Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 102013
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
213 PM MDT THU JUL 10 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY

ISOLATED SHOWERS AND THUNDERSTORMS HAVE FINALLY BEGUN TO FORM THIS
AFTERNOON. MOST OF THIS ACTIVITY HAS FORMED OVER CENTRAL
PORTIONS...WITH SOME SHOWERS MOVING OVER THE STAR VALLEY INTO THE
NORTHERN PORTIONS OF THE UPPER GREEN RIVER BASIN. NEEDED
INGREDIENTS REMAIN IN PLACE...NAMELY AMPLE MOISTURE.
HOWEVER...EXTENSIVE CLOUD COVER FROM THIS MORNING HAS KEPT CAPE
VALUES LOW...AS WELL AS MID LEVEL TEMPERATURES RELATIVELY WARM.
THIS WILL LIMIT ANY WIDESPREAD CONVECTIVE DEVELOPMENT FOR THE REST
OF THIS AFTERNOON AND EVENING.

ANY NOCTURNAL DEVELOPMENT...ESPECIALLY ACROSS EASTERN WY...WILL
IMPACT THE CONVECTIVE POTENTIAL TOMORROW. A WEAK COLD FRONT THAT
STALLED ACROSS CENTRAL PORTIONS THIS MORNING...WILL SURGE
SOUTHWARD LATER TONIGHT...ALLOWING FOR EASTERLY WINDS AT THE
SURFACE ACROSS THE EASTERN HALF OF THE FORECAST AREA. MOST OF THE
STORMS ARE EXPECTED TO FORM ACROSS NORTHERN AND EASTERN PORTIONS
FRIDAY AFTERNOON. CAPE VALUES AND INSTABILITY LOOK TO BE MAXIMIZED
IN THESE AREAS...WHILE A WEAK SHORT WAVE MOVES NORTHWARD FROM UTAH
INTO WESTERN PORTIONS. THIS SHOULD HELP GENERATE SHOWERS AND
STORMS ACROSS THE WEST...ALTHOUGH INSTABILITY STILL LOOKS TO BE
MARGINAL. WITH THAT SAID...ANY STORM DEVELOPMENT FRIDAY WILL
DEPEND ON THE CLOUD COVER. THERE COULD BE A REPEAT OF TODAY IF ITS
AS EXTENSIVE AS IT WAS THURSDAY MORNING.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY NIGHT

THE DIRTY RIDGE OVER THE ROCKIES AND GREAT BASIN WILL CONTINUE INTO
THE WEEKEND...WITH AMPLE MOISTURE IN THE MID LEVELS COMBINED WITH
WEAK FORCING FOR SCATTERED SHOWERS AND THUNDERSTORMS FROM FRIDAY
NIGHT INTO SATURDAY NIGHT.  ALTHOUGH THE GFS AND ECMWF APPEAR TO BE
IN GOOD AGREEMENT ON THE LARGE SCALE PATTERN...THE ECMWF IS MUCH
MORE BULLISH FOR STORM ACTIVITY SATURDAY FROM NW TO SE WYOMING ALONG
A WEAK FRONTAL BOUNDARY.  THE GFS INDICATES A SIMILAR BOUNDARY...BUT
WITH A STRONGER RIDGE OVER NV AND UT...IT SHOWS LIMITED STORM
ACTIVITY.  ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE AGAIN
SUNDAY...YET ALL INDICATIONS ARE FOR LOWER CHANCES...ALONG THE
DIVIDE AND TO THE EAST IN CENTRAL WY.  SUNDAY LOOKS TO BE THE DRIER
DAY OF THE WEEKEND...WITH TEMPERATURES EAST OF THE DIVIDE NEAR OR
BELOW NORMAL DUE TO THE INFLUENCE OF THE LARGE LONGWAVE TROUGH OVER
THE GREAT LAKES.

