FXUS65 KRIW 132212
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
312 PM MST SAT MAR 13 2010
.SHORT TERM...TONIGHT THROUGH MONDAY NIGHT
PACIFIC UPPER LEVEL TROUGH SPLITTING WITH SOUTHERN END DIGGING
SOUTH INTO SOUTHERN GREAT BASIN INTO SOUTHWEST UTAH WILL PASS
THROUGH THE FOUR CORNERS AREA WHILE THE NORTHERN TROUGH IN WESTERN
MONTANA MOVES EAST ACROSS MONTANA AND NORTHERN WYOMING. SURFACE
CYCLOGENESIS FROM NORTH CENTRAL WYOMING SOUTH THROUGH THE DESERT
SOUTHWEST WITH HIGH PRESSURE ACROSS NORTHERN IDAHO...MONTANA AND
SOUTHERN ALBERTA. SURFACE WINDS HAVE TURNED NORTH TO NORTHEAST
ACROSS NORTHERN WYOMING. THE MAIN COLD FRONT HAS PASSED THROUGH
BILLINGS MT WITH AREA OF PRECIPITATION OVER AND NORTH OF BEARTOOTH
MOUNTAINS AND ACROSS NORTH WESTERN MOUNTAINS OF WYOMING. COLD
FRONT WILL SWEEP SOUTH THROUGH THE EVENING WITH DEEP UPSLOPE FLOW
DEVELOPING WITH LOW LEVEL FRONTOGENESIS ACROSS CENTRAL WYOMING
WITH DEEPEST MOIST UPSLOPE FLOW WITH SPEEDS OF 20 TO 25 KTS FROM
09Z THROUGH 15Z SUNDAY. MODELS HAVE THEIR DIFFERENCES BUT ALL
SHOW SIMILAR UPSLOPE FLOW AND TYPICAL PRECIPITATION PATTERN INTO
NORTH SLOPES OF OWL CREEK/BRIDGER MOUNTAINS AND EAST SLOPES OF
WIND RIVER MOUNTAINS. BUFFER SOUNDING FOR LANDER SHOWS SATURATION
THROUGH -20 WITH WEAK LOW LEVEL INSTABILITY IN THE UPSLOPE FLOW.
THIS IS LIKELY WHY THE NAM12 AND WRF HAVE THE HIGHEST QPF ALONG
THE EAST SLOPES OF THE WIND RIVER MOUNTAINS. GFS AND SREF HAVE
BROADER WASHED OUT QPF PATTERN TYPICAL OF LOWER RESOLUTION MODELS.
HIGH RESOLUTION NMM/ARW AND NAMDNG AND RUC ALL SHOW PATTERN CLOSER
TO NAM12. MOST OF THE AREA WILL GET A DUSTING OF SNOW TO ONE INCH.
LOCAL OROGRAPHICALLY FAVORED AREAS SHOULD SEE 2 TO 3 INCHES MAINLY
ABOVE 6000 FEET WITH LOCAL MOUNTAIN AREAS OF 2 TO 5 INCHES LOCALLY
POSSIBLE. MOST MOUNTAIN AREAS SHOULD SEE 2 TO 4 INCHES. SNOWFALL
SHOULD BE DONE BY MID MORNING WITH VERY LIGHT SHOWERS MID DAY
DECREASING RAPIDLY TO MAINLY ISOLATED MOUNTAIN SHOWERS SUNDAY
AFTERNOON. HIGH PRESSURE BUILDS IN SUNDAY AFTERNOON AND EVENING
ACROSS THE WEST SPREADING EAST THROUGH SUNDAY NIGHT AND MONDAY
WITH CLEARING. SOME LOW STRATUS MAY GET TRAPPED IN THE VALLEYS AND
BASINS WITH PATCHY FOG MONDAY MORNING. THIS IS TOO TOUGH TO CALL
AT THIS TIME AND WILL LARGELY BE DRIVEN WHERE HEAVIEST
PRECIPITATION OCCURS OVER THE NEXT 12 TO 15 HOURS. TEMPERATURES
WILL COOL SUNDAY AND SUNDAY NIGHT THEN REBOUND MONDAY AND MONDAY
NIGHT WITH LOCAL COLD VALLEY TEMPERATURES REMAINING IN THE WEST
MONDAY NIGHT IN THE UPPER GREEN RIVER BASIN...BONDURANT AND HOBACK
CANYON AND JACKSON HOLE AND STAR VALLEY BEING THE COLDER AREAS
ALONG WITH THE YELLOWSTONE PLATEAU.
