636
FXUS66 KSEW 190321
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
821 PM PDT SUN OCT 18 2026
SYNOPSIS
A TROUGH WILL BE DEPARTING SOUTH AND WELL OFFSHORE TOMORROW INTO
TUESDAY, WITH ZONAL FLOW THROUGH THE MIDDLE OF THE WEEK. THE
NEXT FEW MORNINGS WILL BE ON THE COLDER SIDE FOR POTENTIAL
FROSTS, NAMELY IN THE SOUTH PUGET SOUND AND CHEHALIS VALLEY. A
WEAK SYSTEM IS POSSIBLE LATE IN THE WEEK FOR LIGHT RAIN.
SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
THE LATEST FORECAST REMAINS ON TRACK THIS EVENING WITH NO
UPDATES. HIGH CLOUDS ARE MOVING ONSHORE COURTESY OF THE UPPER
LEVEL TROUGH TRANSITING SOUTH, BUT FAR OFFSHORE. LOW
TEMPERATURES TOMORROW MORNING WILL BE IN THE MID 30S FOR AREAS
INCLUDING OLYMPIA AND SOUTH THROUGH THE I-5 CORRIDOR. MID 40S
ARE EXPECTED ELSEWHERE. LOWS DECREASE A FEW DEGREES FURTHER INTO
TUESDAY MORNING FOR FROST POTENTIAL IN THE AFOREMENTIONED AREAS
BUT ALSO THE CASCADES AND VALLEYS. PATCHY MORNING FOG WILL
REMAIN POSSIBLE THROUGH EARLY IN THE WEEK AND WILL BE MORE
LIKELY IN THE VALLEYS AND TYPICALLY FOG PRONE LOCATIONS.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
EXTENDED MODELS AND THE ENSEMBLES ARE FAVORING GULF OF ALASKA
TROUGHING TO BUILD ON THE DEEPER LOW MOVING INTO SOUTHERN
CALIFORNIA WEDNESDAY AND BEYOND. POSITIONING OF THE LOW BECOMES
LESS CLEAR BY FRIDAY INTO NEXT WEEKEND BUT THE INDICATION AS OF
NOW ISN'T FOR MUCH IN THE WAY OF IMPACTFUL WEATHER. SOME LIGHT
RAIN MAY BE POSSIBLE THURSDAY INTO FRIDAY. SNOW LEVELS DURING
THAT TIME COME DOWN TO AROUND 4,000-4,500 FEET, SO SOME LIGHT
SNOW FLURRIES MAY BE POSSIBLE AT THESE ELEVATIONS AND HIGHER IF
PRECIPITATION DOES MATERIALIZE.
21
AVIATION
SOUTHWESTERLY FLOW ALOFT IS EXPECTED TONIGHT INTO MONDAY AS AN UPPER
TROUGH DIGS SOUTHWARD OFFSHORE. INCREASING HIGH LEVEL MOISTURE LATER
TONIGHT IS EXPECTED TO LIMIT AREAL COVERAGE OF LOW CLOUDS ON MONDAY
MORNING WITH THE EXCEPTION OF MORE FOG PRONE LOCATIONS IN THE
SOUTHWEST INTERIOR AND EXTREME SOUTHERN PUGET SOUND FOR THE
POTENTIAL OF IFR/LIFR CONDITIONS. IMPACTED TERMINALS EXPECTED TO
IMPROVE BY THE AFTERNOON, FOR WIDESPREAD VFR CONDITIONS. LIGHT
NORTHERLY TO CALM WINDS TONIGHT. WINDS WILL SHIFT MORE SOUTHERLY
MONDAY MORNING THEN TRANSITION BACK NORTHERLY IN THE EVENING.
KSEA...VFR CONDITIONS WILL CONTINUE TONIGHT. HIGH AND MID LEVEL
MOISTURE SPREADING IN THE REGION AHEAD OF UPPER TROUGH DIGGING
SOUTHWARD OFFSHORE. THE EXPECTATION REMAINS THAT THIS WILL LIMIT FOG
DEVELOPMENT TONIGHT AND WILL KEEP LOW CEILINGS/VIS OUT OF UPCOMING
TAF FOR NOW. SURFACE WINDS LIGHT AND VARIABLE LATE TONIGHT INTO
MONDAY A.M. WINDS WILL SHIFT MORE SOUTHERLY LATE MONDAY MORNING,
BEFORE TRANSITIONING NORTHWESTERLY AFTER 19Z-21Z AT 5-7 KT.
27/29
MARINE
A LOW PRESSURE SYSTEM PASSING SOUTHWARD WELL OFFSHORE WILL KEEP
WINDS NORTHERLY OR WEAKLY OFFSHORE INTO MONDAY. WEAK HIGH PRESSURE
WILL REMAIN ACROSS THE WATERS INTO THE MIDDLE OF THE COMING WEEK FOR
RATHER QUIET CONDITIONS. A LARGER SWELL TRAIN NEAR 10-12 FEET
GENERATED BY ACTIVE WEATHER WELL OFFSHORE IS EXPECTED TO REACH THE
COASTAL WATERS AROUND THURSDAY ALONG WITH AN INCREASE IN ONSHORE
FLOW. A FRONT MAY REACH THE WATERS TOWARD THE END OF THE WEEK.
27
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page