Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 010538
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1138 PM MDT TUE SEP 30 2014

.SHORT TERM...TONIGHT AND WEDNESDAY

PART ONE OF OUR TWO PART STORM SYSTEM IS BRINGING WIDESPREAD RAIN
SHOWERS TO THE LOWER ELEVATIONS OF THE WEST WITH SNOW ABOVE 9K OR
SO. OUR SYSTEM FROM THE PAST COUPLE DAYS IS WRAPPING UP OVER WRN SD
WITH THE OUTER SHIELD WRAPPING SOME CLOUDS BACK INTO NRN AND ERN
JOHNSON COUNTY. WEAK INSTABILITY DEVELOPING OVER ERN IDAHO AND IN
SRN WYO WITH A FEW LIGHTNING STRIKES TO OUR WEST EARLY THIS
AFTERNOON. PART TWO OF OUR STORM HAS THE COLDER AIR WITH -25C COLD
POCKET AT H5. NO SIGNIFICANT CHANGE TO THIS SYSTEM YESTERDAY EXCEPT
FOR THE FACT THAT IT LOOKS LIKE IT WILL BE ABOUT 1 TO 1.5C COLDER
AT H7. INSTEAD OF SNOW LEVELS NEAR 6K FEET IN THE CODY FOOTHILLS
STARTING TO LOOK LIKE THEY WILL LOWER TO AROUND 5K BY TOMORROW
MORNING. UPPER LOW TRACKS INTO ERN IDAHO OVERNIGHT AND THEN IS
STILL FORECAST TO WEAKEN AND BECOME MORE DISORGANIZED DURING THE
DAY WEDNESDAY AS IT TRACKS SE ACROSS OUR AREA. MODERATE QG FORCING
IS STILL EXPECTED TO MOVE INTO THE WEST HALF TONIGHT AND SPREAD SE
DURING THE DAY. THE LOW LEVEL UPSLOPE AND UPPER LEVEL SUPPORT
SHOULD PRODUCE WIDESPREAD PCPN IN THE WEST...MOUNTAINS AND CODY
FOOTHILLS WITH LESSER CHANCES FURTHER SOUTH UNTIL ROUND TWO
ARRIVES DURING THE DAY WEDNESDAY. WITH THE NAM...GFS AND WRF ALL
SHOWING H7 TEMPERATURES DROPPING TO AROUND -5 TO -5.5C AROUND CODY
BY 12Z-15Z WEDNESDAY WITH STEADY PCPN...HAVE OPTED TO CHANGE THE
RAIN TO SNOW ABOVE 5K IN THE CODY FOOTHILLS BY TOMORROW MORNING
WITH SOME LIGHT ACCUMULATION. LOOKS LIKE THE ABSAROKAS ABOVE 9K
WILL GET 3 TO 6 INCHES WITH 1 TO 3 INCHES IN THE FOOTHILLS AND A
SKIFF TO 2 INCHES DOWN TO 5K. AS THIS SYSTEM MOVES FURTHER SOUTH
DURING THE DAY WEDNESDAY...IT WILL BE WARMER AT THE SURFACE IN THE
CENTRAL AREAS BUT THE COLD CORE ALOFT MAY END UP AIDING IN SOME
CONVECTIVE SHOWERS WHICH WITH TEMPERATURES ONLY IN THE 40S TO
AROUND 50 MAY END UP BEING SNOW SHOWERS AT TIMES. OTHERWISE...A
CHILLY...UNSETTLED START TO OCTOBER FOR MOST OF THE AREA WITH SOME
EMBEDDED THUNDER POSSIBLE JUST ABOUT ANYWHERE TOMORROW.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

LINGERING PRECIPITATION POSSIBLE THROUGH WEDNESDAY
NIGHT...ASSOCIATED WITH THE PASSING WAVE OF LOW PRESSURE. SHOWER
ACTIVITY IS EXPECTED TO TAPER OFF OVERNIGHT...WITH BUILDING
NORTHWEST FLOW. MODELS INDICATE AN INCREASED PRESSURE
GRADIENT...ESPECIALLY OVER CENTRAL AND NORTHEASTERN WYOMING. THIS
WILL RESULT IN THE POTENTIAL FOR GUSTY NORTHWEST WIND OVER THE AREA
ON THURSDAY AND THURSDAY NIGHT...ESPECIALLY OVER CENTRAL AND EASTERN
WYOMING.

BUILDING HIGH PRESSURE TAKES OVER THE FORECAST AREA LATE
THURSDAY...WITH GENERALLY DRY CONDITIONS EXPECTED THROUGH THE
REMAINDER OF THE FORECAST PERIOD. TEMPERATURES WILL BE
SEASONABLE...WITH HIGH TEMPERATURES IN THE MID TO UPPER 60S. MODELS
LINE UP WELL DURING THE MEDIUM AND EXTENDED RANGES CONCERNING THE
HIGH PRESSURE AND DRY CONDITIONS.

