Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 271957
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
157 PM MDT SAT SEP 27 2014

.SHORT TERM...TONIGHT THROUGH SUNDAY

FORECAST ON TRACK WITH LARGE UPPER LEVEL LOW CUTTING OFF OVER
CENTRAL CALIFORNIA AND THE WESTERN GREAT BASIN...SPREADING
SIGNIFICANT SUBTROPICAL MOISTURE NORTH ACROSS UTAH...WESTERN
COLORADO...IDAHO AND SOUTHERN AND WESTERN WYOMING.  THIS AIR MASS
IS UNSTABLE WITH STRONG UPPER LEVEL DIVERGENCE...INCREASING MID
LEVEL DEFORMATION AND FRONTOGENESIS OVER THE AREA. A SURFACE COLD
FRONT HAS MOVED SOUTH TO THE CONTINENTAL DIVIDE AND WILL CONTINUE
TO PUSH THROUGH THE REST OF THE AREA TONIGHT.  CLOUDS AND
PRECIPITATION WILL SPREAD NORTH AND EAST ACROSS THE AREA TONIGHT
AND WILL CONTINUE THROUGH SUNDAY. MUCH OF THE SOUTH AND WEST WILL
EXPERIENCE EMBEDDED THUNDERSTORMS WITH GUSTY WINDS AND SMALL HAIL.
WITH THE CONVECTION BEING SUPPORTED BY THE STRONG UPPER
DIVERGENCE...THE THUNDERSTORMS WILL CONTINUE TO BE A THREAT
THROUGH THE NIGHT.  TEMPERATURES WILL BE GENERALLY COLDER OVER
MUCH OF THE AREA...BUT CLOUD COVER AND PRECIPITATION WILL MODERATE
THE COOLING IN THE WEST. SNOW LEVELS WILL LOWER TO AROUND 9500 FEET
AND REMAIN NEAR THAT LEVEL THROUGH SUNDAY...LOWERING TO 9000 FEET
LATE SUNDAY AFTERNOON. LOCAL HEAVY RAIN IS EXPECTED...ESPECIALLY
IN THE WESTERN AND CENTRAL MOUNTAINS WITH 1 TO 2 INCHES OF RAIN
POSSIBLE THROUGH SUNDAY AFTERNOON.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

THE BEST LIFT AND MOST CONCENTRATED RAIN WITH THE UPPER LEVEL LOW
LIFTING NORTHWARD IS EXPECTED TO LIFT EAST TO NORTHEASTWARD ACROSS
THE AREA ON SUNDAY EVENING. THE MODELS DO HAVE SLIGHT TIMING
DIFFERENCES AND ARA OF HEAVIEST PRECIPITATION. HOWEVER...CONTINUITY
HAD THIS PORTRAYED FAIRLY WELL SO WE MADE FEW CHANGES TO POPS OF
QPF. THE HEAVIEST PRECIPITATION SHOULD SHIFT EAST OF THE AREA LATER
SUNDAY NIGHT WITH LEFTOVER LIGHTER ACTIVITY THROUGH THE OVERNIGHT
HOURS. AS FOR THE CHANCE OF THAT WHITE STUFF STARTING WITH THE
LETTER S...WE AGREE WITH THE PREVIOUS SHIFT THAT THIS IS NOT A
REALLY COLD SYSTEM AND ANY DECENT ACCUMULATIONS WILL BE CONFINED TO
ABOVE PASS LEVELS...AROUND 9500 FEET.

BY MONDAY THE SYSTEM LOOKS MORE LIKE AN OPEN WAVE SITUATION. THE
BEST LIFT AND PRECIPITATION LOOKS TO STAY EAST OF THE AREA.
HOWEVER...THE GFS DOES TRY TO WRAP SOME HEAVIER PRECIPITATION BACK
INTO EASTERN PORTIONS OF THE COUNTY WARNING AREA...MAINLY FROM THE
BIGHORN RANGE AND EASTWARD. THE REST OF THE AREA LOOKS TO HAVE
MAINLY LIGHTER PRECIPITATION. NEVERTHELESS...IT LOOKS LIKE ANOTHER
MAINLY CLOUD AND COOL DAY.

