965
FXUS65 KRIW 171000
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
400 AM MDT Sat Aug 17 2024

.KEY MESSAGES...

- A surge of monsoonal moisture will bring showers and
  thunderstorms this afternoon to southwestern Wyoming.
  Isolated flash flooding is possible.

- Strong winds are likely to accompany this activity; locations
  east of the Divide will see the wind even when showers/storms
  die off late this afternoon and evening.

- Shower and thunderstorm chances continue Sunday and Monday.

&&

.DISCUSSION...
Issued at 357 AM MDT Sat Aug 17 2024

Today will start off fairly uneventful as we initially stay under
the influence of the dominating high to our south. Temperatures will
peak a little warmer, especially east of the Divide where highs will
return to the 90s. However, a strong mid-level shortwave will
quickly approach from Utah after 18Z. This will advect in a notable
surge of monsoonal moisture, with PWATs increasing from around
a third of an inch to around or just over an inch across
southwestern Wyoming. Accordingly, showers and thunderstorms
will accompany the arrival of this airmass, first across Uinta
County and then moving northeast to the Continental Divide by
around 23Z. This activity will struggle to make it over the
Divide with the loss of diurnal heating, and most of the rain
associated with this activity will remain across southwestern
Wyoming. Isolated flash flooding will be possible with any
training storms this afternoon.

The other concern with this surge of moisture is wind. Hi-
resolution models are in good agreement with showing not only
the convection but decently strong accompanying wind. This
threat is further seen with forecast surface pressure, which
shows a strong gradient setting up given the advancing cold pool
/ mesohigh. Wind gusts of 40 to 50+ mph are not out of the
question this afternoon and evening as the showers move
northeast, likely outlasting the convection and advancing east
of the Divide perhaps as far north as the Bighorn Basin.

Showers will be on the decrease after 03Z, mostly ending by 06Z.
Sunday and Monday will see a more widespread shower and thunderstorm
threat as broader shortwaves rotate around the ridge. An
isolated flash flooding threat will remain given the ample
moisture that will still be in place.

Further ahead, the general synoptic pattern will persist,
though a decrease in available moisture will keep precipitation
chances a little lower Tuesday through at least midweek.
Temperatures will remain on the warmer side, generally around
normal to five degrees above normal for this time of year.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1020 PM MDT Fri Aug 16 2024

VFR conditions will be in place through much of the TAF period for
most sites. SKC skies and light winds will remain in place
tonight through 18Z. Winds will increase at all locations
around 18-20Z with increasing mid level clouds surging in from
the southwest. Wind gusts around 20 kt will be common.
Monsoonal moisture will bring in showers and thunderstorms at
KRKS after 21Z and KBPI and KPNA by 23Z. KRKS has the best
chance to be directly impacted and have opted for PROB30 groups
for KBPI/KPNA at this time. These storms will continue toward
the northeast, impacting KLND/KRIW between 00Z-02Z for the end
of the period. These storms should then be impacting KCPR after
02Z through the end of the forecast period. Winds will increase
to 25+kt with these storms, with outflow boundaries reaching
KWRL as well. Locally stronger winds could occur at KLND.
Winds will diminish for most areas outside of the convective
activity after 00Z.

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...Myers
AVIATION...LaVoie
FIRE WEATHER...Myers