Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 011538
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
838 AM PDT SUN MAY 1 2016

.DISCUSSION...TODAY WILL FEATURE WARM AND SUNNY CONDITIONS ACROSS
THE FORECAST AREA AS WE EXPERIENCE THE LAST DAY OF THIS OFFSHORE
FLOW AND DRY AIR MASS. SEXTON SUMMIT AT 4000 FEET IS 12 DEGREES
WARMER THAN 24 HOURS AGO...EVIDENCE OF THE WARMING AIR MASS
ALOFT. AS THE DAY PROGRESSES THIS WARM AIR WILL MAKE IT TO THE
SURFACE AND TEMPERATURES WILL BE 5 TO 15 DEGREES ABOVE NORMAL FOR
THIS TIME OF YEAR. NORTH BEND STARTED OFF AT A COOL 45 DEGREES
THIS MORNING WITH FOG SOMEHOW MANAGING TO FORM IN THE DRY OFFSHORE
FLOW...BUT HAS SINCE CLEARED AND TEMPERATURES HAVE RISEN 8 DEGREES
IN THE PAST HOUR...SO HAVE LEFT A WARM 77 DEGREES FOR THEIR HIGH
TEMPERATURE TODAY.

THE WEATHER PATTERN BECOMES A BIT MORE ACTIVE MONDAY...WITH
SIMILAR INLAND TEMPERATURES...AS FLOW TURNS SOUTHERLY AS AN UPPER
TROUGH MOVES TOWARDS THE FORECAST AREA. THE CHANCE FOR SHOWERS
GRADUALLY INCREASES FROM MONDAY THROUGH WEDNESDAY. THUNDERSTORM
CHANCES WILL ALSO INCREASE. PLEASE SEE THE PREVIOUS FORECAST
DISCUSSION BELOW FOR MORE DETAILS.

&&

.AVIATION...FOR THE 01/12Z TAF CYCLE...CONDITIONS WILL REMAIN VFR
AREA-WIDE THROUGH THE TAF PERIOD EXCEPT FOR LOCAL IFR
CIGS/VISIBILITIES IN KOTH AND COQUILLE VALLEY AND IN PORTIONS OF THE
UMPQUA VALLEY EARLY THIS MORNING. /CC

&&

.MARINE...UPDATED 600 AM PDT SUN 1 MAY 2016...A THERMAL
TROUGH WILL BRING CONTINUED GUSTY NORTH WINDS AND STEEP TO VERY
STEEP SEAS THIS MORNING. THE STRONGEST WINDS AND VERY STEEP
HAZARDOUS SEAS ARE EXPECTED FROM CAPE ARAGO SOUTHWARD, ESPECIALLY
BEYOND 10 NM FROM SHORE. WINDS HAVE LOWERED AT BUOY 27AND BUOY 15
EARLY THIS MORNING BUT SEAS REMAIN STEEP TO VERY STEEP DUE TO CHOPPY
WIND SEAS. AS THE THERMAL WEAKENS TODAY INTO TONIGHT, WINDS AND SEAS
WILL CONTINUE TO GRADUALLY SUBSIDE.  A COLD FRONT WILL MOVE THROUGH
THE WATERS TUESDAY INTO TUESDAY NIGHT. BEHIND THIS FRONT...HIGH
PRESSURE BUILDS OFFSHORE AND AREAS OF MODERATE NORTH WINDS AND STEEP
SEAS MAY DEVELOP WEDNESDAY THROUGH FRIDAY. /CC

&&

.PREV DISCUSSION... /ISSUED 415 AM PDT SUN MAY 1 2016/

DISCUSSION...MODEL AGREEMENT IS ABOVE AVERAGE INTO FRIDAY WHICH
IS A BIT IMPRESSIVE GIVEN THE COMPLEXITY OF THE PATTERN EVOLUTION.
THE CHANGES TO THE FORECAST WERE RELATIVELY MINOR THOUGH THE
PATTERN CHANGE THIS WEEK WILL BE SUBSTANTIAL.

