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FXUS65 KRIW 141740
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1139 AM MDT TUE MAY 14 2013

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
A VIGOROUS VORT MAX ALONG THE WESTERN MONTANA CANADIAN BORDER
WILL TRACK EAST ALONG THE REST OF THE BORDER TODAY. THE FIRST OF
TWO DRY COLD FRONTS THAT WILL BE EJECTED BY THIS VORT/SHORTWAVE IS
NOW TRACKING SOUTH ACROSS MONTANA AND WILL PUSH SOUTH ACROSS
WYOMING THIS MORNING. NORTH WINDS SHOULD INCREASE IN SPEED IN
JOHNSON COUNTY THIS MORNING WITH 3 HOURLY 6MB SURFACE PRESSURE
RISES THERE BEHIND THE FRONT. THE SECOND COLD FRONT WILL PUSH
SOUTHWEST ACROSS AREAS EAST OF THE DIVIDE THIS EVENING AND WASH
OUT BY THE TIME IT REACHES THE DIVIDE. 3 HOURLY 6MB SURFACE
PRESSURE RISES WILL COVER A WIDER AREA THIS EVENING SO MORE OF AN
AREA WILL EXPERIENCE THE POST FRONTAL WINDS BY THEN.
HOWEVER...WEST SOUTHWEST WINDS WILL BLOW OUT AHEAD OF THIS NEXT
SURFACE BOUNDARY ACROSS THE SOUTHERN WIND CORRIDOR TODAY. HIGH
TEMPERATURES TODAY WILL BE 15 DEGREES COOLER IN JOHNSON COUNTY
TODAY...10 DEGREES COOLER IN THE BIG HORN BASIN AND ABOUT 5
DEGREES COOLER ELSEWHERE EAST OF THE DIVIDE TODAY. TEMPERATURES
WILL BE 5 DEGREES COOLER IN SWEETWATER COUNTY...THE UPPER GREEN
RIVER BASIN...7 OR 8 DEGREES COOLER IN THE STAR VALLEY...AND ABOUT
10 DEGREES COOLER IN THE JACKSON VALLEY AND YELLOWSTONE PARK.
EXPECT SIMILAR TEMPERATURES ON WEDNESDAY. EXPECT ISOLATED
AFTERNOON AND EVENING THUNDERSTORMS WEDNESDAY AS A WEAK VORT LOBE
TRACKS ACROSS THE REGION. THEN ON THURSDAY A TROUGH NOW WAY OFF
THE PACIFIC COAST WILL TRACK EAST AND REACH THE PACIFIC COAST AND
EJECT A LEAD SHORTWAVE THAT WILL CATCH UP TO ANOTHER SLOWER MOVING
WEAKER SHORTWAVE AND WILL INCREASE THE CHANCES OF THUNDERSTORMS
LATE THURSDAY...MAINLY OVER THE HIGHER ELEVATIONS. THESE STORMS
WILL LINGER INTO THE NIGHT AS THE MAIN TROUGH DRAWS CLOSER TO THE
GREAT BASIN TURNING OUR FLOW TO THE SOUTHWEST. AN ASSOCIATED COLD
FRONT WILL ENHANCE LIFT.

