Area Forecast Discussion
Issued by NWS Riverton, WY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KRIW 012046
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
246 PM MDT TUE SEP 1 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS THE SOUTH INTO THE
EVENING ALONG THE EDGE OF A MOISTURE PLUME AND WEAK THETA E RIDGE.
THE GFS TRIES TO BRING THIS AREA OF MID LEVEL MOISTURE AS FAR
NORTH AS THE ABSAROKAS EARLY IN THE PERIOD...WHICH COULD KICK OFF
A FEW MOUNTAIN THUNDERSTORMS WITH GUSTY OUTFLOW WINDS AND LITTLE
RAIN...ESPECIALLY INTO THE FOOTHILLS AND BASINS. THE NAM HAS A
DIFFERENT STORY FOR TONIGHT WITH MUCH LESS MOISTURE AVAILABLE. AS
OF LATE THIS AFTERNOON IT APPEARS AS THOUGH THE MORE MODEST NAM
IS VERIFYING A LITTLE BETTER BUT NEITHER MODEL RAMPS UP THE
ACTIVITY FURTHER NORTH UNTIL ABOUT 00Z THROUGH 06Z. WENT WITH A
BLEND OF THE TWO INTO THE EVENING THOUGH GIVEN THE CRITICAL NATURE
OF ANY LIGHTNING ACTIVITY THIS LATE IN THE FIRE SEASON.

ALSO ADDED THE OTHER REGIONS OF THE FORECAST AREA WITH CRITICALLY
DRY VEGETATION INTO THE RED FLAG WARNING TO COVER THE POTENTIAL
FOR DRY STORMS WITH GUSTY OUTFLOW WINDS...HIGH HAINES INDEX AND
VERY LOW HUMIDITY...WHICH HAS ALSO BEEN LOWER THAN GUIDANCE THE
PAST TWO DAYS. LOOKS LIKE WINDS ARE STARTING TO PICK UP THIS
AFTERNOON WITH WIDESPREAD WIND GUSTS OVER 25 MPH SHOWING UP IN THE
OBSERVATIONS. NOT BAD FOR A DAY THAT LOOKED VERY MARGINAL IN THE
MODELS A COUPLE OF DAYS AGO.

GOING INTO WEDNESDAY...THIS HAS CONSISTENTLY BEEN THE DAY
ADVERTISED WITH THE MOST WIDESPREAD LOW HUMIDITY AND STRONG WIND
AND IT IS STILL LOOKING THAT WAY TODAY. EXPECT SOUTHWEST FLOW TO
PICK UP AHEAD OF A TROUGH APPROACHING FROM THE NORTHWEST. THERE IS
STILL SOME INCONSISTENCY BETWEEN THE MODELS AS TO HOW MUCH
MOISTURE COMES UP INTO THE SOUTHWEST FLOW AHEAD OF THIS TROUGH.
SOME MID LEVEL MOISTURE COULD MAKE IT UP AS SOON AS WEDNESDAY
AFTERNOON...WHICH COULD KEEP RELATIVE HUMIDITY FROM BOTTOMING OUT
ACROSS THE WEST.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

