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000
FXUS65 KRIW 282255
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
355 PM MST THU NOV 28 2013

.SHORT TERM...TONIGHT THROUGH FRIDAY

MID AND UPPER LEVEL MOISTURE IN SOUTHWEST FLOW ALOFT WILL
PRODUCE VARIABLE CLOUD COVER OVER WESTERN AND CENTRAL WYOMING
TONIGHT AND FRIDAY.  THE CLOUD COVER WILL HELP MODERATE OVERNIGHT
TEMPERATURES TONIGHT. SOUTHWEST SURFACE WINDS OF 15 TO 25 MPH WILL
DEVELOP FROM ROCK SPRINGS THROUGH CASPER IN THE AFTERNOON FRIDAY.
TEMPERATURES WILL CONTINUE THE SLOW WARMING TREND ON FRIDAY.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

THE WEATHER WILL BE RATHER BENIGN AND DRY ACROSS THE AREA FRIDAY
NIGHT AND SATURDAY WITH THE EXCEPTION OF FAR WESTERN WY WHERE PATCHY
LIGHT SNOWFALL WILL DEVELOP AS THE INCREASING NW FLOW BRINGS IN
INCREASING PACIFIC MOISTURE AND MOISTENS UP THE BOUNDARY LAYER.

THE CIRCULATION AND THE ASSOCIATED FRIGID AIR THAT WAS OFF THE
ALEUTIANS AT 170W 24 HOURS AGO HAS NOW PROGRESSED TO 165W. AS THIS
WEATHER SYSTEM APPROACHES THE INCREASINGLY DIFLUENT FLOW WILL
INCREASE IN SPEED AND BACK TO A MORE WEST NORTHWEST DIRECTION
INCREASING THE SNOWFALL IN FAR WESTERN WYOMING SUNDAY AS A LEAD
SHORTWAVE TRACKS ACROSS THE AREA. SNOWFALL WILL BEGIN TO ACCUMULATE
MORE SIGNIFICANTLY AS THE STRONG LOW CENTER MAKES ITS WAY SOUTHEAST
ALONG THE BC COASTLINE BRINGING DOWN WITH IT FRIGID AIR. AS THE LOW
DRAWS EVER CLOSER...THE SNOWFALL INTENSITY WILL CONTINUE TO INCREASE
IN FAR WESTERN WY WITH SNOWFALL BEGINNING TO ENCROACH UPON FAR
NORTHERN WYOMING AHEAD OF THE ASSOCIATED STRONG COLD FRONT SUNDAY
EVENING. LIGHT SNOWFALL WILL SPREAD SOUTHEAST INTO CENTRAL WYOMING
DURING THE DAY MONDAY BUT NOT BEFORE INCREASING SOUTHWEST WINDS TAKE
PLACE FROM THE RED DESERT TO CPR COINCIDENT WITH THE DEVELOPMENT OF
A STRONG LEE SIDE TROUGH OUT AHEAD OF THIS APPROACHING SYSTEM. EVEN
THREW IN ISOLATED THUNDER FOR YNP ON MONDAY EVENING WITH NEGATIVE
LIFTED INDICES AHEAD OF THE APPROACHING FRONT THERE. THE ASSOCIATED
700MB LOW WILL BE IN THE VCNTY OF YNP DURING THAT TIME FRAME AS
WELL. BY TUESDAY MORNING SNOWFALL WILL LIKELY BE AS PREVALENT EAST
OF THE DIVIDE AS IT WILL BE WEST AFTER THE SNOWFALL SPREADS INTO
NATRONA AND SWEETWATER COUNTIES WITH THE UPPER LOW OVER THE PAC NW
BY THEN ALONG WITH THE SFC LOW PROPAGATING SOUTH ACROSS WYOMING.

