158
FXUS66 KPQR 151223 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
423 AM PST SUN DEC 15 2024
UPDATED AVIATION AND MARINE DISCUSSION, AND HAZARDS.
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
SHOWERS PERSIST THIS MORNING
WITH PERIODS OF HEAVY RAIN AND CASCADE SNOW. SNOW ACCUMULATIONS
ARE VARIED DUE TO THE SHOWERY ACTIVITY BUT IN GENERAL A FAIRLY
STEADY STREAM OF LIGHT SNOW. HAVE SEEN ANYWHERE FROM NO
ACCUMULATION TO 6 INCHES OF SNOW WITHIN THE LAST 24 HOURS.
LOOKING AT SATELLITE IMAGERY, A BATCH OF DRIER AIR IS PREPARING
TO MOVE INLAND WHICH WILL CAUSE SHOWERS TO WEAKEN THROUGH THE
DAY.
THE BREAK TODAY WILL BE SHORT LIVED IF NOTICED AT ALL AS YET
ANOTHER FRONTAL SYSTEM WILL MOVE OVER THE REGION LATE SUNDAY
INTO EARLY MONDAY. THIS FRONTAL SYSTEM IS ASSOCIATED WITH A
CLOSED LOW IN THE NORTHEAST PACIFIC. THIS LOW WILL ADVECT
EASTWARD REACHING IT'S DEEPEST POINT WELL OFFSHORE NEAR 45.5N,
-141.8W OVERNIGHT. THE FRONT ALONG THE LEADING EDGE IS ROBUST
WITH AMPLE SUPPORT ALOFT FROM THE JET STREAM AND AT THE MID-
LEVELS. DUE TO THE WESTERLY FLOW OF THE SYSTEM, THE COAST RANGE
AND CASCADES WILL EXPERIENCE THE HIGHEST PRECIPITATION AMOUNTS
WHILE THERE WILL BE LOWER ACCUMULATION IN THE INLAND VALLEYS.
BASED ON THE NBM, GOING TO SEE AROUND 0.5-0.75 INCH OF RAIN
ALONG THE COAST, AROUND 1 INCH IN THE COAST RANGE, AND AROUND
0.3 INCH THROUGH THE WILLAMETTE VALLEY IN 24 HOURS ENDING AT 10
AM MONDAY. THE SPREAD BETWEEN THE 25TH AND 75TH PERCENTILE IS
STILL QUITE LARGE WITH A DIFFERENCE OF AROUND 0.7 INCH ALONG THE
COAST AND CASCADES AND 0.3 INLAND. HIGHER RESOLUTION MODELS
THOUGH CONFLICT SLIGHTLY WITH THAT SPREAD BEING NARROWER, AND
SLIGHTLY LOWER PRECIPITATION AMOUNTS. THIS IS MAINLY DUE TO THE
LIFT WITH THIS SYSTEM AND THE TRACK OF THE LOW CENTER. IF THE
LOW SHIFTS FURTHER SOUTH, ACCUMULATIONS WILL BE LOWER AS WE SIT
ON THE NORTHERN AND WEAKER PORTION OF THE LOW. IF IT SHIFTS
SLIGHTLY MORE NORTHERLY WE WILL SEE MORE PRECIPITATION.
WITH THIS INCOMING PRECIPITATION, THE MAIN CONCERN IS GOING TO
BE SNOW IN THE CASCADES. THERE IS AROUND A 50% CHANCE OF SEEING
12 INCHES OR MORE OF SNOW IN 36 HOURS STARTING VERY EARLY MONDAY
MORNING THROUGH TUESDAY. WHILE THAT MAY BE THE PROBABILISTIC
FORECAST, THERE IS STILL A LACK OF CONFIDENCE ON EXACTLY WHERE
THE LOW WILL TRACK. HIGHEST SNOWFALL ACCUMULATIONS WILL BE ABOVE
5000 FT. THERE IS HIGHER CONFIDENCE IN 6 INCHES OR MORE
THROUGHOUT MOST OF THE CASCADES DIPPING INTO SOME OF THE HIGHER
VALLEYS OF THE FOOTHILLS. -MUESSLE
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 PERTIBATIONS 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
NORTHWEST FLOW ALOFT BECOMING WESTERLY TODAY. SHOWERS
ARE EXPECTED TO DECREASE THIS MORNING AS WEAK HIGH PRESSURE BRINGS
MORE STABLE CONDITIONS. PREDOMINATELY VFR, BUT MVFR CIGS WILL BE
POSSIBLE THROUGH THIS AFTERNOON, WITH HIGHEST CHANCES ACROSS THE
NORTHERN WILLAMETTE VALLEY. RAIN INCREASES AFTER 00Z MONDAY AS A
WARM FRONT LIFTS ACROSS THE AREA. CHANCES FOR MORE WIDESPREAD MVFR
CONDITIONS INCREASE AFTER 06-08Z MONDAY.
PDX AND APPROACHES...PREDOMINATELY MVFR CIGS THROUGH THIS MORNING,
LIKELY IMPROVING TO VFR LATER THIS AFTERNOON. DECREASING SHOWERS
TODAY. THE NEXT WEATHER SYSTEM WILL BRING RAIN INCREASING AFTER
02Z MONDAY. CONDITIONS TREND TOWARD MVFR AFTER 08Z MONDAY.
SOUTHEAST WINDS EXPECTED AROUND 4-8 KT, INCREASING LATER TONIGHT.
-DH
MARINE
WESTERLY WINDS TURN SOUTHERLY AGAIN TODAY AHEAD OF AN
APPROACHING FRONTAL SYSTEM. LOW PRESSURE WELL OFFSHORE WILL SEND A
WARM FRONT ACROSS THE COASTAL WATERS LATER TODAY, 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.
SEAS AROUND 12 TO 14 FT THIS MORNING WILL CONTINUE TO SUBSIDE
THROUGH THIS AFTERNOON TO AROUND 9 TO 10 FT. 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 WESTERLY
SWELL PUSHES INTO THE COASTAL WATERS, BUILDING SEAS AGAIN INTO THE
MID TO UPPER TEENS MON NIGHT INTO TUESDAY MORNING.
ACTIVE WEATHER CONTINUES THROUGH THE MIDDLE OF NEXT WEEK AS
ANOTHER FRONTAL SYSTEM LIKELY APPROACHES THE AREA. SOUTHERLY WINDS
ARE AGAIN LIKELY TO INCREASE WITH AT LEAST A 70% CHANCE OF GALES.
-DH
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR
ORZ126>128.
WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING
FOR ORZ126>128.
WA...WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY MORNING
FOR WAZ211.
PZ...SMALL CRAFT ADVISORY UNTIL 6 AM PST MONDAY FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 4 PM PST MONDAY FOR PZZ251>253.
SMALL CRAFT ADVISORY UNTIL 4 PM PST THIS AFTERNOON FOR
PZZ271>273.
GALE WARNING FROM 4 PM THIS AFTERNOON TO 4 AM PST MONDAY FOR
PZZ271>273.
WWW.WEATHER.GOV/PORTLAND
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