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.  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab OR Page
The Nexlab CA Page Main Text Page