Area Forecast Discussion
Issued by NWS Medford, OR

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704
FXUS66 KMFR 011115
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
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.

&&

.AVIATION...FOR THE 01/06Z TAF CYCLE...CONDITIONS WILL REMAIN VFR
AREA-WIDE THROUGH THE TAF PERIOD. GUSTY NORTH WINDS AND SOME LOW-
LEVEL INSTABILITY MAY MAKE FOR A BUMPY APPROACH TO ALL TERMINALS
DURING THE AFTERNOON AND EVENING. -SVEN

&&

.MARINE...UPDATED 945 PM PDT SAT 30 APR 2016...A THERMAL
TROUGH WILL WILL CONTINUE TO PRODUCE GUSTY WINDS WITH VERY HEAVY
AND STEEP SEAS SOUTH OF CAPE ARAGO. OBSERVATIONS AT BUOY 27 HAVE
SHOWN A SIGNIFICANT RISE IN BOTH WINDS AND SEAS, WHICH SUGGESTS
THE MAIN AXIS OF THE COASTAL JET IS CLOSER TO SHORE THAN TYPICAL.
HAVE MADE ADJUSTMENTS TO ILLUSTRATE THIS IN THE UPDATED FORECAST.
THE THERMAL TROUGH WILL WEAKEN INTO MONDAY AND WINDS AND SEAS
WILL GRADUALLY SUBSIDE AS IT DOES SO. A WEAK COLD FRONT WILL MOVE
THROUGH THE WATERS TUESDAY INTO TUESDAY NIGHT, WITH ONLY A BRIEF
PERIOD OF SMALL CRAFT CONDITIONS POSSIBLE WITH ITS PASSAGE.
-BPN/SVEN

&&

.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 FROM 11 AM THIS MORNING
     TO 11 PM PDT THIS EVENING FOR PZZ376.

$$

DW/CC/BMS



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