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000
FXUS66 KMFR 150430
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
930 PM PDT FRI JUN 14 2013

.UPDATE...
AN UPDATE HAS BEEN MADE TO THE FORECAST FOR SATURDAY AFTERNOON AND
EVENING. MODEL CONSENSUS INDICATES A GOOD CHANCE OF THUNDERSTORMS
OVER THE OREGON CASCADES FROM MT MCLOUGHLIN NORTH AND
NORTHEASTWARD, SO HAVE INCREASED PROBABILITIES THERE. ALSO ADDED
SOME SLIGHT CHANCE MENTION IN NORTHERN CALIFORNIA. BTL

&&

.DISCUSSION...
BENIGN WEATHER THIS EVENING WILL FEATURE A SUBTLE CHANGE THAT
WILL LIKELY RESULT IN SOME RUMBLES OF THUNDER ON SATURDAY
AFTERNOON AND EVENING, PRIMARILY FROM AROUND CRATER LAKE NATIONAL
PARK NORTHEASTWARD. A FRONTAL SYSTEM CURRENTLY CROSSING 130 WEST
LONGITUDE WILL PUSH INTO THE FORECAST AREA TOMORROW AFTERNOON
PROVIDING SOME UPPER LEVEL FORCING FOR THUNDERSTORM ACTIVITY ALONG
AND NEAR THE CASCADES. GFS40, NAM12, AND SREF GUIDANCE ALL
INDICATE MOISTURE TO BE SUFFICIENT FOR ISOLATED THUNDERSTORM
ACTIVITY ALONG WITH SUFFICIENT INSTABILITY IN SOME OF THE
MENTIONED AREA. THE TRINITY ALPS AREA IN NORTHERN CALIFORNIA COULD
GET IN ON THE THUNDER, BUT IT IS LESS LIKELY THERE. THE MAIN AREA
OF CONCERN IS CRATER LAKE NORTHEASTWARD, WHERE ORGANIZED MULTICELL
THUNDERSTORMS COULD RESULT IN SCATTERED LIGHTNING COVERAGE DURING
THE EARLY TO MID EVENING HOURS. BTL

&&

.AVIATION...
BASED ON THE 15/00Z TAF CYCLE.

LATEST HIGH-RESOLUTION RAP MODEL DATA SUGGESTS THE MARINE LAYER AND
LIKELY MVFR CEILINGS WILL AFFECT THE COAST...MOST LIKELY ALONG AND
NORTH OF CAPE BLANCO...BY AROUND 02Z WITH OTHER GUIDANCE SUGGESTING
AROUND 08Z RETURN OF CEILINGS...SO THERE IS SOME UNCERTAINTY WITH
TIMING HERE. GIVEN WARMING TEMPERATURES ALOFT...EXPECT THE MARINE
LAYER TO REMAIN COMPRESSED ENOUGH TO KEEP CEILINGS JUST WEST OF
ROSEBURG OVERNIGHT. COASTAL CEILINGS ARE EXPECTED TO CONTINUE INTO
SATURDAY AFTERNOON. CEILINGS IN THE 1000 TO 1500 FOOT RANGE ARE
EXPECTED TO REMAIN IN ALMOST ALL OF THE COASTAL WATERS OUT TO 60 NM
FOR THE NEXT 24 HOURS. ELSEWHERE...AREAS WELL INLAND FROM THE COAST
SHOULD STAY VFR THROUGH TOMORROW. SVEN

&&

.PREV DISCUSSION... /ISSUED 233 PM PDT FRI JUN 14 2013/

DISCUSSION...THE COMBINATION OF WEAK UPPER RIDGING AND A WEAK LOW
LEVEL THERMAL TROUGH ALONG THE NORTHERN CALIFORNIA COAST IS
LEADING TO A SUNNY AND WARMER DAY TODAY ACROSS THE ENTIRE AREA
TODAY. TEMPERATURES ARE GENERALLY RUNNING 5-10 DEGREES WARMER THAN
YESTERDAY AT THIS TIME. WE MAY SEE SOME AFTERNOON CUMULUS OVER THE
MOUNTAINS AS HEATING CONTINUES TODAY, BUT FORECAST SOUNDINGS SHOW
US REMAINING CAPPED BELOW THE LCL, SO WE SHOULDN`T SEE MUCH IN THE
VALLEYS. WHATEVER CUMULUS DOES DEVELOP WILL DISSIPATE AROUND
SUNSET WITH CLEAR SKIES AGAIN TONIGHT. THE EXCEPTION WILL BE AT
THE COAST WHERE STRATUS WILL LIKELY DEVELOP RIGHT ALONG THE
COASTAL STRIP LATER TONIGHT.

