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000
FXUS66 KMFR 110441
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
841 PM PST TUE DEC 10 2013

.DISCUSSION...ANOTHER COLD NIGHT IS ON TAP FOR MOST AREAS.
LAKEVIEW...EAST OF THE CASCADES...IS CURRENTLY ZERO
DEGREES...WITH WEST SIDE VALLEYS DROPPING WELL BELOW FREEZING
ALREADY. AN UPPER RIDGE AXIS IS NUDGING OVER THE FORECAST AREA
TONIGHT...KEEPING RATHER MOTIONLESS AND COLD WEATHER THROUGH
TOMORROW...WITH THE POTENTIAL FOR FREEZING FOG IN MANY WEST SIDE
VALLEYS. WINDS WILL BE LIGHT AND TEMPERATURES WILL 10 TO 20
DEGREES BELOW NORMAL AGAIN ON WEDNESDAY. A FREEZE WARNING
CONTINUES AT THE COAST TO ACCOUNT FOR THIS ABNORMALLY COLD
WEATHER...AND AN AIR STAGNATION ADVISORY REMAINS THROUGH THURSDAY.

QUIET WEATHER WILL CONTINUE THROUGH THURSDAY MORNING...WITH A RATHER
WEAK FRONTAL SYSTEM ARRIVING LATE THURSDAY INTO THURSDAY NIGHT. WITH
A MODIFIED ARCTIC AIR MASS STILL HANGING ON AT THE SURFACE AND WARM
AIR ALOFT...THERE IS SLIGHT POTENTIAL FOR FREEZING RAIN THURSDAY
NIGHT IN SOME WEST SIDE VALLEYS AND JUST EAST OF THE CASCADES...AND
THIS IS DISCUSSED IN THE PREVIOUS DISCUSSION BELOW. FORECASTERS
TONIGHT WILL BE LOOKING AT THIS SITUATION CLOSELY.

&&

.AVIATION...WIDESPREAD VFR CONDITIONS ARE OVER THE AREA. HOWEVER AN
INVERSION IS STRENGTHENING ACROSS VALLEY LOCATIONS WITH COLD AIR
TRAPPED IN THE VALLEYS AND WARMER AIR ARRIVING ALOFT. THIS PATTERN
IS CONDUCIVE TO LOW CLOUDS AND FOG LEADING TO WIDESPREAD IFR CIGS
AND VIS TO DEVELOP TONIGHT...ESPECIALLY FOR LOCATIONS WEST OF THE
CASCADES.

EXPECT IFR CIGS AND FOG TO DEVELOP TONIGHT FOR INLAND VALLEYS WEST
OF THE CASCADES BETWEEN 04Z AND 10Z, INCLUDING AT KRBG AND KMFR.
ALONG THE COAST, AREAS OF LOW CLOUDS AND PATCHY FOG ARE POSSIBLE,
ESPECIALLY  IN THE COQUILLE VALLEY AND NEAR KOTH LATE TONIGHT INTO
WEDNESDAY MORNING. EAST OF THE CASCADES EXPECT MAINLY VFR. HOWEVER
ISOLATED MVFR/IFR CONDITIONS IN FOG MAY DEVELOP LATE TONIGHT INTO
EARLY WEDNESDAY MORNING NEAR AREAS WITH WATER SOURCES, SUCH AS IN
THE KLAMATH BASIN AND AT KLMT.  LOW CLOUDS AND FOG WILL PERSIST
INTO WEDNESDAY MORNING, WITH GRADUALLY IMPROVING TO VFR BETWEEN
18Z-21Z. OF CONCERN WILL BE THE POTENTIAL FOR LOCALIZED IFR/MVFR
CIGS PAST 21Z IN SOME WEST SIDE VALLEYS, ESPECIALLY FOR THE KRBG
AREA.


&&

.PREV DISCUSSION... /ISSUED 309 PM PST TUE DEC 10 2013/

SHORT TERM...THROUGH FRIDAY...
HIGH LEVEL CLOUDS STREAMING THROUGH THE AREA THIS AFTERNOON ARE
DAMPENING AFTERNOON HEATING. THIS IS LIKELY TO PREVENT MANY VALLEY
AREAS FROM REACHING THE FREEZING MARK THIS AFTERNOON. MEANWHILE,
CLEARING TONIGHT COUPLED WITH INCREASING RELATIVE HUMIDITIES AS
THE AIRMASS MODERATES AND SNOW MELTS AND SUBLIMATES WILL LIKELY
INCREASE THE AMOUNT OF FOG ACROSS VALLEY LOCATIONS ON WEDNESDAY
MORNING. I`VE INCREASED FOG COVERAGE ACROSS THE AREA FOR THE LATE
NIGHT AND MORNING.

