Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 301200 AAA
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
500 AM PDT SAT APR 30 2016

UPDATED AVIATION AND MARINE DISCUSSIONS...

.DISCUSSION...THE 00Z MODELS ARE IN GOOD AGREEMENT ON THE GENERAL
EVOLUTION OF THE LARGE SCALE PATTERN THROUGH THURSDAY AND SHOW
QUITE A BIT OF CONSISTENCY WITH THEIR PRIOR SOLUTIONS. THUS..
THE FORECAST CHANGES WERE GENERALLY SMALL.

AN OFFSHORE RIDGE WILL BUILD INTO THE PACIFIC NORTHWEST THROUGH
THE WEEKEND. CLOUD COVER WILL DIMINISH TODAY WITH MOSTLY SUNNY TO
SUNNY AND WARM WEATHER THROUGH THE WEEKEND. OFFSHORE FLOW WILL
DEVELOP TODAY WITH A THERMAL TROUGH ALONG THE COAST. THIS PATTERN
WILL THEN PERSIST THROUGH SUNDAY. I HAVE BUMPED THE FORECAST HIGH
TEMPERATURE FOR BROOKINGS TODAY BACK UP BY A FEW DEGREES. THERE
WAS CONCERN ON THE PREVIOUS SHIFT THAT FLOW WOULD BE NORTH RATHER
THAN NORTHEAST UNTIL THIS EVENING. BOTH THE NAM AND GFS INDICATE
THAT WHILE COASTAL FLOW IS STARTING THE DAY FROM THE
NORTH...OFFSHORE WINDS WILL DEVELOP BEFORE THE END OF THE DAY AND
PRODUCE SOME DOWNSLOPE WARMING. THIS WARMING WILL BE MORE
SUBSTANTIAL ON SUNDAY. IT WILL BE MUCH COOLER AT THE COAST MONDAY
BUT THE WARMING TREND IS EXPECTED TO PEAK INLAND ON MONDAY AS THE
THERMAL TROUGH TRACKS INLAND.

THE RIDGE WILL REACH THE ROCKIES ON MONDAY AND A BROAD TROUGH WILL
APPROACH FROM THE WEST. THE FLOW WILL SHIFT FROM EASTERLY TO
SOUTHERLY ON MONDAY AND THIS CHANGE WILL BRING AN INCREASE IN MID-
LEVEL MOISTURE. THERE WILL LIKELY BE CUMULUS BUILDUPS OVER THE
HIGHER TERRAIN AND THERE IS A SLIGHT CHANCE OF SHOWERS.
BUT...WITHOUT A STRONG TRIGGER WILL CONTINUE TO LIMIT MENTION OF A
SLIGHT CHANCE OF THUNDERSTORMS TO THE SOUTHERN OREGON CASCADES AND
THE WARNER MOUNTAINS.

THE PATTERN WILL CONTINUE TO SHIFT ON TUESDAY WITH THE START OF A
COOLER AND WETTER PATTERN OF MORE FREQUENT SHOWERS AND ISOLATED
THUNDERSTORMS. THERE WILL BE A COUPLE OF SHORTWAVES IN THE SOUTH-
SOUTHWEST FLOW ON TUESDAY AND AVAILABLE MOISTURE WILL CONTINUE TO
INCREASE. THE SREF INDICATES THE HIGHEST PROBABILITY OF A
THUNDERSTORM WILL BE OVER OUR NORTHERN TIER FROM AROUND CRATER
LAKE NORTH AND NORTHEASTWARD.

THE FLOW ALOFT WILL BECOME SPLIT ON TUESDAY WITH THE NORTHERN
BRANCH HEADED NORTHEAST INTO CANADA AND THE SOUTHERN BRANCH TOWARD
THE NORTHERN CALIFORNIA COAST BY WEDNESDAY. THE MODELS DO START TO
HAVE DIFFERENCES IN THE POSITION OF FEATURES ON WEDNESDAY BUT
STILL POINT TO IT AND WEDNESDAY NIGHT AS THE WETTEST AND MOST
UNSTABLE PERIOD OF THE WEEK.

BY THURSDAY...THE GFS SOLUTION IS MORE PROGRESSIVE IN SENDING THE
UPPER TROUGH INLAND ACROSS SOUTHERN CALIFORNIA TOWARD THE FOUR
CORNERS/DESERT SOUTHWEST. WITH SUCH A LARGE SCALE CLOSED LOW...THE
LONG TERM FORECAST CONTINUES TO LEAN TOWARD THE SLOWER ECMWF.
THUS...A MENTION OF A SLIGHT CHANCE TO CHANCE OF SHOWERS AND
SLIGHT CHANCE OF AFTERNOON AND EVENING THUNDERSTORMS WAS
MAINTAINED FOR THURSDAY THROUGH SATURDAY. WITH SOME EASTWARD
MOVEMENT OF THE TROUGH LIKELY...BY SATURDAY THE PROBABILITY OF
LINGERING WRAP-AROUND SHOWERS WILL BE HIGHER ON THE EAST SIDE.

&&

.AVIATION...FOR THE 30/12Z TAF CYCLE...EXPECT MAINLY VFR THIS
EVENING MORNING...BUT AREAS OF MVFR CIGS OVER THE COASTAL WATERS
WILL GRADUALLY SPREAD INLAND THIS MORNING WITH THE HIGHER TERRAIN
BECOMING OBSCURED. THE LOWER CONDITIONS WILL CLEAR OFF TO VFR BY
SATURDAY AFTERNOON AND CONDITIONS WILL REMAIN VFR THROUGH SATURDAY
NIGHT. WINDS WILL BE GUSTY OVER THE AREA THROUGH THIS EVENING. -BS

&&

.MARINE...UPDATED 500 AM PDT SAT 30 APR 2016...WIND DRIVEN AND STEEP
TO VERY STEEP SEAS ARE EXPECTED TODAY AND TONIGHT AS A THERMAL
TROUGH STRENGTHENS ALONG THE COAST AND BRINGS INCREASED NORTH WINDS.
NORTH GALES ARE EXPECTED TO DEVELOP THIS AFTERNOON AND EVENING SOUTH
OF CAPE BLANCO WITH HIGH AND VERY STEEP SEAS OVER AREAS SOUTH OF
CAPE ARAGO. ELSEWHERE EXPECT STEEP SEAS AND SMALL CRAFT ADVISORY
LEVEL WINDS. THE THERMAL TROUGH WILL WEAKEN SUNDAY INTO SUNDAY NIGHT
WITH WINDS AND SEAS GRADUALLY SUBSIDING. ANOTHER COLD FRONT WILL
MOVE THROUGH THE WATERS TUESDAY INTO TUESDAY NIGHT. /CC

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 2 PM PDT THIS
     AFTERNOON FOR PZZ356-376.
     SMALL CRAFT ADVISORY FROM 5 AM TO 11 AM PDT SUNDAY FOR
     PZZ356-376.
     GALE WARNING FROM 2 PM THIS AFTERNOON TO 5 AM PDT SUNDAY FOR
     PZZ356-376.
     HAZARDOUS SEAS WARNING UNTIL 5 AM PDT SUNDAY FOR PZZ356.
     SMALL CRAFT ADVISORY UNTIL 11 AM PDT SUNDAY FOR PZZ350-370.
     HAZARDOUS SEAS WARNING FROM 2 PM THIS AFTERNOON TO 5 AM PDT
     SUNDAY FOR PZZ350-370.
     HAZARDOUS SEAS WARNING UNTIL 11 AM PDT SUNDAY FOR PZZ376.

$$

DW/CC/BMS


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