Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 222105 CCA
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
259 PM MDT FRI MAY 22 2015

.SHORT TERM...TONIGHT THROUGH SATURDAY

...WET UNSETTLED PATTERN TO CONTINUE...

LOW CLOUDS AND COOL TEMPERATURES EAST OF THE DIVIDE ARE PREVALENT
ALONG AND SOUTH OF THE OWL CREEK MTNS AND ALONG AND EAST OF THE BIG
HORN MTNS INCLUDING AREAS ACROSS THE WIND RIVER BASIN INTO NATRONA
AND JOHNSON COUNTIES. A COOL NORTHEASTERLY FLOW IS FEEDING LOW LEVEL
MOISTURE INTO THESE AREAS AND FOR THIS REASON...DO NOT EXPECT MUCH
IN THE WAY OF THUNDERSTORMS FOR THE REMAINDER OF THIS AFTERNOON AND
EVENING IN THESE AREAS. THE AIRMASS IS MUCH MORE UNSTABLE WEST OF
THE DIVIDE. THE BIG HORN BASIN HAS RECEIVED MORE SUNSHINE THEN THE
REST OF THE AREA EAST OF THE DIVIDE SO THIS AREA COULD ALSO BE
PRIMED FOR MORE THUNDERSTORM ACTIVITY FOR THE REST OF TODAY. A
THUNDERSTORM HAS ALREADY FORMED NEAR MEETEETSE WITH OTHER T STORMS
PREVALENT WEST OF THE DIVIDE. CURRENTLY THE MAIN CIRCULATION OF OUR
NEXT CLOSED LOW APPEARS TO BE OVER THE NEVADA/CALIFORNIA/ARIZONA
TRIPLE POINT. THE SSW SOMEWHAT DIFLUENT FLOW WILL ENCOURAGE
THUNDERSTORM DEVELOPMENT FOR THE REST OF TODAY EXCEPT IN THE
AFOREMENTIONED STABLE AREAS. THE LOW WILL TRAVEL TO UTAH TONIGHT AND
THEN TOWARD WYOMING SATURDAY ALONG WITH A TROUGH TROUGH EXTENDING TO
WYOMING OUT AHEAD OF IT. SOME SNOW IS EXPECTED TO FALL ABOVE 9500
FEET OR SO LATE TONIGHT WITH UP TO AN INCH AND A HALF OF SNOW
EXPECTED AT THESE ELEVATIONS IN THE WIND RIVER RANGE AFTER MIDNIGHT
TONIGHT. MORE WIDESPREAD THUNDERSTORM ACTIVITY IS EXPECTED SATURDAY
WITH SOMEWHAT MILDER TEMPS EXPECTED THANKS TO THE SSW FLOW AHEAD OF
THE APPROACHING LOW BEFORE SHORT LIVED COOLER AIR FLOWS IN AROUND
THE BACKSIDE OF THE LOW. HOWEVER...THE STRONGEST STORMS SHOULD HOLD
OFF UNTIL AFTER 21Z SATURDAY SINCE WITH AREAS EAST OF THE DIVIDE
STILL CONTENDING WITH A COOL MOIST EASTERLY FLOW MAKING IT DIFFICULT
TO TAKE ADVANTAGE OF MUCH SOLAR INSULATION AT LEAST UNTIL THEN AS
SFC CYCLOGENESIS TAKES PLACE IN SE CO. AS HAS BEEN THE CASE THESE
LAST COUPLE OF WEEKS...ANY THUNDERSTORMS THAT DO FORM WILL LIKELY
PRODUCE LOCALLY HEAVY RAINFALL AND SMALL HAIL GIVEN THE LOW LEVEL LC
AND LOW ELEVATION WET BULB ZEROS. IN ADDITION...A WEAK 700MB
CIRCULATION WILL DRIFT FROM WESTERN WYOMING THIS EVENING TO
NORTHEAST WY LATER SATURDAY...ADDING TO THE
CONVERGENCE/LIFT...ENHANCING PRECIP AMOUNTS.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

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
SUNDAY MORNING.  A CANADIAN COLD FRONT WILL SLIDE SOUTH THROUGH MUCH
OF THE AREA 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 IN THE
EVENING TO SUPPORT ISOLATED THUNDERSTORMS WITH SMALL HAIL.  SNOW
LEVELS WILL LOWER THROUGH SATURDAY NIGHT DOWN TO AROUND 7500 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.  THE FLOW ALOFT WILL BECOME
ZONAL THURSDAY AND FRIDAY WITH DRYING AND WARMING.  THIS WILL KEEP
SOME SHOWERS AND ISOLATED THUNDERSTORMS IN THE WESTERN AND NORTHERN
MOUNTAINS. MODELS BEGIN TO DIVERGE WITH THE FASTER MOVING SHORT WAVE
TROUGHS IN THE ZONAL FLOW WHICH DECREASES THE CONFIDENCE IN THE
STRENGTH AND TIMING OF PRECIPITATION.

&&

.AVIATION.../00Z ISSUANCE/

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

EXCEPT FOR THE BIG HORN BASIN WHERE CLOUD BASES WILL BE BETWEEN 3
AND 4K IN SOME AREAS...NORTHERLY TO EASTERLY LOW LEVEL MOIST FLOW
WILL KEEP LOW CLOUDS/MVFR/IFR/MTN OBSCURATIONS AROUND FOR MUCH OF
THE EVENING AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM MOVING
INTO THE AREA FROM THE SOUTHERN GREAT BASIN AREA. INSTABILITY THIS
EVENING WILL BE RELATIVELY WEAK SO MAINLY JUST RAIN SHOWERS ARE
EXPECTED AROUND THE AREA. THESE CONDITIONS ARE EXPECTED TO PERSIST
ON AND OFF THROUGH ABOUT 21Z SATURDAY AFTER WHICH TIME THE
ATMOSPHERE WILL BECOME MORE UNSTABLE GIVING RISE TO SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS ACCOMPANIED BY LOCALLY HEAVY
RAIN AND SMALL HAIL.

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

SCATTERED TO NUMEROUS THUNDERSTORMS MOVE IN FROM COLORADO...UTAH
AND IDAHO RESULTING IN LOCAL MVFR/IFR CONDITIONS/MTN OBSCURATIONS/LOCALLY
HEAVY RAIN AND SMALL HAIL. THESE THUNDERSTORMS WILL CONTINUE WELL
INTO THE EVENING WITH LINGERING SHOWERS THEREAFTER. IN
ADDITION...THERE WILL BE PATCHES OF CLOUDS WITH BASES RANGING
FROM 3 TO 4K THROUGHOUT THE REGION. ANOTHER ROUND OF THUNDERSTORMS
IS EXPECTED TO MOVE IN FROM THE SOUTH SATURDAY AS THE LOW PRESSURE
CENTER NEAR LAS VEGAS TRACKS NORTHEAST TO WYOMING.

&&

.FIRE WEATHER...

FIRE DANGER LOW AND WILL REMAIN LOW THROUGH THE HOLIDAY WEEKEND
AS COOL AND RELATIVELY WET WEATHER REMAINS IN PLACE AS YET ANOTHER
VIGOROUS UPPER LEVEL SYSTEM ROTATES ACROSS THE REGION. WIDESPREAD
PRECIPITATION WITH LIGHT MOUNTAIN SNOW IS EXPECTED EACH DAY...WITH
EMBEDDED THUNDERSTORMS POSSIBLE EACH AFTERNOON AND EARLY EVENING.

&&

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

$$

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








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