Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 181009
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
309 AM PDT SAT APR 18 2015

.DISCUSSION...UNUSUALLY WARM AND DRY WEATHER WILL CONTINUE OVER
OUR AREA THIS WEEKEND. WHILE THERE IS A LOT OF LOW LEVEL
INSTABILITY (PARTICULARLY SURFACE-BASED) AND EVEN A WEAK UPPER
TRIGGER IN THE FORM OF A SHORTWAVE TODAY, MOISTURE IS SEVERELY
LACKING. THIS FACT COMBINED WITH A FAIRLY STRONG MID LEVEL CAP
MEANS THAT WE PROBABLY WON`T EVEN SEE MUCH CLOUDINESS LET ALONE
ANY CONVECTION OVER MOST OF THE AREA TODAY. AS THIS SHORTWAVE
MOVES FURTHER SOUTH, THERE IS SOMEWHAT LESS CAPPING AND A BIT
MORE MOISTURE AND SO WE MAY SEE CUMULUS BUBBLE UP OVER THE
NORTHERN CALIFORNIA MOUNTAINS. WE STILL AREN`T EXPECTING ANY
SHOWERS OR THUNDERSTORMS, THOUGH.

ON SUNDAY, AN UPPER RIDGE BUILDS RIGHT OVER US AND THIS WILL
LIKELY BE THE HOTTEST DAY OF THE FORECAST PERIOD. INSTABILITY
INCREASES, BUT THERE IS LITTLE MOISTURE AND NO TRIGGER, SO WE
DON`T EXPECT MUCH MORE THAN A FEW MOUNTAIN CUMULUS. MONDAY WILL
ALSO BE QUITE WARM AND LOW LEVEL INSTABILITY FINALLY STARTS TO
ERODE THE CAP ENOUGH THAT WE CAN`T RULE OUT A SHOWER OR
THUNDERSTORM OVER THE MOUNTAINS. MOISTURE AND TRIGGER WILL STILL
BE THE LIMITING FACTORS ON MONDAY.

TUESDAY IS LIKELY TO BE MUCH MORE CONVECTIVE AS THE RIDGE BREAKS
DOWN AND MOVES EAST AND A TROUGH APPROACHES THE COAST. INSTABILITY
IS FAIRLY IMPRESSIVE ON TUESDAY, AND MODEL SOUNDINGS SHOW LITTLE
TO NO CAPPING BY AFTERNOON, ESPECIALLY OVER THE MOUNTAINS.
MOISTURE WILL INCREASE AS WELL, AND IT IS PROBABLY JUST A LACK OF
A FOCUSING MECHANISM (IE TRIGGER) THAT WILL KEEP US FROM HAVING A
BIG THUNDERSTORM OUTBREAK TUESDAY. NEVERTHELESS, WE SHOULD SEE
STORMS OVER THE MOUNTAINS, AT LEAST, ON TUESDAY, AND IT WILL BE
POSSIBLE EVERYWHERE INLAND FROM THE COAST.

LITTLE WAS CHANGED IN THE EXTENDED FORECAST THIS MORNING. THE
MODELS STILL DIFFER IN THE DETAILS, BUT FROM WEDNESDAY ON LOOKS
SHOWERY AND COOL AS BROAD TROUGHINESS AFFECTS THE PACIFIC
NORTHWEST. -WRIGHT

&&

.AVIATION...FOR THE 18/06Z TAF CYCLE...MVFR CIGS HAVE DEVELOPED
ALONG THE COAST NORTH OF CAPE BLANCO, CAUSING PARTIAL TERRAIN
OBSCURATION OF THE COASTAL RANGE. THE AREA SHOULD CLEAR TO VFR
THROUGH THE MORNING, AND NORTH WINDS WILL INCREASE DURING THE
MORNING AND REMAIN GUSTY THROUGH THE AFTERNOON.

ELSEWHERE, EXPECT VFR CONDITIONS TO PREVAIL THROUGHOUT THE TAF
PERIOD. THERE IS A SMALL CHANCE THAT SOME LOW CLOUDS COULD DEVELOP
WITHIN THE UMPQUA BASIN LATE TONIGHT AND INTO THE EARLY MORNING,
INCLUDING KRBG, BUT CONFIDENCE IS LOW. -BPN

&&

.MARINE...UPDATED 800 PM PDT FRIDAY APR 17 2015...A THERMAL TROUGH
NEAR THE COAST AND OFFSHORE HIGH PRESSURE WILL COMBINE TO CREATE
STRONG WINDS AND CHOPPY SEAS THROUGH SUNDAY EVENING. GALE FORCE
WINDS WILL BE LIMITED TO THE SOUTHERN OUTER WATERS BEYOND 10NM FROM
SHORE AND SOUTH OF CAPE BLANCO. MOST OF THE REST OF THE
AREA...EXCEPT VERY CLOSE TO SHORE...WILL SEE SMALL CRAFT ADVISORY
WINDS. HAZARDOUS SEAS WILL OCCUR OVER A WIDER AREA...BUT MOSTLY
BEYOND 10NM OFFSHORE. ALMOST ALL OF THE INNER WATERS WILL SEE SMALL
CRAFT ADVISORY SEAS. STRONG NORTH WINDS AND CHOPPY SEAS WILL
DIMINISH SUNDAY NIGHT. A COLD FRONT WILL MOVE ONSHORE TUESDAY.
-JRS/BPN

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 AM SUNDAY TO 5 AM
     PDT MONDAY FOR ORZ022-618.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 2 AM SUNDAY TO 5 AM
     PDT MONDAY FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT MONDAY FOR
     PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 2 AM PDT SUNDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 2 AM PDT SUNDAY FOR PZZ376.

$$


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