Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 230501
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1101 PM MDT TUE APR 22 2014

.SHORT TERM...TONIGHT AND WEDNESDAY (ISSUED AT 205 PM MDT)

SHOWERS ALREADY FORMING IN THE SOUTHWEST AND EVEN CENTRAL PORTIONS
WITH A COUPLE LIGHTNING STRIKES IN THE SW BY NOON. IN BETWEEN THIS
FIRST SHORTWAVE AND OUR MAIN SYSTEM AND COLD FRONT IS A CLEAR SLOT
OVER ERN ID THAT IS ALREADY FILLING WITH SOME DEVELOPING CONVECTION.
MORNING FORECAST SOUNDINGS INDICATE SOME MODEST CAPE IN THE WEST
THIS AFTERNOON...ESPECIALLY THE NW WITH 400-700 J/KG POSSIBLE ALONG
WITH FAVORABLE SHEAR PROFILE IN THE FIRST COUPLE KM TO GET SOME
STRONGER CELLS FIRING. WILL KEEP OUR SVR WORDING IN THE FAR W AND NW
THROUGH 02Z FOR THIS POTENTIAL. HIGHEST RISK IS WIND DAMAGE BUT A
COUPLE CELLS COULD PRODUCE SOME MARGINALLY SEVERE HAIL. EAST OF THE
DIVIDE...THERE IS ALSO SOME CAPE IN THE FORECAST SOUNDING WITH
200-400 J/KG IN SPOT. SO IDEA OF AT LEAST ISOLATED THUNDERSTORMS
ALONG WITH SOME SHOWERS IS STILL GOOD THERE. OTHERWISE...WINDY TO
VERY WINDY WITH STILL SOME POTENTIAL OF HIGH WINDS MAINLY THIS
EVENING ALONG THE EAST SLOPE OF THE WIND RIVER MTNS AND LANDER
FOOTHILLS AS COLD FRONT APPROACHES AND STRONG JET ALOFT MOVES IN.
WILL LOOK CLOSELY AT WHETHER WE NEED A HIGH WIND WARNING OR STRONGLY
WORDED SPS. ANY SHOWERS OR THUNDERSTORMS IN THE AREA WILL ADD TO THE
OVERALL AMBIENT GRADIENT FLOW SIMILAR TO A COUPLE DAYS AGO. THE WIND
RIVER BASIN UP TO DUBOIS WILL ALSO HAVE TO BE WATCHED AS THE FRONT
APPROACHES AND BLASTS THROUGH. TIMING IS LATER THAN OPTIMUM SO THAT
MAY HELP BUT STILL IT NEEDS TO BE WATCHED. AFTER THE INITIAL BLAST
OF SHOWERS AND THUNDERSTORMS OUT WEST...THE SNOW LEVEL WILL LOWER
FROM 10K FEET TO THE VALLEY FLOOR BY MIDNIGHT WITH OFF AND ON SNOW
SHOWERS THROUGH THE DAY WEDNESDAY. EAST OF THE DIVIDE...IT WILL BE
20-25 DEGREES COOLER WITH STRONG WEST TO NORTHWEST WIND AND A FEW
SHOWERS AROUND...ESPECIALLY NEAR THE FOOTHILLS AND UP NORTH. A
BETTER CHANCE IN THE FAR NORTH WITH THE SWD MOVING FRONT IN THE
MORNING.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

THERE SHOULD BE A GRADUAL WANING IN ACTIVITY WEDNESDAY NIGHT AS THE
TROUGH AXIS MOVES AWAY TO THE EAST AND HEIGHTS BEGIN TO BUILD. WE
STILL HAVE SOME NORTHWEST FLOW WHICH CAN NOT BE TRUSTED...ESPECIALLY
THIS YEAR. ALSO...BOTH THE NAM AND GFS ARE SHOWING SOME 50 KNOT
WINDS AT 700 MILLIBARS SO THIS WILL HAVE TO BE WATCHED FOR POTENTIAL
HIGH WIND HIGHLIGHTS. WIND SHOULD DECREASE LATER AT NIGHT AS THE
PRESSURE GRADIENT SLACKENS AS THE TROUGH MOVES AWAY.

WE SHOULD THEN ENTER A LULL IN THE WEATHER AS SOME FLAT...SHORT WAVE
RIDGING BUILDS ACROSS THE STATE. THERE WILL STILL BE A BIT OF ENERGY
RIDING OVER THE TOP OF THE RIDGE SO WE HAVE MAINTAINED SOME POPS
ACROSS THE NORTHWESTERN MOUNTAINS. HOWEVER...ANY AMOUNTS ARE
EXPECTED TO BE LIGHT. ALL MODELS HAVE TRENDED DRIER EAST OF THE
DIVIDE SO WE REMOVED POPS FROM MOST AREAS EXCEPT FOR THE MOUNTAINS.
WE STILL EXPECT BREEZY CONDITIONS FOR MANY AREAS AS WELL ALTHOUGH
NOT AS WINDY AS THE PREVIOUS COUPLE OF DAYS. TEMPERATURES SHOULD
REBOUND CLOSE TO NORMAL LEVELS WITH MORE SUNSHINE AND RISING
THICKNESSES.

