Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 032019
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
219 PM MDT MON AUG 3 2015

.SHORT TERM...TONIGHT THROUGH TUESDAY

UPPER LEVEL MCV CONTINUES TO ROTATE OVER NORTHERN UTAH THIS
AFTERNOON. THERE IS MINOR NORTHERN MOVEMENT AT THIS TIME...WITH THE
LOW CENTER LOCATED OVER UINTA AND SOUTHERN LINCOLN COUNTIES.
ISOLATED THUNDERSTORMS HAVE ALSO DEVELOPED ON THE EASTERN SIDE OF
THIS CIRCULATION...WITH ADDITIONAL ISOLATED ACTIVITY MOVING INTO
EASTERN SWEETWATER COUNTY. ISOLATED LIGHTNING STRIKES ARE ALSO
OCCURRING WITHIN A LINE OF SHOWERS THAT HAVE SLOWLY BEEN PUSHING
NORTHWARD. THIS LINE NOW EXTENDS FROM SOUTHERN TETON TO EASTERN
CARBON COUNTY.

THE SHORTWAVE/MCV WILL CONTINUE ITS NORTHWARD TREK TONIGHT ALONG
WESTERN PORTIONS...BEFORE TURNING NORTHEASTWARD OVER NORTH-CENTRAL
WYOMING BY 12Z TUESDAY. IT WILL CONTINUE IN THIS DIRECTION AND BE
OVER EASTERN WYOMING...AND OUT OF THE CWA BY 00Z WEDNESDAY.

IN SHORT...EXPECT SCATTERED SHOWERS WITH ISOLATED/EMBEDDED
THUNDERSTORMS THE REST OF THIS AFTERNOON AND INTO THE EVENING HOURS.
DUE TO THE MONSOONAL NATURE OF THIS SYSTEM...ALONG WITH THE
POTENTIAL FOR CONTINUED UPSLOPE FLOW...ESPECIALLY OVER THE WIND
RIVER MOUNTAINS AND SALT AND WYOMING RANGES...HEAVY RAIN WILL BE THE
MAIN THREAT WITH THIS ACTIVITY. ALTHOUGH STORMS THAT FORM FROM KCPR-
KCOD COULD HAVE SMALL HAIL AND BRIEF STRONG WINDS. A FLASH FLOOD
WATCH REMAINS IN EFFECT THROUGH 09Z WEDNESDAY.

SHOWERS AND THUNDERSTORMS WILL MAINLY BE CONFINED FROM EASTERN
PORTIONS OF THE BIG HORN BASIN TO NATRONA COUNTY EASTWARD
TUESDAY...WITH CONDITIONS RAPIDLY IMPROVING LATE TUESDAY AFTERNOON.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY NIGHT

EXPECTING CLEARING TUESDAY NIGHT INTO WEDNESDAY MORNING AS THE
STRONG SHORTWAVE TROUGH DISSIPATES INTO THE NORTHERN PLAINS AND WEAK
HIGH PRESSURE BUILD OVER THE ROCKIES.  HOWEVER...A WEAK SHORTWAVE
TROUGH WILL MOVE QUICKLY FROM NORTHERN CA INTO NW WY
WEDNESDAY...BRINGING CLOUDS...INSTABILITY...AND MOISTURE BACK TO THE
AREA.  WEDNESDAY AFTERNOON AND EVENING THUS LOOKS FAVORABLE FOR
ISOLATED SHOWERS AND THUNDERSTORMS WITH A DECENT POTENTIAL FOR GUSTY
OUTFLOW WIND ACROSS THE NORTHERN TWO-THIRDS OF WY. SOUTHERN WY
LIKELY TO BE WINDY AND DRIER...WITH TEMPERATURES REMAIN NEAR NORMAL
FOR THIS TIME OF YEAR.  EXTREME NW WY AND THE NORTHERN BIGHORN
MOUNTAINS MAY SEE A THUNDERSTORM OR TWO THURSDAY AFTERNOON...BUT THE
REST OF THE AREA LOOKS QUITE SEASONAL WITH MOSTLY CLEAR SKIES AND
BASIN TEMPS IN THE MID 80S.

