815  
FXUS66 KMFR 211608  
AFDMFR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MEDFORD OR  
908 AM PDT THU OCT 21 2021  
   
SHORT TERM
 
SATELLITE IMAGERY SHOWS A LOW PRESSURE CENTERED NEAR  
47N AND 135W WITH A FRONT OFF THE PACNW COAST. THIS STRONG AND  
MOIST FRONT WILL BRING MODERATE TO HEAVY RAIN AND STRONG GUSTY  
WINDS TO THE AREA TODAY INTO FRIDAY MORNING. MODELS AND ENSEMBLES  
REMAIN ON TRACK SHOWING STRONG WINDS DEVELOPING ALONG THE COAST  
LATER THIS MORNING INTO THIS AFTERNOON. ALSO STRONG, GUSTY WINDS  
WILL DEVELOP ACROSS MANY INLAND AREAS INCLUDING OVER THE  
MOUNTAINS, THE SOUTHERN ROGUE VALLEY, THE SHASTA VALLEY, SUMMER  
LAKE AREA AND THE HIGHER TERRAIN EAST OF THE CASCADES. SOUTH WINDS  
ARE PICKING UP THIS MORNING WITH GUSTS TO NEAR 50 MPH IN THE  
SOUTHERN SHASTA VALLEY AND GUSTS NEAR 40 MPH AT THE COAST AND OVER  
THE MOUNTAINS. AS THE WINDS ALOFT AND PRESSURE GRADIENT INCREASE  
TODAY, EXPECT WINDS TO INCREASE FURTHER WITH STRONG WINDS PEAKING  
IN THE LATE MORNING AND AFTERNOON AT THE COAST, PEAKING IN THE  
AFTERNOON AND EVENING FOR INLAND AREAS CASCADES WEST AND PEAKING  
IN THE LATE AFTERNOON INTO TONIGHT FOR AREAS EAST OF THE CASCADES.  
STRONG WINDS MAY RESULT IN TREE DAMAGE, ITEMS BEING BLOWN AROUND  
AND DAMAGED AND TRAVEL DIFFICULTY FOR HIGH PROFILE VEHICLES. HIGH  
WIND WARNINGS ARE IN EFFECT AT THE COAST TODAY AND WIND ADVISORIES  
ARE IN EFFECT FOR INLAND AREAS TODAY INTO EARLY FRIDAY MORNING.  
PLEASE SEE THE NPWMFR FOR DETAILS.  
 
PRECIPITATION WILL SPREAD INLAND TODAY AND TONIGHT. THE HIGH  
RESOLUTION MODELS SHOW LIGHT PRECIPITATION SPREADING INTO THE  
COAST AND SOME AREAS FROM THE CASCADES WEST THIS MORNING AND EARLY  
THIS AFTERNOON. THEN, THE MAIN FRONTAL BAND WITH MODERATE TO  
LOCALLY HEAVY PRECIPITATION WILL GRADUALLY MOVE ACROSS THE AREA  
LATE THIS AFTERNOON THROUGH FRIDAY MORNING. WIDESPREAD MODERATE TO  
LOCALLY HEAVY RAINFALL IS EXPECTED WITH AMOUNTS RANGING FROM  
0.75-2.00 INCHES, EXCEPT 2.00-4.00 INCH AMOUNTS IN AREAS WHERE  
UPSLOPE FLOW AND OROGRAPHIC ENHANCEMENT IS MAXIMIZED (COAST RANGES  
AND IN PORTIONS OF SISKIYOU COUNTY). HIGH RESOLUTION HRRR  
FORECASTS SHOW HOURLY RAIN RATES OF UP TO 0.5-0.8 INCHES IN THE  
COASTAL MOUNTAINS IN CURRY COUNTY AND 0.4-0.7 IN PORTIONS OF  
WESTERN AND SOUTHERN SISKIYOU COUNTY WHERE OROGRAPHIC ENHANCEMENT  
IS MAXIMIZED. HEAVY PRECIPITATION RATES ARE BELOW THE GUIDANCE  
CRITERIA FOR FLASH FLOOD IN THE MCCASH AND RIVER BURN SCARS.  
HOWEVER, THIS WILL BE CLOSELY MONITORED THROUGH THE EVENT. FOR  
OTHER AREAS, MODERATE TO HEAVY RAIN MAY RESULT IN SOME IMPACTS ON  
ROADWAYS WITH PONDING OF WATER OR IMPACTS FROM BLOCKED STORM  
DRAINS. FOR ADDITIONAL DETAILS ON THE WIND AND RAIN IMPACTS WITH  
THIS SYSTEM, PLEASE SEE THE DISCUSSION BELOW.  
 

