AREA FORECAST DISCUSSION

 
 FXUS66 KSEW 230520
 AFDSEW
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE SEATTLE WA
 920 PM PST SUN NOV 22 2009
 
 .SYNOPSIS...A WARM FRONT WILL BRUSH THE NORTHWEST PORTION OF THE 
 STATE LATE TONIGHT AND A COLD FRONT WILL MOVE THROUGH THE AREA MON 
 EVENING. WEAK HIGH PRESSURE WILL MOVE ACROSS THE AREA ON TUESDAY. A 
 ANOTHER WEAK WARM FRONT WILL MOVE THROUGH THE AREA TUESDAY NIGHT AND 
 WILL BE FOLLOWED BY ANOTHER WEAK COLD FRONT WEDNESDAY NIGHT OR 
 THURSDAY. ANOTHER WEAK COLD FRONT IS POSSIBLE FRIDAY NIGHT OR 
 SATURDAY.
 
 &&
 
 .SHORT TERM...IT APPEARS THAT WE SHOULD BE HEADING INTO A MORE 
 BENIGN WEATHER PATTERN FOR THE UPCOMING WEEK. WHILE IT WILL BE 
 MAINLY CLOUDY WITH OCCASIONAL BANDS OF LIGHT RAIN AS WEAK FRONTAL 
 SYSTEMS MOVE THROUGH THE AREA...WINDS...RAIN RATES...AND MOUNTAIN 
 SNOWFALL RATES SHOULD NOT BE A MAJOR ISSUE AS WEAK LONG WAVE RIDGING 
 FORMS OVER THE WESTERN U.S. AND FRONTS HAVE A TENDENCY TO WEAKEN AS 
 THEY MOVE ACROSS THE AREA.
 
 TONIGHT ONSHORE PRESSURE GRADIENTS ARE SLOWLY RELAXING AS THE LOW 
 PRESSURE SYSTEM THAT MOVED THROUGH THE AREA EARLIER PULLS AWAY INTO 
 MONTANA. RADAR AND OBSERVATIONS SHOW PRECIPITATION RATES IN THE 
 CASCADES WITH SHOWERS AND A WEAK CONVERGENCE ZONE FROM CENTRAL 
 SNOHOMISH COUNTY INTO SOUTHERN WHATCOM COUNTY DECREASING RAPIDLY 
 THIS EVENING. WILL ALLOW THE WINTER STORM WARNING IN THE CASCADES 
 EXPIRE...AND WILL UPDATE THE ZONES TO REMOVE THE HEADLINES. ON THE 
 COAST THE SEAS HAVE FALLEN BELOW 20 FEET...SO WILL ALSO ALLOW THE 
 HIGH SURF ADVISORY EXPIRE AND UPDATE THE COASTAL ZONES TO REMOVE 
 THOSE HEADLINES.
 
 A WEAK WARM FRONT NOW SITTING IN THE OFFSHORE WATERS WILL MOVE NE 
 THROUGH THE COASTAL WATERS LATER TONIGHT AND WILL CLIP THE OLYMPIC 
 PENINSULA EARLY MONDAY. 
 
 A COLD FRONT NOW SEEN JUST OUTSIDE OF 135W AT 50N IS MAKING STEADY 
 EASTWARD PROGRESS. ITS PRECIPITATION SHIELD SHOULD MOVE ONSHORE 
 DURING THE AFTERNOON HOURS MONDAY AND REACH THE INTERIOR MID TO LATE 
 AFTERNOON. LOW END GALE FORCE WINDS ARE LIKELY IN THE COASTAL 
 WATERS...BUT OTHER AREAS SHOULD SEE ONLY WINDS TYPICAL OF A WEAK TO 
 MODERATE FRONTAL SYSTEM MON NIGHT.
 
 WARMER AIR ALOFT AND LIGHTER FLOW WILL COMBINE WITH LONG NIGHTS AND 
 LIGHTER FLOW TO GIVE MORE ABUNDANT STRATUS AND FOG TUESDAY. WILL 
 LEAVE THIS CHANGE TO THE NEXT SHIFT. 
 
 TEMPERATURES WILL BE GENERALLY MILD FOR THE LATTER PART OF NOVEMBER 
 FOR THE NEXT SEVERAL DAYS. ALBRECHT 
 
 .LONG TERM...PREVIOUS LONG TERM DISCUSSION FOLLOWS...I HAVE KEPT THE 
 GRIDS/FCSTS CLOSE TO CLIMO AND DO NOT SEE ANY WEATHER SYSTEMS THRU 
 SATURDAY THAT LOOK IMPRESSIVE OR NOTEWORTHY. THE FREEZING LEVEL 
 SHOULD TREND DOWN THRU THE WEEK AFTER PEAKING ARND 6500FT EARLY IN 
 THE WEEK. AFTER THE WEAK FRONT ON THANKSGIVING THERE IS ANOTHER 
 FRONT POSSIBLE LATE FRI...A WEAK TROF AT 500MB BUT THE GFS HARDLY 
 HAS A SURFACE REFLECTION. THE ECMWF IS STRONGER WITH COLD FRONT BY 
 12Z FRI...IT SHOWS A SFC LOW DEEPENING A BIT AS IT MOVES EAST ALONG 
 40N THURSDAY AND AS THAT SHIFTS INLAND BY FRIDAY MORNING SOMEWHERE 
 EAST OF THE CASCADES THERE IS FAIRLY STRONG ONSHORE FLOW INTO WRN 
 WA. THEN...IF THE GLOBAL MODELS ARE RIGHT HIGH PRES BUILDS OVER THE 
 PACNW FOR NEXT WEEKEND. 19
 
