Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 290515
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
915 PM PST WED JAN 28 2015

.DISCUSSION...A WEAK TROUGH IS PRESENT ALONG THE OREGON COAST
WITH MID LEVEL AND UPPER LEVEL CLOUDS ACROSS MUCH OF OUR AREA. IT
IS PRODUCING SOME VIRGA OVER THE SOUTHERN OREGON COAST THIS
EVENING, EVIDENT ON OUR KMAX RADAR. THE TROUGH WILL MOVE NORTHEAST
INTO NORTHERN OREGON BY THURSDAY MORNING WITH A NOTABLE DECREASE
IN THE CURRENT CLOUD COVER AFTER AROUND 5 AM PST. OTHERWISE, THE
BLANKET OF HIGHER CLOUDS HAS LIMITED/DELAYED THE DEVELOPMENT OF
WEST SIDE VALLEY LOW CLOUDS AND FOG THIS EVENING. LOW CLOUDS AND
FOG ARE EXPECTED TO DEVELOP IN THE WEST SIDE VALLEYS OVERNIGHT
WITH THE MOST WIDESPREAD COVERAGE BETWEEN 4 AM AND 10 AM PST.

A HIGH PRESSURE RIDGE WILL BUILD TO THE COAST THURSDAY NIGHT THEN
ACROSS THE AREA THROUGH SATURDAY NIGHT. THE 00Z GFS INDICATES A
PERIOD OF LIGHT TO MODERATE PRECIPITATION SUNDAY NIGHT THROUGH
MONDAY MORNING WITH SNOW LEVELS GENERALLY 6000 TO 7000 FEET.
HIGH PRESSURE IS LIKELY TO RETURN THEREAFTER INTO MID-WEEK.

&&

.AVIATION...BASED ON THE 29/00Z TAF CYCLE...IFR CIGS/VSBYS OVER THE
WEST SIDE VALLEYS WILL RETURN TO THE SAME AREAS LATE TONIGHT THROUGH
LATE MORNING THURSDAY.  THE REMAINDER OF THE AREA WILL REMAIN
VFR. /FB

&&

.MARINE...UPDATED AT 130 PM WEDNESDAY 28 JANUARY 2015...HIGH
PRESSURE WILL BUILD INTO THE COASTAL WATERS BEHIND THE COLD FRONT
WITH A SURFACE TROUGH EXPANDING NORTH FROM CALIFORNIA NORTH INTO
WESTERN OREGON VALLEYS. THIS WILL LEAD TO MODERATE NORTHERLY WINDS
THURSDAY INTO FRIDAY...RESULTING IN INCREASED CHOP...ESPECIALLY
SOUTH OF CAPE BLANCO. SMALL CRAFT CONDITIONS MAY DEVELOP THERE
THURSDAY NIGHT. THE HIGH PRESSURE WILL WEAKEN SATURDAY NIGHT AS THE
NEXT FRONT APPROACHES...AND THAT FRONT WILL MOVE ONSHORE SUNDAY
NIGHT. /FB


&&

.PREV DISCUSSION... /ISSUED 218 PM PST WED JAN 28 2015/

DISCUSSION...CURRENT VISIBLE IMAGE SHOWS A FEW HIGH CLOUDS MOVING
OVER THE AREA AND MID LEVEL CLOUDS IN CURRY AND JOSEPHINE COUNTY.
THE LAST OF THE LOW CLOUDS ARE BURNING OFF IN THE UMPQUA BASIN AND
SHOULD BE MAINLY CLEAR THIS EVENING. LITTLE CHANGE IN THE PATTERN
IS EXPECTED TONIGHT WITH LOW CLOUDS AND AREAS OF FOG EXPECTED
AGAIN FOR THE SAME AREAS AS IN PREVIOUS NIGHT/MORNINGS. ELSEWHERE
EXPECT MOSTLY CLEAR SKIES.

