Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 220943
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
343 AM MDT WED APR 22 2015

.SHORT TERM...WEDNESDAY THROUGH FRIDAY NIGHT

GUESS WHAT DAY IT IS? WELL...I WILL STOP THERE BEFORE WE HAVE A
COPYRIGHT VIOLATION BY A WELL KNOWN INSURANCE COMPANY. WELL...IT IS
WEDNESDAY. AND...IT LOOKS LIKE THE WEATHER WILL TURN MORE ACTIVE
OVER THE NEXT FEW DAYS. ALL IN ALL...TODAY LOOKS LIKE QUIETEST OF
THE THREE DAYS. ALL IN ALL...IT LOOKS FAIRLY SIMILAR TO TUESDAY WITH
ABOVE NORMAL TEMPERATURES AS WELL AS A FEW SHOWERS AND THUNDERSTORMS
AROUND...MAINLY OVER THE MOUNTAINS WITH THE HIGH ELEVATION HEAT
SOURCE. AND...WITH A BIT MORE MOISTURE ADVECTING IN FROM THE
SOUTHWEST...MAYBE MORE COVERAGE ACROSS SOUTHWESTERN WYOMING.
AND...LIKE YESTERDAY...WITH VERY WEAK STEERING WINDS THUNDERSTORMS
WILL HAVE A DIFFICULT TIME MOVING OFF OF THE MOUNTAINS SO MOST OF
THE LOWER ELEVATIONS EAST OF THE DIVIDE SHOULD STAY RAIN FREE. THERE
IS NOT A TREMENDOUS AMOUNT OF CAPE OR INSTABILITY SO NO WIDESPREAD
THUNDERSTORMS ARE EXPECTED.

THE CONVECTION MAY BECOME A BIT MORE ACTIVE FOR THURSDAY HOWEVER.
THE MODELS SHOW A SHORTWAVE TROUGH MOVING TOWARD WYOMING WITH WILL
LOWER HEIGHTS AND PROVIDE A LITTLE EXTRA LIFT. INSTABILITY INDICES
ARE A BIT HIGHER AS WELL WITH CAPE VALUES AROUND 700 J/KG IN
SOUTHEASTERN PORTIONS OF THE VIEWING AREA AND LIFTED INDICES FALLING
TO AROUND MINUS 3 ON THE NAM. HOWEVER...THE GFS IS MORE STABLE WITH
LESS CAPE. WINDS REMAIN FAIRLY WEAK THROUGH THE ATMOSPHERE THOUGH.
WET BULB ZERO LEVELS ARE FAIRLY LOW HOWEVER SO ALTHOUGH WE DID NOT
ADD IT TO THE FORECAST YET...THERE COULD BE SOME HAIL WITH THE
STORMS THAT FORM AND MOVE IN A GENERAL SOUTHWEST TO NORTHEAST
DIRECTION. OTHERWISE...EXPECT A MIX OF CLOUDS AND SUNSHINE WITH
TEMPERATURES ONCE AGAIN A BIT ABOVE NORMAL.

THE CHANCE OF SHOWERS AND THUNDERSHOWERS WILL LINGER INTO FRIDAY AS
WELL. BOTH THE NAM AND GFS SHOW STABILITY INDICES A LITTLE LESS
IMPRESSIVE SO THE CHANCE OF STRONGER THUNDERSTORMS WILL LIKELY BE A
BIT LESS. HOWEVER...WITH TROUGHINESS STILL OVER THE AREA AND
MOISTURE CONTINUING TO ADVECT IN FROM THE SOUTH AND WEST. THERE WILL
STILL BE A CHANCE OF THUNDERSTORMS...ALTHOUGH MAYBE A BETTER CHANCE
EAST OF THE DIVIDE WHERE A WEAK FRONTAL BOUNDARY MAY PROVIDE A
FOCUSING MECHANISM.

.LONG TERM...SATURDAY THROUGH WEDNESDAY

SYNOPSIS...A PACIFIC STORM SYSTEM WILL BRING INCREASING SHOWERS AND
A FEW THUNDERSTORMS ACROSS THE AREA SATURDAY...AND THEN MUCH
COOLER CONDITIONS WITH MORE WIDESPREAD RAIN AND SNOW ON
SUNDAY...ESPECIALLY ACROSS THE CENTRAL AND SOUTH. PRECIPITATION
WILL DECREASE NORTHWEST TO SOUTHEAST SUNDAY NIGHT AND MONDAY WITH
DRY AND WARMER WEATHER FOLLOWING ON TUESDAY AND WEDNESDAY.

