Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 300449
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
849 PM PST THU JAN 29 2015

.DISCUSSION...AN UPDATE TO THE FORECAST IS NOT NECESSARY.
SCATTERED HIGH CLOUDS ARE LINGERING OVER THE EAST SIDE AS A WEAK
UPPER LEVEL TROUGH IS ON ITS WAY INTO THE GREAT BASIN. OTHERWISE,
LOW CLOUDS AND FOG ARE PERSISTENT IN THE UMPQUA VALLEY AND WILL
DEVELOP IN THE OTHER WEST SIDE INLAND VALLEYS OVERNIGHT. ANOTHER
HIGH PRESSURE RIDGE IS OFFSHORE AND WILL BUILD INTO OUR AREA BY
SATURDAY THEN PERSIST INTO SUNDAY MORNING. THUS, THERE WILL BE
LITTLE CHANGE IN THE PATTERN OF CONDITIONS WITH OFFSHORE EASTERLY
WINDS KEEPING THE COAST CLEAR...ABOVE NORMAL TEMPERATURES...VALLEY
INVERSIONS WITH POOR MIXING OF THE AIR MASS...AND WEST SIDE
VALLEY LOW CLOUDS AND FOG.

AN OCCLUDED FRONT WILL ARRIVE SUNDAY AFTERNOON WITH RAIN MAINLY
FROM SOUTHWEST OREGON NORTHWARD AND A SNOW LEVEL AROUND 7500 FEET.
A MEAGER AMOUNT OF PRECIPITATION WILL LIKELY MAKE IT TO THE EAST
SIDE SUNDAY NIGHT. OF GREATER NOTE IS THAT THIS WILL LIKELY USHER
IN A CHANGE IN THE PATTERN. OUR WEATHER NEXT WEEK WILL LIKELY BE
ACTIVE WITH A SERIES OF FRONTAL SYSTEMS ARRIVING...ESPECIALLY IN
THE LATTER PORTION.

&&

.AVIATION...BASED ON THE 30/00Z TAF CYCLE...VFR PREVAILS ACROSS
THE AREA THIS EVENING...EXCEPT IN THE UMPQUA BASIN AND AT KRBG
WHERE IFR CIGS EXIST. IFR/LIFR LOW CLOUDS/FOG WILL DEVELOP AND
EXPAND TO MANY OF THE OTHER WEST SIDE VALLEYS OVERNIGHT INTO
FRIDAY MORNING, INCLUDING AT KMFR. ALSO EXPECT IFR TO RETURN TO
THE COAST NORTH OF CAPE BLANCO. WHILE AREAS NEAR THE COAST CAN
EXPECT TO IMPROVE TO VFR QUICKLY AFTER SUNRISE...BREAK OUT TIMES
WILL BE LATER OVER THE INTERIOR VALLEYS...GENERALLY BETWEEN 18Z
(KMFR) AND 21Z (KRBG). CONFIDENCE IN THE BREAK OUT AT KRBG IS A
BIT LOWER SINCE IT DIDN`T BREAK TODAY. ELSEWHERE, EXPECT VFR
THROUGH FRIDAY EVENING. /SPILDE

&&

.MARINE...UPDATED AT 200 PM THURSDAY 29 JANUARY 2015...HIGH PRESSURE
OFFSHORE WILL BUILD TONIGHT THROUGH FRIDAY...MODERATE NORTHERLY
WINDS ARE EXPECTED...RESULTING IN INCREASED WIND CHOP...ESPECIALLY
SOUTH OF CAPE BLANCO. THE HIGH PRESSURE WILL WEAKEN SATURDAY NIGHT
AS THE NEXT FRONT APPROACHES. THE FRONT WILL PRODUCE WEAK SOUTH
WINDS AND MODERATE WEST SWELL ON SUNDAY THEN MOVE ONSHORE SUNDAY
NIGHT. /SPILDE

