Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 262202
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
402 PM MDT TUE APR 26 2016

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

THE CENTER OF THE CIRCULATION RESPONSIBLE FOR THE ONGOING SPRING
SNOW EVENT TAKING PLACE...MAINLY EAST OF THE DIVIDE IN WY...APPEARS
TO BE OVER EXTREME NORTH CENTRAL CO. THE CIRCULATION HAS MOVED
ENOUGH TO THE EAST OF THE AREA TO WHERE THE PRECIP OVER OUR CWA
HAS TRANSITIONED FROM Q VECTOR FORCING/WRAP AROUND ISENTROPIC
LIFT AND ANY DYNAMICS DIRECTLY ASCT WITH THE LOW TO MORE OF AN
UPSLOPE COMPONENT AS THE FLOW CONTINUES TO BACK. AFTER AREAS LIKE
THE GREEN MTNS RECEIVED AROUND 8 INCHES OF SNOWFALL AND MANY LOWER
ELEVATIONS REPORTED 1 TO 4 INCHES...FAVORED UPSLOPE AREAS DURING
THE MORNING AND AFTERNOON HOURS CAUGHT UP RAPIDLY WITH AS MUCH AS
15 TO 17 INCHES REPORTED ON CASPER MTN AND 14 INCHES IN SINKS
CANYON ABOVE LANDER. THE ELEVATION OF ACCUMULATING SNOW SLANTS
DOWNWARD FROM NW TO SE CLOSER TO THE COLD CORE OF THE LOW. THE
WIND RIVER BASIN IS ONE OF THOSE AREAS THAT HAS BEEN GETTING
SNOWFALL ALL DAY BUT IS NOT ACCUMULATING. NAM FCST SOUNDINGS
INDICATE THAT THE DEEP LAYER OF STRONG UPSLOPE...WHICH IS MAXING
OUT ATTM...WILL REMAIN DEEP THROUGH THIS EVENING BUT WILL BECOME
WEAK AND DEEP BEFORE BACKING TO THE NW ONCE THE LOW MIGRATES NORTH
TO NE WY BY 06Z TONIGHT WHICH WILL SHUT OFF THE UPSLOPE MACHINE TO
AN EXTENT. DECIDED TO CANCEL THE ADVISORY FOR THE WIND RIVER
BASIN AND THE OWL CREEK MTNS WHERE NOT AS MUCH PRECIP HAS FALLEN.
DOWNGRADED THE LND FTHLS TO AN ADVISORY WHERE THE PERSISTENT
SNOWFALL IS ALSO HAVING A TOUGH TIME PILING UP. KEPT THE OTHER
HILITES GOING AS IS THROUGH 06Z TONIGHT. LEFT THE WARNING GOING
THROUGH 12Z WED FOR CPR MTN AS THEY WILL BE CLOSER TO THE DYNAMICS
FROM THE LOW. ALSO BY 06Z WED...CYCLOGENESIS/REDEVELOPMENT WILL
TAKE PLACE WHERE OK/CO/KS/TX/NM ALL COME TOGETHER BEFORE THIS LOW
HEADS OUT FOR THE CENTRAL PLAINS. SOUTHWEST WY WILL ALSO SEE SOME
ENHANCED SNOWFALL ACTIVITY TONIGHT...TO A LESSER EXTENT...AS THE
CIRCULATION FROM THIS LOW CONVERGES WITH A WEAK NW FLOW THERE. WE
WILL STILL BE INFLUENCED BY THE ORIGINAL WEAKENED LOW/TROUGH AS IT
RETROGRADES AND EXTENDS INTO NW WY. WITH THE TROUGHINESS STILL
AROUND AND THE COL REGION MOVING IN FROM THE SOUTHWEST AHEAD OF
THE NEXT IN A LONG SERIES OF LOWS APPROACHES FROM NEVADA...A GOOD
CHANCE OF RAIN AND SNOW SHOWERS WILL CONTINUE THROUGH WEDNESDAY.
AS H7 TEMPS WARM FROM -7C TO -2C FROM THE SOUTHWEST...THE
TRANSITION FROM SNOW TO RAIN WILL TAKE PLACE FROM SOUTHWEST TO
NORTHEAST AS THE COLD POOL EXITS NE. HIGH TEMPS WILL BE A FEW
DEGREES MILDER WED BUT STILL COOL FOR THIS TIME OF YEAR.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

