Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 200948 CCA
AFDRIW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE RIVERTON WY
346 AM MDT WED MAY 20 2015

.SHORT TERM...WEDNESDAY THROUGH FRIDAY NIGHT

RIGHT NOW...THE SNOW AND RAIN EVENT IS BEGINNING TO WIND DOWN ACROSS
THE AREA. I ALWAYS WONDERED ABOUT RAIN EVENT...DOESN`T IT SOUND LIKE
SOMETHING YOU WANT TO BUY TICKETS TO. THANK YOU TO THE LATE...GREAT
GEORGE CARLIN FOR THAT QUOTE. ANYWAY...INFRARED SATELLITE IMAGERY SHOWS
THE CLOUD TOPS WARMING AS THE LOW SHEARS APART. WE STILL HAVE SOME
PRECIPITATION IN THE WIND RIVER BASIN WITH A WEAK CIRCULATION OVER
THE AREA BUT THIS SHOULD END FOR THE MOST PART BY FIRST LIGHT.
ALSO... WITH THE PRECIPITATION BECOMING LIGHT FOR THE MOST PART WE
WILL CANCEL THE WINTER WEATHER ADVISORIES. FOR THE REST OF
DAY...LOOK FOR SHORTWAVE RIDGING TO BRING A DRIER DAY FOR MOST
AREAS. THERE WILL BE SOME PATCHY FOG AROUND THIS MORNING WITH THE
TON OF MOISTURE THAT FELL YESTERDAY...BUT SHOULD BURN OFF. MANY
AREAS SHOULD SEE SOME BLUE SKY BY AFTERNOON. AS FOR
PRECIPITATION...A WEAK SHORTWAVE AND SOME MOISTURE MOVING IN FROM
THE WEST WILL BRING SOME ISOLATED TO SCATTERED CONVECTION WEST OF
THE DIVIDE THIS AFTERNOON AND EVENING. EAST OF THE DIVIDE...ALL
MODELS DRY THINGS OUT SO WE WENT MAINLY DRY EXCEPT FOR THE HIGHER
ELEVATIONS WHERE HIGH ELEVATION HEAT SOURCE COULD TOUCH OFF SOME
ISOLATED CONVECTION. TEMPERATURES WILL BE WARMER THAN YESTERDAY BUT
STILL BELOW NORMAL FOR THIS TIME OF YEAR.

FOR TOMORROW...FLOW WILL TURN MORE SOUTHERLY AND THIS SHOULD BRING A
RETURN TO MORE SEASONABLE TEMPERATURES. AS FOR THE CHANCE OF
CONVECTION...AGAIN THE BEST CHANCE WILL BE ACROSS WESTERN WYOMING.
THERE IS A CHANCE SOME STORMS COULD FIRE EAST OF THE DIVIDE.
HOWEVER...AT THIS POINT IT APPEARS A DECENT MAJORITY OF THE AREA
EAST OF THE DIVIDE SHOULD BE DRY MOST OF THE TIME.

THINGS LOOK TO TAKE A WETTER TURN HOWEVER AS WE HEAD INTO FRIDAY.
ANOTHER UPPER LEVEL LOW WILL TRACK INTO THE DESERT SOUTHWEST AND
PUSH ANOTHER AREA OF DEEPER MOISTURE OVER THE REGION FOR FRIDAY INTO
FRIDAY NIGHT. AT THIS POINT...THIS SYSTEM LOOKS TO BE A BIT WARMER
THAN THE LAST ONE. BY FRIDAY NIGHT...700 MILLIBAR TEMPERATURES ARE
STILL HOLDING AROUND 0 DEGREES CELSIUS OR SO SNOW LEVELS WOULD BE
FAIRLY HIGH...ABOVE 8500 OR 9000 FEET. OTHERWISE...IT LOOKS COOLER
WITH A FAIR COVERING OF SHOWERS AND EVEN SOME THUNDERSTORMS. AND
ONCE AGAIN...THE MAIN THREAT WITH COOL AIR ALOFT WOULD BE FOR SOME
MORE SMALL HAIL.

.LONG TERM...SATURDAY THOUGH WEDNESDAY

SYNOPSIS...AN UPPER TROUGH OF LOW PRESSURE WILL LINGER OVER THE
AREA THROUGH THE MEMORIAL DAY WEEKEND WITH SCATTERED TO NUMEROUS
SHOWERS OVER THE AREA ALONG WITH ISOLATED THUNDERSTORMS. SNOW
LEVELS WILL BE BETWEEN 8000 AND 9000 FEET. CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL CONTINUE INTO TUESDAY AND WEDNESDAY WITH A
WARMING TREND...TEMPERATURES RETURNING CLOSER TO SEASONAL NORMALS.

