AREA FORECAST DISCUSSION

 
 FXUS66 KPQR 251700
 AFDPQR
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE PORTLAND OR
 900 AM PST WED NOV 25 2009
 
 .SYNOPSIS...AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL REMAIN OVER 
 THE REGION THROUGH MOST OF TODAY. A SLOW MOVING FRONT OFFSHORE WILL 
 EASE INTO THE FAR NORTHWEST PART OF THE REGION LATER TODAY AND BEGIN 
 MOVING INLAND ON THANKSGIVING DAY. AN UPPER LEVEL TROUGH WILL DIG 
 INTO THE BACK SIDE OF THE FRONT THURSDAY AND SLOW THE EASTWARD 
 PROGRESSION OF THE FRONT.  THE UPPER LEVEL TROUGH WILL MOVE ACROSS 
 THE REGION ON FRIDAY WITH A RIDGE OF HIGH PRESSURE BUILDING INTO THE 
 REGION LATE IN THE WEEKEND. 
 
 &&
 
 .SHORT TERM...SURFACE OBSERVATIONS SHOW QUITE A FEW AREAS OF FOG IN 
 THE INTERIOR VALLEYS THIS MORNING. A FEW OCCASIONAL AIRPORT
 OBSERVATIONS AND SPOTTER REPORTS FROM THIS AREA INDICATE THE FOG IS
 LOCALLY DENSE...LOCALLY REDUCING VISIBILITY TO ONE QUARTER MILE OR 
 LESS.  THE FOG MAY TAKE A WHILE TO DISSIPATE TODAY AS IT BECOMES 
 MORE DIFFICULT FOR THE SOLAR HEATING FROM THE LOW SUN ANGLE THIS 
 TIME OF YEAR TO OVERCOME VALLEY INVERSIONS. AS A RESULT OF 
 THIS...SOME OF THE INTERIOR VALLEYS MAY REMAIN TRAPPED IN COOL 
 INVERSIONS MUCH OF THE DAY...AND STRUGGLE TO REACH 50 DEGREES THIS 
 AFTERNOON. ON THE OTHER HAND...INCREASED TODAYS HIGH TEMPERATURE 
 FORECAST A BIT IN THE HIGHER ELEVATIONS...AS THE WARM AIR MASS ALOFT 
 (+8 TO +10 DEG C AT 850 MB) SHOULD ALLOW MOST OF THE FOOTHILLS... 
 ABOVE THE VALLEY INVERSIONS...TO REACH THE 50S OR EVEN LOWER 
 60S...MUCH LIKE YESTERDAY.
 
 TO OUR WEST...A SLOW MOVING COLD FRONT REMAINS POISED TO MOVE ONSHORE
 FOR THE UPCOMING HOLIDAY. MODELS REMAIN IN GOOD AGREEMENT SHOWING 
 THE OFFSHORE COLD FRONT SAGGING TO NEAR THE S WA/N OREGON COAST LATE 
 TODAY...THEN PUSHING A LITTLE FURTHER INTO SW WA TONIGHT. ELSEWHERE 
 MOISTURE AND POPS WILL REMAIN RATHER LOW THROUGH TONIGHT.  
 
 INCREASED THE QPF ASSOCIATED WITH THE FRONTAL SYSTEM AS IT MOVES 
 ONSHORE...TO BRING IT MORE IN LINE WITH RFC GUIDANCE. IT APPEARS 
 SOME AREAS IN THE COAST RANGE COULD RECEIVE AS MUCH AS 2-4 INCHES OF 
 RAIN LOCALLY...WITH INLAND LOCATIONS RECEIVING A BIT LESS...CLOSER 
 TO ONE HALF TO ONE INCH. FOR NOW...IT APPEARS THIS WILL NOT BE 
 ENOUGH TO CREATE ANY MAJOR HYDROLOGIC PROBLEMS IN OUR AREA...BUT 
 WILL CONTINUE TO MONITOR AS IT APPEARS THIS FRONTAL SYSTEM DOES HAVE 
 ACCESS TO SOME SUBTROPICAL MOISTURE.  
 
 MODELS SHOW THE THE UPPER TROUGH DIGGING INTO THE BACK SIDE OF THE
 OFFSHORE FRONT ON THURSDAY CAUSING SOME BACKING OF THE STEERING FLOW
 AS THE SYSTEM INTENSIFIES. THIS SLOWS THE INLAND PROGRESSION OF THE
 FRONT UNTIL LATE THURSDAY AFTERNOON OR THURSDAY NIGHT. MODELS
 CONTINUE TO HAVE SOME DIFFERING SOLUTIONS REGARDING THE TRACK AND
 INTENSITY OF THE ASSOCIATED SURFACE LOW THAT LIFTS NNE BEHIND THE 
 FRONT.CURRENT MODELS SUGGEST BREEZY/WINDY CONDITIONS BUT PROBABLY 
 NO HIGH WINDS. INCREASING OROGRAPHICS AND LOWERING SNOW LEVELS 
 SHOULD CAUSE SOME DECENT SNOW ACCUMULATIONS IN THE CASCADES LATER 
 THU NIGHT INTO FRI...POSSIBLY ENOUGH TO CONSIDER WINTER WEATHER 
 ADVISORY FOR SEVERAL INCHES OF SNOW.  WEAGLE/TW
 
