303
FXUS66 KPQR 180518 AAA
AFDPQR
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PORTLAND OR
1015 PM PDT FRI APR 17 2026
..UPDATED AVIATION DISCUSSION
SYNOPSIS
A WARMING TREND CONTINUES INTO SATURDAY WITH MILD
SPRING CONDITIONS EXPECTED. ATTENTION THEN TURNS TO EARLY NEXT WEEK,
WHERE MODERATE TO HIGH CONFIDENCE EXISTS IN A DEVELOPING UPPER-
LEVEL-LOW OFFSHORE INFLUENCING TEMPERATURES AND PRECIPITATION
CHANCES. A WEAK FRONTAL SYSTEM MAY BRING A FEW LIGHT SHOWERS LATE
SATURDAY, THOUGH IMPACTS APPEAR MINIMAL.
SHORT TERM...NOW THROUGH SUNDAY NIGHT
A WARMING TREND IS
UNDERWAY THIS AFTERNOON, WITH TEMPERATURES RISING INTO THE UPPER 50S
TO LOW 60S INLAND AND MID TO UPPER 50S ALONG THE COAST UNDER PARTLY
TO MOSTLY CLEAR SKIES. A WEAK THERMAL TROUGH REMAINS IN PLACE
THROUGH SATURDAY, SUPPORTING LIGHT OFFSHORE FLOW ALONG THE EAST
SLOPES OF THE COAST RANGE AND CASCADES AND GENERALLY LIGHT NORTHERLY
FLOW THROUGH THE WILLAMETTE VALLEY. THIS PATTERN WILL MAINTAIN
MOSTLY DRY CONDITIONS ASIDE FROM THE LIMITED LATE-DAY SHOWER
POTENTIAL.
CONDITIONS TONIGHT WILL BE MORE MARGINAL FOR WIDESPREAD FROST
DEVELOPMENT COMPARED TO RECENT MORNINGS, THOUGH LOCALIZED IMPACTS
REMAIN POSSIBLE IN FAVORED VALLEY LOCATIONS. A FROST ADVISORY HAS
BEEN ISSUED FOR THE SOUTHERN WILLAMETTE VALLEY AND UPPER HOOD RIVER
VALLEY FOR TONIGHT INTO SATURDAY MORNING. WHILE OVERALL CONDITIONS
ARE MARGINAL, VARIABILITY IN CLOUD COVER WILL PLAY A KEY ROLE IN
OVERNIGHT COOLING, WITH MORE PERSISTENT BREAKS POTENTIALLY ALLOWING
FOR LOCALIZED FROST DEVELOPMENT IN SHELTERED AREAS. WHILE MOST
INLAND LOCATIONS ARE EXPECTED TO FALL INTO THE UPPER 30S TO LOW 40S,
THE SOUTHERN WILLAMETTE VALLEY AND UPPER HOOD RIVER VALLEY MAY DROP
INTO THE MID 30S. PROBABILITIES FOR TEMPERATURES DROPPING BELOW 37
DEGREES REMAIN AROUND 40-50% IN THE SOUTHERN WILLAMETTE VALLEY, 50-
70% IN THE UPPER HOOD RIVER VALLEY ABOVE 1500 FT, AND 10-30%
ELSEWHERE INLAND.
ON SATURDAY, WEAK RIDGING SUPPORTS CONTINUED MILD CONDITIONS, WITH
INLAND HIGHS REACHING THE LOW 70S AND COASTAL AREAS REMAINING IN THE
UPPER 50S TO LOW 60S. A WEAK FRONTAL BOUNDARY APPROACHING FROM THE
NORTHWEST MAY BRING INCREASING CLOUD COVER AND A SLIGHT CHANCE OF
LIGHT SHOWERS LATE IN THE DAY, THOUGH RECENT TRENDS CONTINUE TO
WEAKEN THIS SYSTEM WITH MINIMAL EXPECTED IMPACTS.
AN UPPER-LEVEL LOW DEVELOPS OFFSHORE ON SUNDAY, INTRODUCING
INCREASING UNCERTAINTY. CURRENT GUIDANCE FAVORS THE SYSTEM REMAINING
OFFSHORE, THOUGH THIS WILL SUPPORT INCREASED CLOUD COVER ACROSS THE
REGION AND LIMITED PRECIPITATION CHANCES PRIMARILY ALONG THE COAST.
