Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 280540
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1040 PM MST TUE JAN 27 2015

.SHORT TERM...TONIGHT THROUGH TUESDAY (ISSUED AT 345 PM MST)

THINGS ARE A BIT MORE ACTIVE TODAY THAN YESTERDAY. FIRST...THERE
CONTINUES TO BE SOME FOG AROUND ALTHOUGH NOT QUITE AS DENSE AS
YESTERDAY. THIS SHOULD MOVE OUT BY AROUND 3 PM. OF GREATER CONCERN
IN THE NEXT WEATHER MAKER IN THE FORM OF A SYSTEM MOVING UP FROM THE
SOUTH. POCATELLO RADAR ALREADY SHOWS SOME PRECIPITATION BREAKING OUT
ACROSS SOUTHERN IDAHO WITH SOME WARM ADVECTION AND LEFT FRONT
QUADRANT JET DYNAMICS. MOST OF IT IS REMAINING WEST OF WYOMING RIGHT
NOW. HOWEVER...THE WAVE IS EXPECTED TO MAKE A RIGHT TURN AND HEAD
INTO WESTERN WYOMING LATE THIS AFTERNOON AND TONIGHT. THE MODELS
HAVE RAISED THE QPF WITH THIS SYSTEM. WITH THE INCREASE...WE HAVE
DECIDED TO HOIST WINTER WEATHER ADVISORIES FOR THE TETONS AS WELL AS
THE JACKSON AND STAR VALLEYS...ALTHOUGH AMOUNTS MAY BE BORDERLINE.
THE PRECIPITATION MAY START AS RAIN BEFORE TURNING OVER TO SNOW. THE
HEAVIEST SNOW IS STILL EXPECTED LATER TONIGHT INTO EARLY TOMORROW
MORNING BEFORE TAPERING OFF. AND THIS LEADS US TO THE NEXT SITUATION.

THAT IS WHAT HAPPENS EAST OF THE DIVIDE. SOME MODELS...ESPECIALLY
THE NAM...SHOW AN AREA OF PRECIPITATION BREAKING OUT LATE TONIGHT
AND TOMORROW MORNING ACROSS THE NORTHEASTERN BIG HORN BASIN WITH
SOME ISENTROPIC LIFT. THE GFS AND EUROPEAN ALSO HAVE IT ALTHOUGH A
BIT LATER ON TOMORROW MORNING. WE HAVE BEEN BURNED ON THIS
BEFORE...SO WE BUMPED UP POPS AND QPF A BIT. AT THIS TIME...WE LEFT
THINGS BELOW ADVISORY CRITERIA BUT THIS WILL HAVE TO BE WATCHED.
OTHERWISE...EXPECT THE WAVE TO MOVE ACROSS WYOMING WITH A BATCH OF
SHOWERS ON WEDNESDAY. AS A RULE...AMOUNTS ARE NOT EXPECTED TO BE
HEAVY. HOWEVER...WITH NORTHWEST FLOW WE WILL HAVE TO WATCH FOR
POSSIBLE BANDING OF PRECIPITATION. PLACEMENT OF THE BANDS IS
IMPOSSIBLE AND IT MAY BE WARM ENOUGH FOR JUST RAIN OR A MIX IN MANY
AREAS. THE OTHER CONCERN IS FOR SOME GUSTY WINDS IN AREAS FAVORED
WITH SOUTHWESTERLY FLOW THROUGH TONIGHT. THE CRITERIA DOES NOT LOOK
TO BE QUITE ENOUGH FOR HIGH WIND...SO WE ISSUED AS SPS TO COVER FOR
IT.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

SHOWER ACTIVITY WILL TAPER OFF THROUGH THE EARLY PORTION OF THE
FORECAST PERIOD...WITH A BRIEF RETURN OF HIGH PRESSURE EXPECTED.
PERIODS OF DRY CONDITIONS WILL BE FOUND THURSDAY MORNING THROUGH
FRIDAY MORNING.

