794
FXUS66 KPQR 191120
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
320 AM PST THU DEC 19 2024
SYNOPSIS
THE WEATHER PATTERN REMAINS FAIRLY ACTIVE GOING
THROUGH THE NEXT WEEK, HOWEVER, CONDITIONS LOOK RELATIVELY
QUIET THROUGH FRIDAY. WEAK FRONTS BRING CHANCES FOR LIGHT
PRECIPITATION TO THE REGION, MAINLY ALONG THE COAST AND COAST
RANGE - MINIMAL WEATHER IMPACTS. THEN WIDESPREAD RAIN RETURNS
THIS WEEKEND INTO EARLY NEXT WEEK AS A PARADE OF WEATHER SYSTEMS
TAKE AIM AT THE PACIFIC NORTHWEST.
SHORT TERM...TODAY THROUGH SATURDAY NIGHT
EXPECT A BRIEF
CONTINUATION OF CALMER CONDITIONS AS FAR AS DECEMBER WEATHER IS
CONCERNED THROUGH FRIDAY AS A COUPLE WEAKER WEATHER
DISTURBANCES CLIP THE REGION. CURRENT SATELLITE AND RADAR
OBSERVATIONS EARLY THIS MORNING SHOW A SOME LIGHT PRECIPITATION
MOVING INTO FAR NW OREGON, THE SOUTH WASHINGTON COAST, AND
WILLAPA HILLS ASSOCIATED WITH A WARM-FRONTAL BOUNDARY.
OTHERWISE, DRY WEATHER PREVAILS. MODELS CONTINUE TO SHOW THE
BULK OF THIS PRECIPITATION HOLDING ALONG THE COASTLINE INTO THE
COAST RANGE, KEEPING THE WILLAMETTE VALLEY AND OREGON CASCADES
DRY. CAN’T COMPLETELY RULE OUT (15-20%) A SHOWER CLIPPING THE
PORTLAND/VANCOUVER METRO THIS MORNING BUT QPF FROM ANY ACTIVITY
WOULD LIKELY(80%) BE LESS THAN 0.05”. COME THE LATE AFTERNOON
AND EVENING HOURS A TRAILING COLD FRONT THEN SWINGS INTO THE
WESTERN OR/WA RETURNING PRECIPITATION CHANCES AND PROVIDING AN
ADDITIONAL 0.1-0.2" ALONG THE NORTH OREGON AND SOUTH WASHINGTON
COAST/COAST RANGE. THE LATEST NBM SUGGESTS A 20-30% CHANCE
THESE LOCATIONS RECEIVE MORE THAN 0.50 INCH OF QPF THROUGH
THURSDAY NIGHT, WHICH WOULD MOST LIKELY OCCUR IF THESE FRONTS
END UP MORE PERSISTENT AND STRONGER THAN FORECAST - SOMETHING TO
WATCH. STILL, THIS SECOND FRONTAL FEATURE IS EXPECTED TO WEAKEN
AND MOVE EASTWARD OUT THE AREA MID TO LATE EVENING FOLLOWED BY
DRIER CONDITIONS RETURNING THURSDAY NIGHT.
FRIDAY LOOKS SIMILAR TO THE DAY PRIOR (THURSDAY) WITH MOSTLY
DRY CONDITIONS PERSISTING FOR INLAND VALLEY LOCATIONS,
ESPECIALLY DURING THE MORNING HOURS. YET ANOTHER WEAK FRONTAL
SYSTEM SWINGS INTO WESTERN OREGON AND WASHINGTON DURING THE
AFTERNOON BRINGING LIGHT PRECIPITATION TO THE COAST AND COAST
RANGE AGAIN. THE TOTAL RAINFALL ASSOCIATED WITH THIS THIRD
DISTURBANCE SHOULD ONLY AMOUNT TO 0.1-0.2” FOR THE COAST/COAST
RANGE ACCORDING TO THE NBM, LESS ELSEWHERE.
