516
FXUS66 KSEW 181014
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
314 AM PDT SUN OCT 18 2026
SYNOPSIS
UPPER LEVEL TROUGH EXITING THE GULF OF ALASKA TODAY WILL MOVE
BY TO THE WEST MONDAY. THE TROUGH WILL CONTINUE TO MOVE SOUTH
TUESDAY WITH A WEAK UPPER LEVEL RIDGE OVER THE AREA. ANOTHER
UPPER LEVEL TROUGH WILL APPROACH THE COAST WEDNESDAY. THE
ASSOCIATED WEAKENING FRONT WILL MOVE THROUGH WESTERN WASHINGTON
THURSDAY. COOL UPPER LEVEL TROUGH OVER THE AREA FRIDAY AND
SATURDAY.
SHORT TERM /TODAY THROUGH TUESDAY/
SATELLITE IMAGERY SHOWS A PATCH OF STRATUS OVER GRAYS HARBOR
COUNTY AND FOG IN THE SNOHOMISH RIVER VALLEY OTHERWISE CLEAR
SKIES OVER THE AREA. TEMPERATURES AT 3 AM/10Z WERE IN THE UPPER
30S TO NEAR 50.
ZONAL FLOW ALOFT BECOMING SOUTHWESTERLY TODAY AS AN UPPER LEVEL
TROUGH DIGS SOUTH WELL OFFSHORE. AT THE SURFACE, HIGH PRESSURE
WILL WEAKEN WITH LIGHT NORTHERLY FLOW. NARROW TEMPERATURE
DEWPOINT SPREADS EARLY THIS MORNING WITH LIGHT GRADIENTS SO
EXPECT MORE FOG TO DEVELOP ESPECIALLY OVER THE SOUTHWEST
INTERIOR AND NEAR THE PUGET SOUND AND HOOD CANAL. THE FOG THAT
DOES FORM WILL BE GONE BY LATE MORNING. MOSTLY SUNNY THIS
AFTERNOON WITH HIGHS IN THE MID 50S TO LOWER 60S.
UPPER LEVEL TROUGH CONTINUING TO MOVE SOUTH TONIGHT AND MONDAY
WITH THE TROUGH AXIS NEAR 130W MONDAY AFTERNOON. THIS IS TOO FAR
WEST TO BRING ANY WEATHER TO WESTERN WASHINGTON OTHER THAN SOME
MIDDLE AND HIGH LEVEL CLOUDS. ANOTHER ROUND OF PATCHY MORNING
FOG IN THE FOG PRONE PLACES LATE TONIGHT THROUGH MID MORNING.
LOWS IN THE MID 30S TO MID 40S. HIGHS MONDAY A COUPLE OF
DEGREES EITHER SIDE OF 60.
LARGE UPPER LEVEL LOW DEVELOPING IN THE TROUGH MONDAY NIGHT INTO
TUESDAY ENDING UP OFF THE CENTRAL CALIFORNIA COAST TUESDAY
AFTERNOON. WEAK UPPER LEVEL RIDGE OVER WESTERN WASHINGTON WITH
LIGHT/SPLIT FLOW ALOFT. LIGHT SURFACE GRADIENTS ALLOWING FOR A
LITTLE MORE FOG COVERAGE TUESDAY MORNING. LIKE MOST OF THE FOGGY
MORNINGS THIS MONTH THE FOG WILL BE GONE BEFORE NOON. LOWS IN
THE MID 30S TO MID 40S. HIGHS IN THE UPPER 50S TO MID 60S.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
EXTENDED MODELS IN GOOD AGREEMENT WITH THE UPPER LEVEL LOW
SPINNING AROUND OFF THE CALIFORNIA COAST TUESDAY NIGHT AND
WEDNESDAY. WEAKER UPPER LEVEL TROUGH MOVING OUT OF THE GULF OF
ALASKA STILL WELL OFFSHORE WEDNESDAY. ANOTHER SUNNY DAY IN STORE
WITH AREAS OF MORNING FOG AND LOCAL FREEZING FOG. LOWS IN THE
30S TO LOWER 40S. HIGHS IN THE LOWER TO MID 60S.
