Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 310524
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1124 PM MDT THU OCT 30 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY NIGHT (ISSUED AT 310 PM MDT)

A FAIRLY UNEVENTFUL FORECAST THROUGH THE SHORT TERM. SATELLITE
IMAGERY DOES SHOW SOME MID TO HIGH LEVEL CLOUDS MOVING OVER THE TOP
OF THE RIDGE SO SOME AREAS...ESPECIALLY IN THE NORTHERN AND EASTERN
PORTIONS OF THE COUNTY WARNING AREA WILL SEE A BROKEN DECK OF CLOUDS
BUT NO PRECIPITATION IS EXPECTED. THIS PATTERN IS EXPECTED TO
CONTINUE THROUGH TONIGHT AS WELL AND INTO TOMORROW. AS A RESULT...WE
HAVE INCREASED SKY COVER A BIT IN THOSE AREAS BUT ONLY TO PARTLY
CLOUDY FOR MOST AREAS. THE OTHER CONCERN WILL BE FOR INCREASE IN THE
BREEZE LATE TONIGHT AND ESPECIALLY TOMORROW AS A SYSTEM APPROACHES
FROM THE WEST. THIS WILL TIGHTEN THE PRESSURE GRADIENT A BIT AND
BRING A GUSTY SOUTHWESTERLY BREEZE...ESPECIALLY ACROSS THE FAVORED
AREAS LIKE FROM ROCK SPRINGS TO CASPER. HOWEVER...700 MILLIBAR WINDS
TOP OUT AT ONLY 35 KNOTS SO IT LOOKS ONLY BREEZY...NOT WINDY AND ANY
HIGH WIND HIGHLIGHTS ALMOST CERTAINLY WILL NOT BE NEEDED.
TEMPERATURES WILL CONTINUE TO BE WELL ABOVE NORMAL WITH HIGHS
POSSIBLY REACHING THE 70S IN SOME WARMER BASIN LOCATIONS ALTHOUGH IF
CLOUDS ARE A BIT MORE WIDESPREAD THIS MAY INHIBIT HEATING JUST A
BIT. AS FOR HALLOWEEN NIGHT AND THE ALL IMPORTANT TRICK OR TREATING
FORECAST...IT LOOKS LIKE A PARTLY TO MOSTLY CLEAR SKY AND
TEMPERATURES GENERALLY IN THE 40S AND 50S DEPENDING ON YOUR
ELEVATION SO THINGS LOOK GOOD FOR THE ANNUAL CANDY GATHERING. LATE
AT NIGHT AFTER THE KIDS HAVE HOPEFULLY GONE TO SLEEP...SOME MOISTURE
ADVECTING FROM THE SOUTH AND WEST COULD BRING A FEW SPRINKLES OR
FLURRIES TO THE HIGHER ELEVATIONS WEST OF THE DIVIDE BUT THESE LOOK
INCONSEQUENTIAL ENOUGH THAT WE LEFT THEM OUT OF THE FORECAST.

.LONG TERM...SATURDAY THROUGH THURSDAY

BEGINNING OF FCST...END OF UPR RIDGING WITH SOUTHWEST FLOW FIRMLY IN
PLACE AHEAD OF WRN CONUS TROF AND FIRST INFLUENCES OF JET STREAK/SW
BEING FELT OVR THE WRN FA. HOWEVER...LOW MOISTURE CONTENT OF THE
ATMOSPHERE AT THIS TIME WILL KEEP QPF ON THE LOW SIDE AT LEAST THRU
THE FIRST 12 HRS OF THE FCST. WEAK CYCLOGENESIS JUST STARTING TO
PROCEED OVR THE GREAT BASIN WITH LEE SIDE TROFFING SETTING EAST OF
THE BIGHORNS. AS SFC P GRAD INCREASES WITH THIS DEVELOPING STORM
SYSTEM...WIND SPEEDS ACROSS THE USUAL WIND CORRIDOR WITH ALSO
INCREASE BY SAT AFTERNOON...WITH GUSTS 45 TO 50 MPH COMMON INTO THE
EVENING PERIOD BEFORE DECREASING OVERNIGHT. THE WIND WILL RETURN
AGAIN BY SUNDAY AFTERNOON.