WITH THE CENTER OF THE HIGH MOSTLY OVER NEW MEXICO DURING THE
WEEK...COMBINED WITH ANOTHER SHORTWAVE TROUGH FROM CA...CLOUDINESS
WILL INCREASE ON FRIDAY AS MID-LEVEL MOISTURE PUSHES UP FROM THE
GREAT BASIN.  FRIDAY NIGHT INTO SATURDAY MORNING MAY SEE SOME
ISOLATED SHOWERS...THEN SCATTERED SHOWERS AND THUNDERSTORMS ARE
POSSIBLE SATURDAY AFTERNOON INTO THE EVENING HOURS.  IF THE TROUGH
HAS MORE OF A SOUTHERLY TRAJECTORY...THE STORMS MAY BECOME STRONGER.
THE RIDGE THEN BUILDS BACK OVER THE ROCKIES SUNDAY AND
MONDAY...RESULTING IN MOSTLY CLEAR SKIES AND WARMER TEMPERATURES.
NEXT MONDAY AND TUESDAY COULD SEE OROGRAPHICALLY INDUCED
THUNDERSTORMS OVER THE HIGHER TERRAIN.

OVERALL THROUGH THE LONG TERM...THE CONFIDENCE SEEMS RATHER HIGH
GIVEN THE CONSISTENCY OF THE FEATURES AND PATTERN DESCRIBED ABOVE IN
THE GFS AND ECMWF. TEMPERATURES WILL BE NEAR NORMAL THROUGH THE
PERIOD...WITH MODERATE PRECIPITATION CHANCES THROUGHOUT THE AREA.
WINDS ARE EXPECTED TO INCREASE THOUGH...WITH SOME DRYING BETWEEN
WEATHER SYSTEMS.

&&

.AVIATION.../00Z ISSUANCE/

AN UPPER LEVEL LOW PRESSURE SYSTEM OVER NORTHERN UTAH WILL DRIFT NE
ACROSS WYOMING TONIGHT. THIS SYSTEM WILL SPREAD SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS ACROSS MUCH OF THE AREA. AREAS OF MVFR
CONDITIONS WITH LOCAL IFR CONDITIONS...ALONG WITH MOUNTAIN
OBSCURATIONS...WILL DEVELOP ALONG THE LINE OF -SHRA/TSRA PUSHING
NORTH. THE LINE OF SHOWERS WILL BE MAINLY ALONG AND EAST OF THE
CONTINENTAL DIVIDE BY 12Z TUESDAY...CAUSING MVFR/IFR CONDITIONS
AND FREQUENT MOUNTAIN OBSCURATIONS. CONDITIONS WILL RAPIDLY
IMPROVE FROM WEST TO EAST...WITH VFR CONDITIONS OVER JOHNSON
COUNTY BY 00Z WEDNESDAY.

&&

.FIRE WEATHER...

FIRE DANGER DECREASES THIS AFTERNOON...AND REMAINS ON THE LOWER
SIDE THROUGH AT LEAST WEDNESDAY...AS MOIST AND SOMEWHAT COOLER
CONDITIONS ACCOMPANY AN UPPER LEVEL DISTURBANCE THAT WILL ROTATE
ACROSS THE FORECAST AREA TONIGHT...EXITING LATER ON TUESDAY.
MINIMUM RH VALUES WILL INCREASE EVERYWHERE TODAY ABOVE CRITICAL
LEVELS EXCEPT FOR THE NORTHERN BIGHORN BASIN WHERE VALUES WILL
STILL DROP INTO THE MID TEENS (PERCENT). MONSOONAL-LIKE MOISTURE
WILL REMAIN IN PLACE TONIGHT AND TUESDAY...WITH SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS EXPECTED. STORM ACTIVITY WILL END FROM
SOUTHWEST TO NORTHEAST TONIGHT...WITH SHOWERS AND STORMS GRADUALLY
ENDING BY 00Z WEDNESDAY OVER THE BIG HORN BASIN AND JOHNSON AND
NATRONA COUNTIES. HEAVY RAIN IS EXPECTED AT TIMES. LATER WEDNESDAY
WILL SEE A RENEWED CHANCE FOR MORE RAINFALL ACROSS THE
REGION...ALTHOUGH ON A MORE ISOLATED TO WIDELY SCATTERED BASIS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR WYZ014-015-024.

&&

$$

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



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