&&

.PREV DISCUSSION... /ISSUED 644 PM PST THU JAN 29 2015/

SHORT TERM...A VERY WEAK UPPER SYSTEM WILL CONTINUE TO SLIDE BY
LARGELY UNNOTICED THIS AFTERNOON, AND THEN THE UPPER RIDGE
REBUILDS STRONGLY AND RULES OUR WEATHER FRIDAY THROUGH SATURDAY.
LOW LEVEL OFFSHORE FLOW HAS ALREADY RESUMED AT THE COAST, AND
THEY`VE CLEARED OUT NICELY. INLAND, STRATUS HAS BURNED OFF WITH
THE EXCEPTION OF PORTIONS OF THE UMPQUA VALLEY. IT IS ALSO SLOWLY
ERODING IN THE UMPQUA, BUT IT MAY NOT FULLY BURN OFF BEFORE IT
BEGINS TO FILL IN AGAIN THIS EVENING. THERE HAS BEEN LITTLE
CHANGE, SYNOPTICALLY, SO LOW LEVEL INVERSIONS WILL LEAD TO ANOTHER
ROUND OF FOG IN WEST SIDE VALLEYS TONIGHT. IN FACT, INVERSIONS
WILL CONTINUE THROUGH THE WEEKEND, AND THUS I`VE EXTENDED THE AIR
STAGNATION ADVISORY ONE MORE DAY (UNTIL SUNDAY AFTERNOON). SINCE
THE PATTERN IS SO PERSISTENT, FEW CHANGES WERE MADE TO THE
FORECAST FOR THE SHORT TERM.

ONE NOTE ABOUT THE COAST: OFFSHORE FLOW CONTINUES THROUGH SATURDAY
AND THIS WILL KEEP MOST OF THE COAST (ESPECIALLY THE CURRY COAST)
CLEAR AND MILD. THE OFFSHORE FLOW PEAKS FRIDAY NIGHT INTO
SATURDAY, AND I`VE RAISED TEMPERATURES FOR THE CURRY COAST AND
ADJACENT MOUNTAINS FOR FRIDAY THROUGH SATURDAY.

THE RIDGE WEAKENS AND SHIFTS EAST ON SUNDAY. THIS WILL MEAN AN
INCREASE IN CLOUD FOR SUNDAY AND ALSO THE CHANCE FOR SOME RAIN
LATE. RAIN USUALLY HAS A HARD TIME MAKING MUCH PROGRESS INLAND IN
THE WAKE OF A STRONG RIDGE, SO THE HIGHEST POPS HAVE BEEN CONFINED
TO THE WATERS AND NORTH COAST SUNDAY INTO SUNDAY NIGHT. HOWEVER,
EVENTUALLY SOME RAIN WILL PROBABLY MAKE IT INLAND, SO I HAVE
RAISED POPS FURTHER INLAND AS WELL. -WRIGHT

LONG TERM...MONDAY THROUGH THURSDAY.

THROUGH THE FIRST HALF OF NEXT WEEK..THE UPPER LEVEL FLOW TURNS
TOWARD ZONAL WESTERLY ACROSS THE EASTERN PACIFIC. THIS WILL ALLOW
A SERIES OF FRONTS TO MOVE INLAND. HOWEVER THE STORM TRACK EITHER
REMAINS NORTH OF OR STAYS IN THE NORTHERN THIRD OF OUR FORECAST
AREA. AS A RESULT RAINFALL AMOUNTS WILL BE LIGHT WITH VERY LITTLE
RAIN SOUTH OF THE SISKIYOU MOUNTAINS INTO NORTHERN CALIFORNIA.

THE LONG WAVE RIDGE WILL REDEVELOP OFFSHORE TUESDAY AND MOVE BACK
ONSHORE WEDNESDAY. THIS IS IN RESPONSE TO A DEEPENING LOW PRESSURE
AND TROUGH IN THE GULF OF ALASKA. BOTH OF THE MEDIUM-RANGE MODEL
SOLUTIONS SUPPORT THIS SCENARIO...BUT THE EC IS WEAKER AND A BIT
MORE PROGRESSIVE WITH THE RIDGE. BOTH MODELS BRING A WARM FRONT
INTO THE COASTAL WATERS TOWARD THE END OF NEXT WEEK. WE HAVE
INTRODUCED RAIN CHANCE FOR SW OREGON IN THE SECOND HALF OF NEXT
WEEK ALTHOUGH CONFIDENCE IS NOT VERY HIGH ON WHEN THE MID WEEK
RIDGE WILL WEAKEN. HOWEVER WITH BOTH MODELS SHOWING WETTING RAIN
BY DAY 10...CONFIDENCE APPROACHES MODERATE THAT WE WILL SEE RAIN
DURING THE FIRST WEEKEND OF FEBRUARY. /FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...AIR STAGNATION ADVISORY UNTIL 1 PM PST SUNDAY FOR
     ORZ023-024-026-616-620-622.
     AIR STAGNATION ADVISORY UNTIL 1 PM PST SUNDAY FOR
     ORZ029>031-623>625.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS
     UNTIL 10 PM PST FRIDAY FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 4 AM PST SATURDAY FOR
     PZZ376.

$$

DW/DW/MAS


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