645
FXUS66 KMFR 280446
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
846 PM PST SAT FEB 27 2021
DISCUSSION
THE ONE CHANGE TO THE FORECAST WAS TO INCREASE
WINDS MONDAY MORNING. AN AREA OF SHORTWAVE ENERGY MOVES DOWN THE
FRONT SIDE OF THE RIDGE AXIS INTO THE BAY AREA, AS THE CUT OFF LOW
MOVING ALONG THE COAST REVERSES THE FLOW FROM THE SOUTH AND MOVES
THAT ENERGY BACK INTO THE REGION. THIS WILL BRING SOME ADDITIONAL
TIGHTENING OF THE PRESSURE GRADIENT FROM MEDFORD TO REDDING, BUT
STILL DOES NOT LOOK TO HAVE THE ENERGY OR MOISTURE TO WARRANT A
CHANGE TO THE QPF OR POP FORECAST.
THE CHANGES WILL BRING INCREASED WINDS ACROSS THE RIDGES OF
SISKIYOU, MODOC, JACKSON, JOSEPHINE, SOUTHERN KLAMATH AND LAKE
COUNTIES. SOME VALLEYS IN N. CAL., INCLUDING THE SHASTA VALLEY,
AND ACROSS LAKE COUNTY WILL ALSO BE EFFECTIVE. THERE IS NOT STRONG
EVIDENCE TO SUGGEST THE GRADIENT IS STRONG ENOUGH TO BRING THE
WINDS INTO THE CENTRAL ROGUE VALLEY. THERE ARE LIKELY TO BE GUSTS
IN THE SOUTHERN PORTION NEAR ASHLAND. THE NBM PUTS THE CHANCE FOR
GUSTS EQUAL TO OR GREATER THAN 20 MPH AT 28%, WHICH SEEMS A BIT
LOW, BUT DOES FAIRLY REPRESENT THAT MODERATE TO STRONG GUSTS WILL
BE THE EXCEPTION RATHER THAN THE RULE. AT WEED, CA THE PROBABILITY
OF REACHING 20 MPH IS 100% PER THE NBM AND OF 30 MPH IS 10%. THIS
10% DOES SEEM LOW BECAUSE HI-RES MODELS SUPPORT SOUTHERLY 35 TO
45 MPH 700 AND 850 MB FLOW ON A STRONG MIXING DAY THAT COULD
RESOLVE AS SURFACE GUSTS. WOULD ADVISE PREPARATION FOR GUSTS UP
TO 40 MPH, BUT DO NOT ANTICIPATE ANY GUSTS REACHING ADVISORY
CRITERIA IN THE SHASTA VALLEY.
AGAIN, THE REST OF THE FORECAST LOOKS ON TRACK. THE PREVIOUS
DISCUSSION IS BELOW FOR FURTHER DETAIL ON THE REST OF THE
FORECAST. -MILES
AVIATION....AVIATION...FOR THE 28/00Z TAF CYCLE
GENERALLY VFR CONDITIONS
WITH MINOR TERRAIN OBSCURATION ALONG THE HIGHEST PORTIONS
OF THE CASCADES. SHOWERS CONTINUE TO DIMINISH THIS EVENING.
MVFR AND LOCAL IFR WILL RETURN TO SOME AREAS TONIGHT, PARTICULARLY
ALONG THE COAST NORTH OF CAPE BLANCO AND ALSO THE UMPQUA BASIN.
THERE COULD ALSO BE SOME LOW CLOUDS AND FOG AROUND MEDFORD SUNDAY
MORNING, BUT CONFIDENCE WASN'T HIGH ENOUGH TO INCLUDE IN THE TAF AT
THIS TIME. -MILES
MARINE
UPDATED 800 PM PST SATURDAY 27 FEB 2021..SEAS WILL
GRADUALLY DIMINISH INTO SUNDAY MORNING BUT THEY WILL REMAIN HIGH AND
STEEP, DUE TO A COMBINATION OF MODERATE NORTHWEST SWELL AND CHOPPY
WIND-DRIVEN SEAS. NORTH WINDS HAVE SUBSIDED OVER MUCH OF THE WATERS,
EXCEPT THEY'LL REMAIN GUSTY AND AT ADVISORY STRENGTH THROUGH
LATE THIS EVENING FROM CAPE FERRELO SOUTH WITHIN 15 NM OF SHORE.
SEAS WILL REMAIN RELATIVELY LOW FROM MONDAY INTO TUESDAY. HOWEVER,
A NORTHWEST SWELL WILL BUILD LATE MONDAY NIGHT INTO TUESDAY, PUSHING
SEAS UP TO 10 TO 13 FEET ACROSS MOST OF THE WATERS. WITH PERIODS
AROUND 12 TO 14 SECONDS, THESE SEAS WILL BECOME HAZARDOUS TO SMALLER
CRAFTS TUESDAY INTO TUESDAY NIGHT.
