521
FXUS65 KRIW 171138
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
538 AM MDT Fri May 17 2024

.KEY MESSAGES...

- Elevated to critical fire weather conditions are expected
  today with humidity below 20 percent and widespread wind
  gusts of 35 to 50 mph.

- A few showers and thunderstorms are possible across northern
  Wyoming this afternoon. Strong wind gusts are the main concern
  with this activity.

- Elevated fire weather conditions continue on Saturday.

- Slightly increased chances for precipitation on Sunday. Wetter
  and cooler conditions arrive early next week.

&&

.DISCUSSION...
Issued at 437 AM MDT Fri May 17 2024

Westerly flow continues today, though will become more cyclonically
curved this afternoon as a shortwave begins pushing in. This is
related to a larger system rotating across Montana. We will see some
impacts from this, but most of the precipitation will remain to our
north. The more widespread impact today will be elevated to critical
fire weather conditions. Temperatures will peak a few degrees warmer
today east of the Divide and across southern areas, which will align
with humidity values dropping into the teens. Moreover, westerly
wind gusts of 35 to 50 mph will be widespread by early
afternoon as a strong west to east surface pressure gradient
sets up across the state.

While the majority of the area will remain dry and windy, a
few showers and thunderstorms are expected across northern Wyoming
ahead of an approaching weak cold front associated with the wave.
Guidance suggests that the Bighorn Basin through Johnson County will
have the best chances (20-40%) given the slightly better instability
expected there this afternoon. With a deeply mixed atmosphere near
the surface, any shower or storm today could throw out some strong
wind gusts.

Wind and any ongoing convection will wane after sunset, leaving dry
conditions as the cold front pushes south overnight. A dominant
westerly flow will become reestablished over the area for
Saturday. Temperatures will be a little cooler behind the front,
but still generally a few degrees above normal. It will be
another breezy day, though not nearly to the extent of Friday.
However, fire weather concerns will continue as humidity values
again drop into the teens. With an even drier airmass overhead,
humidity may approach 10 percent across most of the basins
Saturday afternoon. Otherwise, some late day convection may
develop across far southern Wyoming as Pacific moisture edges
into the area.

The prevailing flow becomes more southwesterly on Sunday as a trough
deepens over Idaho. This will result in increased precipitation
chances across the area (currently around 30-40%), though most of
the area should remain on the dry and breezy side.

On Monday and Tuesday the trough mentioned above is forecast to drop
south and impact the area with widespread cooler temperatures and
precipitation chances. With the associated low placement, locations
east of the Divide appear favored to pick up the most precipitation.

Further ahead, ensemble guidance is hinting toward a continued
active pattern through the end of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 538 AM MDT Fri May 17 2024

VFR conditions are expected to prevail through the TAF period. Skies
will remain mostly SKC, with a few periods of FEW100-200 during the
day Friday. Most terminals can expect to see westerly winds increase
between 15Z and 18Z with gusts around 25 knots during this time. The
strongest winds arrive by the early afternoon, with widespread gusts
of 30 to 35 knots. KCPR, KWRL, KCOD, and KRKS may see periodic gusts
near 40 to even 45 knots through the afternoon hours. Light winds
return to most terminals by the end of the TAF period.

A few isolated showers are possible across portions of northern and
western WY during the day Friday. Confidence is low regarding
potential impacts on any nearby terminals. KCOD, KCPR, and KWRL
would be the only terminals that may see any impacts and it
currently looks unlikely, with a (10-20%) chance of an isolated
shower. More likely impacts at KCOD, KCPR, KRIW and KWRL will be
outflow winds from distant thunderstorms expected across southeast
MT and far northeastern WY. A briefly gusty north to northeast wind
will be possible (20 to 40% chance) at the aforementioned terminals
during that time.

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

&&

.FIRE WEATHER...
Issued at 437 AM MDT Fri May 17 2024

Widespread elevated to critical fire weather conditions are expected
today as a surface pressure gradient increases ahead of a weak cold
front. Sustained west wind of 25 to 35 mph is expected to develop by
early afternoon, with gusts of 40 to 50 mph. At the same time,
humidity values are expected to drop below 20 percent across most of
the area. A drier airmass will move in for Saturday, bringing
humidity values down below 15 percent for most basins. Wind will not
be as strong Saturday, but will still be breezy. Warm and mainly dry
conditions will continue Sunday before cooler and wetter conditions
arrive Monday.

&&

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

&&

$$

DISCUSSION...Myers
AVIATION...Dziewaltowski/Hensley
FIRE WEATHER...Myers