Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281813
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1113 AM MST SAT FEB 28 2015

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

A WEAK DISTURBANCE MOVING THROUGH NORTHERN WYOMING WILL BRING SOME
VERY LIGHT SHOWERS ACROSS THE AREA TODAY. THE MORE SIGNIFICANT
SYSTEM IS THE AREA OF LOW PRESSURE MOVING DOWN THE PACIFIC
COASTLINE.

THE NEARBY LOW PRESSURE WILL SEND PUSHES OF MOISTURE ACROSS SOUTHERN
WYOMING BY THIS EVENING...MAINLY IMPACTING THE SOUTHERN HALF OF
SWEETWATER COUNTY. THE SHOWERS WILL WEAKEN LATER TONIGHT AS THE
SYSTEM MOVES NEAR SOUTHERN CALIFORNIA.

THE AREA OF LOW PRESSURE IS THEN EXPECTED TO START MOVING INLAND AND
CONTINUE ON AN EASTERLY TRACK. AS THE SYSTEM REACHES CLOSER TO THE
FOUR CORNERS REGION ON MONDAY EVENING...IT WILL SEND ANOTHER ROUND
OF SHOWER ACTIVITY ACROSS SOUTHERN WYOMING. SIMULTANEOUSLY...A WAVE
OF LOW PRESSURE WILL MOVE INTO NORTHERN WYOMING FROM
CANADA..USHERING COOLING TEMPERATURES ACROSS THE AREA. MODELS
ATTEMPT TO HAVE THESE TWO APPROACHING SYSTEMS MERGE BY LATE MONDAY
NIGHT...RESULTING IN WIDESPREAD PRECIPITATION ACROSS THE FORECAST
AREA. MODELS ARE IN DECENT AGREEMENT WITH THIS SOLUTION...AIDING TO
SOME INCREASED CONFIDENCE IN ITS DEVELOPMENT. HOWEVER...IT IS IN FAR
REACHES OF THE FORECAST PERIOD...SO DID NOT TREND POP FORECAST TOO
HIGH.

.LONG TERM...TUESDAY THROUGH SATURDAY

SYSTEM MOVING TOWARDS WRN ALASKA REMAINS OUR MONDAY NIGHT/TUESDAY
STORM SYSTEM. MODELS CONTINUE TO HAVE VARIATION IN HOW THE ENERGY
DIVES DOWN THE FRONT SIDE OF THE RIDGE AND HOW MANY PIECES THERE MAY
BE. THEY ALL HAVE A DECENT PIECE OF ENERGY THAT DIVES DOWN INTO ERN
IDAHO/WRN WYO LATE MONDAY NIGHT OR TUESDAY MORNING CLOSING OFF A
H7 LOW NEAR JAC. THE GFS/EURO BY 12Z TUE AND THE GEM BY 18Z TUE. BY THE
START OF THIS PERIOD...THE FRONT HAS ALREADY PUSHED THROUGH ALL
BUT THE SW PART OF THE FORECAST AREA. IN ADDITION...THE WEAKENING
UPPER LOW TO THE SOUTH WILL CONTINUE TO STREAM MOISTURE INTO THE
SRN PART OF THE AREA POTENTIALLY OVERRUNNING THE COLD...MOIST DOME
ADVANCING FROM THE NORTH. ACTIVE JET STREAM DYNAMICS START MONDAY
NIGHT AND CARRYOVER JUST SLIGHTLY INTO TUESDAY MORNING IN OUR SERN
ZONES. THE SHORTWAVE TO THE WEST AND JET STREAK PROVIDE SOME
FORCING IN THE W AND THEN SW INTO TUESDAY EVENING. SNOW FOR MANY
AREAS ON TUESDAY WITH TEMPERATURES STEADY OR FALLING. RAN DIURNAL
FROM MOS FOR THE START OF THIS PERIOD TO INDICATE FALLING TEMPS
TUESDAY BEHIND THE FRONT. CLEARING FROM THE NORTH TUESDAY NIGHT WITH
BITTER COLD OVERNIGHT LOWS EXPECTED AS H7 TEMPS PLUMMET TO BETWEEN
-25C AND NEAR -30C IN THE FAR NRN/NERN ZONES POTENTIALLY. CLEARING
SKY COULD RESULT IN RECORD LOWS WEDNESDAY MORNING. THE COLDER
AREAS COULD SEE 10 TO 20 BELOW ZERO WITH COLDER YET IN YNP. ABOUT
THE ONLY THING THAT COULD STOP IT IS SLOWER CLEARING TUESDAY
NIGHT. RAW DAY WEDNESDAY BUT AT LEAST WE COULD SEE SOME DECENT
SUN. RIDGE IS THEN FORECAST TO DEAMPLIFY AND REMAIN TO THE WEST
WITH RAPIDLY MODERATING MID LEVEL TEMPS. SOME LEE TROUGHING
DEVELOPING WEDNESDAY/WED NGT TO MODERATE THE WIND CORRIDOR AND
POSSIBLY CODY FOOTHILLS SOME WITH OTHER AREAS REMAINING QUITE
COLD. HIGHS SHOULD MODERATE THURSDAY INTO FRIDAY AND POSSIBLY
THROUGH SATURDAY AS MARCH SUN PROVIDES SOME ASSISTANCE THAT
WOULDN`T HAVE HELPED MUCH BACK IN DEC/JAN OR EVEN EARLY FEB. SO
20S AND 30S THURSDAY AND THEN 30S AND 40S MOST AREAS FRI AND SAT.

