AREA FORECAST DISCUSSION

 
 FXUS66 KSEW 101138
 AFDSEW
 
 AREA FORECAST DISCUSSION 
 NATIONAL WEATHER SERVICE SEATTLE WA
 338 AM PST WED FEB 10 2010
 
 .SYNOPSIS...AN APPROACHING FRONT WILL SPREAD RAIN ACROSS WESTERN 
 WASHINGTON TODAY. AFTER A BRIEF LULL THIS EVENING...AN APPROACHING 
 WARM FRONT WILL BRING MORE RAIN LATE TONIGHT AND THURSDAY 
 MORNING...FOLLOWED BY A SURFACE LOW AND COLD FRONT THURSDAY EVENING. 
 A WEAKER FRONT WILL CROSS THE AREA LATER FRIDAY...FOLLOWED BY A 
 WETTER WINDIER FRONTAL SYSTEM LATE SATURDAY AND SUNDAY. 
 
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 .SHORT TERM...THE FRONTAL SYSTEM JUST OFFSHORE DOES NOT LOOK REALLY 
 NOTABLE ON IR IMAGERY...BUT THE GFS IS SHOWING FAIRLY GOOD WARM 
 ADVECTION WITH THE FRONT. LAST FEW FRAMES OF THE IR LOOP SHOW A 
 SMALL AREA OF CLOUD TOP COOLING RIGHT WHERE THE STRONGEST 850 MB 
 WARM ADVECTION SHOULD BE...AND JUST N OF WHERE A 90+ KNOT JET STREAK 
 IS INTERSECTING THE FRONT. MODEL TIMING AGREES ON SPREADING RAIN 
 INLAND JUST ABOUT TO PUGET SOUND BY 18Z THEN TO THE CASCADE CREST BY 
 21Z. MODELS SHOW SW WINDS ALOFT AT 850 AND 700 MB SO ANY RAIN 
 SHADOWING CAUSED BY THE OLYMPICS SHOULD BE TO THE NE OF THE 
 MOUNTAINS...SO HAVE GONE ALONG WITH MOS CATEGORICAL POPS FOR THE 
 PUGET SOUND REGION. QPF AMOUNTS SHOULD BE GENERALLY LIGHT. SNOW 
 LEVELS WILL BE DOWN TO NEAR PASS LEVELS OVER THE CASCADES...BUT SNOW 
 AMOUNTS WILL BE BELOW ADVISORY LEVELS. 
 
 AFTER A POST FRONT LULL THIS EVENING...THE MODELS HAVE BEEN MOSTLY 
 CONSISTENT IN BRINGING WARM FRONT PRECIP UP OVER THE AREA FROM THE 
 SW LATE TONIGHT AND THURSDAY. GFS HAS JUMPED AROUND JUST A BIT ON 
 TIMING...SO THERE IS A LITTLE UNCERTAINTY ON JUST HOW FAR N THE WARM 
 FRONT RAIN WILL REACH BY 12Z THURSDAY. WENT WITH A BLEND OF THE 
 MODELS AND PUT THE 12Z CATEGORICAL POP LINE FROM ABOUT TACOMA 
 SOUTHWARD. HAD TO PLAY WITH THE PRECIP WORDING IN THE ZONES A BIT 
 FOR TONIGHT TO REFLECT THE LULL AND THEN THE APPROACHING WARM FRONT. 
 
 THURSDAY SHOULD HAVE PERIODS OF RAIN...WARM FRONT EARLY...THEN A 
 PAUSE...FOLLOWED BY A SURFACE LOW AND COLD FRONT LATE. MODELS SHOW 
 SIGNIFICANT DIFFERENCES IN THE TRACK OFF THE APPROACHING LOW. THE 
 06Z GFS BRINGS A 995 MB LOW ACROSS THE OFFSHORE WATERS THURSDAY 
 EVENING WITH A CENTRAL VANCOUVER ISLAND LANDFALL 06Z FRIDAY. 00Z 
 ECMWF AND 06Z NAM KEEP THE LOW FARTHER OFFSHORE. GFS TRACK SHOWS A 
 NEAR MISS FOR POSSIBLY HIGH WINDS ON THE COAST...WITH THE STRONGEST 
 GRADIENT JUST TO SOUTH OF THE FORECAST AREA. ECMWF/NAM SOLUTIONS 
 WITH JUST A SURFACE TROUGH KEEP WINDS BELOW HIGH WIND CRITERIA. 
 THURSDAY EVENING IS A LITTLE TOO FAR OUT TO CONSIDER A 
 WATCH...ESPECIALLY GIVEN THE MODEL DIFFERENCES...SO JUST MONITOR 
 THIS FOR NOW. 
 