 .LONG TERM...NO CHANGES. PREVIOUS DISCUSSION FOLLOWS...ALL THE MODELS
 SHOW A SHORT WAVE MOVING THROUGH FRIDAY NIGHT FOR SOME PRECIPITATION 
 WITH SNOW LEVEL NEAR OR BELOW THE CASCADE PASSES. AFTER THAT...THE 
 MODELS SHOW RIDGING OVER THE PACIFIC NORTHWEST THE RESULT OF ENERGY 
 OUT AROUND 140W OR 150W. THIS CAUSES THE MAIN JET TO LIFT NORTH OF 
 OUR AREA EARLY NEXT WEEK...WITH PERHAPS SOME PRECIPITATION BRUSHING 
 THE NORTH COAST AT TIMES. ANOTHER SYSTEM BRUSHES THE AREA MONDAY AND 
 MONDAY NIGHT WITH THE BEST CHANCES OF ANY PRECIPITATION IN THE NORTH 
 PART OF OUR FORECAST AREA. THE RIDGE APPEARS TO REBOUND AGAIN FOR 
 THE MIDDLE OF NEXT WEEK. ENSEMBLE SPREADS STARTING TO INCREASE EARLY 
 NEXT WEEK BUT NOT AS MUCH AS SEEN YESTERDAY. EXPECT TO SEE SOME 
 PERIODS OF VALLEY FOG DURING THE DRIER PERIODS. TOLLESON
 
 &&
 
 .AVIATION...NORTH COAST WILL HAVE PRECIPITATION AND A DEFINITE 
 RETURN TO LOW MVFR OR IFR CLOUDS THIS AFTERNOON AS NEXT FRONT 
 ARRIVES  AND REMAINS THROUGH THU. CENTRAL COAST NOT AFFECTED MUCH BY 
 CLOUDS UNTIL THU MORNING...PERHAPS A BRIEF PERIOD OF MVFR THIS 
 AFTERNOON. INLAND SITES UNHINDERED BY FRONTAL SYSTEM TODAY...VFR 
 THROUGH THE AFTERNOON AND TONIGHT.
 
 KPDX AND APPROACHES...EXPECT VFR CONDITIONS AFTER 18Z. MID AND HIGH 
 LEVEL CLOUDS WILL INCREASE IN THE AFTERNOON. VFR CONDITIONS THROUGH 
 THU AM. 
 
 &&
 
 .MARINE... LATEST MODEL GUIDANCE CONTINUES TO SHOW SMALL CRAFT WIND 
 OVER THE OUTER WATERS OF ZONE 270...BUT PRIMARILY THE NORTHWEST 
 THIRD. SEAS RISE ABOVE 11 FT THIS AFTERNOON AS THE NEXT FRONTAL 
 SYSTEM ARRIVES. WINDS EXPECTED TO EASE A BIT THIS AFTERNOON AS THE 
 FRONTAL BOUNDARY STALLS OFFSHORE. A SECONDARY LOW PRES CENTER FORMS 
 ON THE FRONT OFF THE COAST BRINGING IN NEXT ROUND OF SMALL CRAFT 
 WINDS  BY 18Z THU...THEN SPREADING NORTH THANKSGIVING DAY. GALES 
 POSSIBLE AS LOW PRES MOVES INLAND BUT TIMING STILL SOMEWHAT 
 UNCERTAIN. SEAS BUILD TO MID AND UPPER TEENS THU AND FRI. SEAS NOT 
 LIKELY TO DROP BELOW 10 FT UNTIL LATE WEEKEND OR EARLY NEXT WEEK.
 
 &&
 
 .PQR WATCHES/WARNINGS/ADVISORIES...
 WA/OR...SMALL CRAFT ADVISORY FOR WIND CAPE SHOALWATER TO 
   CASCADE HEAD THROUGH 7 PM THIS EVENING.  
 SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS CAPE 
   SHOALWATER TO FLORENCE LATE THIS MORNING THROUGH 
   THU NIGHT.   
 SMALL CRAFT ADVISORY FOR ROUGH COLUMBIA RIVER BAR 
   CONDITIONS THIS MORNING THROUGH LATE THU NIGHT. 
 
 
 
 &&
 
 

 
 MORE WEATHER INFORMATION ONLINE AT...
 HTTP://WEATHER.GOV/PORTLAND
 
 
 THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON FROM
 THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS COMMONLY
 REFERRED TO AS THE FORECAST AREA.