THERE IS A LARGE UPPER TROUGH CENTERED AROUND 50N/140W OVER THE
NORTHEAST PACIFIC THAT IS SLOWLY CHURNING IN OUR DIRECTION. SW
FLOW ALOFT WILL RESULT IN GRADUALLY INCREASING MOISTURE AND
INSTABILITY OVER THE WEEKEND. FORECAST SOUNDINGS SHOW THE CAP
WEAKENING OVER THE VALLEYS BUT NOT QUITE BREAKING, WHEREAS THE
MOUNTAINS WILL BECOME UNCAPPED DURING THE AFTERNOONS. THIS WILL
LEAD TO AFTERNOON AND EVENING CONVECTION OVER THE MOUNTAINS BOTH
SATURDAY AND SUNDAY. EVEN THOUGH THERE IS NO TRIGGER, HEATING
ALONE SHOULD BE SUFFICIENT TO ALLOW SOME THUNDERSTORM DEVELOPMENT
IN THE MOUNTAINS. I DON`T THINK THE VALLEYS WILL GET IN ON THIS
ACTION, SO I HAVE LOWERED POPS IN VALLEY LOCATIONS. THE EXCEPTION
IS NORTHERN KLAMATH COUNTY WHERE SW UPPER FLOW COULD PUSH STORMS
OUT OFF THE MOUNTAINS AT TIMES.

EVEN THOUGH HEIGHTS FALL OVER THE WEEKEND AS THIS SYSTEM NEARS,
TEMPERATURES WILL REMAIN NORMAL TO ABOVE. THERE WILL LIKELY BE A
GREATER MARINE PUSH SATURDAY NIGHT INTO SUNDAY INTO THE UMPQUA AS
THE FLOW BECOMES ONSHORE WITH SUNDAY TEMPERATURES A LITTLE LOWER
THERE.

HAVEN`T MADE ANY SUBSTANTIAL CHANGES TO THE EXTENDED. WE`LL COOL
OFF A BIT MONDAY WITH A GREATER CHANCE OF SHOWERS AND
THUNDERSTORMS AS THE TROUGH EDGES CLOSER TO THE COAST. THE MODELS
ARE FAIRLY CONSISTENT IN BRINGING THE TROUGH ONSHORE TUESDAY,
LINGERING IT OVER THE PACNW WEDNESDAY, AND THEN MOVING IT EAST
THURSDAY. THIS WILL RESULT IN A COOL, SHOWERY PATTERN FROM TUESDAY
THROUGH THURSDAY WITH TEMPERATURES 5-10 DEGREES BELOW NORMAL. WE
WILL BEGIN TO REBOUND FRIDAY AS A RIDGE BUILDS ALONG THE COAST IN
THE WAKE OF THE UPPER LOW. -WRIGHT

AVIATION...VFR CONDITIONS WITH CLEAR SKIES EXIST OVER THE ENTIRE
FORECAST AREA EARLY THIS AFTERNOON. LATEST HIGH-RESOLUTION RAP
MODEL DATA SUGGESTS THE MARINE LAYER AND LIKELY MVFR CEILINGS WILL
AFFECT THE COAST...MOST LIKELY ALONG AND NORTH OF CAPE BLANCO...BY
AROUND 02Z WITH OTHER GUIDANCE SUGGESTING AROUND 08Z RETURN OF
CEILINGS...SO THERE IS SOME UNCERTAINTY WITH TIMING HERE. GIVEN
WARMING TEMPERATURES ALOFT...EXPECT THE MARINE LAYER TO REMAIN
COMPRESSED ENOUGH TO KEEP CEILINGS JUST WEST OF ROSEBURG
OVERNIGHT. COASTAL CEILINGS ARE EXPECTED TO CONTINUE INTO SATURDAY
AFTERNOON. ELSEWHERE...AREAS WELL INLAND FROM THE COAST SHOULD
STAY VFR THROUGH TOMORROW. SK

&&

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

CA...NONE.

PACIFIC COASTAL WATERS...
- SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THIS EVENING FOR
  PZZ356.
- SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
  EVENING FOR PZZ356.
- SMALL CRAFT ADVISORY FOR WINDS UNTIL 5 AM PDT SATURDAY FOR
  PZZ376.
- HAZARDOUS SEAS WARNING UNTIL MIDNIGHT PDT TONIGHT FOR
  PZZ376.

$$

BTL/SVEN/WRIGHT