Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200956
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
256 AM MST TUE JAN 20 2015

.SHORT TERM...TUESDAY THROUGH THURSDAY NIGHT

AT THIS TIME WE ARE UNDER THE INFLUENCE OF NORTHWEST FLOW WITH SOME
WEAK DISTURBANCES MOVING THROUGH THE FLOW. AND IN THE WINTER YOU
KNOW THAT THAT MEANS. THOSE ANNOYING SNOW SHOWERS AND SNOW BANDS
THAT THE MODELS DO SUCH A GOOD JOB WITH...NOTE SARCASM...AND ARE
ENOUGH TO MAKE A FORECASTER RIP THIS HAIR OUT. SINCE PINPOINTING
THEM IS DIFFICULT AT BEST...WE HAVE KEPT ISOLATED POPS ACROSS MUCH
OF THE NORTHERN HALF OF THE COUNTY WARNING AREA TODAY WITH HIGHER
POPS ACROSS THE HIGHER ELEVATION. SINCE THE WAVE IS MOISTURE
STARVED...WE DON`T EXPECT ANY BIG TOTALS AT THIS TIME. AS FOR
TEMPERATURES...LOOK FOR A COOLER DAY THAN YESTERDAY WITH THE COLD
ADVECTION. HOWEVER...STILL NOT BAD FOR THIS TIME OF YEAR. THE SNOW
SHOWERS SHOULD WANE LATE TONIGHT AS THE SHORTWAVE MOVES AWAY AND
RISING HEIGHTS BRING MORE SETTLED WEATHER. IF THERE IS ENOUGH
CLEARING...WE COULD SEE SOME FOG IN FAVORED AREAS SO WE KEPT
CONTINUITY IN THAT REGARD.

FAIRLY SETTLED WEATHER SHOULD THEN DOMINATE THROUGH THURSDAY AS HIGH
PRESSURE BUILDS ACROSS WYOMING. WITH LIGHT FLOW WE HAVE TO WATCH OUT
FOR INVERSIONS IN THE VALLEYS AND BASINS. HOWEVER...EAST OF THE
DIVIDE...THE RECENT WARMER WEATHER HAS MELTED A DECENT AMOUNT OF THE
SNOW AND THE LEFTOVER SNOW HAS A LOWER ALBEDO SO TEMPERATURES SHOULD
NOT BE FRIGID. HOWEVER...IT WILL BE COOLER THAN THE RECENT FEW DAYS.
THE COLDER SPOTS WOULD BE THE WESTERN VALLEYS WHERE THE RECENT FRESH
SNOW COVER SHOULD AID IN RADIATIONAL COOLING. THE NEXT TROUGH MAY
APPROACH BY LATE THURSDAY NIGHT. HOWEVER...THE MODELS ARE SPLIT ON
THE TIMING SO KEPT THINGS DRY THROUGH THE SHORT RANGE. MORE ON THIS
IN THE LONG RANGE PORTION OF THE DISCUSSION.

.LONG TERM...FRIDAY THROUGH TUESDAY

A WEAK WEATHER SYSTEM MOVES THROUGH THE AREA ON FRIDAY. MOISTURE IS
LIMITED AND SOME LIGHT MOUNTAIN SNOW SHOULD OCCUR. LOWER ELEVATIONS
SHOULD BE DRY FRIDAY. THE ECMWF MODEL HAS A MOIST NW FLOW FOR
SATURDAY THROUGH SUNDAY EVENING WITH PERIODS OF PRECIP FOR THE
MOUNTAINS AND POSSIBLY SOME PRECIP OVER THE LOWER ELEVATIONS OF THE
NORTH AND EAST ZONES. THE GFS CONTINUES TO COME AROUND TO THE ECMWF
SOLUTION WHICH ADDS TO THE FORECAST CONFIDENCE. HAVE MADE MINOR
ADJUSTMENTS TO THE FORECAST SATURDAY THROUGH SUNDAY EVENING. THE
REST OF THE REGION WILL BE DRY SATURDAY AND SUNDAY. THE WEATHER
PATTERN TURNS DRY FOR NEXT MONDAY AND TUESDAY PER BOTH LONG RANGE
MODELS. HIGH TEMPS FRIDAY THROUGH SUNDAY WILL BE AT OR SLIGHTLY
ABOVE SEASONAL NORMALS. NEXT MONDAY AND TUESDAY WILL BE QUITE MILD.
LOCATIONS THAT ARE SNOW FREE WILL LIKELY WARM UP THE MOST.

&&

.AVIATION.../12Z ISSUANCE/

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

DISTURBANCES IN THE NORTHWEST FLOW ALOFT SHOULD RESULT IN ISOLATED
TO SCATTERED MOUNTAIN SNOW SHOWERS POSSIBLY IMPACTING THE LOWER
ELEVATIONS. ONE DISTURBANCE SHOULD EXIT BY AROUND 15Z...WHILE
ANOTHER ONE WILL IMPACT THE AREA BETWEEN 21Z TUESDAY AND 06Z
WEDNESDAY. THE BULK OF THE IMPACT FROM THIS LATTER SYSTEM WILL BE
ACROSS THE NORTHERN AND CENTRAL PORTIONS OF THE BIGHORN MOUNTAINS
WHERE IFR/LIFR CONDITIONS ARE LIKELY AT TIMES IN SNOW AND LOW
CLOUDS. TERMINALS ARE EXPECTED TO REMAIN VFR...BUT CANNOT RULE A
STRAY SNOW BAND PUSHING EAST SOUTHEAST OFF THE MOUNTAINS AND
IMPACTING A TERMINAL OR TWO AT TIMES. THE MAIN IMPACT FROM BOTH
SYSTEMS WILL BE CONSIDERABLE MIDLEVEL CLOUDINESS...WITH PARTIAL
CLEARING BETWEEN SYSTEMS. WINDS WILL GENERALLY BE LIGHT FROM THE
WEST TO NORTHWEST. THE EXCEPTIONS WILL BE BREEZY NORTHWEST WINDS AT
KDUB AND KBYG.

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

STRATOCU AND SOME PATCHY FOG WILL BE POSSIBLE THIS MORNING OVER THE
VALLEYS...BUT MID LEVEL CLOUDINESS AND ISOLATED MOUNTAIN SNOW
SHOWERS SHOULD LIMIT THE EXTENT OF FOG/STRATUS. OTHERWISE...ISOLATED
MOUNTAIN SNOW SHOWERS...POSSIBLY SHIFTING INTO THE LOWER ELEVATIONS
WILL OCCUR TODAY. A BETTER CHANCE FOR STRATUS AND FOG WILL OCCUR
OVER THE WESTERN VALLEYS TONIGHT...ESPECIALLY KJAC.  WINDS WILL
GENERALLY BE LIGHT FROM THE WEST TO NORTHWEST THROUGH THE FORECAST
PERIOD.

&&

.FIRE WEATHER...

WIDESPREAD SNOW COVER WILL CONTINUE WITH COOL TEMPERATURES AND
FAVORABLE RELATIVE HUMIDITY. LIMITED MOISTURE IN NORTHWEST FLOW WILL
BRING SOME VERY LIGHT SNOWFALL TO THE NORTHERN HALF OF WYOMING.
WINDS WILL BE LIGHT TO MODERATE ACROSS MOST AREAS.  MIXING HEIGHTS
WILL BE LOW WITH GENERALLY POOR SMOKE DISPERSAL. MAINLY DRY WEATHER
WITH POSSIBLE VALLEY AND BASIN INVERSIONS WILL BE THE RULE FOR
WEDNESDAY INTO THURSDAY.

&&

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

&&

$$

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




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