659
FXUS66 KPQR 152304
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
304 PM PST SUN DEC 15 2024
SYNOPSIS
PRECIPITATION THROUGH THE NEXT SEVERAL DAYS WITH
PERIODS OF HEAVY SNOW OVER THE CASCADES ON MONDAY. RIDGING ON
FRIDAY AND THEN A LOW PRESSURE SYSTEM ARRIVES ONCE AGAIN. BREEZY
EASTERLY WINDS POSSIBLE ON FRIDAY AND SATURDAY.
SHORT TERM...NOW THROUGH MONDAY
CONDITIONS REMAIN BENIGN
THIS AFTERNOON AND INTO THE EVENING AS A TRANSIENT RIDGE CROSSES
THE AREA. A TROUGH SITUATED OVER THE NORTHEAST PACIFIC IS
SUPPORTING A ~984 MB SURFACE LOW NEAR 47.0 N AND 147.0 W WITH A
FRONTAL SYSTEM EXTENDING SOUTHEAST TOWARD THE WEST COAST. THE
LOW IS EXPECTED TO SHIFT EASTWARD TOWARD THE PNW COAST TONIGHT
AND WILL BRING RAIN TO THE LOWLANDS AND MODERATE TO HEAVY SNOW
IN THE CASCADES. RAINFALL TOTALS THROUGH 10 AM MONDAY IN THE
WILLAMETTE VALLEY ARE EXPECTED TO BE BETWEEN 0.5-0.75 INCHES
WITH PROBABILITIES OF 0.5 INCHES AROUND 60-80% AND 0.75 PROBS
AROUND 20-30%. HIGHER TOTALS ARE EXPECTED ACROSS THE COAST AND
COAST RANGE AT 0.75 TO 1.25 INCHES. SNOW IN THE CASCADES WILL BE
HEAVY ABOVE 4000 FEET WHERE 12 TO 20 INCHES COULD FALL TONIGHT
THROUGH MONDAY NIGHT. SNOW AROUND THE PASSES WILL MAKE TRAVEL
HAZARDOUS, WARRANTING A WINTER WEATHER WARNING ABOVE 4000 FEET
FOR THE OR CASCADES. WA CASCADES WILL SEE SNOW TOTALS GENERALLY
BETWEEN 4-10 INCHES PROMPTING A WINTER WEATHER ADVISORY. THERE
IS STILL SOME UNCERTAINTY IN WHERE EXACTLY THE LOW TRACKS
TONIGHT BUT A SLIGHT DECREASE IN SPREAD IS APPARENT IN THE
LATEST MODEL SUITE. LOOKS LIKE THE LOW WILL BE OFF THE SOUTHERN
WA AND NORTHERN OR COASTS. WOULD EXPECT THE LOWER END OF THE
EXPECTED PRECIP IF THE LOW STAYS FARTHER NORTH WITH THE HIGHER
AMOUNTS EXPECTED IF THE LOW TAKES THE PATH THAT IS SLIGHTLY
SOUTH. -BATZ
LONG TERM
ONSHORE ZONAL FLOW PERSISTS ONCE THE LOW PRESSURE
SYSTEM FROM MONDAY ERODES. OVERALL THOUGH THE PATTERN CAN BE
DESCRIBED AS A SERIES OF SHORT WAVE PERTURBATIONS EACH BRINGING
PERIODS OF SHOWERS AND LIGHT PRECIPITATION. ENSEMBLE MODELS SHOW
A MIXED BAG OF OPTIONS FOR A FORECAST SO CONFIDENCE IS
INCREDIBLY LOW AT THIS POINT. ULTIMATELY, PREPARE FOR SHOWERY
CONDITIONS. ONE FEATURE THAT IS COMING INTO LIGHT IS A TROUGH
ALOFT ON FRIDAY. THIS TROUGH CAN EASILY BE OBSERVED IN THE JET
STREAM AND 500 MB HEIGHTS. THIS SYSTEM WILL BRING PRECIPITATION
ONCE AGAIN BUT, JUST HOW MUCH WILL BE DEPENDENT ON WHERE THE LOW
SETS UP. ONE ASPECT OF THE FORECAST WILL BE ON EASTERLY WINDS
THROUGH THE COLUMBIA RIVER GORGE. THE DETERMINISTIC GFS IS
SHOWING A PRESSURE GRADIENT UP TO -8 MB, WHERE THE GEFS IS
AROUND -3 MB. THIS SHOWS THAT THERE IS THE POTENTIAL FOR A WINDY
DAY ON FRIDAY. -MUESSLE
AVIATION
NEXT SYSTEM WILL BE A WARM FRONT THAT WILL SPREAD RAIN
ACROSS THE AREA THIS EVENING WITH A COLD FRONT LATE TONIGHT.