WITH THE WESTERN US RIDGE AMPLIFYING ON SUNDAY...BOTH GLOBAL MODELS
SHOW A SMALL SHORTWAVE FROM THE PACIFIC MOVING FROM THE PAC NW INTO
THE NORTHERN ROCKIES...THEN DROPPING SOUTH THROUGH WY INTO THE
CENTRAL ROCKIES.  THE INFLUENCE OF THIS FEATURE IS LIKELY TO START
IMPACTING NW WY BY MONDAY EVENING.  THE GFS IS SLIGHTLY MORE
PROGRESSIVE WITH THE TROUGH FROM TUESDAY INTO WEDNESDAY...WITH THE
ECMWF HOLDING IT BACK IN NORTHERN WY WEDNESDAY NIGHT.
REGARDLESS...ALL INDICATIONS ARE THAT THE TROUGH ON THE BACKSIDE OF
THE RIDGE ALONG WITH LOW LEVEL EASTERLY FLOW PUSHING UP TO THE
DIVIDE...SHOULD PROVIDE A PATTERN OF A GOOD CHANCE OF PRECIPITATION
ACROSS THE AREA FROM TUESDAY INTO WEDNESDAY.  HAVE HEDGED THE
FORECAST MORE TOWARD THE GFS SOLUTION AT THIS TIME RATHER THAN
KEEPING PRECIPITATION AROUND LIKE THE ECMWF DESIRES IN THE MIDDLE OF
THE WEEK.  WOULD NOT BE SURPRISED TO SEE SOME AREAS RECEIVE AROUND
AN INCH TOTAL PRECIPITATION IN 48 HOURS WITH THIS PATTERN.

OVERALL...THE PATTERN FROM SATURDAY THROUGH NEXT THURSDAY LOOKS TO
PROMOTE TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL FOR MUCH OF THE
AREA...WITH SW WY LIKELY THE WARMEST.  SUNDAY AND THURSDAY LOOKS TO
BE THE WARMEST DAYS...WITH SATURDAY...AND MONDAY THROUGH WEDNESDAY
HAVING DECENT CHANCES OF PRECIPITATION.  WITH RELATIVELY WEAK WINDS
FROM THE BOUNDARY LAYER THROUGH THE MID LEVELS...ALONG WITH
RELATIVELY HIGH PRECIPITABLE WATER VALUES...STORMS THAT FORM WILL
MOVE SLOWLY AND LIKELY PRODUCE HEAVY RAIN AT TIMES.

&&

.AVIATION.../00Z ISSUANCE/

ISOLATED SHOWERS AND THUNDERSTORMS HAVE BECOME A BIT MORE
WIDESPREAD THIS AFTERNOON...WITH MOST OF THE ACTIVITY FOCUSED EAST
OF THE DIVIDE. THIS ACTIVITY WILL SUBSIDE BY 06Z. CLOUDS ARE EXPECTED
TO REMAIN ACROSS THE AREA OVERNIGHT...WITH A FEW BREAKS POSSIBLE
DURING THE DAY FRIDAY. WIDESPREAD THUNDERSTORM ACTIVITY IS STILL
EXPECTED FRIDAY AFTERNOON BETWEEN 20Z-06Z SATURDAY.

&&

.FIRE WEATHER...

PERIODS OF SHOWERS AND THUNDERSTORMS WILL OCCUR AGAIN FRIDAY AND
SATURDAY. ALTHOUGH LIGHTNING AND GUSTY WINDS WILL BE POSSIBLE WITH
ANY THUNDERSTORM...THE MAIN THREAT WITH THESE STORMS WILL BE HEAVY
RAIN. A BUILDING RIDGE OF HIGH PRESSURE WILL IMPACT THE STATE BY
SUNDAY...BRINGING SOME DRIER CONDITIONS. ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS WILL STILL REMAIN POSSIBLE...ESPECIALLY
OVER THE NORTHERN HALF OF THE FORECAST AREA. TEMPERATURES WILL
GENERALLY COOL THROUGH THE PERIOD...THOUGH SOME WARMING
TEMPERATURES ARE NOTED ON SATURDAY AND SUNDAY OVER SOUTHWESTERN
WYOMING.

&&

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

$$

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





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