Small Craft Advisory 51, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
856 PM PDT FRI APR 29 2016

.UPDATE...

&&

.DISCUSSION...

NO MAJOR CHANGES FROM THE PREVIOUS FORECAST(SEE PREVIOUS
DISCUSSION). THE THERMAL TROUGH IS STILL EXPECTED TO FORM DURING
 THIS WEEKEND. THE MAJOR FORECAST CHALLENGE WILL BE TEMPERATURES
FOR THE WEST SIDE AND BROOKINGS. LOOKING AT 850 MB WINDS, THEY
SHOULD BE MOVING DOWN THE CHETCO AND SOME OF OUTLING GUIDANCE IS
SUGGESTING HIGHS IN THE UPPER 70'S FOR BROOKINGS AFTER 0Z SUNDAY.
WILL LET THE NIGHT SHIFT MAKE THE FINAL DECISION ON THAT.

ALSO ADJUSTED SOME OF THE WINDS TOWARDS THE HIGHER RES MODELS FOR
THE MARINE WINDS.

&&

.AVIATION...FOR THE 30/00Z TAF CYCLE...FROM THE CASCADES
WEST...EXPECT MAINLY VFR THIS EVENING...BUT AREAS OF MVFR CIGS OVER
THE COASTAL WATERS WILL GRADUALLY SPREAD INLAND THIS EVENING WITH
MORE HIGHER TERRAIN BECOMING OBSCURED. THE LOWER CONDITIONS WILL
CLEAR OFF TO VFR BY SATURDAY AFTERNOON AND CONDITIONS WILL REMAIN
VFR THROUGH SATURDAY NIGHT.  EAST OF THE CASCADES...VFR CONDITIONS
WILL PREVAIL THROUGH SATURDAY...BUT SOME HIGHER TERRAIN WILL BE
OBSCURED THROUGH SATURDAY MORNING. WINDS WILL BE GUSTY OVER THE AREA
THROUGH THIS EVENING AND SOME ISOLATED THUNDERSTORMS MAY DEVELOP
OVER LAKE AND MODOC COUNTIES. GUSTY WINDS WILL RETURN TO THE EAST
SIDE SATURDAY. -BPN

&&

.MARINE...UPDATED 850 PM PDT FRI 29 APR 2016... A THERMAL TROUGH
WILL BUILD NEAR THE COAST TONIGHT INTO SATURDAY...THEN MOVE OVER THE
COASTAL WATERS SATURDAY NIGHT. NORTH GALES ARE EXPECTED SATURDAY
AFTERNOON AND EVENING SOUTH OF CAPE BLANCO WITH HIGH VERY STEEP SEAS OVER
NEARLY ALL AREAS. THE THERMAL TROUGH WILL WEAKEN SUNDAY INTO MONDAY
AND WINDS AND SEAS WILL SUBSIDE AS IT DOES SO. ANOTHER COLD FRONT
WILL MOVE THROUGH THE WATERS TUESDAY INTO TUESDAY NIGHT. -BPN/CZS

&&

.PREV DISCUSSION... /ISSUED 247 PM PDT FRI APR 29 2016/

SHORT TERM...THIS AFTERNOON THROUGH MONDAY...SHOWERS ARE
WIDESPREAD THIS AFTERNOON...WITH RAIN AMOUNTS GENERALLY LESS THAN
A TENTH OF AN INCH SO FAR. MODELS HAVE UNDERFORECAST COVERAGE OF
SHOWERS SO FAR...AND HAVE UPPED PRECIPITATION CHANCES THROUGH THE
AFTERNOON FOR MOST PLACES. THERE IS STILL A CHANCE OF
THUNDERSTORMS IN PORTIONS OF LAKE AND MODOC COUNTIES THROUGH THE
EVENING. THESE SHOWERS ARE ASSOCIATED WITH A COLD FRONT THAT IS
MOVING THROUGH THE FORECAST AREA...AND THE INSTABILITY BEHIND THE
FRONT. THE AIR MASS BECOMES STABLE TONIGHT AND DRIES OUT
SIGNIFICANTLY TOMORROW...RESULTING IN ABOVE NORMAL TEMPERATURES
AND PARTLY TO MOSTLY SUNNY SKIES SATURDAY AFTERNOON FOR MOST
LOCATIONS.

ON SUNDAY TEMPERATURES WILL RISE ANOTHER 10+ DEGREES AS OFFSHORE
FLOW PEAKS ACROSS THE AREA. COASTAL TEMPERATURES WILL LIKELY RISE TO
80 DEGREES...AND POSSIBLY HIGHER AT BROOKINGS. WE HAVE INCREASED
FORECAST HIGHS AT THE COAST AND WINDS OVER THE MOUNTAINS BASED ON
LATEST DATA. NAM12 H8 WINDS PEAK AROUND 25KT ON SUNDAY MORNING.
ENSEMBLE PERCENTILES SUGGEST THIS IS A STATISTICALLY SIGNIFICANT
OFFSHORE FLOW EVENT...IN TERMS OF MAGNITUDE OF EASTERLY FLOW...FOR
THIS TIME OF YEAR.

