Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222021
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
221 PM MDT Sat Sep 22 2018

.SHORT TERM...This evening through Tuesday

Overview...Dry southwesterly winds return over the region, as a
trough of low pressure moves onshore over the PACNW. This trough
will deepen as it continues to move onshore today and tonight. This
will increase the winds into Sunday, before the trough moves over
the forecast area Sunday night. A reinforcing trough from Canada
will quickly follow on the heels and impact the area late Monday
afternoon through the overnight hours.

Synopsis...Dry conditions will continue today, as breezy to windy
conditions continue across much of the forecast area this afternoon.
Single digit RH values this afternoon in places, after a poor
recovery last night. This could repeat again tonight, especially
east of the Divide along the Bighorns, Casper Mountain and the
Lander Foothills. Winds increase Sunday, in advance of the trough,
with southwest winds with gusts of 35 to 40 mph across all but the
central basins and northern portions of Johnson County. RH values
will be above critical values over the far north, but Red Flag
conditions will continue elsewhere. Precipitation chances will
increase over the far north and south Sunday night, as the cold
front and trough begin to move over the area. Isolated to scattered
showers will remain possible during the day Monday across the north,
as the cold front associated with the second trough approaches. With
the cold front Sunday night, fire weather concerns will be shifted
west of the Divide once again. This will be in place Monday and
Tuesday. Red Flag conditions will continue over Lincoln, Sublette
and Sweetwater counties Monday, with critically low RH values and
west-northwest winds gusting to 35 mph. Fire weather conditions will
remain elevated in these areas, including Teton County, however west-
northwest winds will thankfully be much lighter with isolated gusts
up to 20 mph.

.LONG TERM...Tuesday night through Saturday night

Dry and cool Tuesday night. Wednesday will be dry with breezy areas.
The next weather system heads into the northern plains states
Wednesday night into Thursday. A cold front moves south Wed night,
and by Thursday morning it lies along the Continental Divide.
Scattered showers are to develop over the Bighorn mountains and
Johnson county after midnight Wednesday night through Thursday
morning, as the system clips our area. Otherwise, Thursday will be
dry and cool east of the Divide, while the west will be milder as
the cold air will have limited impact. Dry and warmer on Friday
with breezy areas. Next Saturday also looks dry, warm and breezy
now as the models have slowed down the next weather system and the
cold front.

&&

.AVIATION...For the 00Z TAFS through 00Z Monday

VFR conditions will prevail at the terminal sites through the
period. MVFR visibilities are expected along and northwest of a KBPI
to KPNA line due to smoke from the wildfires. Upper level smoke
plumes will continue to drift east across central WY tonight. The
gusty west to southwest wind will diminish toward 02Z. Between 16Z
and 18Z Sunday, a gusty west to southwest wind of 15 to 25 knots
will redevelop at many terminal sites with higher gusts. Smoke
plumes are expected to develop again Sunday afternoon and propagate
east across central WY once again.

&&

.FIRE WEATHER...

...RED FLAG WARNINGS IN EFFECT FROM THROUGH 8PM WEDNESDAY EVENING
FOR ZONES 277, 278, 279, 280, 281, 283, 285, 288, 289, 300, 414,
415 AND 416...

Temperatures will be warmer tonight across the area. RH values
will be 15 to 35 percent lower across northern and central
portions, with widespread readings of 30 to 50 percent. Dry
conditions will continue tonight and Sunday, before isolated
showers become possible across the north and portions of zone 279
Sunday night. Red Flag conditions will continue Sunday across the
current zones. A cold front will move across the forecast area
Sunday night, with isolated to scattered showers continuing
across the north Monday. Red flag conditions will also continue
across the south Monday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT Sunday for WYZ277>281-283-285-
288-289-300-414>416.

&&

$$

SHORT TERM...LaVoie
LONG TERM...Ross
AVIATION...Ross
FIRE WEATHER...LaVoie


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