Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 211805
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1205 PM MDT TUE JUL 21 2015

.PREV DISCUSSION... /ISSUED 334 AM MDT TUE JUL 21 2015/

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT

SHOWERS CONTINUE TO STREAM ACROSS EASTERN WYOMING THIS MORNING.
SHOWER ACTIVITY IS EXPECTED TO WEAKEN THROUGH THE EARLY MORNING
HOURS BUT MAY NOT DRY OUT COMPLETELY. ANOTHER WEAK DISTURBANCE WILL
MOVE THROUGH NORTHERN WYOMING THROUGH THE DAY...WITH A PUSH OF
MOISTURE MOVING UP FROM THE SOUTH. WARMING TEMPERATURES WILL
REMAIN OVER THE AREA TODAY...WITH SHOWER COVERAGE INCREASING
THROUGH THE AFTERNOON. SOME STORMS MAY CONTAIN GUSTY AND ERRATIC
WIND...WITH STORM ACTIVITY ESPECIALLY FAVORED OVER THE MOUNTAINS.
COVERAGE WILL WEAKEN THROUGH THE LATE EVENING HOURS. AN AREA OF
LOW PRESSURE WILL MOVE ACROSS SOUTHWESTERN CANADA LATE TUESDAY AND
INTO WEDNESDAY.

AS THIS SYSTEM PROGRESSES ON WEDNESDAY...IT WILL BRING A
TIGHTENED PRESSURE GRADIENT OVER THE FORECAST AREA. THIS PRESSURE
GRADIENT WILL LEAVE A FAVORABLE SCENARIO FOR BREEZY WINDS ACROSS
THE WIND CORRIDOR BETWEEN ROCK SPRINGS AND CASPER. MEANWHILE...A
TROUGH OF LOW PRESSURE IS AN INFLUENCING FACTOR OF SHOWER ACTIVITY
ON WEDNESDAY WITH MUCH OF THE AREA SEEING THE POTENTIAL FOR STORM
ACTIVITY. COVERAGE OF STORMS WILL REMAIN GENERALLY OVER THE
NORTH AND WEST ON THURSDAY AFTERNOON AS THE TROUGH ADVANCES
TOWARDS THE AREA. THE BEST COVERAGE FOR STORMS WILL REMAIN
ESPECIALLY PROMINENT OVER THE NORTHWESTERN MOUNTAINS. CONDITIONS
WILL THEN WEAKEN THROUGH THURSDAY NIGHT AS THE TROUGH AXIS PASSES
THROUGH CENTRAL WYOMING.

.LONG TERM...FRIDAY THROUGH TUESDAY

TROUGH AXIS AND AN ASSOCIATED WEAK FRONT LOOK TO PUSH ACROSS THE
REGION THURSDAY NIGHT INTO FRIDAY. THIS WEAK FRONT LOOKS TO STALL
ACROSS THE REGION FRIDAY...COMBINED WITH LINGERING
MOISTURE...MODERATE INSTABILITY...AND SOME ENHANCED SHEAR FROM A
STRONG JET OVERHEAD...ANOTHER ROUND OF ISOLATED TO SCATTERED
THUNDERSTORMS WILL BE POSSIBLE. THUNDERSTORMS WILL BE MAINLY
CONFINED TO WESTERN AND NORTHERN PORTIONS...WITH A FEW ISOLATED
STORMS POSSIBLE ACROSS CENTRAL PORTIONS. LIGHTNING AND GUSTY WINDS
WILL BE THE MAIN THREATS WITH THESE STORMS. CONTINUED ENHANCED PRESSURE
GRADIENT WILL ALSO BRING MORE GUSTY WINDS TO THE WIND CORRIDOR
FROM ROCK SPRINGS TO CASPER...ALONG WITH SOME AREAS IN FREMONT
COUNTY...ON FRIDAY. BUILDING HIGH PRESSURE TO THE SOUTH WILL THEN
BRING DRY AND WARM SOUTHWESTERLY FLOW FOR THE WEEKEND. SEVERAL
WEAK DISTURBANCES TRY TO RIDE OVER THIS RIDGE...HOWEVER...ONLY A
VERY ISOLATED MOUNTAIN STORM IS EXPECTED THROUGH THE WEEKEND...AS
INGREDIENTS FOR THUNDERSTORMS ARE LACKING. HIGH TEMPS IN THE UPPER
80S TO LOW 90S ARE ALSO EXPECTED TO RETURN THIS WEEKEND EAST OF
THE DIVIDE.