 GFS/ECMWF/NAM ALL AGREE ON BRINGING AN UPPER LEVEL AND SURFACE 
 TROUGH NE ACROSS THE AREA LATER FRIDAY. KAM
 
 .LONG TERM...THE ACTIVE PATTERN CONTINUES SATURDAY INTO EARLY NEXT 
 WEEK. GFS/ECMWF ARE IN PRETTY GOOD AGREEMENT WHICH LENDS SOME 
 CONFIDENCE TO THE FORECAST. BOTH SATURDAY AND SUNDAY WILL BE RAINY. 
 WARM FRONT ON SATURDAY THEN A COLD FRONT MOVES ACROSS THE AREA 
 SUNDAY MORNING. MODELS HAVE MAINTAINED THE WEAKER TREND WITH THE 
 SYSTEM SO IT DOES NOT LOOK LIKE THERE WILL BE SIGNIFICANT HEAVY 
 RAIN. NEXT SYSTEM REACHES THE AREA MONDAY NIGHT. KAM
  
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 .HYDROLOGY...AN ACTIVE RAINY WEATHER PATTERN WILL PERSIST TODAY INTO 
 EARLY NEXT WEEK. MODELS ARE IN GOOD AGREEMENT THOUGH THAT A 
 SIGNIFICANT HEAVY RAIN EVENT WILL NOT BE DEVELOPING. THE FIRST FRONT 
 TODAY WILL BRING JUST LIGHT QPF AMOUNTS. THE WARM FRONT LATE TONIGHT 
 FOLLOWED BY THE SURFACE LOW/COLD FRONT LATE THURSDAY COULD PRODUCE 
 HEAVIER RAIN OVER THE OLYMPICS...PERHAPS 2.5-3.0 INCHES IN 24 HOURS 
 ENDING 12Z FRIDAY PER THE 06Z NAM. HOWEVER THIS WILL ONLY BE ENOUGH 
 TO GENERATE SOME RISES ON THE RIVERS...ESPECIALLY WITH A LULL 
 BETWEEN THE WARM FRONT AND COLD FRONT. FRIDAYS FRONT WILL BE FAST 
 MOVING AND LIGHT ON QPF. FINALLY...THE LATE SATURDAY/SUNDAY MORNING 
 FRONTAL SYSTEM WILL BRING ANOTHER ROUND OF HEAVIER PRECIP...BUT THIS 
 LOOKS WEAKER AND SHORTER IN DURATION THAN THE MODELS SHOWED 24 HOURS 
 AGO. 
 
 WITH ONLY A COUPLE OF SYSTEMS THIS WEEK POTENTIALLY PRODUCING HEAVY 
 RAIN...AND THEN ONLY IN BRIEF PERIODS WITH SIGNIFICANT BREAKS 
 IN-BETWEEN THE STRONGER SYSTEMS...FLOODING IS NOT EXPECTED THIS 
 WEEK. THE PROBABILITY OF FLOODING ON THE GREEN RIVER IS VERY LOW. KAM
  
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 .AVIATION...A UPPER LEVEL RIDGE WILL MOVE EAST OF THE AREA TODAY 
 WITH MODERATE WSW FLOW ALOFT.  A COLD FRONT WILL APPROACH THE COAST 
 EARLY THIS AFTERNOON AND THEN MOVE EAST OF THE AREA THIS EVENING AS 
 IT WEAKENS...SPREADING RAIN ACROSS THE REGION TODAY.  A LARGE AREA 
 OF STRATUS AND FOG HAS FORMED SOUTH OF SEATTLE WITH PATCHY FOG TO 
 THE NORTH.  THIS WILL BE SLOW TO BREAK UP THIS MORNING.  I EXPECT IT 
 TO LIFT INTO A LOW STRATUS DECK AS THE LIGHT BREEZE PICKS UP THIS 
 MORNING...THEN BREAK UP MID DAY.  
 
 KSEA...BREEZE DIDN/T KICK IN QUICK ENOUGH...SO FOG/STRATUS WILL 
 LINGER A FEW MORE HOURS.  THE FOG IS EXPECTED TO VERY SLOWLY LIFT 
 INTO A LOW STRATUS DECK /400-700 FT/ AS THE BREEZE PICKS UP THROUGH 
 16Z.  THEN EXPECT IT TO BREAK UP LATE MORNING /18Z-20Z/ AS THE RAIN 
 BEGINS.  SOUTHERLY WIND PICKING UP SLOWLY THROUGH THE MORNING. 
 
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 .MARINE...A WEAKENING COLD FRONT WILL MOVE ACROSS THE COASTAL WATERS 
 AND INLAND TODAY WITH SCA WINDS EXPECTED OVER THE COASTAL WATERS AND 
 PORTIONS OF THE NORTH INLAND WATERS.  A WARM FRONT WILL LIFT ACROSS 
 THE AREA EARLY THU MORNING FOLLOWED BY AN ASSOCIATED COLD FRONT THU 
 NIGHT.  WINDS AHEAD OF THIS COLD FRONT COULD BE GALE FORCE OVER THE 
 COASTAL WATERS THU AFTERNOON AND EVENING AND SCA ACROSS THE INLAND 
 WATERS NORTH OF EVERETT. 
 
 ADDITIONAL FRONTAL SYSTEMS WILL AFFECT THE AREA LATER FRI...SAT INTO 
 EARLY SUN AND AGAIN DURING THE EARLY PART OF THE COMING WEEK.   
 CERNIGLIA
 
 &&
 
 .SEW WATCHES/WARNINGS/ADVISORIES...
 PZ...SMALL CRAFT ADVISORY COAST...WEST AND EAST ENTRANCE TO THE 
       STRAIT...NORTHERN INLAND AND ADMIRALTY INLET. 
      .GALE WATCH COAST THU AFTERNOON AND EVENING. 
 WA...NONE. 
 
 

 
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