|
|
Printer Friendly |
Current
Version
Previous Version: 1 2 3 4 5 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. && .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 && .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 && .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. && .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.
WWW.WEATHER.GOV/SEATTLE FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION PLEASE SEE WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML (ALL LOWERCASE).
| |