Area Forecast Discussion
Issued by NWS Riverton, WY
FXUS65 KRIW 300556 AAA
Area Forecast Discussion...UPDATED
National Weather Service Riverton WY
1156 PM MDT FRI JUL 29 2016
.UPDATE...Added 06z aviation discussion.
West of the Continental Divide...KJAC/KBPI/KPNA/KRKS
Smoke from the Cliff Creek Fire near Bondurant and the Lava Mountain
Fire west of Dubois may bring some terrain obscurations over
Togwotee Pass and the northern Wind River Range through the period
Otherwise, VFR conditions will prevail through 12z Sunday. Some
high level monsoonal moisture will rotate into southwest Wyoming
Saturday afternoon while a weak upper level disturbance pushes into
northwest Wyoming. These elements will combine to produce isolated
showers and thunderstorms primarily between 21z Saturday - 03z
Sunday. A dry sub-cloud layer will result in the potential for
erratic wind gusts 30-40kts near any showers or thunderstorms.
Surface W-NW winds of 10-20kts will otherwise prevail Saturday
afternoon and early evening.
East of the Continental Divide...KCOD/KCPR/KLND/KRIW/KWRL
A few showers along and east of the Bighorn Range will exit the area
by 08z. Otherwise, VFR conditions will prevail through 12z Sunday,
with smoky areas continuing in the primarily in the vicinity of the
northern Wind River Range and Togwotee Pass. Some monsoonal
moisture will rotate across southern Wyoming Saturday afternoon
where some high-based showers and thunderstorms will develop
primarily vcnty and south of a KLND-KCPR line. A dry sub-cloud
layer will result in the potential for erratic wind gusts of 30-40
knots in the vicinity of any showers or thunderstorms. A weak upper
level disturbance may bring some isolated showers with a few
thunderstorms across northern Wyoming Saturday evening into early
.PREV DISCUSSION... /issued 153 PM MDT FRI JUL 29 2016/
SHORT TERM...Tonight Through Monday
Convection looking better attm compared to yesterday with
approaching shortwave and good day of heating with warmer temps and
dew points still up. Will have to watch these into the evening hours.
Monsoonal moisture is lurking as far north as ecntrl nv and wcntrl
ut. As the upper high gets slowly suppressed swd...the models are
trying to bring the first round of mid level moisture into far
wrn/swrn Wyoming during the day Saturday. Not the most favorable
flow pattern through Saturday but all the guidance is trying to
bring it in around the wrn/nwrn edge of the high. Little better
chance Saturday night into Sunday with developing wsw flow in the
mid levels and trough helping as it moving into srn Canada and the
far nwrn part of the PacNW. Just another concern for the fire conds
with dry lightning/gusty wind potential near any isold storms.
Otherwise, very warm to hot with some breezes around. Limited mainly
mid level moisture spread through the entire area Saturday night
into Sunday giving most everyone at least a slight chance of high
based storms. Moisture likely gets suppressed Monday so just hot and
dry with local breezes.
LONG TERM...Monday Night Through Friday
Weak convection possible Monday evening, but overall it will be
quiet Monday night and Tuesday morning. Medium-range models in
good agreement with upper low tracking along the US/Canada border
near the Idaho Panhandle on Tuesday. Southwest flow aloft ahead
of this feature will boost temperatures well into the 90s across
many of the lower elevations and winds will also increase. Looks
like this could be another critical fire weather day, and
highlights will depend upon fuels status and where the wind blows
most. Tough to discount the possibility of at least isolated
convection with the best chance over the western mountains and
potentially southwest Wyoming. As the low tracks east along the
northern Montana border Tuesday night, cooler air will push south
into Wyoming and affect mainly areas east of the Continental
Divide. Temperatures will be several degrees cooler Wednesday and
more seasonal for this time of year. Drier and more stable
westerly flow will limit any convection to areas near the Utah and
Colorado borders. Overall trend is for drier zonal flow Thursday
with gradual backing of the upper flow to southwest by Friday.
Temperatures will continue around seasonal normals with convection
largely limited to the far southern tier of the forecast area.
Winds will increase on Friday across mainly southwest Wyoming.
Drier flow will lead to low dew points and falling relative
humidities. Many lower elevation locations will see poor overnight
Expect VFR conditions to prevail through 00Z/Sunday. Convection
this afternoon has developed as expected over the Absaroka and
Bighorn ranges tracking over points downstream. Will go with VCSH
at KCOD and KCPR but axis ov&&
er northern Natrona may not shift much
to the south as convections tracks southeast of the southern end
of the Bighorn Range. So, confidence is less at KCPR. Convection
will diminish with the setting sun and benign conditions will be
the rule overnight. West-northwest surface wind 12-22kts at KRKS
will continue until around 02Z/Sat. Similar speeds expected to
develop by 21Z/Fri at KBPI and KPNA. Weak boundary will allow for
northeast surface wind at KRIW and KCPR through much of the
evening. Wind speeds at southwest terminals will increase again
Saturday afternoon, likely between 18Z at KRKS and by 20Z at KBPI,
KPNA, and KJAC. Any convection Saturday should be confined to the
southwest mountains and nearby basins. Therefore, have included
VCSH at KBPI and KPNA.
..Fire Weather Watch for Saturday afternoon and evening for fire
zones 283...288...289...414...415 and 416...
Isolated thunderstorms will prevail through the evening with the
potential for gusty wind near any storms. A surge of higher level
subtropical moisture will move into the southwest during the day
Saturday with a little bit spilling over the divide. Isolated to
widely scattered gusty thunderstorms will occur near any of these.
Fire conditions will worsen in the western mountains and as far east
as the Wind River Basin and nearby Green and Rattlesnake Ranges due
to breezes, hot temps, low rh`s, 5-6 haines index and isolated to
widely scattered dry lightning.
Fire Weather Watch from Saturday afternoon through Saturday
evening for WYZ283-288-289-414>416.