Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220942
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
342 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.../12Z ISSUANCE/

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

EXPECT CONDITIONS TO BE VFR THROUGH AT LEAST 00Z/SAT AT ALL
TERMINALS. WEST-EAST ORIENTED AREA OF CONVECTION WILL LIFT NORTH
ACROSS THE FORECAST AREAS BETWEEN 21Z/FRI AND 03Z/SAT...SIMILAR TO
WHAT WAS SEEN THURSDAY. INSTABILITY LOOKS A LITTLE MORE FAVORABLE
FOR WEAK CONVECTION AT KCPR. MAIN HAZARD WITH THE SHOWERS AND STORMS
WILL BE HEAVY RAIN. MID-LEVEL CIRCULATION ALONG THE WESTERN WYOMING
BORDER AT 00Z. CONVERGENCE AXIS WILL PINWHEEL NORTH DURING THE
EVENING AND PROVIDE PERHAPS A BETTER PERIOD OF WIDESPREAD SHOWERS
AND STORMS. PLENTY OF ENERGY AND MOISTURE TO WORK WITH THROUGH AT
LEAST 06Z/SAT. HAVE KEPT VCSH AT MANY TERMINALS BUT COULD SEE MORE
DEFINITIVE PERIOD OF PREVAILING -SHRA BETWEEN 00Z-06Z/SAT. LEFT EXIT
REGION OF 100KT+ JET MAY ALSO ASSIST LIFT FRIDAY EVENING...
ESPECIALLY ACROSS CENTRAL WYOMING. 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

STEADY STREAM OF SHORTWAVE ENERGY WILL HEAD NORTH ACROSS THE
FORECAST AREA TODAY. VFR CONDITIONS WILL LARGELY BE THE RULE THROUGH
00Z/SAT...WITH THE EXCEPTION BEING MVFR CONDITIONS WITH THE
STRONGEST STORMS LATE TODAY. SHORTWAVE IN SOUTHERN COLORADO WILL
CONTINUE TO LIFT AS THE KICKER UPPER LOW MOVES EAST. EXPECT
CONVECTION TO ORIENT IN A WEST-EAST BAND ACROSS FAR SOUTHERN WYOMING
BY 18Z TODAY. 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. MAIN HAZARD WILL BE HEAVY
RAIN. AFTER 00Z/SAT...700MB CIRCULATION AND LOW-LEVEL SOUTHERLY FLOW
MAY ENHANCE PRECIPITATION ACROSS THE GREEN RIVER BASIN FROM KBPI TO
KPNA. THIS WOULD BE THE MOST LIKELY PERIOD OF MVFR CONDITIONS AT
THESE TWO TERMINALS. MOUNTAIN TOP OBSCURATIONS WILL BE COMMON
THROUGH THE FORECAST PERIOD WITH LOWERING CEILINGS AFTER 00Z/SAT.

&&

.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...CNJ
FIRE WEATHER...BRAUN





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