THEN WE GET INTRODUCED TO A REAL TASTE OF WINTER BEGINNING TUESDAY
AFTERNOON. AS THE ARCTIC FRONT BEGINS TO NOSE INTO NORTHERN WY
TUESDAY AFTERNOON...HEAVIER SNOWFALL ALONG WITH STRONG NORTH
WINDS...BLOWING AND DRIFTING SNOW AND MUCH COLDER AIR WILL SEEP DOWN
INTO NORTHERN WY. THIS WILL KEEP HIGHS FROM GETTING ABOVE THE TEENS
AND LOW TWENTIES AT THE LOWER ELEVATIONS IN NORTHERN WY WITH 25 TO
30 COMMON ELSEWHERE. ON TUESDAY EVENING THE COLD...WIND AND SNOW
ALONG WITH BITING WIND CHILLS WILL SPREAD INTO ALL AREAS EAST OF THE
DIVIDE AND THEN INTO SWEETWATER COUNTY AFTER MIDNIGHT TUESDAY NIGHT.
ISENTROPIC LIFT RIDING UP AND OVER THE FRONT TUESDAY NIGHT AND EVEN
INTO WEDNESDAY WILL ENHANCE THE SNOWFALL. THE H7 LOW WILL
REESTABLISH ITSELF OVER SLC WEDNESDAY WITH THE SFC LOW TO THE SOUTH
OVER CO. ALONG AND BEHIND THE FRONT...WHICH WILL STALL OUT A LITTLE
BEYOND THE DIVIDE INTO SW WY...DEEPENING UPSLOPE FLOW WILL BE
UNDERWAY AS SNOWFALL FROM THIS MECHANISM GETS FED BY THE ISENTROPIC
LIFT AND Q VECTOR FORCING ABOVE. IN ADDITION...THE BEST DENDRITIC
GROWTH APPEARS TO TAKE PLACE TUESDAY NIGHT THROUGH WEDNESDAY
OVERALL. HIGHS ON WEDNESDAY WILL STRUGGLE TO GET ABOVE THE TEENS
WITH SOME 20S EXPECTED IN SOUTHERN SWEETWATER CO AND THE FAR WESTERN
VALLEYS SOUTH AND EAST OF THE MAIN THRUST OF THE FRONT AS THE FRONT
STALLS OUT. AS TEMPS ALOFT CONTINUE TO FALL WEDNESDAY
NIGHT...SNOWFALL WILL BECOME LIGHTER WITH LESS THAN FAVORABLE
DENDRITIC GROWTH. BY THURSDAY MORNING THE COLDER GFS INDICATES -26C
H7 TEMPS ACROSS N WY WITH THE ECMWF ADVERTISING -21C. THIS COLD
INTRUSION WILL BE THE COLDEST AIR OF THE SEASON THUS FAR WITH ALMOST
ALL AREAS RUNNING ZERO TO 10 BELOW ALONG WITH CHILLING NORTHEAST
WINDS WEDNESDAY NIGHT/THU MORNING. LIGHT SNOWFALL WILL CONTINUE
THURSDAY WITH THE SFC LOW REMAINING TO THE SOUTH OVER SE CO AND THE
SFC HIGH OVER NW MT...LIGHT UPSLOPE SNOW WILL CONTINUE THROUGH
THURSDAY WITH HIGHS IN THE SINGLE DIGITS EAST OF THE DIVIDE AND
TEENS WEST. THE GFS AND THE EURO ARE MORE IN LINE WITH THIS SCENARIO
AND THIS WINTER WEATHER EVENT HAS BEEN ADVERTISED FOR THE LAST
SEVERAL DAYS SO THE OVERALL LEVEL OF CERTAINTY THAT THIS WEATHER
EVENT WILL UNFOLD IS HIGHLY LIKELY. THE COLDEST NIGHT OF THE SEASON
WILL FOLLOW THURSDAY NIGHT WITH FRESH SNOW COVER IN PLACE. THIS
ASSOCIATED LONG WAVE TROUGH SHOWS NO SIGN OF MOVING AWAY FROM THE
WESTERN UNITED STATES FOR THE FORESEEABLE FUTURE. BRING IT
ON!

&&

.AVIATION.../00Z ISSUANCE/

VFR CONDITIONS WITH MAINLY LIGHT WINDS WILL PREVAIL AT THE AIRPORTS
ACROSS WESTERN AND CENTRAL WYOMING THROUGH 18Z FRIDAY.
CONSIDERABLE MID AND HIGH LEVEL CLOUDINESS WILL OCCUR AT
TIMES...PROBABLY THICKER EAST OF THE DIVIDE WHERE LEE ENHANCED
CIRRUS AND ALTOCUMULUS STANDING LENTICULAR CLOUDS WILL OCCUR.
CLOUDS WILL INCREASE OVER THE WESTERN MOUNTAINS FROM 18Z THROUGH
00Z SATURDAY WITH LOCAL MVFR CEILINGS DEVELOPING ABOVE 8500 FEET
WHILE THE REMAINDER OF WESTERN AND CENTRAL WYOMING REMAINS VFR.

&&

.FIRE WEATHER...

VARIABLE MID AND HIGH CLOUDS WILL CONTINUE TO MOVE ACROSS WESTERN
AND CENTRAL WYOMING IN WEST SOUTHWEST FLOW ALOFT.  THE CLOUD COVER
WILL MODERATE TEMPERATURES TONIGHT. FRIDAY WILL CONTINUE THE SLOW
WARMING TREND. THE LOWER AIR MASS WILL BE STABLE WITH LOW MIXING
HEIGHTS AND GENERALLY POOR SMOKE DISPERSAL. SOUTHWEST WINDS OF 15
TO 25 MPH WILL DEVELOP FROM ROCK SPRINGS THROUGH CASPER IN THE
AFTERNOON.

&&

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

$$

SHORT TERM...C.BAKER
LONG TERM...LIPSON
AVIATION...C.BAKER
FIRE WEATHER...C.BAKER