MOST INLAND AREAS REMAIN DRY, THOUGH SKIES MAY TREND MOSTLY CLOUDY
AT TIMES. DESPITE THIS, TEMPERATURES REMAIN UNSEASONABLY WARM, WITH
HIGHS IN THE LOW TO MID 70S EXPECTED AS A RESULT OF SOUTHERLY FLOW.
LONG TERM...MONDAY THROUGH THURSDAY
THE PRIMARY FORECAST
CONCERN EARLY NEXT WEEK CENTERS ON THE EVOLUTION OF A DEVELOPING
UPPER-LEVEL LOW OFFSHORE, WHICH WILL INTRODUCE INCREASING
UNCERTAINTY IN TEMPERATURE TRENDS AND PRECIPITATION CHANCES.
ON MONDAY, A RANGE OF OUTCOMES REMAINS POSSIBLE DEPENDING ON THE
POSITION OF THIS LOW. A FARTHER OFFSHORE TRACK WOULD SUPPORT
RELATIVELY MILD AND DRIER CONDITIONS, WHILE A CLOSER OR MORE
NORTHERLY SOLUTION WOULD FAVOR INCREASED CLOUD COVER AND A HIGHER
LIKELIHOOD OF SHOWERS. AT THIS TIME, LOW-END PRECIPITATION CHANCES
INCREASE AND BECOME MORE WIDESPREAD BY LATE IN THE DAY, WITH
TEMPERATURES GENERALLY ABOVE SEASONAL AVERAGES.
TUESDAY, ATTENTION TURNS TO A MORE ORGANIZED PACIFIC FRONTAL SYSTEM
APPROACHING THE REGION. CONFIDENCE INCREASES THAT THIS SYSTEM WILL
BRING A RETURN TO MORE WIDESPREAD PRECIPITATION LATE TUESDAY INTO
WEDNESDAY, THOUGH SOME TIMING DIFFERENCES REMAIN AMONG ENSEMBLE
MEMBERS. SPECIFICALLY, CURRENT GUIDANCE SUGGESTS THE START TIME OF
PRECIPITATION REACHING INLAND WILL VARY FROM ANY TIME BETWEEN
TUESDAY EVENING AND WEDNESDAY AFTERNOON. FROM 5 PM MONDAY TO 5 PM
TUESDAY, PRECIPITATION TOTALS IN THE LOWLANDS WILL VARY FROM 0 TO
0.6 INCHES (HIGHEST ALONG THE COAST) UNDER BEST AND WORST SCENARIOS,
WHICH CONTINUES TO REFLECT THE POOR AGREEMENT BETWEEN MODELS AT THIS
TIME.
THE MOST IMPACTFUL PERIOD LOOKS TO BE EARLY WEDNESDAY, WITH
WIDESPREAD RAIN EXPECTED ACROSS THE REGION AS THE FRONT MOVES
THROUGH, BRINGING UP TO 0.6 TO 0.9 INCHES TO THE LOWLANDS FROM 5 PM
TUESDAY TO 5 PM WEDNESDAY IN A WORST-CASE SCENARIO. WHILE EXACT
RAINFALL TOTALS REMAIN SOMEWHAT UNCERTAIN (A BEST CASE SCENARIO
COULD STILL RESULT IN 0 INCHES OF RAINFALL TOTALS), THIS SYSTEM
REPRESENTS A MORE NOTABLE SHIFT BACK TO WETTER CONDITIONS COMPARED
TO EARLIER THIS WEEK. INTO THURSDAY, THE PATTERN BEGINS TO
TRANSITION ONCE AGAIN AS THE UPPER-LEVEL SYSTEM SHIFTS INLAND AND
HEIGHTS START TO RISE. THIS WILL SUPPORT A TREND TOWARD DECREASING
PRECIPITATION AND A GRADUAL RETURN TO DRIER CONDITIONS. ~12
AVIATION
VFR CONDITIONS PREVAIL ACROSS ALL TERMINALS THROUGH
THE TAF PERIOD. EXPECT SCT/BKN HIGH CLOUDS ACROSS THE REGION
TONIGHT. TERMINALS WITH THE CLEAREST SKIES TONIGHT WILL EXPERIENCE
