Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 052052
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
252 PM MDT SUN JUL 5 2015

.SHORT TERM...TONIGHT THROUGH MONDAY

A WINTER LIKE STORM WILL INTENSIFY OVER WESTERN AND CENTRAL
WYOMING THIS EVENING. HIGHS ACROSS THE NORTH WERE 30 TO 35 DEGREES
COLDER TODAY FROM YESTERDAY. THIS COOLING WILL CONTINUE. SHOWERS
HAVE BECOME WIDESPREAD WITH MOST THUNDERSTORM ACTIVITY IN THE
SOUTH BUT SOME HAVE ALSO OCCURRED IN THE BIGHORN MOUNTAINS.
A MID LEVEL CYCLONIC CIRCULATIONS IS EXPECTED TO DEVELOP IN THE
MUDDY GAP AREA AND THIS WILL CAUSE RAPID INTENSIFICATION OF
PRECIPITATION RATES. FREEZING LEVELS WILL LOWER TO 9500 TO 9000
FEET AND SNOWFALL OF 3 TO 6 INCHES...LOCALLY MUCH HIGHER WILL
OCCUR ABOVE 9500 FEET TONIGHT CONTINUING THROUGH MONDAY AS
TEMPERATURES WILL WARM LITTLE AND IN SOME AREAS WILL CONTINUE
TO FALL OR AT BEST REMAIN STEADY TONIGHT THROUGH MONDAY.
SOME AREAS AROUND THE WIND RIVER...ABSAROKA AND BIGHORN MOUNTAINS
HAVE THE POTENTIAL FOR 1.5 TO 2 INCHES OF RAIN...THIS ALSO
INCLUDES CASPER MOUNTAIN. THE NAM12 PUTS 3.5 INCHES OVER THE
HIGHEST ELEVATIONS OF THE WIND RIVER MOUNTAINS. THANKFULLY RIVER
LEVELS HAVE FALLEN AS THE SNOW MELT RUNOFF IS ALL BUT OVER...BUT
SIGNIFICANT RIVER RISES ARE POSSIBLE THROUGH MONDAY.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY

SIMILAR SOLUTIONS AGAIN OFFERED BY MEDIUM-RANGE FORECAST MODELS
REGARDING OVERALL EVOLUTION OF THE SYNOPTIC WEATHER PATTERN THIS
COMING WEEK AND WEEKEND. GFS AND ECMWF SOLUTIONS BOTH DEPICT MID-
LEVEL CIRCULATION OVER SOUTHWEST/SOUTHCENTRAL WYOMING EARLY TUESDAY.
SUSPECT THAT SHOWERS WILL PERSIST OVERNIGHT AND PRIOR TO ONSET OF
DEEPER CONVECTION TUESDAY AFTERNOON. HAVE AT LEAST TRIED TO TREND IN
THAT DIRECTION WITH PRECIP FORECAST ACROSS SOUTHERN WYOMING FROM 12Z-
18Z/TUESDAY. THIS CIRCULATION WILL SLOWLY DRIFT EAST TUESDAY
AFTERNOON AND EVENING...AND THEREFORE HAVE INCREASED PRECIP CHANCES
GENERALLY ALONG AND EAST OF A LINE FROM ROCK SPRINGS TO CASPER.
INSTABILITY PARAMETERS LOOK BETTER FOR MORE WIDESPREAD CONVECTION
THROUGH TUESDAY EVENING...BUT WIND PROFILES REMAIN UNIMPRESSIVE FOR
ANYTHING MORE THAN TYPICAL SUMMER THUNDERSTORMS. WEAK SHORTWAVE TO
OUR NORTH WILL NUDGE A WEAK COLD FRONT SOUTH ACROSS THE NORTHERN AND
CENTRAL ZONES WEDNESDAY MORNING. THIS BOUNDARY COULD BE THE FOCUS
FOR AFTERNOON CONVECTION...PARTICULARLY ACROSS THE BIG HORN BASIN
AND JOHNSON. BEST DYNAMICS WILL ALSO BE ACROSS THE NORTH WHERE
SHORTWAVE ENERGY IS EXPECTED TO BE IN PLAY. SPEED SHEAR PROFILES
WILL STILL REMAIN UNIMPRESSIVE...BUT DIRECTIONAL SHEAR WILL BE MORE
FAVORABLE WITH NORTHERLY TO EASTERLY LOWER LEVEL FLOW. OVERALL...
WEDNESDAY LOOKS TO BE A TYPICAL SUMMER DAY IN WYOMING WITH
CONVECTION BEING SCATTERED AND DIURNALLY DRIVEN. AN UPPER LOW WILL
BEGIN TO MOVE ONSHORE IN CALIFORNIA THURSDAY CAUSING THE UPPER FLOW
TO BACK MORE TO THE SOUTHWEST. THUS...IT LOOKS TO BE DRIER AND
WARMER FOR THURSDAY. BEST CHANCE FOR SHOWERS AND STORMS WILL BE
ACROSS THE WEST BOTH THURSDAY AND FRIDAY. THE LOWER ATMOSPHERE WILL
DRY ACROSS SOUTHWEST WYOMING FRIDAY AS GUSTY SOUTHWEST WIND
INCREASES IN RESPONSE TO THE UPPER LOW TRACKING ACROSS THE GREAT
BASIN. FRIDAY SHOULD BE THE WARMEST DAY OF THE WEEK. WARMER MID-
LEVEL TEMPERATURES COMBINED WITH THE GUSTY WIND AND DRYING
ATMOSPHERE COULD LEAD TO WARMER TEMPERATURES THAN WHAT ARE CURRENTLY
FORECAST. SATURDAY WILL BE JUST A BIT COOLER WITH A BETTER CHANCE OF
CONVECTION ACROSS NORTHWEST WYOMING AS THE UPPER LOW MOVES ACROSS
THE WESTERN FORECAST AREA. BOTH THE GFS AND ECMWF SOLUTIONS OFFERED
TODAY ARE QUICKER WITH THE PROGRESSION OF THIS UPPER LOW.
THEREFORE...SATURDAY NOW APPEARS COOLER THAN WHAT IT DID WITH THE
MODEL RUNS FROM YESTERDAY. POTENTIALLY NEXT SUNDAY COULD BE A
PLEASANT DAY IN THE WAKE OF THE DEPARTING UPPER LOW.

