Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 120531
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
931 PM PST THU FEB 11 2016

.DISCUSSION...AN UPDATE HAS BEEN MADE TO THE FORECASTS OF THE
PROBABILITY OF PRECIPITATION AND PRECIPITATION QUANTITY TONIGHT
THROUGH FRIDAY. A WEAK COLD FRONT IS OFFSHORE AND WILL TRACK
EAST AND DISSIPATE THROUGH FRIDAY. THERE IS A HIGH PROBABILITY OF
LIGHT RAIN NEAR THE COAST AND OVER THE COASTAL RANGE...TAPERING TO
CHANCE TO LIKELY POPS IN THE REMAINDER OF SOUTHWEST OREGON AND A
SLIGHT CHANCE FOR MUCH OF KLAMATH COUNTY AND CENTRAL SISKIYOU
COUNTY. WITH A SHALLOW MOIST LAYER, THIS WILL BE A LIGHT DRIZZLY
RAIN WHERE IT DOES RAIN INLAND. DESPITE THE CLOUD
COVER...TEMPERATURES WILL REMAIN WELL ABOVE NORMAL ON FRIDAY.

TEMPERATURES WILL BE A BIT COOLER...AROUND NORMAL ON SATURDAY.
THE NEXT SYSTEM WILL HAVE ITS FOCUS NORTH OF OUR AREA BUT THE GFS
CONTINUES TO INDICATE IT WILL BRING LIGHT RAIN NORTH OF THE UMPQUA
DIVIDE SATURDAY NIGHT THROUGH SUNDAY WITH THE PROBABILITY
DIMINISHING AS ONE TRAVELS FARTHER TO THE SOUTH AND EAST.

HIGH PRESSURE LOOKS TO BUILD SUNDAY NIGHT INTO TUESDAY NIGHT. THE
TIMING...STRENGTH AND POSITION OF THE NEXT TROUGH ARE STILL IN
QUESTION BUT THERE HAS BEEN CONSISTENCY IN INDICATING A CHANGE IN
THE PATTERN AND THE ARRIVAL OF A STRONGER SYSTEM AT MID-WEEK. THE
00Z GFS HAS TRENDED FARTHER SOUTH WITH A FOCUS OF PRECIPITATION
FROM AROUND MT SHASTA SOUTHWARD TO CENTRAL CALIFORNIA.

&&

.AVIATION...FOR THE 12/00Z TAF CYCLE... VFR CONDITIONS WILL PREVAIL
INTO TONIGHT. AREAS OF MVFR CIGS/VSBYS IN LIGHT RAIN WILL DEVELOP
ALONG THE COAST LATE TONIGHT AND SPREAD INLAND TO THE CASCADES DURING
THE DAY FRIDAY WITH AREAS OF HIGHER TERRAIN BECOMING OBSCURED.
-JRS

&&

.MARINE...UPDATED 900 PM PST THU FEB 11 2016...MIXED HIGH WEST
SWELL AT 19 TO 20 SECONDS AND MODERATE SOUTHWEST SWELL AT 10 TO 11
SECONDS WILL STEEPEN AND INCREASE INTO FRIDAY MORNING WITH THE
PERIOD BECOMING 17 TO 18 SECONDS. SEAS WILL THEN REMAIN WESTERLY
WITH A GRADUALLY DIMINISHING PERIOD THROUGH SUNDAY. COMBINED SEAS
WILL BUILD TO 13 TO 14 FEET THROUGH FRIDAY MORNING...SUBSIDE TO 12
FEET FRIDAY AFTERNOON THROUGH SATURDAY...REBUILD TO 12 TO 13 FEET
SATURDAY NIGHT...THEN SUBSIDE BELOW 10 FEET SUNDAY AFTERNOON. A
WEAK COLD FRONT WILL MOVE ONSHORE FRIDAY MORNING...AND THIS WILL
BRING SMALL CRAFT WINDS TO THE NORTHERN OUTER WATERS TONIGHT.
OFFSHORE HIGH PRESSURE WILL BUILD FRIDAY...THEN WEAKEN SATURDAY. A
SLIGHTLY STRONGER COLD FRONT WILL MOVE ONSHORE SATURDAY NIGHT.
OFFSHORE HIGH PRESSURE WILL REBUILD SUNDAY...THEN WEAKEN TUESDAY
AS A STRONGER FRONT APPROACHES THE AREA. -JRS

