FXUS66 KMFR 021707
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
907 AM PST WED DEC 2 2009

.DISCUSSION...ADJUSTED SKY COVER OVER THE EAST SIDE IN OREGON TO
ACCOUNT FOR CLOUDS THERE THIS MORNING. ALSO NUDGED MAX
TEMPERATURES DOWNWARD DUE TO THE CLOUDS. EXPECT THEY WILL BREAK
SOME THIS AFTERNOON, BUT PERHAPS NOT COMPLETELY. LOW CLOUDS AND
FOG ON THE WEST SIDE WILL AGAIN HAVE A DIFFICULT TIME BREAKING.
THEY WILL LAST AT LEAST UNTIL EARLY AFTERNOON OVER THE ROGUE AND
ILLINOIS VALLEYS AS WELL AS THE UMPQUA BASIN. IF THEY DO BREAK, IT
WILL ONLY BE FOR A COUPLE OF HOURS LATE THIS AFTERNOON. THIS WILL
KEEP TEMPERATURES FROM REACHING 40 DEGREES WHERE THE CLOUDS DO NOT
BREAK. ELSEWHERE, MAINLY SUNNY, MILD CONDITIONS WILL PREVAIL
TODAY. NO OTHER CHANGES WERE MADE THIS MORNING. 

&&

.AVIATION...MVFR TO IFR CIGS MAINLY NORTH OF KLMT THIS MORNING ON
THE EAST SIDE. THESE ARE EXPECTED TO BREAK UP AS THE DAY
PROGRESSES, BUT PERHAPS NOT COMPLETELY. KLMT WILL HAVE MOSTLY VFR
CONDITIONS. ON THE WEST SIDE, KMFR WILL HAVE LIFR CONDITIONS
THROUGH EARLY AFTERNOON. THERE IS THE POTENTIAL FOR IT TO BREAK
OUT FOR AN HOUR OR TWO LATE THIS AFTERNOON, BUT LIFR CIGS AND
VISIBILITY ARE EXPECTED AGAIN TONIGHT. IFR CIGS OVER KRBG WILL
PERSIST THROUGH THE DAY. VFR CONDITIONS WILL PREVAIL AT KOTH. 

&&

.PREV DISCUSSION... /ISSUED 106 AM PST WED DEC 2 2009/ 

DISCUSSION...01/00Z NAM/GFS IN.  

THE SHORT-RANGE FORECAST IS STRAIGHTFORWARD. HIGH PRESSURE ALOFT WILL
REMAIN IN PLACE OVER THE AREA INTO FRIDAY WITH LIGHT WINDS. SKIES
WILL REMAIN MOSTLY CLEAR OVER MOST OF THE AREA...BUT AREAS OF LOW
CLOUDS AND FOG WILL PERSIST IN MOST OF THE VALLEYS WEST OF THE
CASCADES AND LATE NIGHT THROUGH EARLY MORNING LOW CLOUDS AND FOG
WILL ALSO DEVELOP OVER SOME AREAS EAST OF THE CASCADES.

A SIGNIFICANT CHANGE WILL OCCUR FRIDAY OR SATURDAY...BUT THE EXACT
NATURE OF THE CHANGE IS MURKY WITH SIGNIFICANT DIVERGENCE IN THE
MEDIUM-RANGE MODEL SOLUTIONS. THE 02/00Z GFS SOLUTION DIGS A COLD
CLOSED LOW INTO WESTERN MONTANA FRIDAY AFTERNOON...BRINGING ARCTIC
AIR INTO THE INTERMOUNTAIN STATES AND INTO THE MEDFORD CWA EAST OF
THE CASCADES.  A STRONG SHORT WAVE ROTATING AROUND THIS LOW THEN
SWEEPS OVER THE MEDFORD CWA SATURDAY. AFTER THAT A SECOND CLOSED
LOW DEVELOPS OVER THE CWA SUNDAY AND HANGS AROUND THROUGH SUNDAY
NIGHT.

MEANWHILE...THE 01/12Z ECMWF DIGS THAT CLOSED LOW INTO WASHINGTON
FRIDAY AFTERNOON AND INTO OREGON SATURDAY...KEEPING IT THERE INTO
SUNDAY NIGHT. THIS WOULD SUPPORT A WETTER SOLUTION...AND A WARMER
SCENARIO FOR EAST OF THE CASCADES. THE CLIMATE PREDICTION CENTER
MEDIUM-RANGE FORECAST FOLKS ARE FAVORING THIS SOLUTION...WHICH IS
IN LINE WITH THE 02/00Z CANADIAN SOLUTION.

EITHER SOLUTION SUPPORTS A WEAKENING OF THE INVERSION WITH COOLER
AIR ALOFT...SO ENDING THE AIR STAGNATION ADVISORY FRIDAY LOOKS
LIKE A GOOD CALL AT THIS TIME. EITHER SOLUTION ALSO WOULD SUPPORT
SNOW LEVELS IN THE 2000-3000 FOOT RANGE WEST OF THE CASCADES AND
TO THE VALLEY FLOORS ON THE EAST SIDE.

ONCE THE LOW DEPARTS THE AREA BOTH THE ECMWF AND THE GFS
SOLUTIONS DEPICT A RETURN TO A WET PROGRESSIVE PATTERN FOR NEXT
WEEK...AS HAS BEEN FORECAST FOR THE PAST FEW DAYS NOW.

WILL NOT BE MAKING ANY CHANGES IN THE EXTENDED FORECAST AT THIS
TIME GIVEN THE UNCERTAINTY AND OFFICE POLICY.  

AVIATION...IFR/LIFR CIGS/VSBYS CONDITIONS IN THE WEST SIDE
VALLEYS WILL PERSIST THROUGH THURSDAY MORNING...LIFTING TO MVFR
CIGS MOST AREAS IN THE AFTERNOON BEFORE LOWERING BACK TO IFR/LIFR
WEDNESDAY EVENING. MVFR CIGS OVER NORTHERN KLAMATH COUNTY WILL
PERSIST THROUGH MID-MORNING WEDNESDAY CLEARING TO VFR BY
AFTERNOON. VFR CONDITIONS WILL PREVAIL ELSEWHERE THROUGH THURSDAY
MORNING. 

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL NOON PST FRIDAY FOR ORZ024-ORZ026-
     ORZ029-ORZ030-ORZ031.

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

SPILDE