Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220929
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
229 AM MST THU JAN 22 2015

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT

A DIRTY RIDGE CONTINUES TO BUILD TO THE WEST WHILE DRYING ALOFT
KEEPS SKIES MOSTLY CLEAR THIS MORNING. WAA ALOFT WILL CONTINUE TO
CHARGE SOME OF THE TRAPPED BASINS AND VALLEYS WITH SOME PATCHY
MORNING FOG EXPECTED TO LAST THROUGH THE MORNING...ESPECIALLY IN
THE WIND RIVER BASIN.

LEE SIDE TROUGHING AT THE SURFACE WILL DIG ENOUGH TODAY TO TURN
BACK ON THE WIND MACHINE BETWEEN EASTERN SWEETWATER COUNTY AND
KAYCEE THIS AFTERNOON. THIS SHOULD ENCOURAGE SOME DECENT MIXING AND
MILD TEMPERATURES THIS AFTERNOON ALONG THE SOUTHERN WIND CORRIDOR
AND ALONG THE CODY FOOTHILLS WHERE SOME GAP FLOW IS EXPECTED THIS
AFTERNOON AS WELL.

THERE WILL BE INCREASING CLOUDS TONIGHT AS THE FIRST SHORT WAVE
MOVES OVER THE RIDGE AND INTO THE FORECAST AREA. THIS SHOULD
RESULT IN LITTLE MORE THAN SOME OVERCAST SKIES AND LIGHT SNOW OR
FLURRIES ACROSS THE NORTHERN MOUNTAINS TONIGHT...WORKING SOUTH
THROUGH THE OVERNIGHT HOURS AND INTO THE WIND RIVER RANGE BY MID
DAY ON FRIDAY. THERE WILL BE CLEARING BEHIND THE WAVE WITH ANOTHER
CLEAR AND CALM NIGHT EXPECTED TOMORROW NIGHT...ALONG WITH WAA AND
BASIN FOG FOR SATURDAY MORNING.

THE NEXT WAVE IS ON THE DOORSTEP FOR SATURDAY WITH FLOW SHIFTING
NORTHWEST. THERE WILL NOT BE MUCH OF A COLD POOL WITH THIS ONE AND
THERE WILL NOT BE MUCH MOISTURE TO SPEAK OF EITHER. THERE COULD
BE A FEW PERIODS OF RAIN AND SNOW BUT THIS IS NOT EXPECTED TO BE
A HIGH IMPACT SYSTEM. LEE SIDE TROUGHING HOLDS AT THE SURFACE
WITH DECENT MIXING OF MILD MID LEVEL TEMPERATURES EXPECTED DURING
THE DAY ON SATURDAY. MANY LOCATIONS EAST OF THE DIVIDE WILL BE
ABOVE FREEZING DURING THE DAY ON SATURDAY WITH MANY AREAS TOPPING
OUT INTO THE MID TO UPPER 40S.

.LONG TERM...SUNDAY THROUGH THURSDAY

SYNOPSIS...UPPER RIDGE BUILDS OVER THE GREAT BASIN AND ROCKIES
SUNDAY THROUGH TUESDAY FOR MAINLY DRY AND UNSEASONABLY MILD
WEATHER...EXCEPT FOR WESTERN VALLEYS AND LOWER CENTRAL BASINS UNDER
STEEP INVERSIONS.  A WEAK STORM SYSTEM WILL LIFT NORTHEAST ACROSS
THE GREAT BASIN ON WEDNESDAY BRINGING A CHANCE OF RAIN AND SNOW
SHOWERS MAINLY ACROSS THE WEST.