DISCUSSION...THE MAIN WEATHER MAKER DURING THIS PERIOD WILL BE AN
UPPER LOW MOVING EAST ACROSS THE GULF OF ALASKA THIS MORNING.
MEDIUM-RANGE MODELS HAVE BEEN ALL OVER THE MAP WITH THIS SYSTEM OVER
THE PAST FEW RUNS BUT SEEM TO BE REACHING A CONSENSUS THIS MORNING
ON LESS SPLITTING OR A MORE CONSOLIDATED...COLDER SYSTEM DIGGING SSE
ACROSS THE INTERMOUNTAIN WEST ON SATURDAY...INTO THE FOUR CORNERS
REGION ON SUNDAY.  THIS SYSTEM HAS PLENTY OF COLD AIR...-40C AT
H5...TO TAP INTO ON THE BACKSIDE OVER THE ALASKAN INTERIOR THAT
SHOULD RESULT IN SOME STRENGTHENING AS IT HEADS TOWARD THE WEST
COAST OF CANADA.  SW DIFLUENT FLOW TAKES SHAPE OVER WYOMING SATURDAY
AS THIS SYSTEM DIGS SSE ACROSS THE INTERMOUNTAIN WEST.  BEST
MOISTURE AND INSTABILITY WILL BE ACROSS SOUTHERN AND EASTERN WYOMING
SATURDAY AFTERNOON WHERE THUNDERSTORM DEVELOPMENT WILL BE MORE
LIKELY.  SURFACE FLOW BEGINS TO TURN UPSLOPE EAST OF THE DIVIDE
SATURDAY AFTERNOON AND EVENING WITH H5 CLOSED LOW NEAR THE FOUR
CORNERS BY 18Z SUNDAY.  THOUGH A SIMILAR TRACK TO THE APRIL 15-16
STORM THIS SYSTEM IS NOT EXPECTED TO BE AS COLD NOR CUTOFF FROM THE
FLOW...STAYING ON THE MOVE INTO THE SOUTHERN/CENTRAL PLAINS ON
MONDAY.  BOTH GFS AND ECMWF SHOW H7 TEMPS OF -4C ACROSS MOST AREAS
EAST OF THE DIVIDE DURING THE TIME OF EXPECTED MAXIMUM PRECIPITATION
COVERAGE SUNDAY EQUATING TO SNOW LEVELS AROUND 6.5KFT...SO EXPECTING
MOSTLY RAIN ACROSS THE CENTRAL BASINS.   PREFER THE ECMWF KEEPING
THE NORTHERN AND SOUTHERN STREAMS SEPARATED AS THIS SYSTEM EXITS OUT
INTO THE PLAINS MONDAY WITH BROADER UPPER RIDGE PUSHING INTO THE
AREA.  UPPER RIDGE WILL THEN REMAIN OVER THE AREA THROUGH MID-WEEK.
TEMPERATURES WERE COOLED SIGNIFICANTLY SUNDAY AND MONDAY WITH HIGHS
IN THE 40S ON SUNDAY POSSIBLY STILL A BIT OPTIMISTIC IN WET UPSLOPE
CONDITIONS.    HIGH TEMPERATURES ARE EXPECTED TO QUICKLY REBOUND
INTO THE 60S ON TUESDAY WITH SOME 70S IN THE LOWER BASINS ON
WEDNESDAY.


&&

.AVIATION.../12Z ISSUANCE/

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

SCATTERED SHOWERS AND ISOLATED STORMS WILL DEVELOP AFTER 19Z OVER
OR ALONG THE ABSAROKA AND WIND RIVER MOUNTAINS. SHOWERS WILL BE MORE
ISOLATED OVER THE BIGHORN MOUNTAINS. SOME OF THE SHOWER ACTIVITY
WILL DRIFT OFF THE MOUNTAINS AND IMPACT THE LOWER ELEVATIONS. NOT
ALL TERMINAL SITES WILL SEE SHOWERS AND VCSH WILL APPEAR IN SOME
TERMINAL FORECASTS. EXPECT OCCASIONAL MOUNTAIN OBSCURATION THIS
AFTERNOON INTO THE EVENING. MOST OF THE SHOWERS WILL DISSIPATE BY
06Z THURSDAY. VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES
THROUGH THE PERIOD. THERE MAY BE LOCAL MVFR CONDITIONS OVER AND NEAR
THE MOUNTAINS.

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

SCATTERED SHOWERS WILL DEVELOP OVER THE WESTERN MOUNTAINS AFTER 19Z
WITH ISOLATED THUNDERSTORMS. THE ACTIVITY WILL DECREASE AFTER 03Z
THURSDAY. TERMINAL SITES MAY SEE SHOWERS AT TIMES FROM 21Z UNTIL 03Z
THURSDAY. MOST TERMINAL FORECASTS WILL HAVE VCSH FOR NOW. EXPECT
OCCASIONAL MOUNTAIN OBSCURATION THIS AFTERNOON INTO THE EVENING. VFR
CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH THE PERIOD.
THERE MAY BE LOCAL MVFR CONDITIONS OVER AND NEAR THE MOUNTAINS.
&&

.FIRE WEATHER...

TODAY LOOKS LIKE THE DRIEST AND MOST STABLE DAY OF THE NEXT THREE
WITH ISOLATED TO SCATTERED AFTERNOON SHOWERS AND THUNDERSTORMS IN
THE MOUNTAINS WITH THE LOWER ELEVATIONS REMAINING LARGELY DRY. THE
CHANCE OF SHOWERS AND THUNDERSTORMS WILL INCREASE THURSDAY AND
FRIDAY BUT WIDESPREAD ACTIVITY IS NOT EXPECTED AND WIDESPREAD
WETTING RAIN IS NOT EXPECTED THROUGH THE REST OF THE WORKWEEK.
&&

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

$$

SHORT TERM...HATTINGS
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...HATTINGS








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