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000
FXUS66 KMFR 131547
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
847 AM PDT MON MAY 13 2013

.UPDATE...SOMETIME OVERNIGHT...MODELS TRENDED DOWNWARD
SIGNIFICANTLY ON PRECIPITATION FOR TODAY. THIS...ALONG WITH
UNIMPRESSIVE RADAR AND SATELLITE IMAGERY...AND ANALYSIS/FORECASTS
SHOWING THE BULK OF MOISTURE TRANSPORT STAYING NORTH OF
THE CWA...HAS WARRANTED A DECREASE IN POP AND QPF ACROSS THE BOARD
THIS MORNING. OTHERWISE...THE FORECAST APPEARS ON TRACK...AND NO
OTHER CHANGES HAVE BEEN MADE.

WILL BE PAYING ATTENTION TO EAST SIDE AND MARINE WINDS TODAY WITH
THE PASSAGE OF THE COLD FRONT...AS WELL MUCH COOLER TEMPERATURES
AND INCREASED PRECIPITATION CHANCES THROUGHOUT THE WEEK. EXPECT NO
MAJOR CHANGES...BUT WILL LIKELY BE MAKING MANY ADJUSTMENTS AS PER
LATEST MODEL TRENDS AND SEASONAL EXPECTATIONS.


.AVIATION...BASED ON THE 13/12Z TAF CYCLE.

LIGHT RAIN AND WIDESPREAD IFR CIGS WILL CONTINUE ALONG AND THE COAST
THIS MORNING AND IS EXPECTED TO LIFT TO MVFR CIGS AROUND 17Z. THEN
EXPECT MVFR CIGS TO PERSIST ALONG THE COAST THIS AFTERNOON...ALTHOUGH
AREAS OF VFR MAY DEVELOP LATE IN THE MID AFTERNOON...WITH WIDESPREAD
IFR/MVFR CIGS RETURNING IN THE EVENING.  INLAND...ISOLATED MVFR CIGS
WILL CONTINUE THIS MORNING FOR LOCATIONS WEST OF THE SOUTHERN OREGON
CASCADES...MAINLY IN THE UMPQUA VALLEY. VFR CONDITIONS ARE
EXPECTED ELSEWHERE TODAY INTO TONIGHT. ISOLATED MOUNTAIN
OBSCURATIONS WILL OCCUR FROM THE SOUTHERN OREGON CASCADES WEST
THROUGH EARLY THIS AFTERNOON. ALSO TODAY...WINDS WILL BECOME GUSTY
OVER THE AREA...ESPECIALLY FROM THE CASCADES EAST...WITH WINDS OUT
OF THE SOUTHWEST CHANGING TO WEST NORTHWEST IN THE AFTERNOON.
LOW LEVEL TURBULENCE IS THEREFORE POSSIBLE...ESPECIALLY IN THE
AFTERNOON AND EARLY EVENING.


&&

.PREV DISCUSSION... /ISSUED 335 AM PDT MON MAY 13 2013/

DISCUSSION...A COLD FRONT WILL BRING MUCH COOLER TEMPERATURES TO
THE FORECAST AREA TODAY...AND WITHOUT AN EXPECTED REBOUND TO HOT
TEMPERATURES EXPECTED IN THE NEXT WEEK OR SO...THIS SIGNALS A
PATTERN SHIFT FOR THE REGION AFTER WEEKS OF CONSISTENTLY WELL
ABOVE NORMAL TEMPERATURES.

THE COLD FRONT IS SLOWLY MOVING TOWARDS THE COAST AND IS CLEARLY
EVIDENT ON IR IMAGERY. PRECIPITABLE WATER VALUES ALONG THE FRONT ARE
HIGH...AROUND AN INCH+...SO THIS HAS THE POTENTIAL TO SUPPORT
PRECIPITATION FOR A PORTION OF THE FORECAST AREA. HOWEVER...THIS
MOISTURE IS NARROW AND NOT VERY DEEP...AND THUS PRECIPITATION
AMOUNTS WILL LIKELY BE LIGHT. MOST AREAS WILL NOT SEE ANY
PRECIPITATION AND SHOULD SEE AT LEAST PARTLY SUNNY SKIES.
PRECIPITATION CHANCES ARE MAINLY FOCUSED IN THE UMPQUA BASIN...AT
THE COAST...AND ALONG THE CASCADES NORTH OF CRATER LAKE. MODEL
OUTPUT SUGGESTS VERY LITTLE PRECIPITATION IN THESE AREAS AND NONE
ELSEWHERE...BUT HAVE KEPT A SLIGHT CHANCE OF RAIN IN AREAS LIKE
THE ROGUE VALLEY AND PORTIONS OF THE EAST SIDE...SIMPLY TO ACCOUNT
FOR THE MOISTURE ALONG THIS FRONT.

