Weather Service Report


698 
FXUS65 KRIW 292113
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
313 PM MDT MON AUG 29 2016

.SHORT TERM...TONIGHT THROUGH THURSDAY

SO FAR, ONE CONVECTIVE CELL HAS FORMED OVER THE EXTREME SOUTHERN BIG
HORN MOUNTAINS. OTHER TOWERING CU ARE BARELY DISCERNABLE FROM THE
GROUND THROUGH THE UNIFORM LAYER OF DRIFT SMOKE. WITH RELATIVELY
WEAK INSTABILITY, LITTLE MOISTURE, AND RELATIVELY LIGHT STEERING
WINDS, WE ARE ONLY EXPECTING SOME ISOLD T STORMS LATER THIS
AFTERNOON ANCHORED OVER THE HIGHER MOUNTAINS. ON TUESDAY, THE
SHORTWAVE OFF THE CALIFORNIA COAST WILL TRACK NORTHEAST ACROSS THE
PAC NW AND CONTRIBUTE SOME PVA TO THE NW. HIGHEST PW VALUES WILL
BE SEEN OVER OUR NORTHEAST ZONES. THE END RESULT, ONLY A VERY
SLIGHTLY BETTER CHANCE OF A ROGUE THUNDERSTORM OVER THE NORTHERN
HIGHER MTNS. TUESDAY SHOULD BE THE HOTTEST DAY OF THE WEEK, AND
FOR A WHILE, WITH THE RIDGE AMPLIFYING OVER THE AREA. IT APPEARS
THAT THE BEST CANDIDATE FOR A FIRE WEATHER WATCH TUESDAY WOULD BE
ZONE 281 WHERE THE COMBINATION OF STRONG SOUTH WINDS WILL COUPLE
WITH AN RH IN THE MID TEENS FOR TUESDAY AFTERNOON AND EARLY
EVENING. THE REST STOP FIRE MAY STILL BE TAKING PLACE THERE BY
THEN. ELSEWHERE, THE RH WILL DIP DOWN TO AROUND 12 PERCENT ACROSS
FREMONT, SWEETWATER, AND LINCOLN COUNTIES, BUT THE WINDS WILL NOT
BE THERE. WILL GO AHEAD AND ISSUE A FIRE WEATHER WATCH FOR ZONE
281 VALID FROM 1200 THROUGH 2000 TUESDAY. BY WEDNESDAY, THE CLOSED
LOW OFF BC WILL BEGIN TO SHOVE THE ASCT TROUGH EASTWARD AND MOVE
THE RIDGE EAST TO THE PLAINS. HIGHER CAPES WILL RESULT AS
INCREASING MOISTURE MOVES IN FROM THE SOUTHWEST AND LIFTED INDICES
LOWER IN WESTERN WY. THIS WILL RESULT IN THE NEXT DECENT CHANCE OF
THUNDERSTORMS, MAINLY IN THE NORTHWEST MOUNTAINS ON WEDNESDAY
AFTERNOON, BUT MUCH OF THIS ACTIVITY WILL BE OF THE DRY VARIETY
WITH GUSTY WINDS ONE OF THE MAIN THREATS. ON THURSDAY, THE CHANCES
OF MAINLY LATE DAY THUNDERSTORMS WILL CONTINUE TO INCREASE AS JET
ENERGY MOVES OVERHEAD, A SLIGHT MID LEVEL CIRCULATION DEVELOPS
OVER THE AREA, THE SOUTHWEST FLOW BECOMES SLIGHTLY DIFLUENT, AND
CAPES INCREASE ALONG WITH LIFTED INDICES BETWEEN -3 AND -4.

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY

Major pattern change during the medium range period as the upper
ridge/high over the Southern Plains weakens allowing a large scale
trough to gradually develop over the Western U.S. At the beginning
of this period, we get a backing sw flow ahead of a cold trough just
off the PACNW. Some moisture and possible weak waves may be caught
in this flow leading to at least somewhat better chance of showers
and a few thunderstorms through Friday, especially in the west with
the approaching cold front late Friday. This cold front then sweeps
east of the divide Friday night with some showers and a few tstms
with it. It looks quite warm and breezy to windy east of the divide
Friday with increased fire weather concerns once again while
showers/storms increase out west. Front looks like it will hang
around the north on Saturday with some weak instability and
possibility of a few showers/storms. Things potentially get much
more interesting on Sunday as cold trough approaches the west and
then moves across the area into Sunday night. Strong cold front,
active dual jet structure, qg forcing and at least some weak
instability should produce a good chance of showers/storms with
falling temperatures. Snow levels will likely lower to around 9K
feet or so if model trends continue with a couple inches possible
over the higher elevations. GFS is most bullish right now but others
are trending stronger. Another shortwave in the flow may keep a cool
wly flow over the area into Monday with the best chance of
instability showers over the mountains, centered on the
afternoon/early evening hours. So we start out quite warm with 80s
to even a few 90s then cool considerably if not sharply, Sunday into
Monday with potential h7 temps dropping into the low single digits.

&&

.AVIATION.../00Z ISSUANCE/

Very isolated showers or virga are possible in the mountains along
the Divide and in the Bighorn Mountains for the rest of this afternoon
and evening. The main hazard from this activity if it develops
would be gusty winds. Otherwise...VFR conditions with some high-
based cumulus and cirrus. Winds will be light. There will also be
smokey skies from wildfires, but any VSBY restrictions to MVFR
would be brief. Little change is expected for Tuesday except for
late day afternoon and evening isolated thunderstorms in the
northern mountains.

&&

.FIRE WEATHER...

Winds will generally blow/gust below critical levels through the
day Tuesday for most areas except for Johnson county Tuesday
afternoon and evening where winds will gust out of the south to
around 25 mph at times and could affect the Rest Stop fire if not
out by then. this combined with minimum relative humidity readings 
expected to be in the mid teens, a fire weather watch has been
issued for fire weather zone 281 valid from 1200 noon through
2000 Tuesday. Isolated thunderstorms, mainly in the northern 
mountains, for the rest of this afternoon and early evening as
well as late on tuesday are expected.



&&

.RIW Watches/Warnings/Advisories...
Fire Weather Watch from Tuesday afternoon through Tuesday 
evening for WYZ281.

&&

$$

SHORT TERM...Lipson
LONG TERM...Skrbac
AVIATION...Lipson
FIRE WEATHER...Lipson

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Western Regional Climate Center, wrcc@dri.edu