Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 161954
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
154 PM MDT SAT MAY 16 2015

.SHORT TERM...TONIGHT THROUGH SUNDAY

WV IMAGERY SHOWING LARGE TROF ACROSS THE WRN CONUS WITH EMBEDDED
CLOSED LOW CENTERED OVR NW WY. CYCLOGENESIS STARTING TO TAKE SHAPE
FROM E OF THE FRONT RANGE OF CO...NWD THRU ERN WY. FRONTOGENESIS
ALSO TAKING PLACE OVR CNTRL MT. SFC OBS CONFIRM GENERAL
STRENGTHENING LOW PRESSURE AREA ACROSS NERN CO...ERN WY...AND INTO
WRN SD AND NE.

DRYSLOTTING AS EXPECTED TODAY ACROSS MOST OF THE REGION EXCEPT FAR
WEST AND NORTH... WITH A JUMP IN CYCLOGENESIS TAKING PLACE OVR
ERN/NERN WY...INTO THE HIGH PLAINS. GOOD MID/UPR MOISTURE WILL ALSO
ACCOMPANY THIS SYSTEM...PARTICULARLY INTO THE WRN AND NRN CWA...
WHILE THE BEST AREA FOR RESIDUAL LL MOISTURE WILL NOW BE FOUND OVR
THE BIGHORN BASIN...EWD INTO JOHNSON COUNTY. MODEST LL WARMNG UNDER
UPPER LEVELS BECOMING INCREASINGLY COLD WILL DESTABILIZE THE
ATMOSPHERE...WHILE CURRENT ROTATION AROUND THIS SYSTEM WILL PEG
FIRST CI OVR THE ABSAROKAS AND NRN BIGHORN BASIN THIS AFTERNOON.
LOTS OF SHEAR IN THIS AREA AROUND THE DEVELOPING LOW...FUNNEL CLOUDS
POSSIBLE. OTHERWISE...LOCALLY SLOW MOVING HEAVY RAIN AND SMALL HAIL
THE MOST LIKELY CULPRITS HERE...UNTIL THE UPR LOW FINALLY KICKS OUT.
DEVELOPING COLD FRONT WILL THEN SWING DOWN FROM MT LATER TODAY AS
THE LEE LOW LIFTS EWD INTO THE PLAINS...BRINGING NORTH WINDS AND A
DROP IN TEMPERATURE TO THE BIGHORN BASIN AND JOHNSON COUNTY
FIRST...THEN THE WIND RIVER BASIN AND NATRONA COUNTY BY SUNDAY
MORNING. HEAVIEST 24 HR PRECIP WILL BE FOUND OVER THE
MOUNTAINS...ESPECIALLY THE WIND RIVERS...ABSAROKAS AND
BIGHORNS...WITH UP TO AN ADDITIONAL INCH OF LIQUID TONIGHT THRU THE
DAY SUNDAY...LOCALLY MORE. GENERALLY LESSER AMOUNTS ELSEWHERE WITH A
QUARTER INCH OR SO REPRESENTING THE HIGHER SIDE OF QPF ACROSS THE
LOWER ELEVATIONS AND WEST. ALWAYS A CHANCE HOWEVER FOR A GOOD
CONVECTIVE BURST UNDER A SLOW MOVING SHOWER TO GET 3 OR 4 TIMES THAT
AMOUNT ON AN ISOLATED BASIS. SNOW LEVELS WILL START OUT AROUND 10K
FT TODAY...DROPPING TO ABOUT 8K FT IN THE NORTHWEST AND NORTH
FA...SAME FOR THE NORTHEAST LATER ON SUNDAY. PLACES IN THE NRN
BIGHORN BASIN MAY SEE THE POSSIBILITY OF SNOW MIXING WITH RAIN DOWN
TO THE VALLEY/BASIN FLOOR BY SUNDAY MORNING. LOCATIONS 8500 FEET
ABOVE ...WITH 3 TO 7 INCHES OVR THE WIND RIVERS AND ABSAROKAS...AND
4 TO 7 WITH LOCALLY 8 INCHES OF NEW SNOW POSSIBLE OVR PORTIONS OF
THE BIGHORNS BY DAYS END ON SUNDAY.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY

