Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 050928
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
328 AM MDT THU MAY 5 2016

.SHORT TERM...THURSDAY THROUGH SATURDAY NIGHT

QUITE AN ACTIVE WEATHER PATTERN LOOKS TO BE SHAPING UP FOR THE NEXT
THREE DAYS. TODAY LOOKS TO BE THE LEAST ACTIVE DAY THOUGH. A SURGE
OF MID LEVEL MOISTURE AHEAD OF AN UPPER LEVEL AND SOME JET ENERGY
WILL BRING THE CHANCE OF A FEW SHOWERS AND THUNDERSTORMS WEST OF THE
DIVIDE THIS AFTERNOON AND EVENING. HOWEVER...MOST OF TODAY SHOULD BE
LARGELY RAIN FREE. MEANWHILE...EAST OF THE DIVIDE...THERE SHOULD BE
ONE MORE DRY DAY. THIS WILL BE THE WARMEST DAY...THE WARMEST FOR
MANY AREAS SO FAR THIS YEAR AS SOME SOUTHWESTERLY BREEZES BRING IN
SOME WARM AIR AHEAD OF THE UPPER LEVEL LOW. THERE WILL BE MANY HIGHS
IN THE 80S IN THE LOWER ELEVATIONS TODAY. AS FOR THE CHANCE OF
CONVECTION...A FEW SPOTS COULD SEE SOMETHING THIS EVENING...BUT MOST
AREAS SHOULD BE LARGELY DRY THROUGH TONIGHT.

THE MORE ACTIVE WEATHER STARTS TOMORROW. THE REGION WILL BE IN
SQUEEZE PLAY BETWEEN A COLD FRONT DROPPING DOWN FROM THE NORTH AND
AN UPPER LEVEL LOW THAT WILL PASS TO THE SOUTH OF WYOMING. THIS WILL
LIKELY PUMP COPIOUS AMOUNTS OF MOISTURE INTO THE AREA BEGINNING ON
FRIDAY. THERE IS ALSO THE CHANCE OF A FEW STRONGER THUNDERSTORMS.
THE STORM PREDICTION CENTER HAS A MARGINAL RISK ACROSS SOUTHERN AND
WESTERN PORTIONS OF THE COUNTY WARNING AREA. THERE IS A DECENT
AMOUNT OF SHEAR IN THIS AREA SO A FEW STORMS COULD HAVE SOME HAIL
AND THE ALWAYS PRESENT STRONG WINDS IN WYOMING THUNDERSTORMS. THE
LIMITING FACTOR MAY BE SURFACE HEATING DUE TO CLOUD COVER HOWEVER.
FOR NOW...WE KEPT THE FORECAST FAIRLY CLOSE TO CONTINUITY.
HOWEVER...ALL AREAS WILL HAVE A CHANCE FOR THUNDERSTORMS.
TEMPERATURES WILL BE A CHALLENGE WITH THE GUIDANCE HAVING UP TO 12
DEGREES SPREADS FOR HIGH TEMPERATURES. WITH THE UNCERTAINTY...WE
KEPT THINGS FAIRLY SIMILAR OR JUST A BIT COOLER THAN CONTINUITY.

THE MAIN EVENT LOOKS TO BE FRIDAY NIGHT INTO SATURDAY IN THE FORM OF
A GOOD AMOUNT OF RAIN AS EAST TO EAST-NORTHEAST UPSLOPE FLOW
DEVELOPS. THIS WOULD PUT THE HEAVIEST RAIN OVER THE WIND RIVER BASIN
TO THE LANDER FOOTHILLS AND WIND RIVER RANGE AS WELL AS THE EAST
SLOPES OF THE ABSAROKAS AND THE BIG HORN RANGE. THE PREVIOUS
DISCUSSION MENTIONED UP 1 TO 2 INCHES IN THE LOWER ELEVATIONS AND WE
THINK THAT SEEMS FAIRLY REASONABLE. AT THIS TIME...THE HEAVIEST
PRECIPITATION LOOKS TO BE FRIDAY NIGHT INTO SATURDAY MORNING. WITH
SNOW LEVELS...STARTING OFF FAIRLY HIGH...OVER 10000 FEET...THIS
COULD BRING SOME RAPID SNOWMELT THAT COULD BRING SOME FLOODING
PROBLEMS. HOWEVER...WITH THE RECENT WARM WEATHER A DECENT AMOUNT OF
THE SNOW HAS MELTED AND THIS MAY MITIGATE THINGS JUST A BIT. IN
ADDITION...A COLD POOL MAY ROTATE OVER THE AREA AND LOWER SNOW
LEVELS DOWN TO AROUND 9000 FEET BY SATURDAY EVENING. THIS COULD ALSO
LIMIT SNOWMELT A BIT. THIS NEEDS TO BE WATCHED CLOSELY THOUGH. AS
FOR THE EFFECT OF THE SNOW...SOME AREAS WILL LIKELY SEE 1 TO 2 FEET
OF NEW SNOW. THESE WOULD BE WELL ABOVE PASS LEVEL MOST OF THE TIME
AND IMPACTS MAY BE MINIMAL EXCEPT FOR PEOPLE HEADING INTO THE
BACKCOUNTRY. IN ADDITION...ANY SNOW THAT FALLS ON PAVED SURFACES
DURING THE DAY WOULD LIKELY MELT WITH THE HIGH MAY SUN ANGLE. THE
STEADIEST PRECIPITATION MAY END BY SATURDAY EVENING AS THE BEST BEST
UPPER LEVEL SUPPORT MOVES AWAY TO THE EAST. THE PRECIPITATION WILL
NOT END...JUST BECOME LIGHTER. TEMPERATURES WILL ALSO BE A SHOCK TO
THE SYSTEM WITH SOME AREAS HAVING HIGHS AROUND 30 DEGREES COOLER FOR
HIGHS SATURDAY COMPARED TO THURSDAY.

