Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220530
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1130 PM MDT THU MAY 21 2015

.SHORT TERM...TONIGHT THROUGH FRIDAY

AREAS OF LOW CLOUDS AND FOG HAVE LIFTED INTO A LOW CUMULUS CLOUD
DECK BETWEEN 3 AND 4K AS ABUNDANT GROUND MOISTURE CONTINUES TO
CONTRIBUTE TO THE LOWER AIRMASS AS TEMPS AND CORRESPONDING LCLS
RISE. THE STUBBORN HIGH IN WESTERN CANADA HAS DIVERTED ANOTHER
CLOSED LOW SOUTH TO OFF THE CALIFORNIA COAST. THE CIRCULATION
AROUND THIS LOW IS ARRIVING AS A SOUTH SOUTHWEST DIFLUENT FLOW
ACROSS WYOMING OUT AHEAD OF IT. SCATTERED THUNDERSTORMS UNDERNEATH
THIS FLOW HAVE ERUPTED ACROSS YELLOWSTONE PARK/ABSAROKAS AS WELL AS
ACROSS SOUTHWEST WY WHERE A SHORTWAVE/VORT LOBE IS TRACKING NORTH
NORTHEAST WITHIN THE SSW DIFLUENT FLOW IN SOUTHERN WY. WITH THE
RELATIVELY LOW LCL AND LOW WET BULB ZERO...MANY OF THESE CELLS
COULD PRODUCE LOCALLY HEAVY RAINFALL AND SMALL HAIL. AS THIS
SHORTWAVE TRACKS NNE...THE TREND WILL BE FOR MORE STORM CELLS TO
DEVELOP ACROSS THE REST OF NORTHERN AND ALSO CENTRAL AND EASTERN
PORTIONS OF THE CWA. TONIGHT THE LOW CENTER WILL TRACK EAST ACROSS
SOUTHERN CALIFORNIA ALONG WITH A WEAK TROUGH EXTENDING NORTHEAST
FROM THE LOW NORTHEAST INTO WYOMING. WITH THE TROUGHINESS OVHD
FRIDAY...EXPECT NUMEROUS SHOWERS TO DEVELOP ACROSS CENTRAL AND
SOUTHERN WY FRIDAY BY LATE MORNING. THE STORMS WILL BE LAST TO
ARRIVE IN NORTH CENTRAL AND NORTHEAST WY WHERE MORE SOLAR
INSULATION WILL TAKE PLACE THROUGH THE LATER AFTERNOON HOURS FOR
FEWER...LATER BUT STRONGER THUNDERSTORMS AS THE TROUGHINESS
CONTINUES TO EXTEND NORTHEAST. TEMPS WILL WARM UP TO MORE SEASONAL
LEVELS BY FRIDAY.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

A PACIFIC LOW PRESSURE TROUGH OVER THE GREAT BASIN WILL MOVE
SLOWLY EAST SPREADING PACIFIC MOISTURE INTO WESTERN AND CENTRAL
WYOMING WITH SOUTHWEST FLOW ALOFT OVER THE AREA. THE AIRMASS WILL
BE UNSTABLE WITH SHOWERS...RATHER WIDESPREAD OVER THE WESTERN
MOUNTAINS AND ISOLATED THUNDERSTORMS PASSING THROUGH DURING THE
EVENING. SHOWERS WITH SOME SNOW IN THE HIGHER MOUNTAINS WILL
LINGER INTO SATURDAY MORNING. A CANADIAN COLD FRONT WILL SLIDE
SOUTH THROUGH MUCH OF THE ARA ON SATURDAY AS THE UPPER LOW DRIFTS
SLOWLY EAST OVER THE COLD FRONT. SHOWERS WILL BE WIDESPREAD ACROSS
THE AREA WITH COOL TEMPERATURES. ENOUGH INSTABILITY WILL BE OVER
THE AREA SATURDAY AFTERNOON AND EVENING TO SUPPORT ISOLATED
THUNDERSTORMS WITH SMALL HAIL. SNOW LEVELS WILL LOWER THROUGH
SATURDAY NIGHT DOWN TO AROUND 8000 FEET. SUNDAY WILL BE COOL AND
REMAINING SHOWERY WITH A FEW ISOLATED AFTERNOON AND EVENING
THUNDERSTORMS AS THE UPPER LEVEL LOW EXITS TO THE EAST AS ANOTHER
INTENSIFIES OVER THE GREAT BASIN. SHOWERS WILL DECREASE THROUGH
SUNDAY NIGHT AND MONDAY MORNING WITH SOME LINGERING OVER THE
WESTERN MOUNTAINS. LESS MOISTURE WILL BE OVER THE AREA ON MONDAY
BUT SCATTERED MOUNTAIN SHOWERS CAN BE EXPECTED AGAIN WITH ISOLATED
AFTERNOON AND EVENING THUNDERSTORMS. MONDAY NIGHT WILL SEE A
SIGNIFICANT DECREASE IN SHOWERS BUT SOME WILL LINGER OVER THE
WESTERN MOUNTAINS INTO TUESDAY MORNING. THE GREAT BASIN TROUGH
WILL SPREAD INCREASING MOISTURE INTO THE SOUTH AND WEST TUESDAY
AND TUESDAY NIGHT WITH MORE SHOWERS... ESPECIALLY OVER THE WESTERN
AND NORTHERN MOUNTAINS. TEMPERATURES SHOULD BE SLIGHTLY WARMER.
THE TROUGH WILL REMAIN TO THE WEST SPREADING PACIFIC MOISTURE
NORTH AND EAST ACROSS THE AREA WITH INCREASING SHOWERS AND
ISOLATED THUNDERSTORMS WEDNESDAY AND WEDNESDAY EVENING. THE TROUGH
WILL BEGIN MOVING EAST OVER THE AREA AGAIN AS ANOTHER CANADIAN
COLD FRONT MOVES SOUTH BRINGING GENERAL COOLING.


