River Flood Watch 30, NWS Medford, OR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
850 AM PST TUE NOV 27 2012

.DISCUSSION...MORNING UPDATE. ENJOY THE DAY OF CALM BECAUSE MODELS
ARE STILL LOCKED INTO AN ABRUPT TURN IN THE PATTERN TONIGHT INTO
WEDNESDAY WITH A GOOD TROPICAL TAP OF MOISTURE. THE FORECAST FOR
TODAY LOOKS ON TRACK AND WILL NOT UPDATE AT THIS TIME.

PREVIOUS DISCUSSION...THE WEATHER PATTERN IS ABOUT TO CHANGE...AND
ABRUPTLY. TODAY WILL BE THE LAST FAIR WEATHER DAY FOR SOUTHWEST
OREGON AND NORTHERN CALIFORNIA FOR AT LEAST THE NEXT 5 DAYS. THE
RIDGE THAT BROUGHT THE DRY WEATHER WILL PUSH TO THE EAST AND THIS
WILL ALLOW A STRONG TROUGH DEVELOPING OVER THE GULF OF ALASKA TO
SEND MULTIPLE FRONTS INTO THE WEST COAST WEDNESDAY THROUGH THE
WEEKEND.

THE FIRST SYSTEM WILL ARRIVE AT THE COAST BY WEDNESDAY MORNING
WITH SOME RAIN. THE 00Z NAM HAD BEEN THE ODD MODEL OUT BRINGING
THE SURFACE LOW INSIDE 130 W BUT ITS 06Z RUN HAS NOW COME IN LINE
WITH THE 00Z GFS/ECMWF KEEPING THE LOW ALONG OR JUST OUTSIDE 130.
EVEN SO, PRESSURE GRADIENTS WILL INCREASE ACROSS THE AREA WITH
MFR-RDD GRADIENT ABOUT 4-6 MB LATE TONIGHT THROUGH WEDNESDAY. 700
MB WINDS INCREASE TO 50-70KT WEDNESDAY MORNING INTO THE AFTERNOON.
THIS SYSTEM IS TAKING ON A NEGATIVE TILT, SO WE ARE NOT EXPECTING
WINDS HIGH ENOUGH FOR WARNING CRITERIA AT THE COAST...DUE TO THE
OFFSHORE COMPONENT. HOWEVER, HAVE GONE WITH A WIND ADVISORY
(NPWMFR) FOR THE SHASTA, ROGUE VALLEY AND PORTIONS OF THE EAST
SIDE NEAR SUMMER LAKE FOR GUSTY WINDS. RAINFALL WILL BE LIGHT TO
MODERATE FOR MOST AREAS BUT MAY NOT BE MUCH AT ALL HERE IN THE
ROGUE VALLEY DUE TO THE STRONG DOWNSLOPE FLOW. FARTHER SOUTH, THERE
SHOULD BE A 6-9 HOUR PERIOD OF STRONG SOUTH UPSLOPE FLOW FROM
12-21Z WEDNESDAY AROUND MOUNT SHASTA. SNOW LEVELS WILL BE AROUND
5000 FEET BUT MAY WAVER DOWN AS LOW AS 4500 FEET DURING TIMES OF
HEAVY PRECIP. HAVE GONE WITH A WINTER WEATHER ADVISORY (WSWMFR)
FOR ELEVATIONS ABOVE 5000 FEET FOR 4-6 INCHES OF SNOW.

ANOTHER STRONGER FRONT WILL MOVE IN FROM THE PACIFIC WEDNESDAY
NIGHT INTO THURSDAY. A STRONG COASTAL JET IS EXPECTED TO SET UP
JUST OFFSHORE AND THE FLOW WILL BE MORE ONSHORE THAN ITS
PREDECESSOR. AS A RESULT, HAVE GONE WITH A HIGH WIND WATCH
(NPWMFR) FOR THIS PERIOD ALONG THE COAST. MODEL 925 MB WINDS ARE
SHOWN TO BE AROUND 80 KT AND THIS IS USUALLY A GOOD PROXY FOR WIND
GUSTS AT THE HEADLANDS WITH SLIGHTLY LOWER SPEEDS AT THE IMMEDIATE
COAST. SINCE WINDS WILL BE ACCOMPANIED BY VERY HEAVY RAIN, EXPECT
DOWNED TREES AND POWER LINES TO BE AN ISSUE. TRAVEL WILL BE VERY
DIFFICULT ON HIGHWAY 101 SHOULD TREES FALL ACROSS THE ROAD. THESE
WINDS ARE LIKELY TO SPREAD ACROSS REST OF THE CWA THURSDAY INTO
THURSDAY NIGHT. HAVE HELD OFF ON THE HIGH WIND WATCH FARTHER
INLAND THOUGH FOR NOW, BUT FUTURE SHIFTS WILL NEED TO CONSIDER
THIS LIKELIHOOD. REGARDING QPF...SINCE THIS FRONT WILL HAVE PLENTY
OF SUBTROPICAL PACIFIC MOISTURE TO TAP, A PERIOD OF VERY HEAVY
RAIN WILL ACCOMPANY THE FRONT THROUGH JUST ABOUT ALL OF THE CWA.
THE EXCEPTION BEING THE FAR EAST SIDE...WHERE LIGHTER RAIN IS
EXPECTED. AMOUNTS IN THIS TIME FRAME ALONE (THURSDAY) COULD BE IN
THE 2 TO 5 INCH RANGE ALONG THE CURRY COAST AND PARTS OF WESTERN
SISKIYOU COUNTY.

