Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 240324
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
824 PM PDT TUE SEP 23 2014

.DISCUSSION...A MAJOR CHANGE IN OUR WEATHER IS IMMINENT WITH A
SLOW MOVING COLD FRONT POISED TO BRING SIGNIFICANT RAINFALL TO
OUR AREA. ALSO, TEMPERATURES ARE EXPECTED TO BE NEAR TO SLIGHTLY
BELOW NORMAL FOR THE NEXT WEEK.

THE MAIN HAZARDS IN THE NEAR TERM ARE FLOODING ON THE BURN SCARRED
AREAS OF SISKIYOU COUNTY AND SLICK ROADS DUE TO THE MONTHS-LONG
ACCUMULATION OF OIL IN OUR DROUGHT PARCHED AREA. THERE WILL ALSO
BE GUSTY SOUTHERLY WINDS THAT WILL BE STRONGEST AT THE COAST, OVER
THE HIGHER TERRAIN, IN THE SHASTA VALLEY, AND EAST OF THE
CASCADES.

THE FORECAST WAS UPDATED EARLY THIS EVENING TO MOVE UP THE START
OF THE FLASH FLOOD WATCH FOR PORTIONS OF WESTERN AND CENTRAL
SISKIYOU COUNTY BY SEVERAL HOURS...TO 6 AM WEDNESDAY MORNING.
ALSO, THE QUANTITY OF PRECIPITATION FORECAST WAS NUDGED SLIGHTLY
HIGHER FOR JOSEPHINE COUNTY AND WESTERN SISKIYOU COUNTY.

THE 00Z NAM MODEL DATA HAS RECENTLY ARRIVED AND HAS SIMILAR TIMING
OF RAINFALL AND QPF AS BOTH ITS PREVIOUS RUN AND THE 18Z GFS.
LIGHT RAIN HAS BEGUN IN CURRY COUNTY AND WILL VERY SHORTLY SPREAD
TO ALL OF THE OREGON AND NORTHERN CALIFORNIA COAST. THE HEAVIEST
RAIN AT THE COAST WILL OCCUR THIS EVENING THROUGH WEDNESDAY
MORNING WITH THE FRONT EDGE OF THE MODERATE TO HEAVY RAINFALL
REACHING THE CASCADES WEDNESDAY MORNING AND CONTINUING THROUGH
WEDNESDAY EVENING. RAINFALL WILL REACH WESTERN AND NORTHERN
KLAMATH COUNTY WEDNESDAY AFTERNOON BUT LAKE AND MODOC COUNTIES
WILL REMAIN MAINLY DRY UNTIL LATE WEDNESDAY NIGHT THROUGH THURSDAY
MORNING.

THE REMNANTS OF THE COLD FRONT ARE INDICATED TO FINALLY EXIT EAST
OF OUR AREA THURSDAY AFTERNOON. A COOL AIR MASS AND LIGHT SHOWERS
ARE EXPECTED BEHIND THE FRONT DURING THURSDAY THEN AN UPPER LEVEL
LOW WILL SWING INLAND ON FRIDAY WITH AN UPTICK IN THE COVERAGE AND
FREQUENCY OF LIGHT SHOWERS COMPARED TO THURSDAY DUE TO AN
INCREASE OF LOW LEVEL MOISTURE AND UPLIFT.

MODEL SOLUTIONS ON THE TRACK OF THE UPPER LOW BEGIN TO DIVERGE ON
SATURDAY. BUT IT IS LIKELY SAFE TO SAY THAT THE PROBABILITY OF LINGERING
WRAP AROUND SHOWERS WILL BE HIGHEST EAST OF THE CASCADES. THE
MODEL DIFFERENCES INCREASE EARLY NEXT WEEK WITH UNCERTAINTY ON HOW
QUICKLY THE TROUGH WILL EXIT AND HOW QUICKLY THE NEXT TROUGH WILL
ARRIVE FROM THE WEST OR NORTHWEST.


