007
FXUS66 KSEW 161041
AFDSEW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SEATTLE WA
242 AM PST THU JAN 16 2025
SYNOPSIS
A WEAK FRONTAL SYSTEM WILL MOVE THROUGH WESTERN
WASHINGTON TODAY, BRINGING A CHANCE FOR RAIN TO PORTIONS OF THE
AREA. SURFACE HIGH PRESSURE WILL REBUILD OFFSHORE TONIGHT AND REMAIN
THE MAIN WEATHER FACTOR INTO THE MIDDLE OF NEXT WEEK. THIS WILL
RESULT IN DRIER CONDITIONS AND COLD TEMPERATURES.
SHORT TERM /TODAY THROUGH SUNDAY/
LATEST SATELLITE IMAGERY SHOWS
PLENTY OF LOW CLOUDS AND FOG OVER W WA THIS MORNING WITH MANY
OBSERVATION SITES REPORTING AT LEAST SOME RESTRICTION TO VISIBILITY.
IT IS WORTH NOTING THAT APPROACHING FRONT MAY HAVE ACTUALLY
CONTRIBUTED TO SOME IMPROVEMENT IN CONDITIONS AS SOME SPOTS HAVE
SEEN VISIBILITY INCREASE FROM ONE-QUARTER OF A MILE. THIS
IMPROVEMENT VARIES HOWEVER, AS SEA-TAC HAS ONLY CLIMBED TO ONE-HALF
MILE WHILE MOST OTHER STATIONS THAT SAW REDUCED VISIBILITIES
RECOVERING TO BETWEEN 2-5 MILES. INCOMING WEAK FRONT SHOULD HELP TO
TRIGGER SOME MIXING TO CLEAR OUT THE NEAR-SURFACE LEVELS, EVEN
THOUGH CONDITIONS WILL REMAIN CLOUDY THROUGHOUT THE DAY.
REGARDING SAID FRONT, THE FEATURE SHOULD REACH THE COAST DURING THE
LATE MORNING AND PUSH EASTWARD THROUGHOUT THE DAY. NEITHER
DETERMINISTIC MODEL NOR ANY OF THE ENSEMBLE MEMBERS PUT A LOT OF
STOCK IN THIS SYSTEM PRODUCING MUCH IN THE WAY OF PRECIP OVER THE
AREA, ALTHOUGH THE COAST AND THE MOUNTAINS WILL BE FAVORED...THE
COAST SEEING POPS TOPPING AT AROUND 40 PCT WHILE THE CASCADES MAX
OUT AROUND 60 PCT...ESPECIALLY OVER THE NORTH CASCADES. EXPECTED QPF
ALSO LARGELY UNCHANGED WITH RAINFALL AMOUNTS EXPECTED TO REMAIN
BELOW 0.10 OF AN INCH.
UPPER LEVEL RIDGING WILL RESUME ITS REIGN OVER THE PAC NW AS A
STRONG RIDGE OVER THE PACIFIC CONTINUES TO AMPLIFY FOR THE REMAINDER
OF THE SHORT TERM. THE COMBINATION OF LOW-LEVEL MOISTURE FROM THE
EXITING FRONT AND THIS RETURN TO HIGH PRESSURE WILL LIKELY ALLOW FOR
ANOTHER ROUND OF PATCHY FOG LATE TONIGHT AND FRIDAY MORNING,
HOWEVER, CONDITIONS DRY OUT QUICKLY WITH NO FOG EXPECTED FOR EITHER
EARLY SATURDAY OR EARLY SUNDAY. THIS WILL MAKE THE MAIN FEATURE OF
THIS REGIME THE BRISK TEMPERATURES. AFTERNOON HIGHS TODAY WILL BE
THE WARMEST OF THE SHORT TERM PERIOD RANGING IN THE LOWER TO MID
40S, WHILE THE REMAINING DAYS WILL LARGELY HOVER IN THE LOWER
40S...WITH MAYBE SOME MID 40S ALONG THE COAST. OVERNIGHT LOWS
TONIGHT WILL ECHO THE HIGHS TODAY IN BEING THE WARMEST OF THE
PERIOD, RANGING IN THE LOWER TO MID 30S. THE REST OF THE WEEK AND
INTO THE WEEKEND WILL SEE LOWS IN THE UPPER 20S TO LOWER 30S, WHERE
SOME LOCATIONS MAY BE IN NEED OF COLD WEATHER HEADLINES.
18
LONG TERM /MONDAY THROUGH THURSDAY/
AS STATED IN THE SYNOPSIS,
ONCE IN THE THRALL OF THIS UPPER RIDGE, W WA WILL REMAIN UNDER ITS
INFLUENCE INTO AT LEAST EARLY NEXT WEEK. AS THE RIDGE AXIS SHIFTS
EASTWARD, THE RIDGE DOES EASE. THIS SHIFT WILL ALLOW FOR A WEAK
TROUGH TO PUSH THROUGH TUESDAY, BUT MODELS IN STRONG AGREEMENT THAT
THIS FEATURE WOULD BE A DRY ONE. BEYOND THIS POINT IN THE FORECAST,
UPPER LEVEL RIDGING REBUILDS WEDNESDAY INTO THURSDAY.
SOME VERY GRADUAL WARMING THROUGHOUT THE LONG TERM. HIGHS FOR THE
EARLY PART OF NEXT WEEK WILL STILL LINGER IN THE LOWER 40S WITH
MAYBE A DEGREE OR TWO OF WARMING BETWEEN MONDAY AND TUESDAY. MIDWEEK
WILL SEE TEMPERATURES CLIMB BACK INTO THE MID TO UPPER 40S.
