738
FXUS65 KRIW 091535
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
835 AM MST TUE FEB 9 2010
UPDATE
ISSUED MINOR UPDATE TO TRY AND CAPTURE CURRENT...AND VERY TRICKY...AREAS
OF LOW STRATUS CLOUDS OVER THE WEST FOR THIS MORNING. FLURRIES STILL
BEING REPORTED AT KBPI. LOWERED MAXIMUM TEMPS SEVERAL DEGREES AS
WELL FOR THIS AFTERNOON IN AREAS THAT DROPPED TO NEAR -10F. LOW
STRATUS STILL EXPECTED TO GRADUALLY ERODE DURING THE LATE MORNING
AND EARLY AFTERNOON HOURS.
PREV DISCUSSION
/ISSUED 313 AM MST TUE FEB 9 2010/
SHORT TERM...TODAY THROUGH THURSDAY NIGHT
WYOMING IN BETWEEN UPPER LOW OVER THE MID PLAINS AND SHORTWAVE RIDGE
JUST WEST OF THE DIVIDE. STUBBORN LOW CLOUDS STILL HANGING ON OVER
THE WIND RIVER BASIN...GREEN RIVER BASIN...JACKSON HOLE...STAR
VALLEY AND SWEETWATER COUNTY. SOME PATCHY FOG OUT THERE AS
WELL...WAS THICK FOR A WHILE OVER SOUTH PASS FOR A BRIEF WHILE THIS
PAST EVENING. LOW CLOUDS SO FAR HAVE KEPT TEMPERATURES FROM
PLUMMETING. BIG PINEY STILL AT 15 ABOVE AS OF 08Z. THE RIDGE MOVES
ACROSS WYOMING TODAY WITH A WEST TO NORTHWEST FLOW BUILDING IN. LOW
LEVEL MOISTURE (BELOW 700MB) REMAINS OVER THE WEST WITH SOME WEAK
ISENTROPIC LIFT. PROBABLY NOT ENOUGH MOISTURE FOR ANY APPRECIABLE
CHANCE OF SNOW...SO HAVE REMOVED POPS THIS AFTERNOON...AS WELL AS
OVERNIGHT THROUGH 18Z WEDNESDAY. SPLIT TROUGH MOVES THROUGH WESTERN
WYOMING WEDNESDAY AFTERNOON WITH A BETTER CHANCE OF LIGHT SNOW.
DYNAMICS WEAK DUE TO THE SPLIT TROUGH...THO THERE IS SOME ISENTROPIC
LIFT. NORTHWEST FLOW INCREASES BEHIND THE TROUGH WITH BETTER
ISENTROPIC LIFT AS WELL AS BETTER MOISTURE SOURCE OFF THE PACIFIC.
SO SHOULD SEE A DECENT CHANCE FOR SIGNIFICANT SNOW ON THURSDAY AND
THURSDAY NIGHT OVER WESTERN WYOMING. TEMPERATURES WILL WARM BACK
INTO THE 20S WITH LOCALLY SOME 30S. THEN WARMING SOME MORE FOR
WEDNESDAY AND THURSDAY.
LONG TERM...FRIDAY THROUGH TUESDAY
MEDIUM RANGE DETAILS CONTINUE TO FLUCTUATE WITH EACH MODEL RUN
BUT THE OVERALL PATTERN IS STILL DOMINATED BY A RIDGE AXIS JUST TO
THE WEST WITH TEMPORARY FLATTENING AS SHORTWAVES RIDE OVER THE RIDGE.
ISENTROPIC UPGLIDE ACCOMPANIES EACH OF THESE SHORTWAVES WITH A
PERIOD OF LIGHT SNOW EXPECTED IN THE FAR WEST WITH EACH ONE. THE
MODELS ARE STILL TRYING TO INDICATE THAT THIS SATURDAY SHORTWAVE
MAY HAVE A MORE FAVORABLE NW TO SE TRAJECTORY AND BRING A LITTLE
LIGHT SNOW EAST OF THE DIVIDE. WILL PUT IN SOME 20 POPS FOR ALL
AREAS EAST OF THE DIVIDE FOR NOW AND LET THE NEXT CREW LOOK AT
THIS AGAIN TONIGHT. BASIN AND VALLEY TEMPERATURES WILL BE A LITTLE
TRICKY AS DEPENDING ON THE STRENGTH OF THESE WAVES SOME OF THESE
AREAS COULD MIX...AT LEAST PARTIALLY. DETAILS WILL CONTINUE TO
CHANGE AS THEY HAVE FOR THE PAST 4 NIGHTS BUT THE BIGGER PICTURE
REMAINS FAIRLY STABLE AND CONDUCIVE TO SOME PERIODS OF AT LEAST
LIGHT SNOW OR FLURRIES OUT WEST AT TIMES IN LIGHT TO MODERATE
ISENTROPIC UPGLIDE PATTERN AT TIMES.
AVIATION...
MVFR CONDITIONS WILL LINGER IN PARTS OF SOUTHWEST AND CENTRAL WY
UNTIL 16Z BEFORE THE LOW CLOUDS DISSIPATE. IN ADDITION AREAS OF FOG
ARE POSSIBLE IN WESTERN AND CENTRAL WY WITH IFR CONDITIONS THROUGH
17Z BEFORE DISSIPATING. VFR CONDITIONS WILL PREVAIL AFTER 18Z OVER
THE WHOLE REGION. BREEZY CONDITIONS WILL OCCUR AROUND KCPR AIRPORT
TODAY...DIMINISHING AFTER 01Z THIS EVENING.
FIRE WEATHER...
LOW CLOUDS...PATCHY FOG AND EVEN SOME FLURRIES WILL PERSIST OVER THE
WESTERN AND CENTRAL VALLEYS AND BASINS THIS MORNING. THE CLOUDS AND
FOG WILL BURN OFF AROUND MID DAY...WITH CLEAR SKIES PREVAILING.
TEMPERATURES WILL BEGIN TO WARM EAST OF THE DIVIDE BUT WILL STILL BE
BELOW NORMAL. WIND OVER THE WIND CORRIDORS WILL BEGIN TO INCREASE
TODAY AND CONTINUE TO INCREASE SOME FOR WEDNESDAY AND THURSDAY. A
GOOD CHANCE OF SNOW IS EXPECTED WEDNESDAY AFTERNOON AND CONTINUE
INTO THE WEEKEND OVER THE WEST. SMOKE DISPERSAL WILL BE GENERALLY
BE POOR...THOUGH SOME FAIR AREAS WILL OCCUR IN THE BREEZIER AREAS.
RIW WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...CHURCH
SHORT TERM...TWB
LONG TERM...SKRBAC
AVIATION...AR
FIRE WEATHER...TWB
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