Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA

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000
FXUS66 KSEW 311029
AFDSEW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
329 AM PDT SUN AUG 31 2014

.SYNOPSIS...WEAK DISTURBANCES EMBEDDED IN THE STRONG WESTERLY FLOW
ALOFT OVER THE AREA WILL KEEP THE WEATHER SOMEWHAT UNSETTLED
TODAY. A LOW PRESSURE SYSTEM PASSING TO OUR NORTH WILL RESULT IN
A CHANCE OF LIGHT RAIN TONIGHT. HIGH PRESSURE ALOFT WILL PREVAIL
OVER THE REGION ON LABOR DAY. LOOK FOR A STRONGER AND COLDER
SYSTEM TO IMPACT THE AREA ON TUESDAY.

&&

.SHORT TERM...
AN UPPER JET WILL REMAIN DRAPED OVER THE REGION TODAY. POORLY
DEFINED AND FAST-MOVING DISTURBANCES EMBEDDED IN THE FLOW WILL
RESULT IN SOME INSTABILITY SHOWERS OVER THE CWA...HENCE THE CHANCE
POPS.

THE MODELS WERE IN AGREEMENT IN TAKING THE VIGOROUS SHORT TROF...
PRESENTLY NEAR THE GULF OF AK...ACROSS BRITISH COLUMBIA TONIGHT.
THE UPPER JET WILL LIFT NORTHWARD TONIGHT...ALLOWING
HEIGHTS/THICKNESSES TO BUILD OVER THE AREA. HESITATED TO
COMPLETELY REMOVE POPS FROM THE TONIGHT FORECAST SINCE IT IS
CONCEIVABLE THAT THERE COULD BE SOME SPOTTY LIGHT PRECIP DUE TO
WARM AIR ADVECTION.

THERE MIGHT BE SOME SPOTTY LIGHT RAIN OR DRIZZLE OVER THE
NORTHWEST PART OF THE CWA MON MORNING...OTHERWISE LABOR DAY WILL
BE A DRY DAY WITH NEAR NORMAL TEMPS UNDER HIGH PRESSURE ALOFT.

A STRONGER AND COLDER LOW PRESSURE SYSTEM WILL IMPACT THE REGION
ON SUNDAY. THE BEST CHANCE OF SHOWERS WILL BE ACROSS THE NORTHERN
ZONES. DAYTIME TEMPS ON TUE SHOULD BE 5-10 DEGREES COOLER THAN
MON. ALTHOUGH THE MODELS DID NOT INDICATE IT...WOULD NOT BE
SURPRISED IF IT BECOMES LOCALLY BREEZY IN THE AFTERNOON.

THE SNOW LEVEL IS EXPECTED TO FALL TO NEAR 5500 FEET LATE SUNDAY
NIGHT IN THE NORTH CASCADES...THUS DO NOT BE SURPRISED TO SEE A
RAIN/SNOW MIX AT THIS ELEVATION LATE SUNDAY NIGHT.

.LONG TERM...
AN UPPER RIDGE WILL BUILD OVER THE REGION ON WED FOR THE
ESTABLISHMENT OF DRY...NORTHERLY FLOW. WED NIGHT WILL LIKELY BE
THE CHILLIEST MORNING THIS WEEK...WITH THE MIN TEMP AT MANY
LOWLAND SITES PREDICTED TO BE IN THE 40S.

EXPECT AN UPPER RIDGE TO DOMINATE THE WEATHER PATTERN OVER THE
AREA DURING MUCH OF THIS PERIOD. HOWEVER THE MEDIUM RANGE
SOLUTIONS DIFFERED ON THE STRENGTH OF THE RIDGE. BEYOND FRI...
CONFIDENCE IN THE FORECAST WAS LOW DUE TO DIFFERENCES IN THE
MEDIUM RANGE SOLUTIONS...THAT IS AN UPPER TROF VERSUS AN UPPER
RIDGE. THE ONLY CHANGES MADE WERE TO BLEND BETTER WITH
NEIGHBORING OFFICES.

&&

.AVIATION...LIGHT NW FLOW ALOFT TODAY BETWEEN WEATHER SYSTEMS. A
WEAK WEATHER SYSTEM WILL DISSIPATE AS IT MOVES INTO THE AREA ON
MONDAY.  MOIST AND WEAKLY UNSTABLE ATMOSPHERE. ISOLATED SHOWERS.
AREAS OF MVFR CIGS EXPECTED THIS MORNING. CLOUDS SHOULD LIFT AND
SCATTER BY MIDDAY.

KSEA...MVFR CIGS THIS MORNING...LIFTING ABOVE 3K FT AND SCATTERING
BY AROUND 18Z. S-SW WIND 4-8 KT BECOMING NLY FOR A FEW HOURS THIS
EVENING. A PUGET SOUND CONVERGENCE ZONE MAY REFORM AND PRODUCE
ADDITIONAL SHOWERS LATE THIS AFTERNOON AND EVENING...OTHERWISE JUST
ISOLATED SHOWER ACTIVITY.

&&

.MARINE...A WEAK DECAYING TROUGH WILL PASS NORTH OF THE AREA TONIGHT
ENHANCING ONSHORE FLOW THIS EVENING. WESTERLY WINDS MAY REACH
LOW-END SMALL CRAFT TO 25 KNOTS FOR A FEW HOURS THIS EVENING IN THE
CENTRAL/E STRAIT. ANOTHER STRONGER SURFACE TROUGH WILL BRING
INCREASED ONSHORE FLOW TUESDAY AND WEDNESDAY. SMALL CRAFT WINDS ARE
AGAIN LIKELY AT TIMES IN THE CENTRAL/E STRAIT.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...NONE.
PZ...NONE.

&&

$$

WWW.WEATHER.GOV/SEATTLE

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




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