237
FXUS66 KPQR 192020
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
120 PM PDT MON OCT 19 2026
SYNOPSIS
LARGELY DRY WEATHER EXPECTED THROUGH MIDWEEK. NEAR
NORMAL TEMPERATURES TODAY WILL WARM ABOVE AVERAGE TUESDAY AND
WEDNESDAY. CHANCES FOR WETTER AND COOLER WEATHER RETURN LATE IN
THE WEEK WITH POTENTIAL FOR A MORE ROBUST SYSTEM NEXT WEEKEND.
DISCUSSION...NOW THROUGH SUNDAY
AN UPPER-LEVEL TROUGH OVER
THE NORTHEAST PACIFIC IS TAKING ON AN ELONGATED APPEARANCE IN
SATELLITE IMAGERY AS IT BEGINS TO CUTOFF FROM THE MEAN FLOW. THE
DEVELOPING UPPER LOW IS CENTERED NEAR 44.5N/131.5W AS OF MIDDAY
MONDAY, OR JUST OVER 350 MILES WEST OF NEWPORT, AND IS EXPECTED
TO TRACK SOUTH OFF THE CALIFORNIA COAST THROUGH TONIGHT. A
NARROW BAND OF CLOUDS WITHIN A DEFORMATION ZONE ON THE EASTERN
FLANK OF THE TROUGH IS CONTINUING TO PRODUCE MODEST RADAR
RETURNS EAST OF THE CASCADE CREST, HOWEVER OBSERVATIONS OF RAIN
REACHING THE SURFACE HAVE BEEN FEW AND FAR BETWEEN. AS THIS
FEATURE PIVOTS WEST, THERE ARE LOW CHANCES, 10-20%, OF LIGHT
RAIN IN THE LINN AND LANE COUNTY CASCADES THROUGH THIS EVENING.
OTHERWISE, DRY CONDITIONS ARE EXPECTED THROUGH AT LEAST
THURSDAY. UPPER-LEVEL RIDGING DEVELOPING OVER TOP OF THE CLOSED
LOW WILL SUPPORT OFFSHORE FLOW, ALTHOUGH THE MAGNITUDE OF THE
PRESSURE GRADIENT SHOULD NOT BE ENOUGH TO YIELD IMPACTFUL WINDS.
NONETHELESS, TYPICALLY WINDY SPOTS IN THE WESTERN COLUMBIA GORGE
AND NEAR EXPOSED RIDGES IN THE CASCADES WILL LIKELY SEE PERIOD
OF BREEZY EAST WINDS, ESPECIALLY OVERNIGHT AND IN THE EARLY
MORNING. THIS OFFSHORE FLOW WILL ALSO SUPPORT TEMPERATURES
REACHING AROUND 10 DEGREES ABOVE NORMAL TUESDAY AND WEDNESDAY,
TRANSLATING TO AFTERNOON HIGHS IN THE 60S ON THE COAST AND IN
TERRAIN, AND IN THE LOW TO MID 70S WITHIN INLAND VALLEYS.
THERE CONTINUES TO BE GOOD CONSENSUS THAT PROGRESSIVE TROUGHING
WILL RETURN TO THE REGION THURSDAY INTO FRIDAY, WHILE THE UPPER
LOW ALSO MOVES INLAND OVER CALIFORNIA SUPPORTING MOISTURE
TRANSPORT ABOUT ITS EASTERN FLANK AND INTO CENTRAL OREGON. THIS
COMBINATION WILL SUPPORT MODEST PRECIPITATION CHANCES AS HIGH AS
25-50% IN THE LANE AND LINN COUNTY CASCADES, BUT MORE WIDESPREAD
CHANCES OF 10-15%. WHERE RAIN DOES FALL, IT WILL LIKELY BE VERY
LIGHT AND FAIL TO AMOUNT TO SIGNIFICANT ACCUMULATIONS. THE
APPROACHING TROUGH WILL ALSO RESTORE ONSHORE FLOW AND SEE
TEMPERATURES FALL BACK TO MORE SEASONABLE VALUES FROM THURSDAY
THROUGH THE WEEKEND.
UNCERTAINTY IN THE FORECAST INCREASES THIS WEEKEND AS LONG-RANGE
GUIDANCE REMAINS MIXED ON THE EVOLUTION OF YET ANOTHER TROUGH
OVER THE GULF OF ALASKA. MOST ENSEMBLE MEMBERS DEPICT AN
OCCLUDING SURFACE LOW APPROACHING THE COAST SOMEWHERE BETWEEN
FLORENCE AND CAPE FLATTERY AT THE NORTHWESTERN TIP OF THE
OLYMPIC PENINSULA, WITH SOME THEN BRINGING THE SYSTEM INLAND
WHILE OTHERS SEE IT FILL AND RETROGRADE OVER THE WATERS OFF
WASHINGTON STATE. THE INTENSITY OF THIS LOW ALSO REMAINS IN
QUESTION, WITH A LOW TO MODERATE CHANCE OF DEEPENING TO AROUND
990 HPA OR LOWER. IMPACTS FROM THIS SYSTEM MAY BE TWO-FOLD:
THERE IS POTENTIAL FOR WIDESPREAD RAINFALL AND STRONG WINDS
CANNOT BE RULED OUT. IN TERMS OF RAINFALL, EASTWARD MOISTURE
TRANSPORT ON THE SOUTHERN FLANK OF THE LOW COULD AMOUNT TO THE
FIRST ATMOSPHERIC RIVER OF THE SEASON, HOWEVER THE DURATION OF
THE MOISTURE FLUX AS WELL AS THE MOISTURE FLUX MAGNITUDE DO NOT
AT THIS POINT APPEAR SUFFICIENT TO YIELD PRECIPITATION TOTALS
WHICH WOULD RAISE FLOODING CONCERNS AS AREA RIVERS REMAIN NEAR
ANNUAL MINIMUM STREAMFLOW THANKS TO A LARGELY DRY OCTOBER THUS
FAR. IF THE SURFACE LOW BECOMES DEEP ENOUGH AND APPROACHES NEAR
ENOUGH TO THE COAST, COASTAL COMMUNITIES MAY EXPERIENCE STRONG
WINDS. AT THIS POINT, THE CHANCES FOR PEAK WIND GUSTS OF 40 MPH
OR HIGHER AT THE COAST ON SATURDAY ARE 15-25%.