MODELS ARE SHOWING ANOTHER STRONG LOW AND COLD FRONT SWING THROUGH
TOWARDS THE END OF NEXT WEEK. WE ARE NOT THAT CONFIDENT IN THE
EXACT TIMING. HOWEVER, WE ARE CONFIDENT THAT HAZARDOUS SEAS OR GALE
FORCE WINDS WILL BE OBSERVED AT SOME POINT FROM LATE THURSDAY
THROUGH MOST OF FRIDAY. MODELS ARE FORECASTING WIND DRIVEN SEAS TO
PUSH UP TO 20 FEET OVER MOST OF THE REGION.
-SMITH/CC
PREV DISCUSSION
/ISSUED 234 PM PST SAT FEB 27 2021/
SHORT TERM...THIS AFTERNOON THROUGH MONDAY NIGHT...SHOWER COVERAGE
CONTINUES TO TREND LESS THIS AFTERNOON, WITH REMAINING SHOWER
ACTIVITY FOCUSED ALONG THE CASCADES AND NORTH OF THE UMPQUA
DIVIDE. PRECIPITATION AMOUNTS ARE RELATIVELY LIGHT, WITH LATEST
OBSERVATIONS SHOWING AROUND A TENTH OF AN INCH OR LESS IN THE LAST
HOUR. BREEZY CONDITIONS CONTINUE EAST OF THE CASCADES WHERE GUSTS
OF 20 TO 30 MPH ARE COMMON. WINDS ARE EXPECTED TO DIMINISH WITH
TIME, SO AM NOT ANTICIPATING ANY ADDITIONAL HEADLINES FOR STRONG
WINDS. OVERALL, CONDITIONS WILL TREND DRIER AS WE HEAD INTO THE
EVENING AND SHOWERS COME TO AN END. UPPER LEVEL RIDGING BUILDS IN
THIS EVENING INTO SUNDAY AND WE'LL SEE A BREAK IN THE WEATHER. FOR
MOST AREAS, THIS BREAK WILL CONTINUE THROUGH MUCH OF THE WEEK,
WHILE FOR LOCATIONS ROUGHLY ALONG AND WEST OF I-5, THE BREAK WILL
ONLY LAST UNTIL MONDAY MORNING/AFTERNOON.
SOME MORNING FOG AND LOW CLOUDS WILL BE POSSIBLE TONIGHT INTO SUNDAY
MORNING. FOR AREAS THAT DON'T SEE ANY FOG/LOW CLOUDS, EXPECT SOME
COLD TEMPERATURES OVERNIGHT UNDER CLEAR SKIES. ANY LOW CLOUDS THAT
DO DEVELOP WILL GIVE WAY TO SUN BY LATE SUNDAY MORNING WITH COLD
MORNING TEMPERATURES WARMING SEASONAL NORMALS FOR THE AFTERNOON.
RIDGING BREAKS TO THE EAST LATE SUNDAY NIGHT INTO MONDAY MORNING AS
AN UPPER LEVEL TROUGH APPROACHES THE AREA. OVERNIGHT TEMPERATURES
WILL TREND WARMER COMPARED TO TONIGHT/SUNDAY MORNING AS FLOW BECOMES
MORE SOUTHWESTERLY. DEPENDING ON HOW MUCH HIGH LEVEL CLOUD COVER
ARRIVES IN ADVANCE, OVERNIGHT/MORNING FOG AND LOW CLOUDS COULD BE
MUCH MORE LIMITED SUNDAY NIGHT COMPARED TO SUNDAY MORNING.
MODELS CONTINUE TO COME INTO BETTER AGREEMENT REGARDING THE TROUGH
APPROACHING THE AREA MONDAY. A SPLIT FLOW SCENARIO IS LIKELY TO
OCCUR AS THE TROUGH APPROACHES AND THE BULK OF THE ENERGY SPLITS TO
THE SOUTH, FORMING A CLOSED LOW OFF THE CALIFORNIA COAST THAT
MEANDERS SOUTHWARD MONDAY NIGHT INTO TUESDAY. THESE SCENARIOS
TYPICALLY RESULT IN DRY CONDITIONS FOR MUCH OF THE FORECAST AREA, IF
NOT ALL, AND HAVE ADJUSTED POPS TO THIS THINKING. WHILE THE
DETERMINISTIC EC MAINTAINS A DRY SOLUTION FOR MOST AREAS, THERE ARE
STILL A CONSIDERABLE AMOUNT OF ITS ENSEMBLES THAT SHOW SOME LIGHT
PRECIPITATION ARRIVING AT THE COAST AND POSSIBLY AS FAR WEST AS I-5.
