Area Forecast Discussion
Issued by NWS Riverton, WY

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093
FXUS65 KRIW 210846
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
246 AM MDT THU JUL 21 2016

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

IN NORTHWEST WYOMING, A SMOKE PLUME WAS SEEN STREAMING NORTHEAST ON
WEDNESDAY ORIGINATING FROM THE CLIFF CREEK FIRE ALONG WITH A SMALL
CONTRIBUTION OF SMOKE FROM THE LAVA FIRE. AN INCREASE IN SOUTHWEST
WINDS HELPED THE FIRE ALONG WEDNESDAY. THEN ONCE THE WINDS DIED DOWN,
DRAINAGE WINDS TOOK OVER WITH THE NORTHWEST DRAINAGE WINDS DRAGGING THE
SMOKE ALONG WITH IT SOUTHEAST ALONG THE WIND RIVER BASIN, DELIVERING
SMOKE TO THE RIVERTON AREA BRIEFLY BEFORE CLEARING OUT FROM THE NW. IT
REMAINS TO BE SEEN HOW THE AREAL SMOKE COVERAGE WILL PLAY OUT AT
SUNRISE RESULTING FROM THE NOCTURNAL WIND Regime TO BETTER AID IN
PREDICTING THE AREAL Coverage OF SMOKE FOR TONIGHT. TODAYS WINDS WILL BE
LIGHTER THAN THEY WERE ON WEDNESDAY WITHOUT ANY UPPER LEVEL WEATHER
FEATURE TO STIR THE WINDS UP TODAY. HOWEVER, THE MINIMUM RELATIVE
HUMIDITY WILL BE DOWN IN THE LOW TEENS AT THE LOWER ELEVATIONS EAST OF
THE DIVIDE AND IN THE MID TO UPPER TEENS WEST. THE HAINES WILL BE A SIX
TODAY WHERE THE CLIFF CREEK AND THE LAVA FIRES ARE BURNING. THE ONLY
AREAS WE EXPECT ANY CONVECTION TO DEVELOP WILL BE ALONG THE HIGHER
PEAKS WHERE THEY WILL REMAIN WITHOUT ANY STEERING FLOW TO PULL THEM OFF
THE MOUNTAINS. SOUTHERN SWEETWATER COUNTY MAY ALSO SEE SOME ISOLD
CONVECTIVE ACTIVITY CLOSER TO THE MONSOON PLUME STILL LURKING TO THE
SOUTHEAST. TODAY WILL SEE HIGH TEMPS WELL UP INTO THE 90S IN MANY LOWER
ELEVATIONS EAST OF THE DIVIDE WITH 80S WEST.

THE TROUGH OFF THE PACIFIC COAST AT AROUND 140W MARKED BY A COUPLE OF
PROMINENT CIRCULATIONS, WILL BE APPROACHING THE PACIFIC NW ON FRIDAY.
AS IT DOES, THE PRESSURE GRADIENT WILL ONCE AGAIN INCREASE RESULTING IN
AN INCREASE IN WEST SOUTHWEST WINDS ON FRIDAY. RIGHT NOW IT APPEARS
THAT THESE WINDS WILL LIKELY BE ABOUT AS STRONG AS THEY WERE ON
WEDNESDAY. THE ACTUAL TROUGHPA WILL NOT TAKE PLACE UNTIL 12Z SATURDAY.
HIGH TEMPERATURES WILL BE A COUPLE OF DEGREES WARMER FRIDAY MUCH LIKE
THEY WERE WEDNESDAY WITH THE ADDED DOWNSLOPE WARMING EFFECT WHICH WILL
JACK THE HIGH TEMPS UP OVER 100 IN THE BIG HORN BASIN AND IN JOHNSON
COUNTY ONCE AGAIN. THE MINIMUM RELATIVE HUMIDITY WILL DROP DOWN COUPLE
OF PERCENTS AS WELL. THIS ADDS UP TO THE POTENTIAL FOR ANOTHER CRITICAL
FIRE WEATHER DAY FRIDAY. LATER SHIFTS MAY WANT TO CONSIDER THE IDEA OF
FIRE WEATHER HILITES FOR FRIDAY. AS FAR AS ANY CONVECTION IS CONCERNED
WITH THIS APPROACHING PACIFIC WEATHER FEATURE, A FAST MOVING BAND OF
THUNDERSTORMS WILL LIKELY RACE EAST ACROSS THE CWA FRIDAY AFTERNOON
WITH THE MAIN FEATURE WITH ANY T CELLS BEING STRONG GUSTY WINDS ONCE
AGAIN.

