Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 221757
AFDRIW

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE RIVERTON WY
1156 AM MDT FRI MAY 22 2015

TODAY THROUGH SUNDAY NIGHT

WV IMAGERY SHOWING LARGE DEEP TROF WRN CONUS...CLOSED LOW OVR
CALIFORNIA...SW RIDGE CNTRL CONUS...DEEP TROF ERN CONUS. WEAK SW
MOVING NWD THRU CNTRL WY THIS EVENING...WITH STRONGER SW TO THE
SOUTH...ROTATING ANTI-CLOCKWISE AROUND THE CLOSED LOW...SPREADING
OVR COLORADO. SFC HAS HIGH P CNTRL CONUS...LOW P AND NEARLY
STATIONARY FRONT WEST OF WY...DRAPED FROM NRN ID...SWD THRU UT AND
INTO WRN NM. ISOLATED TO WIDELY SCATTERED SHOWERS SPRINKLED AROUND
THE FA TONIGHT.

THRU TODAY...SW CURRENTLY OVR COLORADO WILL CONTINUE TO
ROTATE NWD ACROSS WY THIS AFTERNOON/EVENING/OVERNIGHT...WITH SW AXIS
BISECTING WY FROM SW TO NE BY THIS TIME TOMORROW. THIS WILL AID IN
KICKING OFF ANOTHER BATCH OF SHRA/TSRA. OTHERWISE...LL ERN FLOW
ACROSS MOST OF THE AREA E OF THE DIVIDE WILL STRENGTHEN...KEEPING
GOOD AMOUNTS OF LL MOISTURE ACROSS THE FA...WHILE MORE MID/UPR LVL
MOISTURE MOVES INTO THE REGION FROM THE SOUTH. DIRECTIONAL AND SPEED
SHEAR NOT PARTICULARLY IMPRESSIVE WITH RATHER WEAK MID/UPR FLOW IN
PLACE. BUOYANCY WILL BE MODEST WITH ML CAPE RANGING FROM 300 TO 500
J/KG FOR MOST OF THE CNTRL AND WRN FA...WEAKER TO THE EAST. STRONGER
STORMS OF THE DAY CURRENTLY LOOK TO FORM ACROSS THE FAR WEST...FROM
N OF JACKSON S TO AROUND KEMMERER WHERE WHERE SOME MARGINALLY
BETTER CHANCES FOR SUNSHINE WILL OCCUR...ALONG WITH CHCS FOR MAINLY
SMALL HAIL.

THE REST OF THE FCST FOR THE MEMORIAL DAY WEEKEND...COOL AND WET.
UPR LOW MIGRATES FROM NEAR THE 4 CORNERS REGION TO THE NRN HIGH
PLAINS BY THE END OF THE FCST...WHILE SFC CYCLOGENESIS TAKES PLACE
FROM ERN/NERN CO INTO THE CNTRL PLAINS THRU THE SAME PERIOD. BETWEEN
LOW TO MID LVL MOISTURE RETURN AROUND THE SFC LOW...AND MID UPR
MOISTURE FROM ACCOMPANYING THE UPR WAVE/CLOSED LOW...RELATIVELY
PLENTIFUL RAINFALL AND SOME SNOWFALL WILL BE HAD OVER THE SAME
PERIOD. THIS WILL...HOWEVER...BE A COMPARATIVELY WARM SYSTEM THE WAY
IT STANDS NOW WITH H7 TEMPS NOT DROPPING AT ANY ONE TIME TO MUCH
LESS THAN -1/-2DEG C...AND EVEN THEN FOR ONLY SHORT PERIODS AS THE
UPR LOW ROTATES ACROSS THE STATE. SUNDAY MORNING WILL LIKELY SEE THE
COLD TEMPS OVR THE NW FCST QUAD...BUT WITH LITTLE ATTENDING SNOWFALL
AS THE SYSTEM PULLS AWAY. GENERALLY...A TRACE TO AND INCH OR TWO
WILL BE POSSIBLE DURING THE COLDEST PORTION OF THE NIGHTS AND ONLY
ACROSS THE HIGHEST ELEVATIONS...ISOLATED 3 INCHES. SEVERE WX SHOULD
REMAIN MOSTLY EAST TO SOUTHEAST OF FA THROUGH THE PERIOD WITH ONLY
ISOLATED SMALL HAIL A SMALL THREAT THROUGHOUT. EARLY MORNING FOG
WILL ALSO BE POSSIBLE OVR MANY AREAS THROUGHOUT THE FCST.
.SHORT TERM...

