Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 300601
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1059 PM MST THU JAN 29 2015

UPDATE...ADDED 06Z AVIATION DISCUSSION BELOW.


.SHORT TERM...TONGIHT THROUGH FRIDAY (ISSUED AT 159 PM MST)

FOG HAS FINALLY BEGUN TO DISSIPATE NEAR ROCK SPRINGS AND SOUTHERN
LINCOLN COUNTY...BUT CONTINUES TO LINGER NEAR GREYBULL. THIS
PORTION OF THE BIGHORN BASIN WILL REMAIN FOGGY THROUGH FRIDAY
MORNING...AND WILL SPREAD TOWARD WORLAND DURING THE OVERNIGHT
HOURS. FOG IS ALSO EXPECTED TO RETURN IN THE UPPER GREEN RIVER
BASIN AND JACKSON HOLE. AS AREAS...EXCEPT NEAR GREYBULL...SHOULD
DISSIPATE LATE FRIDAY MORNING...AS H7 TEMPS COOL AND UPPER LEVEL
CLOUDS SPREAD ACROSS THE AREA.

THE FORECAST AREA WILL REMAIN DRY THROUGH FRIDAY...EXCEPT SOUTHERN
PORTIONS OF SWEETWATER COUNTY. A MOIST CUT OFF LOW...MOVING INTO
THE FOUR CORNERS AREA...WILL BRING MID TO HIGH CLOUDS ACROSS THE
SOUTHWESTERN HALF OF THE FORECAST AREA. THIS SYSTEM WILL ALSO
BRING AN INFLUX OF MOISTURE INTO SOUTHERN WYOMING. RAIN AND SNOW
SHOWERS WILL BE POSSIBLE THROUGH THE DAY ON FRIDAY. ANY SNOW
ACCUMULATION WILL BE LITTLE TO NONE.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY NIGHT

A LOW PRESSURE SYSTEM MOVING UP INTO THE FOUR CORNERS REGION WILL
EVENTUALLY BE PUSHED BACK TO THE SOUTH BY A SYSTEM MOVING SOUTHEAST
OUT OF CANADA EARLY IN THE PERIOD. MOISTURE WRAPPING AROUND THE LOW
COULD RESULT IN A FEW SHOWERS ACROSS OUR AREA AS FAR NORTH AS FARSON
ON FRIDAY NIGHT BUT MOST OF THE ENERGY FROM THIS SYSTEM WILL REMAIN
WELL TO OUR SOUTH. THE SECOND PIECE OF ENERGY MOVING OUT OF THE
NORTH WILL ALSO PROVIDE A GLANCING BLOW TO OUR FAR NORTHEASTERN
ZONES. THE MODELS HAVE BEEN TRENDING FURTHER AND FURTHER EAST WITH
THIS SYSTEM...WHICH WOULD KEEP MOST OF THE PRECIP OUT OF OUR AREA.
HOWEVER...THERE IS A DECENT COLD POOL WITH THIS ONE THAT COULD
ENCOURAGE SOME SNOW BANDING IN ADDITION TO A CHANCE FOR SOME
MEASURABLE SNOW ALONG THE COLD FRONT AS IT DROPS SOUTH ON
SATURDAY NIGHT. AT THIS TIME...IT LOOKS LIKE MOST OF THE
PRECIPITATION WILL BE FROM THE BIGHORNS EAST...WITH A SLIGHT
CHANCE AS FAR SOUTH AS CASPER. GIVEN ITS ORIGINS...NOT MUCH
MOISTURE WILL COME ALONG WITH THIS SYSTEM WITH NO SECONDARY
MOISTURE FEED TO WORK WITH...NOT MUCH SNOW IS EXPECTED.