MORE EFFICIENT COOLING, AND THUS POTENTIAL FOR FROST DEVELOPMENT
OVER METAL SURFACES. THE HIGHEST CHANCES (40-50%) FOR FROST
DEVELOPMENT WILL BE ACROSS THE SOUTHERN WILLAMETTE VALLEY INCLUDING
KEUG. THREAT FOR FROST ENDS AFTER 15Z SAT ONCE DAYTIME HEATING
PROGRESSES. HIGH CLOUDS WILL BREAK OUT INTO MOSTLY SUNNY SKIES BY 18-
21Z SAT AS HIGH PRESSURE BUILDS OVERHEAD. VARIABLE WINDS AROUND 5 KT
OR LESS FOR MOST TERMINALS, EXCEPT SLIGHT TIGHTENING OF KTTD-KDLS
PRESSURE GRADIENTS WILL RESULT IN EASTERLY WINDS AROUND 5-10 KT IN
THE FAR EAST PORTLAND METRO (KTTD). ALONG THE COAST, LIGHT OFFSHORE
WINDS TONIGHT TURN MORE SOUTHWESTERLY AFTER 18Z SAT. THIS OFFSHORE
FLOW ALONG THE COAST WILL HELP PREVENT LOW MARINE STRATUS FROM
DEVELOPING.
KPDX AND APPROACHES...VFR CONDITIONS THROUGH THE TAF PERIOD WITH
HIGH SCT/BKN CLOUDS TONIGHT. HIGH CLOUDS GRADUALLY DECREASE ON
SATURDAY. VARIABLE WINDS AROUND 5 KT OR LESS. LIGHT EASTERLY WINDS
DEVELOPS THROUGH THE COLUMBIA RIVER GORGE AFTER 12Z SAT, BUT NOT
EXPECTED TO REACH KPDX. -10
MARINE
RELATIVELY BENIGN MARINE CONDITIONS CONTINUE THROUGH
THIS WEEKEND. NORTHERLY WINDS AROUND 10 KT CONTINUE INTO TONIGHT,
THEN TURN SOUTHERLY AHEAD OF A WEAKENING COLD FRONT ON SATURDAY.
GUSTS UP TO 20 KT MAY CONTINUE THIS AFTERNOON SOUTH OF CAPE FALCON
WITHIN 20 NM, BEFORE EASING THIS EVENING. SEAS WILL CONTINUE TO FALL
TO 3-5 FT BY TONIGHT, BUILDING ONLY SLIGHTLY TO 4-6 FT AS THE WEAK
FRONT APPROACHES.
THERE IS HIGHER FORECAST UNCERTAINTY FOR WINDS AND SEAS EARLY NEXT
WEEK AS AN AREA OF LOW PRESSURE OFFSHORE APPROACHES THE COAST. THE
PLACEMENT OF THE LOW WILL DETERMINE THE CONDITIONS ACROSS THE
WATERS, WITH THE FORECAST AT THIS LEAD TIME FAVORING INCREASING
ONSHORE FLOW THROUGH WEDNESDAY, WHEN WNW GUSTS MAY REACH 20-25 KT
BEYOND 30 NM. HIGHER WINDS AND A FRESHLY ARRIVING NW SWELL MAY PUSH
SEAS TO 10-12 FT WEDNESDAY INTO THURSDAY.
VERY STRONG EBB CURRENTS WILL CONTINUE ACROSS THE COLUMBIA RIVER BAR
EACH MORNING THROUGH TUESDAY. WITH SEAS EXPECTED TO BUILD SLIGHTLY
BY EARLY NEXT WEEK, A STEEP EBB CHOP MAY NECESSITATE SMALL CRAFT
ADVISORIES IN THE HOURS AROUND PEAK FLOW EACH DAY. -36
PQR WATCHES/WARNINGS/ADVISORIES
OR...FROST ADVISORY FROM 1 AM TO 8 AM PDT SATURDAY FOR ORZ116>118-
121.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
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X.COM/NWSPORTLAND
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