.LONG TERM...MONDAY THROUGH FRIDAY

THE LONG RANGE MODELS ARE IN MODEST AGREEMENT WITH THE WEATHER
PATTERN MONDAY THROUGH FRIDAY. MEMORIAL DAY WILL BE DRIER FOR MOST
PLACES WITH MAINLY ISOLATED AFTERNOON SHOWERS OR STORMS. ACTIVITY
COULD BE A LITTLE MORE NUMEROUS IN THE FAR WEST LATE IN THE DAY INTO
MONDAY EVENING. HIGH TEMPS ON MEMORIAL DAY WILL BE AT OR SLIGHTLY
BELOW NORMAL WITH 50S AND 60S...40S TO LOW 50S FOR THE MOUNTAINS.

FOR TUESDAY THROUGH THURSDAY...A WEATHER SYSTEM SETTLES INTO THE
PACIFIC NW PER THE GFS MODEL AND MOVES INTO IDAHO THURSDAY NIGHT.
THEN IT BRINGS THE WEATHER SYSTEM THROUGH THE REGION FRIDAY. THE
ECMWF MODEL IS A BIT DIFFERENT AND FASTER AS IT DROPS THE WEATHER
SYSTEM INTO IDAHO TUESDAY NIGHT AND ACROSS THE ROCKIES WED NIGHT
AND THURSDAY MORNING. THEN THE ECMWF MODEL HAS FAIRLY QUIET
WEATHER FOR NEXT FRIDAY. BOTH MODELS HAVE BEEN CONSISTENT IN THEIR
TIMING THE PAST FEW MODEL RUNS. WILL LEAN TOWARD THE GFS SOLUTION
TONIGHT. THIS MEANS A CHANCE OF SHOWERS AND STORMS EACH AFTERNOON
AND EVENING FROM TUE THROUGH FRI. COVERAGE SHOULD INCREASE OVER
THE WEST AND NORTH LATER NEXT WEEK AS THE SYSTEM GETS CLOSER AND
EVENTUALLY PASSES THROUGH THE AREA. WILL SEE HOW THINGS LOOK
TONIGHT AND SEE IF ANY CHANGES ARE NEEDED. AS FOR HIGH TEMPS TUE
THROUGH FRI...LITTLE DAY TO DAY CHANGE WITH 60S TO LOW 70S AND 50S
FOR THE MOUNTAINS. OF COURSE TOO MUCH CLOUD COVER WILL PRODUCE
COOLER THAN FORECASTED HIGHS.

&&

.AVIATION.../18Z ISSUANCE/

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

EXCEPT FOR THE BIG HORN BASIN...NORTHERLY TO EASTERLY LOW LEVEL
MOIST FLOW WILL KEEP LOW CLOUDS/MVFR/IFR/MTN OBSCURATIONS AROUND FOR
MUCH OF THE AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM
MOVING INTO THE AREA FROM THE SOUTHERN GREAT BASIN AREA. INSTABILITY
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 RESULTING IN SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS ACCOMPANIED BY LOCALLY HEAVY RAIN AND SMALL HAIL.

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

VFR CONDITIONS WILL START THE AFTERNOON OUT...EXCEPT FOR KRKS WHERE
OCCASIONAL MVFR CONDITIONS DUE TO LOW CIGS WILL OCCUR...BEFORE
ANOTHER ROUND OF SCATTERED TO NUMEROUS THUNDERSTORMS MOVE IN FROM
COLORADO AND UTAH 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. 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...BRAUN
LONG TERM...AR
AVIATION...LIPSON
FIRE WEATHER...BRAUN








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