Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 182129
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
229 PM PDT FRI APR 18 2014

.SHORT TERM...A SHORTWAVE RIDGE WILL PERSIST OVER THE AREA THIS
EVENING. THEN MODELS CONTINUE TO SHOW A WEAK FRONT MOVING INLAND
SATURDAY MORNING AND AFTERNOON. LIGHT RAIN IS EXPECTED TO SPREAD
INTO THE COAST DURING SATURDAY MORNING THEN SPREAD INLAND INTO AREAS
FROM THE CASCADES WEST IN THE AFTERNOON. EXPECT THE BEST CHANCE
FOR RAIN INLAND TO BE OVER THE COASTAL MOUNTAINS INTO THE UMPQUA
BASIN AND IN SOUTHERN OREGON CASCADES. RAINFALL AMOUNTS
ARE EXPECTED TO BE VERY LIGHT WITH GENERALLY A TENTH OF AN INCH OR
LESS ACROSS THESE AREAS ON SATURDAY. BEHIND THIS FRONT EXPECT
CLEARING AND DRYING CONDITIONS BY SATURDAY EVENING.

THEN SATURDAY NIGHT INTO SUNDAY A UPPER LEVEL RIDGE BUILDS INTO
THE REGION WHILE AN UPPER TROUGH DEVELOPS OFFSHORE. THE RIDGE IS
EXPECTED TO BRING WARM AND DRY CONDITIONS TO THE AREA ON SUNDAY.
MORNING LOW CLOUDS AND PATCHY FOG ARE EXPECTED THOUGH ON  SUNDAY
FOR AREAS ALONG THE COAST AND INTO THE UMPQUA BASIN...AND POSSIBLY
INTO THE GRANTS PASS AND ILLINOIS VALLEY. LOW CLOUDS AND PATCHY
FOG ARE EXPECTED TO BURN OFF IN THE LATE MORNING.

ON MONDAY....AN UPPER TROUGH IS FORECAST TO SHIFT TOWARDS THE
PACNW COAST WITH AN UPPER LOW CENTERED OFF THE BRITISH COLUMBIA
COAST. MODELS SHOW GOOD AGREEMENT THAT A SURFACE LOW WILL MOVE
INLAND INTO BRITISH COLUMBIA AND BRING A FRONT TOWARDS THE AREA
DURING THE DAY MONDAY WITH THE FRONT EXPECTED TO MOVE INLAND
MONDAY EVENING AND NIGHT. AHEAD OF THIS FRONT, MODELS INDICATE
SOUTHERLY  MOISTURE MOVING INTO THE AREA ALONG WITH A SOUTHWEST
JET ALOFT. ADDITIONALLY THE NAM AND GFS INDICATE WEAK INSTABILITY
DEVELOPING EAST OF THE CASCADES DURING THE AFTERNOON. THIS PATTERN
IS EXPECTED TO BRING CLOUDY SKIES AND SOME SHOWERS TO THE AREA
DURING THE DAY MONDAY AHEAD OF THE FRONT. GIVEN THE VERY WEAK
INSTABILITY WITH LIFTED INDICES OF 0 TO -1, THINK THERE IS VERY
LITTLE CHANCE FOR THUNDERSTORMS SO HAVE KEPT THEM OUT OF THE
FORECAST.

MONDAY EVENING AND NIGHT...MODELS SHOW GOOD AGREEMENT WITH THE
FRONT MOVING INLAND AND BRINGING LIGHT TO MODERATE PRECIPITATION
TO MOST THE AREA. HAVE INCREASED THE CHANCE PRECIPITATION TO MATCH
THE LATEST MODEL FORECASTS. SNOW LEVELS ARE FORECAST TO BEGIN
AROUND 6000 TO 7000 FEET MONDAY EVENING AND LOWER MONDAY NIGHT TO
4500 TO 5000 FEET. THIS IS EXPECTED TO ALLOW FOR SOME LIGHT SNOW
ACCUMULATION ON AREA MOUNTAINS MONDAY NIGHT INTO TUESDAY MORNING.

.LONG TERM...TUESDAY THROUGH SATURDAY...THE OPERATIONAL EC AND
GFS ARE IN RELATIVELY GOOD AGREEMENT WITH THE OVERALL PATTERN
THROUGH THE PERIOD. CONFIDENCE IS MODERATE IT WILL BE COOLER AND
UNSTABLE MOST OF THE TIME. A HIGH AMPLITUDE TROUGH DIGGING OFF THE
OREGON COAST WILL SEND A COLD FRONT INTO THE AREA EARLY TUESDAY
MORNING WITH COLD AIR ALOFT MOVING OVERHEAD. THE EC AND GFS SHOW
500MB TEMPERATURES BETWEEN -29 AND -32C MOVING OVERHEAD TUESDAY
AFTERNOON. THIS ALONG WITH SURFACE HEATING WILL MOST LIKELY RESULT
IN SCATTERED TO NUMEROUS SHOWERS OVER MOST OF THE AREA. SOME OF
THOSE SHOWERS COULD PRODUCE MODERATE TO HEAVY PRECIPITATION WITH
SMALL HAIL AND ISOLATED THUNDER. FOR NOW LEFT IT OUT OF THE
FORECAST DUE TO LOW CONFIDENCE, BUT IT`S SOMETHING THAT WE`LL
CONTINUE TO MONITOR.