.LONG TERM...SUNDAY THROUGH THURSDAY

THE MODELS DRIFT THIS WEATHER SYSTEM INTO EAST OR SOUTHEAST WY
SUNDAY AND MOVE IT INTO THE WESTERN HIGH PLAINS SUNDAY NIGHT.
THIS KEEPS RAIN SHOWERS IN THE FORECAST FOR MOST PLACES SUNDAY
INTO SUNDAY NIGHT ALONG AND EAST OF THE CONTINENTAL DIVIDE. AREAS
WEST OF THE DIVIDE WILL SEE SCATTERED SHOWERS SUNDAY INTO SUNDAY
EVENING. THE NEXT STORM SYSTEM DROPS INTO IDAHO MONDAY AFTERNOON
AND THEN ACROSS WY MONDAY NIGHT THROUGH TUESDAY. THE CURRENT TRACK
OF THIS SYSTEM WOULD PLACE THE HEAVIEST PRECIP OVER THE NORTH
HALF...SAY ALONG AND NORTH OF A CASPER TO JACKSON LINE MONDAY
NIGHT THROUGH TUESDAY WITH LESSER PRECIP OVER THE SOUTH HALF. THEN
TUESDAY NIGHT INTO WEDNESDAY THE STORM SYSTEM SLOWLY MOVES EAST
INTO THE HIGH PLAINS STATES. THE ECMWF IS SLOWER THAN THE GFS
WEDNESDAY AND THUS HAS MORE PRECIP EAST OF THE DIVIDE WED THAN THE
GFS. WEST OF THE DIVIDE...PRECIP WILL BE ON THE DECLINE TUESDAY
NIGHT AND WEDNESDAY. THE PRECIP DECREASES WED NIGHT EAST OF THE
DIVIDE AS THE SYSTEM MOVES OUT. NEXT THURSDAY LOOKS DRIER WITH
MAINLY ISOLATED SHOWERS OR STORMS. GFS MODEL HAS MORE COVERAGE
THAN THE ECMWF MODEL. WILL KEEP A LOW CHANCE FOR THE MOUNTAINS AND
ISOLATED FOR THE LOWER ELEVATIONS. TEMPS WILL BE NEAR TO BELOW
NORMAL DURING THE PERIOD.

&&

.AVIATION.../12Z ISSUANCE/

CONDITIONS WILL REMAIN VFR THROUGH THE FORECAST PERIOD WITH POSSIBLE
MVFR IF LOCAL SHOWERS IMPACT A TERMINAL. INCREASING SOUTH TO
SOUTHWEST FLOW AHEAD OF A WEATHER SYSTEM NEAR SOUTHERN CALIFORNIA
WILL SPREAD MID-LEVEL MOISTURE ACROSS WESTERN WYOMING TODAY.
ENOUGH MOISTURE WILL BE PRESENT TO GENERATE CONVECTION OVER THE HIGHER
TERRAIN AFTER 19Z. HAVE INCLUDED VCSH AT KJAC AND KBPI TO ACCOUNT FOR
CONVECTION MOVING OFF THE HIGHER TERRAIN THROUGH 02Z. POSSIBLE LIGHT
SHOWERS AFTER 02Z OVER FAR WEST WY. EXPECT SOUTH TO SOUTHWEST WIND TO
INCREASE BY EARLY AFTERNOON WITH THE WIND LOWERING BY 02Z IN MOST PLACES.

EAST OF THE CONTINENTAL DIVIDE...KCPR/KCOD/KRIW/KWRL/KLND AIRPORTS

CONDITIONS WILL REMAIN VFR THROUGH THE FORECAST PERIOD. INCREASING
MOISTURE FROM THE SOUTH-SOUTHWEST WILL REACH CENTRAL WYOMING THIS
AFTERNOON. CONVECTION WILL GENERALLY BE CONFINED TO THE HIGHER
TERRAIN WITH VCSH ONLY NEEDED AT KCOD THIS AFTERNOON AND EVENING.
ONLY TERMINAL WITH WIND OF SIGNIFICANCE WILL BE KCPR...WHERE SPEEDS
OF 15 KTS GUSTING TO NEAR 25 KTS ARE ANTICIPATED FROM 16Z UNTIL 00Z.

&&

.FIRE WEATHER...

AN AREA OF LOW PRESSURE WILL MOVE TOWARD WYOMING OVER THE NEXT FEW
DAYS AND BRING INCREASINGLY COOL AND WET WEATHER. A FEW AFTERNOON
THUNDERSTORMS WILL BE POSSIBLE ACROSS THE WESTERN MOUNTAINS THIS
AFTERNOON. MEANWHILE...AREAS EAST OF THE DIVIDE WILL SEE ONE MORE
WARM AND DRY DAY WITH A SOUTHWESTERLY BREEZE DEVELOPING. SOME AREAS
WILL HAVE RELATIVE HUMIDITY FALL INTO THE LOWER TEENS. WET WEATHER
WILL RETURN FRIDAY AND ESPECIALLY FRIDAY NIGHT INTO SATURDAY WITH A
WETTING RAIN LIKELY FOR MANY AREAS...ESPECIALLY EAST OF THE
DIVIDE.

&&

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

&&

$$

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


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