 &&
 
 .HYDROLOGY...THE ONLY CURRENT RIVER FLOOD PROBLEM IS THE SKOKOMISH 
 RIVER. IT IS JUST ABOVE FLOOD STAGE THIS EVENING AND WILL LIKELY 
 REMAIN ABOVE FLOOD STAGE INTO MONDAY AFTERNOON AS WATER IS RELEASED 
 FROM CUSHMAN DAM #2. THE SYSTEM WHICH WILL MOVE THROUGH WESTERN 
 WASHINGTON MONDAY AFTERNOON AND EVENING IS NOT A FLOOD-PRODUCING 
 RAIN SYSTEM BUT IT IS A WARM FRONT...SO RIVERS WILL PROBABLY STOP 
 RECEDING AND OLYMPIC RIVERS MIGHT TREND UP A BIT FOR A DAY. THE 
 FRONTAL SYSTEM WEDNESDAY NIGHT OR THURSDAY AND THE COLD FRONT LATE 
 IN THE WEEK LOOK RATHER WEAK AND AS IF THEY ARE MOVING INTO A MEAN 
 RIDGE POSITION. THE SNOW LEVEL WILL PROBABLY TREND DOWN THRU THE 
 WEEK AFTER PEAKING WED. THE BAROCLINIC ZONE THAT GETS HUNG UP ON 
 VANCOUVER ISLAND WED IS WORTH WATCHING BUT AT THIS TIME WE DO NOT 
 SEE A RISK FOR RIVER FLOODING. FLOODING IS NOT EXPECTED ON THE GREEN 
 RIVER OVER THE NEXT WEEK. ALBRECHT/19
 
 &&
 
 .AVIATION...A BRIEF LULL BETWEEN WEATHER SYSTEMS IS COMING UP 
 OVERNIGHT. THE PUGET SOUND CONVERGENCE ZONE ON THE BACK END OF THE 
 OUTGOING WEATHER SYSTEM IS DISSIPATING AS MORE GENERAL SOUTHERLY 
 FLOW STARTS TO TAKE OVER IN ADVANCE OF THE NEXT FRONT TO ARRIVE LATE 
 MON. BRIEF CLEARING OF SKIES OVERNIGHT COULD EASILY ALLOW LOCALIZED 
 FOG IN SHELTERED VALLEYS...BUT INCREASED SOUTHERLY WINDS ON MON 
 MORNING SHOULD MIX OUT ANY FOG. ON MON MORNING...AN OFFSHORE 
 COMPONENT TO THE LOW-LEVEL FLOW WILL LIMIT CLOUDS BELOW 040...EXCEPT 
 NEAR HOOD CANAL. THE FRONT SHOULD CROSS WRN WA FROM 00Z-06Z ON MON 
 EVENING...BUT THE FRONT WILL BE WEAKENING AND DISSIPATING AS IT 
 PASSES BY. 
 
 KSEA...THE RECENT TREND OF IMPROVING CIGS WILL CONTINUE OVERNIGHT 
 AND MON MORNING AS A TURN TO AN OFFSHORE LOW-LEVEL FLOW COMPONENT 
 INHIBITS LOW CLOUDS. A COLD FRONT WILL PASS KSEA BTWN 21Z-24Z ON 
 MON. WINDS ALOFT SHOULD PEAK AROUND THE TIME OF FROPA...WITH 
 SOUTHWEST 850 MB WINDS NEAR 40 KNOTS ARND 24Z. LOW-LEVEL MOISTURE 
 WILL INCREASE BEHIND THE FRONT WITH CIGS DETERIORATING TO IFR ON MON 
 NIGHT.      HANER
 
 &&
 
 .MARINE...ONSHORE FLOW IS CURRENTLY WEAKENING AND WILL TURN TO 
 INCREASING SOUTHERLY FLOW OVERNIGHT AND MON MORNING IN ADVANCE OF 
 THE NEXT FRONT. THE FRONT IS NOT FAR WEST OF BUOY 46036...WHICH HAS 
 RECENTLY HAD GALE FORCE GUSTS. EXPECTING THE FRONT TO SUPPORT 
 LOW-END GALE FORCE SOUTHERLIES ALONG THE COAST...BUT THE FRONT WILL 
 BE WEAKENING QUICKLY AS IT MOVES INLAND ON MON AFTN AND EVNG. AS A 
 RESULT...NOT EXPECTING GALES ALONG THE COAST TO TRANSLATE TO THE 
 NORTH INTERIOR. SMALL CRAFT WINDS OVER THE INLAND WATERS ARE THE 
 MOST LIKELY OUTCOME AT THIS POINT. HIGH PRES WILL BUILD OVER THE 
 WATERS ON MON NIGHT AND TUE WITH LIGHT OFFSHORE FLOW DEVELOPING. 
 HANER
 
 &&
 
 .SEW WATCHES/WARNINGS/ADVISORIES...
 WA...A FLOOD WARNING REMAINS IN EFFECT FOR THE SKOKOMISH RIVER
      IN MASON COUNTY.
 PZ...GALE WARNING COAST AND WEST ENTRANCE.
      SMALL CRAFT ADVISORY ALL OTHER WATERS.
      SMALL CRAFT ADVISORY FOR ROUGH BAR CONDITIONS AT GRAYS HARBOR 
         ENTRANCE.
    
 

 
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