.LONG TERM...FRIDAY THROUGH TUESDAY
HIGHER AMPLITUDE PATTERN LOOKS TO BE DEVELOPING AGAIN IN THE MEDIUM
RANGE PERIOD WITH MORE ACTIVE WEATHER ONCE AGAIN EXPECTED FOR MUCH
OF THIS PERIOD AND POTENTIALLY BEYOND. MODELS DIVERGE EARLY NEXT
WEEK WITH THE ECMWF SHOWING A STRONGER SECONDARY SHORTWAVE THAT
COMES DOWN IN THE NW FLOW BEHIND OUR WEEKEND SYSTEM. THE ECMWF
EVOLUTION LOOKS VERY POSSIBLE WITH BUILDING RIDGE OFFSHORE AND SPLIT
OVER THE ROCKIES WITH A HIGH OVER LOW LOOK. COULD EASILY SEE THE GFS
LEANING MORE THIS WAY WITH TIME. GAVE THE ECMWF SOME WEIGHT FOR
EARLY NEXT WEEK WHICH MEANS HIGHER POPS IN THE CENTRAL ZONES WHERE
UPSLOPE COULD DEVELOP. THE ECMWF IS QUITE BULLISH NEXT SUNDAY NIGHT
AND MONDAY WITH A CLOSED CIRCULATION AND PLENTY OF PRECIPITATION ON
CENTRAL WYO. THE GFS HAS A WEAKER DISTURBANCE IN THE COOL NW FLOW
SUNDAY NIGHT AND MONDAY BEFORE SHORTWAVE RIDGING MOVES IN MONDAY
NIGHT. BIG DIVERGENCE CONTINUES ON TUESDAY WITH THE ECMWF SHOWING A
DEFORMATION AXIS ACROSS THE AREA WITH A WEAK DISTURBANCE ACROSS MT
AND FAR NRN WYOMING WHILE THE GFS HAS A SW FLOW AHEAD OF YET ANOTHER
CLOSED LOW OVER THE PACNW. THE ECMWF IS SHOWING THIS SYSTEM JUST
FARTHER NORTH IN SWRN B.C. SCATTERED TO NUMEROUS SHOWERS AND SOME
THUNDERSTORMS FRIDAY AND SATURDAY ACROSS MUCH OF THE
AREA...ESPECIALLY WEST AND NORTH. IF THE ECMWF COMES TO
FRUITION...CONDITIONS WILL DETERIORATE FURTHER IN THE CENTRAL ZONES
LATE SUNDAY INTO MONDAY WITH WIDESPREAD BASIN RAIN AND
MOUNTAIN/FOOTHILL SNOW. THE GFS WOULD STILL PRODUCE A FAIR AMOUNT OF
SHOWERS AND SOME THUNDERSTORMS SUNDAY...DECREASING ON MONDAY. BUMPED
UP THE POPS SUNDAY NIGHT AND MONDAY AS MENTIONED TO GIVE AT LEAST
SOME WEIGHT TO THE ECMWF DURING THIS PERIOD. EVEN MORE CHALLENGING
BY TUESDAY WITH A GENERALLY DRY SW FLOW ON THE GFS AND ANOTHER
DISTURBANCE IN THE NW FLOW SHOWN THE ECMWF. ADDED IN SOME ISOLATED
SHOWERS AND THUNDERSTORMS MAINLY OVER THE MOUNTAINS AND WEST FOR
NOW.

&&

.AVIATION.../18Z ISSUANCE/
VFR CONDITIONS WILL CONTINUE THROUGH 12Z WEDNESDAY. WEAK COOL FRONT
WILL TRY TO PUSH INTO NWRN WY TONIGHT...BUT WILL MOSTLY STALL AND
WASH OUT BEFORE DEVELOPING CYCLONE OVER SW CONUS PUSHES INTO SWRN WY
WITH TROF/FRONT STRETCHING TO NE WY...EFFECTIVELY HALTING THE
PROGRESS OF THE COOL FRONT . ADDITIONALLY...HEIGHT FALLS ALOFT WILL
KEEP ATMOSPHERE COOLER ALOFT AND MORE UNSTABLE TOMORROW THAN TODAY.
WE CAN EXPECT ISOLATED THUNDERSTORMS FOR MOST OF THE TERMINALS ON
WEDNESDAY EXCEPT IN AND AROUND CPR WHICH MAY EXPERIENCE MORE IN THE
WAY OF SCATTERED COVERAGE DUE TO INCREASED MOISTURE AND BETTER
INSTABILITY OVER THE MEDICINE BOW AND GREEN MOUNTAIN RANGES.


&&

.FIRE WEATHER...
A COLD FRONT WILL MOVE SOUTH TODAY. AS A
RESULT...HIGH TEMPERATURES TODAY WILL BE 15 DEGREES COOLER IN
JOHNSON COUNTY TODAY...10 DEGREES COOLER IN THE BIG HORN BASIN AND
ABOUT 5 DEGREES COOLER ELSEWHERE EAST OF THE DIVIDE TODAY.
TEMPERATURES WILL BE 5 DEGREES COOLER IN SWEETWATER COUNTY...THE
UPPER GREEN RIVER BASIN...7 OR 8 DEGREES COOLER IN THE STAR
VALLEY...AND ABOUT 10 DEGREES COOLER IN THE JACKSON VALLEY AND
YELLOWSTONE PARK. EXPECT ISOLATED THUNDERSTORMS LATE
WEDNESDAY...MAINLY IN THE HIGH COUNTRY. ON THURSDAY EXPECT A BETTER
CHANCE OF LATE DAY THUNDERSTORMS LINGERING WELL INTO THE NIGHT AS A
MORE SIGNIFICANT TROUGH OF LOW PRESSURE APPROACHES FROM THE GREAT
BASIN.


&&

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

$$

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