National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS66 KSEW 271709
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
910 AM PST FRI FEB 27 2015

.SYNOPSIS...A WEAK WEATHER SYSTEM WILL PRODUCE WIDESPREAD SHOWERS
ACROSS WESTERN WASHINGTON TODAY AS IT MOVES SOUTHEAST FROM THE COAST
TOWARD OREGON. A FEW INCHES OF SNOW WILL FALL IN THE MOUNTAINS. AN
UPPER RIDGE AND OFFSHORE FLOW WILL BRING SUNNY DAYS AND COOL NIGHTS
THIS WEEKEND. A WEAK SYSTEM WILL MOVE THROUGH SUNDAY NIGHT AND
MONDAY...WITH DRY WEATHER AGAIN TUESDAY AND WEDNESDAY.

&&

.SHORT TERM...AN UPPER LOW OVER SOUTHWEST WASHINGTON WILL SHIFT
SOUTH OF THE STATE LATER TODAY. SHOWERS OVER THE AREA THIS MORNING
WILL BEGIN TO DECREASE FROM NORTH TO SOUTH THIS AFTERNOON AS THE
UPPER LOW PULLS AWAY. SHOWERS SHOULD PRETTY MUCH COME TO AN END
AFTER MIDNIGHT TONIGHT AS DRIER NORTHERLY FLOW ALOFT DEVELOPS ALONG
WITH LOW LEVEL OFFSHORE FLOW. A SURFACE HIGH MOVING INTO SOUTHERN
BRITISH COLUMBIA WILL RESULT IN LOCALLY BREEZY NORTHERLY WINDS
TONIGHT AND SATURDAY. OTHERWISE...SATURDAY SHOULD BE A SUNNY DAY
AFTER SOME LINGERING EARLY MORNING CLOUDS BURN OFF WITH OFFSHORE
FLOW IN CONTROL. SUNDAY SHOULD BE ANOTHER SUNNY DAY. LOW LEVEL
OFFSHORE FLOW WILL WEAKEN AND FLOW ALOFT WILL BACK TO NORTHWEST AS A
WEATHER SYSTEM APPROACHES FROM THE NORTHWEST FOR LESS WIND.

FOR TODAY...THE MOUNTAINS WILL GET SOME SNOW FOR THE FIRST TIME IN
QUITE AWHILE. SNOW APPEARS TO BE ACCUMULATING ABOVE ABOUT 3500 FEET.
PARADISE ON MOUNT RAINIER HAS PICKED UP 5 INCHES SO FAR AND WILL
PROBABLY REACH LOW END ADVISORY TOTALS BY LATE THIS MORNING BUT
OTHER AREAS LOOK LIKE THEY WILL STAY BELOW ADVISORY CRITERIA.
SCHNEIDER

.LONG TERM...PREVIOUS DISCUSSION...AN UPPER SHORTWAVE THAT MOVES
INTO WESTERN WASHINGTON SUNDAY NIGHT WILL MAINTAIN A CHANCE OF
SHOWERS MONDAY AND MONDAY NIGHT...BUT AGAIN AMOUNTS LOOK LIGHT AND
COVERAGE SHOULD BE SPOTTY. DRY NORTHERLY FLOW WILL TAKE OVER AGAIN
TUESDAY AHEAD OF A STRONG UPPER RIDGE OFFSHORE OUTSIDE OF 130W. THE
UPPER RIDGE WILL MOVE SLOWLY TOWARD THE REGION FOR ANOTHER DRY DAY
WEDNESDAY. IT WILL WEAKEN AS IT MOVES INLAND THURSDAY...AND A WEAK
SYSTEM MOVING OVER THE NORTH SIDE OF THE RIDGE COULD BRING SOME
PRECIPITATION TO WESTERN WASHINGTON. THE MODELS ALL AGREE ON THIS
GENERAL SCENARIO.   MCDONNAL

&&

.HYDROLOGY...FLOODING IS UNLIKELY FOR THE NEXT 7 DAYS.

