Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 200923
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
323 AM MDT WED AUG 20 2014

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
THE MID LEVEL CIRCULATION ASCT WITH THE SHORTWAVE TROUGH...WHICH IS
TRACKING EAST ACROSS WESTERN WY...APPEARS TO BE OVER THE RED DESERT
ALONG THE BACK EDGE OF THE WIDESPREAD AREA OF PATCHY LIGHT RAIN
EXTENDING FROM CODY TO RIW TO RKS THAT USED TO BE CONVECTIVE
ACTIVITY OVER IDAHO BEFORE THE PRECIP MOVED INTO MORE STABLE AIR
OVER WY. THE DRY SLOT WILL MOVE NORTHEAST INTO CENTRAL WY AND INTO
JOHNSON COUNTY ALONG WITH THE MID LEVEL CIRCULATION BY 12Z THIS
MORNING. ADDITIONAL RAIN SHOWERS WILL LINGER IN THE MOUNTAINS LATER
INTO THE MORNING AS THE BACK EDGE OF THE SHORTWAVE TROUGH CLEARS
THROUGH. THEN BEHIND THIS AREA OF EXITING CLOUDINESS...CONVECTION
WILL FIRE RAPIDLY ACROSS WESTERN WY WITHIN THE DIFLUENT WEST
SOUTHWESTERLY FLOW AHEAD OF THE NEXT APPROACHING VORT LOBE ROTATING
AROUND THE BASE OF THE MAIN TROUGH OVER SOUTHWEST CANADA WHERE THE
BEST CAPES WILL BE. NUMEROUS TO SCT SHOWERS AND THUNDERSTORMS ARE
EXPECTED IN WESTERN WY WITH MAINLY SCT EAST. TOTAL TOTALS WILL BE
FAVORABLE FOR WIDESPREAD CONVECTION. THEN ON THURSDAY ANOTHER VORT
LOBE WILL ROTATE AROUND THIS TROUGH FOR MORE CONVECTION MAINLY IN
THE NORTH AND WEST. THEN ON FRIDAY MORNING...THE MAIN TROUGH WILL
CLOSE OFF OVER WASHINGTON AND TRACK TO IDAHO BY FRIDAY NIGHT. THE
GFS HAS COME MORE INTO LINE WITH THE FASTER ECMWF WITH THIS SOLN. AS
THE DYNAMICS...INCLUDING LEFT FRONT QUAD JET DYNAMICS...AND
INCREASING SOUTHWEST DIFLUENT FLOW INCREASE WITH THIS APPROACHING
LOW...WITH ITS ASCT WEAK H7 CIRCULATION APPROACHING NW WY...SHOWERS
AND THUNDERSTORMS WILL BECOME MORE WIDESPREAD FRIDAY AND FRIDAY
NIGHT ALONG WITH COOLER TEMPS AS A RESULT OF THE ADDED CLOUDS AND
PRECIP. A SFC LOW WILL TRACK ACROSS CASPER ASCT WITH THE SOUTHERN
STREAM H5 LOW THAT THE GFS HAS OVER CO ADDING TO THE DYNAMICS AND
PULLING SOME COOLER AIR BEHIND IT FRIDAY EVE. THE ECMWF HAS THE H5
LOW OVER AZ DURING THIS TIME. COOLER AIR WILL FILTER INTO THE
NORTHWEST PORTION OF WY FRI NT AS THE MAIN PAC NW WEATHER SYSTEM
NEARS WITH H7 TEMPS EXPECTING TO DROP TO 2.2C BY 12Z SAT OVER NW WY
WHERE SNOW LEVELS COULD DROP TO 9500 FEET.

.LONG TERM...SATURDAY THROUGH WEDNESDAY
SIGNIFICANT COOL LATE AUGUST TROUGH IS EXPECTED TO SWING ACROSS
THE AREA ON SATURDAY WITH A GOOD CHANCE OF SHOWERS AND SOME
THUNDERSTORMS ALONG WITH SKIFF OF SNOW TO THE HIGHER MOUNTAINS.
SNOW LEVELS WHICH SHOULD BE ABOVE 10-11K FEET DURING THE DAY
SATURDAY WILL LOWER SATURDAY EVENING TO AS LOW AS 8.5-9K FEET
IN THE FAR NRN MOUNTAINS. SUNDAY WILL BE DRIER AND MORE STABLE
EXCEPT IN THE NW WHERE NEXT APPROACHING TROUGH IS ALREADY
SPREADING SOME MOISTURE AND FORCING INTO THE AREA. NEXT COOL
TROUGH WILL BRING IN ANOTHER ROUND OF SHOWERS AND SOME
THUNDERSTORMS MONDAY INTO TUESDAY FOR MANY AREAS...ESPECIALLY
THE MOUNTAINS...NORTH HALF AND THE SERN CORNER. ANOTHER COUPLE
UNSEASONABLY COOL DAYS WITH THIS TROUGH AS H7 TEMPERATURES DROP
WELL DOWN INTO THE SINGLE DIGITS. ANOTHER SKIFF OR MORE OF
MOUNTAIN SNOW IS VERY POSSIBLE AGAIN ABOVE 10-11K MONDAY THROUGH
TUESDAY AT TIMES. ECMWF HAS MORE RIDGING BY WEDNESDAY WHILE THE
GFS IS STILL SHOWING A MORE MOIST NW FLOW. WILL KEEP IT FAIRLY DRY
FOR NOW WITH ONLY A HINT OF HIGHER MOUNTAIN SHOWERS IN THE NRN
MOUNTAINS.

&&

.AVIATION.../12Z ISSUANCE/
AN UPPER LEVEL LOW PRESSURE SYSTEM WILL LIFT INTO EASTERN MONTANA
THIS MORNING WITH SHOWER ACTIVITY DECREASING ACROSS NORTHERN WYOMING
12Z-15Z.   AN UPPER TROUGH OVER THE NW U.S. WILL EJECT THE NEXT
DISTURBANCE ACROSS IDAHO THIS AFTERNOON AND ACROSS NORTHERN WYOMING
TONIGHT.  EXPECT ISOLATED TO SCATTERED THUNDERSTORMS TO SPREAD INTO
WESTERN WYOMING THROUGH THE AFTERNOON WITH THE BETTER COVERAGE VCNTY
AND NORTH OF A KJAC-KDUB LINE.  THIS ACTIVITY WILL SPREAD INTO NORTH
CENTRAL WYOMING THROUGH THE LATE AFTERNOON AND EVENING.  SHOWER AND
THUNDERSTORM ACTIVITY WILL BE MUCH MORE ISOLATED ACROSS CENTRAL
WYOMING WED AFTN/EVE...VCNTY KLND-KRIW-KCPR.

&&

.FIRE WEATHER...
WAVES OF ENERGY COMING OFF THE PACIFIC BISECTING MONSOON ENERGY WILL
KEEP A GOOD CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS GOING ALL
WEEK. MIN RH WILL GENERALLY RUN IN THE 20S AT THE LOWER ELEVATIONS
...EXCEPT 30S IN THE WESTERN VALLEYS...THROUGH THURSDAY BEFORE INCREASING.
A COOLER PACIFIC WEATHER SYSTEM WILL BRING MORE WIDESPREAD
SHOWERS AND THUNDERSTORMS FRIDAY AND SATURDAY WITH COOLER AIR
FILTERING IN. THE SNOW LEVEL SHOULD LOWER TO 9500 FEET OR SO BY
SATURDAY MORNING IN ZONE 140.

&&

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

&&

$$

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








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