Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 201743
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1143 AM MDT MON OCT 20 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

ONE MORE WARM DAY UNDERNEATH THE RIDGE TODAY AND TONIGHT
..TEMPERATURES WILL REMAIN 10 TO 15 DEGREES ABOVE NORMAL FOR THIS
TIME OF YEAR. A COLD FRONT WILL APPROACH THE WEST EARLY TUESDAY
MORNING...SWEEPING EAST THROUGH THE DAY. THE APPROACHING TROUGH
AND ASSOCIATED FRONT WILL CREATE A WINDY DAY FOR MUCH OF THE AREA
ON TUESDAY OTHERWISE THERE WILL BE A CHANCE FOR SOME RAIN...AND
SNOW ABOVE 6KFT RISING TO ABOUT 8.5KFT IN THE AFTERNOON...MAINLY
IN THE NORTHWESTERN MOUNTAINS AND YELLOWSTONE. SOME RAIN WILL BE
SPILLING ACROSS THE SOUTH AND INTO SOME AREAS EAST OF THE DIVIDE.
IT IS STARTING TO LOOK A BIT MORE UNSTABLE FOR TUESDAY AFTERNOON
THAN PREVIOUS RUNS...SO A SLIGHT CHANCE FOR THUNDER WAS INCLUDED
WITH THIS PACKAGE FOR THE 18Z TUE-00Z WED TIMEFRAME. THIS
INSTABILITY COULD HELP OVERCOME SOME OF THE DOWNSLOPING AFFECTS OF
THE SWIFT WEST AND SOUTHWEST FLOW...BRINGING A CHANCE FOR SOME
SHOWERS INTO THE FOOTHILLS AND BASINS EAST OF THE DIVIDE...KEPT
POPS QUIET FOR NOW BUT WOULD NOT BE SURPRISED IF A SHOWER OR TWO
MADE IT INTO THESE AREAS. THIS WILL NOT BE A SIGNIFICANT RAIN OR
SNOW PRODUCER BUT IT WILL COOL THINGS OFF A BIT...INCREASE CLOUD
COVER AND WIND SPEEDS ACROSS THE REGION TUESDAY AND TUESDAY
NIGHT...ESPECIALLY ALONG THE CODY FOOTHILLS AND THE UPPER WIND
RIVER BASIN OVERNIGHT AS THE SUBSIDENT BACK SIDE OF THE WAVE
PASSES OVERHEAD. THIS SHOULD HELP FORCE DOWN SOME STRONGER WIND
GUSTS INTO THE FOOTHILLS. CROSS SECTIONS ALONG THE ABSAROKAS SHOW
THE POTENTIAL FOR A BREAKING MOUNTAIN WAVE ALONG THE WESTERN CODY
FOOTHILLS OVERNIGHT...THIS WAVE COULD PRODUCE WIND GUSTS OVER 60
MPH AROUND CLARK AND WEST OF CODY. THE WAVE LIFTS OUT ON
WEDNESDAY...LEAVING BEHIND SOME COOLER BUT AVERAGE TEMPERATURES
FOR THIS TIME OF YEAR...AND SOME BREEZY WESTERLIES ACROSS THE
SOUTH.

.LONG TERM...THURSDAY THROUGH MONDAY

SYNOPSIS...UNSEASONABLY MILD AND DRY CONDITIONS WILL PREVAIL
THURSDAY THROUGH SATURDAY WITH RECORD OR NEAR RECORD HIGHS POSSIBLE
ON SATURDAY.  A TROUGH OF LOW PRESSURE AND ASSOCIATED COLD FRONT
WILL MOVE ACROSS THE AREA SUNDAY AND MONDAY BRINGING A CHANCE OF
RAIN AND SNOW SHOWERS ALONG WITH COLDER TEMPERATURES.

DISCUSSION...UPPER HIGH STRENGTHENS OVER THE SOUTHERN ROCKIES
THURSDAY AND FRIDAY WITH BUILDING HEIGHTS ACROSS WYOMING WHILE
PACIFIC TROUGH SHARPENS NEAR 130W ON FRIDAY. UPPER TROUGH IS
FORECAST TO MAKE LANDFALL ALONG THE WEST COAST LATE SATURDAY WITH
LEAD SHORTWAVE EJECTING NE ACROSS THE INTERMOUNTAIN WEST INTO
SOUTHERN ALBERTA. THIS WILL BRING INCREASING SW FLOW ACROSS THE
AREA SATURDAY WITH LEE SIDE LOW DEVELOPMENT EXPECTED OVER CENTRAL
MONTANA PUTTING CENTRAL WYOMING IN WARM SECTOR. RECORD HIGH
TERRITORY FOR MANY LOCATIONS IS UPPER 60S TO LOWER 70S (73 AT
LND...72 AT CPR) SO THESE RECORDS WILL LIKELY BE IN JEOPARDY...AND
WITH GUSTY SOUTHWEST WIND...FIRE DANGER WILL BE ELEVATED.

