Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 310819 CCA
AFDRIW

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE RIVERTON WY
219 AM MDT MON AUG 31 2015

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT

THE THUNDERSTORMS THAT OCCURRED EARLIER THIS EVENING WERE FAST MOVING
WITH HEAVY RAINFALL BUT WITH A SHORT RESIDENCE TIME AND FREQUENT
LIGHTNING ALONG WITH UP TO 40 MPH WIND GUSTS. THE FROPA AND
HAS OCCURRED AND THE SHOWERS HAVE EXITED OFF TO THE EAST AND
DISSIPATED. CONFLUENT FLOW HAS TAKEN OVER. TODAY SOME INSTABILITY
WILL LINGER IN THE FAR SOUTH AND UP INTO SOUTHWEST NATRONA COUNTY
WHERE ISOLATED T STORMS ARE EXPECTED WITH SOME CONVECTION
STREAMING OFF THE UINTAS INTO SOUTHERN SWEETWATER COUNTY. ON
TUESDAY EXPECT ISOLD T STORMS ONLY IN THE NW MTNS WHEN CAPES
INCREASE SLIGHTLY BUT ARE NOT EXPECTED TO MOVE OFF THE MTNS.
WEDNESDAY WILL FEATURE INCREASE SOUTHWEST WINDS AS A CLOSED LOW
MOVES INLAND INTO BC AND THE ASCT TROUGH MAKES LANDFALL ONTO THE
PAC NW COAST THUS INCREASING OUR SOUTHWEST GRADIENT. TEMPS WILL BE
SLIGHTLY COOLER TODAY AND THEN BEGIN A WARMING TREND TUESDAY WITH
WEDNESDAY BEING THE WARMEST DAY OF THE PERIOD.

.LONG TERM...THURSDAY THROUGH MONDAY

MAJOR MEDIUM RANGE DIFFERENCES TONIGHT AS TO THE EVOLUTION OF OUR
LATE WEEK TROUGH. THE MODELS DO AGREE THAT THERE WILL BE A COLD
TROUGH OVER THE PACNW/NRN ROCKIES TO START THE PERIOD BUT HOW THIS
TROUGH TRANSLATES EWD WITH TIME IS WHERE THEY DEPART SIGNIFICANTLY.
THE GFS IS THE FASTEST TO MOVE THIS TROUGH OUT OF THE WAY BY
SATURDAY NIGHT WHILE THE ECMWF/GEM DON`T SWING THE TROUGH THROUGH
UNTIL MONDAY MORNING. THE FIRST SHORTWAVE THAT GETS KICKED OUT BY
THE DEVELOPING COLD TROUGH SHOULD LIFT NE ACROSS THE NRN ROCKIES
THURSDAY INTO THURSDAY NIGHT LEADING TO THE FRONT SAGGING SWD INTO
OUR NRN ZONES BEHIND THIS WAVE. THE GFS THEN KEEPS THIS FRONT IN THE
FAR NORTH PRETTY MUCH THROUGH THE PERIOD WITH SHARPLY COOLER TEMPS
BEHIND IT. THE ECMWF WASHES IT OUT EXCEPT MAYBE NEAR THE NRN BORDER
AS IT DEVELOPS AN INTENSE UPPER LOW OVER IDAHO ON SATURDAY THAT
LIFTS ACROSS THE PARK SATURDAY NIGHT WITH -4C AIR AT H7. LEANING
TOWARDS A STRONGER...SLOWER TROUGH...MAYBE NOT ECMWF STRONG...BUT
MORE TOWARDS THAT TIMING. WILL HAVE TO LOOK AT THIS AGAIN TONIGHT
AND HIT THE POPS MUCH HARDER IF THESE TRENDS CONTINUE AND THE MODELS
COME INTO BETTER AGREEMENT. POTENTIAL FOR A COLD LABOR DAY WEEKEND
WITH COLD RAIN AND MOUNTAIN SNOW IS STILL QUITE POSSIBLE IN THE
NORTHWEST PART OF WYOMING INCLUDING YELLOWSTONE NATIONAL PARK.
OTHERWISE...STILL WARM AND BREEZY TO WINDY AHEAD OF THE FRONT
THURSDAY AND IN THE SOUTH THROUGH AT LEAST FRIDAY BEFORE COOLER TO
COLDER AIR FILTERS IN. THE  WEST AND NORTH WILL SEE THE LONGEST
PERIOD OF COOLER WEATHER AND POTENTIALLY DOWNRIGHT COLD IN YNP OVER
THE WEEKEND.

&&

.AVIATION.../12Z ISSUANCE/

A COLD FRONT WILL PLUNGE SOUTH ACROSS NORTH AND CENTRAL WYOMING THROUGH 09Z.
GUSTY NORTH WIND AT 15 TO 25 KT WILL FOLLOW THE FRONT VCNTY AND
NORTH OF A KGEY TO KBYG LINE WITH WINDS NOT QUITE AS STRONG
FURTHER SOUTH. A FEW THUNDERSTORMS WILL ALSO CONTINUE VCNTY AND
SOUTH OF INTERSTATE 80 THROUGH 9Z. WINDS WILL DIMINISH BY 12Z.

ON MONDAY...ISOLATED TO WIDELY SCATTERED THUNDERSTORMS WILL DEVELOP MONDAY
AFTERNOON VCNTY OF A KRKS-KCPR LINE. SURFACE HIGH PRESSURE WILL
KEEP NORTHERN WYOMING UNDER PREVAILING SKC-FEW FL150-200
CONDITIONS AND S-SE WINDS AROUND 10KTS. THUNDERSTORM ACTIVITY WILL
MOSTLY END ACROSS THE SOUTH BY 3Z TUESDAY.

&&

.FIRE WEATHER...

IT WILL BE DRY TODAY BEHIND THIS MORNINGS COOL FRONT BUT A BIT
COOLER. THERE WILL BE SOME 20 MPH BREEZES IN THE AFTERNOON BUT RED
FLAG CONDITIONS ARE NOT EXPECTED. FOR THE REST OF THE WEEK THE
MINIMUM RELATIVE HUMIDITY WILL BE MAINLY IN THE TEENS AT THE LOWER
ELEVATIONS EAST OF THE DIVIDE AND 20S WEST. SOUTHWEST WINDS WILL
INCREASE WEDNESDAY OUT AHEAD OF THE NEXT DEVELOPING PACIFIC
TROUGH.

&&

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

&&

$$

SHORT TERM...LIPSON
LONG TERM...PS
AVIATION...AEM
FIRE WEATHER...LIPSON



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