textproduct: Portland

SYNOPSIS

Unseasonably warm and dry conditions continue through Thursday with areas of early morning valley and coastal fog. Weak offshore flow will see slightly warmer temperatures midweek, before a trough brings a return to cooler temperatures with chances for light rain Friday into the weekend.

LONG TERM...Friday through Sunday

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 still maintain light rain arriving along the north Oregon and south Washington coast around midday Friday, reaching inland areas by Friday afternoon. Potential rainfall amounts continue to look very light, with a 10% or less chance for even 0.1 inches of rain for most.

As the core of the upper trough moves overhead, much cooler air aloft will allow for sharply cooler low temperatures Saturday 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 35-65% and including lower elevations near Odell on Sunday morning, as well as near 10% in Hood River proper. Chances for frost will also reach 30-50% in north Oregon Coast Range valleys, 15-30% in the southern Willamette Valley and Cascade foothills from Cowlitz County south to Lane County, and 5-10% in the central Willamette Valley on Sunday. Chances for a true freeze Sunday morning are limited to 25-35% in the Upper Hood River Valley near Parkdale and Dee, and 5-10% 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

AVIATION...Through 12z Tuesday

Latest terminal observations again show areas of IFR/LIFR cigs/vis as low clouds or areas of fog/mist reoccur early this morning. Coastal terminals are largely seeing LIFR conditions, although satellite imagery shows clearing only 10 miles or so offshore off the north OR and south WA coasts, meaning KAST/KTMK and other small terminals may see improved conditions earlier if nearshore clouds break up. Farther south along the central OR coast, the low cloud deck is more solid, leading to higher confidence in persistent LIFR condition this morning. As diurnal northwest winds increase to 10-15 kt with gusts of 20-25 kt after 17-19z Mon, mechanical mixing will help lift and break up low clouds, with a period of VFR conditions favored after 20-21z Mon. Winds ease and low clouds bringing vis/cig restrictions return this evening by 00-03z Tue.

At inland terminals, areas of fog/mist are also beginning to develop in favored locations, notably including the southern Willamette Valley and lower Columbia/Cowlitz Valleys where largely LIFR conditions prevail. Elsewhere, VFR conditions remain in place, but chances for IFR vis will increase to 30-60% in the hours around sunrise; TEMPO groups in TAFs at all terminals reflect the chances for intermittent MVFR/IFR vis as local pockets of fog develop through 16-17z Mon, after which daytime heating and diurnal north to northwest winds rising to 5-10 kt will clear any remaining low clouds.

KPDX AND APPROACHES...VFR conditions most likely to prevail throughout the period. Chances for fog/mist to produce IFR vis restrictions increases to 40% from 14-17z Mon, after which there is high confidence in a return to VFR as daytime heating and northwest winds rising to 5-8 kt aid in mixing out any remaining clouds. -36

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 as cloud bases are compressed down to the surface. Dense Fog Advisories for widespread visibility of 1 SM or less also remain in effect across the coastal waters including the Columbia River Bar until noon PDT today.

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 and chances for rain return to the region Friday into the weekend. 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. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Dense Fog Advisory until noon PDT today for PZZ210-251>253- 271>273. Small Craft Advisory from 11 AM this morning to 11 PM PDT this evening for PZZ252-253-273.