993
FXUS65 KRIW 071610
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
910 AM MST SAT NOV 7 2009
UPDATE
JUST SENT QUICK UPDATE TO INCREASE CLOUD COVER AND INTRODUCE A
SLIGHT CHANCE FOR LIGHT RAIN IN THE NORTHERN BIG HORN BASIN THIS
MORNING WITH KGEY ASOS REPORTING LIGHT RAIN. STRONG MID AND UPPER
LEVEL DIFLUENCE ASSOCIATED WITH A 110KT JET STREAK OVER NORTHEAST
WYOMING PRODUCING THE LARGE 12-13K FEET AGL CLOUD DECK EAST OF THE
DIVIDE THIS MORNING. THE JET STREAK AND ASSOCIATED CLOUD DECK WILL
GRADUALLY TRANSLATE EAST OF THE AREA DURING THE AFTERNOON.
PREV DISCUSSION
/ISSUED 308 AM MST SAT NOV 7 2009/
SHORT TERM...TODAY THROUGH MONDAY NIGHT
SHORTWAVE APPROACHING THE PAC WEST COAST THIS MORNING WITH BACKING
SOUTHWEST FLOW OVER WYOMING. JET STRENGTHENING AS WELL OVER THE
NORTHERN PLAINS AND ACROSS MONTANA. RIGHT ENTRANCE REGION SETTING
UP OVER NORTHERN WYOMING AS WELL OFFERING SOME LIFT. THIS WILL KEEP
THE SHOWERS GOING THERE TODAY...THOUGH THE MOISTURE FETCH WILL BE
LIMITED. CLOUD TOPS COOLING EARLY THIS MORNING WITH PERHAPS A BIT
OF A WEAK BAROCLINIC LEAF FORMING UNDER THE BACKING FLOW AND JET
DYNAMICS. HOWEVER...RADAR ECHOES ON THE DECREASE. SOME SOUTHWEST
WINDS WILL CONTINUE TODAY BUT WILL BE MUCH LESS THAN THE PAST FEW
DAYS. THE SHORTWAVE MOVES THROUGH THIS AFTERNOON AND EVENING WITH
DRYING AIR MOVING IN OVERNIGHT ENDING THE SHOWER ACTIVITY. WILL
ALSO SEE CLOUDS DISSIPATE AS WELL. ZONAL FLOW REMAINS OVER WYOMING
SUNDAY WITH RELATIVELY LIGHT WINDS AT THE SURFACE. WILL HAVE SOME
HIGH CLOUDS MOVING THROUGH AS HIGH LEVEL MOISTURE MOVES THROUGH.
RIDGE BUILDS IN FOR MONDAY WITH DRY CONDITIONS AND LIGHT WINDS
CONTINUING. RIDGE SHIFTS EAST MONDAY NIGHT AS THE NEXT PACIFIC
TROUGH APPROACHES. THIS WILL ALLOW THE SOUTHWEST GRADIENT TO
DEVELOP AS THE LEE TROUGH DEVELOPS. TEMPERATURES WILL BE MILD TODAY
OVER MOST OF THE AREA THOUGH COOLER THAN YESTERDAY. THEY COOL A
LITTLE FOR TOMORROW AND MONDAY...WITH NEAR NORMAL READINGS.
LONG TERM...TUESDAY THROUGH SATURDAY
FAST PROGRESSIVE ZONAL FLOW WITH A BROAD FLAT TROUGH WILL EXTEND
FROM THE EASTERN PACIFIC ACROSS THE PACIFIC NORTHWEST...THE
NORTHERN GREAT BASIN AND ACROSS WYOMING INTO THE NORTHERN AND
CENTRAL PLAINS. A SERIES OF FAST MOVING SHORT WAVE TROUGHS WILL
BRING PACIFIC MOISTURE INTO THE WESTERN MOUNTAINS BRINGING LOCAL
SHOWERS TO THE WESTERN MOUNTAINS, THIS WILL BRING BREEZY AREAS
EAST OF THE CONTINENTAL DIVIDE AND ACROSS THE SOUTH. TUESDAY THE
FLOW BACKS AHEAD OF A DEEPENING PACIFIC TROUGH. WIND SHOULD PICK
UP AND TEMPERATURES SHOULD RISE. PACIFIC MOISTURE REMAINS TO THE
WEST UNTIL WEDNESDAY AS THE PACIFIC TROUGH MOVES INLAND.
