FXUS66 KSEW 271120
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
330 AM PST FRI NOV 27 2009
.SYNOPSIS...A LOW PRESSURE SYSTEM ALOFT THAT WAS OVER THE AREA THIS
MORNING WILL MOVE EAST OF THE CASCADES BY NOON. THUS LOOK FOR THE
PRECIPITATION OVER THE SOUTHERN PORTION TO COME TO AN END. DRY
WEATHER WILL PREVAIL OVER THE AREA THIS AFTERNOON UNDER HIGH
PRESSURE ALOFT. A WEAK SYSTEM PASSING TO OUR NORTH WILL GIVE THE
REGION A THREAT OF LIGHT PRECIPITATION TONIGHT THROUGH SATURDAY
NIGHT. BUILDING HIGH PRESSURE ALOFT WILL THEN BRING DRY WEATHER BACK
TO THE AREA ON SUNDAY.
&&
.SHORT TERM...
AN UPPER TROF WAS MOVING ACROSS WRN WA AT THIS TIME AND WILL BE E OF
THE AREA BY NOON. THEREFORE ANTICIPATE THE PRECIP OVER THE SE
PORTION OF THE CWA TO COME TO AN END LATER THIS MORNING...WITH DRY
WEATHER PREVAILING OVER THE ENTIRE AREA THIS AFTERNOON. A WEAK...
SHORT WAVE RIDGE WILL FOLLOW ON THE HEELS OF THE UPPER TROF THIS
AFTERNOON. THERE WILL PROBABLY BE A BRIEF BREAK IN THE CLOUD COVER
OVER THE NW HALF OF THE CWA TODAY...HOWEVER CLOUDS WILL BE ON THE
INCREASE AGAIN THIS AFTERNOON IN ADVANCE OF A WMFNT OVER THE ERN
PAC. OVERRUNNING MOISTURE WILL SPREAD ACROSS THE AREA TONIGHT...WITH
SOME LIGHT PRECIP DEVELOPING OVER ROUGHLY THE NW THIRD OF THE CWA
OVERNIGHT.
THE WMFNT SHOULD REMAIN TO OUR W AND N ON SATURDAY...BUT RISING
HEIGHTS/THICKNESSES ASSOCIATED WITH AN AMPLIFYING UPPER RIDGE WILL
STILL TRANSLATE TO WAA THROUGH SATURDAY NIGHT. THE SNOW LEVELS ARE
EXPECTED TO RISE INTO THE 5K TO 6500 FT RANGE BY EARLY SUNDAY.
ANTICIPATE THE PRECIP THREAT TO BECOME SHUNTED NWD INTO BRITISH
COLUMBIA DURING THE DAY SUNDAY AS THE UPPER RIDGE AMPLIFIES FURTHER.
DAYTIME TEMPS ON SUNDAY WILL RUN ABOVE NORMAL...ESPECIALLY IN THE
MOUNTAINS.
.LONG TERM FROM THE PREV DISCUSSION...
A MAJOR AND LIKELY WELCOME CHANGE IN THE WEATHER PATTERN BEGINS TO
TAKE SHAPE MONDAY. A WEAK COLD FRONT IS FORECAST TO SLIDE SE ACROSS
THE REGION OR POSSIBLY JUST BRUSH BY...THEN AN UPPER LEVEL RIDGE
WILL BUILD OVER THE EASTERN PACIFIC AND THE WESTERN EDGE OF THE
NORTH AMERICA. AFTER THE WEAK FRONT MOVES BY...DRY WEATHER WILL
TAKE HOLD TUESDAY AND LIKELY CONTINUE THROUGH AT LEAST THURSDAY AND
ONE MODEL IS EVEN SUGGESTING IT MIGHT CONTINUE INTO NEXT WEEKEND.
WE ALREADY DRIED OUT THE FORECAST TUESDAY ONWARD YESTERDAY SO I JUST
EXTENDED THAT TREND INTO THURSDAY. CERNIGLIA
&&
.HYDROLOGY FROM THE PREV DISCUSSION...
THE WARM ADVECTION SYSTEMS THAT WILL SPREAD LIGHT PRECIPITATION OVER
WESTERN WASHINGTON THIS WEEKEND WILL BE RATHER WEAK AND AS A RESULT
WILL NOT PRODUCE ENOUGH RAIN TO CAUSE ADDITIONAL RIVER PROBLEMS.
BEYOND THAT THE FORECAST IS MAINLY DRY WELL INTO NEXT WEEK AND
LIKELY INTO THE FOLLOWING WEEKEND. AS A RESULT NO NEW FLOODING IS
EXPECTED THROUGH NEXT WEEK AND AREA RIVERS WILL RETURN TO LOWER FLOW
LEVELS.
NO FLOODING IS EXPECTED ON THE GREEN RIVER THROUGH NEXT WEEK.
33/CERNIGLIA
&&
.AVIATION...UPPER TROUGH MOVING EAST THROUGH THE AREA AS SURFACE
HIGH PRESSURE BUILDS FROM THE WEST. AIR MASS MOIST AND STABILIZING.
STILL SOME RAIN IN THE SOUTHWEST BUT THIS IS DIMINISHING RAPIDLY.
CEILINGS ARE GENERALLY 1-2K FT. THERE WILL BE SLOW IMPROVEMENT
THROUGH THE DAY WITH POSSIBLY VFR CONDITIONS IN THE LATE AFTERNOON.
KSEA...N WIND 6-10 KT THIS MORNING...SWINGING AROUND TO SW AFTER
21Z. FORECAST ABOVE HOLDS FOR KSEA. CHB
&&
.MARINE...NORTHERLY WINDS HANGING TOUGH THROUGH PUGET SOUND AND HAVE
EXTENDED THE SMALL CRAFT ADVISORY THERE THROUGH 15Z. THE REST OF THE
INLAND WATERS ALSO HAVE SMALL CRAFT ADVISORY NORTHERLIES...AND THESE
WILL LAST INTO THE EARLY AFTERNOON. SMALL CRAFT ADVISORY WINDS WILL
CONTINUE ON THE COAST OFF AND ON THROUGH THE AFTERNOON. HEAVY SWELL
ON THE COAST WILL ALSO CONTINUE...PROBABLY THROUGH TONIGHT.
A WARM FRONT WILL BRUSH WESTERN WASHINGTON ON SATURDAY. HAVE
INDICATED SMALL CRAFT ADVISORY CONDITIONS OVER THE COASTAL WATERS...
THE STRAIT ENTRANCES...AND THE NORTHERN INLAND WATERS.
UPPER RIDGE BUILDS SUNDAY AND WINDS SHOULD BE LIGHT EARLY NEXT WEEK.
CHB
&&
.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE COASTAL WATERS...
EAST ENTRANCE TO THE STRAIT OF JUAN DE FUCA...ADMIRALTY
INLET...AND NORTHERN INLAND WATERS THROUGH THIS AFTERNOON.
A SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS IS IN EFFECT FOR
THE WEST ENTRANCE TO THE STRAIT OF JUAN DE FUCA THROUGH
THIS EVENING.
A SMALL CRAFT ADVISORY FOR ROUGH GRAYS HARBOR BAR CONDITIONS
REMAINS IN EFFECT THROUGH THIS EVENING.
$$
WWW.WEATHER.GOV/SEATTLE
FOR AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION...PLEASE SEE
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML.