THE UPPER TROUGH WILL MOVE INTO THE INTER-MOUNTAIN WEST WEDNESDAY,
BUT THE MODELS DIFFER ON HOW QUICK THAT HAPPENS. AT ANY RATE, WE
COULD CATCH A RELATIVE BREAK IN THE WEATHER FROM WEDNESDAY AFTERNOON
INTO WEDNESDAY NIGHT, BEFORE A WARM FRONT SPREADS MORE PRECIPITATION
OVER THE REGION. ANOTHER LARGE UPPER LOW ORIGINATING FROM THE
ALEUTIANS WILL DROP SOUTHEAST INTO THE EASTERN PACIFIC THURSDAY
SENDING ANOTHER FRONTAL BOUNDARY TOWARDS THE FORECAST AREA. IT`S
POSSIBLE THIS FRONT COULD GET HUNG UP OR SLOW DOWN SOME BECAUSE IT`S
NEARLY PARALLEL WITH THE UPPER FLOW. HOWEVER THE UPPER LOW WILL DIG
SOUTH AND A SHORTWAVE WILL ROTATE AROUND THE BASE OF THE UPPER LOW,
THUS DRIVING THE FRONT INTO THE AREA, BUT THAT MAY NOT HAPPEN UNTIL
FRIDAY. OF NOTE THE RELATIVE MEASURE OF PREDICABILITY (RMOP) SHOWS
A HIGH PROBABILITY (56%) OF A DEEPENING TROUGH IN THE EASTERN
PACIFIC FRIDAY EVENING, MOVING TOWARDS THE OREGON COAST SATURDAY
EVENING (49%), THEN OVER OUR AREA NEXT SUNDAY (43%) THESE ARE
PRETTY HIGH VALUES THIS FAR OUT. -PETRUCELLI


&&

.AVIATION...BASED ON 18/18Z TAF CYCLE...VFR CONDITIONS WILL PREVAIL
FOR ALL TERMINALS THROUGH THIS EVENING. THERE IS A CHANCE FOR MVFR
CIGS TO DEVELOP TOWARDS DAYBREAK AT KRBG, BUT MUCH WILL DEPEND ON
THE AMOUNT OF CLOUD COVER AHEAD OF THE NEXT FRONT. FOR NOW DID NOT
PUT ANYTHING IN THE TAF, BUT LATER SHIFTS WILL NEED TO TAKE ANOTHER
LOOK AT THIS. CIGS WILL LOWER ALONG THE COAST TONIGHT WITH MVFR CIGS
DEVELOPING BETWEEN 12-14Z AND WINDS WILL INCREASE AHEAD OF THE NEXT
FRONTAL BOUNDARY. -PETRUCELLI


&&

.MARINE...CONFIDENCE IN THE FORECAST IS PRETTY HIGH AS THE MODELS
HAVE REMAINED LOCKED ON TO THE VARIOUS FEATURES OF CONCERN FOR A
WHILE NOW. NORTHERLY WINDS WILL GRADUALLY DIMINISH THROUGH THIS
EVENING AND THEN SWITCH TO SOUTH AND BEGIN TO INCREASE TONIGHT AS A
COLD FRONT APPROACHES. THE FRONT WILL MOVE THROUGH ON SATURDAY AND
PRODUCE A PERIOD OF SMALL CRAFT ADVISORY WINDS FROM MID MORNING
THROUGH EARLY AFTERNOON, MAINLY FROM CAPE BLANCO NORTH. SEAS WILL
ALSO RISE TO SMALL CRAFT ON SATURDAY, PRIMARILY DUE TO THE WIND WAVE
COMPONENT, ALTHOUGH WEST SWELL WILL BEGIN TO INCREASE LATE IN THE
DAY AS WELL.  A VERY LARGE WEST-NORTHWEST SWELL WILL ARRIVE SATURDAY
NIGHT AND CONTINUE INTO SUNDAY MORNING. WITH SWELLS OF 18-20 FEET
AND PERIODS OF ONLY 16 SECONDS, SEAS WILL BE VERY STEEP, ESPECIALLY
OVER THE OUTER WATERS. SWELLS WILL DECAY SOME PRIOR TO REACHING THE
INNER WATERS, SO THE WARNING DOES NOT EXTEND ALL THE WAY TO THE
COAST, BUT SEAS WILL BE AT HIGH END SMALL CRAFT CONDITIONS OVER THE
INNER WATERS. THE WATCH WAS UPGRADED TO A HAZARDOUS SEAS WARNING FOR
THAT TIME FRAME AND EXPANDED TO COVER A LARGER AREA. WINDS WILL BE
FAIRLY LIGHT THROUGH MUCH OF NEXT WEEK, BUT SEAS WILL REMAIN STEEP
THROUGH AT LEAST WEDNESDAY AS VARIOUS SWELL TRAINS PROPAGATE THROUGH
THE REGION. -WRIGHT


&&


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...HIGH SURF ADVISORY FROM 11 PM SATURDAY TO 11 AM PDT SUNDAY FOR
     ORZ021-022.

CA...NONE.

PACIFIC COASTAL WATERS...HIGH SURF ADVISORY FROM 11 PM SATURDAY TO 11 AM PDT SUNDAY FOR
     PZZ310.
     SMALL CRAFT ADVISORY FOR WINDS FROM 5 AM TO 2 PM PDT SATURDAY
     FOR PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING FROM 5 AM TO 11 AM PDT SUNDAY FOR
     PZZ350-356-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 AM SATURDAY TO 11
     AM PDT SUNDAY FOR PZZ350-356-376.
     HAZARDOUS SEAS WARNING FROM 11 PM SATURDAY TO 11 AM PDT SUNDAY
     FOR PZZ370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 5 AM SATURDAY TO 5
     AM PDT SUNDAY FOR PZZ370.

$$

CC






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