&&

.AVIATION...BASED ON THE 24/00Z TAF CYCLE...A VERY WET COLD FRONT
WILL SLOWLY MOVE ACROSS THE REGION OVER THE NEXT 24 HOURS. MODERATE
TO HEAVY RAINFALL IS EXPECTED TO BRING WIDESPREAD MVFR CIGS AND VIS
TO ALL AREAS WEST OF THE CASCADES WITH A PERIOD OF IFR CONDITIONS
POSSIBLE DURING THE FRONTAL PASSAGE. THE FRONT IS EXPECTED TO REACH
THE COAST AROUND DAWN WEDNESDAY AND THEN REACH THE CASCADES BY
EVENING. GUSTY SOUTH WINDS...MOUNTAIN OBSCURATION...AND MOUNTAIN
WAVE TURBULENCE CAN ALL BE EXPECTED OVER THE WEST SIDE THROUGH
TOMORROW. THE FRONT IS NOT EXPECTED TO REACH THE EAST SIDE LOCATIONS
UNTIL WEDNESDAY NIGHT, BUT STRONG, GUSTY SOUTH TO SOUTHWEST WINDS
WILL IMPACT EAST SIDE TERMINALS AND MOUNTAIN WAVE TURBULENCE WILL
LEAD TO BUMPY APPROACHES. -WRIGHT

&&

.MARINE...UPDATED 300 PM PDT TUE 23 SEP 2014...
SOUTH WINDS WILL CONTINUE TO INCREASE THROUGH EARLY EVENING AHEAD OF
A COLD FRONT...WHICH WILL BRING PERIODS OF RAIN...STRONG WINDS...AND
HEAVY SEAS TO THE COASTAL WATERS. GALES AND VERY STEEP AND HAZARDOUS
SEAS ARE EXPECTED OVER MUCH OF THE COASTAL WATERS THROUGH EARLY
WEDNESDAY MORNING. WINDS WILL DIMINISH AND STEEP TO VERY STEEP WIND
DRIVEN SEAS WILL SUBSIDE LATE TONIGHT...BUT HEAVY WEST SWELL WILL
BUILD ON WEDNESDAY KEEPING SEAS STEEP INTO THURSDAY NIGHT. UNSETTLED
WEATHER IS LIKELY THROUGH THE END OF THE WEEK. BTL/WRIGHT

&&

.PREV DISCUSSION... /ISSUED 315 PM PDT TUE SEP 23 2014/

DISCUSSION...AN ATMOSPHERIC RIVER...OR A LONG STRETCH OF DEEP AND
CONCENTRATED MOISTURE...IS AIMED AT THE NORTHERN CALIFORNIA AND
SOUTHERN OREGON COAST. THIS FEATURE COULD BRING SIGNIFICANT
IMPACTS TO THE FORECAST AREA ON WEDNESDAY. THESE IMPACTS INCLUDE
THE POTENTIAL FOR LIFE- AND PROPERTY-THREATENING FLASH FLOODING
AND DEBRIS FLOWS IN AND AROUND WILDFIRE BURN SCARS...AND TRAVEL
PROBLEMS FOR MOST OF THE FORECAST AREA WHEN OILS ON THE ROAD FROM
MONTHS OF MOSTLY DRY WEATHER MIX WITH WATER AND MAKE FOR VERY
SLIPPERY ROADS.

CURRENT SATELLITE-DERIVED PRECIPITABLE WATER IMAGERY SHOWS A PLUME
OF MOISTURE...WITH VALUES OF 1.6 INCHES...NEARING THE COASTLINE.
THIS REPRESENTS A MOISTURE FEED THAT ONLY OCCURS EVERY 5-10 YEARS OR
MORE DURING THE LATE SEPTEMBER TIME FRAME. THIS WET FRONTAL SYSTEM
WILL BRING SIGNIFICANT RAINS TO THE COAST BY TONIGHT...AND AS THE
WINDS TURN TOWARD A MORE WESTERLY DIRECTION TONIGHT...LIFT OVER THE
MOUNTAINS OF CURRY COUNTY WILL BE ENHANCED AND AREAS LIKE RED MOUND
WILL LIKELY SEE RAINFALL RATES OF 1 INCH PER HOUR EARLY WEDNESDAY
MORNING. RIVERS WILL RISE SHARPLY WITH SUCH HEAVY RAIN.
HOWEVER...NO MAIN STEM RIVER FLOODING IS EXPECTED WITH THIS SYSTEM
BECAUSE OF THIS BEING THE FIRST WET SYSTEM OF THE FALL AND
ANTECEDENT RIVER LEVELS ARE VERY LOW.