SWIFT NORTHWEST FLOW SETS UP BEHIND THE SYSTEM ON SATURDAY. THERE
WILL BE A SERIES OF DISTURBANCES MOVING THROUGH THE END OF THE
PERIOD. OVERALL...THERE WILL BE BREEZY PERIODS THROUGHOUT THE LONG
TERM PERIOD WITH OCCASIONAL CHANCES FOR RAIN AND SNOW WITH EACH
DISTURBANCE. THE BEST CHANCE FOR SNOW WILL BE IN THE WESTERN
MOUNTAINS AND IN THE BIGHORNS BUT THERE COULD BE A FEW DROPS AND
FLAKES THAT MAKE IT EAST OF THE DIVIDE POTENTIALLY ON TUESDAY...AS
A MORE ROBUST WAVE MOVES THROUGH WITH ENOUGH DYNAMIC FORCING TO
HELP SOME MOISTURE MAKE IT EAST OF THE DIVIDE.

TOWARD THE END OF THE PERIOD...GLOBAL MODELS ARE BUILDING A RIDGE
ACROSS THE WEST WITH A TROUGH OVER THE MIDWEST. THERE ARE SOME
DIFFERENCES AS TO HOW STRONG THE RIDGE IS BUT THE OVERALL PATTERN
WOULD SUGGEST A MILD AND DRY END TO THE WEEK NEXT WEEK.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD WITH PATCHY MORNING
FOG PARTIALLY OBSCURING TERRAIN.  N-NE SFC WINDS WILL PREVAIL ACROSS
THE AREA AFTER 18Z FRIDAY WITH SOME LOWER CIGS EXPECTED TO FORM
ALONG THE EAST SLOPES OF THE DIVIDE AND OTHER UPSLOPE FAVORED AREAS
INCLUDING VCNTY KCPR.  MOST OF THESE CIGS ARE EXPECTED TO REMAIN VFR
OBSCURING HIGHER MTNS...BUT LOCAL MVFR CIGS WILL BE POSSIBLE.
CLEARING IS EXPECTED AFTER 06Z SATURDAY WITH PATCHY FOG REFORMING
MAINLY IN THE LOWER CENTRAL BASINS...OR VCNTY KGEY-KRIW.

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

AN UPPER LEVEL LOW PRESSURE SYSTEM OVER SOUTHERN CALIFORNIA WILL
CONTINUE TO PUSH UP MOISTURE INTO SOUTHERN WYOMING THROUGH THE
PERIOD WITH CIGS EXPECTED TO GRADUALLY LOWER VCNTY AND SOUTH OF
INTERSTATE 80 WITH SOME ISOLD TO SCT -SHSN MOVING IN AFTER 09Z ALONG
WITH LCL MVFR/IFR CONDITIONS.  MVFR/IFR CONDITIONS WITH ARE EXPECTED
TO BECOME MORE PREVALENT IN THIS AREA AFTER 00Z SATURDAY.

NORTH OF INTERSTATE 80...VFR CONDITIONS WILL PREVAIL THROUGH THE
PERIOD WITH SOME PATCHY MORNING FOG PARTIALLY OBSCURING TERRAIN.

&&

.FIRE WEATHER...

FIRE DANGER IS LOW FOR ALL AREAS...AND WILL REMAIN SO THROUGH NEXT
WEEK. MEASURABLE PRECIPITATION WILL NOT FALL ACROSS THE FORECAST
AREA UNTIL LATE SATURDAY INTO SUNDAY MORNING EAST OF THE DIVIDE.
FROM SUNDAY NIGHT THROUGH THE NEXT WORK WEEK...A SERIES OF
DISTURBANCES WILL RIDE THROUGH THE REGION...AFFECTING MAINLY THE
WESTERN AND NORTHERN DISPATCH ZONES. SMOKE DISPERSION WILL BE POOR
ACROSS MOST OF THE REGION FRIDAY. SATURDAY WILL SEE IMPROVEMENT
IN BOTH MIXING ABILITY AND DISPERSION...ESPECIALLY EAST OF THE
DIVIDE AND ACROSS THE SOUTHERN ZONES.

&&

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

$$

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








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