FIRST...OFFSHORE FLOW WILL CONTINUE TODAY WITH MOSTLY SUNNY TO
SUNNY SKIES AND MUCH ABOVE NORMAL TEMPERATURES. A RIDGE EXTENDS
FROM THE PACIFIC NORTHWEST TO THE ROCKIES WHILE A WEAK BUT BROAD
TROUGH IS OVER CENTRAL CALIFORNIA INTO NEVADA AND ANOTHER BROADER
TROUGH LOCATED OFFSHORE IS MOVING EASTWARD.

THE CLOSER PROXIMITY OF THE PACIFIC TROUGH WILL SHIFT OUR EASTERLY
FLOW TO SOUTHERLY. THIS WILL BRING COOLER TEMPERATURES TO
BROOKINGS BUT IT WILL REMAIN MUCH WARMER THAN NORMAL INLAND. THE
SOUTHERLY FLOW WILL TAP INTO LINGERING MOISTURE FROM THE
CALIFORNIA TROUGH AND ALSO SEND A WEAK SHORTWAVE ACROSS THE AREA.
THIS WILL PRODUCE A SLIGHT CHANCE TO CHANCE OF SHOWERS AND SLIGHT
CHANCE OF THUNDERSTORMS...MAINLY FROM THE CASCADES WESTWARD FROM
MONDAY AFTERNOON THROUGH MONDAY NIGHT. ONE OF THE FORECAST
CHANGES...IN COLLABORATION WITH THE PORTLAND AND PENDLETON OFFICES
WAS TO EXTEND THE MENTION OF A SLIGHT CHANCE OF THUNDERSTORMS IN
DOUGLAS COUNTY BEYOND MONDAY EVENING INTO MONDAY NIGHT.

MONDAY WILL BE THE TRANSITION DAY THEN THE PACIFIC TROUGH WILL BE
THE MAIN DRIVER OF OUR WEATHER TUESDAY AT LEAST THROUGH FRIDAY.
HIGH TEMPERATURES WILL TREND TO SLIGHTLY BELOW NORMAL BY WEDNESDAY
WHILE SHOWERS TUESDAY AFTERNOON THROUGH THURSDAY EVENING WILL BE
NUMEROUS AND ACCOMPANIED BY ISOLATED THUNDERSTORMS. BY THEIR
NATURE...THE MAIN FORECAST CHALLENGE IN THE NEAR TERM IS
DETERMINING THE QUANTITY OF PRECIPITATION AND FAVORED LOCATIONS
FOR IT TO OCCUR. PRECIPITATION AMOUNTS AND SHOWER COVERAGE LOOKS
TO BE GREATEST DURING WEDNESDAY AFTERNOON AND EVENING AS THE UPPER
LOW REACHES THE NORTHERN CALIFORNIA COAST...WHICH IS EXPECTED TO
BE ITS CLOSEST PROXIMITY TO OUR AREA. THE LOW WILL THEN CONTINUE
SOUTHEASTWARD TO SOUTHERN CALIFORNIA. AT LEAST THURSDAY THROUGH
FRIDAY WILL SEE A SOUTHEAST TO EAST FLOW WITH WRAP AROUND SHOWERS
THAT WILL BE MOST NUMEROUS EAST OF THE CASCADES. THERE WILL ALSO
REMAIN A SLIGHT CHANCE OF THUNDERSTORMS.

MODEL AGREEMENT FINALLY BREAKS DOWN AT THE END OF THE WEEK WITH
THE ECMWF AS THE MOST PROGRESSIVE MODEL REGARDING THE APPROACH OF
ANOTHER TROUGH TO THE PACIFIC NORTHWEST THAT MAY POTENTIALLY
FINALLY KICK EASTWARD THE PREVIOUS TROUGH OVER THE WESTERN STATES.
LINGERING WRAP AROUND SHOWERS AND THUNDERSTORMS NEXT WEEKEND WILL
HAVE THE LOWEST PROBABILITY AT THE COAST AND THE HIGHEST EAST OF
THE CASCADES.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR PZZ350-356-370.
     HAZARDOUS SEAS WARNING UNTIL 11 AM PDT THIS MORNING FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR PZZ376.

$$

NSK/DW/CC



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