THE FRONT AND ASSOCIATED HEAVY RAIN WILL REACH WILDFIRE BURN SCAR
AREAS IN SISKIYOU COUNTY WEDNESDAY MORNING AND CONTINUE THROUGH THE
AFTERNOON. MODELS ARE IN GOOD AGREEMENT ON THESE AREAS OF WESTERN
SISKIYOU COUNTY RECEIVING 1 TO 2 INCHES OF RAIN...WITH THE HEAVIEST
RAIN COMING WEDNESDAY MORNING INTO EARLY AFTERNOON.  A FLASH FLOOD
WATCH AT FFAMFR HAS BEEN ISSUED FOR THESE BURN SCARS...AND RESIDENTS
AND TRAVELERS IN THIS AREA SHOULD BE AWARE OF THE POTENTIAL FOR
FLASH FLOODING...MUDSLIDES...AND ROCK SLIDES. SOME OF THE ROADS IN
AND AROUND THE BURN SCARS INCLUDE HIGHWAY 96...SAWYERS BAR
ROAD...AND SCOTT RIVER ROAD.

ELSEWHERE...WETTING RAINS ARE LIKELY IN ALL LOCATIONS ALONG AND WEST
OF THE CASCADES...WITH ONE HALF INCH EXPECTED IN THE ROGUE
VALLEY...MORE THAN AN INCH IN THE CASCADES. LESSER RAIN AMOUNTS ARE
EXPECTED EAST OF THE CASCADES...WITH AROUND A QUARTER INCH IN
KLAMATH FALLS. GIVEN THAT THIS IS THE FIRST WIDESPREAD RAIN SINCE
LAST SPRING...THERE WILL BE TRAVEL CHALLENGES FOR DRIVERS ON
WEDNESDAY BECAUSE OF SLIPPERY ROADS. OILS BUILD UP OVER TIME AND
WILL BE RELEASED ONTO THE SURFACE TOMORROW AS RAIN HITS THE
ROADS...AND DRIVERS SHOULD ALLOW FOR MORE TIME TO GET TO THEIR
DESTINATION.

THIS SYSTEM IS ALSO BRINGING SIGNIFICANT SOUTH TO SOUTHWEST WINDS TO
THE REGION...AND THESE WINDS WILL CONTINUE THROUGH TOMORROW EAST OF
THE CASCADES. A RED FLAG WARNING AT RFWMFR HAS BEEN ISSUED FOR THESE
WINDS.

RAIN CHANCES WILL DIMINISH SIGNIFICANTLY ON THURSDAY BUT RAIN
CHANCES DO LINGER THROUGH SATURDAY AS UPPER TROUGHING IS SLOW TO
EXIT THE AREA. THE GFS SUGGESTS DRY WEATHER SUNDAY INTO EARLY NEXT
WEEK WHILE THE ECMWF BRINGS IN ANOTHER TROUGH AND RAIN BY SUNDAY
NIGHT INTO MONDAY. WE HAVE CHOSEN A COMPROMISE AND HAVE KEPT SLIGHT
CHANCE POPS FOR MOST OF THE AREA...FOCUSED FROM THE CASCADES
WEST...WITH THE MOST LIKELY AREAS TO SEE RAIN BEING THE UMPQUA BASIN
AND COAST.

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...RED FLAG WARNING UNTIL 11 PM PDT WEDNESDAY FOR ORZ624-625.

CA...RED FLAG WARNING UNTIL 11 PM PDT WEDNESDAY FOR CAZ285.
     RED FLAG WARNING UNTIL 11 PM PDT THIS EVENING FOR CAZ281-284.
     FLASH FLOOD WATCH FROM 6 AM PDT WEDNESDAY THROUGH LATE WEDNESDAY
     NIGHT FOR CAZ080-081-083.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 AM
     PDT WEDNESDAY FOR PZZ350-356.
     HAZARDOUS SEAS WARNING UNTIL 5 AM PDT WEDNESDAY FOR
     PZZ350-356-370-376.
     GALE WARNING UNTIL 2 AM PDT WEDNESDAY FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THURSDAY
     FOR PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM PDT THURSDAY FOR
     PZZ370-376.

$$

DW/TRW/BTL





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