358
FXUS66 KMFR 202214
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
214 PM PST SAT DEC 20 2025
SYNOPSIS...
THE NORTHERN EDGE OF AN ATMOSPHERIC RIVER WILL PRODUCE MINOR
TRAVEL IMPACTS THIS WEEKEND. OUR REGION WILL LIKELY SEE
ACCUMULATING SNOW OVER HIGHER TERRAIN THROUGH CHRISTMAS. THE BULK
OF THE SNOW WILL FALL OVER NORTHERN CALIFORNIA NEXT WEEK.
DISCUSSION...
PRECIPITATION HAS STARTED TO ENTER THE AREA FROM THE SOUTH, WITH
CLOUD COVERAGE INCREASING QUICKLY ACROSS THE ENTIRE REGION.
PRECIPITATION COVERAGE WILL SPREAD TO THE NORTH AND RATES WILL
PICK UP AS WE MOVE THROUGH THE DAY, AND ESPECIALLY TOWARDS THE
OVERNIGHT HOURS IN NORTHERN CALIFORNIA AND SOME OF THE HIGHER
TERRAIN. INTEGRATED WATER VAPOR TRANSPORT(IVT) WILL RISE TO
BETWEEN 250 AND 400, WHICH IS CONSIDERED A FAIRLY WEAK ATMOSPHERIC
RIVER(AR) COMPARED TO THE 750 TO 1000 IVTS WE CAN SEE DURING
THESE WINTER STORMS. IN ADDITION, THE EXTREME FORECAST INDEX FOR
QPF IS SHOWING SOME VALUES AROUND 0.8 IN OUR NORTHERN CALIFORNIA
AREAS, WHICH SUGGESTS DECENT RAIN AND SNOW FALL, ALTHOUGH NOTHING
EXTREME WITH RAIN OR SNOW.
THEREFORE, WE DECIDED TO STAY AWAY FROM A FLOOD WATCH FOR OUR
FORECAST AREA FOR TODAY INTO SUNDAY NIGHT. SNOW ACCUMULATION
SUGGESTS SOME DECENT ACCUMULATION ABOVE 5000 FEET. WE'RE
FORECASTING UP TO 12 INCHES AROUND CRATER LAKE AND 5 TO 9 INCHES
AROUND WILLAMETTE PASS TONIGHT THROUGH SUNDAY NIGHT. THEREFORE,
IMPACTS WILL BE SOMEWHAT MINOR AND CONCENTRATED IN THE HIGHER
CASCADES AROUND DIAMOND LAKE AND HIGHWAY 62 GOING TO CRATER LAKE.
GIVEN THAT HOLIDAY TRAVEL HAS BEGUN, HAVE OPTED TO ISSUE A WINTER
WEATHER ADVISORY FOR AREAS ABOVE 5000 FT IN THE CASCADES NORTH OF
MT MCLOUGHLIN. DETAILS ON THIS CAN BE FOUND AT PDXWSWMFR. SNOW
LEVELS TO THE SOUTH WILL BE TOO HIGH TO RESULT IN ANY SIGNIFICANT
WINTER WEATHER CONCERNS.
A WARM FRONT AND THE LEADING EDGE OF THE NEXT AR WILL PUSH INTO
NORTHERN CALIFORNIA AND SOUTHERN OREGON SOMETIME AROUND SUNDAY
NIGHT, SO LOOK FOR SNOW LEVELS TO SHOOT HIGHER IN CALIFORNIA AND
STAY RELATIVELY LOWER FARTHER TO THE NORTH. FOR EXAMPLE, SNOW
LEVELS WILL REACH AROUND 6500 FEET AROUND MODOC COUNTY, ALTHOUGH
REMAIN AROUND 4000 FEET OVER MOST OF SOUTHERN OREGON MONDAY NIGHT
TUESDAY WILL KIND OF BE A TRANSITION DAY AS THE AR WILL WEAKEN
OVER OUR FORECAST AREA AND MEAN SEA LEVEL PRESSURE BEGINS TO
BUILD JUST BRIEFLY. SHOWERS WILL LIKELY LINGER AROUND THE FORECAST
AREA, ALTHOUGH ACCUMULATION SHOULD BE PRETTY LIMITED DURING THE
DAY.
BY MORNING OF CHRISTMAS EVE, THE FORECAST LOOKS A LITTLE MORE
UNCERTAIN. ENSEMBLES ARE SHOWING A DEEP TROUGH IN THE PACIFIC.
THERE IS A SMALL SUBSET OF ENSEMBLES MEMBERS(~20%) SHOWING A MESO
LOW SPINNING UP OFF THE NORTHERN CALIFORNIA COAST AND BRINGING
QUITE THE SNOW STORM DOWN TO THE VALLEY FLOORS TO OUR REGION.