 
   
AVIATION...21/12Z TAFS
 
AIRPORT WEATHER WARNINGS HAVE BEEN ISSUED  
FOR MEDFORD/MFR FROM 17Z TO 23Z WITH SOUTHERLY GUSTS TO 35 KT  
EXPECTED, AND KLAMATH FALLS/LMT FROM 17Z TO 01Z WITH SOUTHERLY GUSTS  
TO 40 KT EXPECTED. EARLY THIS MORNING ACROSS MUCH OF THE AREA, AND  
THEN IN SHELTERED AREAS THROUGH THE REMAINDER OF THE DAY, LOW LEVEL  
WIND SHEAR WILL BE PRESENT.  
 
CONDITIONS WILL REMAIN MAINLY VFR THIS MORNING, WITH THE NOTABLE  
EXCEPTION OF AREAS OF VALLEY LIFR FOG. AS WINDS SURFACE AND INCREASE  
SHORTLY AFTER SUNRISE, VFR WILL PREVAIL. WIND SPEEDS WILL GENERALLY  
PEAK DURING THE AFTERNOON WITH MODERATE RAIN AND MVFR REACHING THE  
COAST THEN CONTINUING INLAND THROUGH TONIGHT. -DW  
 

 
   
MARINE...UPDATED 300 AM PDT THURSDAY, 21 OCTOBER 2021
 
SOUTHERLY  
GALES IN THE OUTER WATERS EARLY THIS MORNING WILL SPREAD ACROSS THE  
WATERS TODAY WITH A STRONG COLD FRONT. A MIX OF FRESH SWELL AND  
LONGER PERIOD WEST SWELL WILL CONTINUE HIGH TO VERY HIGH AND VERY  
STEEP SEAS AT 12 TO 20 FT TONIGHT INTO FRIDAY. ANOTHER FRONT WILL  
FOLLOW FRIDAY NIGHT INTO SATURDAY WITH WINDS AGAIN APPROACHING  
GALES. THE ACTIVE WEATHER PATTERN WILL CONTINUE NEXT WEEK WITH THE  
POTENTIAL FOR ANOTHER EPISODE OF VERY HIGH AND VERY STEEP SEAS  
AROUND SUNDAY THROUGH MONDAY. -DW  
 

 
   
PREV DISCUSSION
 
/ISSUED 422 AM PDT THU OCT 21 2021/  
 
DISCUSSION...A MATURE CYCLONE OVER THE NE PACIFIC OCEAN IS  
CENTERED NEAR 47N AND 136W EARLY THIS MORNING. AND, THE UPPER  
TROUGH THAT MOVED THROUGH THE AREA YESTERDAY MORNING IS NOW ALL  
THE WAY INTO SOUTHERN ALBERTA, CANADA. WE'VE BEEN IN A RELATIVE  
BREAK BETWEEN THESE SYSTEMS YESTERDAY AND LAST NIGHT, DESPITE SOME  
LIGHT UPSLOPE PRECIPITATION CONTINUING IN THE VICINITY OF MT.  
SHASTA.  
 
SKIES CLEARED JUST ENOUGH LAST EVENING TO ALLOW FOR SOME SHALLOW  
FOG IN THE VALLEYS WEST OF THE CASCADES (THOSE THAT ARE SHELTERED  
FROM THE WIND). SO, WE HAD AREAS OF FOG DEVELOP HERE AT THE  
AIRPORT FOR A WHILE, BUT IT HAS JUST CLEARED IN THE LAST HOUR.  
SOME FOG THOUGH COULD BE BRIEFLY DENSE THIS MORNING, SO BE ON THE  
LOOKOUT FOR THAT ON THE MORNING COMMUTE.  
 
MEANTIME, PRESSURE GRADIENTS AND MID-LEVEL SOUTHERLY WINDS HAVE  
STRENGTHENED OVERNIGHT AND THIS HAS BROUGHT BREEZY TO WINDY  
CONDITIONS TO THE SHASTA VALLEY AND ALSO PORTIONS OF THE ROGUE  
VALLEY SOUTH OF MEDFORD TO AROUND ASHLAND WHERE GUSTS OF 35 TO 45  
MPH HAVE BEEN OBSERVED. ONCE THE SUN RISES THIS MORNING, THE LOW-  
LEVEL INVERSION WILL BREAK, WINDS WILL SURFACE AND MIX OUT THE  
FOG. IT'LL ALSO LIKELY TURN BREEZY FOR A WHILE HERE IN MEDFORD.  
WIND ADVISORIES ARE UP AT NPWMFR. THE COLD FRONT ASSOCIATED WITH  
THE OFFSHORE CYCLONE WILL APPROACH THE COAST THIS AFTERNOON. WE  
EXPECT SOME SIGNIFICANT WINDS (GUSTS TO 60 MPH) AGAIN ALONG THE  
COAST, SO WE HAVE A HIGH WIND WARNING UP THERE UNTIL 5PM THIS  
AFTERNOON.  
 