THE MAJORITY OF THE GEFS ENSEMBLES CONTINUE WITH DRY SOLUTIONS AS
WELL, HOWEVER, THERE ARE A FEW THAT ALSO SHOW SOME LIGHT
PRECIPITATION POTENTIAL FOR THE SAME AREAS. GIVEN THIS, HAVE
MAINTAINED SLIGHT CHANCE POPS FOR AREAS ROUGHLY ALONG AND WEST OF I-
5 WHILE REMOVING ANY PRECIPITATION POTENTIAL FROM AREAS EAST OF THE
CASCADES AND IN NORTHERN CALIFORNIA. IF PRECIPITATION DOES OCCUR,
AMOUNTS ARE EXPECTED TO BE LIGHT AND LIKELY FOCUSED ALONG THE COAST
AND NORTH OF THE UMPQUA DIVIDE. WHILE IT'S LIKELY TO REMAIN DRY FOR
MUCH OF THE AREA, THE MORE NOTABLE EFFECTS OF THIS SYSTEM WILL BE
MARKED BY WINDS. ALTHOUGH NOT AS STRONG AS YESTERDAY'S FRONT, THERE
COULD BE SOME GUSTY SOUTH TO SOUTHWEST WINDS ACROSS THE EAST SIDE
AND SHASTA VALLEY. CURRENTLY IT DOESN'T LOOK LIKE ANY WIND HEADLINES
WILL BE NEEDED, BUT GUIDANCE INDICATES WIND GUSTS OF 25 TO 35 MPH
ARE POSSIBLE MONDAY AFTERNOON. WILL MONITOR TRENDS IN THE
GUIDANCE AND MAKE ADJUSTMENTS AS NECESSARY. /BR-Y
LONG TERM...LONG TERM...TUESDAY THROUGH SATURDAY, MARCH 2-6,
2021...SPLIT FLOW WILL RESULT IN A CLOSED LOW DIGGING
SOUTHEASTWARD OFF THE CALIFORNIA COAST TUESDAY WITH A WEAK UPPER
TROUGH MOVING THROUGH WASHINGTON AND OREGON. THE CLOSED LOW WILL
KICK OUT ACROSS THE SOUTHWEST U.S. ON WEDNESDAY WHILE ZONAL FLOW
DOMINATES TO OUR NORTH. OUR FORECAST AREA WILL BASICALLY BE THE
PIVOT POINT FOR THESE TWO DIFFERENT FLOW REGIMES. WHILE A COUPLE
OF SHOWERS COULD ACCOMPANY THE TROUGH PASSAGE TO OUR NORTH ON
TUESDAY, OUR FORECAST AREA WILL LIKELY REMAIN DRY BOTH DAYS. WHAT
THIS BOILS DOWN TO IS A COUPLE OF FINE, LATE-WINTER DAYS FOR EARLY
MARCH (IN LIKE A LAMB?) WITH SOME SUNSHINE, CHILLY MORNINGS (COLD
EAST SIDE) AND SEASONABLY MILD AFTERNOONS.
AN UPPER RIDGE AXIS WILL NOSE INTO THE GREAT BASIN AND STRENGTHEN
WEDNESDAY NIGHT INTO THURSDAY WITH BROAD SOUTHWEST FLOW ALOFT OVER
THE PACIFIC NORTHWEST. THIS SHOULD RESULT IN THE MILDEST DAY OF THE
STRETCH FOR MOST OF SW OREGON AND NORTHERN CALIFORNIA THURSDAY WITH
HIGHS IN THE LOW TO MID 60S WEST OF THE CASCADES AND HIGHS LARGELY
IN THE 50S OVER THE EAST SIDE AND NE CALIFORNIA. MEANTIME, THE NEXT
DEEP UPPER TROUGH AND ASSOCIATED CLOSED LOW WILL DROP SOUTHWARD TO
NEAR 50N AND 140W WITH A HEALTHY FRONTAL SYSTEM OFF THE PACNW COAST,
WHICH IS SUPPORTED BY A 130-140KT JET. PRECIPITATION CHANCES ARE
EXPECTED TO BE MINIMAL THURSDAY SINCE THE FRONTAL SYSTEM WILL REMAIN
LARGELY OFFSHORE. BUT, INCREASING PRESSURE GRADIENTS COULD RESULT
IN BREEZY TO WINDY CONDITIONS, WINDIEST ALONG THE COAST AND OVER THE
COASTAL WATERS.
SOME UNCERTAINTY STILL REMAINS WITH JUST HOW FAST AND HOW STRONG
THIS FRONT WILL BE WHEN IT MOVES ONSHORE LATE FRIDAY INTO SATURDAY,
BUT IT SHOULD BRING A CHANGE TO WETTER WEATHER AT LEAST FROM THE
CASCADES WEST DURING THIS TIME FRAME ALONG WITH SOME POTENTIAL FOR
GUSTY WINDS. SNOW LEVELS FOR THIS FRONT ARE FORECAST TO BE IN THE
4-6K FOOT RANGE. -SPILDE
MFR WATCHES/WARNINGS/ADVISORIES
OR...
CA...NONE.
PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY UNTIL 4 AM PST SUNDAY FOR
PZZ350-356-370-376.
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