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000
FXUS66 KMFR 122252
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
252 PM PST THU DEC 12 2013

.SHORT TERM...AS FEARED...COLD AIR HAS REMAINED TRAPPED IN MANY
VALLEYS IN JOSEPHINE...JACKSON AND SISKIYOU COUNTIES. THE FRONT
COMING ASHORE TONIGHT IS NOT SPECTACULAR IN ANY WAY. ON
SATELLITE...IT IS RATHER DIFFUSE. UPPER AIR SUPPORT FROM A JET
STREAM IS VERY MINIMAL. THE 300 MB WINDS ARE AROUND 70 TO 80 KTS BUT
THE 850 MB WINDS ARE ONLY 15 KTS. THE CURRENT TIMING OF TH ONSET OF
PRECIPITATION APPEARS TO BE ON TRACK WITH IT STARTING ON THE COAST
AROUND 00Z AND REACHING THE CASCADES AROUND 05Z. THE COLD AIR
REMAINING IN THE VALLEYS HAS RAISED THE CONFIDENCE IN SOME FREEZING
RAIN FALLING. THE MOST LIKELY AREAS FOR THIS WILL BE THE ILLINOIS
AND APPLEGATE VALLEYS AND THE ROGUE VALLEY AROUND GRANTS PASS. THE
ROGUE VALLEY IN JACKSON COUNTY HAS ALSO STAYED COLD SO SHOULD SEE
SOME LIGHT FREEZING RAIN STARTING AROUND 8 PM/04Z.  AN ADVISORY WILL
BE ISSUED SHORTLY FOR AREAS IN JACKSON AND JOSEPHINE COUNTIES MOST
LIKELY TO SEE FREEZING RAIN.  SOME AREAS IN SISKIYOU AND KLAMATH
COUNTIES COULD SEE PATCHY FREEZING RAIN BUT THE PROBABLILITY IS MUCH
LESS. THE PRECIPIATION IN KLAMATH COUNTY COULD FALL AS SLEET SINCE
THE ATMOSPHERE IS MUCH COLDER EAST OF THE CASCADES. THE 00Z SOUNDING
FROM MEDFORD WILL BE VERY TELLING AS TO THE CHANCES OF FREEZING RAIN
BUT THAT DATA WON`T BE AVAILBLE FOR SEVERAL HOURS YET.

FOLLOWING THIS WEAK FRONT...THE MIDDLE LEVELS OF THE ATMOSPHERE COOL
WHICH COULD ALLOW THE INVERSIONS TO BREAK WHICH WILL BRING WARMER
AFTERNOON TEMPERATURES THROUGH THE WEEKEND.

.LONG TERM...MONDAY THROUGH THURSDAY...THE FORECAST FOR EARLY NEXT
WEEK WILL BE INFLUENCED BY THREE UPPER LEVEL FEATURES. ON EARLY
MONDAY MORNING...THERE WILL BE A TROUGH IN THE GULF OF ALASKA, A
RIDGE OVER CALIFORNIA THAT EXTENDS ACROSS OUR AREA INTO THE SOUTHERN
OREGON OFFSHORE WATERS, AND ALSO A CLOSED LOW FAR OFFSHORE FROM
CALIFORNIA. WITH THIS REX BLOCK PATTERN IN PLACE, THERE IS VERY HIGH
CONFIDENCE IN THE FORECAST FOR MONDAY AND HIGH CONFIDENCE FOR
TUESDAY. CONDITIONS ON MONDAY WILL RESEMBLE THOSE FROM SUNDAY. IT
WILL BE DRY AND THERE WILL BE A STRONG INVERSION IN PLACE WITH
PATCHY LATE NIGHT AND MORNING FOG AND FREEZING FOG IN WEST SIDE
VALLEYS. THE MOST DIFFICULT PORTION OF THE MONDAY FORECAST IS THE
FORECAST OF HIGH TEMPERATURES IN WEST SIDE VALLEYS AS THEY WILL
DEPEND UPON THE RAPIDITY OF STRATUS AND FOG DISSIPATION.

