Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 082121
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
321 PM MDT TUE JUL 8 2014

.SHORT TERM...TONIGHT THROUGH WEDNESDAY

IT DOES NOT LOOK LIKE WE ARE GOING TO REACH CONVECTIVE TEMPERATURE
LATE THIS AFTERNOON FOR THUNDERSTORMS TO DEVELOP...OFTEN THE
COOLING ALOFT THAT TAKES PLACE A LITTLE AFTER SUNSET CAN BE ENOUGH
TO BREAK THE CAP BUT MODEL SOUNDINGS ARE NOT SHOWING THAT THE
COOLING WILL BE ENOUGH EITHER...SO PERHAPS JUST A FEW SHALLOW CU
OVER THE MOUNTAINS WITH SOME SPRINKLES WILL BE IT EARLY IN THE
PERIOD. IT WILL STILL BE FAIRLY DRY TONIGHT AND EARLY TOMORROW
WITH DEW POINTS IN THE THIRTIES TO LOW FOURTIES SO OVERNIGHT LOWS
WILL DIP QUITE A BIT TONIGHT. THE MID LEVEL MOISTURE IS EXPECTED
TO ENCROACH ON THE WEST AND SOUTH AROUND NOON...EARLIER THAN
PREVIOUS RUNS WOULD BRING IT IN...AND IT WILL FIRE OFF A FEW EARLY
STORMS BUT IT WILL STILL BE DRY AT THE SURFACE SO THESE STORMS
WILL BE HIGHER BASED WITH GUSTY WIND POTENTIAL. THE REENFORCEMENTS
REALLY ARRIVE LATE ON WEDNESDAY AS A SHORT WAVE TRAVELLING ALONG
THE TOP OF THE RIDGE ARRIVES. SO WHILE THERE WILL BE SOME ACTION
EARLY...IT SHOULD BE MAINLY A LATE AFTERNOON SHOW.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

SHORTWAVE NOW OVER THE GREAT BASIN WILL TRACK ACROSS SOUTHERN
MONTANA WEDNESDAY EVENING AND OVERNIGHT. MOST CONVECTION WILL BE
DIURNALLY DRIVEN...BUT EXPECT WEAK SHOWERS AND STORMS TO CONTINUE
ACROSS THE FAR NORTHERN MOUNTAINS AND ADJACENT BASINS THROUGH
12Z/THURSDAY. DRIER AIR WILL WORK INTO NORTHWEST WYOMING THURSDAY
BEHIND THIS DEPARTING WAVE. NAM IS MUCH DRIER THAN EITHER THE
ECMWF OR GFS FOR THURSDAY AFTERNOON. FEELING HERE IS THAT THERE
WILL BE ENOUGH LINGERING MOISTURE TO GENERATE AT LEAST ISOLATED
CONVECTION ACROSS THE NORTHWEST. DID GO AHEAD AND TRIM CHANCE OF
SHOWERS ACROSS THAT AREA THURSDAY AFTERNOON AND EVENING. ANOTHER
SOUTHERLY SURGE OF MOISTURE WILL PUSH INTO THE REGION FRIDAY AS
HIGH PRESSURE OVER THE FOUR CORNERS REGION SLIDES SLIGHTLY FARTHER
EAST. PRECIPITABLE WATER VALUES RISE TO AROUND ONE INCH OVER
JOHNSON AND NATRONA COUNTIES WHERE LOW-LEVEL FLOW WILL BE
EASTERLY. THIS AREA ALONG WITH THE HIGHER TERRAIN OF WESTERN
WYOMING WILL BE THE FOCUS FOR THE STRONGEST CONVECTION ON FRIDAY.
SLIGHTLY DRIER AIR BEGINS TO GRADUALLY PUSH INTO SOUTHWEST WYOMING
FRIDAY AND MORE EARNESTLY OVER THE WEEKEND. THIS WILL LIMIT
CONVECTION IN THIS QUADRANT OF THE STATE. THINGS CHANGE A LITTLE
MORE OVER THE WEEKEND AS FLOW LOOKS TO BECOME MORE NORTHWESTERLY.
THIS WILL BE IN RESPONSE TO DIGGING AREA OF LOW PRESSURE MOVING
SOUTH OUT OF CANADA INTO THE HEARTLAND WHILE RIDGE BUILDS
ACCORDINGLY TO OUR WEST. LOW-LEVEL FLOW WILL BE MORE NORTHEASTERLY
THROUGH THE WEEKEND AS A SERIES OF WEAK BOUNDARIES DROP SOUTH
THROUGH WYOMING. DIRECTIONAL SHEAR PROFILES WOULD SUPPORT STRONGER
CONVECTION EAST OF THE DIVIDE SATURDAY...BUT BULK SHEAR LOOKS TO
BE LACKING. ALSO...JET SUPPORT WILL REMAIN TO OUR EAST SO DYNAMICS
WILL BE LIMITED. SATURDAY IS THE MORE LIKELY DAY OF THE WEEKEND
FOR WIDESPREAD CONVECTION AS DRIER AIR WILL PUSH INTO WESTERN
WYOMING FOR SUNDAY. LOOKS LIKE THE NEXT WAVE OF MOISTURE WILL
ROTATE INTO WESTERN WYOMING FOR MONDAY. MEDIUM RANGE MODELS IN
GOOD AGREEMENT UNTIL EARLY NEXT WEEK WHEN DIFFERENCES EMERGE IN
HOW THE UPPER PATTERN WILL EVOLVE. ECMWF ADVERTISES A MERGING OF
ENERGY TO OUR SOUTHWEST WHICH THEN ROTATES NORTH A MORE TROPICAL
AIRMASS FROM THE SOUTHWEST U.S. LARGE SCALE CYCLONIC FLOW
ASSOCIATED WITH DIGGING CANADIAN LOW REMAINS TO OUR EAST IN THIS
SCENARIO. THE GFS PROPOSES TO CARVE OUT MORE OF THE CYCLONIC FLOW
ACROSS WYOMING AS SHORTWAVE ENERGY GELS IN THE NORTHERN ROCKIES
AND THEN PUSHES SOUTH INTO WYOMING FOR TUESDAY. GFS HAS SWUNG
BACK-AND-FORTH SO FOR NOW AM PREFERRING THE ECMWF SOLUTION.
TEMPERATURES THROUGH THE WEEKEND WILL BE AT OR SLIGHTLY BELOW
SEASONAL NORMALS. NORTHWEST FLOW ALOFT WILL LEAD TO A COOLER START
TO NEXT WEEK WITH READINGS 6 TO 12 DEGREES BELOW NORMAL.

