862
FXUS65 KRIW 151211
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
611 AM MDT Sat Jun 15 2024

.KEY MESSAGES...

- Elevated fire weather risk Saturday afternoon and early
  evening.

- Cooler temperatures and increasing precipitation chances
  Sunday night through Wednesday.

- Dry and warming trend by end of the week and into next
  weekend.

&&

.DISCUSSION...
Issued at 1232 AM MDT Sat Jun 15 2024

IR currently depicts the low that affected the CWA push further
east into the Great Plains with another low over the Pacific
northwest. Highly meridional upper level flow southwesterly
aloft across the upper Rockies. A couple sporadic rain showers
are dissipating with a mainly dry Saturday ahead. A weak frontal
boundary will continue to slide slowly east through the CWA
throughout the day Saturday. This could spark a couple isolated
thunderstorms along and east of the I-25 corridor with better
ingredients for severe weather further east in the state and beyond.
Thunderstorms are progged to develop near the CWA line with CYS
after 20Z with the FV3 extending this line through Sweetwater
County. Confidence is low at this point (<15%), and even if so, they
will push east quickly within an hour or two.

The main story for Saturday will be elevated fire weather
conditions in the afternoon and early evening time frame. With
the aforementioned front, the gradient will tighten to around
6-7 mb across the CWA. As a result, expect wind gust to over 40
mph from Sweetwater County through the Rattlesnakes and along
the I-25 corridor. Other points east of the Divide to include
the Wind River and Bighorn Basins, expect gusts up to 30-35 mph
and less than 25-30 mph to the west. Relative humidity values
will be in the 10-25 percent range, lowest for Sweetwater County
but with green-up ongoing. confidence is low on any widespread
fire concerns.

Otherwise, winds will diminish towards sunset with radiational
cooling and subside to less than 10-15 mph after midnight
heading into Sunday morning. The next system coming from the
Pacific northwest will slowly progress east towards the CWA and
deepen due to increasing divergence aloft. PVA anomalies look to
effect northwest portions of the CWA first early Monday morning
expanding eastward throughout the day. Precipitation chances
increase across northern portions of the CWA with models in
better agreement this last set of runs with this northern
progression. Light snow is possible for higher terrain above
7-8kft across Yellowstone and northern Absarokas for overnight
and early morning hours, with rain showers lower and further
east. Best chance looks to be late Monday and much of Tuesday
with the PVA set across this area before quickly exiting
northeastward into Montana and the upper Great Plains into
Wednesday as the low becomes more progressive at that point in
time. Accumulation amounts are still of low confidence, but
nothing stands out in any models for a great impact at this
point in time. Regardless, cooler temperatures can be had up to
10 to 15 degrees below average by Tuesday.

Next up, will be a more ridging to more zonal pattern through
the remainder of the work week and into next week. Subtle
disturbances look to still perpetrate through the upper level
pattern sparking some weak precipitation chances for higher
terrain pushing into some lower valleys and basins but of
minimal impacts. A warming trend is in store for this period
back to average temperatures by Thursday and above for this time
of year by the weekend with low 90s possible east of the Divide
for some. All in all, rainfall amounts do not look that great
for the first half of the work week, but will be the best chance
for the wider spread amounts for the northern half of the
viewing area.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 608 AM MDT Sat Jun 15 2024

Conditions will remain VFR through the TAF period. A line of storms
moving through KBPI and KPNA at TAF time, will clear them and then
push over the Wind River Mountains. Expect showers to briefly impact
KLND and KRIW around 13Z. Winds will begin to increase this morning,
becoming very strong across the area through the afternoon. Wind
gusts will average 25-35 knots (as high as 45 knots) Saturday
afternoon.

Models continue to show convective development in Natrona
and Johnson County for this afternoon, which means a chance for
storms in the vicinity of KCPR for a couple of hours. Strong surface
winds should prevent any rogue outflow boundaries associated with
this convection from pushing west and initiating more convection in
the area, so thinking is just a short window for thunderstorms at
KCPR Saturday afternoon. The gusty winds will continue until late
this evening, 03Z or so, before finally dropping to 10 knots or
below for the overnight hours.


Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence
forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Lowe
AVIATION...Rowe/Swanson