CURRENTLY VFR PREVAILS BUT WITH A SOLID AREA OF MVFR NORTH OF
ABOUT KUAO. HREF SHOWS PROBABILITIES FOR MVFR DECREASING (AND VFR
INCREASING) FROM ABOUT 00Z MON. THEN AFTER 05Z MON WIDESPREAD MVFR
DEVELOPS WHICH WILL LIKELY LAST TO 15Z MONDAY, THEN MAY SEE
BETTER CHANCES FOR VFR CONDITIONS. THEN ANOTHER SYSTEM ROTATES
INTO THE AREA MONDAY NIGHT FOR ANOTHER ROUND OF RAIN AND MVFR
CONDITIONS.
PDX AND APPROACHES...PREDOMINATELY MVFR CIGS IN THE AREA EXPECTED
TO TREND TO VFR AFTER 00Z MON PER HREF PROBABILITIES. BUT GIVEN
RAIN DEVELOPING RIGHT OVER THE AREA, MIGHT BE DELAYED A BIT.
THEN AFTER ABOUT 05Z MON MVFR RETURNS AS RAIN INCREASES. SOUTHEAST
WINDS EXPECTED AROUND 4-8 KT, INCREASING 8 TO 12 KT LATER
TONIGHT. /MH /DH
MARINE
SOUTH TO SOUTHEAST WINDS INCREASE TONIGHT AHEAD OF AN
APPROACHING FRONTAL SYSTEM. LOW PRESSURE WELL OFFSHORE WILL SEND
A WARM FRONT ACROSS THE COASTAL WATERS, WITH GALES EXPECTED
ACROSS THE OUTER COASTAL WATERS TONIGHT WITH GUSTS UP TO 45 KT,
STRONGEST BEYOND 20 NM. SOUTHEASTERLY WINDS ACROSS THE INNER
COASTAL WATERS WILL LIKELY REMAIN BELOW GALE FORCE CRITERIA EXCEPT
FOR AN HOUR OR TWO AS AN OCCLUDING COLD FRONT SWEEPS ACROSS THE
COASTAL WATERS AFTER MIDNIGHT. WINDS REMAIN SOUTHERLY ON MONDAY AS
ANOTHER, BUT WEAKER, FRONT MOVES ACROSS THE WATERS LATER MONDAY.
THEN A STRONGER FRONT APPROACHES TUESDAY, LIKELY (70% CHANCE) FOR
GALES BY TUESDAY AFTERNOON.
SEAS NEAR 10 FT THIS AFTERNOON. THE NORTHWESTERLY SWELL WILL
CONTINUE TO SUBSIDE THROUGH TONIGHT, BUT A FRESH SOUTHWESTERLY
SWELL WILL BUILD SEAS TO AROUND 13 TO 15 FT BY EARLY MONDAY
MORNING. SEAS SUBSIDE AGAIN BEFORE A MID PERIOD SOUTHWESTERLY
SWELL PUSHES INTO THE COASTAL WATERS, BUILDING SEAS AGAIN INTO THE
MID TO UPPER TEENS MON NIGHT INTO TUESDAY MORNING. WITH THAT HAVE
ISSUED A HAZARDOUS SEAS WATCH FOR MONDAY NIGHT THROUGH TUESDAY
MORNING. SEAS WILL LIKELY REMAIN IN THE MID TO UPPER TEENS BEYOND
TUESDAY MORNING WITH GALES PROBABLY RETURN TUESDAY AFTERNOON.
ACTIVE PATTERN CONTINUES BUT AFTER MID-WEEK, VARIOUS MODEL
GUIDANCE ARE NOT IN GREAT AGREEMENT IN TIMING/STRENGTH OF SYSTEMS
AFFECTING THE WATERS. /MH
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER STORM WARNING FROM 8 PM THIS EVENING TO 10 AM PST TUESDAY
FOR ORZ126>128.
WA...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 10 AM PST
TUESDAY FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 6 AM PST MONDAY FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 4 PM PST MONDAY FOR PZZ251>253.
HAZARDOUS SEAS WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING
FOR PZZ251>253-271>273.
SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR
PZZ271>273.
GALE WARNING UNTIL 4 AM PST MONDAY FOR PZZ271>273.
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