BY SAT NIGHT...ADDITIONAL CHANGES FROM THE APPROACHING...
INTENSIFYING AND  EVOLVING SYSTEM REALLY START TO COME INTO PLAY AS
SFC/UPR LOW SPINS UP OVR NRN WY/SRN MT...ALONG/NEAR INTERSECTION
WITH LEE TROF. AS CYCLONE SPINS UP...EXPECT VERY STRONG WINDS ALOFT
INVOF LOW SAT NIGHT INTO SUN MORNING AFFECTING THE MOUNTAIN PEAKS
WEST OF BUFFALO FOR A SHORT PERIOD BEFORE THE LOW MOVES OFF TO THE
NNE. ACROSS THE WRN CWA...N/S ORIENTED JET MOVES OVERHEAD...
SUBSTANTIALLY INTENSIFYING PRECIP ASSOCIATED WITH...BY THIS
TIME...INCREASED  MOISTURE. THIS FIRST BURST OF PRECIP...AND RAIN
CHANGING SNOW...WILL MOVE QUICKLY NORTH AND INTO CNTRL MT BY SUN
MORNING. MOUNTAINS SHOULD RECEIVE UP TO 3 INCHES OF WET SNOWFALL
FROM THIS FIRST HIT. THEN...AS THE CYCLONE MATURES RATHER QUICKLY
WITH RAPIDLY DEVELOPING INSTABILITY UNDER COOL UPR TEMPS...AND
DECENT BAROCLINICITY...A LARGE AREA OF PRECIPITATION WILL BREAK OUT
WEST OF THE SFC LOW...WITH GREATEST INTENSITY NEARLY DIRECTLY UNDER
THE H5 TROF AXIS OVR NERN ID/WRN MT. THIS WILL RESULT IN A BIT
LIGHTER BUT MORE PERSISTENT RAINFALL/SNOWFALL ACROSS THE WRN TO NRN
CWA. ANOTHER AREA OF GOOD PRECIP WILL BE CO-LOCATED WITH THE UPR JET
FROM NCNTRL CO THRU SERN WY...WELL OUT OF THE FA. ATTM...IT WOULD
APPEAR THAT THE MOUNTAINS OF SW YELLOWSTONE AND PERHAPS THE TETONS
TO THE SOUTH WILL BE IN THE BEST POSITION FOR GREATEST SNOWFALL
POTENTIAL...WITH MUCH OF THIS REGION RECEIVING 3 TO 6 INCHES IN A 24
HR PERIOD...WITH LOCALIZED PREFERRED AREAS GETTING UP TO 8 INCHES.
PERHAPS ANOTHER INCH OR TWO MAY BE HAD SUNDAY NIGHT INTO MONDAY
MORNING...ALTHOUGH THIS IS MUCH MORE SPECULATION THAN EMPIRICAL
SCIENCE AT THIS POINT. LOWER ELEVATIONS LOOK TO BE THE RECIPIENTS OF
UP TO 3 INCHES OF SNOW OVER THE SAME PERIOD OF TIME. ALL THESE
SNOWFALL NUMBERS PUT THE WRN FA DANGEROUSLY CLOSE TO ADVISORY
CONDITIONS. IF THE LOCATION OF THE UPR AND SFC LOWS HAD PLACED
CYCLOGENESIS FURTHER EWD...OR WAS SLOWER TO DEVELOP AND
EVOLVE...THIS WOULD/COULD HAVE BEEN MUCH WORSE THAN IT WILL BE.
STILL...THE CURRENT DEVELOPMENT OF THIS SYSTEM WARRANTS CONTINUED
MONITORING IN CASE THERE ARE SIGNIFICANT SPATIAL OR TEMPORAL
DIFFERENCES BETWEEN NOW AND THEN THAT MAY CAUSE POTENTIAL SNOWFALL
TO INCREASE. LATER SUNDAY EVENING/OVERNIGHT WILL BE THE ONLY
REALISTIC PERIOD WHERE MOST LOWER ELEVATIONS WILL SEE ANY CHANCE FOR
PRECIP REACHING THE GROUND AS TROF AXIS SWINGS THRU.

BY MON AFTERNOON...MOST TRACES OF THE STORM SYSTEM...BOTH SFC AND
ALOFT...WILL HAVE MOVED E TO SE OF WY...LEAVING BEHIND CLEARING
SKIES AND COLDER TEMPS. SLOW WARMING AND MOSTLY DRY CONDITIONS UNDER
CONTINUING NW FLOW UNTIL UNTIL AT LEAST THURSDAY...WHEN A TRANSITION
TO FLAT RIDGING MAY ENSUE. WINDS LOOK TO INCREASE ACROSS THE USUAL
SPOTS TUE NIGHT INTO WED MORNING. OTHERWISE...OVER THE FINAL THREE
DAYS OF THE FCST...THE ONLY AREA WHICH MAY HAVE SMALL CHCS FOR
PRECIP WILL BE ACROSS THE NW MOUNTAINS UNDER MODEST MID LVL TERRAIN
FORCED CONDITIONS..FAVORING THE UPR WRN SLOPES.

&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS WILL OCCUR THROUGH 06Z SATURDAY. EXPECT SOME
AFTERNOON WIND AT KCPR AND KRKS TERMINAL SITES.

&&

.FIRE WEATHER...

A RIDGE OF HIGH PRESSURE IS EXPECTED TO LAST THROUGH SATURDAY
MORNING AND BRING MAINLY DRY WEATHER. A GUSTY SOUTHWESTERLY BREEZE
WILL DEVELOP TOMORROW FROM THE RED DESERT THROUGH NATRONA AND
JOHNSON COUNTIES ON FRIDAY. THE NEXT POTENTIAL ROUND OF
PRECIPITATION MAY BE FOUND BEGINNING SATURDAY AFTERNOON AS AN AREA
OF LOW PRESSURE APPROACHES WESTERN WYOMING.

&&

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

&&

$$

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






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