Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 180527
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1127 PM MDT THU JUL 17 2014

.SHORT TERM...TONIGHT THROUGH FRIDAY (ISSUED AT 237 PM MDT)

DRY STABLE CONDITIONS TODAY W/ MODEST UPR LVL RIDGING AND
WARMING...IN ADDITION TO RELATIVELY WEAK FLOW ALOFT BEHIND LARGE SW
TROF THAT HAS PLAGUED THE FA FOR THE LAST COUPLE OF DAYS. LATE THIS
AFTERNOON...THE WEAK TAIL END OF A STRONGER SW TROF WELL TO THE N IN
CANADA...WILL BRING AN  UPR LVL SW/JET STREAK...NOW LOCATED JUST TO
THE WEST OF THE NW CORNER OF THE CWA...THROUGH THE BUILDING RIDGE
AND FLATTEN IT SOME...RESULTING IN A FEW SHOWERS AND THUNDERSTORMS
MAINLY ACROSS HIGH TERRAIN OF THE NW ZONES INCLUDING THE
ABSAROKAS...TAKING ADVANTAGE OF INCREASED CONVERGENCE OVR MOUNTAIN
TOPS FROM DIURNAL HEATING OF THE DAY. THIS UPR LVL EVOLUTION COULD
ALSO AFFECT THE WESTERN WIND RIVER MOUNTAINS AND BIG HORN MOUNTAINS
THIS EVENING. STRONGEST CONVECTIVE ACTIVITY SHOULD OCCUR EARLY THIS
EVENING. WITH ONLY MODEST MID LVL MOISTURE AVAILABLE FOR CONVECTION
BY LATE AFTERNOON...ML CAPE WILL REMAIN AOB 500 J/KG EVEN OVR
MOUNTAIN TOPS. THIS TOGETHER WITH LITTLE SHEAR TO WORK WITH WILL
KEEP STORM GROWTH RELATIVELY LOW AND UNDER CONTROL FOR THE MOST
PART. A STRONGER STORM OR TWO ARE MOST LIKELY TO PRODUCE GUSTY WINDS
AT LESS THAN 40 MPH...AND SMALL HAIL. OTHERWISE...THE BEGINNING OF A
WARMING AND DRYING PERIOD...WITH HIGH TEMPS ACROSS THE FORECAST AREA
RISING SOME 5 TO 10 DEG OVR THOSE WEDNESDAY...AND RH VALUES DROPPING
SOME 10 TO 15 PERCENT.

SHOWERS AND ISO THUNDER DECREASE OVR NIGHT AS HEAT CONVERGENCE IS
LOST OVR THE MOUNTAINS AND SUBSIDENCE BEGINS TO BATTLE LIFT FROM
THE UPR SW. FRIDAY...WEAK RIDGING AND WARMING CONTINUES AS SW/JET
STREAK PASSES TO THE E...AND HEIGHTS/THICKNESS SLOWLY
RISE/INCREASE....WITH RELATIVELY FLAT RIDGING TAKING PLACE.
UPSTREAM COMING INTO CNTRL CALIFORNIA AND SWRN NV...ANOTHER UPR LVL
SW IS STARTING TO INTRUDE INTO THE GREAT BASIN. THIS FEATURE WILL
ARRIVE NEAR THE SWRN PORTION OF WY BY MID-DAY FRI AND MAX
HEATING...INCREASING UPR FLOW AND LAPSE RATES OVR THE SWRN/SRN
ZONES. HOWEVER...W/ LITTLE MOISTURE BEING ADVECTED INTO THIS
AREA...AND THE BOUNDARY LAYER DRYING OUT...ML CAPE WILL REMAIN LOW
AT LESS THAN 200 J/ KG...PROVIDING FOR MAINLY ISOLATED CONVECTION...
AND MOST OF IT ON THE DRY SIDE WITH LITTLE RAIN...BUT GUSTY WINDS
AND OCCASIONAL LIGHTNING...WHICH WILL INCREASE FIRE DANGER A BIT.
HOWEVER...ACTIVITY DOES LOOK TO REMAIN QUITE ISOLATED ALONG WITH
LOWER LIGHTNING PRODUCTION...IN ADDITION TO NON-CRITICAL DRY FUEL
STATUS STILL IN PLACE FOR NOW. ONLY VERY ISOLATED MOUNTAIN
CONVECTION EXPECTED ELSEWHERE.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

GENERALLY NORTHWEST FLOW STARTS OFF THE FORECAST PERIOD. SOME
EMBEDDED MOISTURE WILL KEEP SHOWERS AND THUNDERSTORMS OVER WESTERN
AND CENTRAL WYOMING. HOWEVER...THE BEST OPPORTUNITY LOOKS TO BE
OVER THE HIGHER TERRAIN....WITH VERY LITTLE IN THE WAY OF MOISTURE
ACROSS THE VALLEY OR BASIN LOCATIONS.

