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000
FXUS66 KMFR 201558
AFDMFR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEDFORD OR
858 AM PDT MON MAY 20 2013

.DISCUSSION...MORNING UPDATE. EXCEPT FOR SOME STRATUS LINGER IN THE
WILLAMETTE VALLEY...THE COQUILLE AND WISPS OF CIRRUS THE REGION IS
CLEAR THIS MORNING AS OFFSHORE FLOW IS SPREAD ACROSS THE ENTIRE
REGION INLAND. THIS RIDE IS NEARING THE TOP OF THE FIRST BIG RISE
TODAY...WITH THE FRONT BRINGING THE BIG STEEP DROP TUESDAY. SIMPLE
AND NICE SITUATION TODAY THAT WILL REQUIRE NO UPDATE. SVEN

PREVIOUS DISCUSSION...SEVERAL OPTIONS TO WEIGHT THIS MORNING FOR THE
FORECAST...ALL PERTAINING TO THE POSSIBLE EFFECTS OF THE POTENT
CLOSED LOW EXPECTED TO TAKE UP RESIDENCE OVER THE PACIFIC
NORTHWEST THIS WEEK. HAVE MADE MANY ADJUSTMENTS TO VARIOUS FIELDS
THIS MORNING...BUT A FAIR AMOUNT OF UNCERTAINTY REMAINS. WHILE
CONFIDENCE IS HIGH IN THE OVERALL PATTERN AND THE GENERAL WEATHER
THAT CAN BE EXPECTED...UPDATES WILL NECESSARILY HAVE TO BE MADE AS
CONDITIONS WARRANT....ESPECIALLY AS DETAILS BECOME MORE APPARENT
AND CONFIDENCE RISES.

IN THE MEANTIME...SOUTHERN OREGON AND NORTHERN CALIFORNIA WILL BE
ABLE TO ENJOY AT LEAST ONE MORE PLEASANT DAY BEFORE THE STORM
ARRIVES. RIDGING ALOFT...CLEAR SKIES...AND THE THERMAL TROUGH TO
THE SOUTH...WILL ALL COMBINE FORCES TO ALLOW TEMPERATURES TO RISE
TO ABOUT 10 DEGREES ABOVE SEASONAL NORMALS IN MOST INLAND AREAS
TODAY. THE CHETCO EFFECT WILL ALSO RESULT IN WARM TEMPERATURES
ALONG THE SOUTHWESTERN OREGON COAST. ALL OF THIS WILL BE
SHORT LIVED...AS THE INCOMING LOW WILL BEGIN TO MAKE ITSELF KNOWN
MONDAY NIGHT INTO TUESDAY MORNING.

THE CLOSED LOW IS EXPECTED TO DIG SOUTHWARD ALONG THE CANADIAN
COASTLINE MONDAY NIGHT...AND TAKE UP RESIDENCE OVER THE PACIFIC
NORTHWEST BY TUESDAY NIGHT. THIS WILL RESULT IN NEARLY CONSTANT
PRECIPITATION CHANCES FOR THE REGION THROUGH HAT LEAST FRIDAY. THE
EXACT TIMING AND AMOUNTS OF PRECIP WILL BE HARD TO TACK
DOWN...BUT CONFIDENCE IS HIGH FOR ONGOING
PRECIPITATION...ESPECIALLY WITH THE INITIAL COLD FRONT AND WITH
SEVERAL ORBITING SHORTWAVES PASSING OVER THE AREA. HAVE UPPED POPS
TO REFLECT THIS.

THE INITIAL STRONG COLD FRONT WILL PUSH THROUGH THE AREA TUESDAY
AFTERNOON AND EVENING...AND TEMPERATURES ARE LIKELY TO DROP
SHARPLY WITH ITS PASSAGE. GUSTY WINDS ARE ALSO A CONCERN...AS MANY
OF THE LATEST MODEL RUNS HAVE PICKED UP ON A STRONG WEST TO EAST
SURFACE PRESSURE GRADIENT. WINDS WILL BE GUSTY...PARTICULARLY OVER
HIGHER TERRAIN AND THE EAST SIDE. DUE TO THE DIRECTION OF THE
FLOW...THE ROGUE VALLEY AND THE EAST TO WEST VALLEYS OF THE
CASCADE FOOTHILLS COULD SEE WINDS APPROACH 20 TO 25 MPH TUESDAY
AFTERNOON AND/OR EVENING. WINDS LOOK TO REMAIN BELOW ADVISORY
CRITERIA FOR NOW...BUT WILL NEED TO WATCH MODEL UPDATES FOR
POTENTIAL HEADLINES.