THIS FAIRLY BENIGN PATTERN DOES COME TO AN END EARLY SATURDAY
MORNING AS AN ELONGATED NEGATIVELY TILTED UPPER-LEVEL TROUGH
AND ACCOMPANYING COLD FRONT SWINGS INTO THE PACIFIC NORTHWEST
FACILITATING MORE WIDESPREAD PRECIPITATION COMPARED TO THE
EARLIER SYSTEMS. THE CURRENT TIMING BRINGS RAIN TO THE COAST
DURING EARLY MORNING HOURS 4AM-9AM FOLLOWED BY THE INTERIOR
VALLEYS AND CASCADES 9AM-NOON. OVERALL QPF VALUES WILL BE
DECENT OWING TO GOOD MOISTURE TRANSPORT WITH 0.5-1.5” FOR THE
COAST/COAST RANGE, 0.2-0.5” IN THE WILLAMETTE VALLEY, AND
0.4-1.3” ACROSS THE CASCADES (SNOW LEVELS 5000-6000FT) THROUGH
SATURDAY NIGHT. THAT SAID, DETERMINISTIC AND ENSEMBLE GUIDANCE
KEEP THE HIGHEST QPF VALUES TO OUR SOUTH IN FAR SW OREGON AND
NW CALIFORNIA. SHOULD THE AXIS OF THE HEAVIER PRECIPITATION
SHIFT NORTHWARD QPF WOULD NEED TO BY NUDGED UPWARD SIGNIFICANTLY
BUT FOR NOW THIS SEEMS LIKE AN OUTLYING SCENARIO.
IT’S ALSO WORTH HIGHLIGHTING DUE TO THE TRACK AND ORIENTATION
OF THE TROUGH, SURFACE PRESSURE GRADIENTS ACROSS THE CASCADES
WILL TIGHTEN LEADING TO BREEZY/GUSTY EAST WINDS THROUGH THE
COLUMBIA RIVER GORGE PEAKING LATE FRIDAY NIGHT INTO EARLY
SATURDAY MORNING - THE GFS AND NAM HAVE THE TTD TO DLS GRADIENT
STRENGTHENING TO A -6MB TO -8MB DIFFERENCE. OFFSHORE WINDS WILL
BE PRESENT THURSDAY AND FRIDAY TOO BUT WON’T BE NEARLY AS STRONG
COMPARATIVELY. GIVEN THE AFOREMENTIONED GRADIENT IT’S A PRETTY
SAFE BET SPOTS LIKE TROUTDALE WILL SEE GUSTS UP TO 30-45 MPH
WITH GUSTS CLOSER TO 45-50+ MPH FOR CORBETT AND THREE CORNER
ROCK. -SCHULDT
LONG TERM...SUNDAY THROUGH THURSDAY
BOTH ENSEMBLE AND
DETERMINISTIC GUIDANCE IS IN FAIRLY GOOD AGREEMENT PORTRAYING AN
ACTIVE AND PROGRESSIVE WEATHER PATTERN MOVING FORWARD WITH
BROAD SOUTHWEST TO WEST-SOUTHWEST FLOW ALOFT STEERING A PARADE
WEATHER SYSTEMS INTO THE PACIFIC NORTHWEST. CONFIDENCE REMAINS
HIGH IN THE ARRIVAL OF ANOTHER ROBUST FRONTAL SYSTEM ON SUNDAY
INTO SUNDAY NIGHT. AFTER A TRANSIENT RIDGE ON MONDAY ANOTHER
SYSTEM LIKELY MOVES OVERHEAD COME TUESDAY. ON AND ON THIS
PATTERN REPEATS WITH A TROUGH FEATURE MOVING WSW TO ENE INTO
WESTERN CONUS EVERY 24-48 HOURS THROUGH THE END OF THE WEEK. THE
WPC CLUSTERS SHOW SURPRISINGLY LITTLE VARIATION BETWEEN
ENSEMBLE MEMBERS RESOLVING THE LARGE SCALE PATTERN EVEN OUT
PAST DAYS SEVEN AND EIGHT. STILL, FINER DETAILS LIKE THE
SURFACE LOW PRESSURE PLACEMENT ASSOCIATED WITH A STRONG SYSTEM
SLATED FOR THE WEDNESDAY/THURSDAY TIME PERIOD WILL MODULATE OUR
IMPACTS LOCALLY - WE CONTINUE TO MONITOR CHANCES FOR
POTENTIALLY STRONG WINDS BUT CONFIDENCE AT THIS TIMESCALE IS LOW
TO MODERATE. WITH THE WET PATTERN CONTINUING ALL OF NEXT WEEK,
WILL ALSO SEE RISES ON LOCAL RIVERS AS SNOW LEVEL BOUNCE BETWEEN
3,500 AND 7,000FT. THE LATEST HEFS SUGGESTS A 15-35% CHANCE
THAT RIVERS ALONG THE COAST/COAST RANGE REACH AT LEAST MINOR
FLOOD STAGE IN THE NEXT 10 DAYS. -SCHULDT
AVIATION
LIFR FOG DEVELOPED LAST EVENING AND SPREADING
OVERNIGHT ACROSS INLAND TERMINALS. BUT EAST WINDS FROM THE GORGE
IS MAINTAINING VFR IN THE PDX AREA. EUG IS THE OTHER HOLDOUT FROM
FOG/LOW CLOUDS, BUT SOME GUIDANCE SHOWS IFR CONDITIONS 12-17Z.
