Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 040037
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
537 PM MST TUE MAR 3 2015

.UPDATE...CANCELLED REMAINING WINTER HIGHLIGHTS OVER SWEETWATER
COUNTY AND LOWERED POPS FOR THIS EVENING AS MOST ACCUMULATING SNOW
HAS MOVED OUT OF THE AREA. MAINLY VERY LIGHT SNOW FALLING FROM
THIN STRATUS LINGERING LATE THIS AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 305 PM MST TUE MAR 3 2015/

SHORT TERM...TONIGHT THROUGH WEDNESDAY

CLEARING IS EXPECTED TO CONTINUE FROM NORTH TO SOUTH THROUGH THE
EVENING HOURS. SEVERAL OF THE WARNINGS AND ADVISORIES WERE ENDED
EARLY BUT THE HIGHLIGHTS ACROSS THE SOUTH WERE ALLOWED TO RIDE
THROUGH THE END OF THE VALID PERIOD AS PORTIONS OF INTERSTATE
80 REMAINS CLOSED AND A POCKET OF INSTABILITY KEEPS SOME SHOWERS
GOING INTO THE EVENING.

CONCERNS FOR TONIGHT INCLUDE CLOUD COVER...PATCHY FOG AND HOW THAT
WILL AFFECT MINIMUM TEMPERATURES. A VERY COLD AIRMASS WITH 700MB
TEMPERATURES MORE THAN TWO STANDARD DEVIATIONS BELOW THE MEAN FOR
THIS TIME OF YEAR...WILL TEAM UP WITH FRESH SNOW COVER IN AREAS
WHERE SKIES ARE CLEAR...TO ALLOW FOR RAPIDLY DROPPING
TEMPERATURES THAT COULD BOTTOM OUT NEAR 20 BELOW IN SOME OF THE
LOWER LYING AREAS. IN ADDITION...THERE WILL BE SOME BREEZY AREAS
DEVELOPING ALONG THE I25 CORRIDOR...ESPECIALLY NEAR CASPER.
TEMPERATURES ARE COLD ENOUGH ALOFT TO WHERE THE WIND WILL NOT
MODERATE TEMPERATURES...CREATING AREAS OF VERY LOW WIND CHILLS.
MOST OF THE AREA WILL SEE WIND CHILLS AROUND 20 BELOW WITH SOME
SPOTS DIPPING TO AROUND 30 BELOW AROUND CASPER...THOUGH VALUES
BELOW 30 BELOW ARE NOT EXPECTED TO BE WIDESPREAD ENOUGH FOR A WIND
CHILL WARNING.

THE GOOD NEWS IS THAT A MORE MODERATE AIRMASS WILL MOVE IN BEGINNING
ON WEDNESDAY. IT IS LIKELY THAT THE WIND RIVER BASIN WILL REMAIN
TRAPPED ALONG WITH SOME OF THE WESTERN VALLEYS THAT DID RECEIVE SOME
MEASURABLE SNOW MONDAY NIGHT. THE HIGH SUN ANGLE WILL TRY TO DO SOME
WORK ON THE SNOW PACK DURING THE DAY ON WEDNESDAY BUT IT WILL NOT
LIKELY BE ENOUGH TO SAVE OUR HIGH TEMPERATURES ON WEDNESDAY.

LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY NIGHT

DRY CONDITIONS ARE EXPECTED THROUGH MUCH OF THIS PERIOD. THE MAIN
FORECAST CHALLENGE IS THE WEAK SHORTWAVE ON FRI/SAT. BOTH THE GFS
AND ECMWF 12Z SOLUTIONS HAVE RESOLVED THIS SYSTEM MOVING MUCH
FARTHER EAST INTO THE NORTHERN PLAINS...AND THE GFS ONCE AGAIN
REMAINING BULLISH. HOWEVER...THIS SYSTEM APPEARS THAT IT WILL NOT
IMPACT THE CWA. WITH THAT SAID...KEPT SLIGHT CHANCE POPS ACROSS
NORTHERN PORTIONS TO GRADUALLY DECREASE POPS FROM THE PREVIOUS
FORECAST PACKAGE AND IN CASE THE MODELS FLIP-FLOP AGAIN.

A WARMING TREND IS EXPECTED BY THURSDAY...WITH TEMPERATURES
RETURNING TO MORE SEASONAL AVERAGES.

AVIATION.../00Z ISSUANCE/

THE NORTHERN PORTION OF THE AREA WILL GENERALLY BE VFR OVERNIGHT BUT
AREAS OF STRATO CU MAY PRODUCE BRIEF MVFR CONDS. IN ADDITION PATCHY
FOG MAY DEVELOP BEFORE MORNING...PRODUCING LCL IFR CONDS IN
CIGS/VSBY. THE SOUTHERN PORTION OF THE AREA GENERALLY FROM KRIW
AND KLND EAST TO KCPR AND SWD WILL SEE LIGHT SNOW OR FLURRIES WITH
MVFR TO LCL IFR CONDS THROUGH 02Z BEFORE GRADUAL IMPROVEMENT TO
VFR TO...AT TIME...MVFR DUE TO OCNL SNOW FLURRIES AND STRATO CU.
PATCHY FOG MAY DEVELOP AFTER MIDNIGHT WITH LCL BRIEF IFR IN
CIGS/VSBY THROUGH 16Z. OTHERWISE...MAINLY VFR CONDS ON WEDNESDAY.
MTNS WILL REMAIN OBSCURED AT TIMES THROUGH THE NIGHT.

FIRE WEATHER...

THERE WILL BE SIGNIFICANT COLD AIR SETTLING IN TONIGHT WITH BASIN
AND VALLEY INVERSIONS EXPECTED TO FORM AND THEN HOLD THROUGH AT
LEAST THURSDAY MORNING...PERHAPS LONGER IN THE WIND RIVER BASIN AND
AROUND CASPER. A WARMING TREND BEGINS ON WEDNESDAY...AT LEAST IN THE
MOUNTAINS THAT WILL LAST THROUGH THE WEEKEND. NO PRECIPITATION IS
EXPECTED AFTER THIS STORM...THROUGH AT LEAST NEXT MONDAY AS A
RIDGE BUILDS IN FROM THE WEST.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

UPDATE...AEM
SHORT TERM...ALLEN
LONG TERM...LAVOIE
AVIATION...SKRBAC
FIRE WEATHER...ALLEN





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