Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 182229
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
329 PM PDT SAT APR 18 2015

.DISCUSSION...WEAK INSTABILITY IS PRESENT IN THE MOUNT SHASTA AREA
WITH SOME SHOWERS DEVELOPING IN THAT AREA AT THIS TIME.
HOWEVER...WITH THE 700MB WINDS FROM THE NORTHEAST AT AROUND 15KT
AND CUMULUS THAT DEVELOPS SHOULD MOVE SOUTHWEST OUT OF THE REGION
BEFORE DROPPING ANY LIGHTNING. THE SOUTHERLY FLOW THAT FED
MOISTURE INTO THE REGION BECOMES OFFSHORE DOWN SOUTH OF THE REGION
AS WELL WITH SUNDAY SEEING A DRIER AND MORE STABLE AIR MASS.
OFFSHORE FLOW REMAINS IN THE EXTREME SOUTHERN COAST AND THE
BROOKINGS AREA SHOULD SEE YET ANOTHER NIGHT OF WARM LOW
TEMPERATURES WITH HIGHS REACHING INTO THE UPPER 80S. ON MONDAY THE
FLOW BECOMES SOUTHERLY AND BEGINS TO FEED MOISTURE INTO THE
SOUTHERN FRINGES OF THE AREA WITH THUNDERSTORMS POSSIBLE IN THE MT
SHASTA AREA. ON TUESDAY THE FLOW HAS BEEN CONTINUAL WITH A COOLER
IAR MAS MOVING IN ALOFT INCREASING THE INSTABILITY ACROSS MUCH OF
THE REGION. SVEN

.LONG TERM DISCUSSION...WEDNESDAY THROUGH SATURDAY...ONE VERY LIKELY
FEATURE OF THE LONG TERM WILL BE COOLER TEMPERATURES...ESPECIALLY
COMPARED TO RECENT READINGS OF 15 TO 20 DEGREES ABOVE NORMAL. THE
LESS CERTAIN ASPECT OF THE EXTENDED IS PRECIPITATION. BOTH THE EC
AND GFS SUGGEST OUR FORECAST AREA WILL BE IN BETWEEN A CUTOFF LOW
OVER SOUTHERN CALIFORNIA...AND ANOTHER UPPER LOW TO THE NORTH. THIS
WILL BASICALLY MEAN JUST ENOUGH DYNAMICS AND MOISTURE TO GENERATE
SHOWERS...BUT NOT WIDESPREAD WETTING RAINS. GIVEN THE ENSEMBLE
CONSENSUS ON TROUGH AXIS PLACEMENT BY WEDNESDAY AFTERNOON...THE
BETTER CHANCE FOR PRECIPITATION WILL BE ALONG AND EAST OF THE
CASCADES.

BY THURSDAY AFTERNOON PRECIPITATION CHANCES DIMINISH AHEAD OF AN
UPPER TROUGH AND COLD FRONT.  MODELS DIVERGE SIGNIFICANTLY BY FRIDAY
AFTERNOON WITH THE ECMWF SHOWING SIGNIFICANT PRECIPITATION AND A
DIVING TROUGH OVER THE CWA...WHILE THE GFS SHOWS VERY WEAK UPPER
RIDGING AND DRY CONDITIONS. WE HAVE BLENDED BETWEEN THESE TWO
SOLUTIONS. GFS ENSEMBLES SUPPORT THIS APPROACH BASED ON A VERY LARGE
SPREAD BETWEEN MEMBER SOLUTIONS...SO WE BASICALLY HAVE CHANCE POPS
ACROSS THE FORECAST AREA.  SATURDAY FEATURES DIMINISHED RAIN CHANCES
AGAIN...BUT CAN`T REMOVE THEM COMPLETELY BASED ON MODELS VARYING RUN
TO RUN...AND TROUGHING BOTH UP- AND DOWNSTREAM ON THE ECMWF.

&&

.AVIATION...FOR THE 18/18Z TAF CYCLE...DRY...OFFSHORE FLOW WILL KEEP
MOST LOCATIONS VFR THROUGH TOMORROW. EXPECT GUSTY NORTH WINDS TO BE
FOCUSED AT THE IMMEDIATE COASTLINE AND OVER THE WATERS THIS
AFTERNOON...AND GENERALLY BREEZY CONDITIONS UNDER NORTHERLY FLOW
ELSEWHERE. SOME MODEL GUIDANCE SUGGESTS A BRIEF PERIOD OF IFR
CONDITIONS AT THE COAST NORTH OF CAPE BLANCO EARLY SUNDAY
MORNING...BUT WE BELIEVE OFFSHORE NORTHEAST WINDS SHOULD KEEP THESE
CLOUDS OFFSHORE. SK

&&

.MARINE...UPDATED 200 PM PDT SATURDAY APR 18 2015...A THERMAL TROUGH
NEAR THE COAST AND OFFSHORE HIGH PRESSURE WILL PRODUCE STRONG NORTH
WINDS AND STEEP TO VERY STEEP CHOPPY SEAS THAT WILL REACH A PEAK
THIS EVENING THEN SLOWLY LOWER SUNDAY INTO MONDAY AS BOTH OF THESE
FEATURES WEAKEN. A COLD FRONT WILL MOVE ONSHORE TUESDAY EVENING WITH
SEAS BUILDING INTO WEDNESDAY. OFFSHORE HIGH PRESSURE AND THE THERMAL
TROUGH WILL BOTH REBUILD THURSDAY.

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 AM PDT MONDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 AM PDT MONDAY
     FOR PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING UNTIL 11 AM PDT SUNDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 2 AM PDT SUNDAY FOR PZZ376.

$$


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