textproduct: Portland

SYNOPSIS

Expect areas of morning frost Friday morning, aside from central/eastern portions of the Portland metro, the Columbia River Gorge, and along the coast. An upper level ridge will strengthen over the area this weekend, bringing well above normal temperatures Saturday through Monday with widespread high temperatures in the upper 60s to upper 70s across the lowlands, coolest at the coast. Northwest flow aloft Tuesday through Thursday will favor more seasonable temperatures with dry conditions most likely continuing, albeit with a 10-20% chance of light showers each day west of the Cascades and a 20-40% chance in the Cascades.

LONG TERM...Tuesday through Thursday night

The long term forecast is highlighted by relatively cooler temperatures compared to the weekend with an 80-90% chance for continued dry conditions west of the Cascades. There is some uncertainty as to how much cooler conditions will become, as model spread suggests highs could range anywhere from the mid 50s to upper 60s per the NBM 10th-90th percentile. Most of this uncertainty stems from the exact track of a closed upper level low over the Pacific that will be slowly moving towards California, and how far south an upper level trough will dig over the Pacific Northwest along the northern periphery of this closed low.

Most ensemble guidance (>50-60%) tracks this upper level low far enough to the south to allow for a northwesterly flow regime in western WA and northwest OR, which would bring relatively cooler temperatures along with mainly dry conditions. However, if the aforementioned upper low tracks far enough to the north to allow for southerly flow aloft in northwest OR, temperatures would likely be a touch warmer with increasing chances for showers and possibly even a few thunderstorms. The probability for precipitation each day Tuesday through Thursday ranges between 10-20%, except 20-40% over the Cascades, which makes sense given the most likely outcome is for the closed low to track far enough to the south to allow for dry northwest flow aloft. Note probabilities for thunderstorms per the latest NBM guidance are very low at this time, ranging between 1-10%. -23

AVIATION

Calm winds and VFR flight conditions remain in place this morning under high pressure. Scattered high clouds this morning to the north of KEUG should lift northward out of the area Friday afternoon. Some patchy shallow ground fog possible in the vicinity of KEUG through 15-16z Friday, potentially resulting in brief visibility reductions (15-20% chance). Note temperatures in the 30s this morning may result in frost formation, especially at KHIO, KSLE, and KEUG where temperatures are coldest. Frost is unlikely at KAST, KPDX and KTTD where temperatures are relatively warmer.

KPDX AND APPROACHES...Calm winds this morning under high pressure. Expect VFR flight conditions to continue through 12z Saturday with mostly clear skies, aside from scattered high clouds Friday morning. -23

MARINE

High pressure remains in place over the waters. Buoy observations from early Friday morning showed seas hovering between 6 to 8 ft at 12 seconds with south winds around 5-10 kt. Seas should fall another foot or two Friday afternoon. Light south winds will give way to increasing northerly winds late Friday afternoon through Saturday evening before winds turn more offshore on Sunday and weaken. It appears the next chance for small craft advisory level wind gusts (upwards of 25 kt) is Saturday afternoon through Saturday night, potentially beginning as early as late Saturday morning over the far outer central/southern waters. The strongest winds are expected late Saturday afternoon through late Saturday evening. Despite the uptick in winds, seas are not expected to respond much, likely staying below 8 ft. Nevertheless, Small Craft Advisories have been issued for the central and southern outer waters to cover this threat. It appears wind gusts will generally stay below 21 kt over the inner waters, aside from a 1-3 hour period where winds may peak right around 21-22 kt late Saturday afternoon/early evening. Winds become northwesterly early next week with seas remaining relatively low. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 10 AM PDT this morning for ORZ104>110- 113>115-119-123.

Freeze Warning until 10 AM PDT this morning for ORZ116>118-121- 124-125.

WA...Frost Advisory until 10 AM PDT this morning for WAZ203>205-208.

PZ...Small Craft Advisory until 9 AM PDT this morning for PZZ210.

Small Craft Advisory from 11 AM Saturday to 5 AM PDT Sunday for PZZ272-273.