Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 230516
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1116 PM MDT SUN MAR 22 2015

.SHORT TERM...TONIGHT THROUGH MONDAY (ISSUED AT 204 PM MDT)

CLOUDS WILL MOVE IN ACROSS THE AREA WITH SHOWERS DEVELOPING OVER
THE WESTERN MOUNTAINS OVER NIGHT AND INCREASING AND SPREADING
ACROSS THE SOUTH THROUGH THE MORNING.  TEMPERATURES WILL BE COOLING
AS SHOWERS BECOME RATHER WIDESPREAD OVER THE MOUNTAINS AND
INCREASE OVER THE LOWER ELEVATIONS. THUNDERSTORMS WILL BECOME
EMBEDDED IN THE DENSE CLOUD SHIELD AFTER NOON WITH STRONG GUSTY
WINDS AND SMALL HAIL. THE HIGHER MOUNTAIN AREAS COULD SEE 3 TO 5
INCHES OF SNOWFALL WHILE THE LOWER ELEVATIONS SHOULD SEE MAINLY
RAIN.  SOME SHOWERS AND ISOLATED THUNDERSTORMS WILL SPREAD EAST OF
THE CONTINENTAL DIVIDE BUT SHOULD NOT BE AS WIDESPREAD AS AREAS TO
THE WEST.  OVER AND NEAR THE EAST SLOPES OF THE MOUNTAINS
STRONGER DOWN SLOPE WINDS WILL OCCUR. CLOUD COVER AND STRONGER LOW
TO MID LEVEL MIXING SHOULD LIMIT THE INSTABILITY WITH THIS TROUGH
SO THE COVERAGE OF THUNDERSTORMS SHOULD BE ISOLATED.  NO LIGHTNING
HAS BEEN OBSERVED OVER THE WESTERN U.S. WITH THIS SYSTEM SO FAR
TODAY.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

BY MONDAY NIGHT THE MAIN ENERGY WITH THE FIRST OR SEVERAL WAVES
CROSSING THE AREA SHOULD BE EXITING TO THE EAST. AS A RESULT...WITH
THE LOSS OF FORCING AND DAYTIME HEATING THE COVERAGE OF SHOWERS
SHOULD WANE ACROSS THE AREA...ESPECIALLY AFTER MIDNIGHT.
AGAIN...WITH THE CONVECTIVE NATURE OF THE ACTIVITY PINPOINTING THE
HEAVIER SHOWERS IS NEARLY IMPOSSIBLE AT THIS POINT.

THE MODELS HAVE COME INTO BETTER AGREEMENT ON TIMING WITH THE NEXT
WAVE THAT WILL MOVE INTO THE WEST LATER ON TUESDAY AND THEN CROSS
THE STATE ON TUESDAY NIGHT. BOTH MODELS DO GIVE THE WEST A DECENT
AMOUNT OF SHOWERS SO WE BUMPED UP POPS AND QPF A BIT ACROSS THE
AREA. 700 MILLIBAR TEMPERATURES ARE FAIRLY COLD SO MUCH OF THIS WILL
FALL AS SNOW. EAST OF THE DIVIDE...HOWEVER...THERE IS STILL MUCH
UNCERTAINTY. WITH FAIRLY STRONG WESTERLY WINDS ACROSS THE AREA THERE
WILL BE SOME DOWNSLOPING SO MUCH OF THE DAYTIME HOURS COULD BE DRY
FOR MANY AREAS. SOMETHING INTERESTING DOES HAPPEN AT NIGHT THOUGH.
AFTER THE PASSAGE OF A COLD FRONT THE WIND DOES TURN MORE NORTHERLY
LATE AT NIGHT AND COULD BRING A PERIOD OF UPSLOPE AFTER MIDNIGHT
THAT COULD BRING SOME SNOW. THERE IS DISAGREEMENT WITH THE EXACT
PLACEMENT HOWEVER. SO...SOMETHING TO WATCH. COVERAGE OF
PRECIPITATION FROM THIS WAVE SHOULD DECREASE WEDNESDAY AS THE ENERGY
MOVES AWAY TO THE SOUTH AND EAST. TEMPERATURES WILL ALSO BE MUCH
COOLER THAN RECENT DAYS. CERTAINLY NOTHING UNUSUAL FOR LATE MARCH IN
WYOMING BUT CERTAINLY A SLAP IN THE FACE AFTER THE LONG STRETCH OF
MILD TEMPERATURES MUCH OF LAST WEEK.