ANOTHER SYSTEM WILL PUSH NORTH INTO THE FOUR CORNERS REGION FRIDAY
MORNING...POTENTIALLY SENDING SOME PRECIPITATION ACROSS EXTREME
SOUTHERN WYOMING. IMPACTS ARE NOT ANTICIPATED TO BE SIGNIFICANT...AS
THE BRUNT OF THE PRECIPITATION IS EXPECTED TO REMAIN GENERALLY SOUTH
OF THE WYOMING BORDER. ANY ASSOCIATED PRECIPITATION WOULD TAPER OFF
BY SATURDAY AFTERNOON. MODELS THEN VARY A BIT ON ANOTHER SYSTEM
APPROACHING FROM THE NORTH ON SATURDAY AFTERNOON.

THE ECMWF INDICATES A SURGE OF MOISTURE MOVING INTO NORTHEASTERN
WYOMING SATURDAY AFTERNOON AND EVENING...SPREADING PRECIPITATION
ACROSS MUCH OF THE EASTERN PORTION OF THE STATE. HOWEVER...THE GFS
MAINTAINS A DRIER SOLUTION...AND PLACES THE BRUNT OF MOISTURE ACROSS
SOUTH DAKOTA. FORECAST HAS A WEAK MENTION OF MOISTURE ASSOCIATED
WITH THIS SYSTEM UNTIL MODELS COME INTO BETTER AGREEMENT.

A RIDGE THEN LOOKS TO BUILD OVER THE AREA...HOWEVER THE RIDGE WILL
BE DIRTY...WITH SURGES OF MOISTURE MOVING INTO NORTHWESTERN WYOMING
THROUGH THE EARLY PORTION OF NEXT WEEK.

&&

.AVIATION.../06Z ISSUANCE/

A WEATHER SYSTEM WILL MOVE THROUGH WYOMING LATE TONIGHT AND
WEDNESDAY. IT WILL EXIT THE AREA AROUND 00Z THURSDAY. AREAS OF SNOW
WILL OCCUR IN THE WEST UNTIL 20Z...THEN COME TO AN END BY 00Z THURS.
EXPECT MVFR TO IFR CONDITIONS AT TIMES THROUGH 20Z...THEN VFR
CONDITIONS WILL PREVAIL BY 00Z THROUGH 06Z THURS.

EAST OF THE CONTINENTAL DIVIDE AREAS OF SNOW...POSSIBLY MIXED WITH
RAIN WILL OCCUR OVER THE REGION WEDNESDAY. EXPECT MVFR TO IFR
CONDITIONS AT TIMES AS THE PRECIPITATION BECOMES ALL SNOW.
CONDITIONS WILL IMPROVE IN THE NORTH AFTER 19Z AS THE SNOW
ENDS...THEN IMPROVING IN THE CENTRAL BETWEEN 22Z AND 00Z. VFR
CONDITIONS WILL PREVAIL AFTER 00Z THURS EAST OF THE DIVIDE.

PLEASE SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

&&

.FIRE WEATHER...

THE NEXT SYSTEM WILL SPREAD SOME SNOW ACROSS AREAS WEST OF THE
DIVIDE TONIGHT INTO TOMORROW. SOME OF THIS PRECIPITATION WILL MOVE
EAST OF THE DIVIDE LATE TONIGHT AND TOMORROW ALTHOUGH AMOUNTS ARE
EXPECTED TO BE LIGHT IN MOST AREAS. GUSTY SOUTHWEST WINDS WILL
CONTINUE FROM THE RED DESERT THROUGH CASPER THROUGH TONIGHT BEFORE
DECREASING ON WEDNESDAY.
&&

.RIW WATCHES/WARNINGS/ADVISORIES...

WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 11 AM MST
WEDNESDAY WYZ012-013-023.

&&

$$

SHORT TERM...HATTINGS
LONG TERM...BRANHAM
AVIATION...AR
FIRE WEATHER...HATTINGS





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