Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 290955
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
355 AM MDT MON SEP 29 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

OUR RESIDENT LOW WILL CONTINUE ITS TREK NORTHEAST TODAY...WORKING
ON ITS TRANSITION TO AN OPEN WAVE WITH A DISTINCTLY NEGATIVE TILT AS
THE DAY WEARS ON. THERE WILL BE MORE INSTABILITY TO WORK WITH TODAY
AND THERE COULD STILL BE SOME DECENT RAINFALL AMOUNTS EVEN THOUGH
PWAT VALUES ARE RETURNING CLOSER TO NORMAL. COOLER AIR WILL
ALSO BE MOVING INTO THE WEST...DROPPING SNOW LEVELS TO ABOUT 8000FT
LATE TONIGHT BUT THE MORE ABUNDANT MOISTURE WILL BE MOVING EAST OF
THE AREA BY THIS TIME SO NOT MUCH ACCUMULATION IS EXPECTED.

ON TUESDAY...MOST OF THE ACTIVITY WILL BE EAST OF THE AREA AS WE
TRANSITION TO MOIST WESTERLY FLOW. RAPID LEE CYCLOGENESIS WILL OCCUR
EARLY IN THE DAY NEAR THE NE/WY/SD TRIPLE POINT...WHICH WILL
TRANSLATE TO A NOTICEABLE INCREASE IN WESTERLY WINDS ACROSS THE
FORECAST AREA...BUT ESPECIALLY ACROSS THE SOUTH EARLY. THE LOW WILL
MOVE NORTH AND EAST DURING THE MORNING...SWITCHING WINDS TO THE
NORTHWEST ACROSS OUR NORTHERN HALF OF THE FORECAST AREA...WHICH
COULD LEAD TO SOME 40 TO 50 MPH WINDS IN NORTHERN JOHNSON COUNTY IF
EVERYTHING LINES UP RIGHT. ASIDE FROM THE WIND...AND A COLD WIND AT
THAT...OROGRAPHIC LIFT ACROSS THE WEST AND A DEFORMATION AXIS POKING
INTO OUR EASTERN ZONES COULD KEEP SOME MORE PERSISTENT RAIN GOING IN
THESE AREAS...WITH SNOW ABOVE 8500FT IN THE WESTERN MOUNTAINS AND
YELLOWSTONE. IT WILL BE VERY WEAKLY UNSTABLE ELSEWHERE...AND THAT
COMBINED WITH DECENT RESIDUAL MOISTURE COULD ALLOW FOR SOME ISOLATED
AFTERNOON SHOWERS IN BETWEEN. IT WILL DEFINITELY STILL BE A
COOL...MOIST AND RAW DAY FOR MUCH OF THE AREA.

OVERNIGHT TUESDAY INTO WEDNESDAY...A REENFORCING SHOT COULD ARRIVE
IN THE WESTERLY FLOW...WITH YET ANOTHER...EVEN COLDER...WAVE NIPPING
AT ITS HEELS FOR WEDNESDAY ESSENTIALLY KEEPING SHOWERS IN THE
FORECAST THROUGH MUCH THE SHORT TERM PERIOD AND DIPPING SNOW LEVELS
DOWN BELOW 7000FT ACROSS THE WEST AND NORTH. THESE NEXT COUPLE OF
DISTURBANCES WILL NOT HAVE AS MUCH MOISTURE AVAILABLE AS THE CURRENT
STORM SYSTEM BUT THERE COULD BE A FEW INCHES OF SNOW ACCUMULATING IN
THE MOUNTAINS. OUR LAST WAVE SHOULD EXIT WEDNESDAY EVENING LEAVING
BEHIND A VERY COOL AND FROSTY NIGHT FOR MUCH OF THE FORECAST AREA.

.LONG TERM...THURSDAY THROUGH MONDAY

IT APPEARS THAT THURSDAY WILL BE DRY FOR THE REGION WITH JUST
ISOLATED AFTERNOON SHOWERS IN THE NORTHERN BIGHORN MOUNTAINS. THE
GFS/ECMWF MODELS NOW KEEP THE BULK OF THE WEATHER SYSTEM TO THE
NORTHEAST OF OUR FORECAST AREA. A WEAK COLD FRONT APPEARS LIKELY TO
IMPACT JOHNSON COUNTY AND THE NORTHERN BIGHORN MOUNTAINS THURSDAY
NIGHT WITH A WIND SHIFT AND SOME COOLING FOR LOWS THURS NIGHT. THE
WEATHER PATTERN STAYS QUIET FRIDAY THROUGH SUNDAY. THE GFS HINTS AT
A WEATHER SYSTEM MONDAY THAT CLIPS THE NORTH...YET THE ECMWF DOES
NOT SHOW THIS SYSTEM AT THIS TIME. HAVE GONE WITH A DRY FORECAST
FRIDAY THROUGH MONDAY FOR NOW. THERE LOOKS TO BE SOME PASSING HIGH
AND MID CLOUDS IN THE NW FLOW AT TIMES FRI THROUGH MON. 700MB TEMPS
WARM GRADUALLY FRIDAY THROUGH SUNDAY...THEN LITTLE CHANGED NEXT
MONDAY. HAVE TO FACTOR IN THE LONGER NIGHTS AND BASIN INVERSIONS
THIS TIME OF YEAR...SO HIGH TEMPS WILL NOT MAKE THEIR FULL POTENTIAL
IN PLACES. THOSE AREAS THAT GET A LITTLE MIXING IN THE AFTERNOON
WILL BE THE WARMEST OVER THE WEEKEND. OVERALL A PLEASING WAY TO
USHER IN THE FIRST WEEK OF OCTOBER AFTER GETTING SOME WELL NEEDED
MOISTURE AT THE END OF SEPTEMBER.

&&

.AVIATION.../12Z ISSUANCE/

THE BULK OF THE SHOWER ACTIVITY OVER WESTERN AND NORTHERN AREAS
EARLY THIS MORNING SHOULD LIFT AWAY...BUT IN ITS WAKE WILL BE
STRATUS AND FOG /MVFR AND IFR/ IN MANY PLACES. THESE LOW CEILINGS
AND FOG SHOULD LIFT BY BETWEEN 16Z AND 18Z IN MOST AREAS. THEN THE
COMBINATION OF DAYTIME HEATING AND AN UPPER LOW MOVING OVER THE AREA
WILL RESULT IN ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS
DEVELOPING ACROSS THE ENTIRE AREA...WITH AN EMPHASIS ACROSS THE
WEST. MUCH OF THIS ACTIVITY SHOULD DISSIPATE BY AROUND 03Z. SOME
FOG/STRATUS IS EXPECTED AGAIN TONIGHT...BUT NOT NEARLY AS WIDESPREAD
AS WHAT OCCURS THIS MORNING.

&&

.FIRE WEATHER...

WETTING RAIN LIKELY ACROSS WESTERN AND CENTRAL WYOMING AGAIN
TODAY...THOUGH NOT AS MUCH AS THERE WAS THIS WEEKEND. SHOWERS AND
STORMS BECOME MORE ISOLATED TO SCATTERED ON TUESDAY BUT IT WILL
REMAIN COOL AND CLOUDY. ANOTHER REENFORCING SHOT OF COLD AIR
POSSIBLE ON WEDNESDAY WITH MORE WETTING RAIN AND MOUNTAIN SNOW
POSSIBLE.

&&

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

&&

$$

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




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