textproduct: Portland

SYNOPSIS

Unseasonably warm and dry conditions continue through Thursday with areas of early morning valley and coastal fog. Weak offshore flow will bring slightly warmer temperatures Wednesday and Thursday, before a trough brings a return to cooler temperatures with chances for light rain Friday into Saturday. Chances for morning frost increase next weekend, especially Sunday morning in rural valleys away from urban cores.

LONG TERM...Friday through Sunday night

Late in the week and into this weekend, long-range ensemble guidance supports an upper- level trough developing over the Pacific Northwest, bringing a return to onshore flow, cooler and more seasonable temperatures, and low chances for light rain. While there continues to be uncertainty in its evolution, the majority of ensemble members from the ENS/GEPS still maintain light rain arriving along the north Oregon and south Washington coast around midday Friday, reaching inland areas by Friday afternoon. The GEFS is still trending drier than the ENS/GEPS, with 30-45% of the total ensemble space remaining dry through Saturday. Potential rainfall amounts continue to look very light, with only a 1-10% chance for rain amounts of 0.10" or higher Friday into Saturday, except for a 15-30% chance in the south WA Cascades and north Oregon Cascades.

As the core of the upper trough moves overhead, much cooler air aloft will allow for sharply cooler low temperatures Saturday morning and especially Sunday morning. Chances for temperatures in the mid 30s supporting frost will reach 25-35% in the Upper Hood River Valley around Parkdale and Dee on Saturday morning, increasing to 35-70% and including lower elevations near Odell on Sunday morning, and near 10% in Hood River proper. Chances for frost Sunday morning reach 15-30% in north Oregon Coast Range valleys, the southern Willamette Valley and Cascade foothills from Cowlitz County south to Lane County, and 5-10% in the central Willamette Valley. Chances for a true freeze Sunday morning are limited to 25-35% in the Upper Hood River Valley near Parkdale and Dee, and 5-15% along OR-58 between Eugene and Oakridge. Those with agricultural interests or home growers with sensitive outdoor plants should continue to monitor the forecast this week. -36/23

AVIATION...Through 00z Wednesday

MVFR/IFR/LIFR conditions are slowly dissipating along the coast Monday afternoon. As diurnal northwest winds continue to increase to 10-15 kt with gusts of 20-25 kt, mixing will help lift and break up low clouds, with a period of VFR conditions favored after 20-21z Mon. However, there's a 20-35% chance that lowered conditions do not improve to VFR at all at TAF sites. Winds are expected to ease below 10 kts after 00-03z Tue, allowing the return of marine stratus and IFR/LIFR restrictions through Tuesday morning.

At inland terminals, VFR conditions prevail. Fog/low stratus are likely to return at most terminals again around sunrise Tuesday, with IFR/LIFR conditions expected by 12-14z. Expect these conditions to remain through around 17-20z Tue. North to northwest winds today rise to 7-10 kt after 21z, falling below 5 kts after 00-04z Tue.

KPDX AND APPROACHES...Prevailing VFR conditions. There's high confidence that fog/low stratus returns Tuesday morning around 11-13z with IFR/LIFR conditions. Expect these conditions to remain through 18-20z Tue. North to northwest winds increase to around 6-8 kts after 21z Mon, decreasing to less than 5 kts after 02-04z Tue. -03

MARINE

High pressure offshore will continue to maintain diurnal northerly winds through the week with peak afternoon and evening wind gusts of 20-25 kt today through Wednesday. Small Craft Advisories remain in effect from 11 AM until 11 PM PDT today within 10 NM south of Cape Falcon and out to 60 NM south of Cape Foulweather. Expect largely wind-driven seas around 4-6 ft through midweek, with a west-northwest swell of 3-4 ft at 10-12 seconds. High pressure aloft will also support areas of dense fog developing nightly through the morning hours as cloud bases are compressed down to the surface.

More active marine conditions are likely in the latter half of the week as troughing over the Gulf of Alaska generates a building northwest swell. Seas will increase to 7-10 ft Wednesday into Thursday, with the longer-period swell also supporting a moderate risk for sneaker waves to the coast. Chances for rain return to the region Friday into the weekend, though rain amounts are not expected to be very impactful. -03/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ252-253-273.