Area Forecast Discussion
Issued by NWS Riverton, WY

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495
FXUS65 KRIW 040455
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1055 PM MDT TUE MAY 3 2016

.SHORT TERM...TONIGHT THROUGH FRIDAY

A DRY...WARM AND QUITE PERIOD THE NEXT COUPLE DAYS. THINGS BEGIN TO
CHANGE AS EARLY AS THURSDAY WEST OF THE DIVIDE AS DEVELOPING UPPER
LOW NEARING THE CALIFORNIA COAST BEGINS TO SPREAD ITS INFLUENCE.
DAYTIME HEATING...APPROACHING JET AND SOME MID LEVEL MOISTURE WILL
LIKELY AID IN SOME SHOWERS AND A FEW THUNDERSTORMS BY AFTERNOON.
MAYBE A FEW VERY LIGHT SHOWERS EVEN IN THE MORNING. THE MORE
SIGNIFICANT CHANGES BEGIN FRIDAY AS THE UPPER LOW MOVES INTO THE
DESERT SOUTHWEST AND A NRN SHORTWAVE ALLOWS A WEAK FRONT BOUNDARY TO
DROP SOUTH ALONG WITH A SURFACE HIGH DEVELOPING TO THE NORTH. MODELS
HAVE BEEN CONSISTENT IN SHOWING A WEAK SHORTWAVE LIFTING NORTH INTO
CENTRAL WYOMING BY SUNRISE FRIDAY WITH POTENTIAL FOR SOME LIGHT
SHOWERS OR SPRINKLES EARLY IN THE DAY FOLLOWED BY A MIDDAY BREAK FOR
AT LEAST THE LOWER ELEVATIONS OF FREMONT COUNTY. THINGS GET MORE
INTERESTING BY AFTERNOON AS COLD FRONT DROPS SOUTH AND INTERACTS
WITH WARMER...UNSTABLE AIR TO THE SOUTH. UPPER TROUGH DYNAMICS AND
APPROACHING JET HAVE THE POTENTIAL TO INTERACT ALONG AND AHEAD OF
THE FRONT TO PRODUCE STRONG TO SEVERE THUNDERSTORMS FRIDAY
AFTERNOON. SEEMS LIKE THE BEST CAPE AND SHEAR LIE FROM FAR SOUTHERN
NATRONA THROUGH SRN FREMONT...INTO SWEETWATER AND NW TO THE JACKSON
AREA. CAPES VARY FROM 600-1000+J/KG ALONG WITH SOME POTENTIAL
SIGNIFICANT SHEAR. ADDED HAIL/WIND/HEAVY RAIN WORDING FOR NOW. AS
THE UPPER LOW DRAWS CLOSER...SIGNIFICANT RAIN AND HIGHER MTN SNOW
STILL LOOKS CERTAIN FOR AREAS OF CENTRAL WYOMING FRIDAY NIGHT AND
SATURDAY. MORE ON THAT IN THE EXTENDED PERIOD.

