478
FXUS65 KRIW 131900
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
100 PM MDT Sat Jul 13 2024

.KEY MESSAGES...

- Wind gusts of 40 to 60 mph will be common from isolated showers
  and thunderstorms through sunset Saturday.

- Elevated to near-critical fire weather conditions are expected through
  the weekend as temperatures remain above normal. Relative
  humidity will improve slightly on Sunday.

- Smoke, originating primarily from Oregon wildfires, will
  continue to circulate into the state from the west creating
  hazy conditions through at least Sunday morning.

- Seasonal temperatures the first half of the work week begin to
  increase late next week as another ridge of high pressure
  builds across the western US.

&&

.DISCUSSION...
Issued at 100 PM MDT Sat Jul 13 2024

Midday water vapor imagery indicating a better push of mid-level
moisture arriving from the southwest Saturday afternoon.
Precipitable water rose from 0.44 Friday evening to 0.58 inches at
KRIW this morning, while KSLC showed 0.64 inches. Weak convection,
although isolated, has already ignited over the higher terrain of
the west-central and far southwest. CAMS and trends over the
recent few days point to more coverage of showers and storms
particularly after 3 PM Saturday. Dew points in the lower 50s in
the far north will allow for rain to reach the surface,
primarily across northern portions of the Bighorn Basin and
Johnson County. Jet energy and weakly cyclonic flow at 700mb
also favors stronger convection in these areas. Elsewhere,
boundary layer moisture is limited with temperature-dew point
spreads of 40 to nearly 60 degrees at midday. Thus, again
expect gusty outflow wind of 40 to perhaps 60 mph to be the
primary hazard over central and southwest Wyoming until 6 or 7
PM Saturday. Daytime highs again top-out well above normal
Saturday afternoon, as readings reach 88 to around 100F. Smoke
from Oregon wildfires will continue to spread east into the
state as it rotates around a Four Corners high. The main impacts
will be a noted reduction in the 50+ mile visibility we are
used to. Higher terrain will be hazy or obscured from a
distance.

The Four Corners high will continue to spin moisture north and east
into the forecast area for Sunday. Precipitable water climbs to 0.60
to 0.80 inches by Sunday afternoon, dew points increase about 10F,
and CAPE of 500-750 J/kg is expected. This combination leads to
better coverage of wet showers and storms Sunday afternoon and early
evening. Jet energy remains along and north of the Montana border
taking with it a shortwave east through the Canadian Prairie
Provinces Sunday and Sunday night. The weakly cyclonic flow
persists over the far north where convective chances increase
late Sunday. The cloud cover and precipitation leads to
slightly cooler daytime highs Sunday. Convection wanes with the
setting sun. After another hot day, overnight lows stay above
normal.

All areas to be cooler Monday and Tuesday as the last Canadian
shortwave flattens the ridge. Weak northerly flow at the surface
follows for areas east of the Continental Divide, while the west
sees a west-northwest afternoon breeze. Temperatures return to
seasonal for Monday and Tuesday, possibly lingering through
Wednesday. Mid-level moisture rotating into the state from the south
allows for typical diurnal convection, with areas east of the
Continental Divide seeing the best chance. By late next week,
ensemble clusters give confidence in the return of another
ridge of high pressure across the western US. Above normal
temperatures and a downturn in afternoon convection would be
favored in this pattern.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1121 AM MDT Sat Jul 13 2024

VFR conditions prevail through the period. Like the previous few
days, shower and thunderstorm chances occur this afternoon. They
will be isolated, so it is difficult to put confidence in the TAF;
have VCSH in a few locations where high-resolution models have more
consensus in showers, though even at those locations, low confidence
(about a 20% chance). The bigger impact from these isolated showers
will be gusty outflow winds. Gusts 40 to 50 knots are possible with
the stronger outflows.

Smoke continues to pass through the area. Currently, VFR conditions
are expected to remain, though some mountain obscuration continues.

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 100 PM MDT Sat Jul 13 2024

A very dry lower atmosphere, much above normal temperatures, and
gusty west wind and convective outflows combine to create elevated
to near-critical fire weather conditions through sunset Saturday.
Isolated showers and thunderstorms bring the threat of gusty and
erratic outflow gusts of 40 to 60 mph, particularly across the high
deserts of southwest Wyoming. With most lower elevation zones seeing
relative humidity from 8 to 11 percent Saturday afternoon, overnight
recovery will remain poor. Moisture from the southwest rotates into
the state late tonight and Sunday. This provides a better chance of
wet thunderstorms Sunday afternoon, along with slightly cooler
temperatures and marginally better minimum relative humidity. This
trend of more showers and storms continues into Monday leading to
more cloud cover and temperatures closer to seasonal averages.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 10 PM MDT Sunday for WYZ004>006-010-011-
017-018-020.

&&

$$

DISCUSSION...CNJ
AVIATION...Wittmann
FIRE WEATHER...CNJ