GFS REMAINS MORE PROGRESSIVE THAN THE ECMWF BRINGING UPPER TROUGH
AND ASSOCIATED FRONT ACROSS THE AREA SUNDAY...AND 20/00Z ECMWF
DETERMINISTIC IS OUT AHEAD OF THE EC ENSEMBLE MEAN.  SO ALTHOUGH
AGREEMENT BETWEEN THE GFS AND ECMWF DETERMINISTIC RUNS IS MUCH
BETTER THIS MORNING...MEDIUM-RANGE MODELS HAVE YET TO SHOW ANY
DEGREE OF RUN-TO-RUN CONSISTENCY TO GAIN MUCH CONFIDENCE IN
TIMING OF COLD FRONT AND ONSET OF PRECIPITATION...WITH AN OVERALL
PREFERENCE TOWARD SLOWER PROGRESSION PER THE EC ENSEMBLE MEAN.
THIS RESULTS IN BRINGING CHANCES OF PRECIPITATION INTO THE WEST ON
SUNDAY AND SPREADING ACROSS THE AREA SUNDAY NIGHT INTO MONDAY.
TEMPERATURES ON MONDAY ARE EXPECTED TO BE SOME 20-25F COOLER THAN
NEAR RECORD HIGH TEMPERATURES ON SATURDAY...OR 5-10F BELOW NORMAL.

.AVIATION.../18Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL IN THE LOWER ELEVATIONS...INCLUDING
THE AIRPORTS THROUGH 18Z TUESDAY. AN APPROACHING PACIFIC LOW PRESSURE
TROUGH WILL BRING INCREASED CLOUD COVER AND SHOWER ACTIVITY OVER
THE MOUNTAINS ALONG AND EAST OF THE CONTINENTAL DIVIDE AFTER 10Z
WITH AREAS OF MVFR TO IFR CEILINGS...AND VISIBILITIES REDUCED IN
SHOWERS INCREASING AND OBSCURING THE HIGHER MOUNTAINS. STRONG
WEST TO SOUTHWEST WINDS WILL ALSO MOVE IN WITH THE SHOWERS AND
CLOUDS BECOMING 25-30KTS WITH GUSTS TO 40KTS ALONG AND NEAR THE
EAST SLOPES OF THE MOUNTAINS AND THROUGH THE WIND CORRIDOR FROM
KRKS TO KCPR.

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

VFR CONDITIONS WILL PREVAIL IN THE LOWER ELEVATIONS...INCLUDING
THE AIRPORTS THROUGH 10Z TUESDAY. AN APPROACHING PACIFIC LOW
PRESSURE TROUGH WILL BRING INCREASED CLOUD COVER AND SHOWER
ACTIVITY OVER THE MOUNTAINS AND FAR WESTERN VALLEYS AFTER 07Z
WITH AREAS OF MVFR TO IFR CEILINGS...AND VISIBILITIES REDUCED IN
SHOWERS INCREASING AND OBSCURING THE HIGHER MOUNTAINS. BRIEF MVFR
CONDITIONS MAY OCCUR AT KJAC...KAFO...KEMM...KBPI AND KPNA AFTER
10Z. STRONG WEST TO SOUTHWEST WINDS WILL ALSO MOVE IN WITH THE
SHOWERS AND CLOUDS BECOMING 20-25KTS WITH GUSTS TO 35KTS OVER THE
MOUNTAINS AND THROUGH THE WIND CORRIDOR FROM KEVW TO KRKS.

.FIRE WEATHER...

SEASONABLY WARM TEMPERATURES AND LOW WIND SPEEDS CONTINUE AGAIN TODAY.
WHILE RELATIVE HUMIDITY VALUES MAY DIP INTO THE LOWER 20S OR EVEN
UPPER TEENS AT TIMES...WINDS SPEEDS WILL REMAIN ON THE LOW
SIDE...HELPING TO AVOID ENHANCED FIRE DANGER. HOWEVER...WIND SPEEDS
WILL INCREASE ON TUESDAY AHEAD OF THE NEXT STORM. CHANCES OF WETTING
RAIN WILL BE FAIRLY HIGH ACROSS THE HIGHER ELEVATIONS...THE WEST AND
ACROSS RAWLINS DISPATCH...WITH A LOW CHANCE EAST OF THE DIVIDE.

&&

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

$$

SHORT TERM...ALLEN
LONG TERM...AEM
AVIATION...C.BAKER
FIRE WEATHER...ALLEN






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