218
FXUS65 KRIW 180420
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1020 PM MDT Sat Aug 17 2024

.KEY MESSAGES...

- Increasing monsoonal moisture today with widely scattered
  thunderstorms expected this afternoon and evening.

- Storm activity will be a bit further east of the Divide
  Sunday.

- Continued active but weaker pattern throughout the week with
  more seasonable temperatures expected.

&&

.DISCUSSION...
Issued at 1235 PM MDT Sat Aug 17 2024

Current IR depicts the ridge of higher heights extending in from
the south to southeast as monsoonal moisture starts to pump
more northeastward across the Rocky Mountain West. Radar shows
increasing activity across Utah currently pushing northeast
towards far reaches of southwest Wyoming. Areas along the border
should start to see activity cross over by 2-3PM, spreading
northeast into the rest of the afternoon and evening hours.
Flooding concerns are at low confidence at this point with the
bulk of the stronger instability and vort max in northern Utah
pushing into Idaho. PWAT values less than half an inch at this
point for areas of deep southwest Wyoming, but something to
keep an eye on for a more localized threat. Otherwise, stronger
winds are the main concern as 40-50 mph gusts are possible with
the strongest cells as they push out of northeastern Utah.
Currently any reports are calling for these values to be max at
this point where as the further northeast these get, the weaker
of an environment to flourish in. With moderate steering flow
speeds, expect faster moving storms in a multicell structure
making for the aforementioned lower flood threat and higher in
the wind department. Modest CAPE and lapse rate values at best,
indicate a lower end severe threat as these storms enter the CWA
but these far reaches of the area will be the most to be
concerned with.

Otherwise, these storms will progress towards the Winds by 5-6PM
with uncertainty on if these will hold together and make it into
the Wind River Basin and beyond towards sunset into the
overnight hours. Some models indicate this occurring but others
not so much. Thus, confidence is low, and even if this occurs,
little to no threats will occur with them. Areas along the Wind
Corridor stretching to Casper and the I-25 Corridor will see
these storms hold better together southeast of the Winds, but
again any stronger threat will be diminished with the setting
sun and loss of stability into the overnight hours. These will
push east out of the CWA by the early Sunday morning hours with
another round expected for Sunday afternoon and evening
progressing further east of the Divide as the monsoonal push
furthers itself into eastern portions of the CWA. Similar
threats expected Sunday with wind the main hazard with this
next compact shortwave across the state.

Going forward, monsoonal moisture weakens throughout the week,
although a continued active pattern with the upper level low
ongoing across the Pacific Northwest. This will continue to
weaken the upper level high with increasing divergence aloft as
it moves more east into the southeastern portions of the US.
Otherwise, the aforementioned low will slowly fill and push east
finally kicking out to the east by Saturday of next week.
Seasonable temperatures and winds expected throughout as well.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1010 PM MDT Sat Aug 17 2024

Virga showers will continue to end through the first couple of
hours of the TAF period. Winds have already subsided across much
of the area, however winds of 15 to 20 kt will continue/develop
at KCPR and KRIW through 12Z respectively. The winds at KRIW
will subside by 16Z, while the winds at KCPR gradually decrease
through 19Z and turn more north-northwest. Showers and
thunderstorms will develop across areas west of the Divide and
the Bighorn Basin between 19Z and 21Z, spreading toward the
northeast through 00Z. Confidence is low on the timing of these
storms, so have left PROB30 groups for impacted terminals for
now. These storms are expected to cross into the Wind River
Basin after 00Z, possibly impacting KLND/KRIW through 05Z. Any
remaining showers/thunderstorms will be isolated toward the end
of the TAF period, as gusty outflow winds continue across the
forecast area. Gusts of 20 to 30 kt are expected with the storms
Sunday, although isolated gusts of 40 to 45 kt cannot be ruled
out.

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

&&

.FIRE WEATHER...
Issued at 357 AM MDT Sat Aug 17 2024

Elevated fire weather conditions are expected for much of the area
this afternoon ahead of surging monsoonal moisture that will arrive
to southwestern Wyoming around noon. This will bring showers and
thunderstorms mainly west of the Divide, as well as strong
southwesterly wind that will eventually move east of the Divide late
this afternoon and evening. While humidity will increase notably,
the wind will likely arrive suddenly and could cause issues for
ongoing fires.

&&

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

&&

$$

DISCUSSION...Lowe
AVIATION...LaVoie
FIRE WEATHER...Myers