LONG TERM...ACTIVE PATTERN WILL CONTINUE THURSDAY NIGHT THROUGH
THE WEEKEND. MODELS DO SHIFT THE MAIN AXIS OF PRECIPITATION
ASSOCIATED WITH AN ATMOSPHERIC RIVER (AR) SOUTH OF THE AREA BY
FRIDAY MORNING. SO THERE MAY BE A BRIEF BREAK IN THE PRECIP, BUT
BOTH THE ECMWF/GFS SHOW ANOTHER SHORTWAVE ARRIVING AT THE COAST
FRIDAY NIGHT AND PUSHING INLAND SATURDAY. ANOTHER AR EVENT MAY SET
UP OVER THE CWA THIS WEEKEND. SO, IT ALMOST GOES WITHOUT SAYING
THAT WE WILL ONCE AGAIN LIKELY BE DEALING WITH FLOOD CONCERNS WEST
OF THE CASCADES LATE THIS WEEK INTO THE WEEKEND. SNOW LEVELS WILL
REMAIN HIGH MOSTLY 5500 TO 6500 FEET THROUGH SATURDAY, BUT MAY
LOWER A BIT BY SATURDAY NIGHT INTO SUNDAY. SPILDE

&&

.AVIATION......BASED ON 27/06Z TAFS...

MVFR CIGS IN THE VALLEYS WITH AREAS OF IFR CIGS/VSBYS WILL
PREVAIL THROUGH MID-MORNING TUESDAY OVER THE COAST...COASTAL
VALLEYS...UMPQUA BASIN...ILLINOIS VALLEY...KLAMATH BASIN...UPPER
DESCHUTES VALLEY...SCOTT VALLEY...LOWER KLAMATH VALLEY...AND THE
FORT ROCK/CHRISTMAS VALLEYS AREAS. ALL AREAS WILL CLEAR TO VFR BY
THIS AFTERNOON. ELSEWHERE...VFR CONDITIONS WILL PREVAIL. AREAS OF
MVFR CIGS WILL DEVELOP NEAR THE COAST TONIGHT AS A FRONT APPROACHES
THE COAST. WINDS WILL ALSO INCREASE TONIGHT ALONG THE COAST...OVER
THE RIDGES...IN THE SHASTA VALLEY...AND EAST OF THE CASCADES.

&&

.MARINE...PLEASE SEE THE MARINE WEATHER MESSAGE AND COASTAL WATERS
FORECAST FOR FURTHER DETAILS. THERE WILL BE A SERIES OF STRONG TO
VERY STRONG STORMS IMPACTING THE AREA THIS AFTERNOON THROUGH THE
WEEKEND BRINGING WARNING LEVEL WINDS AND WAVES TO THE AREA. THE
FIRST OF THESE IS MOST LIKELY TO BRING GALES. SINCE THE FLOW WILL
BE MOSTLY SOUTHEAST TO NORTHWEST BECOMING SOUTH TO NORTH MOST OF
THE STRONGER WINDS WILL REMAIN AWAY FROM THE IMMEDIATE COAST
THROUGH WEDNESDAY MORNING. BY WEDNESDAY EVENING...AND THROUGH
THURSDAY...A STRONGER FRONT WILL PUSH ACROSS THE WATERS WITH STORM
FORCE WINDS LIKELY. EXPECTATIONS ARE FOR A COASTAL JET TO DEVELOP
WITH THIS ONE. THERE WILL BE AT LEAST TWO MORE FRONTS THAT WILL
AFFECT THE COAST FROM CAPE MENDOCINO TO THE MOUTH OF THE COLUMBIA
RIVER THROUGH THIS WEEKEND. HOW STRONG AND WHERE THESE END UP IS A
BIT IN QUESTION. BUT...THE GFS AND ECMWF DO AGREE ON TIMING THE
NEXT STRONG FRONT FRIDAY NIGHT. THEN THE ECMWF SOLUTION IS
STRONGER THAN THE GFS WITH A FOLLOWING FRONT SATURDAY NIGHT. SO, I
WENT WITH A BLEND BETWEEN THE GFS AND ECMWF WINDS IN THE EXTENDED.
BTL/DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY FROM 7 AM TO 4 PM PST WEDNESDAY FOR ORZ030-031.
     HIGH WIND WATCH FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY
     AFTERNOON FOR ORZ021-022.
     WIND ADVISORY FROM 4 AM TO 4 PM PST WEDNESDAY FOR ORZ026.

CA...WINTER WEATHER ADVISORY FROM 7 AM TO 7 PM PST WEDNESDAY ABOVE
     5000 FEET FOR CAZ082-083.
     WIND ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST WEDNESDAY FOR
     CAZ081.

PZ...SMALL CRAFT ADVISORY FOR WINDS FROM 1 AM TO 10 AM PST WEDNESDAY
     FOR PZZ350-356.
     STORM WATCH FROM WEDNESDAY EVENING THROUGH THURSDAY MORNING FOR
     PZZ350-356-370-376.
     HAZARDOUS SEAS WARNING FROM 10 AM WEDNESDAY TO 4 AM PST FRIDAY
     FOR PZZ350-356.
     GALE WARNING FROM 10 AM TO 10 PM PST WEDNESDAY FOR PZZ350-356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 1 AM TO 10 AM PST
     WEDNESDAY FOR PZZ350-356.
     SMALL CRAFT ADVISORY FOR WINDS FROM 4 PM THIS AFTERNOON TO 10
PM
     PST THIS EVENING FOR PZZ370-376.
     HAZARDOUS SEAS WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     FRIDAY FOR PZZ370-376.
     GALE WARNING FROM 10 PM THIS EVENING TO 10 PM PST WEDNESDAY FOR
     PZZ370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS FROM 4 PM THIS
AFTERNOON
     TO 10 PM PST THIS EVENING FOR PZZ370-376.

SPILDE/DW/MSO