499
FXUS66 KMFR 210556
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
956 PM PST THU FEB 20 2025
DISCUSSION...UPDATED AVIATION SECTION
AVIATION...21/06Z TAFS
VFR CONDITIONS PREVAIL WITH HIGH CLOUDS
PASSING EASTWARD. SATELLITE SHOWS THAT LOW CLOUDS ARE BEGINNING TO
DEVELOP IN WEST SIDE VALLEYS AND THIS WILL CONTINUE TO GROW TO MORE
AREAS TONIGHT. A STABILIZING AIR MASS IS EXPECTED TO RESULT IN AREAS
OF MAINLY WEST SIDE VALLEY IFR/LIFR, LOW CLOUDS AND FOG LATER
TONIGHT INTO TOMORROW MORNING. MVFR/IFR IS ALSO POSSIBLE EAST OF THE
CASCADES TONIGHT. -DW/HERMANSEN
PREV DISCUSSION
/ISSUED 827 PM PST THU FEB 20 2025/
DISCUSSION...THE FORECAST REMAINS ON TRACK. A HIGH PRESSURE
RIDGE REMAINS IN CONTROL OF THE AREA THROUGH TONIGHT AND FRIDAY
MORNING. THIS IS BRINGING STABLE AND DRY WEATHER WITH COLD MORNING
TEMPERATURES AND AREAS OF VALLEY FOG/LOW CLOUDS EXPECTED. THE
RIDGE WILL WEAKEN FRIDAY AFTERNOON AND EVENING AS A FRONT MOVES
ONSHORE. THIS FRONT WILL WEAKEN AS IT PUSHES INLAND FRIDAY EVENING
AND NIGHT, RESULTING IN LIGHT PRECIPITATION SPREADING INLAND,
WITH BEST CHANCES FOR LIGHT PRECIPITATION ALONG THE COAST, COASTAL
MOUNTAINS, DOUGLAS COUNTY AND SOUTHWEST JOSEPHINE COUNTY.
THEN, A STRONGER AND MOISTER, ATMOSPHERIC RIVER SYSTEM ARRIVES
SATURDAY INTO SUNDAY BRINGING CHANCES FOR HEAVY RAIN TO THE COAST
AND COASTAL MOUNTAINS. THE NATIONAL BLEND OF MODELS SHOWS A 70-90%
CHANCE FOR AN INCH OR MORE OF RAIN IN 24 HOURS ALONG THE COAST
AND INTO THE COASTAL MOUNTAINS DURING THIS PERIOD AND A 20-50%
CHANCE FOR UP TO 3 INCHES OR MORE OF RAIN ACROSS COASTAL CURRY
COUNTY AND THE KALMIOPSIS MOUNTAINS INLAND OF THE CURRY COAST.
FOR INLAND AREAS, MODERATE TO LOCALLY HEAVY PRECIPITATION (AROUND
0.5 TO 1.5 INCHES) IS EXPECTED FOR MANY AREAS FROM THE CASCADES
WEST AND LIGHT TO MODERATE PRECIPITATION IS EXPECTED EAST OF THE
CASCADES. HIGH SNOW LEVELS (6000 FEET RISING TO 8000 FEET) ARE
LIKELY AS THIS SYSTEM MOVES INTO THE AREA. BREEZY TO GUSTY SOUTH
WINDS ARE EXPECTED OVER THE MOUNTAINS AND FOR AREAS EAST OF THE
CASCADES AS THIS FRONT MOVES INTO THE AREA. THEN, THE ACTIVE
PATTERN CONTINUES INTO EARLY NEXT WEEK WITH THE ARRIVAL OF ANOTHER
FRONTAL SYSTEM MONDAY AND MONDAY NIGHT. FOR ADDITIONAL DETAILS ON
THESE SYSTEMS, PLEASE SEE THE DISCUSSION BELOW.