DISCUSSION...UPPER HIGH TO PUSH IN FROM THE EASTERN PACIFIC INTO THE
WESTERN GREAT BASIN ON SUNDAY WITH NW FLOW REMAINING ACROSS WYOMING
WITH POSSIBLY A FEW SNOW SHOWERS LINGERING OVER THE NORTHERN
MOUNTAINS.  THE MAIN STORY HOWEVER WILL BE A VERY WARM AIRMASS WILL
ADVECT INTO THE AREA MONDAY AND TUESDAY AS UPPER RIDGE AXIS
TRANSLATES THE ROCKIES.  BOTH GFS AND ECMWF HAVE H7 TEMPS OF 5C TO
6C OVER THE AREA WITH H7 THERMAL RIDGE MONDAY AND TUESDAY.
EXPECTING WELL MIXED CONDITIONS UNDER STRONGER NW FLOW TO ELIMINATE
MUCH OF THE REMAINING OLD SNOW COVER OVER THE CENTRAL BASINS OVER
THE WEEKEND...SO WHEN THIS WARMER AIRMASS AND LIGHTER WIND ARRIVE
EARLY NEXT WEEK THERE WILL BE A LOWER ALBEDO...AND NOT QUITE THE
STEEP INVERSIONS OF INVERSIONS SEEN EARLIER IN JANUARY.
HOWEVER...THE SNOW-COVERED WESTERN VALLEYS...ESPECIALLY THE JACKSON
AND STAR VALLEYS...WILL LIKELY REMAIN UNDER STEEP INVERSIONS AT
LEAST THROUGH TUESDAY.   THUS...THERE WILL LIKELY BE A WIDE RANGE OF
TEMPERATURES ACROSS THE AREA MONDAY AND TUESDAY RANGING FROM NEAR 60
ALONG CODY FOOTHILLS AND EASTERN FOOTHILLS OF THE BIGHORN RANGE TO
NEAR 30 OR COLDER IN THE FAR WEST VALLEYS.  ECMWF AND GFS SHOW MUCH
MORE SPREAD THIS MORNING LIFTING AN UPPER LOW OUT OF THE BAJA AREA
INTO THE BACKSIDE OF UPPER RIDGE OVER THE ROCKIES WITH AN OVERALL
FURTHER SOUTH AND EAST TRACK.  GFS FASTER AND FURTHER NORTH LIFTING
THIS ENERGY ACROSS THE GREAT BASIN INTO WYOMING TUESDAY NIGHT AND
WEDNESDAY WHILE ECMWF FRAGMENTS THE UPPER LOW WITH A MUCH WEAKER
REMNANT SHEARING OUT INTO A CONFLUENT FLOW ACROSS THE CENTRAL
ROCKIES EARLY THURSDAY.  FORECAST KEEPS IDEA OF LOW CHANCE POPS
ACROSS THE WEST WEDNESDAY AND THURSDAY WITH CONTINUED DRY CONDITIONS
EAST OF THE DIVIDE.   TEMPERATURES WILL TREND COOLER DURING THIS
PERIOD BUT STILL REMAIN ABOVE NORMAL IN MOST AREAS.


&&

.AVIATION.../12Z ISSUANCE/

IFR/LIFR FOG WILL OBSCURE TERRAIN VCNTY AND NORTH OF KRIW THROUGH
16Z. OTHERWISE...PATCHY FOG MAY PARTIALLY OBSCURE TERRAIN THROUGH
MID MORNING IN BASINS AND VALLEYS. AN APPROACHING WEAK DISTURBANCE
WILL RESULT IN INCREASING MID/HIGH CLOUDINESS FROM NW TO SE
BETWEEN 21Z THURSDAY AND 03Z FRIDAY...BUT VFR CONDITIONS WILL
CONTINUE EVEN OVER MOUNTAINS. BETWEEN 06Z AND 12Z FRIDAY...EXPECT
CONSIDERABLE MID CLOUDS OVER THE LOWER ELEVATIONS WITH CEILINGS
BETWEEN 080-120 KFT AGL. ISOLATED SNOW SHOWERS COULD BEGIN TO ALSO
BREAKOUT ACROSS THE NORTHWEST AND NORTHERN MOUNTAINS WHERE
MVFR/IFR CONDITIONS WILL BE POSSIBLE. THE BASINS AND VALLEYS WILL
SEE FAIRLY LIGHT WINDS THROUGH THE PERIOD...WHILE THE WIND
CORRIDOR FROM KRKS TO KCPR...AS WELL AS KDUB WILL BE BREEZY TO
WINDY.

&&

.FIRE WEATHER...

SOME GUSTY WIND DEVELOPING BETWEEN ROCK SPRINGS AND CASPER TODAY.
OTHERWISE CLEAR SKIES AND POOR MIXING EXPECTED AGAIN. MIXING
HEIGHTS WILL REMAIN LOW THROUGH THE WEEKEND...ESPECIALLY IN THE
BASINS AND VALLEYS OF WESTERN AND CENTRAL WYOMING.

&&

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

$$

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







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