NRN PIECE OF OUR CURRENT UPPER LOW IS EXPECTED TO GRADUALLY SHEAR
APART ACROSS OUR NRN/NERN ZONES AT THE BEGINNING OF THIS PERIOD
KEEPING THE CHANCE OF MAINLY SNOW SHOWERS TO THIS AREA THRU WED
NGHT. IN ADDITION...A WEAK SHORTWAVE MAY ROTATE WWD INTO JOHNSON
COUNTY THU MRNG KEEPING THIS AREA UNDER THE CHANCE OF MORE PCPN. THE
NEXT UPPER LOW IS ALREADY FCST TO BE ON THE WEST COAST AT THE START
OF THIS PERIOD WITH THE LOW EXPECTED TO HEAD TOWARDS SRN UT/4-
CORNERS AREA THU INTO THU NGT BEFORE MOVING ACROSS COLORADO ON
FRIDAY. MOST OF THE ENERGY IS SOUTH OF OUR AREA BUT THERE SHOULD BE
ENOUGH MOISTURE TO PRODUCE RAIN AND SNOW SHOWERS...ESPECIALLY WITH
SOME DAYTIME HEATING THURSDAY. PROBABLY MORE -RW IN THE LOWER
ELEVATIONSWITH -SW IN THE MTNS. A FEW TSTMS WILL PROBABLY RUMBLE
IN THE FAR WEST THU AFTN. AS THIS LOW MOVES EAST INTO CO...THE
POTENTIAL FOR SHOWERS WILL INCREASE ACROSS OUR ERN ZONES.
MOIST...DIFFLUENT FLOW WITH DAYTIME HEATING WILL KEEP SHOWERS AND
ISOLD TSTMS IN THE FORECAST FOR THE WEST ON FRIDAY. THIS UPPER LOW
MAY THEN LIFT NWD INTO WRN NE SAT AND STALL OUT KEEPING AT LEAST
THE ERN ZONES UNSETTLED WITH A GOOD CHANCE OF SNOW IN THE MTNS AND
A MIXTURE ACROSS THE LOWER ELEVATIONS. THE NEXT SYSTEM CURRENTLY
OUT NEAR THE ELATION CHAIN DROPS DOWN INTO THE PACNW FRIDAY NIGHT
AND INTO THE GREAT BASIN ON SATURDAY. WHAT HAPPENS AFTER THAT IS A
LITTLE MORE CHALLENGING. NEW GFS/GEM/ECMWF RUNS HAVE A STRONG
BLOCKING RIDGE TO THE EAST WHICH CAUSES THIS LOW TO BOTTOM OUT
OVER THE SRN GREAT BASIN OR DESERT SW OVER THE WEEKEND AND THEN
MOVE NWD BACK INTO THE NRN GREAT BASIN/INTERMOUNTAIN WEST EARLY
NEXT WEEK. THE END RESULT WOULD BE MORE UNSETTLED...SHOWERS AND
EVEN SOME SNOW ONCE AGAIN...OR CONTINUING. QUITE THE ACTIVE
PATTERN CONTINUES. PRETTY AMAZING PATTERN AS THE GUIDANCE ALSO
KEEPS ALMOST A CONTINUOUS AT LEAST WEAK UPSLOPE PATTERN EAST OF
THE DIVIDE FOR MOST OF THE NEXT 10 DAYS. MORE MOISTURE TO COME IN
THIS BUSY PATTERN WITH INCREASING WATER PROBLEMS POSSIBLE WITH
TIME.

&&

.AVIATION.../00Z ISSUANCE/

WEST OF THE CONTINENTAL DIVIDE...KJAC/KRKS/KPNA/KBPI AIRPORTS

DOWNSLOPE NE FLOW WILL BRING PRIMARILY VFR CONDITIONS ACROSS THE
JACKSON VALLEY AND NW WYOMING...WITH THE CONTINENTAL DIVIDE OBSCURED
FURTHER EAST IN -SN.

ACROSS SW WYOMING...IFR/MVFR CONDITIONS IN RASN ARE EXPECTED TO
PREVAIL THROUGH 9Z WEDNESDAY ALONG THE INTERSTATE 80 CORRIDOR
INCLUDING KRKS WITH SOME GRADUAL IMPROVEMENT BY 12Z WEDNESDAY.  KPNA
AND KBPI WILL SEE INCREASING SNOW SHOWERS (IFR/MVFR CONDITIONS)
THROUGH THIS AFTERNOON AS SHOWERS MOVE NORTHWARD INTO THE UPPER
GREEN RIVER BASIN. GRADUAL IMPROVEMENT IS EXPECTED IN THIS AREA AS
WELL AFTER 9Z WEDNESDAY.

EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

WIDESPREAD MVFR/IFR CONDITIONS AND MTN OBSCURATIONS IN SNOW... LOW
CLOUDS AND FOG WILL CONTINUE FOR MOST OF CENTRAL WYOMING THROUGH
TONIGHT WITH GRADUAL IMPROVEMENT BY LATER WEDNESDAY MORNING. SOME
MIXED PCPN MAY OCCUR AT TIMES IN THE NORTH HALF OF THE AREA.

&&

.FIRE WEATHER...

A SERIES OF LOW PRESSURE SYSTEMS WILL CONTINUE TO IMPACT THE STATE
FOR THE NEXT FEW DAYS. WIDESPREAD SNOWFALL IS EXPECTED THROUGH
WEDNESDAY FOR AREAS EAST OF THE DIVIDE...AND ACROSS SOUTHERN WYOMING
WHERE WINTER WEATHER HIGHLIGHTS REMAIN IN EFFECT. COOLER DAYTIME
TEMPERATURES AND INCREASED HUMIDITY ARE EXPECTED THROUGH AT LEAST
THURSDAY AS ANOTHER AREA OF LOW PRESSURE GAINS INFLUENCE WEDNESDAY
AND THURSDAY. THIS NEXT SYSTEM WILL BRING SHOWERS AND THUNDERSTORMS
ACROSS SOUTHWESTERN WYOMING BY THURSDAY AFTERNOON. AS THIS SYSTEM
IMPACTS SOUTHWESTERN WYOMING...THE FIRST AREA OF LOW PRESSURE WILL
MOVE BACK OVER SOUTH CENTRAL MONTANA...ALSO KEEPING SHOWERS OVER
NORTHERN WYOMING AND INCLUDED MOUNTAIN RANGES. COOL SHOWERY
WEATHER WILL CONTINUE THROUGH NEXT WEEKEND AND AT LEAST INTO EARLY
NEXT WEEK AS THE UNSETTLED WEATHER PATTERN CONTINUES WITH HIGH RH
AND LOW FIRE DANGER.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 6 AM MDT WEDNESDAY FOR WYZ022.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT MDT TONIGHT FOR
WYZ008>011-028>030.

WINTER STORM WARNING UNTIL MIDNIGHT MDT TONIGHT FOR WYZ015-019-
020.

WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ018.

&&

$$

SHORT TERM...LIPSON
LONG TERM...SKRBAC
AVIATION...SKRBAC
FIRE WEATHER...LIPSON



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