.AVIATION.../18Z ISSUANCE/

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

COLD NORTH NORTHEAST LOW LEVEL FLOW WITH WEAK WEST OVERRUNNING
FLOW IN THE MID LEVELS WILL CONTINUE TO PRODUCE CONDITIONS
FAVORABLE FOR WIDESPREAD STRATUS...FLURRIES TO LIGHT SNOW AND LOCAL
FOG. IFR TO MVFR CONDITIONS WILL BE RATHER WIDESPREAD THROUGH 18Z
SUNDAY WITH LOCAL VFR CONDITIONS AT TIMES. THIS WILL CAUSE
WIDESPREAD MOUNTAIN OBSCURATIONS.

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

COLD NORTH NORTHEAST LOW LEVEL FLOW WITH WEAK WEST OVERRUNNING
FLOW IN THE MID LEVELS WILL CONTINUE TO PRODUCE CONDITIONS
FAVORABLE FOR WIDESPREAD STRATUS...FLURRIES TO LIGHT SNOW AND LOCAL
FOG. IFR TO MVFR CONDITIONS WILL BE RATHER WIDESPREAD THROUGH 18Z
SUNDAY WITH LOCAL VFR CONDITIONS AT TIMES. THIS WILL CAUSE
WIDESPREAD MOUNTAIN OBSCURATIONS.

.FIRE WEATHER...

PERIODS OF LIGHT SNOW AND FOG WILL BE POSSIBLE TODAY. SOUTHERN
WYOMING LOOKS TO TAKE THE BRUNT OF ANY ACTIVITY...THOUGH MODELS
HAVE RELAXED A BIT FROM PREVIOUS FORECASTS. A RELATIVELY QUIET
COUPLE DAYS INTO THE EARLY PORTION OF THE WEEKEND AHEAD OF THE
NEXT WINTRY SYSTEM. SNOWFALL WILL MOVE INTO SOUTHERN WYOMING LATE
MONDAY NIGHT...WHILE A SEPARATE SYSTEM SENDS SNOWFALL ACROSS
NORTHERN WYOMING. THE TWO SYSTEMS ARE EXPECTED TO MERGE LATE
MONDAY NIGHT...POTENTIALLY CREATING WIDESPREAD SNOWFALL.

&&

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

$$

SHORT TERM...BRANHAM
LONG TERM...SKRBAC
AVIATION...C.BAKER
FIRE WEATHER...BRANHAM





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