RAIN WILL BE CONSISTENT IN THE UPSLOPE AREAS AROUND MT. SHASTA  
TODAY, BUT DOWNSLOPING WILL LARGELY KEEP WEST SIDE VALLEYS DRY TIL  
THIS EVENING AND IT WILL LIKELY REMAIN DRY OVER THE EAST SIDE.  
PRECIPITATION WILL BREAK OUT OVER WESTERN SISKIYOU COUNTY, THE  
COAST RANGES AND AT THE COAST THIS AFTERNOON. EXPECT MODERATE TO  
HEAVY RAINFALL TO ACCOMPANY THE FRONT ONSHORE THIS EVENING AND  
OVERNIGHT, PUSHING EASTWARD INTO LAKE AND MODOC COUNTIES BY FRIDAY  
MORNING. THIS FRONT HAS A VERY NICE INLAND AR SIGNAL, SO EVERYONE  
IN THE CWA WILL GET WET TONIGHT INTO FRIDAY. AMOUNTS RANGING FROM  
0.75-2.00 INCHES WILL BE COMMON, EXCEPT 2.00-4.00 INCH AMOUNTS  
ARE POSSIBLE IN AREAS WHERE UPSLOPE FLOW AND OROGRAPHIC  
ENHANCEMENT IS MAXIMIZED (COAST RANGES AND IN PORTIONS OF SISKIYOU  
COUNTY). THIS IS LARGELY GOOD NEWS, WITH SOME HIGHER MOUNTAIN  
SNOW PACK DEVELOPING AND WATER BEGINNING TO REFILL THE BADLY  
DEPLETED RESERVOIRS. HOWEVER, WE STILL NEED TO MONITOR RECENTLY  
BURNED AREAS FOR POTENTIAL DEBRIS FLOWS AND FLASH FLOODING. RIGHT  
NOW, WE ARE NOT ANTICIPATING RAINFALL RATES TO CAUSE FLASH  
FLOODING FOR THE BURN SCARS. HI-RES GUIDANCE DOES SHOW THE  
POTENTIAL FOR AROUND 0.50"/HR RATES FOR MCCASH/RIVER COMPLEX  
SCARS, ESPECIALLY FROM 6-12Z FRIDAY, BUT THIS IS STILL WELL BELOW  
ESTABLISHED CRITERIA OF 0.80"/HR. DURING THE TIME OF HEAVIEST  
RAINFALL TONIGHT, THERE COULD BE PONDING OF WATER ON ROADWAYS AT  
TIMES, ESPECIALLY SINCE RECENT WINDS HAVE CAUSED PLENTY OF LEAVES  
TO FALL AND THESE COULD POTENTIALLY BLOCK STORM DRAINS. SNOW  
LEVELS WILL BE QUITE HIGH UNTIL FRIDAY MORNING, WHEN THEY'LL COME  
DOWN TO AROUND 5500 FEET. A COUPLE OF INCHES COULD ACCUMULATE UP  
AROUND CRATER LAKE, BUT WINTER IMPACTS WILL BE SMALL.  
 
A WEAKER FRONT WILL MOVE THROUGH LATE FRIDAY NIGHT INTO SATURDAY,  
BUT THEN A MUCH STRONGER FRONT WILL ARRIVE AND MOVE ONSHORE  
SATURDAY NIGHT INTO SUNDAY. WE EXPECT ANOTHER ROUND OF STRONG  
WINDS AND HEAVY RAINFALL TO ACCOMPANY THIS SYSTEM. THIS ONE  
APPEARS TO DIRECT THE HEAVIEST PRECIPITATION INTO NORCAL. DETAILS  
ONE THIS ONE CAN BE GLEANED FROM YESTERDAY AFTERNOON'S DISCUSSION.  
-SPILDE  
 