THE FLOW BECOMES MORE SOUTHWESTERLY LATE SUNDAY EVENING. THIS MAY
INTRODUCE A BIT MORE MOISTURE...WITH SHOWER AND THUNDERSTORM
ACTIVITY POSSIBLE ACROSS SOUTHERN WYOMING SUNDAY NIGHT.
ADDITIONALLY...A SURGE OF MOISTURE WILL RESULT IN ISOLATED TO
SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS ON
MONDAY...ESPECIALLY ACROSS NORTHWESTERN WYOMING. A RETURNING RIDGE
OF HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE AREA DURING THE
EARLY PORTION OF NEXT WEEK. SOME TRAPPED MOISTURE COULD RESULT IN
VERY ISOLATED SHOWERS AND THUNDERSTORMS...ESPECIALLY DURING THE
AFTERNOON HOURS.

THE FLOW WILL THEN TURN A BIT MORE WESTERLY THROUGH THE DAY ON
THURSDAY...WITH LITTLE TO NO MOISTURE CURRENTLY EXPECTED.
TEMPERATURES THROUGH THE FORECAST PERIOD ARE GENERALLY EXPECTED
TO WARM...THOUGH A COUPLE COOL DOWNS WILL BE POSSIBLE AS SYSTEMS
SHIFT TO ALLOW SOME COOLER AIR TO MOVE OVER THE AREA.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ISOLATED SHOWERS AND
STORMS WILL OCCUR FROM 20Z UNTIL 06Z SATURDAY IN THE ABSAROKA AND
BIG HORN MOUNTAINS. A FEW OF THESE WILL DRIFT EAST ACROSS THE LOWER
ELEVATIONS OF THE NORTH. GUSTY OUTFLOW WIND TO 40 MPH WILL BE THE
MAIN THREAT TO AVIATION.

TAF SITES WEST OF THE CONTINENTAL DIVIDE...KJAC/KBPI/KPNA/KRKS

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD. ISOLATED SHOWERS AND
STORMS WILL OCCUR IN FAR SOUTHERN WY FROM 20Z UNTIL 04Z SATURDAY.
THE MAIN THREAT WILL BE THE GUSTY OUTFLOW WIND TO 40 MPH. THE
ACTIVITY SHOULD REMAIN SOUTH OF THE KRKS AIRPORT.

&&

.FIRE WEATHER...

WEAK UPPER LEVEL RIDGING WILL BEGIN...BRINGING A WARMING AND
DRYING TREND TO THE FORECAST AREA. ANOTHER CHANCE FOR ISOLATED  TO
WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL COME TO THE
NORTHWEST AND CENTRAL MOUNTAINS AND VALLEYS...LATE THIS AFTERNOON
AND EVENING...AS A WEAK UPPER LEVEL DISTURBANCE MOVES OVERHEAD.
GUSTY WINDS COULD ACCOMPANY THIS ACTIVITY THROUGH MID EVENING.
SHOWERS AND THUNDER WILL DECREASE OVERNIGHT BEFORE MODEST WARMING
AND DRYING CONTINUE AGAIN ON FRIDAY. ISOLATED CHANCES FOR RELATIVELY
HIGH BASED SHOWERS AND THUNDERSTORMS WILL COME TO PORTIONS OF
SOUTHWESTERN WYOMING...PERHAPS REACHING TO THE CENTRAL MOUNTAINS.
THIS CONVECTIVE ACTIVITY WILL BE CHARACTERIZED AS HIGH BASED...WITH
LITTLE RAIN BUT GUSTY WINDS LIKELY ALONG WITH OCCASIONAL
LIGHTNING...ALTHOUGH EVEN LIGHTNING PRODUCTION LOOKS TO REMAIN ON
THE LOWER SIDE. THIS ALONG WITH  BREEZY WEST WINDS 15 TO 20 MPH AND
RH VALUES DROPPING INTO THE MID TEENS WILL BEGIN TO SIGNIFICANTLY
ENHANCE FIRE DANGER ACROSS THE SOUTH AND SOUTHWEST ZONES...ALTHOUGH
DRY FUEL STATUS IS NOT CONSIDERED TO BE CRITICAL IN THIS REGION AS
OF YET. THROUGH THE WEEKEND...WINDS WILL CONTINUE OUT OF THE WEST
AND BREEZY IN THE AFTERNOONS...CONTINUING TO SLOWLY INCREASE FIRE
WEATHER CONCERNS AS FUELS CONTINUE TO DRY OUT AND OCCASIONAL
EPISODES OF ISOLATED HIGH BASED/DRY THUNDERSTORMS ENSUE.

&&

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

&&

$$

SHORT TERM...BRAUN
LONG TERM...BRANHAM
AVIATION...AR
FIRE WEATHER...BRAUN





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