MARINE...UPDATED 815PM PST THURSDAY, FEBRUARY 20, 2025...LIGHT TO
MODERATE NORTH WINDS AND SWELL DOMINATED SEAS CONTINUE THROUGH
TOMORROW MORNING. INCREASING SOUTH WINDS AND BUILDING SEAS ARE
EXPECTED TOMORROW AHEAD OF COLD FRONT WITH STEEP SWELL DOMINATED
SEAS EXPECTED TOMORROW INTO SATURDAY. A STRONGER FRONT IS EXPECTED
LATER SATURDAY WITH A GOOD CHANCE OF SOUTH GALES SATURDAY NIGHT. THE
PROBABILITY OF WIND GUSTS HIGHER THAN 41 KNOTS IS ABOUT 80 PERCENT
AND 30 PERCENT FOR HIGHER THAN 48 KNOTS. A GALE WATCH IS OUT
SATURDAY NIGHT INTO SUNDAY MORNING. HIGH AND VERY STEEP CHAOTIC SEAS
ARE LIKELY WITH THIS FRONTAL PASSAGE. THE HIGH AND STEEP SEAS WILL
PERSIST INTO SUNDAY AND MONDAY BEFORE SOME 16 TO 18 FOOT WAVES
ARRIVE ON TUESDAY.
-SMITH/HERMANSEN
PREV DISCUSSION... /ISSUED 243 PM PST THU FEB 20 2025/
DISCUSSION...CEILINGS PERSISTED INTO THE AFTERNOON IN VALLEYS AND
BASINS ACROSS NORTHERN CALIFORNIA AND SOUTHERN OREGON, BUT HAS
EITHER CLEARED OUT OR AT LEAST PARTIALLY BROKEN UP AS OF WRITING
THIS FORECAST. THIS WILL ALLOW FOR THE SURFACE TO WARM, WHICH WILL
THEN SUPPORT CHANCES FOR FOG TO DEVELOP IN THESE AREAS ONCE AGAIN ON
FRIDAY MORNING. WORKING AGAINST THESE CONDITIONS IS THAT A WEAK
UPPER RIDGE IS BEING PUSHED TO THE EAST, CHANGING SURFACE FLOW FROM
EASTERLY TO SOUTHERLY. WINDS FROM THE SOUTH HAVE A BETTER CHANCE OF
GETTING INTO VALLEYS AND MIXING THE AIR A BIT. HOWEVER, THESE
SOUTHERLY WINDS ARE LIGHT AND MAY NOT PROVIDE SUFFICIENT MIXING TO
FULLY PREVENT DEVELOPMENT. FOG IS EXPECTED TO RETURN TO THESE AREAS
TONIGHT INTO FRIDAY MORNING, BUT MAY REMAIN PATCHY OVERNIGHT AND
CLEAR EARLIER IN THE MORNING.
FRIDAY LOOKS TO REMAIN LARGELY UNEVENTFUL AS THE WEAK UPPER RIDGE
FLATTENS, ALLOWING A WEAK FRONT TO APPROACH THE OREGON COAST LATE
FRIDAY NIGHT INTO SATURDAY. THIS FIRST FRONT WILL BE UNIMPACTFUL,
BRINGING SOME SHOWERS OVER THE COAST AND OVER HIGHER TERRAIN WEST OF
AND ALONG THE CASCADES. IN GENERAL, AREAS THAT MANAGE TO GET RAIN
WILL GET 0.1 INCHES OR LESS FROM FRIDAY AFTERNOON TO SATURDAY
MORNING.
SUSTAINED ACTIVITY LOOKS POSSIBLE FROM SATURDAY AFTERNOON TO TUESDAY
MORNING AS AN ATMOSPHERIC RIVER COULD SET UP AND BRING STEADY
MOISTURE OVER THE AREA. IN THIS TIMEFRAME, SATURDAY AFTERNOON-SUNDAY
MORNING AND MONDAY EVENING-TUESDAY MORNING WILL BE PERIODS OF
INTEREST AS FRONTS ARE EXPECTED TO SUPPORT ADDITIONAL LIFTING AND
BRING MORE ACTIVITY.