THE PATTERN WILL EVOLVE SLOWLY WITH TUESDAY LIKELY TO BE ANOTHER
DRY DAY UNDER A WEAKENING RIDGE. BOTH TROUGHS WILL BE APPROACHING
THE WEST COAST WITH THE SOUTHERN SYSTEM HEADING TOWARD CALIFORNIA
AND THE NORTHERN SYSTEM MOVING INTO BRITISH COLUMBIA. THIS WILL VERY
LIKELY BRING AN INCREASE IN HIGH CLOUDS WHICH WOULD HINDER THE
DISSIPATION OF MORNING WEST SIDE VALLEY LOW CLOUDS AND FOG.

IN A REVERSAL FROM THE NORMAL MODEL BIASES, THE 12Z ECMWF IS FASTER
THAN THE 12Z GFS WITH THE SOUTHERN BRANCH AND BOTH FASTER AND WETTER
WITH THE NORTHERN BRANCH. I HAVE GONE WITH A MODEL BLEND, SLIGHTLY
LEANING TOWARD THE ECMWF. THIS IS CLOSER TO CLIMATOLOGICAL NORMAL
FOR THIS NORMALLY WET TIME OF THE YEAR. AS A RESULT, THE PROBABILITY
OF PRECIPITATION WAS INCREASED FOR WEDNESDAY AND WEDNESDAY NIGHT
WITH A SNOW LEVEL FORECAST TO FALL FROM AROUND 5000 FEET TO AROUND
2500 FEET. THIS DOES NOT LOOK TO BE A MAJOR PRECIPITATION PRODUCER,
WITH A BALLPARK FIGURE OF 3 TO 6 INCHES IN THE SOUTHERN OREGON
CASCADES AND LESS TO THE SOUTH AND EAST.

A NORTHWEST UPPER LEVEL FLOW PATTERN WILL LIKELY FOLLOW THURSDAY
INTO THE END OF THE WEEK WITH A SERIES OF WEAK DISTURBANCES. THIS
WOULD RESULT IN AN OCCASIONAL CHANCE OF MAINLY WEST SIDE
SHOWERS/SNOW SHOWERS AND TEMPERATURES BELOW NORMAL...BUT NOT NEARLY
AS COLD AS THEY HAVE BEEN DURING THE PAST WEEK. /DW

&&

.AVIATION...BASED ON THE 12/18Z TAF CYCLE. VALLEY IFR...MAINLY
WEST OF THE CASCADES...HAS CLEARED TO MVFR THIS AFTERNOON. HOWEVER,
A WEAK FRONT WILL MOVE ONSHORE LATE THIS AFTERNOON AND TRACK
INLAND OVERNIGHT. THIS WILL BRING MVFR CIGS AND VSBYS WITH PERIODS
OF RAIN TO THE COAST. THE MVFR AND PRECIPITATION WILL SPREAD
INLAND TO SOUTH CENTRAL OREGON DURING THE EVENING WITH THE HIGHER
TERRAIN BECOMING OBSCURED. PRECIPITATION WILL CONTINUE UNTIL
AROUND 15Z FRIDAY MORNING AND WILL FALL AS SNOW ABOVE 4500 FT MSL.
BUT WITH TRAPPED COLD AIR... LIGHT FREEZING RAIN IS POSSIBLE IN
THE VALLEYS OF JOSEPHINE, JACKSON, KLAMATH, AND SISKIYOU COUNTIES.
IT WILL REMAIN MOSTLY VFR IN LAKE AND MODOC COUNTIES.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...FREEZING RAIN ADVISORY UNTIL 7 AM PST FRIDAY FOR ORZ024-026.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 1 AM PST FRIDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 1 AM PST FRIDAY
     FOR PZZ350-356-370-376.

$$

JBL/DW/DW