&&

.AVIATION.../06Z ISSUANCE/

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

A LARGE AREA OF LOW CEILINGS AND SCATTERED TO LOCALLY WIDESPREAD
PRECIPITATION IS EXPECTED TO CONTINUE/DEVELOP ACROSS NORTHERN
WYOMING /KBYG...KCOD...KWRL/ IN WAKE OF A COLD FRONT TONIGHT. THIS
WILL RESULT IN WIDESPREAD MVFR CEILINGS...AS WELL AS IFR REDUCTIONS
MAINLY DUE TO LOW VSBY IN PRECIP. ENOUGH COLD AIR IS EXPECTED THAT A
SNOW COULD OCCUR DOWN TO AROUND 5500 FT WEDNESDAY MORNING. FARTHER
SOUTH ACROSS CENTRAL WYOMING /KCPR...KLND...KRIW/ THERE IS LESS
CERTAINTY OF EXTENT/TIMING OF THE STRATUS DEVELOPING THIS MORNING
AFTER FRONTAL PASSAGE. EITHER WAY...THE BULK OF THE PRECIPITATION
SHOULD BE NORTH OF THOSE TERMINALS THIS MORNING. SCATTERED SHOWERS
AND POSSIBLY AN ISOLATED THUNDERSTORM WILL OCCUR IN THE AFTERNOON
WITH PERSISTENT LOW CEILINGS IN THE 020-040 KFT AGL. THE TROUGH
EXITS THE AREA THIS EVENING WITH IMPROVING CONDITIONS...BUT A MOIST
NORTHWEST FLOW COULD RESULT IN SHOWER ACTIVITY FORMING OVER THE
MOUNTAINS AND PUSHING SOUTHEAST INTO THE LOWER ELEVATIONS THROUGH
ABOUT 06Z THURSDAY. MOUNTAINS WILL BE OBSCURED THROUGH MUCH OF THE
DAY...WITH IMPROVING CONDITIONS LATE IN THE DAY INTO THE OVERNIGHT.

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

SHOWER ACTIVITY WILL BE MOST CONCENTRATED ACROSS THE FAR WEST FOR
THE REMAINDER OF TONIGHT INTO WEDNESDAY MORNING IMPACTING KJAC.
MVFR AND POSSIBLY IFR CONDITIONS WILL BE POSSIBLE IN SNOW AT KJAC
THIS MORNING. THIS SHOWER ACTIVITY IS THEN EXPECTED TO OVERSPREAD
THE REST OF THE WEST/SOUTHWEST WYOMING BETWEEN 16Z AND 20Z...AS THE
MAIN TROUGH BEGINS TO PUSH THROUGH. THIS COULD RESULT IN PERIODS OF
MVFR CONDITIONS...BUT NOT OF CONFIDENCE TO PREVAIL MVFR CONDITIONS
AT ANY TERMINAL. RAPIDLY IMPROVING CONDITIONS ARE EXPECTED BETWEEN
22Z AND 02Z...WITH SKIES TRYING TO CLEAR OUT.  SOME WARM AIR
ADVECTION STRATOCU DECK IS THEN EXPECTED TO DEVELOP OVER PORTIONS OF
FAR WEST WYOMING AFTER 06Z THURSDAY.

&&

.FIRE WEATHER...
WIDESPREAD SHOWERS WILL CONTINUE ACROSS WEST INTO THE EARLY EVENING
AND THROUGH THE NIGHT IN THE NORTHWEST WITH LOWERING SNOW LEVELS.
ISOLATED THUNDERSTORMS ARE POSSIBLE IN THE WEST THE REMAINDER OF THE
AFTERNOON AND MAINLY IN THE NORTHWEST OVERNIGHT. A NEW STORM SYSTEM
IS FAST ON THE HEELS OF OUR CURRENT ONE AND WILL BRING LOWERING SNOW
LEVELS TO NOT ONLY THE FAR WEST BUT ALSO CENTRAL WYOMING LATER
TONIGHT INTO WEDNESDAY MORNING DOWN TO BETWEEN 5 AND 6K FEET. THE
BEST CHANCE FOR WETTING RAINS (OR SNOW) WILL BE IN THE CODY
FOOTHILLS AND OF COURSE AROUND ANY OF THE MOUNTAINS TONIGHT INTO
WEDNESDAY. A CHANCE OF SHOWERS WILL CONTINUE FURTHER SOUTH. ISOLATED
THUNDERSTORMS ARE POSSIBLE INTO THE EARLY EVENING AND AGAIN ON
WEDNESDAY.

&&

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

&&

$$

SHORT TERM...SKRBAC
LONG TERM...BRANHAM
AVIATION...WM
FIRE WEATHER...SKRBAC









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