191
FXUS66 KMFR 072255
AFDMFR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
255 PM PST SAT NOV 7 2009
DISCUSSION
CURRENT VISIBLE IMAGE SHOWS AN ENHANCED AREA OF CLOUDS
RUNNING SOUTHWEST TO NORTHEAST NEAR PORTLAND. THIS IS DUE TO A
SHORTWAVE ENERGY THAT IS APPROACHING THE OREGON COAST ALONG WITH
COLD AIR ALOFT. THIS HAS LEAD TO A LINE OF THUNDERSTORMS MAINLY
NORTH OF THE CWA...BUT A FEW STRIKES HAVE SHOWN UP ABOUT 38 MILES
NORTHWEST OF NORTH BEND. THE NAM AND GFS SUGGEST THIS SHORTWAVE WILL
REACH THE COAST IN THE NEXT FEW HOURS. 500 MB TEMPS OF -26 TO -28 C
WILL MOVE OVER THE WATERS THIS EVENING WHICH WILL LEAD TO A FEW
THUNDERSHOWERS. IN ADDITION 700 MB WINDS BETWEEN 35 AND 40 KTS WILL
ALLOW SOME OF THESE STORMS TO MIGRATE INLAND LATE THIS AFTERNOON AND
EARLY EVENING.
ANOTHER SHORTWAVE LOCATED NEAR 43N AND 135 W WILL REACH THE COAST
LATER THIS EVENING AND BRING INCREASING SHOWERS TO SOUTHWEST OREGON.
A MOIST WEST TO SOUTHWEST FLOW WILL CONTINUE OVERNIGHT TONIGHT WITH
MOST SHOWERS ALONG AND WEST OF THE CASCADES AND ALSO MOSTLY CONFINED
TO NORTH OF THE UMPQUA DIVIDE. SNOW LEVELS WILL RANGE BETWEEN
4000 AND 4500 FEET. SO A FEW INCHES OF SNOW IS POSSIBLE BETWEEN NOW
AND MIDNIGHT OVER THE NORTHERN CASCADES ABOVE 6000 FEET.
THE NAM AND GFS BOTH SHOW YET ANOTHER SHORTWAVE ENERGY MOVING NORTH
OF THE CWA SUNDAY MORNING WHICH IF CORRECT WILL KEEP MOST OF THE
SHOWERS CONFINED TO COOS AND NORTHWEST DOUGLAS COUNTIES. ELSEWHERE
CONDITIONS SHOULD REMAIN DRY.
WEAK SHORTWAVE RIDGING MOVES OVER THE AREA SUNDAY NIGHT WITH A WEAK
SURFACE HIGH LOCATED EAST. AT THE SAME TIME BOTH THE NAM AND GFS
SUGGEST A SURFACE LOW WILL DEVELOP AND TRACK NORTHWEST TOWARDS
VANCOUVER ISLAND EARLY MONDAY MORNING. THIS WILL LEAD TO CONTINUED
DRY CONDITIONS. THE MAIN QUESTION WILL BE SKY COVER OR LACK THEREOF
WHICH COULD HAVE AN IMPACT ON MIN TEMPERATURES.
AS MENTIONED ABOVE THE SURFACE LOW THAT DEVELOPS SUNDAY NIGHT WILL
END UP DELAYING THE ONSET OF PRECIPITATION AT THE COAST MONDAY
MORNING. THEREFORE HAVE BACKED OF ON THE POPS FOR MONDAY MORNING.
THE FRONT WILL SLOWLY WORK INLAND MONDAY AFTERNOON THEN IS LIKELY TO
STALL OVER THE CWA MONDAY NIGHT. THE NAM...GFS AND ECMWF ALL SUPPORT
THIS IDEA.
OPERATIONAL AND ENSEMBLE MODEL GUIDANCE INDICATE THE JET STREAM
SINKING INTO CALIFORNIA ON TUESDAY PUTTING THE FORECAST AREA IN A
FAVORABLE UPPER LEVEL PATTERN FOR WIDESPREAD PRECIPITATION. MODEL
SURFACE PROJECTIONS ARE SLOWER THAN WOULD BE EXPECTED UNDER THIS
PATTERN IN BRINGING PRECIPITATION IN FROM THE COAST TUESDAY INTO
WEDNESDAY. WE HAVE...THEREFORE...MAINTAINED HIGHER PRECIPITATION
CHANCES DURING THIS PERIOD THAN THE MODELS GENERALLY INDICATE.
WEDNESDAY INTO THURSDAY MODELS ARE NOW QUITE CONSISTENT IN PUSHING
THE PRIMARY FRONT THROUGH...FOLLOWED BY SHOWERY AND COOL CONDITIONS
AS COLDER PORTION OF THE TROUGH ROTATES IN. MODELS ARE STILL
INCONSISTENT WITH THE TRAJECTORY OF THE COLD CORE WITH THIS SYSTEM.
THE CONSENSUS IS TO PUSH THE UPPER LEVEL COLD CORE JUST NORTH OF THE
AREA. THE PRIMARY POTENTIAL WEATHER IMPACTS OF SIGNIFICANCE TO WATCH
IN THE WEDNESDAY THROUGH THURSDAY NIGHT TIME FRAME IS THE POTENTIAL
FOR SNOW REACHING MANY OF THE EAST SIDE VALLEY FLOORS. THIS WILL
OCCUR IF THE LOW TRACKS FAR ENOUGH SOUTHEAST TO BRING PRECIPITATION TO
THESE AREAS. AT THIS POINT...IT APPEARS VALLEYS LIKELY WILL SEE
LITTLE ACCUMULATION FOCUSED MAINLY IN AND AROUND THURSDAY. THE
MOUNTAINS...PARTICULARLY THE CASCADES AND SISKIYOUS...WILL LIKELY
SEE ACCUMULATIONS THAT MAY WARRANT ADVISORIES. WITH THE MORE NORTHWARD
TRACK OF THE COLD CORE...THE GREATEST ACCUMULATING SNOW THREAT IS
FOCUSED FARTHER NORTH...IN THE CRATER AND DIAMOND LAKE AREAS.
AVIATION
MVFR IN SHOWERS EXPECTED IN SHOWERS THIS EVENING WITH
OCCASIONAL REDUCTION IN VISIBILITY IN HEAVIER SHOWERS. THE
ATMOSPHERE SHOULD REMAIN UNSTABLE ENOUGH TO PREVENT FOG AND LOW
CLOUDS FROM DEVELOPING. HOWEVER IF ENOUGH CLEARING DEVELOPS IN THE
UMPQUA BASIN AND ROGUE VALLEY...IFR CIGS COULD DEVELOP BETWEEN 9 AND
12Z. MVFR CIGS ARE CURRENTLY AT THE KLAMATH BASIN...BUT CLOUD COVER
IS EXPECTED TO BECOME SCATTERED AFTER DARK RESULTING IN VFR
CONDITIONS.
MFR WATCHES/WARNINGS/ADVISORIES
OR...HIGH SURF WARNING UNTIL 10 AM PST SUNDAY FOR ORZ021-ORZ022.
CA...NONE.
PACIFIC COASTAL WATERS...HAZARDOUS SEAS WARNING UNTIL 4 PM PST SUNDAY
FOR PZZ350-PZZ356-PZZ370-PZZ376.
SMALL CRAFT ADVISORY FOR WINDS UNTIL NOON PST SUNDAY FOR PZZ350-
PZZ370.
SMALL CRAFT ADVISORY FOR WINDS FROM MIDNIGHT TONIGHT TO 10 AM
PST SUNDAY FOR PZZ376.
99/99/99
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