000
FXUS65 KRIW 131802
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1102 AM MST FRI DEC 13 2013

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT

SHRINKING TEMPERATURE AND DEW POINT SPREADS NOTED ACROSS THE
WESTERN VALLEYS THIS MORNING...WITH PATCHY FOG EXTENDED THROUGH THE
MID MORNING HOURS. ZONAL FLOW WILL DEVELOP OVER THE AREA THIS
MORNING AHEAD OF AN APPROACHING SHORTWAVE. WIND AROUND THE CLARK
AREA STRONGER THAN ANTICIPATED SO FAR THIS MORNING...BUMPED UP WIND
SPEED THROUGH THE MORNING HOURS TO ACCOUNT FOR INCREASED WIND
SPEEDS.

IMPACTS FROM THIS SHORTWAVE WILL BE FELT BY THE LATE MORNING AND
EARLY AFTERNOON HOURS...WITH THE POTENTIAL FOR LIGHT SNOWFALL ACROSS
THE WESTERN MOUNTAINS AND VALLEYS. THIS SYSTEM WILL ALSO BRING
ANOTHER SHOT OF COLDER H7 AIR ACROSS THE FORECAST AREA. THIS WILL
RESULT IN SOME COOLING ACROSS THE AREA...THOUGH INVERSIONS FROM THE
PAST COUPLE DAYS MAY LIMIT THE IMPACTS FELT BY THIS SHOT OF COOLER
AIR. SNOWFALL ASSOCIATED WITH THIS PASSING SHORTWAVE WILL REMAIN
OVER THE AREA THROUGH SUNDAY MORNING FOR THE NORTHWESTERN
MOUNTAINS...WITH MOST OTHER LOCATIONS SEEING A REPRIEVE AND RETURN TO
NORTHWEST FLOW BY SATURDAY EVENING. SNOWFALL ACCUMULATIONS
ASSOCIATED WITH THIS FEATURE ARE GENERALLY EXPECTED TO BE
INSIGNIFICANT...WITH BETWEEN ONE AND TWO INCHES POSSIBLE OVER THE
MOUNTAIN LOCATIONS.

A DECENT THERMAL GRADIENT IS SET TO DEVELOP SATURDAY NIGHT AND
SUNDAY MORNING ACROSS THE CODY FOOTHILLS. THIS MAY RESULT IN
STRONGER WIND DEVELOPMENT AROUND THE CLARK AREA AGAIN THROUGH THIS
PERIOD. THE GRADIENT RELAXES SOMEWHAT SUNDAY AFTERNOON ALLOWING WIND
SPEEDS TO WEAKEN.

MEANWHILE...WEAKER BOUTS OF MOISTURE WITHIN THE NORTHWEST FLOW MAY
KEEP PERIODS OF LIGHT SNOWFALL ACROSS THE NORTHWEST MOUNTAINS
THROUGH MUCH OF THE FORECAST PERIOD. ADDITIONALLY...THE PRESSURE
GRADIENT ACROSS THE FORECAST AREA WILL TIGHTEN SUNDAY AFTERNOON AND
EVENING...WHICH MAY RESULT IN GUSTY CONDITIONS OVER FAVORED
LOCATIONS...MAINLY THE EASTERN SLOPES OF THE CENTRAL MOUNTAINS AND
THE WIND CORRIDOR BETWEEN ROCK SPRINGS AND CASPER.

.LONG TERM...MONDAY THROUGH FRIDAY

ABOVE AVERAGE TEMPERATURES...MAINLY DRY...WITH BREEZY TO WINDY
CONDITIONS IN TYPICAL AREAS SUMS UP MONDAY THROUGH WEDNESDAY. A
RELATIVELY MOIST NORTHWEST FLOW COULD RESULT IN PERIODS OF LIGHT
SNOW/FLURRIES...MAINLY OVER THE NORTHWEST/NORTHERN MOUNTAINS AT TIMES
MONDAY AND TUESDAY.

