Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 272256
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
256 PM PST THU NOV 27 2014

.DISCUSSION...THE 50 MILE WIDE NEARLY CONSTANT BAND OF PRECIP THAT
EXTEND FROM PORT ORFORD TO THE NORTHEAST THROUGH ROSEBURG WILL
SLOWLY MOVE SOUTHEAST INTO MODOC COUNTY BY LATE TOMORROW MORNING
AS THE AXIS OF THE JET SLOWLY MOVES TO THE SOUTHEAST. LATE
TOMORROW MORNING THE AREA WILL BE UNDER THE RIGHT ENTRANCE REGION
OF A +100 KT JET. 700 MB WINDS FROM THE SOUTHWEST WILL MIX DOWN
PERIODICALLY EAST OF THE CASCADES AHEAD OF THE FRONT BRINGING
ADVISORY STRENGTH WINDS TO PORTIONS OF THE EAST SIDE. WITH THE
BROAD UPPER SUPPORT THE ENTIRE FORECAST AREA BY LATE TOMORROW
AFTERNOON. INSTABILITY IS OVER THE COASTAL WATERS TOMORROW
AFTERNOON AND WITH SOUTHWESTERLY WINDS HAVE INCLUDED SLIGHT CHANCE
THUNDERSTORMS TO A NARROW STRIP OF THE COAST AS WELL. THE JET
CONTINUES TO SHIFT SOUTH OVER CENTRAL CALIFORNIA WITH ANOTHER JET
DIPPING DOWN FROM THE NORTH. HOWEVER THIS SECOND JET SHIFTS EAST
BEFORE MAKING IT DOWN TO SOUTHERN OREGON. A BROAD UPPER TROUGH
PATTERN EXTENDS FROM THE NORTHERN GREAT PLAINS TO A CLOSED LOW
WELL OFFSHORE. THIS PATTERN LEAVES A PERSISTENT BAND OF PRECIP
OVER NORTHERN CALIFORNIA EXTREME SOUTHERN OREGON INTO THE
BEGINNING OF NEXT WEEK.

.EXTENDED TERM...MONDAY THROUGH THURSDAY NIGHT...LONG TERM MODELS
SOLUTIONS CONTINUE TO BE INCONSISTENT FROM RUN TO RUN, AND THE
SOLUTIONS OF THE GFS AND ECMWF CONTINUE TO BE INCREASINGLY DIVERGENT
BEYOND SUNDAY. MUCH OF THIS STEMS FROM THE DIFFICULTY THE MODELS ARE
HAVING WITH THE CLOSED LOW WELL OFFSHORE OF CALIFORNIA. THE BEHAVIOR
OF A FEATURE LIKE THIS IS NOTORIOUSLY DIFFICULT TO PIN DOWN, SO
UNCERTAINTY REMAINS HIGH.

FOR THE PAST SEVERAL DAYS, THERE HAS BEEN SOME CONCERN ABOUT AN
UPSLOPE SNOW EVENT IN THE MT SHASTA AREA, BUT MODEL SOLUTIONS HAVE
AGAIN PUSHED BACK THE EVENT BY 12 TO 24 HOURS, BUT HAVE ALSO
SIGNIFICANTLY WEAKENED THE LOW AND CHANGED THE PROJECTED COURSE.
TAKING THE TRENDS INTO ACCOUNT, IT APPEARS THAT THE SNOW EVENT IS
BECOMING LESS AND LESS LIKELY.  THEREFORE, HAVE REMOVED MENTION OF A
HEAVY UPSLOPE SNOW EVENT FROM THE FORECAST.  INSTEAD, IT APPEARS THE
FORECAST IS TRENDING TOWARDS A MORE TYPICAL TYPE OF SYSTEM, WITH THE
CLOSED LOW WEAKENING AS IT MOVES TOWARDS THE COAST, AND PUSHING
ONSHORE AS AN OPEN TROUGH.

THEREFORE, THE LONG TERM BEGINS WITH A WARM FRONT PUSHING NORTH
THROUGH THE AREA MONDAY, FOLLOWED BY THE COLD FRONT AND THE
ASSOCIATED UPPER LEVEL TROUGH THROUGH WEDNESDAY NIGHT. MOISTURE
INFLOW STILL APPEARS TO BE SIGNIFICANT, SO THERE IS NO REASON TO
REDUCE PRECIPITATION CHANCES. HOWEVER, HAVE ADJUSTED THE TIMING AND
PLACEMENT OF POPS TO FIT THE NEW FORECAST TRENDS, AND CONTINUED
SHOWERS THROUGH THE REMAINDER OF THE FORECAST TERM.

