Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 111700
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1100 AM MDT THU SEP 11 2014

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

LARGE LW TROF ACROSS THE ENTIRE CONUS WITH A STRONG EMBEDDED SW
MOVING THRU THE MAIN FLOW INTO AND ACROSS NRN WY. AT THE
SFC...BACKDOOR STATIONARY FRONT STILL STRETCHES LAZILY FROM SE WY TO
NW WY MAINLY PUSHED BACK ALONG THE ERN SIDE OF THE
MOUNTAINS...EXCEPT FOR THE NRN ABSAROKAS WHERE IT HAS PUSHED EVEN
FURTHER WEST.

THIS MORNING THRU THURSDAY...H7 TEMPS CONTINUE TO FALL...NOW RANGING
FROM -3 TO -6 C ACROSS THE NRN ZONES...WHILE SNOW LVLS HAVE FALLEN
TO AROUND 5000 FEET ACROSS THE NRN ZONES. H7 TEMPS WILL CONTINUE TO
DROP...BOTTOMING OUT AND RANGING FROM -5 TO -10 S TO N...WHICH
WILL MOSTLY CORRESPOND TO THE VALLEY/BASIN FLOOR LVL EAST OF THE
DIVIDE THRU TODAY. BIG QUESTION IS HOW MUCH MOISTURE WILL MAKE IT
INTO THE FA AND HOW FAR SOUTH...WITH THE MAIN TRAJECTORY COMING
IN AT A RATHER SHALLOW ANGLE...LOOKING LIKE THE MORE COPIOUS
AMOUNTS WILL KEEP NORTHERLY WITH MUCH LESS AS YOU GO SOUTH. BEST
CHANCES FOR CNTRL PORTIONS OF THE CWA WILL LIKELY COME THIS
AFTERNOON...AS THE FRONT GETS PUSHED ALL THE WAY THROUGH.
APPROPRIATE WARNINGS/ADVISORIES CURRENTLY OUT AS 4 TO 10 INCHES
WILL BE POSSIBLE ACROSS THE BIG HORNS WITH LOCALIZED HIGHER
AMOUNTS TO A FOOT. 2 TO 4 INCHES OF WET SNOW WILL BE POSSIBLE
ACROSS PORTIONS OF NORTHERN JOHNSON COUNTY...WITH SOME HIGHER
AMOUNTS IN/NEAR THE FOOTHILLS....WITH AN INCH OR TWO OF SNOW
FURTHER SOUTH. EXPECTING SLIGHTLY LESS SNOW OVER THE ABSAROKAS AS
TEMPS WILL NOT BE QUITE AS COLD AND AVAILABLE MOISTURE WILL BE
SOMEWHAT LESS OVER A LONG PERIOD. GENERALLY...LOOKING FOR 3 TO 8
INCHES ACROSS THE HIGHER REACHES OF THE NORTHERN ABSAROKAS WITH
HIGHER AMOUNTS UP TO 10 INCHES POSSIBLE. ELSEWHERE...A TRACE TO 4
INCHES OVER THE WRN BIG HORN BASIN...MORE NEAR/IN THE
FOOTHILLS...AND UP TO AN INCH IN PLACES OVER THE WIND RIVER BASIN
THRU EARLY EVENING. THEN PRECIP...LIQUID AND FROZEN DECREASES
RAPIDLY TONIGHT THRU FRIDAY MORNING...CLEARING OUT CLOUDS FAST
ENOUGH THAT A HARD FREEZE AND PATCHY FROST WILL BE
POSSIBLE/PROBABLE OVER MOST OF THE CENTRAL AND SOUTHERN ZONES THAT
MISSED THE FIRST FREEZING TEMPS OF THE SEASON LAST WEEK. FREEZE
WATCH/WARNING CURRENTLY OUT FOR THAT PERIOD.
OTHERWISE...RELATIVELY STRONG PRESSURE GRAD ACROSS THE SRN ZONES
WILL INCREASE WINDS DRAMATICALLY WITH NORTHEAST WINDS 20 TO 25 MPH
AND GUSTS OF 30 TO 40 MPH POSSIBLE BY THIS AFTERNOON.

FRIDAY/SATURDAY...BENIGN WARMING AND DRYING PERIOD WITH WIDESPREAD
SUNSHINE AND FEW CLOUDS.