SOUTHWEST FLOW WILL CONTINUE WEDNESDAY NIGHT INTO THURSDAY AHEAD OF
THE COLD TROUGH OVER THE PAC NW.  SOME MID-LEVEL MOISTURE MAY
PRODUCE WEAK SHOWERS AND ISOLATED THUNDERSTORMS OVER SW AND WESTERN
WY WED EVENING.  BETTER CHANCE APPEARS TO BE FRIDAY AFTERNOON ACROSS
WESTERN AND NW WY AS THE INFLUENCE OF THE TROUGH MOVES SLIGHTLY TO
THE SE AND STARTS TO DESTABILIZE THE MID LEVELS A BIT.  SOUTHWEST
FLOW ACROSS SOUTHERN AND CENTRAL WY EXPECTED TO CONTINUE WITH MORE
MOISTURE BEING DRAWN UP FROM UTAH AND COLORADO AS WELL.  GFS STILL
GOES GANGBUSTERS WITH THE PRECIPITATION COMPARED TO THE NAM...ECMWF
AND GEM NH DURING THIS TIME.  THE CORE OF THE TROUGH IS MORE IN
PHASE TODAY COMPARED TO 24 HOURS AGO BETWEEN THE GFS AND ECMWF...YET
SOME DETAILS ARE STILL DIFFERENT TO CREATE ENOUGH UNCERTAINTY
SATURDAY AND SUNDAY.  SATURDAY LOOKS TO BE FAIRLY CLOUDY ACROSS THE
AREA...WITH MORE OF A CHANCE OF PRECIPITATION ESPECIALLY ACROSS NW
WY.  THE COLDEST MID LEVEL TEMPS SWEEP FROM WEST TO NORTHEAST ACROSS
NW WY FROM SATURDAY NIGHT INTO SUNDAY.  LIKELY TO SEE SOME SNOW AT
THE LOWER ELEVATIONS OF YNP...WITH A FEW INCHES OF SNOW AT LEAST IN
THE HIGHER TERRAIN.  DURING THIS TIME ALSO...SOUTHERN AND CENTRAL WY
WIND WILL SWITCH TO WEST TO NORTHWEST WITH LIGHT AMOUNTS OF
PRECIPITATION.  A SURFACE BOUNDARY WILL DRAPE ACROSS NORTHERN WY
FROM SATURDAY INTO SUNDAY...POSSIBLY BRINGING MORE RAIN TO THE
NORTHERN BIG HORN BASIN LATE SATURDAY INTO SUNDAY.  THE CLOSED LOW
THEN MOVES RAPIDLY INTO THE NORTHERN PLAINS CREATING BRISK
CONDITIONS SUNDAY EVENING AND A FAIRLY COLD MORNING ON MONDAY.
MONDAY LOOKS TO BE MOSTLY CLEAR AND COOL...WITH TUESDAY WARMING A
BIT AND SEEING SOME CLOUDINESS SNEAKING UP FROM THE SOUTH. AS
ANOTHER TROUGH MOVES INTO THE PAC NW MONDAY INTO TUESDAY...SW BREEZY
FLOW IS LIKELY TO SET UP TUESDAY INTO WEDNESDAY.

&&

.AVIATION.../00Z ISSUANCE/

ISOLATED HIGH BASED SHOWERS AND STORMS POSSIBLE ACROSS THE SOUTH
AND WEST. OUTFLOW WIND GUSTS TO 30 KNOTS WILL BE EASILY ACHIEVED
NEAR ANY SHOWERS OR STORMS. THE SHOWER AND STORM ACTIVITY WILL END
IN THE WEST BY 04Z WED AND IN THE EAST AROUND 09Z WED. WINDS WILL
BE BREEZY FROM THE SOUTHWEST ONCE FULL MIXING OCCURS IN ALL AREAS
THROUGH THE TAF PERIOD.

&&

.FIRE WEATHER...

.ELEVATED FIRE DANGER FOR MUCH OF THE WEEK...

THERE WILL BE DRY AND BREEZY PERIODS FOR THE NEXT SEVERAL DAYS WITH
OCCASIONAL LIGHTNING AND COLD FRONTS LATER IN THE WEEK AS ANOTHER
LARGE UPPER TROUGH APPROACHES...INCREASING FLOW FROM THE SOUTHWEST
FOR WEDNESDAY AND THURSDAY WITH WIDESPREAD LOW HUMIDITY AND GUSTY
WINDS. A PUSH OF MID LEVEL MOISTURE AND INSTABILITY WILL ARRIVE
THIS AFTERNOON WHICH WILL INCREASE THUNDERSTORM COVERAGE...
ESPECIALLY ACROSS THE SOUTH WITH PERHAPS A SECONDARY FOCUS IN THE
WESTERN MOUNTAINS THIS EVENING. SOME OF THESE STORMS COULD
VENTURE INTO THE FOOTHILLS AND SEND OUTFLOW WINDS DEEP INTO THE
BASINS. THESE STORMS WILL BE MAINLY DRY WITH OCCASIONAL WET
THUNDERSTORMS POSSIBLE...MAINLY ABOVE 8000 FEET.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING UNTIL 9 PM MDT THURSDAY FOR WYZ275>277-279>283-
285-287-289-300-414>416.

&&

$$

SHORT TERM...ALLEN
LONG TERM...MCDONALD
AVIATION...ALLEN
FIRE WEATHER...ALLEN


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.