OVERNIGHT LOWS WILL SEE A WARMING TREND OF THEIR OWN, ALBEIT MORE
DEGREE BY DEGREE AS OPPOSED TO SHIFTING RANGES. LOWS MONDAY NIGHT
AND TUESDAY NIGHT WILL REMAIN IN THE MID 20S TO AROUND 30 WHILE LOWS
WEDNESDAY AND THURSDAY NIGHTS WILL RANGE IN THE LOWER TO MID 30S.
18
AVIATION
A WEAK UPPER TROUGH IS DIGGING SOUTHWARD OVER BRITISH
COLUMBIA THIS MORNING WITH WESTERLY FLOW ALOFT OVER WESTERN
WASHINGTON. AN ASSOCIATED WEAK FRONT SLIDING SOUTHEASTWARD DOWN THE
BRITISH COLUMBIA COAST WILL MOVE ACROSS THE REGION LATER THIS
MORNING. THIS WILL ACT TO INCREASE ONSHORE FLOW ACROSS THE AREA AND
DEEPEN LOW LEVEL MOISTURE CURRENTLY IN PLACE ACROSS MUCH OF WESTERN
WASHINGTON. THE APPROACHING FRONT IS EXPECTED TO LIFT WIDESPREAD
LIFR CEILINGS THIS MORNING TO IFR OR MVFR. SURFACE VISIBILITIES WILL
IMPROVE AS WELL TO 3-5SM OR BETTER BY MID-MORNING FOR MOST
TERMINALS. INCREASING CONVERGENCE ASSOCIATED WITH THE FRONT WILL
LEAD TO SOME DRIZZLE OR LIGHT SHOWERS FROM MID-MORNING INTO THIS
AFTERNOON...ESPECIALLY AROUND PUGET SOUND. AREAS OF NORTH AND SOUTH
OF THE CENTRAL PUGET SOUND COULD SEE A BRIEF PERIOD OF VFR LATE THIS
AFTERNOON. POST-FRONTAL ONSHORE FLOW WILL RELAX TONIGHT AND THE
REDEVELOPMENT OF IFR OR LOW MVFR CEILINGS IS EXPECTED OVERNIGHT
TONIGHT.
KSEA...LIFR FOG AS OF 09Z IS EXPECTED TO LIFT TO IFR AS FRONT
APPROACHES THIS MORNING. EXPECTING A MORE CONSOLIDATED MVFR CEILING
BY THIS AFTERNOON WITH SOME DRIZZLE OR LIGHT SHOWERS IN THE AREA
FROM LATE MORNING INTO THIS AFTERNOON AS A WEAK CONVERGENCE ZONE
DEVELOPS OVER PUGET SOUND. THERE IS ABOUT A 50% CHANCE OF A BRIEF
VFR WINDOW 23Z-02Z. CEILINGS WILL THEN DETERIORATE BACK TO LOW MVFR
OR IFR OVERNIGHT TONIGHT. SURFACE WINDS SOUTHERLY RISING TO 7 TO 10
KNOTS THIS MORNING. CURRENT THINKING IS THAT A CONVERGENCE
ASSOCIATED NORTHERLY WIND SHIFT WILL IMPACT THE TERMINAL 21Z-03Z.
27
MARINE
A WEAK COLD FRONT WILL PUSH INLAND ACROSS WESTERN
WASHINGTON THIS MORNING. AN INCREASE IN ONSHORE FLOW BEHIND IT WILL
LEAD TO SMALL CRAFT ADVISORY WINDS ACROSS THE COASTAL WATERS AND IN
THE STRAIT OF JUAN DE FUCA. BROAD SURFACE RIDGING CENTERED OFFSHORE
WILL GRADUALLY SHIFT EASTWARD LATER TODAY INTO FRIDAY. STRONG HIGH
PRESSURE OVER THE INTERIOR WILL LEAD TO OFFSHORE FLOW THIS WEEKEND
INTO MONDAY. A WEAK WEATHER SYSTEM WILL DISSIPATE OFFSHORE ON
TUESDAY BEFORE RIDGING OVER THE INTERIOR REBUILDS ONCE AGAIN BY THE
MIDDLE OF NEXT WEEK.
COASTAL SEAS OVER THE OUTER COASTAL WATERS WILL REMAIN NEAR 10 FEET
TODAY INTO TONIGHT BEFORE SUBSIDING ON FRIDAY AND REMAINING BELOW 10
FEET INTO EARLY NEXT WEEK. 27
HYDROLOGY
NO RIVER FLOODING EXPECTED IN THE NEXT 7 DAYS.
SEW WATCHES/WARNINGS/ADVISORIES
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR COASTAL
WATERS FROM CAPE FLATTERY TO JAMES ISLAND OUT 10 NM-COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE OUT 10 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER OUT
10 NM-WEST ENTRANCE U.S. WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR CENTRAL
U.S. WATERS STRAIT OF JUAN DE FUCA-EAST ENTRANCE U.S.
WATERS STRAIT OF JUAN DE FUCA.
SMALL CRAFT ADVISORY UNTIL 10 AM PST FRIDAY FOR COASTAL WATERS
FROM CAPE FLATTERY TO JAMES ISLAND 10 TO 60 NM-COASTAL
WATERS FROM JAMES ISLAND TO POINT GRENVILLE 10 TO 60 NM-
COASTAL WATERS FROM POINT GRENVILLE TO CAPE SHOALWATER 10
TO 60 NM.
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