ONE TOPIC THAT STILL BEARS WATCHING WILL BE THE EAST SIDE AS THE
WARM FRONT MOVES NORTH MONDAY MORNING. MODEL SOUNDINGS SHOW THE
POTENTIAL OF COLD AIR BECOMING TRAPPED WITHIN THE VALLEYS AS THE
WARMER AIR MOVES OVERHEAD, AND THIS COULD PRODUCE A BRIEF PERIOD OF
ICE BEFORE PRECIPITATION CHANGES OVER TO ALL RAIN. CURRENT
SOLUTIONS SHOW A VERY SMALL CHANCE FOR THIS, BUT IT HAS BEEN AN
ACCOMPANYING FEATURE OF THE WARM FRONT FOR SEVERAL CYCLES. HAVE KEPT
MENTION OUT OF THE FORECAST FOR NOW, AS UNCERTAINTY IS TOO HIGH, BUT
WILL KEEP AN EYE ON THIS POTENTIAL OVER THE NEXT SEVERAL SHIFTS.
-BPN

&&

.AVIATION...BASED ON THE 27/18Z TAF CYCLE...A COLD FRONT HAS STALLED
OVER SOUTHWEST OREGON TODAY. MVFR/IFR CONDITIONS WITHIN MANY OF THE
VALLEYS IN THE AREA WILL BE SLOW TO LIFT TODAY, BUT THE FRONT SHOULD
HELP, ESPECIALLY TO THE NORTH OF THE BOUNDARY. OVERALL, THERE WILL
BE LIGHT RAIN WITH A MIX OF VFR AND MVFR CEILINGS AND WIDESPREAD
MOUNTAIN OBSCURATIONS. THE FRONT WILL LIKELY PRODUCE LIGHT TO
MODERATE LOW LEVEL TURBULENCE IN ALL AREAS OVER THE NEXT 24 HOURS
AND SOME LOW LEVEL WIND SHEAR NEAR THE COAST. CONDITIONS IN VALLEYS
WILL DETERIORATE AGAIN TO A MORE WIDESPREAD MVFR CEILING AND LOCAL
IFR THIS EVENING INTO FRIDAY MORNING, THEN A DISTURBANCE WILL
INCREASE RAINFALL ON FRIDAY AND PUSH THE FRONT INLAND WITH MVFR
CONDITIONS.

-BPN/DW

&&

.MARINE...UPDATED 200 PM PST THU NOV 27 2014...THERE IS HIGH
CONFIDENCE IN THE FORECAST THROUGH FRIDAY NIGHT THEN MODEL
DIFFERENCES INCREASE. SOUTH WINDS AND WIND WAVES WILL INCREASE
TONIGHT AHEAD OF AN INCOMING FRONT. SEAS WILL BECOME CHAOTIC
BUILDING TO A STEEP 10 TO 15 FEET. ANOTHER FRONTAL WAVE ON FRIDAY
WILL CAUSE WINDS TO SURGE UPWARD AGAIN WITH SEAS REACHING A PEAK IN
THE MORNING. THE STRONG SOUTHERLY WINDS WILL TRANSITION TO NORTHERLY
FRIDAY NIGHT WITH THE STRONGEST WINDS IN THE OUTER PORTION OF THE
WATERS. SEAS ARE LIKELY TO DIMINISH FRIDAY NIGHT INTO EARLY NEXT
WEEK. WITH A LONG NORTHERLY FETCH, NORTH TO NORTHWEST WIND WAVES AT
8 SECONDS ARE LIKELY TO MIX WITH A DOMINANT FRESH SWELL AT 10
SECONDS WHILE SMALLER NORTHWEST AND SOUTHWEST SWELL TRAINS PERSIST.
THE PATTERN WILL REMAIN ACTIVE THROUGH THE FIRST HALF OF NEXT WEEK.
/FB

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...WIND ADVISORY FROM 10 AM TO 10 PM PST FRIDAY FOR
     ORZ030-031-624-625.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 4 PM PST FRIDAY FOR
     PZZ350-356-370-376.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 10 PM PST FRIDAY
     FOR PZZ350-356-370-376.

$$


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