THE MODELS SHOW LIGHT OFFSHORE FLOW DEVELOPING ON THURSDAY, BUT
THE INVERSION IS EXPECTED TO REMAIN STRONG IN THE VALLEYS, SO FOG
AND LOW CLOUDS ARE STILL LIKELY. HOWEVER BY THURSDAY NIGHT, THE
OFFSHORE FLOW IS EXPECTED TO INCREASE AND WINDS ALOFT ARE
EXPECTED TO INCREASE AND PRIMARILY FROM THE EAST NORTHEAST
ADVECTING IN A DRIER AIR MASS. SO THERE IS A CHANCE THAT SOME OF
THE DRIER AIR COULD GET MIXED DOWN INTO THE VALLEYS, THUS LIMITING
OR EVEN PREVENTING LOW CLOUDS AND FOG FROM DEVELOPING. THIS WILL
CONTINUE FRIDAY NIGHT INTO SATURDAY MORNING. IF WE GET ENOUGH
MIXING, THEN TEMPERATURES ON FRIDAY AND SATURDAY COULD GET INTO
THE UPPER 50S OR EVEN HIT THE 60 DEGREE MARK IN PARTS OF THE ROGUE
AND ILLINOIS VALLEY AND UMPQUA BASIN.

DRY WEATHER CONTINUES SATURDAY NIGHT WITH INCREASING CLOUDS AHEAD
OF THE NEXT FRONTAL BOUNDARY. -PETRUCELLI

MEDIUM RANGE FORECAST...SUNDAY THROUGH WEDNESDAY.

THE EXTENDED FORECAST PERIOD WITH A WEAKENING RIDGE OVER THE WESTERN
U.S. SHORT WAVES RIDING OVER THE RIDGE WILL CONTINUE TO WEAKEN
IT...WITH FLOW ALOFT BECOMING NEARLY ZONAL SUNDAY NIGHT INTO MONDAY.

THIS WILL OPEN THE STORM DOOR A BIT FOR THE MEDFORD CWA. BOTH THE EC
AND GFS SOLUTIONS MOVE A WEAK FRONT ONSHORE SUNDAY.  A WAVE WILL
DEVELOP ON THE SOUTH END OF THE FRONT OFFSHORE AND THIS WAVE WILL
AMPLIFY AND MOVE ONSHORE SUNDAY NIGHT. THIS WILL BRING MORE
WIDESPREAD PRECIPITATION TO THE AREA AT THAT TIME.  THE FRONTAL ZONE
WILL REMAIN OVER THE AREA MONDAY INTO TUESDAY FOR GENERALLY SHOWERY
UNSETTLED WEATHER.

THE LONG WAVE RIDGE WILL REDEVELOP OFFSHORE TUESDAY AND MOVE BACK
ONSHORE WEDNESDAY. BOTH OF THE MEDIUM-RANGE MODEL SOLUTIONS SUPPORT
THIS SCENARIO...BUT THE EC IS WEAKER AND A BIT MORE PROGRESSIVE WITH
THE RIDGE.  WITH THIS PATTERN...ONE WOULD EXPECT THE SHOWER ACTIVITY
TO END TUESDAY NIGHT INTO WEDNESDAY....WITH WARMER AND DRIER
CONDITIONS AND AIR STAGNATING IN THE INLAND VALLEYS WEDNESDAY INTO
FRIDAY. THE GFS SUPPORTS THIS...BUT THE EC BRINGS SYSTEMS OVER THE
RIDGE AND INTO THE AREA FOR A MOSTLY WET SECOND HALF OF THE WEEK.
GIVEN THE STRENGTH OF THE RIDGE...THINK THE EC SCENARIO IS TOO WET.
WILL STILL HAVE SOME POPS IN THERE FOR WEDNESDAY...BUT NOT AS MUCH
AS THE EC WOULD SUGGEST. -JRS

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...NONE.

$$

DW/DW/FB


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