176
FXUS65 KRIW 202204
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
304 PM MST FRI NOV 20 2009
SHORT TERM
TONIGHT THROUGH MONDAY
FLOW CONTINUES TO BACK TO THE SOUTH OVER WYOMING AS AMPLIFIED TROUGH
ALONG PAC COAST APPROACHES. SCT-BKN HIGH CLOUDS IN THE ADVANCE OF
THE TROUGH PUSHING ACROSS THE AREA SINCE THIS MORNING AND WILL
CONTINUE TO DO SO OVERNIGHT. WEAK BAROCLINIC LEAF LOCATED OVER
CENTRAL WA/OR THIS AFTERNOON WITH RA/SN FALLING UNDERNEATH THIS
FEATURE. 3-5MB/3HR PRESSURE FALLS WIDESPREAD OVER THE GREAT BASIN
AND CENTRAL/NORTHERN ROCKIES THIS AFTERNOON. LEE TROUGH OVER
EASTERN WY/CENT MONTANA GETTING THE CENTRAL WIND CORRIDOR GOING.
TIGHT S TO SSW GRADIENT OVER THE FAR WEST GETTING THE MOUNTAIN
LOCATIONS BLOWING PRETTY GOOD AS WELL. FOR THE OVERNIGHT...GRADIENT
TIGHTENS ACROSS THE AREA...WITH WINDS INCREASING OVER THE CENTRAL
WIND CORRIDOR AND WESTERN MOUNTAINS. AFTER MIDNIGHT...NAM AND LOCAL
WRF SHOWING 50-60KTS OVER THE LEE SLOPES OF THE WINDS AND THE
ABSAROKAS. HAVE INCREASED THE WINDS THERE TO REFLECT THIS. COULD
SEE SOME LOCAL HIGH WINDS IN THE MOUNTAINS OVER THE SOUTHEAST
PORTION OF THE WINDS AND AROUND CHIEF JOSEPH AND OTHER HIGH PEAKS OF
THE EASTERN ABSAROKAS. ALSO...WILL LIKELY SEE FALES ROCK AND CAMP
CREEK BLOW HIGH WIND...BUT AGAIN THIS WILL BE LOCALIZED. THE
EARLIER CONCERNS OF POSSIBLE HIGH WINDS NEAR LANDER ARE NO LONGER
ANTICIPATED WITH LACK OF CRITICAL LAYER AND NO DOWNWARD FORCING TO
SURFACE THESE WINDS ALOFT. WINDS TAPER AROUND 12Z SATURDAY WITH
LIGHT SNOW DEVELOPING IN THE WEST AS THE BAROCLINIC LEAF MOVES INTO
THE WEST. THIS FEATURE WILL WEAKEN AS IT MOVES THROUGH AND LIFTS TO
THE NORTH. EXPECT LIGHT TO LOCALLY MODERATE SNOW TO FALL OVER THE
NORTHWEST MOUNTAINS...WITH MAINLY LIGHT SNOW IN JACKSON HOLE.
SNOWFALL OF 2 TO 4 INCHES EXPECTED IN THE MOUNTAINS WITH AN INCH OR
SO IN THE VALLEY BEFORE TAPERING QUICKLY SATURDAY EVENING.
SHORTWAVE RIDGING BUILDS IN SATURDAY NIGHT BRINGING A BRIEF RESPITE
FROM THE SNOW. HOWEVER...A STRONGER WAVE WHICH IS DIGGING IN BEHIND
THE INITIAL WAVE SOUTH OF ALASKA WILL MOVE IN SUNDAY
MORNING...BRINGING ANOTHER ROUND OF SNOW TO MUCH OF THE WEST. NICE
CYCLONICALLY ORIENTED JET WILL MOVE INTO THE WEST DURING THE DAY
SUNDAY WILL PROVIDE GOOD LIFT. ALSO HAVE GOOD LOW AND MID LEVEL
CONVERGENCE AS WELL AS SOME ISENTROPIC LIFT IN THE MORNING. EXPECT
A DECENT PERIOD OF LIGHT TO MODERATE SNOW WITH THIS FEATURE FROM MID
TO LATE SUNDAY MORNING THROUGH SUNDAY EVENING. A COLD FRONT MOVES
INTO AREAS EAST OF THE DIVIDE SUNDAY NIGHT. COULD SEE SOME DECENT
NORTHWEST WINDS OVER THE WIND RIVER AND BIGHORN BASINS AS WELL AS
JOHNSON COUNTY AS THE TROUGH DIGS SOUTHEAST ACROSS SE MT INTO THE
DAKOTAS. SOME LIGHT SNOW IS POSSIBLE OVER THE BIGHORNS AND JOHNSON
COUNTY SUNDAY NIGHT AS WELL. NORTHWEST FLOW CONTINUES MONDAY OVER
THE AREA...WITH SOME LIGHT SNOW SHOWERS LINGERING OVER THE MOUNTAINS
AND THEIR SOUTHEAST. PRETTY COLD TEMPERATURES WILL MOVE IN BEHIND
EACH TROUGH. H7 TEMPS DOWN TO -17C OVER THE WEST WITH -14C EAST OF
THE DIVIDE. WILL BE SEEING OVERNIGHT LOWS IN THE SINGLE DIGITS AND
TEENS WITH SOME LOWER 20S EAST.
