textproduct: Portland

SYNOPSIS

Largely dry weather expected through midweek while temperatures remain near to above average for mid-October. Chances for rain and cooler temperatures ramp up late in the work week.

DISCUSSION...Now through Saturday

Clear skies and light winds have allowed temperatures to cool off into the 40s throughout the Willamette Valley and into the mid to upper 30s in some of the typical cool spots. The Frost Advisory for the Upper Hood River Valley, Coast Range Valleys and the SW WA Lowlands remains in place as observed temperatures continue to cool into the mid to upper 30s. Despite a cool start to the morning, today should turn out to be a pleasant fall day. Conditions remain dry as with highs topping out in the mid to upper 60s across the interior lowlands and upper 50s to low 60s along the coast.

An approaching trough will bring increasing mid and upper level cloud cover during the evening which will help keep temperatures a bit warmer tonight. Good agreement among the ensembles heading into Monday with the approaching trough elongating and pinching off into a closed upper low that drifts southward toward northern California. Precipitation chances remain low over land with the best chance over the Lane County Cascades at 20%. Cooler air associated with the trough will drop highs to right around normal on Monday with the interior lowlands reaching the low 60s and the coastal areas the upper 50s. Monday night will bring more widespread chances for overnight lows in the 30s for many valleys away from the core urban centers.

Heading into the middle of the week, the upper low will continue to drift toward California while heights rebound locally. This will keep conditions dry and will help temperatures jump back above normal into the low 70s across the interior lowlands on Tuesday and Wednesday. Overnight lows drop into the low 40s for most locations but the typical cool spots may drop into the upper 30s. Will need to watch trends and potential for more frost development. The latter half of the week again trends toward cooler temperatures and modest chances for rain. Cluster analysis shows good agreement in troughing developing over the Gulf of Alaska and dropping southeast toward the PacNW Thursday into Friday. This pattern would favor a return to near normal temperatures and chances for light precipitation. Nightly chances for frost continue within inland valleys. Toward the end of the 7 day period, a more robust trough and associated surface low could bring more significant rainfall to the region next weekend. -19/36

AVIATION...Through 12z Monday

Mainly VFR conditions with light to calm winds across the airspace. Patchy fog and low clouds have developed along the coast and within the Cascade Foothills. Could see some patchy fog develop in the Willamette Valley through 18z or so. There is a 20-30% chance for MVFR/IFR conditions at KEUG, KSLE and KUAO through that time. If any fog does develop, it should clear by mid to late morning. Winds increase from the north to around 5 kt inland and from the northwest along the coast up o 10 kt. An approaching trough will bring increasing mid and high level clouds to the airspace late in the TAF period.

KPDX AND APPROACHES...Expect mainly VFR conditions through 12z Monday. Clear skies and light winds could allow for patchy fog to develop in the area. Chances remain low at 10-15% that they impact the terminal directly through 17z. Light winds will increase to 5 kt from the north after 18z. Increasing mid and upper level clouds ahead of an approaching trough late in the TAF period. -19

MARINE

A westerly swell will continue to move into the waters, keeping seas in the 7-9 foot range at 11-12 seconds through early tonight. Northerly winds will gradually decrease through the day, dropping below 10 kt tonight. This swell will also continue to pose a moderate risk for sneaker waves along the coast; caution should be used by those in or near the water along beaches through this weekend.

Another weather system dropping southward off the coast Monday into Tuesday will generate another westerly swell that moves into the waters. There is a 10-30% chance for seas to push to 10 ft across the waters, particularly beyond 20 NM Tuesday. Higher chances for the outer waters south of Cape Foulweather up to 50%. In addition, there is a 40-70% chance for wind gusts to climb into the 21-25 kt range Tuesday. Winds and seas appear to trend downward midweek with more active weather late in the work week.

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 9 AM PDT this morning for ORZ104-105-121.

WA...Frost Advisory until 9 AM PDT this morning for WAZ205-208.

PZ...None.