Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 210455
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1055 PM MDT MON APR 20 2015

.SHORT TERM...TONIGHT THROUGH TUESDAY (ISSUED AT 224 PM MDT)

OVERALL THE CALMEST AND DRIEST PERIOD THROUGH THE WEEK WILL BE
TONIGHT AND TOMORROW. THERE COULD STILL BE A FEW SHOWERS OVER THE
HIGHER ELEVATIONS AND ACROSS THE SOUTH THIS EVENING AND AGAIN
TOMORROW AFTERNOON BUT NOT MUCH IMPACT IS EXPECTED FROM THIS
ACTIVITY. WINDS WILL BE ON THE LIGHT SIDE AND TEMPERATURES WILL BE
SEASONAL BUT SLIGHTLY WARMER ON TUESDAY THAN THEY WERE TODAY.

EASTERLY WINDS SET UP AGAIN ACROSS SWEETWATER COUNTY TONIGHT. THIS
COULD ADVECT IN MORE MOISTURE AND FOG FROM THE FRESH SNOWPACK EAST
OF RAWLINS WHICH COULD ENCOURAGE MORE FOG TO FORM ALONG THE I80
CORRIDOR FROM GREEN RIVER EAST.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY

QUIET START TO THE PERIOD WITH LIMITED POTENTIAL FOR MAINLY A FEW
SHOWERS IN AND NEAR THE MOUNTAINS TUE EVENING. ON WEDNESDAY...A
PIECE OF THE OFFSHORE CA LOW MAY LIFT NEWD INTO UTAH AND WEAKEN BUT
BRING SOME ADDITIONAL MID LEVEL MOISTURE INTO THE MIX AND PERHAPS A
LITTLE LOWER LEVEL MOISTURE WITH TIME. NOT MUCH BUT A LITTLE. SO A
LITTLE BETTER MOISTURE AND WARMER TEMPS WITH STILL COOL MID LEVELS
RESULTS IN AT LEAST SOME WEAK INSTABILITY ALONG AND WEST OF THE
DIVIDE WED AFTERNOON. ANYTHING EAST OF THE DIVIDE WILL LIKELY BE
CONFINED TO THE MOUNTAINS...IF IT EVEN OCCURS. ON THURSDAY...
MOISTURE HANGS AROUND THE AREA AS THE UPPER LOW MOVES INTO AZ AND
THAT POTENTIAL REMNANT VORT MAX HANGS AROUND OUR SRN OR SERN ZONES.
GENERAL TREND THURSDAY IS A LITTLE ADDITIONAL MOISTURE LEADING TO A
LITTLE MORE INSTABILITY AND PROBABLY THE BEST CHANCE FOR SHOWERS AND
ISOLATED TSTMS. ONE OTHER THING TO WATCH IS THE POTENTIAL FOR RETURN
FLOW MOISTURE TO MOVE IN ON SE WINDS INTO OUR FAR ERN ZONES THURSDAY
OR FRIDAY. THE COMBINATION OF THE DESERT SW LOW MOVING TOWARDS SERN
CO RESULTING IN LEE SIDE CYCLOGENESIS AND PERSISTENT UPPER HIGH OVER
SRN CANADA RESULTS IN AN INCREASED SE FLOW TO OUR EAST. BOTH THE GFS
AND NAM ARE TRYING TO NOSE THIS HIGHER PW AIR NWWD THURSDAY OR
FRIDAY INTO NATRONA AND JOHNSON COUNTY. NO SHEAR OF ANY CONSEQUENCE
TO DEAL WITH AS WINDS LOOK TO REMAIN LIGHT BUT TSTM POTENTIAL WILL
INCREASE IF THIS MOISTURE CAN MAKE IT THIS FAR WEST. THE 12Z GFS
ALSO THREW ANOTHER NEW WRINKLE IN THE MIX WITH STUBBORN WAVE/VORT
THAT MOVES UP THURSDAY THEN GETS LOST IN THE WEAK FLOW RIGHT OVER
THE AREA BETWEEN LANDER AND DUBOIS ON FRIDAY. THE GEM HAS A WEAK
CIRCULATION IN JOHNSON COUNTY AND THE ECMWF HAS AN ELONGATED TROUGH
OVER OUR FAR NRN/NERN ZONES. DUE TO THE UNCERTAINTY WILL MAKE
LIMITED CHANGES WITH CHANCE POPS FOR THE MOUNTAINS AND HIGHER
TERRAIN AND GENERALLY 20-30 PERCENT ELSEWHERE. AS WE MOVE INTO
SATURDAY...WEAKENING TROUGH/FRONT IS STILL FORECAST TO MOVE EAST
ACROSS THE AREA WITH A CHANCE OF MOUNTAIN SHOWERS WITH A FEW ACROSS
THE LOWER ELEVATIONS AND SOME GUSTY TO STRONG WIND WITH FRONTAL
PASSAGE. ANOTHER WEAK SEWD MOVING RIPPLE SUNDAY COULD KEEP A FEW
SHOWERS AROUND INTO SUNDAY BEFORE RIDGE DEVELOPS OVER THE AREA FOR
EARLY NEXT WEEK. WARMER AND DRY TO END THE MEDIUM RANGE PERIOD WITH
THE NEXT SYSTEM NOT POISED TO ARRIVE UNTIL AT LEAST NEXT TUESDAY.

&&

.AVIATION.../06Z ISSUANCE/

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

SCATTERED SHOWERS AND ISOLATED STORMS WILL DEVELOP TUESDAY AFTERNOON
OVER OR ALONG THE ABSAROKA AND WIND RIVER MOUNTAINS. A FEW SHOWERS
WILL ALSO OCCUR IN THE BIGHORN MOUNTAINS. ISOLATED SHOWERS MAY
OCCUR FROM NEAR A KCOD TO KLND LINE LATE TUESDAY AFTERNOON INTO THE
EVENING HOURS. EXPECT OCCASIONAL MOUNTAIN OBSCURATION TUESDAY
AFTERNOON INTO THE EVENING. MOST OF THE SHOWERS WILL DISSIPATE BY
06Z WED. VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH
THE PERIOD. THERE MAY BE LOCAL MVFR CONDITIONS OVER AND NEAR THE
MOUNTAINS.

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

SCATTERED SHOWERS WILL DEVELOP OVER THE WESTERN MOUNTAINS AFTER 19Z
WITH ISOLATED THUNDERSTORMS. THE ACTIVITY WILL DECREASE AFTER 03Z
WED. TERMINAL SITES MAY SEE SHOWERS AT TIMES FROM 21Z UNTIL 06Z WED.
EXPECT OCCASIONAL MOUNTAIN OBSCURATION TUESDAY AFTERNOON INTO THE
EVENING. VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH
THE PERIOD. THERE MAY BE LOCAL MVFR CONDITIONS OVER AND NEAR THE
MOUNTAINS.

.FIRE WEATHER...

TODAY AND TUESDAY LOOK LIKE THE DRIEST AND MOST STABLE DAYS OF THE
WEEK. OTHERWISE...THERE WILL BE A CHANCE FOR SHOWERS OFF AND
ON...ESPECIALLY AFTER WEDNESDAY BUT WITH A LOW CHANCE OF ANY WETTING
RAIN UNTIL LATE IN THE WEEK. OTHERWISE THERE ARE NO MAJOR WIND
EVENTS OR SIGNIFICANT LIGHTNING EPISODES ON THE HORIZON.

&&

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

&&

$$

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





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