THE BREAK IS EXPECTED TO BE A SHORT ONE HOWEVER AS THE NEXT PACIFIC
SYSTEM AND COLD FRONT APPROACH FROM THE WEST ON FRIDAY. THERE ARE
SOME SLIGHT TIMING DIFFERENCES WITH THE ONSET OF THE PRECIPITATION
SO MADE FEW CHANGES TO THE TIMING AT THIS TIME. PRECIPITATION WILL
SPREAD INTO WESTERN AREAS ESPECIALLY IN THE AFTERNOON WITH SNOW
LEVELS RUNNING AROUND 8000 TO 9000 FEET. MEANWHILE...AREAS EAST OF
THE DIVIDE SHOULD HAVE ONE MORE DRY DAY WITH DOWNSLOPING FLOW
KEEPING THINGS DRY. THIS SHOULD ALSO KEEP MILD TEMPERATURES IN THE
FORECAST THROUGH THAT DAY AS WELL.

PRECIPITATION THEN BEGINS TO SPREAD EAST OF THE DIVIDE INITIALLY ON
FRIDAY NIGHT. HOWEVER...THE STEADIEST PRECIPITATION SHOULD HOLD OFF
UNTIL SATURDAY AFTERNOON WHEN THE BEST FORCING ARRIVES.
MEANWHILE...WEST OF THE DIVIDE IT STILL LOOKS FAIRLY UNSETTLED WITH
SNOW IN THE MOUNTAINS AND A MIX OF RAIN AND SNOW ACROSS THE VALLEYS
WITH SNOW LEVELS INITIALLY RUNNING AROUND 8000 FEET THEN FALLING TO
THE VALLEY FLOORS AT NIGHT. THERE APPEARS TO BE POTENTIAL FOR A GOOD
SNOWFALL ACROSS THE AREA ALTHOUGH AMOUNTS ARE UNCERTAIN THIS FAR
OUT.

THEN LEE CYCLOGENESIS OCCURS EAST OF THE ROCK MOUNTAINS AND AN
UPPER LEVEL LOW MOVES NORTHWARD ACROSS THE EASTERN DAKOTAS FOR
SATURDAY NIGHT AND SUNDAY. UNSETTLED WEATHER STILL LOOKS TO HANG
AROUND THROUGH SUNDAY. PRECIPITATION TYPE LOOKS TO BE SNOW IN THE
MOUNTAINS. AS FOR THE VALLEYS...AGAIN STILL SOME UNCERTAINTY. ONE
THING THAT IS CERTAIN IS THAT THE EXTENDED GFS MOS GUIDANCE
TEMPERATURES ARE WAY TOO WARM. AGAIN...LITTLE CHANGE WAS MADE TO
CONTINUITY. THE MODELS THEN GO SPLITS VILLE FOR EARLY NEXT WEEK WITH
THE EUROPEAN KEEPING THINGS UNSETTLED AND GFS DRYING THINGS OUT.
WITH THE THREAT OF SEVERE WEATHER TODAY...WE LEFT CONTINUITY ALONE.

&&

.AVIATION.../06Z ISSUANCE/

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

VFR CONDITIONS WILL OCCUR THROUGH WEDNESDAY NIGHT. ISOLATED SHOWERS
WILL OCCUR UNTIL 12Z AS THE COLD FRONT MOVES EAST ACROSS THE AREA.
GUSTY WIND FOR MUCH OF WEDNESDAY IN MANY PLACES WITH ONLY ISOLATED
SHOWERS OVER THE NORTH. SOME RAIN AND SNOW SHOWERS OVER THE BIGHORN
MOUNTAINS THROUGH 00Z THURSDAY WITH LOCAL MVFR CONDITIONS. SEE
INDIVIDUAL TERMINAL SITES FOR MORE DETAILS.

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

SNOW WILL BE LIKELY OVER THE WESTERN MOUNTAINS UNTIL 15Z. THEN SNOW
SHOWERS WILL BE LIKELY OVER THE NORTHWEST MOUNTAINS THROUGH 06Z
THURSDAY. EXPECT MVFR TO IFR CONDITIONS IN THESE LOCATIONS. THE KJAC
TERMINAL SITE WILL SEE SOME SNOW UNTIL 11Z...THEN SNOW SHOWERS IN
THE VCNTY MUCH OF THE DAY AND EVENING ON WEDNESDAY. THE SOUTHWEST
AND SOUTH WILL SEE ISOLATED RAIN AND SNOW SHOWERS UNTIL 12Z. THEN
MOSTLY DRY CONDITIONS WITH GUSTY WIND. SEE INDIVIDUAL TERMINAL SITES
FOR MORE DETAILS.

&&

.FIRE WEATHER...

...HAZARDOUS BURNING CONDITIONS THROUGH WEDNESDAY...

A STRONG COLD FRONT WILL MOVE EAST ACROSS THE AREA THROUGH TONIGHT
WITH STRONG WINDS...SHOWERS AND EVEN SOME THUNDERSTORMS. SHOWERS AND
THUNDERSTORMS WILL BE MUCH MORE NUMEROUS WEST OF THE DIVIDE WITH
MORE ISOLATED SHOWERS AND THUNDERSTORMS EAST OF THE DIVIDE. RH`S IN
THE TEENS AND 20S COMBINED WITH THE VERY STRONG WIND WILL KEEP THE
RISK OF ANY FIRES GETTING OUT OF CONTROL RATHER HIGH IF THEY OCCUR
EAST OF THE DIVIDE ESPECIALLY. IT WILL CONTINUE VERY WINDY THROUGH
WEDNESDAY. WEDNESDAY WILL ALSO BE CONSIDERABLY COOLER THAN TUESDAY
BUT STILL RATHER DRY EAST OF THE DIVIDE WITH MIN RH`S IN THE TEENS
AND 20S.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...

HIGH WIND WARNING UNTIL 3 AM MDT WEDNESDAY WYZ018.

&&

$$

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






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