ONE LAST WAVE WILL MOVE TOWARD THE AREA FOR THURSDAY. THIS ONE LOOKS
TO MAINLY EFFECT EASTERN PORTIONS OF THE COUNTY WARNING AREA AS
RIDGING BEGINS TO BUILD IN FROM THE WEST THOUGH. RIDGING THEN BUILDS
ACROSS THE AREA FOR FRIDAY AND BRING DRIER AND MILD WEATHER. BOTH
THE GFS AND EUROPEAN HAVE TRENDED SLOWER...WEAKER AND FURTHER EAST
WITH THE NEXT WAVE FOR THE WEEKEND SO WE DRIED THINGS OUT A BIT FOR
SATURDAY. THE MODELS THEN SPLIT ON SUNDAY WITH THE GFS KEEPING
THINGS DRY WITH THE WAVE MOVING WELL TO THE EAST AND THE EUROPEAN A
BIT MORE UNSETTLED.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS WITH INCREASING WEST
WINDS ALOFT THROUGH 18Z MONDAY. CLOUDS WILL LOWER BETWEEN 15Z AND 18Z
WITH MVFR CEILINGS DEVELOPING OVER THE MOUNTAINS WITH RAIN AND SNOW
SHOWERS INCREASING AND RESTRICTING VISIBILITY BELOW 3 MILES ABOVE
9000 FEET.  HIGHER MOUNTAINS WILL BECOME INCREASINGLY OBSCURED WITH
MOUNTAIN TOP WINDS INCREASING TO 40-45KTS.  ISOLATED THUNDERSTORMS
WILL BE POSSIBLE ESPECIALLY OVER THE MOUNTAINS AND ACROSS THE SOUTH
FROM 18Z TO 00Z AS THE AIR MASS BECOMES MORE UNSTABLE. THE CHANCES
OF A THUNDERSTORM OCCURRING AT ANY OF THE AIRPORTS IS LOW BUT BRIEF
MVFR CONDITIONS COULD OCCUR AT ANY OF THE AIRPORTS AS THE SHOWERS
AND THUNDERSTORMS PROGRESS EAST. SCATTERED RAIN AND SNOW SHOWERS
WILL OCCUR AFTER 00Z TUE THROUGH 06Z TUE.

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

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS WITH INCREASING WEST
WINDS ALOFT THROUGH 18Z MONDAY. CLOUDS WILL LOWER BETWEEN 14Z AND
18Z WITH IFR TO MVFR CEILINGS DEVELOPING OVER THE MOUNTAINS WITH
RAIN AND SNOW SHOWERS INCREASING AND RESTRICTING VISIBILITY BELOW 2
MILES ABOVE 8000 FEET. WIDESPREAD MOUNTAIN OBSCURATIONS WILL OCCUR
BY 15Z MONDAY WITH MOUNTAIN TOP WINDS INCREASING TO 40-45KTS. AFTER
18Z IFR TO MVFR CEILINGS AND VISIBILITY WILL BE WIDESPREAD OVER THE
MOUNTAINS.  ISOLATED EMBEDDED THUNDERSTORMS WILL BE POSSIBLE
ESPECIALLY OVER THE MOUNTAINS AND ACROSS THE SOUTH FROM 18Z TO 00Z
AS THE AIR MASS BECOMES MORE UNSTABLE. THE CHANCES OF A THUNDERSTORM
OCCURRING AT ANY OF THE AIRPORTS IS LOW BUT BRIEF IFR TO MVFR
CONDITIONS COULD OCCUR AT ANY OF THE AIRPORTS AS THE SHOWERS AND
THUNDERSTORMS PROGRESS EAST. SCATTERED RAIN AND SNOW SHOWERS WILL
OCCUR AFTER 00Z TUE THROUGH 06Z TUE WITH LOCAL MVFR CONDITIONS.

&&

.FIRE WEATHER...

CLOUDS WILL MOVE IN ACROSS THE AREA WITH SHOWERS DEVELOPING OVER
THE WESTERN MOUNTAINS OVER NIGHT AND INCREASING AND SPREADING
ACROSS THE SOUTH THROUGH THE MORNING.  TEMPERATURES WILL BE COOLING
AS SHOWERS BECOME RATHER WIDESPREAD OVER THE MOUNTAINS AND
INCREASE OVER THE LOWER ELEVATIONS. THUNDERSTORMS WILL BECOME
EMBEDDED IN THE DENSE CLOUD SHIELD AFTER NOON WITH STRONG GUSTY
WINDS AND SMALL HAIL. THE HIGHER MOUNTAIN AREAS COULD SEE 3 TO 5
INCHES OF SNOWFALL WHILE THE LOWER ELEVATIONS SHOULD SEE MAINLY
RAIN. SOME SHOWERS AND ISOLATED THUNDERSTORMS WILL SPREAD EAST OF THE
CONTINENTAL DIVIDE BUT SHOULD NOT BE AS WIDESPREAD AS AREAS TO THE
WEST. RELATIVE HUMIDITY WILL BE INCREASED ACROSS THE AREA AND OVER
AND NEAR THE EAST SLOPES OF THE MOUNTAINS STRONGER DOWN SLOPE WINDS
WILL OCCUR. MIXING HEIGHTS WILL BE LOW IN THE WEST WITH POOR SMOKE
DISPERSAL WHILE EAST OF THE CONTINENTAL DIVIDE BETTER MIXING AND
STRONGER WINDS WILL PRODUCE GENERALLY GOOD SMOKE DISPERSAL.

&&

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

&&

$$

SHORT TERM...C.BAKER
LONG TERM...HATTINGS
AVIATION...C.BAKER/AR
FIRE WEATHER...C.BAKER






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