LONG TERM FROM YESTERDAY'S DISCUSSION...THE ACTIVE WEATHER  
PATTERN WILL PERSIST LATE SATURDAY NIGHT INTO EARLY SUNDAY  
MORNING. THE REMNANTS OF ONE ATMOSPHERIC RIVER(AR), WHICH WILL  
MOVE THROUGH THE AREA SOMETIME ON SATURDAY, WILL BE SHORTLY  
REPLACED BY ANOTHER ONE AROUND SUNDAY EVENING. THIS AR EVENT  
APPEARS TO BE RATHER SIMILAR TO WHAT WE'LL SEE ON THURSDAY  
ACCORDING TO ENSEMBLE DATA. IT ALSO APPEARS THE SUNDAY EVENT WILL  
BE RATHER BRIEF AS THE LOW QUICKLY MOVES THROUGH THE REGION ON  
SUNDAY. INTEGRATED WATER VAPOR TRANSPORT(IVT) VALUES, WHICH SHOW  
HOW EFFECTIVELY WATER VAPOR IS TRANSPORTED BY THE WIND WITHIN THE  
ATMOSPHERE, ARE HIGH AROUND 750. THERE ARE ROUGHLY 15 OUT OF 80  
ENSEMBLE MEMBERS THAT SHOW IVTS AROUND 1000, SO A HEAVIER EVENT IS  
DEFINITELY POSSIBLE.  
 
IN ANY CASE, DEBRIS FLOWS REMAIN A THREAT FOR THE SUNDAY AR EVENT  
WITHIN 2021 AND 2020 BURN SCARS IN CALIFORNIA. WE BELIEVE THE  
THREAT FOR DEBRIS FLOWS IS AROUND 10 TO 15 PERCENT FOR THE SUNDAY  
EVENT. DEBRIS FLOWS HAVE BEEN VERY RARE WITHIN OUR CWA OVER THE  
YEARS, EVEN WITH ALL FIRE ACTIVITY HERE IN RECENT YEARS. HOWEVER,  
THE SHEAR AMOUNT OF RAIN WITHIN SOME 6 HOUR PERIODS HAS A 10 TO 15  
PERCENT CHANCE OF TRIGGERING A DEBRIS FLOW IN OUR OPINION WITHIN THE  
SLATER AND RIVER BURN SCARS. THAT PERCENTAGE COULD TREND HIGHER IF  
WE START TO SEE HIGHER RAINFALL RATES IN HIGH RESOLUTION ENSEMBLE  
FORECAST SYSTEM WHEN IT BECOMES AVAILABLE.  
 
SNOW LEVELS WILL LIKELY START OUT AROUND 7000 FEET AHEAD OF THE COLD  
FRONT BEFORE FALLING DOWN TO 5000 FEET BEHIND IT ON SUNDAY. THE  
MOST PROBABLE SNOW FORECAST SHOWS 6 TO 10 INCHES OF SNOW  
ACCUMULATING ABOVE 5500 FEET THROUGH SUNDAY INTO MONDAY. WE DO FEEL  
CONFIDENT POPULAR DESTINATIONS LIKE CRATER LAKE AND MT. ASHLAND WILL  
SEE AT LEAST 1 TO 2 INCHES OF SNOW BEHIND THE FRONT ON SUNDAY.  
 
THE LAST TOPIC WORTH TALKING ABOUT IS NEXT WEEK WHEN ANOTHER LOW  
WILL EVENTUALLY SWING THROUGH THE FORECAST AREA. MODELS ARE PRETTY  
SPREAD OUT WHEN THAT NEXT SYSTEM EVENTUALLY MOVES THROUGH, SO  
UNCERTAINTY REMAINS HIGH. ENSEMBLE DATA SUGGESTS MEAN IVT VALUES  
REMAIN ELEVATED. LOOKING AT THE INDIVIDUAL MEMBERS, THERE ARE MANY  
WHICH ARE PEAKING BETWEEN 500 TO 1000, SO THIS TELLS US IT'S MORE  
A QUESTION OF WHEN THE NEXT WAVE AND HEAVY PRECIPITATION EVENT  
WILL MOVE THROUGH AFTER SUNDAY. IT COULD VARY FROM TUESDAY THROUGH  
THURSDAY. -SMITH  
 

 
   
MFR WATCHES/WARNINGS/ADVISORIES
 
 
OR...HIGH WIND WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR ORZ021-022.  
WIND ADVISORY UNTIL 8 AM PDT FRIDAY FOR ORZ030-031.  
WIND ADVISORY UNTIL 11 PM PDT THIS EVENING FOR ORZ026.  
 
CA...WIND ADVISORY UNTIL 8 AM PDT FRIDAY FOR CAZ085.  
WIND ADVISORY UNTIL 2 AM PDT FRIDAY FOR CAZ081.  
 
PACIFIC COASTAL WATERS...  
GALE WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR  
PZZ350-356-370-376.  
HAZARDOUS SEAS WARNING FROM 5 PM THIS AFTERNOON TO 11 AM PDT  
FRIDAY FOR PZZ350-356-370-376.  
 

 
 
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