towards sunset.
- Isolated showers across portions of central WY will continue
  to end from west to east through the afternoon, with mostly
  clear skies expected by sunset.
- Warm and dry weather is expected on Saturday.
- Shower and thunderstorm chances increase on Sunday and
  continue through the middle of next week, mainly across
  western Wyoming.
&&
.UPDATE...
Issued at 115 PM MDT Fri Sep 26 2025
For the first time in two days, we actually have clouds in the
Wyoming skies today! With these clouds, a few isolated showers
associated with a weak shortwave continue to spread across
portions of central WY early this afternoon. These have been
mainly virga, but a few light sprinkles will remain possible
with this activity. At the same time, a weak cold front,
associated with a separate shortwave, continues to push
southward across the region through the afternoon. Behind the
front, gusty north winds 15 to 25 mph have been occurring, with
locally stronger winds across favored locations in northern
Johnson County, including the Buffalo area. These winds will
continue through the rest of the day, but will quickly diminish
towards sunset. The shower activity will also end towards
sunset. Mostly clear skies and light winds (just like we have
seen over the past 2 days) will return this evening, and persist
through the day Saturday. Beyond Saturday, there is not much
change to the forecast, but a more active pattern still looks more
likely Sunday through much of next week.
&&
.DISCUSSION...
Issued at 211 AM MDT Fri Sep 26 2025
07Z water vapor imagery shows two areas of interest this morning.
The first being an upper-level low over southern California with an
associated shortwave shifting north across the Great Basin and
southern Rockies. The other is an upper-level trough over the
northwest CONUS with an embedded shortwave making its way into
western Idaho. Both of these features are funneling moisture, mean
PWATs of 0.4" to 0.7", towards western Wyoming and will provide weak
support for isolated showers and thunderstorms through the day
today. Outside of shower or thunderstorm chances, above normal
temperatures persist.
The first shower chances (15-20%) exist across northern Lincoln
County around sunrise this morning, with support coming from the
previously mentioned northwest CONUS trough and shortwave. The
trough is being pushed across the Northern Rockies by an upper-level
jet that is centered over southwestern Canada and Montana with
Wyoming at it`s nose. At the nose of the jet is an area of
tropospheric folding that favors to vertical mixing. As the trough
shifts east through the morning, enhanced vertical mixing aloft,
moisture, and an associated weak front, will shift the shower
chances east across the northern Green River Basin and into the Wind
River Basin through midday today. Chances are that any rain will
remain as virga, however, an isolated rain shower cannot be ruled
out in these locations. Thus, rain chances of 15% to 20% have been
added. Breezy winds are also forecast, mainly across Johnson County,
as the nose of the jet and front shift east through the afternoon.
Wind gusts are forecast to remain largely below 25 mph and relative
humidity values in the 20% range, so fire weather concerns remain
relatively low at this time.
The next shower and thunderstorm chances (25-50%) exist across far
southwestern Wyoming this afternoon. Support for these showers and
thunderstorms will largely be with the Great Basin shortwave.
Convection is forecast to initiate off the Unita Mountains and shift
north and east through the afternoon and early evening. However,
convection is not expected to be sustained for long given the
proximity to the upper-level jet by this time. By tonight, high
pressure returns for Saturday with another day of above normal
temperatures and dry weather.
Guidance remains in consensus that the California low and it`s
moisture will be absorbed into a trough and push into the
Intermountain West on Sunday. This will be the first day of
unsettled weather across southern and western Wyoming. By Monday
into Tuesday, a longwave trough is forecast to situate itself over
the western CONUS. Multiple shortwaves with Pacific moisture are
forecast to round the trough and bring multiple shower and
thunderstorm chances (30-70%) and near normal temperatures to the
west through the middle of next week. At this time, chances are
greatest Monday into Tuesday night for the west (60-70%) as a potent
shortwave moves across the region. Forecasted snow levels are around
or above 10,000 feet AGL, so any snow would be across the higher
elevations of the western mountains. Probabilities of high
elevations seeing more than 0.5" of accumulated snow through next
week are largely less than 50% at this time.
&&
.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 533 PM MDT Fri Sep 26 2025
VFR conditions expected during the next 24 hours with mostly clear
skies. Most mid to high level clouds have moved east, with only a
few left around KCPR. Daytime CU have been limited to highest
elevations, and will be dissipating in the next hour or so. The weak
cold front continues to sweep southward across northern WY,
bringing brief gusty north winds. Once the sun sets, the southward
push will weaken, so most sites east of the Divide will see north to
northeast winds, but will remain light overnight. Southerly winds
reestablish tomorrow morning, but all sites remain under 10kts.
Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hensley
DISCUSSION...Gerhardt
AVIATION...Straub

NWS RIW Office Area Forecast Discussion