THE MODELS THEN LIFT THE LOW OUT OF THE AREA FOR LATER TUESDAY AND
INTO WEDNESDAY...ALTHOUGH A FEW SHOWERS MAY LINGER IN THE
NORTHEAST. ANOTHER SHORTWAVE LOOKS TO ROTATE INTO THE WEST WITH
ANOTHER CHANCE OF SHOWERS. THIS SYSTEM LOOKS COLDER AND COULD LOWER
SNOW LEVELS DOWN TO AROUND 7500 FEET HOWEVER. THERE IS MUCH LESS
MOISTURE TO WORK WITH HOWEVER SO NO HIGHLIGHTS ARE ANTICIPATED AT
THIS TIME. CONTINUITY LOOKED REASONABLE SO WE MADE FEW CHANGES.

YET ANOTHER FAST MOVING CLIPPER WILL MOVE SOUTHEASTWARD TOWARD THE
AREA FOR THURSDAY. THE MODELS CONTINUE TO HAVE DIFFERENCES AS
EXPECTED WITH THE EUROPEAN FURTHER SOUTH WITH THE GFS KEEPING THINGS
FURTHER NORTH. WITH THE UNCERTAINTY...WE CONFINED POPS MAINLY TO THE
NORTHERN HALF OF THE COUNTY WARNING AREA. AGAIN...THIS SYSTEM DOES
NOT HAVE MUCH MOISTURE SO ANY PRECIPITATION IS EXPECTED TO BE
LIGHT.  QUIETER WEATHER SHOULD FINALLY THEN MOVE IN FOR FRIDAY AND
NEXT WEEKEND AS RIDGING REBUILDS ACROSS THE WEST AND BRINGS DRY
CONDITIONS WITH WARMER TEMPERATURE.

&&

.AVIATION.../00Z ISSUANCE/

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

A COLD FRONT HAS PUSHED UP TO THE CONTINENTAL DIVIDE WITH A BREEZY
NORTH TO NORTHEAST WIND BEHIND THE COLD FRONT. CLOUD COVER WILL
INCREASE THROUGH 06Z WITH SUBTROPICAL MOISTURE MOVING NORTH OVER
THE COLDER AIR. VFR CONDITIONS ARE EXPECTED THROUGH 03Z...THEN
AREAS OF MVFR TO IFR CONDITIONS WILL BECOME WIDESPREAD OBSCURING
THE MOUNTAINS ALONG AND EAST OF THE CONTINENTAL DIVIDE SPREADING
NORTH AND EAST THROUGH 18Z THREATENING KLND...KCOD AND KDUB BY 03Z
AND THE REMAINDER OF THE AIRPORTS BY 06Z.

ALTHOUGH SOME THUNDERSTORM ACTIVITY WILL BE POSSIBLE BETWEEN 00Z
AND 06Z...IT SHOULD BE MAINLY CONFINED TO JUST ALONG AND NORTH OF
THE DIVIDE AS STORMS MOVING OVER THE DIVIDE WILL ENCOUNTER A MORE
STABLE ATMOSPHERE.

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

THE UPPER LEVEL LOW PRESSURE CENTER OVER THE GREAT BASIN WILL CONTINUE
TO SPREAD SIGNIFICANT SUBTROPICAL MOISTURE AND INSTABILITY TO
SOUTHERN AND WESTERN WYOMING WITH WIDESPREAD MVFR TO IFR CEILINGS
AND VISIBILITIES IN RAIN...MIXED WITH SNOW IN THE HIGHER MOUNTAINS
THROUGH 00Z...THE LOWER ELEVATIONS WILL SEE MVFR TO IFR CEILINGS
BECOME PREVAILING 00Z TO 03Z AND REMAIN DOWN THROUGH 18Z WITH SOME
IMPROVEMENT IN CEILING HEIGHTS FROM 18Z TO 00Z. EMBEDDED THUNDERSTORMS
WILL PRODUCE STRONG WIND GUSTS AND SMALL HAIL.

&&

.FIRE WEATHER...

COLDER AND WETTER WEATHER WILL SPREAD OVER THE AREA TONIGHT AND WILL
THEN CONTINUE INTO TUESDAY...WITH SNOW LEVELS LOWERING EACH NIGHT IN
THE MOUNTAINS FROM AROUND 9500 FEET TONIGHT...TO 8500 FEET MONDAY NIGHT.

&&

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

$$

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







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