WINDS WILL RAMP UP SHARPLY TODAY...SUPPORTED BY A STRONG PRESSURE
GRADIENT AT THE SURFACE AND HEALTHY 90 KT 300MB JET AND 50-60KT
SOUTHWEST FLOW AT 600MB. A WIND ADVISORY AT NPWMFR HIGHLIGHTS THE
EXPECTED 45 MPH GUSTS IN PORTIONS OF LAKE...KLAMATH...AND MODOC
COUNTIES.

TONIGHT A MARINE LAYER COULD BUILD INTO THE COAST WITH THE
POTENTIAL FOR FOG...AIDED BY BUILDING HIGH PRESSURE OFFSHORE BEHIND
THE FRONT. AFTER TONIGHT...MODELS SUGGEST THE MARINE LAYER BREAKS UP
SOME AND FOG IS NOT IN THE FORECAST AFTER THAT POINT.

TUESDAY AND WEDNESDAY SHOULD BE MOSTLY DRY WITH TEMPERATURES NEAR OR
JUST ABOVE NORMAL. BY THURSDAY RAIN CHANCES INCREASE SIGNIFICANTLY
ACROSS THE FORECAST AREA...WITH WETTING RAINS POSSIBLE MOST PLACES.
MODELS HAVE BEEN TRENDING WETTER FOR THIS TIME PERIOD. TIMING
DIFFERENCES STILL EXIST BETWEEN THE GFS AND EC IN TERMS OF TROUGH
AXIS PROGRESSION...BUT THE GENERAL IDEA OF SHOWERS AFFECTING MUCH
OF THE FORECAST AREA ALONG AND WEST OF THE CASCADES ON THURSDAY IS
CONSISTENT. WITH THE FRONT ON THURSDAY COMES BELOW NORMAL
TEMPERATURES...WARMING SOME ON FRIDAY AS THINGS DRY OUT BEHIND THE
TROUGH. MOSTLY ZONAL FLOW PERSISTS THROUGH SATURDAY BEFORE A RIDGE
BUILDS SUNDAY WITH WARMING TEMPERATURES...ONLY TO BE FOLLOWED BY
ANOTHER TROUGH AND THE POTENTIAL FOR COOL UNSETTLED WEATHER EARLY
NEXT WEEK. ONE BIG CAVEAT TO THIS IDEA IS THAT ENSEMBLE MEMBER
SPREAD IS VERY HIGH BY MONDAY MORNING...WITH SOME MEMBERS
SUGGESTING TROUGHING AND OTHERS RIDGING.

AVIATION...MVFR AND IFR CONDITIONS ARE EXPECTED THROUGH THE
MORNING ALONG THE COAST. RAINFALL CHANCES WILL INCREASE ACROSS
THE WEST SIDE THIS MORNING AS A REINFORCING FRONTAL WAVE PUSHES MORE
MOISTURE ONTO THE COAST AND WEST SIDE. MVFR WILL SPREAD ACROSS THE
COAST RANGE AND FROM THE UMPQUA DIVIDE NORTHWARD TODAY, WITH VFR
CONDITIONS ELSEWHERE. BREEZY WEST WINDS ARE EXPECTED MOST PLACES
TODAY WITH WINDY CONDITIONS EAST OF THE CASCADES WHERE GUSTS COULD
REACH 50 MPH THIS AFTERNOON. LOW LEVEL TURBULENCE IS, THEREFORE,
LIKELY, ESPECIALLY IN THE AFTERNOON AND EVENING.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR ORZ030-031.

CA...WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR CAZ085.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 6 PM PDT THIS
     EVENING FOR PZZ350-370.

$$

BPN/NSK/CMC