.LONG TERM...TUESDAY THROUGH SATURDAY
RIDGE SHOULD BE CENTERED RIGHT OVER THE COWBOY STATE TO START THE
MEDIUM RANGE PERIOD BEFORE THE PATTERN BEGINS TO CHANGE. EVOLUTION
IS A LITTLE DIFFERENT IN ALL THE MODELS. WHAT THEY ALL AGREE ON IS
THAT WE WILL SEE RIDGING DEVELOPING THE GULF OF ALASKA AND AS FAR
NORTH AS ALASKA WHICH WILL SET THE STAGE FOR A DIGGING TROUGH INTO
THE NRN ROCKIES AND INTER-MOUNTAIN WEST WEDNESDAY INTO THURSDAY.
THE ECMWF IS MORE PROGRESSIVE WITH THE RIDGE WHILE THE GFS ANCHORS
A CLOSED OFF HIGH OVER THE NW TERRITORIES OVR THE WEEKEND. FOR MY
MEDIUM RANGE PERIOD...THE ONLY SIGNIFICANT DIFFERENCE WILL BE THE
LAST DAY OF THE FORECAST...SATURDAY. THE GFS HAS ANOTHER
REINFORCING SHOT OF CANADIAN...ARCTIC AIR WITH H7 TEMPS AS COLD AS
-18C. THE ECMWF RIDGE IS SHIFTING EWD ALREADY. FORECAST IS A
COMPROMISE FOR NOW UNTIL WE CAN BETTER RESOLVE THIS PATTERN.
INCREASED POPS WITH UPCOMING TROUGH THURSDAY INTO THURSDAY NIGHT.
LOWERED TEMPS THURSDAY INTO FRIDAY WITH MODELS SHOWING VERY COLD
LATE MARCH AIR WITH H7 TEMPS BETWEEN -10C AND -16C. IN FACT...THE
GFS HAS EVEN COLDER AIR MOVING SWD ON SATURDAY WITH ITS SECOND
WAVE...-19C AT H7. EITHER WAY...THE -10C TO -15C H7 AIR WITH THE
POTENTIAL FOR SNOW AND CERTAIN CLOUD COVER WILL KEEP TEMPS IN THE
20S AND 30S IN MOST OF THE LOWER ELEVATIONS WITH EVEN COLDER
READINGS IN THE HIGH COUNTRY.
&&
.AVIATION...
A SPLITTING TROUGH OF LOW PRESSURE OVER THE PACIFIC NORTHWEST AND
GREAT BASIN WILL CONTINUE TO SPLIT AND TAKE THE BULK OF THE ENERGY
WELL TO THE SOUTH OVER THE FOUR CORNERS REGION ON SUNDAY. BANDS OF
RAIN AND SNOW ASSOCIATED WITH THIS SPLITTING TROUGH WILL CAUSE AREAS
OF MAINLY MVFR AND LOCAL IFR CONDITIONS TO OCCUR ACROSS WESTERN AND
SOUTHWEST WY INCLUDING KJAC...KPNA...KBPI AND KRKS TONIGHT BEFORE
THE ENERGY SHIFTS WELL TO THE SOUTH SUNDAY. A COLD FRONT ASSOCIATED
WITH THE CORRESPONDING TROUGH AXIS WILL BE MOVING SOUTH ACROSS
WYOMING TONIGHT. SNOWFALL ALONG AND BEHIND THE FRONT WILL CAUSE MVFR
AND IFR CONDITIONS TO DEVELOP TONIGHT AND CONTINUE INTO SUNDAY
MORNING ALONG WITH MOUNTAIN OBSCURATIONS...MAINLY ACROSS AREAS EAST
OF THE CONTINENTAL DIVIDE. THE HEAVIEST SNOWFALL WILL OCCUR IN THE
VICINITIES OF KCPR AND KLND.
&&
.FIRE WEATHER...
AREAS OF SNOW OVER THE WEST WILL SHIFT INTO THE NORTH AND SPREAD
SOUTH THROUGH THE NIGHT. MUCH OF THE AREA WILL GET A QUICK SHOT OF
LIGHT SNOW WITH LIGHT ACCUMULATIONS. MUCH OF THE LOWER ELEVATIONS
WILL RECEIVE AN INCH OR LESS. THE FAVORED UPSLOPE AREAS MAY SEE 2
TO 3 INCHES OF SNOW AROUND LANDER AND CAPER. THE MOUNTAINS SHOULD
SEE 2 TO 4 INCHES OF SNOW WITH LOCALLY HIGHER AMOUNTS. SNOW
SHOWERS WILL DECREASE IN THE MORNING ACROSS THE WESTERN MOUNTAINS
WITH SNOW LINGERING ACROSS CENTRAL WYOMING INTO EARLY SUNDAY
AFTERNOON THEN DECREASE RAPIDLY. OVERALL SMOKE DISPERSAL WILL BE
POOR WITH MIXING HEIGHTS OF 2000 FEET OR LESS WITH HIGH RELATIVE
HUMIDITY. TEMPERATURES WILL BE COLDER ACROSS THE AREA.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...C.BAKER
LONG TERM...SKRBAC
AVIATION...LIPSON
FIRE WEATHER...C.BAKER
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