Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 222004
AFDRIW

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

.SHORT TERM...TONIGHT THROUGH MONDAY

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.../00Z 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. A PACIFIC TROUGH WILL SPREAD LAYERED MID
AND HIGH CLOUDS EAST 12Z TO 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.

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

VFR CONDITIONS WILL PREVAIL AT THE AIRPORTS WITH INCREASING WEST WINDS
THROUGH 18Z MONDAY. A PACIFIC TROUGH WILL SPREAD LAYERED CLOUDS
EAST 09Z TO 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.

&&

.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
FIRE WEATHER...C.BAKER






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