A LARGE COOL AND MOIST LOW PRESSURE SYSTEM WILL BE OVER WESTERN AND
CENTRAL WYOMING.  AS THE LOW PRESSURE SYSTEM MOVES EAST...THE AREA
WILL BE UNDER COOL AND MOIST NORTH NORTHWEST FLOW WITH SOME
LINGERING SHOWERS SUNDAY.  WITH DAYTIME HEATING...SOME ISOLATED
THUNDERSTORMS ARE EXPECTED... ESPECIALLY OVER THE MOUNTAINS.  WEAK
TEMPORARY RIDGING WILL OCCUR SUNDAY NIGHT WITH SOME LINGERING
MOUNTAIN SHOWERS.  AS ANOTHER LARGE SCALE LOW PRESSURE SYSTEM MOVES
INLAND FROM THE EASTERN PACIFIC INTO THE CALIFORNIA COAST...MOIST
SOUTHERLY FLOW WILL BEGIN TO SPREAD WIDESPREAD CLOUDS AND SHOWERS
INTO THE SOUTH AND WEST ON MONDAY.  TEMPERATURES WILL BE WARMER ON
THE OUTSET...BUT COOL LATER IN THE AFTERNOON MONDAY AS SHOWERS
SPREAD NORTH AND EAST ACROSS THE AREA.  AGAIN AFTERNOON AND EVENING
THUNDERSTORMS WILL BE A THREAT...ESPECIALLY OVER THE SOUTH AND
WEST.  THE LOW PRESSURE SYSTEM WILL BEGIN TO MOVE EAST INTO THE
GREAT BASIN MONDAY NIGHT AND TUESDAY CONTINUING TO SPREAD PACIFIC
MOISTURE INTO THE AREA KEEPING WIDESPREAD MOUNTAIN SHOWERS WITH
ISOLATED THUNDERSTORMS IN THE AFTERNOON AND EVENING HOURS TUESDAY
AFTERNOON AND TUESDAY EVENING. OVERALL LITTLE CHANGE IN TEMPERATURES
IS EXPECTED WITH LOCALLY COOLER AIR OVER AREAS WITH HEAVY RAINFALL.
A PORTION OF THE GREAT BASIN LOW WILL EJECT NORTHEAST OVER THE AREA
WEDNESDAY KEEPING SCATTERED SHOWERS AND A FEW AFTERNOON AND EVENING
THUNDERSTORMS OVER THE AREA. THE UPPER LEVEL FLOW PATTERN BECOMES
VERY COMPLEX WEDNESDAY NIGHT AND THURSDAY WITH A CONTINUAL THREAT OF
SHOWERS... MOST NUMEROUS OVER THE MOUNTAINS CONTINUING THROUGH
SATURDAY. OVERALL THIS WILL BE A VERY UNSETTLED PERIOD WITH MOST AREAS
RECEIVING PRECIPITATION DAILY.  OVERALL MODELS ARE IN FAIR AGREEMENT
THROUGH THE PERIOD.

&&

.AVIATION.../00Z ISSUANCE/

SHOWERS WITH SOME HIGHER MOUNTAIN SNOWS CONTINUE FOR
WEST...NORTHWEST...AND NORTH WY TONIGHT...BUT DECREASING IN
COVERAGE THROUGH THE EVENING. EXPECT VFR TO MVFR CONDITIONS OVER
FAR NORTH AND WEST WY THROUGH ABOUT 09Z WITH VCFG VCSH AND
FREQUENT MOUNTAIN OBSCURATION...IMPROVING AFTER 15Z. SHOWERS AND
PERHAPS A COUPLE OF THUNDERSTORMS WILL ALSO CONTINUE THIS EVENING
ACROSS SOUTHWEST/SOUTHERN WY...ALSO EXPECTED TO DECREASE IN
COVERAGE THIS EVENING. MVFR OT OCCASIONAL IFR CONDITIONS WILL BE
POSSIBLE EARLY WITH STORMS...BEFORE AREAS OF MVFR CONDITIONS
DEVELOP EAST OF THE DIVIDE AFTER 07Z AS COLDER AIR ASSOCIATED WITH
A COLD FRONT AIDS IN LOW SOME LOW CLOUD FORMATION.

&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW THROUGH THE REST OF THE WEEKEND AS
SEASONAL TO COOL AND RELATIVELY MOIST CONDITIONS PERSIST...WITH
SHOWERS AND A FEW THUNDERSTORMS FORMING INT HE AFTERNOONS AND
EVENING ACROSS THE HIGHER TERRAIN OF THE AREA...AND LATER
ALONG/NEAR A SOUTHWARD MOVING COLD FRONT TONIGHT THROUGH SUNDAY.
SNOW LEVELS MAY EVEN FALL TO NEAR THE VALLEY AND BASIN FLOORS OF
THE AREA...ESPECIALLY THE BIGHORN BASIN...MIXING WITH RAINFALL AT
TIMES...ESPECIALLY OVERNIGHT TONIGHT AND SUNDAY MORNING.

&&

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

$$

SHORT TERM...BRAUN
LONG TERM...C.BAKER
AVIATION...BRAUN
FIRE WEATHER...BRAUN







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