.LONG TERM...SUNDAY THROUGH THURSDAY NIGHT

EXTENDED FORECAST REMAINS ON TRACK FROM THE LAST SEVERAL MODEL
RUNS THIS WEEK. A TRANSITORY RIDGE OF HIGH PRESSURE BUILDS OVER
THE INTERMOUNTAIN WEST STARTING MONDAY. A WEAK SHORTWAVE MOVES
ONSHORE OVER SOUTHERN OREGON AND INTO PORTIONS OF MONTANA. THIS
FEATURE WILL HAVE TO BE WATCHED...AS IT COULD POTENTIALLY FLATTEN
THE RIDGE AS IT MAKES ITS WAY INTO THE NORTHERN PLAINS. THERE WAS
A SIGNAL OF THIS HAPPENING ON WEDNESDAYS 00Z GFS RUN...BUT BOTH IT
AND THE ECMWF RESOLVE THIS FEATURE TO HAVING LITTLE TO NO
IMPACT...AS IT RIDES UP AND OVER THE RIDGE ON WEDNESDAY.

OTHERWISE...DRY AND WARMING CONDITIONS CONTINUE THROUGH THE
PERIOD. TEMPERATURES BECOME SLIGHTLY ABOVE NORMAL BY
TUESDAY...ESPECIALLY EAST OF THE DIVIDE...WITH AFTERNOON HIGHS
RISING INTO THE MIDDLE TO UPPER 70S AND LOWS IN THE 50S.

.AVIATION.../18Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

WIDESPREAD RAIN AND SNOW WITH MVFR/IFR CONDITIONS AND MTN
OBSCURATIONS WILL CONTINUE TO FILL IN ACROSS THE AREA. SNOW
LEVELS AT THE VALLEY FLOORS ACROSS NORTHERN WYOMING...WILL LOWER
TO NEAR THE VALLEY FLOORS FURTHER SOUTH VCNTY KWRL-KCPR-KLND-KRIW
THIS AFTERNOON. SNOW WILL DECREASE FROM NW-SE THROUGH LATE THIS AFTERNOON
AND EVENING AS A MUCH DRIER AIRMASS MOVES IN ALOFT 06Z TO 12Z TONIGHT.
AREAS OF MVFR/IFR CIGS AND AREAS OF FOG WILL LIKELY PERSIST OVER
MUCH OF THE AREA THROUGH 15Z FRIDAY AS THE BOUNDARY LAYER AIRMASS
WILL REMAIN NEARLY SATURATED.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

VFR CONDITIONS WILL PREVAIL ACROSS THE FAR WEST THROUGH THE PERIOD.
A COLD FRONT WILL CONTINUE TO DEEPEN ALONG THE EAST SLOPES OF THE
DIVIDE WITH THIS FRONT PUSHING TO VCNTY KRKS...AND IS EXPECTED TO
BRIEFLY STALL N-E OF KRKS BEFORE PUSHING THROUGH IN THE AFTERNOON.
AREAS OF MVFR CIGS FL080-090 WILL LIKELY FILL IN BEHIND THE
FRONT...OBSCURING HIGHER TERRAIN. SOME OF THESE LOWER CLOUDS MAY
ALSO SPILL OVER THE DIVIDE INTO VCNTY KPNA IN THE LATE MORNING AND
AFTERNOON. THOUGH A DRIER AIRMASS WILL PUSH IN ACROSS MOST OF THE
AREA THURSDAY NIGHT...SOME OF THESE LOWER CIGS MAY LINGER VCNTY
KRKS AND EAST THROUGH 12Z FRIDAY.

.FIRE WEATHER...

FIRE DANGER LOW TODAY AND THROUGH THE REST OF THE WEEK FOR MOST LOCATIONS.
STORM SYSTEM CONTINUES ACROSS THE REGION TODAY...COOLING
TEMPERATURES FURTHER AND KEEPING DECENT PRECIPITATION POTENTIAL EAST
OF THE DIVIDE ALONG WITH LOWER TEMPERATURE AND ELEVATED RH VALUES
EVERYWHERE ELSE. EXPECT RAIN...RAIN/SNOW MIX AND SNOW EAST OF THE
DIVIDE TODAY...ENDING AND CLEARING OUT TONIGHT WITH THE COLDEST
TEMPERATURES OF THE SEASON BY FRIDAY MORNING. FRIDAY BEGINS A
WARMING AND DRYING PERIOD WITH HIGH TEMPERATURES RISING SOME 5 TO 20
DEGREES OVER THOSE OF TODAY WHILE RH VALUES DROP TO NEAR OR JUST
ABOVE SEASONAL AVERAGE VALUES. FIRE DANGER MAY BE SOMEWHAT ENHANCED
ON SATURDAY ACROSS THE SOUTHERN DISPATCH ZONES.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FREEZE WARNING FROM 2 AM TO 9 AM MDT FRIDAY
WYZ004>006-016>020-023-025>030.

WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING WYZ003-011.

WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING WYZ002-008>010.

&&

$$

SHORT TERM...BRAUN
LONG TERM...LAVOIE
AVIATION...C.BAKER
FIRE WEATHER...BRAUN






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