THE ASSOCIATED COOL FRONT WILL DRAW IN COOLER TEMPERATURES FROM THE
NORTHWEST SATURDAY FOR A COOL DOWN OF ABOUT 5 TO 10 DEGREES FOR HIGH
TEMPERATURES ON SATURDAY. SATURDAY WILL FEATURE LIGHTER WINDS ALONG
WITH CONTINUED LOW RH AS THE WESTERLY STEERING FLOW KEEPS CONDITIONS
DRY AND THE MONSOON FLOW WELL TO OUR EAST AND SOUTHEAST.

.LONG TERM...Sunday through Thursday

Beginning of forecast period, Sunday - modest ridging aloft across
the FA with a surge of monsoonal moisture through the southern and
central Rockies into eastern WY. a few showers/storms may catch the
far eastern CWA as moisture is somewhat wrapped back into the area
and tries to flow back towards relative low pressure over
central/western WY...at least into portions of the eastern FA during
the evening period. A few stronger storms expected across eastern
Natrona and Johnson counties.

Monday through Wednesday, relatively flat flow aloft with surface
high pressure set up across the eastern half of the CONUS and low
pressure across the west will keep the moist monsoonal flow through
the southern and central Rockies and into the central and northern
plains. There will be a fair number of MCSs likely to form each
night across the plains but leaving central and western WY
relatively untouched by rainfall except for an occasional spurious
shower/storm over a higher peak or two...or across far southern WY
near the border, closer to the monsoonal moisture and slightly
better instability.

Wednesday night through Thursday, while there are some differences
in the MR models begin to show with regard to the upper level
pattern and subsequent evolution, it is apparent that an upper SW
trof is likely to move across the northern Rockies and high plains,
pushing a front through the FA at least east of the divide. This will
increase chances for showers/storms first across the far north
overnight Wednesday then east of the divide Thursday. Hopefully
this comes to fruition.

With regard to the current fires burning across the western fire
zones, a flattening flow pattern aloft and pressure fields at the
surface will allow winds to turn and blow more out of the west to
northwest instead of the southwest...especially Tuesday through
Thursday...before possibly turning northeast Thursday night.

&&

.AVIATION.../12Z ISSUANCE/

The main aviation concerns:

1. Isolated high based afternoon/early evening convection mainly
along and south of Interstate 80. There could also be very isolated
convection over the mountains, but confidence is lower than farther
south. Thus will only VCTS at KRKS. Gusty/Dry microburst winds will
be the main hazard.

2. Smoke from ongoing wildfires across western Wyoming will cause
MVFR restrictions at times especially on routes between KJAC-KRIW
and KJAC-KBPI/KPNA. KJAC terminal could see MVFR restrictions from
smoke this morning, and will have 6SM FU in KJAC TAF to account for
this. This smoke could also impact KRIW and KCOD, but less than KJAC.

3. Winds outside of convection will be mainly light.

&&

.FIRE WEATHER...

Warm and dry conditions will persist TODAY, with areas still having the
potential for elevated Haines indices OF 6 during the afternoon hours.
Friday will see a disturbance moving through the area. After a
hot,dry,and breezy day Friday, this system will help to cool down
temperatures, increase humidity, and potentially initiate shower
activity over portions of the area by Friday evening. After the exit of
the disturbance, westerly flow will move over the area, with generally
dry conditions through the early weekend.

&&

.RIW Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Lipson
LONG TERM...Braun
AVIATION...WM
FIRE WEATHER...Lipson



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