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[Printable]
622
FXUS66 KMFR 212230
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
230 PM PST SUN DEC 21 2014

.DISCUSSION...RAINFALL IS FINALLY BEGINNING TO TAPER OFF THIS
AFTERNOON ACROSS THE FORECAST AREA, ALTHOUGH PRECIPITATION WILL
NOT COME TO AN END FOR MOST AREAS UNTIL AT LEAST TOMORROW MORNING,
WHILE AREAS ALONG THE COAST AND ALONG THE CASCADES COULD SEE RAIN
CONTINUING THROUGH TOMORROW EVENING. RAINFALL AMOUNTS OVER THE
LAST 48 TO 72 HOURS HAVE BEEN INTERESTING TO SAY THE LEAST, WITH
MOST STATIONS ALONG AND WEST OF THE CASCADES IN OREGON AND WESTERN
SISKIYOU COUNTY IN CALIFORNIA RECEIVING SEVERAL INCHES. THE ROGUE
VALLEY, EAST SIDE, AND THE REST OF NORTHERN CALIFORNIA HAVE SEEN
ANYWHERE FROM A HALF INCH TO AN INCH. RESULTING RUNOFF HAS BROUGHT
SIGNIFICANT RISES TO MANY AREA RIVERS AND STREAMS. WILL KEEP FLOOD
HEADLINES IN PLACE THROUGH THIS AFTERNOON AND EVENING TO COVER
RESIDUAL RUNOFF, BUT IT APPEARS THE HIGHEST WATERS ARE OVER FOR
ALL BUT MAIN STEM RIVERS SUCH AS THE COQUILLE AND UMPQUA. SEE THE
FLOOD STATEMENTS FOR MORE INFORMATION.

AS MENTIONED ABOVE, RAINFALL WILL COME TO AN END, GENERALLY FROM
SOUTH TO NORTH, THROUGH TOMORROW MORNING AS SURFACE HIGH PRESSURE
AND UPPER LEVEL RIDGING BUILDS INTO THE REGION. THERE IS THE
POTENTIAL FOR SOME LIGHT SHOWERS TO CONTINUE ALONG THE NORTHERN TIER
OF THE FORECAST AREA, MOSTLY AS A RESULT OF MOIST ONSHORE FLOW AND
PERHAPS A SHORTWAVE OR TWO PASSING WELL TO OUR NORTH. THE WEATHER
WILL STAY GENERALLY BENIGN UNTIL THE NEXT SYSTEM DUE CHRISTMAS EVE.

THE RIDGE WILL SLIDE EAST AS THE EXPECTED UPPER LEVEL TROUGH PUSHES
INTO THE REGION FROM THE PACIFIC. THE AIR MASS OVER THE AREA WILL BE
WARM, WITH SNOW LEVELS GENERALLY WELL ABOVE 9000 FEET, BUT THE
INCOMING FRONT WILL BRING MUCH COLDER AIR BEHIND IT, DROPPING SNOW
LEVELS SIGNIFICANTLY BY CHRISTMAS MORNING.

FOR THOSE THINKING OF THE APPROACHING HOLIDAY, YES THERE WILL BE
MOISTURE AND COLD AIR MOVING INTO THE REGION CHRISTMAS EVE. HOWEVER,
MOST OF THE PRECIPITATION WILL FALL AS RAIN, WITH SNOW LEVELS NOT
DROPPING FAR ENOUGH FOR SIGNIFICANT AREA COVERAGE OF SNOW UNTIL MOST
OF THE PRECIPITATION HAS ALREADY OCCURRED. THEREFORE, THE CHANCES OF
A WHITE CHRISTMAS WILL DEPEND GREATLY UPON ONE`S LOCATION. THE COAST
AND THE WEST SIDE VALLEYS WILL LIKELY SEE ONLY RAIN, WAKING UP TO A
WET CHRISTMAS MORNING. HOWEVER, FOR THOSE ABOVE 2500 TO 3000 FEET,
THERE IS A GOOD CHANCE OF FRESHLY FALLEN SNOW CHRISTMAS MORNING,
ALTHOUGH AMOUNTS SHOULD BE LIGHT.

UNFORTUNATELY, THIS ELEVATION ALSO INCLUDES MANY AREA PASSES,
INCLUDING SISKIYOU SUMMIT, SNOWMAN`S SUMMIT, BLACK BUTTE SUMMIT, AND
ALL OF THE CASCADE PASSES. LAST MINUTE TRAVEL IN THOSE AREAS COULD
BE IMPACTED, SO THOSE EXPECTING TO DRIVE OVER THE PASSES DURING THIS
TIME SHOULD STAY UPDATED WITH THE LATEST FORECASTS AND KEEP AN EYE
ON DOT ROAD CONDITIONS.

