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.
CC
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