RIDGE OF HIGH PRESSURE SHIFTS SLIGHTLY EASTWARD INTO THE CENTRAL
AND SOUTHERN PLAINS TO START NEXT WEEK. MEANWHILE THE NEXT TROUGH DIGS
ACROSS WESTERN US AND WILL BE THE NEXT POTENTIAL WEATHER MAKER FOR
THE REGION. GFS SOLUTION DIGS THIS DISTURBANCE SLIGHTLY FURTHER
SOUTH THAN THE ECMWF...WHICH WOULD PROVIDE CHANCES FOR SHOWERS AND
THUNDERSTORMS ACROSS THE CWA MONDAY INTO TUESDAY. THE ECMWF GIVES
WYOMING A GLANCING BLOW AND KEEPS THE ACTIVITY MAINLY IN MT. POPS
CURRENTLY LEAN MORE TOWARDS THE FURTHER SOUTH SOLUTION OF THE
GFS...BUT THIS SYSTEM WILL CONTINUED TO BE MONITORED. THIS NEXT
DISTURBANCE COULD ALSO PROVIDE A SLIGHT COOL DOWN IN TEMPS TO
NEAR NORMAL READINGS.

.AVIATION.../18Z ISSUANCE/

AVCTS/VCSH DEVELOPING ACROSS MOST SITES EARLY IN THE PERIOD AND
CONTINUING INTO THE LATE EVENING ACROSS THE WEST. THE TWO MAIN
AREAS OF SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING WILL
OCCUR MAINLY ALONG AND SOUTH OF A KRKS- KCPR LINE AND ACROSS
NORTHWEST WYOMING...OR MAINLY VCNTY AND NORTH OF A KJAC- KCOD
LINE. A DRIER AND MORE STABLE AIRMASS WILL HOLD IN BETWEEN ACROSS
THE CENTRAL BASINS...BUT SOME HIGH-BASED SHOWERS OFF THE HIGH
TERRAIN MAY MOVE INTO THESE AREAS (VCNTY KLND-KRIW- KWRL) AND
PRODUCE ISOLD MICROBURSTS 30-40KTS. THE MOST ACTIVE PERIOD FOR
CONVECTION IS EXPECTED FROM 22Z TUE-05Z WED...WITH PARTLY CLEARING
SKIES AFTER 06Z WED. SHOWERS AND THUNDERSTORMS RETURN AFTER 18Z
WEDNESDAY WITH HEAVY RAIN IN THE WESTERN MOUNTAINS AND 40-50KT
MICROBURSTS POSSIBLE EAST OF THE DIVIDE.

.FIRE WEATHER...

AFTERNOON SHOWERS AND THUNDERSTORMS WILL REMAIN A THEME FOR THE NEXT
COUPLE DAYS. STORMS MAY IMPACT ANY PORTION OF THE FORECAST AREA
THROUGH WEDNESDAY...AND MUCH OF NORTHERN AND WESTERN WYOMING ON
THURSDAY. STORMS MAY CONTAIN GUSTY AND ERRATIC WIND AND SMALL HAIL.
BREEZY WIND WILL BE POSSIBLE WEDNESDAY AFTERNOON ACROSS THE WIND
CORRIDOR BETWEEN ROCK SPRINGS AND CASPER. OVERALL...FIRE BEHAVIOR
WILL REMAIN REDUCED AS THE AREAS WITH THE STRONGEST ANTICIPATED
WIND ARE NOT CURRENTLY EXPECTED TO SEE CRITICAL LEVELS OF
HUMIDITY. PORTIONS OF THE BIG HORN BASIN MAY APPROACH THE MID
TEENS FOR HUMIDITY ON WEDNESDAY... BUT WILL HAVE NEITHER THE
CRITICAL WINDS NOR THE CRITICAL FUELS.

&&

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

$$

SHORT TERM...BRANHAM
LONG TERM...ANGLIN
AVIATION...ALLEN
FIRE WEATHER...BRANHAM


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