UPPER LEVEL TROUGH WITH THE ASSOCIATED FRONT STILL OFFSHORE
WEDNESDAY NIGHT. FRONT WEAKENING AS IT MOVES INLAND THURSDAY
WITH JUST CHANCE POPS IN THE FORECAST. LOWS IN THE MID 30S TO
MID 40S. THE INCREASE IN CLOUD COVER WILL KNOCK A FEW DEGREES
OFF THE HIGHS WITH MID 50S TO NEAR 60 IN THE FORECAST.
COOL UPPER LEVEL TROUGH HANGING OVER THE AREA THURSDAY NIGHT
INTO SATURDAY. VERY LITTLE IN THE WAY OF DYNAMICS WITH THE
TROUGH. WILL HAVE TO KEEP A SLIGHT CHANCE OF SHOWERS AT TIMES
THROUGH THE PERIOD. SNOW LEVELS NEAR 4500 FEET SO CHANCE FOR
SOME VERY LIGHT SNOW IN THE HIGHER ELEVATIONS. HIGHS NEAR
NORMAL, MID 50S TO NEAR 60. LOWS IN THE MID 30S TO MID 40S
FRIDAY MORNING AND 30S TO LOWER 40S SATURDAY MORNING.
VERY LITTLE IN THE WAY OF PRECIPITATION FORECAST FOR THE NEXT
WEEK. SO FAR IN OCTOBER THERE HAS ONLY BEEN 0.08 INCHES OF RAIN
AT SEATTLE-TACOMA AIRPORT. THERE HAVE ONLY BEEN 4 OCTOBERS IN
THE 81 YEARS OF THE RECORDS AT SEATTLE-TACOMA AIRPORT WITH LESS
THAN AN INCH OF RAIN, 1987 0.31 INCHES, 2002 0.67 INCHES, 1972,
0.72 INCHES AND 1978 0.98 INCHES. FELTON
AVIATION
WESTERLY FLOW ALOFT TURNING MORE SOUTHWESTERLY INTO MONDAY. LIGHT
FLOW AND RESIDUAL SURFACE MOISTURE IS LEADING TO THE DEVELOP OF FOG
ACROSS THE AREA THIS MORNING. AREAS OF IFR/LIFR ARE EXPECTED BUT ANY
LINGERING FOG SHOULD SUBSIDE BY 18Z TO WIDESPREAD VFR. MID TO HIGH
LEVEL CLOUD COVERAGE WILL STREAM OVERHEAD SUNDAY AFTERNOON - EVENING
BUT CAN'T RULE OUT ANOTHER ROUND OF PATCHY FOG SUNDAY NIGHT INTO
MONDAY MORNING. NORTHERLY SURFACE WINDS SUNDAY AFTERNOON 5-10 KT.
KSEA...VFR CONDITIONS THIS MORNING. CAN'T RULE OUT VICINITY FOG
AROUND THE TERMINAL AS THE MORNING PROGRESS BUT IF MANIFEST IT
SHOULD SCATTER OUT BY THE AFTERNOON (17-18Z). A TEMPO GROUP HAS BEEN
INTRODUCED INTO THE TAF TO HIGHLIGHT THIS POTENTIAL. NE SURFACE
WINDS THIS MORNING 5-10 KT, SHIFTING TO THE NW 5-10 KT WITH GUSTS TO
18-20 KT DURING THE AFTERNOON. WINDS WILL GRADUALLY DECREASE
OVERNIGHT SUNDAY INTO MONDAY.
41
MARINE
SURFACE HIGH PRESSURE WILL BUILD ACROSS THE WATERS
TODAY. A LOW PRESSURE SYSTEM PASSING SOUTHWARD WELL OFFSHORE WILL
TURN WINDS NORTHERLY OR WEAKLY OFFSHORE SUNDAY 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. SEAS WILL THEN SUBSIDE
INTO THE WEEKEND.
41
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...NONE.
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