AVIATION...THROUGH 00Z WEDNESDAY
A LOW PRESSURE SYSTEM
DROPPING SOUTHWARD WELL OFFSHORE WILL CONTINUE TO SEND SCATTERED
HIGH CLOUDS OVER THE AREA THROUGH 00Z WEDNESDAY. HIGH CLOUDS
SHOULD BECOME THICKER TONIGHT, HELPING TO PREVENT FOG
DEVELOPMENT. CONFIDENCE IS HIGH (>90%) FOR PREDOMINANTLY VFR
FLIGHT CONDITIONS THROUGH 00Z WEDNESDAY. WINDS WILL REMAIN LIGHT
TODAY AND TONIGHT AT LESS THAN 5-10 KT BEFORE OFFSHORE WINDS
DEVELOP SOMETIME BETWEEN 15-18Z TUESDAY, BRINGING INCREASING
EASTERLY WINDS TO KTTD AND INCREASING NORTHEAST WINDS TO KUAO.
WINDS WILL INCREASE OUT OF THE NORTH FROM KSLE TO KEUG.
KPDX AND APPROACHES...VFR FLIGHTS CONDITIONS WILL CONTINUE
THROUGH 00Z WEDNESDAY WITH SCATTERED HIGH CLOUDS BECOMING
BROKEN TONIGHT. LIGHT WINDS SHOULD BECOME NORTHWESTERLY SOMETIME
BETWEEN 22Z MONDAY AND 00Z TUESDAY, SUSTAINED AROUND 5 KT.
EASTERLY WINDS ARE EXPECTED TO DEVELOP AT KPDX AROUND 18-19Z
TUESDAY, SUSTAINED AROUND 8-11 KT. -23
MARINE
A LOW PRESSURE SYSTEM DROPPING SOUTHWARD WELL OFFSHORE
WILL GENERATE A STRONGER WESTERLY SWELL ARRIVING THIS EVENING
WHICH WILL PUSH SEAS TO NEAR 10 FT, HIGHEST BEYOND 10-20 NM
OFFSHORE WHERE A SMALL CRAFT ADVISORY IS IN EFFECT STARTING AT 5
PM TODAY.
WINDS TURN NORTHERLY AFTER SUNSET TODAY AND INCREASE NOTICEABLY
TONIGHT IN THE WAKE OF THE PASSING SYSTEM. WIDESPREAD WIND GUSTS
UP TO 25 KT WILL BE POSSIBLE OVER THE OUTER WATERS BEYOND 10 NM
OFFSHORE LATE TONIGHT INTO TOMORROW AFTERNOON. ALTHOUGH WAVE
HEIGHTS WILL BE ON THE DECREASE TOMORROW, THE INCREASE IN WIND
SPEEDS WILL MAINTAIN HAZARDOUS CONDITIONS FOR SMALL CRAFT.
THEREFORE, THE SMALL CRAFT ADVISORY IN EFFECT FOR THE OUTER
WATERS BEGINNING AT 5 PM TODAY WILL REMAIN IN EFFECT THROUGH 5
PM TOMORROW. BEYOND 5 PM TOMORROW, WINDS AND SEAS WILL BE ON THE
DECREASE AS HIGH PRESSURE RETURNS.
WINDS AND SEAS ARE SET TO INCREASE AGAIN THURSDAY INTO FRIDAY
MORNING WITH THE PASSAGE OF A WEAK COLD FRONT, ESPECIALLY OVER
THE NORTHERN WATERS TO THE NORTH OF CAPE FALCON WHERE
CONDITIONS WILL LIKELY BE HAZARDOUS TO SMALL CRAFT. THERE IS THE
POTENTIAL FOR A STRONGER LOW PRESSURE SYSTEM OVER THE UPCOMING
WEEKEND, BRINGING A 20-40% CHANCE FOR GALE FORCE WIND GUSTS AND
SEAS OVER 10 FEET. OVERALL CONFIDENCE IN THE EXACT TRACK AND
STRENGTH OF THIS POTENTIAL LOW PRESSURE SYSTEM IS LOW AT THIS
TIME, AND THE FORECAST IS WORTH MONITORING OVER THE NEXT SEVERAL
DAYS. -23
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...SMALL CRAFT ADVISORY FROM 5 PM THIS AFTERNOON TO 5 PM PDT
TUESDAY FOR PZZ271>273.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
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