244
FXUS65 KRIW 300807
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
207 AM MDT Sun Jun 30 2024

.KEY MESSAGES...

- Hot and dry today, with elevated fire weather conditions. Red
  Flag Warning for portion of Natrona County this afternoon.
  Burning is discouraged.

- A cold front brings rain chances and cooler temperatures
  Sunday night and Monday.

- Seasonal temperatures and afternoon showers and thunderstorms
  for the middle of the week. Warmer and drier towards the end
  of the week.

&&

.DISCUSSION...
Issued at 205 AM MDT Sun Jun 30 2024

Current water vapor imagery shows the current synoptic pattern well,
that being a ridge over Wyoming shifting eastward, with an incoming
trough over the Pacific Northwest. Starting with the ridge, this
brings hot temperatures and dry air to the area today. Temperatures
east of the Continental Divide peak in the 90s, with near 100 for
warm places like Greybull. West of the Divide, temperatures will
generally be in the mid-80s. Afternoon relative humidities (RH) drop
to the low teens for many locations across the area, with upper
single digits for the Bighorn Basin. Northwest Wyoming and eastern
Sweetwater County look to be around 20%. There is some uncertainty
in RH values in an area from roughly Rock Springs to Midwest.
Moisture moving up from the high to our south brings slightly better
moisture and clouds. Both these would act to limit how low RHs get.
The approaching trough tightens the pressure gradient for today,
with a west-to-southwest wind gusting 20 to 40 mph for most of the
area. The Wind Corridor may be closer to that 40 mph mark. A Red
Flag Warning is in effect for the lower elevations of Natrona County
this afternoon for these conditions, as well as the critical fuels
there. Again, there is a bit of uncertainty due to incoming moisture
and cloud cover, which could keep RHs above 15% (about a 20% chance).

That same incoming moisture may spark some afternoon convection for
Sweetwater County northeast through roughly the Natrona County area.
Current models have isolated (about 20%) showers and thunderstorms
during the afternoon and evening. With such dry conditions, not
expecting these to be big rain producers. Instead, outflow winds
will be the bigger concern. Gusts 40 to 50 mph are possible with any
downbursts. Depending on the extent of the cloud cover, these winds
could vary; less cloud cover would allow more afternoon heating and
thus increase the risk for higher winds. Any of this convection
should end by around 10PM MDT.

Now onto the other feature, the approaching trough. The associated
cold front begins to move through northwest Wyoming around midnight
Sunday night. Rain chances accompany the front, moving south and
east overnight. Chances continue through the day Monday. The best
chance for rain occurs over the north half of the area, through
Monday afternoon may see an isolated shower or storm over southern
areas. Temperatures will be noticeably cooler Monday behind this
front, with places in the the middle 70s to middle 80s. Wind looks
to be the main threat with any storms at this time.

The trough is broad, and its influence continues into Tuesday, with
rain chances remaining over the northern third of the area. Tuesday
also look to be a cool day, with highs below normal. An upper-level
low moves out of Canada and into the Dakotas Thursday. This brings
another cool day with rain chances, mainly across the northern half
of the area. Past Thursday, a strong high pressure system builds
over the western U.S. This acts to shut down much of the moisture
into the area. Depending on its exact position, there may be a few
upper lows that pass through the area, or they would be pushed to
our east. Either way, looks like there is favoring for drier and
warmer conditions for next weekend.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1031 PM MDT Sat Jun 29 2024

All terminals to be VFR through the forecast period. Mainly high
clouds to drift across the region overnight. Upper flow backs to the
southwest Sunday and winds increase ahead of an approaching trough.
Southwest wind 15-30kts develops at most terminals between 16Z-20Z/
Sunday with much drier air filtering into the region. Mid-level
moisture does track into portions of central and southwest Wyoming
Sunday afternoon. Isolated high-based showers develop around
20Z/Sunday with potential impacts from gusty outflow wind, with the
best chance (<20 percent) at KCPR and KRKS. Convection and gusty
winds decrease 02Z-03Z/Sunday. A surface boundary brings northerly
surface wind to the Bighorn Basin terminals Sunday evening.

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 205 AM MDT Sun Jun 30 2024

Elevated fire weather conditions today across most of the area.
Afternoon RHs drop to 8%-25%. Afternoon wind gusts of 20 to 40 mph.
A Red Flag Warning is in effect for Zone 280 this afternoon, from
1PM to 7PM MDT. Some afternoon showers and storms are possible
across Sweetwater, southern Fremont, and Natrona Counties this
afternoon and evening. Not expecting any good rain with these, but
outflow gusts 40 to 50 mph are possible. A cold front moves in
tonight from the northwest, bringing cooler temperatures and rain
chances.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 1 PM this afternoon to 7 PM MDT this
evening for WYZ280.

&&

$$

DISCUSSION...Wittmann
AVIATION...CNJ/LaVoie
FIRE WEATHER...Wittmann