Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 212104
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 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.../00Z ISSUANCE/

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

MOSTLY VFR CEILINGS WILL PREVAIL THROUGH THE FORECAST PERIOD.
THE NEXT IN A SERIES OF SHORTWAVES IS APPROACHING SOUTHWEST WYOMING
THIS AFTERNOON. FAVORABLE INSTABILITY AND DYNAMICS WILL BE TO THE
SOUTHWEST OVER SOUTHWEST WYOMING. ISOLATED THUNDERSTORMS WILL
MAINLY BE CONFINED TO THE HIGHER TERRAIN AFTER 22Z THIS AFTERNOON AND
IS EXPECTED TO DISSIPATE WITH THE SETTING SUN. NOT EXPECTING ANY
THUNDERSTORMS TO SPEAK OF IN THE NORTH CENTRAL...NORTHEAST AND EAST
CWA FOR THE REST OF TODAY WHERE THE AIR IS MUCH MORE STABLE. HAVE
LINGERED VCSH INTO THE 06Z- 08Z/FRI TIME FRAME ACROSS CENTRAL
WYOMING...WITH LITTLE IF ANY SHOWER ACTIVITY IMPACTING KWRL OR
KCOD. EXPECT ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS TO DEVELOP
FRIDAY AS ANOTHER PIECE OF ENERGY SPREADS NORTHEAST FROM A LOW
CENTER IN THE DESERT SOUTHWEST. EXPECT AN EARLY SHOW OF SHOWER
DEVELOPMENT ALONG WITH ISOLATED THUNDERSTORMS. LATER...FEWER BUT
STRONGER THUNDERSTORMS ARE EXPECTED IN THE BIG HORN
BASIN...JOHSNON AND NATRONA COUNTIES AFTER 21Z FRIDAY. EXPECT MVFR
CONDITIONS FROM LOW CLOUDS AND LOCAL MVFR/IFR MTN OBSCURATIONS
FROM SHOWER AND THUNDERSTORM ACTIVITY FRIDAY.

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

THE NEXT IN A SERIES OF SHORTWAVES WILL ROTATE NORTH THIS
AFTERNOON. SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE TO
DEVELOP...MOSTLY OVER THE HIGHER TERRAIN...WITH DEVELOPMENT
OCCURRING THROUGH 23Z TODAY. LIFTED INDICES AND CAPE ARE
SUFFICIENT TO GENERATE SOME ADDITIONAL WIDELY SCATTERED
THUNDERSTORMS AFTER 23Z THIS AFTERNOON. SIMILAR TO LAST
NIGHT...THE SHOWERS AND STORMS WILL CONTINUE UNTIL ABOUT 04Z/FRI
WITH SOME SHOWERS LINGERING UNTIL WELL AFTER 06Z/FRI. CLOUD
HEIGHTS OVERNIGHT TONIGHT INTO FRIDAY WILL BE LOWER...ALBEIT
VFR/MVFR...AS A RESULT OF THE INCREASED LOW-LEVEL MOISTURE FROM SOUTHWEST
WYOMING. EXPECT MVFR CONDITIONS FROM LOW CLOUDS AND LOCAL MVFR/IFR
MTN OBSCURATIONS FROM SHOWER AND THUNDERSTORM ACTIVITY FRIDAY.

&&

.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...LIPSON
FIRE WEATHER...LIPSON






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