364
FXUS65 KRIW 091101
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
501 AM MDT Thu May 9 2024

.KEY MESSAGES...

- Some lingering rain/snow Thursday diminishing in intensity and
  coverage.

- Warming and mainly dry trend Friday and over the weekend.

- Warm with sporadic rain showers and isolated thunderstorms
  minimal in coverage next week with no significant impacts
  expected.

&&

.DISCUSSION...
Issued at 1243 AM MDT Thu May 9 2024

Current IR depicts the positively tilted trough extending from
the Great Lake Region and through the Rockies pushing through
the CWA southeastward. Cloud top temperatures continue to warm
slowly as scattered rain/snow showers diminish as the day
progresses Thursday. Radar shows a mainly upslope nature of
precipitation northeast to southwest with the eastern Winds
seeing the only real impact in terms of accumulations for the
backcountry. Otherwise, very limited impacts to roadways and
town centers at this time. Winter weather headlines will expire
before sunrise Thursday with the exception of the aforementioned
eastern Winds as steady snowfall continues into the afternoon
hours. Snow rates will rapidly decline at that point with only
some lingering light snow into the evening and overnight hours
to include the southern Absarokas and Bighorns as well. An
additional 6-8 inches for the eastern Winds is likely with the
highest probabilities (80-90%) with a smaller chance (20-30%)
for up to a foot. As the surface low pivots further
southeastward, the gradient will start to slacken through the
day Thursday with lingering gusty winds for the Sweetwater
County area along with the higher terrain of the Winds.
Improving sky conditions west of the Divide by early afternoon
with eastern zones remaining cloudy into the overnight hours
seeing improvement come Friday morning. Low stratus and fog for
the areas of rain east of the Divide will be the forecast
challenge Friday morning as models hint at this development with
the lightening of winds and improving skies. BUFKIT soundings
show a very saturated boundary layer, so higher probabilities
are expected, especially for the Wind River Basin and for the
Johnson/Natrona County areas.

Otherwise, Friday will see upper level ridging build in from
the west with increasing convergence aloft as a weak cut off low
develops to the south and pushes southeast into the weekend
with no impacts to the CWA expected. A warming and dry trend
will start for this time period with average temperatures Friday
and above for the weekend. Winds will not be high with pristine
weather expected for the weekend.

Next week will see the upper level ridge continue to set in
place with a series of shortwaves passing to the north clipping
northern areas of the CWA to increase some sporadic chances for
scattered rain showers and isolated thunderstorms. Tuesday
looks to be the best chance for a more widespread chance for
this occurrence but little to no impact looks to be of high
confidence at this time. Mid week onward, expect the blocking
ridge to build in quite strong up from the desert Southwest
pushing the PFJ northward into Canada cutting any precipitation
chances and a warmer than average trend to continue moving
forward.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 457 AM MDT Thu May 9 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

A series of minor shortwaves will continue to parade across the
forecast area through midday today. The north to northeast flow
aloft leads to downsloping and hinders precipitation chances at
KJAC, KBPI, and KPNA through the period, with less than a 1 in 5
chance of a shower. Patchy low clouds are possible though,
especially in vicinity of KPNA. KRKS sees a northeast surface
wind gradually strengthen between 09Z-15Z/Thursday as the
pressure gradient tightens. The weak upslope in the vicinity of
KRKS combined with shortwave energy will lead to a period of
IFR/MVFR conditions with light snow until around 15Z Thursday.
Conditions and ceilings improve at KRKS around midday with VFR
after that time. Gusty east to northeast surface wind 20-35kts
will be common at KRKS by late morning. KBPI and KPNA see
easterly wind 10-20kts develop around midday, while KJAC sees
downvalley northerly wind at similar speeds. The winds at all
terminals decrease around 02Z/Friday, with KRKS seeing breezy
conditions all evening. Mountain tops frequently obscured.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

A parade of shortwaves rotate southwestward through the forecast
area through midday today. In general, MVFR conditions prevail
until 15Z-18Z/Thursday. The favorable north to northeast
upslope flow keeps intermittent light rain in the central basins
through into the midday hours today. There could be some breaks
in the clouds Thursday afternoon, but cold air aloft enables
low- end VFR stratocumulus to reform in the moist environment.
VFR returns to all terminals between 16Z-20Z/Thursday with the
exception of KCPR, where VFR may not return until around
00Z/Friday. Mountain tops obscured, especially above 8-9K ft MSL
through much of the period. MVFR to possibly IFR ceilings may
return after 06Z Friday, but not enough confidence to include in
the forecast at this time.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 AM MDT early this morning for
WYZ002-008-009-022.

Winter Storm Warning until 6 PM MDT this evening for WYZ015.

&&

$$

DISCUSSION...Lowe
AVIATION...Hattings