PRECIPITATION... MAINLY SNOW WITH SOME RAIN IN THE VALLEYS WILL
MOVE INTO THE WEST, WINDS WILL PICK UP EAST OF THE DIVIDE.
THURSDAY THE TROUGH WILL PASS TROUGH THEN FOLLOWED BY A CANADIAN
TROUGH. THIS WILL SPREAD THE THREAT OF PRECIPITATION EAST OF THE
DIVIDE. MODELS HAVE BEEN INCONSISTENT WITH THE STRENGTH OF THE
CLIPPER TROUGH AND THE AMOUNT OF PRECIPITATION WITH IT. FORECAST
RATHER CONSERVATIVE AT THIS TIME DUE TO MODEL FLIP FLOPS. SHOULD
BE COLDER AS ZONAL FLOW BUCKLES WITH A DEVELOPING LONG WAVE TROUGH
OVER THE WEST AND THE FLOW SHIFTING FROM THE PACIFIC TO CANADA.
THERE IS CONSIDERABLE MODEL SPREAD WITH THE FEATURES WITHIN THE
LONG WAVE TROUGH. THERE IS POTENTIAL FOR A MUCH MORE SIGNIFICANT
SPREAD OF PRECIPITATION...JUST AS THERE IS POTENTIAL FOR THE ZONAL
NATURE OF THE FLOW TO HOLD OUT WITH LESS DIGGING OF THE MEAN
TROUGH WITH THE PASSAGE OF A SERIES OF SHORT WAVE TROUGHS. THE
MODELS A FAR APART TO THE NORTH...ACROSS CANADA AND TO THE WEST
ACROSS THE EASTERN PACIFIC AND GULF OF ALASKA BY FRIDAY. THE MAIN
STORY THURSDAY AND FRIDAY WILL BE COLDER AND MAYBE SNOW
SHOWERS...OR MORE ORGANIZED PRECIPITATION ACROSS THE NORTH AND
EAST. MODELS ARE QUITE CHAOTIC ON SATURDAY SO HAVE MAINLY A
PERSISTENCE FORECAST WITH LOWER VALLEY POPS THEN BUT LITTLE CHANGE
IN TEMPERATURES. THIS MAKES FOR LOW CONFIDENCE IN THE EXTENDED
AFTER WEDNESDAY.
AVIATION...
VFR CONDITIONS WILL PREVAIL ACROSS MOST OF THE AREA THROUGH 12Z
SUNDAY WITH LOCAL MVFR CONDITIONS AND OCCASIONAL MOUNTAIN
OBSCURATIONS VCNTY AND NORTH OF A KJAC-KCOD LINE. A FETCH OF
MOISTURE WILL REMAIN JUST SOUTH OF A JET STREAM AXIS...ACROSS IDAHO
INTO NORTHWEST WYOMING. AREAS OF MOUNTAIN SNOW AND LOCAL VALLEY
LIGHT RAIN/SNOW...SNOW LEVELS AROUND 7KFT WILL BE ENCOUNTERED IN THE
NORTHWEST. BKN CLOUD DECKS 120-130MSL WILL EXTEND SOUTH TO VCNTY
KBPI/KPNA. AN UPPER LEVEL DISTURBANCE WILL MOVE INTO THE WEST
AROUND 00Z SUNDAY WITH IMPROVING CONDITIONS BEHIND THIS SYSTEM.
THIS SYSTEM WILL SPREAD SCT-BKN120-150MSL CLOUD DECKS EAST OF THE
DIVIDE 00Z-08Z SUNDAY.
FIRE WEATHER...
SOUTHWEST WINDS WILL CONTINUE TODAY OVER MUCH OF THE AREA THOUGH
LESS SPEED THAN YESTERDAY. SHOWERS WILL CONTINUE OVER THE NORTHWEST
AS WELL TODAY. DRIER AIR MOVES IN TONIGHT WITH DRY CONDITIONS WITH
LIGHT WINDS EXPECTED FOR SUNDAY. IT WILL BE A LITTLE COOLER...BUT
STILL AROUND NORMAL. MONDAY WILL BE NICE DAY AS WELL. WINDS WILL
BEGIN TO INCREASE MONDAY NIGHT AND TUESDAY AS THE NEXT PACIFIC
TROUGH APPROACHES. THIS SYSTEM LOOKS TO BRING WIND AND
PRECIPITATION TO THE REGION MID NEXT WEEK.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...CHURCH
SHORT TERM...TWB
AVIATION...AEM
LONG TERM...C.BAKER
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