&&

.AVIATION.../00Z ISSUANCE/

VFR CONDITIONS WITH RELATIVELY LIGHT WINDS CONTINUE THROUGH THE
NIGHT. A SWATH OF MID LEVEL MOISTURE WILL MOVE SOUTHWEST TO
NORTHEAST AFTER 15Z WED...ENCOURAGING -TSRA DEVELOPMENT
ACROSS THE SOUTH AND WEST FIRST WITH GUSTY OUTFLOW
WINDS...SPREADING NORTH AND EAST AFTER 21Z. SOME OF THESE STORMS
COULD PRODUCE MVFR CIGS AND VSBY.

&&

.FIRE WEATHER...

MONSOONAL MOISTURE ARRIVES TOMORROW...FIRST INTO TETON AND
SOUTHERN RAWLINS DISPATCH AREAS. THE STORMS WILL BE ON THE DRY
SIDE INITIALLY BUT WILL QUICKLY TRANSITION TO MORE WET STORMS
LATER IN THE AFTERNOON AND EVENING. THERE WILL BE A CHANCE FOR A
WETTING RAIN WITH THE THUNDERSTORMS EACH AFTERNOON THROUGH FRIDAY.
THERE WILL CONTINUE TO BE SOME ACTIVITY THROUGH THE WEEKEND AND
INTO NEXT WEEK BUT IT WILL BE MORE ISOLATED. A PATTERN SHIFT LOOKS
POSSIBLE FOR NEXT WEEK TO A COOLER NORTHWEST FLOW PATTERN...IT IS
STILL A STORMY PATTERN FOR US BUT AREAS MORE PRONE TO THIS FLOW
PATTERN...LIKE NORTHERN FREMONT AND NATRONA COUNTIES...ZONES 289
AND 276...AND NORTHERN 415. THE COOLER AIRMASS WILL ALSO ENCOURAGE
HIGHER HUMIDTIES...SO NO ISSUES ARE ANTICIPATED ASIDE FROM THE
INCREASED LIGHTNING ACTIVITY.

&&

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

$$

SHORT TERM...ALLEN
LONG TERM...CNJ
AVIATION...ALLEN
FIRE WEATHER...ALLEN





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