&&

.PREV DISCUSSION... /ISSUED 241 PM PST THU FEB 11 2016/

DISCUSSION...SKIES ARE THINNING OUT IN THE WAKE OF THE WEAK
SHORTWAVE THAT MOVED THROUGH THE AREA THIS MORNING. THIS IS IN
RESPONSE TO AN UPPER RIDGE BUILDING AHEAD OF A DEEPENING TROUGH NEAR
35N/140W. THIS SHOULD SLOW DOWN THE EASTWARD PROGRESSION OF THE
FRONT LATE TONIGHT. CURRENT HRRR MODEL SUGGEST THIS AND IS IN LINE
WITH THE NAM AND GFS. THEREFORE HAVE ADJUSTED POPS DOWN FOR THIS
EVENING AND TONIGHT, KEEPING THE BEST CHANCE FOR ANY RAIN OVER THE
MARINE WATERS AND ALONG THE COAST, NORTH OF CAPE BLANCO. I DON`T
THINK RAINFALL WILL MAKE MUCH IF ANY PROGRESS INLAND TONIGHT, BUT
STILL KEPT IN A SLIGHT CHANCE TO CHANCE ALONG THE SOUTH COAST AND IN
PORTIONS OF COOS AND NORTHWEST DOUGLAS COUNTY. SKIES SHOULD REMAIN
MOSTLY CLEAR THROUGH THIS EVENING BEFORE INCREASING AHEAD OF THE
COLD FRONT TONIGHT.

THE COLD FRONT WILL REACH THE COAST FRIDAY MORNING, THEN MOVING
ONSHORE DURING THE DAY FRIDAY. THIS WILL BRING THE BEST CHANCE FOR
MEASURABLE RAIN WITH MOST OF THE RAIN CENTERED ALONG THE COASTAL
MOUNTAINS AND CASCADES. EVEN THEN, QPF AMOUNTS ARE NOT EXPECTED TO
BE SIGNIFICANT AND MODELS HAVE BEEN TRENDING LOWER WITH QPF AMOUNTS.
SNOW LEVELS WILL LOWER ON FRIDAY, BUT WILL REMAIN ABOVE ALL THE
PASSES THROUGH FRIDAY.

A MOIST WESTERLY FLOW WILL SET UP FRIDAY NIGHT WITH A WEAK SHORT
WAVE MOVING THROUGH. MOST SHOWERS ARE EXPECTED TO REMAIN ALONG AND
WEST OF THE CASCADES, BUT THEY ARE EXPECTED TO BE LIGHT WITH SNOW
LEVELS BETWEEN 4500 AND 5000 FEET. THEREFORE WERE NOT EXPECTING
MUCH, IF ANY IMPACT ON ANY OF THE ROADS IN THE CASCADES.

500 MB HEIGHTS INCREASE SOME AS WEAK RIDGING BUILDS INTO THE AREA
SATURDAY. CONDITIONS SHOULD BE DRY DURING THE DAY, THEN A WARM FRONT
WILL ARRIVE SATURDAY NIGHT BRINGING STEADY LIGHT TO MODERATE
PRECIPITATION. THE BEST CHANCE FOR HEAVIER PRECIPITATION WILL BE IN
THE NORTHERN PART OF THE AREA SATURDAY EVENING, THEN THE FOCUS WILL
SHIFT SOUTH SATURDAY NIGHT THROUGH SUNDAY. SNOW LEVELS SATURDAY NIGHT
WILL INCREASE AND LIKELY BE ABOVE ALL THE PASSES THROUGH SUNDAY.

THE UPPER RIDGE WILL BUILD BACK INTO THE AREA SUNDAY NIGHT WITH
RAIN DECREASING, THEN ENDING FROM SOUTH TO NORTH. -PETRUCELLI

LONG TERM DISCUSSION...MONDAY THROUGH THURSDAY. MODELS AND THE
ENSEMBLE PLOTS START IN REMARKABLY GOOD AGREEMENT MONDAY WITH AN
UPPER LEVEL RIDGE OVER THE WEST COAST SHUNTING SYSTEMS JUST TO THE
NORTH OF THE FORECAST AREA. IT IS NOT UNTIL WEDNESDAY MORNING THAT
THE MODEL PLOTS SHOW ANY SIGNIFICANT DIVERGENCE...BUT THE MAIN
DIFFERENCES ARE WITH TIMING OF THE SHIFTING OF THE UPPER LEVEL RIDGE
TO THE EAST. THE GFS IS SLIGHTLY FASTER ON WEDNESDAY BRINGING
PRECIPITATION ONTO THE COAST WEDNESDAY MORNING, WITH THE ECMWF
BRINGING IT IN IN THE AFTERNOON. FROM THERE THE OVERALL PATTERN OF
AN UPPER LEVEL TROUGH OVER THE WEST COAST REMAINS FOR ALL OF THE
PLOTS...BUT THAT IS THE ONLY AGREEMENT WITH PLOTS ALL OVER THE
PLACE WITH DEPTH AND PLACEMENT OF THESE UPPER TROUGHS. WITH THIS IN
MIND HAVE GONE WITH THE ENSEMBLE MEAN POPS FOR THE REMAINDER OF THE
EXTENDED FORECAST. -SVEN

&&

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

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL
     4 PM PST SUNDAY FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY UNTIL 4 AM PST FRIDAY FOR PZZ370.

$$

DW/MAP/JRS


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