&&

.AVIATION...A SMALL UPPER LEVEL AND SURFACE LOW OVER THE WA COAST AT
16Z WILL MOVE S OVER THE CENTRAL OREGON COAST AROUND 00Z. THE LOW
WILL CONTINUE S OVER N CA BY 12Z SATURDAY...ALLOWING COOLER AND DRY
NE FLOW ALOFT TO SPREAD OVER W WA.

CONDITIONS ACROSS W WA THIS MORNING ARE PREDOMINANTLY MVFR...WITH A
LITTLE IFR MIXED IN OVER S PUGET SOUND AND THE SW INTERIOR...AND
SOME HIGHER OVC030-050 CIGS OVER THE N PUGET SOUND AND THE N
INTERIOR WHERE THE STEADY RAIN IS STILL FALLING. 12Z NAM TIME-HEIGHT
SECTIONS STILL INDICATE CIGS LIFTING FROM THE N THIS AFTERNOON AS
THE LOW CONTINUES S. THIS SEEMS REASONABLE GIVEN THE GOOD VFR
CONDITIONS AT CYVR AND CYYJ...BUT THE PUGET SOUND REGION WILL
PROBABLY STILL HAVE SOME MVFR CIGS ALL THE WAY THROUGH 23Z. UPSLOPE
CONDITIONS CAUSED BY THE OLYMPICS NEAR KCLM SHOULD DELAY IMPROVEMENT
THERE EVEN FURTHER.

KSEA...CIGS AT KSEA ARE EXPECTED TO REMAIN IN THE
MVFR...OVC020-030...OR LOW END VFR RANGE...OVC030-040 THROUGH AROUND
20Z...PER THE LATEST HIGH RESOLUTION HRRR MODEL. SOME PERIODS OF
CIGS BELOW BKN020 ARE NOT OUT OF THE QUESTION. THESE LOWER CIGS
COULD REMAIN IN THE VICINITY OF KSEA THROUGH 23Z. SURFACE WINDS WILL
REMAIN NE 5-8 KT. KAM

&&

.MARINE...A 1005 MB SURFACE LOW OVER THE S WA COAST WILL SLIDE S
OVER THE CENTRAL OREGON COAST THIS AFTERNOON. A 1032 MB SURFACE
RIDGE OVER CENTRAL B.C. WILL MOVE S BEHIND THE SURFACE LOW. THIS
WILL ALLOW N-NE FLOW TO STRENGTHEN OVER W WA TODAY...WITH MODERATE
FLOW CONTINUING THROUGH SATURDAY MORNING. THE SURFACE RIDGE WILL
SETTLE OVER W WA SATURDAY AFTERNOON...ALLOWING NORTHERLY PRESSURE
GRADIENTS TO WEAKEN. SMALL CRAFT ADVISORIES HAVE BEEN ISSUED FOR ALL
THE WA WATERS...BUT SOME TAKE EFFECT LATER TODAY. THERE IS SOME
CONCERN THAT THE NE FLOW OVER THE N INLAND WATERS WILL REACH
BORDERLINE GALE LEVELS...HOWEVER AT THIS POINT THE ONLY MODEL
INDICATING SUCH IS THE 06Z CANADIAN LAM...AND THE 30-35 KT WINDS ARE
RATHER SPOTTY.

THE SURFACE RIDGE WILL LAST OVER W WA SATURDAY AFTERNOON THROUGH
SUNDAY AFTERNOON. A WEAK SHORTWAVE TROUGH WILL MOVE S ALONG THE B.C.
COAST SUNDAY NIGHT...BUT SURFACE REFLECTION WILL BE WEAK. A WEAKER
EPISODE OF N-NE FLOW IS EXPECTED BEHIND THE TROUGH ON MONDAY. KAM

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...SMALL CRAFT ADVISORY ALL WATERS.

&&

$$

YOU CAN SEE AN ILLUSTRATED VERSION OF THE FORECAST DISCUSSION AT
WWW.WEATHER.GOV/SEATTLE/GAFD/LATEST_WEBAFD.HTML