BEYOND CHRISTMAS, THERE IS FAIRLY GOOD CONFIDENCE IN THE DEVELOPMENT
OF ANOTHER RIDGE BUILDING OVERHEAD. THIS SHOULD KEEP MOST OF THE
AREA DRY, ALTHOUGH SOME PRECIPITATION IS POSSIBLE IN THE NORTHERN
HALF OF THE FORECAST AREA AS SWIFT MIDLEVEL FLOW IS LIKELY TO
CONTINUE PUSHING MOISTURE ONSHORE, JUST AS EARLIER IN THE WEEK.  THE
NEXT FRONT EXPECTED TO APPROACH AND POSSIBLY CLEAR THE AREA WOULD BE
ON SATURDAY OR SUNDAY, HOWEVER, MODELS ARE NOT IN CLEAR AGREEMENT,
NOR DO THEY SHOW A STRONG FRONT. CONFIDENCE IS THEREFORE LOW, SO
HAVE NOT ADDED MORE THAN A CHANCE FOR RAIN HEADING INTO NEXT WEEKEND.

DURING THE PERIODS OF HIGH PRESSURE, IT IS COMMON THIS TIME OF YEAR
TO SEE FOG DEVELOPING IN MOST LOW LYING AREAS. CONSIDERING THE
COPIOUS AMOUNTS OF MOISTURE WE HAVE SEEN SO FAR THIS SEASON, FOG,
OR AT LEAST LOW LEVEL CLOUDINESS, SEEMS QUITE LIKELY IN THE VALLEYS
OF THE WEST SIDE, NORTHERN CALIFORNIA, AND THE KLAMATH BASIN.
FORTUNATELY, THE EXPECTED TROUGHS SHOULD CLEAR THE AIR ENOUGH WITH
THEIR PASSAGE TO PREVENT ANY AIR STAGNATION CONCERNS, BUT TRAVELERS
SHOULD BE CAUTIOUS WHEN DRIVING AS FOG COULD BECOME VERY DENSE AT
TIMES, AND MAY PERSIST WELL INTO THE DAY IN SOME LOCATIONS. -BPN


&&

.AVIATION...BASED ON THE 21/18Z TAF CYCLE...A MOIST PACIFIC JET
STREAM REMAINS AIMED AT OUR AREA, BUT MOISTURE WILL DIMINISH
THROUGH THE AFTERNOON AND EVENING. WIDESPREAD MTN OBSCURATION
WITH RAIN AND MVFR CIGS/VIS WILL CONTINUE THROUGH THE DAY AND INTO
THE EVENING. LITTLE IMPROVEMENT IN CEILINGS TONIGHT AS HIGH
PRESSURE BEGINS TO BUILD. RAIN WILL TAPER OFF, BUT VALLEY IFR
FOG/STRATUS IS LIKELY TO BECOME WIDESPREAD INLAND. -BPN

&&

.MARINE...UPDATED 220 PM PST SUN DEC 21 2014...WEAK HIGH PRESSURE
WILL REMAIN OVER THE WATERS THROUGH TUESDAY RESULTING IN RELATIVELY
LIGHT AND VARIABLE WINDS. HOWEVER... MODERATE WEST SWELL WILL
CONTINUE. A COLD FRONT WILL BRING A PERIOD OF STRONG WINDS AND STEEP
SEAS TO THE WATERS CHRISTMAS EVE INTO CHRISTMAS DAY. -WRIGHT

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH WIND WARNING UNTIL 10 PM PST THIS EVENING FOR
     ORZ030-031-624-625.
     FLOOD WATCH UNTIL 10 PM PST THIS EVENING FOR
     ORZ025-027-616-617-624.
     FLOOD WATCH UNTIL 10 PM PST THIS EVENING FOR ORZ024-618-619.
     FLOOD WATCH UNTIL 10 PM PST THIS EVENING FOR ORZ026-620>623.
     FLOOD WATCH UNTIL 10 PM PST THIS EVENING FOR ORZ021-022-615.
     FLOOD WATCH UNTIL 10 PM PST THIS EVENING FOR ORZ023.

CA...HIGH WIND WARNING UNTIL 10 PM PST THIS EVENING FOR CAZ085-285.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
     UNTIL 10 AM PST THURSDAY FOR PZZ350-356-370-376.

$$

BPN/TRW




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