&&

.AVIATION.../00Z ISSUANCE/

PREVAILING MVFR TO IFR CEILINGS AND VISIBILITY REDUCED IN RAIN
MIXED WITH SNOW ABOVE 9000 FEET...AND MIST WILL OBSCURE THE
MOUNTAINS ACROSS WESTERN AND CENTRAL WYOMING. THE LOWER ELEVATIONS
WILL SEE AREAS OF MVFR CEILINGS INCREASE IN COVERAGE BECOMING
PREVAILING BETWEEN 02Z AND 06Z WITH RAIN AND MIST INCREASINGLY
REDUCING VISIBILITIES. ALL AIRPORTS SHOULD EXPERIENCE MVFR
CEILINGS WITH TEMPORARY IFR CEILINGS FROM 06Z TO 15Z. ABOVE 9000
FEET SNOW WILL LIKELY MIX WITH THE RAIN. THIS AFTERNOON AND EARLY
EVENING EMBEDDED THUNDERSTORMS ARE LIKELY WITH STRONG OUTFLOW
WINDS AND SMALL HAIL. OVERALL NORTHEAST WINDS WILL BLOW 15 TO 25
MPH ACROSS THE NORTH AND EAST SPREADING INTO THE SOUTHWEST AFTER
02Z. THE BRISK WINDS WILL PRODUCE AREAS OF LOW LEVEL WIND
SHEAR...ESPECIALLY IN AND NEAR THE MOUNTAINS.

&&

.FIRE WEATHER...

UNSEASONABLY COOL CONDITIONS WITH WIDESPREAD SHOWERS...AND SOME
SNOW ABOVE 9000 FEET IS IN STORE FOR TONIGHT AND MONDAY. ABOVE
9500 FEET SNOW ACCUMULATIONS OF 3 TO 6 INCHES IS POSSIBLE.
VERY HIGH RELATIVE HUMIDITY WITH LOW MIXING HEIGHTS AND POOR
TO FAIR SMOKE DISPERSAL IS EXPECTED.

&&

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

$$

SHORT TERM...C.BAKER
LONG TERM...CNJ
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER



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