FOR WEDNESDAY, LESS CLOUDINESS AND WARMER TEMPERATURES ARE
EXPECTED FOR AREAS THAT CAN SHAKE THE FOG. WITH THE CONTINUING
INVERSION AND RESULTANT AIR STAGNATION AREAS SUCH AS MEDFORD,
GRANTS PASS, AND ROSEBURG WILL HAVE A HARD TIME SHAKING FOG ON
WEDNESDAY. I HAVE, THEREFORE, KEPT TEMPERATURES BELOW GUIDANCE IN
THE VALLEYS WHERE SNOW COVER STILL EXISTS AND CARRIED PATCHY FOG
INTO THE AFTERNOON. STILL SUSPECT WE WILL BE ABOVE FREEZING AT
NEARLY ALL WEST SIDE LOCATIONS.

FOR THURSDAY INTO FRIDAY A WEAKENING FRONTAL SYSTEM WILL BE
PUSHING INTO THE AREA. MODEL GUIDANCE IS NOT WELL AGREED WITH
TIMING AND STRENGTH OF THIS SYSTEM, BUT HAS GENERALLY TRENDED
SLOWER AND WEAKER WITH THIS WEATHER SYSTEM. EXPECT MOST OF THE
PRECIPITATION WITH THIS ONE TO BE FROM THE CASCADES AND MARBLE
MOUNTAINS AND SISKIYOUS NORTH AND WESTWARD. FOLLOWED THE GFS AND
CANADIAN, FOR THE MOST PART, PER SUGGESTIONS FROM WPC. DUE TO
TRAPPED COLD AIR IN ASSOCIATION WITH RECENT COLD AND THE SNOW ON
GROUND, THERE STILL IS SOME CONCERN FOR FREEZING RAIN WITH THIS
SYSTEM. SUSPECT THE CHANCES FOR THIS ARE REDUCING SINCE THE FRONT
WILL BE ARRIVING LATER, BUT STILL CAN NOT RULER IT OUT, SO I HAVE
LEFT SOME MENTION OF IT THE FORECAST. THE WEATHER SYSTEM WILL
LINGER INTO FRIDAY A BIT, BUT EXPECT SOME CLEARING BY AFTERNOON
ALONG WITH RELATIVELY MILD TEMPERATURES. BTL

LONG TERM...
..SATURDAY THROUGH TUESDAY...AFTER THE SHORT WAVE TROUGH AND
THE WEAK FRONT MOVE THROUGH AROUND FRIDAY..THE TREND IS FOR
RIDGING TO EXPAND NORTH. THIS WILL MEAN A WARMING AND DRYING TREND
OVER MOST OF OUR AREA. THE GFS SHOWS A SHORT WAVE TROUGH MOVING
ACROSS NORTHERN HALF OF OREGON KEEPING THE RIDGE FROM EXPANDING
FULLY. THIS MORNINGS ECMWF WAS STRONGER WITH THE SHORT WAVE AND
CONTINUED TO SHOW LIGHT SHOWERS FROM NW OREGON DOWN TO ABOUT THE
UMPQUA DIVIDE. AS A RESULT I HAVE TAPERED OFF THE POPS FOR THE
COAST AND DOUGLAS COUNTY BUT DID NOT REMOVE THEM TOTALLY FROM THE
FORECAST.

WARMING ALOFT THIS WEEKEND WILL CONTINUE TO HELP STRENGTHEN
INVERSIONS. THIS WILL LEAD TO A MORE PERSISTENT LOW CLOUDS AND FOG
IN THE VALLEYS THAT WILL COULD AFFECT AVIATION AND FORECAST HIGH
TEMPERATURES. I WENT SLIGHTLY COOLER IN VALLEY LOCATIONS THAN
GUIDANCE.

THE LAST DAY OF THIS FORECAST PERIOD (TUESDAY) COULD BE A TRANSITION
DAY. BOTH THE GFS AND THE ECMWF ALONG WITH ENSEMBLE MEANS SHOW THE
RIDGE RETROGRADING OFFSHORE ON WEDNESDAY..ALLOWING A MORE NW TO
NORTHERLY FLOW TO RETURN TO THE PAC NW. THIS WILL CERTAINLY POINT TO
OUR AREA RETURNING TO A COOL PATTERN. THE ECMWF HOLDS ON TO THE
RIDGE ON TUESDAY...ONE MORE DAY THAN GFS. HAVE TRENDED THE
TEMPERATURES DOWN SOME ON TUESDAY BUT OTHERWISE KEPT EARLY NEXT WEEK
DRY. /FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FROST ADVISORY UNTIL 10 AM PST WEDNESDAY FOR ORZ021-022.
     FREEZE WARNING UNTIL 10 AM PST WEDNESDAY FOR ORZ021.
     AIR STAGNATION ADVISORY UNTIL NOON PST THURSDAY FOR
     ORZ023>026-028>031.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL MIDNIGHT PST TONIGHT FOR
     PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL MIDNIGHT PST
     TONIGHT FOR PZZ376.

$$

NSK/FJB/CMC