LONG TERM
MONDAY NIGHT THROUGH FRIDAY
A GRADUAL WARMING TREND IS EXPECTED TUESDAY ONWARD WITH A SLIGHT CHANCE
FOR RAIN OR SNOW ACROSS THE NORTH AND EAST TUESDAY NIGHT AND
WEDNESDAY. DRY AND UNSEASONABLY MILD CONDITIONS EXPECTED
THANKSGIVING DAY. BLACK FRIDAY LOOKS MILD AND BREEZY OVER MOST OF
THE AREA WITH A CHANCE OF PRECIPITATION RETURNING TO THE WEST
AHEAD OF A COLD FRONT LIKELY TO MOVE ACROSS THE AREA FRIDAY NIGHT
AND SATURDAY.
MEDIUM-RANGE GLOBAL MODELS CONTINUE TO SHOW SPREAD WITH TROUGH
EXITING INTO THE HIGH PLAINS MONDAY MORNING...THE GFS REMAINS THE
MOST PROGRESSIVE...THE GEM AND UKMET THE SLOWEST AND DEEPEST...AND
THE ECMWF THE PREFERRED COMPROMISE BETWEEN THE THREE. ALL FOUR
MODELS SEEMED TO HAVE SETTLED ON THESE INDIVIDUAL SOLUTIONS OVER THE
LAST FEW RUNS WITH LESS SPREAD THIS MORNING BETWEEN THE FOUR.
FORECAST WEIGHTED TOWARD ECMWF THROUGH THE EXTENDED PERIOD. ALL
MODELS QUICKLY DRY OUT AIRMASS MONDAY BEHIND UPPER TROUGH...THE
ECMWF AND GEM LEAVING LIGHT QPF ACROSS THE FAR WEST AND SOUTHEAST
QUARTER IN COLDER MORE AMPLIFIED FLOW BEHIND TROUGH. SLOWER CLOSED
LOW OVER THE PLAINS ALSO HAS IMPLICATIONS FOR CLIPPER SYSTEM DIVING
INTO BACK SIDE OF CLOSED LOW. GFS FLATTER FLOW RESULTS IN MORE
ISENTROPIC UPGLIDE...PRECIPITATION ACROSS THE NORTH AND WEST TUESDAY
AND TUESDAY NIGHT. ECMWF BRINGS BACKDOOR COLD FRONT INTO NORTHEAST
HALF OF STATE TUESDAY NIGHT WITH SOME LIGHT QPF WHILE KEEPING WEST
DRY. UPPER RIDGE PREVAILS WEDNESDAY AND THANKSGIVING DAY WHERE
MODELS TEND TO COME BACK INTO AGREEMENT. ECMWF SOLUTION PREFERRED
LATE IN THE PERIOD SHOWING PACIFIC ENERGY SPLITTING INTO
INTERMOUNTAIN WEST FRIDAY WITH SLIGHT CHANCES OF PRECIPITATION
RETURNING TO THE NORTHWEST MOUNTAINS. BEYOND THIS PERIOD FOR
HOLIDAY TRAVELERS...COLDER CONDITIONS WITH A CHANCE OF LIGHT SNOW
EXPECTED WYOMING AND THE CENTRAL ROCKIES SATURDAY AS THIS SPLIT
TROUGH MOVES ACROSS THE AREA.
AVIATION
BKN-OVC HIGH CLOUDS WILL CONTINUE TO OVERSPREAD WYOMING THROUGH THIS
EVENING. LIGHT TO MODERATE SOUTHWEST WIND WILL DEVELOP OVER MOST
AREAS THIS EVENING...EXCEPT IN THE WIND CORRIDOR FROM SOUTHEAST
FREMONT INTO NATRONA COUNTY INCLUDING KCPR...WHERE STRONG SOUTHWEST
WINDS BETWEEN 16 AND 22KT ARE EXPECTED...WITH GUSTS AROUND 28 KNOTS
POSSIBLE. SOUTHWEST WIND WILL REMAIN STRONG IN THIS REGION THROUGH
SATURDAY. ELSEWHERE...SOUTHWEST WIND WILL BE ON THE INCREASE TONIGHT
ESPECIALLY ALONG AND IN THE LEE OF THE MOUNTAINS. WIDESPREAD LIGHT
TO MODERATE SNOW IS EXPECTED TO BEGIN OVER THE FAR WEST AFTER ABOUT
10Z SATURDAY. MOUNTAIN OBSCURATIONS...AREAS OF MVFR... AND LOCAL IFR
CONDITIONS ARE EXPECTED TO IMPACT THE KJAC TERMINAL THROUGH THE DAY
SATURDAY.
FIRE WEATHER
THE WEEKEND AHEAD WILL BE UNSETTLED WITH WINDY AND DRY CONDITIONS
EAST OF THE DIVIDE. RH'S WILL BE QUITE LOW OVER THE BASINS SATURDAY
AND SUNDAY POSSIBLY DIPPING INTO THE TEENS. SNOW CAN BE EXPECTED
SATURDAY AND SUNDAY WITH A BRIEF BREAK SATURDAY NIGHT. SNOWFALL OF
THE UP TO 5 INCHES IS POSSIBLE IN THE NORTHWEST EACH DAY...AND IN
THE SOUTHWEST MOUNTAINS ON SUNDAY. A COLD FRONT WILL MOVE THROUGH
SUNDAY NIGHT WITH SOME SNOW SHOWERS POSSIBLE IN THE MOUNTAINS AND
EVEN EAST OF THE DIVIDE THROUGH MONDAY. MILD AND DRY CONDITIONS
RETURN FOR THE REMAINDER OF THE UPCOMING WEEK.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...TWB
LONG TERM...AEM
AVIATION...CHURCH
FIRE WEATHER...TWB
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