DISCUSSION...BLOCKING UPPER RIDGE WILL REMAIN OVER WESTERN CANADA
THROUGH THE PERIOD...WITH RIDGE DOWNSTREAM OVER THE SE U.S.
AMPLIFYING BACK ACROSS THE MIDWEST.  THIS AMPLIFICATION WILL BLOCK
THE EASTWARD PROGRESSION OF NEXT PACIFIC LOW LIFTING OUT OF THE FOUR
CORNERS AREA INTO WYOMING ON SATURDAY.  FURTHER UPSTREAM....UPPER
LOW TRAPPED UNDER RIDGE ALONG THE BRITISH COLUMBIAN COAST WILL
DIVE SSE ACROSS THE NW U.S. OVER THE WEEKEND. THIS SCENARIO
RESULTS IN A BROAD UPPER TROUGH ACROSS THE WESTERN U.S. WITH
EMBEDDED CIRCULATIONS TRAPPED WITHIN. ECMWF AND GFS ARE IN POOR
AGREEMENT THE POSITION AND PROGRESSION OF THESE INDIVIDUAL
CIRCULATIONS...HOWEVER SATURDAY IS LOOKING LIKE THE MOST ACTIVE
AND COOLEST DAY OF THE MEMORIAL DAY WEEKEND WITH MAIN UPPER LOW
EJECTING OUT OF THE GREAT BASIN...WITH A FRAGMENTED SYSTEM
ROTATING DIRECTLY OVER THE AREA THROUGH THE DAY. BY MEMORIAL
DAY...THE REMNANTS OF THIS FIRST SYSTEM ARE FORECAST TO SHEAR OUT
EAST OVER DOWNSTREAM RIDGE...CONFLUENT FLOW. HOWEVER...UPPER LOW
OVER THE NW IS EXPECTED TO ACCELERATE EAST TOWARD THE AREA...THE
GFS FASTER AND FURTHER SOUTH WITH THE TRACK THAN ECMWF. SLOWER
ECMWF BRINGS THIS SYSTEM ACROSS WYOMING TUESDAY NIGHT AND
WEDNESDAY. NOT MUCH CONFIDENCE AT THIS TIME IN PICKING ANY 12-24
HOUR PERIOD THAT WILL BE SHOWER-FREE ACROSS THE AREA. KEEP THAT
RAIN GEAR HANDY IF YOU ARE GOING TO BE OUTDOORS THIS WEEKEND...AND
EXPECT COLD AND WET CONDITIONS IN THE MOUNTAINS WITH OCCASIONAL
SNOW SHOWERS ABOVE 8000-9000 FEET.


&&

.AVIATION.../12Z ISSUANCE/

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

ALTHOUGH RAIN AND SNOW WILL CONTINUE TO QUICKLY DECREASE IN COVERAGE
EARLY THIS MORNING...MVFR AND SOME IFR CEILINGS WILL CONTINUE OVER
MUCH OF THE AREA THROUGH MUCH OF THE MORNING. THERE COULD ALSO BE
SOME FOG DUE TO THE RECENT PLETHORA OF MOISTURE...BUT EXTENSIVE LOW
CLOUDS SHOULD KEEP FOG FROM BECOMING TOO WIDESPREAD. LOW CEILINGS
ARE EXPECTED TO LIFT TO VFR OR EVEN SCATTER OUT BETWEEN 18Z-21Z.
EXCEPT FOR SOME SNOW SHOWERS OVER THE MOUNTAINS THIS AFTERNOON...DRY
CONDITIONS ARE EXPECTED. TONIGHT...FOG AND LOW CLOUDS COULD
REDEVELOP OR ADVECT FROM THE EAST. THE BEST SHOT AT LOW CLOUDS OR
FOG WILL BE AT THE KCPR AIRPORT WITH THE MOIST EASTERLY FLOW
COMBINED WITH RECENT MOISTURE. MOUNTAINS WILL BE OBSCURED IN MUCH OF
THE AREA THIS MORNING.

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

AREAS WITH MVFR CEILINGS ARE EXPECTED THIS MORNING...WITH SOME
MOUNTAIN SNOW/VALLEY RAIN. ALSO...SOME FOG COULD ALSO OCCUR THIS
MORNING. FOG AND LOW CLOUDS ARE EXPECTED TO LIFT TO VFR CONDITIONS
BY AROUND 18Z. SCATTERED MOUNTAIN SNOW/VALLEY RAIN SHOWERS WITH A
FEW THUNDERSTORMS ARE EXPECTED THIS AFTERNOON...WITH BRIEF MVFR/IFR
CONDITIONS. THE BEST...ALTHOUGH WEAK INSTABILITY WILL BE OVER THE
FAR WEST AND WILL HAVE VCTS ONLY AT KJAC FOR NOW. SOME SHOWER
ACTIVITY WILL CONTINUE THROUGH THE OVERNIGHT HOURS. MOUNTAINS WILL
BE OBSCURED THIS MORNING.
&&

.FIRE WEATHER...

FIRE DANGER RELATIVELY LOW AS SEASONAL TO COOL AND RELATIVELY MOIST
CONDITIONS PERSIST. A WEAK AREA OF HIGH PRESSURE WILL BRING DRIER
CONDITIONS TODAY ALTHOUGH ISOLATED CONVECTION WILL REMAIN POSSIBLE
ACROSS AREAS WEST OF THE DIVIDE THROUGH THURSDAY. DEEPER MOISTURE
WILL MOVE TOWARD THE AREA FOR FRIDAY AND BRING ANOTHER CHANCE OF A
WETTING RAIN FROM FRIDAY INTO FRIDAY NIGHT WITH HIGH ELEVATION SNOW
POSSIBLE AS WELL.

&&

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

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...WM
FIRE WEATHER...HATTINGS








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