Hazardous Seas Warning 34, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
100 AM PDT THU JUL 21 2011

.DISCUSSION...21/00Z NAM/GFS IN.

AN UPPER LOW IS NOW MOVING THROUGH BRITISH COLUMBIA AND THE
ASSOCIATED SURFACE FRONT WILL MOVE ONSHORE OVER WASHINGTON STATE
AND NORTHERN OREGON LATER THIS MORNING. THE FRONT WILL BE VERY
WEAK BY THE TIME IT MOVES ONSHORE OVER SOUTHERN OREGON THIS
AFTERNOON. IT WON'T BRING ANY RAIN TO THE AREA...BUT IT WILL
THICKEN THE MARINE LAYER AND SOME DRIZZLE MAY ACCOMPANY THAT
PROCESS. EXPECT SOME MARINE CLOUD COVER TONIGHT INTO THURSDAY OVER
MOST OF THE CWA WEST OF THE CASCADES AND NORTH OF THE SISKIYOUS.
THE REMAINDER OF THE AREA WILL REMAIN MOSTLY CLEAR...ALTHOUGH
THERE MAY BE SOME GUSTY WINDS OVER THE RIDGES AND EAST OF THE
CASCADES THURSDAY AFTERNOON/EVENING.

ONCE THAT UPPER TROUGH DEPARTS THE AREA LATER TODAY...A LONG WAVE
RIDGE WILL BUILD IN FROM THE WEST. THIS WILL INITIATE A WARMING
TREND INLAND. HIGHS WILL WARM TO NEAR SEASONAL NORMALS FRIDAY...AND
ABOVE NORMAL THIS WEEKEND. THE RIDGING AND WARMING ALOFT WILL ACT
TO THIN THE MARINE LAYER AND STRENGTHEN THE INVERSION TOPPING
IT...SO EXPECT OVERNIGHT MARINE CLOUDS TO GRADUALLY RETREAT TO THE
COAST...THOUGH THERE WILL STILL BE A LOT AROUND THURSDAY NIGHT
INTO FRIDAY. IT WILL REMAIN DRY FROM THIS AFTERNOON THROUGH
SATURDAY.

THE RIDGE WILL BREAK TO THE EAST SATURDAY...BUT IT WILL STRENGTHEN
AS IT DOES SO...SO 500 MB HEIGHTS WILL CONTINUE INCREASING INTO
SATURDAY NIGHT. HOWEVER...AS THE FLOW ALOFT BACKS TO
SOUTHWESTERLY...SOME MOISTURE MAY SNEAK UP FROM THE SOUTH ON
SUNDAY. THE GFS SHOWS SOME CONVECTIVE FEEDBACK OVER THE CASCADES
THAT DAY.  THE CURRENT FORECAST HAS A SLIGHT CHANCE OF
THUNDERSTORMS FOR THE CASCADES SUNDAY AFTERNOON AND THAT LOOKS GOOD AT
THIS TIME.

LONG TERM DISCUSSION FROM THE WEDNESDAY AFTERNOON AFD...MONDAY
THROUGH WEDNESDAY. ANOTHER TROUGH WILL BEGIN TO DROP IN FROM THE
NORTHWEST SUNDAY AND EXIT ON MONDAY. THE MODELS ALL AGREE ON THIS
FEATURE BUT DIFFER WHEN IT COMES TO STRENGTH AND TIMING. PREVIOUS
RUNS WERE SLIGHTLY SLOWER THAN THE MOST RECENT 12Z RUNS...WHICH
SPEED UP ITS MOVEMENT AND ALSO WEAKEN IT A BIT. INSTABILITY
DEVELOPS OVER THE CASCADES/SISKIYOUS SUNDAY OUT AHEAD OF THE
TROUGH. PREVIOUS MODEL RUNS ALSO DEVELOPED WEAK INSTABILITY OVER
THE MOUNTAINS AND ACROSS THE EAST SIDE MONDAY AS THE TROUGH MOVED
THROUGH. THE MOST RECENT 12Z RUNS HAVE BACKED OFF THIS IDEA AS THE
TROUGH IS FASTER/WEAKER AND EXITS THE CWA BY EARLY AFTERNOON.
MOISTURE FIELDS APPEAR TO BE LIMITED AND STEERING WINDS ARE MORE
WESTERLY ON MONDAY AS WELL. IN COORDINATION WITH THE FIRE WEATHER
DESK...WE MAINTAINED A SLIGHT CHANCE OF SHOWERS/TSTMS OVER THE
CASCADES SUNDAY AFTERNOON/EVENING AND EXTENDED IT FARTHER EAST TO
THE HIGHER TERRAIN ON THE EAST SIDE ON MONDAY TO ACCOUNT FOR THIS
UNCERTAINTY.

&&

.AVIATION...COAST...MVFR CIGS FROM CAPE BLANCO NORTH TO REEDSPORT
AND NEAR BROOKINGS WILL CONTINUE THROUGH THURSDAY MORNING WITH
LOCAL IFR CIGS DEVELOPING TONIGHT INTO THURSDAY MORNING...THEN
AREAS OF MVFR CIGS CONTINUING THURSDAY AFTERNOON. SOUTH OF CAPE
BLANCO EXCEPT NEAR BROOKINGS EXPECT VFR CONDITIONS THROUGH
THURSDAY AFTERNOON. INLAND...LOW CLOUDS WITH MVFR CIGS AND LOCAL
IFR CIGS WILL SPREAD INTO THE UMPQUA BASIN LATE TONIGHT THROUGH
EARLY THURSDAY MORNING..CLEARING TO VFR IN THE MID TO LATE
MORNING. LOCAL MVFR CIGS MAY ALSO SPILL INTO THE ROGUE AND
ILLINOIS VALLEYS LATE TONIGHT INTO EARLY THURSDAY MORNING BUT WILL
REMAIN MOSTLY VFR. ELSEWHERE EXPECT VFR CONDITIONS THROUGH
THURSDAY AFTERNOON.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PZ...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT FRIDAY FOR
        PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT FRIDAY
        FOR PZZ356.
     GALE WATCH FROM FRIDAY AFTERNOON THROUGH FRIDAY EVENING FOR
        PZZ376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 2 PM PDT FRIDAY FOR PZZ376.
     HAZARDOUS SEAS WATCH FROM FRIDAY AFTERNOON THROUGH FRIDAY
        EVENING FOR PZZ376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 2 PM PDT FRIDAY
        FOR PZZ376.

15/15/04