&&

.AVIATION.../06Z ISSUANCE/

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

CONDITIONS THROUGH 21Z/FRI WILL BE VFR AT ALL TERMINALS. SHORTWAVE
ENERGY WILL ROTATE NORTH AHEAD OF MORE IMPRESSIVE SHORTWAVE OVER
NORTHERN NEW MEXICO. EXPECT THAT SHOWERS OVER THE BIG HORN BASIN
WILL DISSIPATE LATE TONIGHT WHILE KRIW AND KLND COULD SEE ISOLATED
WEAK CONVECTION THROUGH THE OVERNIGHT HOURS. ENERGY WITH THE MORE
VIGOROUS SHORTWAVE WILL REACH CENTRAL WYOMING IN THE 20Z-22Z/FRI
TIMEFRAME. THE EVOLUTION MAY BE VERY SIMILAR TO THURSDAY. APPEARS
THERE COULD BE A LITTLE MORE INSTABILITY TO GENERATE AT LEAST
SHOWERS AT KCPR...WHEREAS STABLE AIR LIMITED THAT THURSDAY. 700MB
LOW SHOULD BE ALONG THE WESTERN WYOMING BORDER BY 00Z/SAT. PLENTY OF
ENERGY AND MOISTURE AVAILABLE TO KEEP SHOWERS AND ISOLATED
THUNDERSTORMS GOING THROUGH 06Z/SAT. HAVE KEPT VCSH AT MANY
TERMINALS BUT COULD SEE MORE DEFINITIVE PERIOD OF PREVAILING -SHRA
BETWEEN 00Z-06Z/SAT. THERE COULD ALSO BE SOME AID FROM THE LEFT EXIT
REGION OF THE JET DURING THAT SPAN. MOUNTAIN TOP OBSCURATIONS WILL
BE WIDESPREAD ABOVE ABOUT 9K-10K MSL THROUGHOUT MUCH OF THE FORECAST
PERIOD...ESPECIALLY ALONG THE WIND RIVER RANGE AND THE SOUTHERN
PORTIONS OF THE ABSAROKA AND BIGHORN RANGES.

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

YET MORE SHORTWAVE ENERGY ROTATING NORTH TONIGHT. CLOUD TOPS ARE
ALREADY COOLING AHEAD OF VIGOROUS SHORTWAVE OVER NORTHERN NEW MEXICO
PER IR IMAGERY. CONVECTION IS LIKELY TO CONTINUE THROUGH THE
NIGHT...WITH VFR CONDITIONS LARGELY THE RULE. COULD SEE SOME
LOCALIZED MVFR WITH THE STRONGER CONVECTION AND IN THE GREEN RIVER
VALLEY AROUND KBPI AND KPNA. NEW MEXICO SHORTWAVE WILL LIFT NORTH
DURING THE DAY AS LARGER UPPER LOW TO THE WEST MOVES FARTHER INLAND.
CONVECTION MAY AGAIN ORIENT WEST-EAST ACROSS FAR SOUTHERN WYOMING BY
18Z/FRI. SIMILAR TO THURSDAY...THIS AREA OF CONVECTION WILL LIFT
NORTH THROUGH 00Z/SAT. THEREFORE...HAVE VCTS BY 19Z/FRI AT KRKS AND
BY 21Z/FRI AT KBPI...KPNA...AND KJAC. CERTAINLY COULD BE A FAIRLY
STEADY PERIOD OF RAIN...ESPECIALLY AT KBPI AND KPNA...DURING THE
LATE AFTERNOON HOURS FRIDAY. MOUNTAIN TOP OBSCURATIONS WILL BE
COMMON THROUGH THE FORECAST PERIOD WITH LOWERING CEILINGS AFTER
00Z/SAT.

&&

.FIRE WEATHER...

FIRE DANGER RELATIVELY LOW AS SEASONAL TO COOL AND RELATIVELY MOIST
CONDITIONS PERSIST. A WEAK UPPER LEVEL DISTURBANCE WILL BRING
ISOLATED CONVECTION MAINLY WEST OF THE DIVIDE FOR THE REST OF THIS
AFTERNOON AND EVENING. DEEPER MOISTURE WILL MOVE TOWARD THE AREA
FOR FRIDAY AND BRING ANOTHER CHANCE OF A WETTING RAIN FROM FRIDAY
INTO FRIDAY NIGHT. THERE WILL BE A CHANCE OF SHOWERS AND
THUNDERSTORMS THAT WILL PERSIST INTO SATURDAY AS WELL. SNOW LEVELS
WILL DROP TO 8000 FEET LATE SATURDAY NIGHT AND SUNDAY MORNING.

&&

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

$$

SHORT TERM...LIPSON
LONG TERM...C.BAKER
AVIATION...CNJ
FIRE WEATHER...LIPSON










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