THE SATURDAY FRONT LOOKS TO BE THE WETTEST PERIOD, WITH AREAS SOUTH
OF CAPE BLANCO FORECAST TO GET 2 TO 3 INCHES OF RAINFALL AND AREAS
TO THE NORTH GETTING 1 TO 1.5 INCHES. SNOW LEVELS OF 8000 FEET OR
HIGHER MAKE SNOWFALL A NON-ISSUE FOR THIS FIRST FRONT. GUSTY WINDS
COULD DEVELOP ALONG THE OREGON COAST AND OVER ELEVATED TERRAIN.
CURRENT GUIDANCE SHOWS THESE WINDS SAFELY OUT OF ADVISORY LEVELS,
BUT THIS WILL BE WATCHED CLOSELY IN FUTURE FORECASTS.
FROM SUNDAY MORNING TO MONDAY MORNING, SHOWERS CONTINUE WITH UPSLOPE
FLOW BEING THE MAIN LIFTING MECHANISM. THE OREGON COAST WILL STILL
SEE THE MOST RAINFALL IN THIS PERIOD, WITH ANOTHER 1 TO 1.5 INCHES
FORECAST FROM BROOKINGS TO REEDSPORT. IN GENERAL, ACTIVITY LOOKS
MORE SPORADIC IN THIS PERIOD. SNOW LEVELS REMAINING OVER 6000 FEET
WILL CONTINUE TO LIMIT SNOWFALL.
FOR THE MONDAY EVENING FRONT, MOISTURE IN THE ATMOSPHERIC RIVER WILL
BE DECREASING. WHILE THIS WILL BE THE "DRIEST" PERIOD OF THE RIVER,
SNOW LEVELS DROPPING TO 4000 FEET WITH THIS FRONT WILL MAKE ACTIVITY
OVER THE CASCADES WORTH CONSIDERING. LONG TERM METEOGRAMS FROM THE
ECMWF AND GFS BOTH SHOW A SPLIT BETWEEN CRATER LAKE GETTING EITHER 1-
2 INCHES OR 4-5 INCHES FOR MONDAY EVENING INTO TUESDAY MORNING. THIS
MIGHT GET INTERPRETED AS 3 INCHES BEING THE MOST LIKELY OUTCOME, BUT
ENSEMBLE GUIDANCE HAD FEW MEMBERS IN THE 2-4 INCH RANGE. OUTCOMES ON
THE HIGHER END ARE STILL SHORT OF ADVISORY SNOWFALL, BUT THE
DIFFERENCE BETWEEN 1 INCH AND 6 INCHES OF SNOWFALL IS WORTH PAYING
ATTENTION TO. RIGHT NOW, THE FORECAST LEANS TOWARDS THE 4-6 INCH
RANGE.
BEYOND THE ATMOSPHERIC RIVER, AN UPPER LEVEL RIDGE LOOKS TO BRING A
DRY PERIOD FROM NEXT WEDNESDAY INTO NEXT WEEKEND. WITH LINGERING
MOISTURE AT THE SURFACE, MORNING VALLEY FOG WILL BE A CONSIDERATION.
TEMPERATURES WEST OF THE CASCADES LOOK TO BE SAFELY ABOVE FREEZING,
WHILE TEMPERATURES EASTWARD ARE EXPECTED TO BE IN THE MID 20S TO LOW
30S UNDER THE RIDGE. -TAD
MFR WATCHES/WARNINGS/ADVISORIES
OR...CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 4 AM FRIDAY TO 1
AM PST SUNDAY FOR PZZ356-376.
SMALL CRAFT ADVISORY FROM 4 AM FRIDAY TO 10 AM PST SATURDAY FOR
PZZ350-370.
GALE WATCH FROM SATURDAY MORNING THROUGH LATE SATURDAY NIGHT FOR
PZZ350-370.
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