MEDIUM RANGE MODELS SHOW A SIGNIFICANT TROUGH IMPACTING THE COWBOY
STATE MID TO LATE NEXT WEEK...WITH TYPICAL TIMING DIFFERENCES
THIS FAR OUT. THE 00Z GFS IS COLDER AND SLOWER...THAN THE 00Z
ECMWF AND GEM WITH THIS SYSTEM. THE 00Z ECMWF SHOWS THE ARCTIC
COLD FRONT PUSHING INTO NORTHERN WYOMING LATE WEDNESDAY NIGHT AND
SWEEPING ACROSS THE COWBOY STATE THURSDAY...WHILE THE 00Z GFS HAS
THIS FRONT PUSHING ACROSS THE AREA THURSDAY AFTERNOON INTO
THURSDAY NIGHT. RIGHT NOW...IT APPEARS SNOW SHOULD BREAK OUT
ACROSS THE WEST WEDNESDAY NIGHT...SPREADING EAST OF THE DIVIDE
THURSDAY/THURSDAY NIGHT DEPENDING TIMING OF COLD FRONT. THIS
SNOWFALL COULD LINGER INTO FRIDAY...ESPECIALLY IF YOU BELIEVE THE
00Z OPERATIONAL GFS SOLUTION. HAVE INCREASED POPS MAINLY INTO THE
CHANCE CATEGORY ACROSS THE ENTIRE AREA THURSDAY/THURSDAY
NIGHT...WITH EVEN SOME LIKELY POPS ACROSS THE WESTERN MOUNTAINS
THURSDAY. THIS SYSTEM HAS THE POTENTIAL TO PRODUCE SOME SIGNIFICANT
SNOWFALL...BUT TOO EARLY TO PINPOINT ANY GIVEN LOCATION.

WELL BELOW AVERAGE TEMPERATURES RETURN FRIDAY...IF NOT THURSDAY
DEPENDING UPON TIMING OF THE COLD FRONT.

.AVIATION.../18Z ISSUANCE/

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

A WEAK UPPER LEVEL DISTURBANCE WILL SPREAD AREAS OF IFR/MVFR CIGS
AND VSBYS WITH -SN...FRQT MTN OBSCURATIONS...VCNTY KJAC AND NORTH
PRIMARILY THRU 23Z FRIDAY. THESE CONDITIONS WILL BE MORE LOCALIZED
OVER THE VALLEYS FURTHER SOUTH...WITH THE NORTHERN END OF THE
WYOMING/SALT AND WIND RIVER RANGES FRQTLY OBSCURED. SOME CLEARING
WILL OCCUR FRIDAY EVENING BEFORE MID-LEVEL CIGS 10-12KFT MSL
RETURN VCNTY KJAC AFTER 06Z SATURDAY. PATCHY FOG WILL RETURN AFTER
06Z SATURDAY AS WELL...PARTIALLY OBSCURING TERRAIN VCNTY KJAC...KBPI
AND KPNA THROUGH 16Z. OTHERWISE VFR CONDITIONS WILL PREVAIL
OVERNIGHT.

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

A WEAK UPPER LEVEL DISTURBANCE WILL PUSH SE ACROSS WYOMING FRIDAY
AFTERNOON BRINGING MAINLY MID-LEVEL CIGS 11-13KFT AND HIGHER MTN
OBSCURATIONS EAST OF THE DIVIDE. ISOLD MVFR -SHSN WILL BE POSSIBLE
PRIMARILY VCNTY AND NORTH OF A KWRL-KCPR LINE WITH SHSN MORE NMRS
OVER THE MTS ALONG WITH FRQT OBSCURATIONS. CLEARING FROM NW-SE
WILL OCCUR TONIGHT...HOWEVER SCATTERED CLOUDS BETWEEN 05-10KFT WILL
REMAIN IN PLACE. AREAS OF NW WIND 10-20KT WILL RETURN AFTER
SUNRISE SATURDAY NEAR KCOD AND KCPR.

.FIRE WEATHER...

MORNING INVERSIONS IS FAVORABLE TO PRODUCE SOME PATCHY MORNING FOG
ACROSS THE WESTERN VALLEYS AND BASINS THIS MORNING. AN APPROACHING
DISTURBANCE IS FAVORABLE TO PRODUCE LIGHT SNOWFALL ACROSS THE
WESTERN MOUNTAINS AND VALLEYS BY THE AFTERNOON AND EVENING
HOURS...THOUGH ANY ACCUMULATION IS GENERALLY EXPECTED TO BE LIGHT.
AREAS OF GUSTY WIND ARE ANTICIPATED TODAY...MAINLY ACROSS THE
NORTHERN END OF THE CODY FOOTHILLS ALONG THE ABSAROKA MOUNTAINS.
WEAK PERIODS OF SNOWFALL WILL REMAIN POSSIBLE ACROSS THE NORTHWEST
THROUGH MUCH OF THE PERIOD...WITH A NORTHWEST FLOW RETURNING TO THE
MAJORITY OF THE REMAINDER OF THE AREA. THIS NORTHWEST FLOW WILL
INCREASE ON SUNDAY...WHICH MAY RESULT IN STRONGER WINDS ACROSS THE
CENTRAL MOUNTAINS AND WIND CORRIDOR BETWEEN ROCK SPRINGS AND CASPER.
THESE SITUATIONS WILL CONTINUE TO BE MONITORED.

&&

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

$$

SHORT TERM...BRANHAM
LONG TERM...WM
AVIATION...LAVOIE
FIRE WEATHER...BRANHAM