FLOW WILL SHIFT FROM EASTERLY TO SOUTHERLY ON MONDAY AND
TEMPERATURES WILL LIKELY PEAK OVER WEST SIDE VALLEYS AS THE THERMAL
TROUGH MOVES WELL INLAND. THE COAST WILL COOL OFF SHARPLY ON MONDAY
AS FLOW TURNS ONSHORE AND A STRATUS SURGE MAKES ITS WAY UP THE
COASTLINE. THE GFS SHOWS SOME INSTABILITY MONDAY AFTERNOON AND HAVE
MAINTAINED SLIGHT CHANCE TO CHANCE SHOWERS WITH A FEW
THUNDERSTORMS OVER THE CASCADES AND MODOC COUNTY. GIVEN ITS THE
FIRST DAY WITH SOUTHERLY FLOW...AND WITH NOT MUCH IN THE WAY OF
SHORTWAVE ACTIVITY...AM NOT TOO OPTIMISTIC ABOUT THUNDER CHANCES
ON MONDAY.

LONG TERM...TUESDAY THROUGH FRIDAY.

THE GFS/EC/DGEX MODELS AND THEIR RESPECTIVE ENSEMBLES ALL DEPICT A
DEEP LONG WAVE TROUGH BETWEEN 130W AND 135W TUESDAY MORNING WITH
SOUTHERLY FLOW ALOFT OVER THE MEDFORD CWA.

THE TROUGH WILL BE SLOW TO PROGRESS AS IT WILL BE SHEARING AS IT
APPROACHES THE COAST.  THIS PROCESS WILL BE COMPLETE BY THURSDAY
MORNING...WHEN WHAT REMAINS OF THE TROUGH MOVES ONSHORE. THE CUTOFF
LOW WILL BE LEFT BEHIND...BUT JUST WHERE IS WHERE THE MODEL
SOLUTIONS...INCLUDING THE ENSEMBLES...DIVERGE. THE GFS40 PUTS IT
OVER SOUTHERN CALIFORNIA WHILE THE DGEX GOES WITH THE BAY AREA.
MEANWHILE THE EC IS THE LEAST PROGRESSIVE...LEAVING THE CUTOFF OUT
NEAR 33N 135W...WHICH IS ABOUT 300 NM OFF THE SOUTHERN CALIFORNIA
COAST. IN EVERY CASE THOUGH THERE WILL BE SOUTHERLY FLOW ALOFT OVER
AT LEAST PART OF THE MEDFORD CWA WITH A DEFORMATION ZONE IN THE
VICINITY.

OVERALL...THIS PATTERN SUPPORTS AN UNSETTLED SHOWERY REGIME
TUESDAY.MODEL LIFTED INDICES INDICATE THAT THUNDERSTORMS ARE
POSSIBLE AS WELL.  THE MOST FAVORED AREA FOR THUNDERSTORMS WILL MOVE
A BIT FARTHER EAST EACH DAY...STARTING OFF OVER MOST OF THE AREA
TUESDAY AND MOVING TO THE EAST SIDE BY THURSDAY. HIGH TEMPERATURES
WILL COOL DURING THIS INTERVAL...STARTING OFF 5 TO 10 DEGREES ABOVE
NORMAL TUESDAY...DROPPING TO AROUND NORMAL TO 5 DEGREES ABOVE NORMAL
THURSDAY.

THE PATTERN WILL CONTINUE TO PROGRESS FRIDAY AND THE CUT OFF LOW
WILL MOSTLY LIKELY BE OVER SOUTHERN CALIFORNIA AROUND THAT TIME.
FLOW ALOFT WILL TURN SOUTHEASTERLY OR EASTERLY.  THE EC SOLUTION
KEEPS SHOWER ACTIVITY IN THE AREA WITH THE CUTOFF LOW OVER NEVADA
AND NORTHEAST FLOW ALOFT. MEANWHILE THE GFS PLACES THE LOW FARTHER
SOUTH...PUTTING THE MEDFORD CWA IN A DRIER AND MORE STABLE REGIME
WITH OFFSHORE FLOW.

OVERALL...THERE IS ENOUGH UNCERTAINTY HERE TO KEEP SHOWERS IN THE
FORECAST FOR FRIDAY. THUNDERSTORMS REMAIN A POSSIBILITY OVER THE
FAR EAST SIDE. BOTH THE EC AND THE GFS CONTINUE THE COOLING
TREND...BUT TO DIFFERENT DEGREES. THE GFS HAS INLAND HIGHS FALLING
TO AROUND 5 DEGREES BELOW NORMAL FRIDAY WHILE THE EC GOES WITH
HIGHS AROUND NORMAL.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 2 PM PDT SATURDAY FOR
     PZZ350-356-370-376.
     GALE WARNING FROM 2 PM SATURDAY TO 5 AM PDT SUNDAY FOR
     PZZ356-376.
     HAZARDOUS SEAS WARNING UNTIL 5 AM PDT SUNDAY FOR
     PZZ350-356-370-376.

CZS/JRS/BPN