HOWEVER, A LARGER SET OF ENSEMBLE MEMBERS KEEP US MUCH DRIER AND
POSTPONE THE SNOW TO LATER AROUND CHRISTMAS AND AT A MUCH HIGHER
ELEVATION. SO THAT WILL BE SOMETHING TO LOOK FOR IN THE NEXT SET
OF ENSEMBLE RUNS TO SEE WHERE ENSEMBLE MEMBERS FALL IN THESE
SCENARIOS. DIFFERING SCENARIOS ALSO POINT TO PERIODS OF STRONG
WINDS ALONG THE COAST, OVER HIGHER TERRAIN, AND ACROSS THE EAST
SIDE, WHILE OTHERS KEEP WINDS CLAM TO JUST BREEZY. AGAIN, UNTIL
GUIDANCE GETS A BETTER HANDLE ON THE SITUATION, THE DETAILS WILL
BE HARD TO DISCERN.
THE ONE COMMON THEME IN ALL THIS IS THE SKI RESORTS AND HIGH
TERRAIN LOCATIONS WILL SEE AT LEAST SOME SNOW THROUGH CHRISTMAS
BREAK. SHASTA SKI PART MIGHT BE THE EXCEPTION HERE AS NORTHERN
CALIFORNIA WILL LIKELY SEE A FAIR CHUNK OF SNOW THROUGH CHRISTMAS.
A 50TH PERCENTILE 72 HOUR NBM FORECAST ENDING THURSDAY EVENING
SHOWS 2 FEET OF SNOW AROUND 5000 FEET IN NORTHERN CALIFORNIA.
FARTHER NORTH, THE TOTALS DROP TO AROUND 9 INCHES IN THE SISKIYOUS
AND HIGH CENTRAL CASCADES OVER CRATER LAKE.
TOWARDS NEXT WEEKEND, CONDITIONS WILL LIKELY TREND DRIER AS THE
PROBABILITY OF PRECIPITATION IS ABOUT 10 TO 20 PERCENT WITH 40
PERCENT ALONG THE COAST.
AVIATION...20/18 TAFS
VFR PREVAILS FOR MUCH OF THE REGION, BUT
MVFR/IFR CEILINGS PERSIST THIS MORNING IN MANY OF THE VALLEYS WEST
OF THE CASCADES, AND FOR A FEW LOCATIONS IN THE KLAMATH BASIN AS
WELL. MOST OF THESE AREAS WILL CLEAR OVER THE NEXT FEW HOURS, WITH
VFR PREVAILING THROUGH THE AFTERNOON. INCREASING CLOUDS THIS
AFTERNOON WILL LEAD TO WIDESPREAD RAIN AND MVFR/IFR CEILINGS/VIS
LATE THIS EVENING AND OVERNIGHT AND CONTINUING THROUGH MUCH OF
SUNDAY AS A SYSTEM ARRIVES FROM THE SOUTH. FREEZING LEVELS OF 2500-
3000 FEET MSL THIS MORNING WILL STEADILY RISE THROUGH THE NEXT 24
HOURS, REACHING 5000 TO 7000 FEET BY SUNDAY MORNING. -BPN
MARINE...UPDATED 200 PM PST FRIDAY, DECEMBER 19, 2025
RELATIVELY
CALM CONDITIONS WITH LIGHT WINDS, RAIN, AND AREAS OF FOG ARE
EXPECTED THROUGH SUNDAY. WINDS AND SEAS INCREASE AHEAD OF A FRONT
SUNDAY NIGHT INTO MONDAY, WITH VERY STEEP SEAS AND ISOLATED GALE
FORCE GUSTS EXPECTED BY MONDAY AFTERNOON. CONDITIONS GRADUALLY
IMPROVE INTO TUESDAY, THEN A SERIES OF SYSTEMS WILL PRODUCE PERIODS
OF GUSTY WINDS AND STEEP TO VERY STEEP SEAS THROUGH THE REMAINDER OF
THE WEEK. -BPN
MFR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY FROM 4 AM SUNDAY TO 4 AM PST MONDAY FOR
ORZ027-028.
CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FROM 10 PM SUNDAY TO 10
AM PST MONDAY FOR PZZ350-370.
HAZARDOUS SEAS WARNING FROM 10 AM TO 10 PM PST MONDAY FOR PZZ350-
356-370-376.
SMALL CRAFT ADVISORY FROM 10 PM SUNDAY TO 10 PM PST MONDAY FOR
PZZ356-376.
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