ANOTHER CONCERN WILL BE SIGNIFICANTLY LOWERING TEMPERATURES AND
SNOW LEVELS. WHILE HIGH TEMPS ON MONDAY SHOULD BE AROUND 10
DEGREES ABOVE NORMAL...HIGHS ON TUESDAY WEDNESDAY WILL BE CLOSER
TO 20 TO 25 DEGREES BELOW NORMAL. A SIMILAR LOW OCCURRING ALMOST
EXACTLY 3 YEARS AGO PRODUCED NUMEROUS RECORD LOW MAXIMUM
TEMPERATURES IN THE AREA...AND THIS SYSTEM HAS THE POTENTIAL TO DO
THE
SAME. MODELS HAVE ALSO BEGUN A TREND OF COLDER MINIMUM
TEMPERATURES...AND LATEST RUNS EVEN DROP TEMPS INTO THE 30S WITHIN
THE ROGUE...ILLINOIS...AND APPLEGATE VALLEYS...AS WELL AS PORTIONS
OF THE UMPQUA BASIN...TUESDAY AND WEDNESDAY NIGHT. FROST AND/OR
FREEZE MAY BE POSSIBLE IN THESE PLACES...ESPECIALLY IF THE MORE
OUTLYING MODEL SOLUTIONS VERIFY.

SNOW LEVELS WILL DROP SIGNIFICANTLY BEHIND THE FRONT...AND WILL
DROP BELOW 3000 FEET TUESDAY NIGHT. THIS...IN CONJUNCTION WITH
AMPLE PRECIPITATION STREAMING INTO THE AREA...COULD PRODUCE
SEVERAL INCHES OF SNOWFALL OVER THE
KALIMIOPSIS...SISKIYOUS...CASCADES...AND PORTIONS OF THE EAST
SIDE. MANY PASSES...ESPECIALLY OVER THE CASCADES...SISKIYOU
SUMMIT...AND THE MOUNT SHASTA AREA WILL RECEIVE SNOW...BUT WITH
THE HIGH SUN ANGLE AND WARM SOIL AND ROAD TEMPERATURES...SNOW ILL
HAVE A TOUGH TIME ACCUMULATING. TRAVELERS SHOULD STILL TAKE
PRECAUTIONS AND PREPARE FOR WINTER TRAVEL THROUGH THE LATTER HALF
OF THE WEEK.

CONFIDENCE IN THE FORECAST PAST THURSDAY DROPS SIGNIFICANTLY.
BOTH THE GFS AND ECMWF...AS WELL AS OTHER LONG TERM MODELS...HAVE
HAD TROUBLE WITH THE EVOLUTION OF THE LOW. VARIOUS MODEL
SOLUTIONS HAVE BEEN PRODUCED...AND SOLUTIONS HAVE CHANGED RUN TO
RUN ALMOST EVERY DAY. SOME SOLUTIONS HAVE MOVED THE LOW EAST...
OTHERS HAVE
PRODUCED WAVES IN THE WESTERLIES THAT KICK AND REPLACE THE LOW
OVERHEAD...AND STILL OTHERS HAVE SIMPLY LEFT THE LOW IN PLACE TO
FILL IN. MODELS HAVE BEEN NOTORIOUS IN HEIR INABILITY TO HANDLE
CLOSED LOWS...AS WELL AS BLOCKING RIDGES...WHICH NUMEROUS MODELS
HAVE PRODUCED OVER CENTRAL NORTH AMERICA DURING THIS TIME. ONE
THING IS CERTAIN HOWEVER...AND THAT IS THAT UNSETTLED WEATHER WILL
CONTINUE OVER THE PACIFIC NORTHWEST FOR THE REMAINDER OF THE TERM.
TO REFLECT THIS...HAVE LEFT TEMPERATURES NEAR OR SLIGHTLY BELOW
NORMAL AND POPS ABOVE CLIMO FOR THE DURATION OF THE EXTENDED
PERIOD. THOSE WITH OUTDOOR INTERESTS AND THOSE TRAVELING THIS
HOLIDAY WEEKEND SHOULD KEEP UPDATED WITH THE LATEST
FORECASTS...AND PREPARE FOR THE COOLER AND WETTER WEATHER.


&&

.AVIATION...BASED ON THE 20/06Z TAF CYCLE.

OFFSHORE FLOW EARLY THIS MORNING WILL LIKELY PREVENT STRATUS/FOG
FORMATION IN MOST AREAS...WITH THE EXCEPTION OF PATCHES OF MVFR
STRATUS/FOG ALONG THE COOS COAST AND IN THE COQUILLE AND UMPQUA
RIVER VALLEYS. EVEN SO, ANY CLOUDS WILL BURN OFF BY 15 OR 16Z MONDAY
MORNING. VFR WILL PREVAIL THROUGH MONDAY AFTERNOON, BUT MVFR WILL
RETURN TO THE COAST AHEAD OF AND ALONG A COLD FRONT MONDAY NIGHT.


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.

CA...NONE.

PACIFIC COASTAL WATERS...SMALL CRAFT ADVISORY FOR WINDS UNTIL 11 PM
PDT THIS EVENING FOR
     PZZ356.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 11 PM PDT THIS
     EVENING FOR PZZ356.
     SMALL CRAFT ADVISORY FOR WINDS UNTIL 8 PM PDT THIS EVENING FOR
     PZZ350-370.
     SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL 8 PM PDT THIS
     EVENING FOR PZZ350-370.
     GALE WARNING UNTIL 8 PM PDT THIS EVENING FOR PZZ376.
     HAZARDOUS SEAS WARNING UNTIL 8 PM PDT THIS EVENING FOR PZZ376.

$$

BPN/MAS