870
FXUS66 KPQR 151115
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
315 AM 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
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
NUMEROUS SHOWERS ARE ONGOING ACROSS THE REGION
ALTHOUGH GENERALLY VFR CONDITIONS BEING REPORTED AT BOTH COASTAL
AND INLAND TERMINALS. AS WAVES OF SHOWER ACTIVITY MOVE THROUGH THE
REGION, AIRPORT SITES MAY EXPERIENCE BRIEF DROPS TO MVFR THROUGH
THIS EVENING - GENERALLY VFR EXPECTED. HOWEVER, GUIDANCES DOES
TREND INLAND SITES TOWARDS MVFR CEILINGS LATE TONIGHT INTO SUNDAY
MORNING - LOW TO MODERATE CONFIDENCE IN THE EXACT TIMING OF THIS
CATEGORY CHANGE. IMPROVEMENT TO ANY DROP IN CIGS WOULD LIKELY
OCCUR IN THE AFTERNOON. IT'S WORTH NOTING THERE IS A SLIGHT
CHANCE OF THUNDER ALONG THE COAST (15-30% PROBABILITY) THROUGH
~15Z SUNDAY AS WELL. ANOTHER APPROACHING WEATHER SYSTEM WILL
INCREASE WINDS ALONG THE COAST AFTER 18-20Z SUNDAY WITH GUSTS BACK
UP TO 20-25 KNOTS. THEN RAIN WITH THE AFOREMENTIONED DISTURBANCE
ARRIVES IN THE 02-05Z MONDAY TIME PERIOD.
PDX AND APPROACHES...GENERALLY VFR CONDITIONS THROUGH THE TAF
PERIOD WITH AROUND A 25-35% CHANCE FOR MVFR CIGS STARTING ~08Z.
THESE PROBABILITIES PEAK AROUND 50% 16-20Z BEFORE QUICKLY FALLING
OFF WITH HIGHER CONFIDENCE IN VFR CONDITIONS SUNDAY AFTERNOON.
EXPECT SOUTH TO SOUTHWEST WINDS AROUND 8 TO 15 KNOTS THROUGH
SUNDAY MORNING TURNING MORE EASTERLY AS THE DAY GOES ON.
-SCHULDT
MARINE
THE LOW WHICH CONTINUES TO BE THE PRIMARY WEATHER
MAKER WILL MAINTAIN SOUTHERLY/SOUTHWESTERLY WINDS THROUGH
TONIGHT AS THE LOW CONTINUES MARCHING INLAND ACROSS VANCOUVER
ISLAND. EVENTUALLY WINDS BECOME WESTERLY WITH GUSTS UP TO 25 KT
BY TONIGHT/EARLY SUNDAY MORNING. CURRENT OBSERVATIONS HAVE SEAS
AROUND 20 TO 24 FT WITH A PERIOD OF 14-15 SECONDS. EXPECT SEAS
TO GRADUALLY SUBSIDE TOWARDS THE UPPER TEENS (17-19 FT) BY EARLY
SUNDAY MORNING. THEREFORE, HAVE ADJUSTED THE TIMING OF THE
CURRENT HAZARDOUS SEAS WITH A SMALL CRAFT ADVISORY COMING ONLINE
VERY EARLY SUNDAY MORNING AS SEAS CONTINUE TO SUBSIDE TOWARD 11
TO 13 FT.
THE SOUTHERLY/SOUTHWESTERLY WINDS WILL BECOME MORE WESTERLY
OVERNIGHT, BUT BECOME SOUTHERLY AGAIN ON SUNDAY AS ANOTHER
FRONTAL SYSTEM IS EXPECTED TO MOVE ACROSS THE WATERS LATE SUNDAY
INTO MONDAY. THIS SYSTEM WILL LIKELY BRING ANOTHER ROUND OF GALES
TO ALL THE COASTAL WATERS, WITH SEAS BUILDING INTO THE LOWER TO
MID TEENS. THEREFORE HAVE ISSUES A GALE WATCH FOR ALL WATERS
STARTING SUNDAY AFTERNOON. OVERALL, EXPECT ACTIVE WEATHER TO
CONTINUE IN SOME FORM THROUGH AT LEAST THE MIDDLE OF THE UPCOMING
WEEK. /42
PQR WATCHES/WARNINGS/ADVISORIES
OR...WINTER WEATHER ADVISORY UNTIL 10 AM PST THIS MORNING FOR
ORZ126>128.
WA...WINTER WEATHER ADVISORY UNTIL 4 AM PST EARLY THIS MORNING FOR
WAZ211.
PZ...HAZARDOUS SEAS WARNING UNTIL 4 AM PST EARLY THIS MORNING FOR
PZZ210-251>253-271>273.
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.
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