.LONG TERM...FRIDAY NIGHT THROUGH TUESDAY

MAJOR UPPER LOW WILL LIKELY START OUT IN THE SOUTHERN CALIFORNIA
AREA TO START THIS PERIOD AND THEN GRADUALLY MEANDER TO SERN NV/SRN
UT AREA BY 00Z SUNDAY. MOST GUIDANCE STILL HAS THE LOW OVER ERN
UT/WRN CO AREA BY 12Z SUNDAY. AFTER THAT...THERE IS AN INCREASING
SPREAD. GFS HAS BEEN TRYING TO LIFT THE LOW NWD INTO WYOMING ON
SUNDAY WHILE THE 00Z EURO AND GEM KEEP IT SOUTH THROUGH
SUNDAY...TRACKING IT ACROSS FAR NRN CO. THE 12Z EURO IS NOW KEEPING
IT SOUTH THRU SUNDAY MORNING AND THEN LIFTING IT NWD INTO CENTRAL WY
SUN AFTN AND GRADUALLY JUST FILLING IT INTO MONDAY MORNING BEFORE IT
FINALLY WEAKENS AND PULLS OFF/OR IS KICKED OFF TO THE EAST. 12Z EURO
IS PROBABLY NOT A BAD COMPROMISE. I WOULD NORMALLY FAVOR A MORE SRN
TRACK LIKE THE GEM/00Z EURO WITH THE MEAN RIDGE OVER THE NWRN HALF
OF THE COUNTRY BUT IT IS EARLY MAY AND UPPER LOWS DO TEND TO LIFT
MORE NWD IN LATE APRIL AND EARLY MAY. WE WILL REALLY HAVE TO WATCH
THE AMOUNT OF RAIN THAT COULD FALL ACROSS THE CENTRAL ZONES WITH
FREMONT COUNTY LIKELY BEING THE CENTER OF THE ACTION ONCE AGAIN. I
WOULD SAY THAT 1-2 INCHES ACROSS THE LOWER ELEVATIONS WITH 2-4
INCHES IN THE SURROUNDING MTNS/FOOTHILLS WOULD BE A REASONABLE EARLY
ESTIMATE OF PCPN AROUND FREMONT COUNTY UP INTO THE SRN ABSAROKAS
WITH SIGNIFICANT PCPN POSSIBLE FURTHER EAST AND NORTH BUT LIKELY NOT
AS LONG OF DURATION AS FREMONT COUNTY. HEAVY RAIN ON MOIST GROUND
AND WET SNOWPACK WILL HAVE TO BE WATCHED CLOSELY FOR RAPID RISES ON
AREA STREAMS AND RIVERS OVER THE WEEKEND. SNOW LEVEL MAY STILL VARY
BUT EARLY INDICATIONS POINT TO 8.5-9K AROUND THE WIND RIVERS/SRN
ABSAROKAS FRIDAY NIGHT AND SATURDAY AND PROBABLY LOWERING SOME
SATURDAY NIGHT AND SUNDAY BUT STILL ABOVE MOST OF THE LOWER FOOTHILL
LOCATIONS. GRADUAL IMPROVEMENT ON MONDAY AS LOW WEAKENS AND MOVES
OFF TO THE EAST. POTENTIAL SHORTWAVE MAY FOLLOW BEHIND ON TUESDAY
BUT STILL A TOUGH CALL AS EURO IS MOST BULLISH WITH THE GEM AND GFS
GENERALLY KEEPING MOST OF THE ENERGY OFF TO THE NORTH AND EAST.
STILL ENOUGH MOISTURE AROUND FOR SOME SHOWERS AND MAYBE A FEW TSTMS
BUT NOT A MAJOR COOLDOWN AGAIN LIKE THE EURO. WILL LEAN TOWARDS THE
GEM/GFS IDEA FOR NOW ON THIS SYSTEM AT THE END OF THE EXTENDED.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL CONTINUE AT ALL TERMINALS THROUGH 12Z/THURSDAY
WITH UPPER RIDGE AXIS OVER THE FORECAST AREA BY THAT TIME. WIND
SPEEDS WILL GENERALLY BE 6-9KTS AFTER ABOUT 20Z/WEDNESDAY...WITH
SLIGHTLY HIGHER SPEEDS OF 10-12KTS AT KRKS. SOME WEAK CONVECTION IS
POSSIBLE OVER THE HIGHER TERRAIN FROM 21Z/WEDNESDAY TO 03Z/THURSDAY.

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

VFR CONDITIONS WILL CONTINUE AT ALL TERMINALS THROUGH 12Z/THURSDAY
WITH UPPER RIDGE AXIS OVER THE FORECAST AREA BY THAT TIME. WIND
SPEEDS WILL BE LESS THAN 10KTS AT ALL SITES WITH ONE EXCEPTION. THAT
WILL BE KCPR WHERE SOUTHWEST WIND AROUND 12KTS WILL INCREASE AROUND
15Z/WEDNESDAY AND CONTINUE UNTIL AROUND 03Z/THURSDAY.

&&

.FIRE WEATHER...

MAINLY DRY WEATHER WILL CONTINUE THROUGH THURSDAY MORNING ALONG WITH
GRADUALLY WARMING TEMPERATURES. RELATIVE HUMIDITY WILL FALL INTO THE
TEENS AT TIMES ACROSS THE LOWER ELEVATIONS THROUGH THURSDAY.
HOWEVER...WINDS ARE EXPECTED TO REMAIN LIGHT TO MODERATE. A SPOT OR
TWO OVER THE MOUNTAINS MAY SEE A LATE DAY SHOWER THROUGH WEDNESDAY.
AN APPROACHING TROUGH WILL BRING A CHANCE OF THUNDERSTORMS WEST OF
THE DIVIDE THURSDAY AFTERNOON AND NIGHT. WITH LIGHT WINDS...EXPECT
FAIR TO POOR SMOKE DISPERSAL TODAY. MIXING WILL INCREASE WEDNESDAY
AND ESPECIALLY THURSDAY AHEAD OF THE APPROACHING TROUGH. A MAJOR
STORM SYSTEM WILL AFFECT THE REGION BEGINNING FRIDAY AND CONTINUING
THROUGH THE WEEKEND.

&&

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

&&

$$

SHORT TERM...PS
LONG TERM...PS
AVIATION...MCDONALD
FIRE WEATHER...PS



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