OVERALL SHOULD SEE FOG DISSIPATING 18-20Z FOR A RETURN TO VFR AS
AN APPROACHING FRONT BRINGS SOME MIXING TO THE LOWER LEVELS. THIS
FRONT SHOULD BRING SOME LIGHT RAIN AND AREAS OF MVFR TO THE
COAST, BUT NOT GET MUCH PAST THE COASTAL MOUNTAINS. A SIMILAR
SETUP FOR FOG AND LOW STRATUS AT INLAND TERMINALS DEVELOP TONIGHT.
PDX AND APPROACHES...VFR THROUGHOUT THE PERIOD. ABOUT A 10-20%
CHANCE FOR LIGHT RAIN LATER THIS AFTERNOON AND EVENING. EAST
WINDS 8 TO 20 KT WITH STRONGEST WINDS TOWARDS THE GORGE.
MARINE
AN ACTIVE WEATHER PATTERN CONTINUES THROUGH THE
MAJORITY OF THE WEEK AS A SERIES OF SYSTEMS MOVE TO THE REGION AS
LOW PRESSURE WELL OFFSHORE ROTATES FRONT TO THE COASTAL WATERS.
THE NEXT SYSTEM WILL ARRIVE TODAY TO BRING SMALL CRAFT ADVISORY
WITH GALES EXPECTED FOR THE OUTER ZONES. AFTER A BRIEF BREAK LATER
TONIGHT INTO FRIDAY MORNING, ADDITIONAL SYSTEMS AFFECT THE WATERS
LATER FRIDAY INTO SATURDAY, AND SUNDAY. THESE STORMS APPEAR A BIT
STRONGER WITH GALE TO STORM FORCE WINDS POSSIBLE.
IN ADDITION TO THE INCREASING WINDS, SEAS ARE ALSO EXPECTED TO
BUILD TOWARDS THE MID-TEENS BY FRIDAY/SATURDAY. SATURDAY
AFTERNOON SEAS IN THE UPPER TEENS WITH THE OUTER WATERS LIKELY
BUILDING TOWARDS 20-22 FT SUNDAY. SEAS WILL REMAIN IN THE LOW 20S
THROUGH SUNDAY AND INTO MONDAY FOR ALL WATERS. THERE REMAINS SOME
UNCERTAINTY AS TO THE EXACT TRACK AND STRENGTH OF THE
AFOREMENTIONED SYSTEMS, BUT WE WILL BE PAYING CLOSE ATTENTION AND
ADJUSTING THE FORECAST AS NEEDED. /MH /42
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY UNTIL 10 PM PST THIS EVENING FOR PZZ210.
SMALL CRAFT ADVISORY UNTIL 4 AM PST FRIDAY FOR PZZ251>253.
GALE WARNING FROM 7 AM THIS MORNING TO 4 PM PST THIS AFTERNOON
FOR PZZ271>273.
WWW.WEATHER.GOV/PORTLAND
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