textproduct: Portland

SYNOPSIS

Remaining dry through at least Jan. 20-21 as strong high pressure remains in place. Widespread dense fog and/or low stratus will continue this morning across the interior lowlands below 1000 feet. By noon, increasing offshore flow will begin to scatter out fog and stratus from north to south, with sunshine breaking out in the Portland metro first and the central Willamette Valley last. The southern Willamette Valley will likely see fog and low clouds persist through the day. Gusty easterly winds develop over the eastern Portland metro, western Columbia River Gorge, and Cascades tonight into Friday. Lighter offshore winds this weekend with mostly clear skies, chilly mornings and mild afternoons.

DISCUSSION...Now through Wednesday night

Strong high pressure will remain in place through at least Jan. 20th, bringing dry weather each day. Webcam, satellite and surface weather observations from early Thursday morning depicted widespread dense fog and low stratus across the interior lowlands of northwest OR and southwest WA. Visibilities are generally lowest in the western Portland metro, central Willamette Valley and southern Willamette Valley, ranging between 1/4 to 3/4 miles. Meanwhile, the eastern Portland metro and Cowlitz Valley are observing more in the way of low stratus rather than fog. Dense Fog Advisories remain in effect for the Willamette Valley, north Oregon Coast Range lowlands, and western Portland metro through Noon today, with impacts to travel for the morning commute.

Fog and low clouds are expected to lift from north to south this afternoon as low-level offshore flow develops, clearing the Portland metro area and Cowlitz Valley first in the late morning or early afternoon, followed by the central Willamette Valley in the mid afternoon. Although most model guidance suggests the southern Willamette Valley will clear out as well, pattern recognition makes this doubtful given the northerly upslope winds that will be in place around Eugene. Assuming fog and low clouds never clear out of the Eugene-Springfield, temperatures will likely struggle to reach 40 degrees, while locations from Salem northward will most likely break 50 degrees, assuming skies clear out quickly enough. The mid slopes of the Cascades will remain the warmest with highs well into the 60s, as these elevations will be poking above a persistent low-level temperature inversion, and thus tapping into warmer temperatures aloft. These elevations will also see sunshine through the day. A good deal of sunshine is expected at the coast as well today, with highs ranging from 55-60 degrees.

Once fog and low clouds clear the interior lowlands later today, expect mainly clear skies across all of northwest Oregon and southwest Washington to continue through at least Tuesday of next week. The main exception will be the southern Willamette Valley, which will continue to see chances for fog and low stratus each night. Temperatures each day will be chilly during the morning with temperatures near or below freezing, and mild during the afternoon. However, temperatures will remain much warmer above 1000 ft, both overnight and during the day.

Chances for rain finally return to the area Wednesday into next Thursday, Jan. 21-22, with PoPs peaking between 25-50%. This is when most model guidance is showing a transition back to onshore flow and more seasonable temperatures. However, PoPs are far from 100% as there is still a handful of ensemble guidance showing very little to no precipitation at all through Jan. 23-26. In other words, it is not clear exactly when this extended dry stretch will end. Odds lean on it ending by Jan. 23rd, but only slightly. -23

AVIATION

High pressure remains firmly in control over the area, supporting IFR/LIFR stratus and areas of dense fog throughout the Willamette Valley and portions of the northern Oregon coast and Coast Range lowlands. Temperatures have remained several degrees above freezing this morning, which means freezing fog is no longer a concern.

There is some uncertainty regarding the exact timing fog and low stratus will lift. Moderate confidence the northern Willamette Valley and Portland metro will begin to see gradual clearing by 18-21z Thursday as low-level offshore flow develops. Fog and low clouds should linger a bit longer for the central Willamette Valley, and likely through the entire day for the southern Willamette Valley, including KEUG.

Expect gusty easterly winds up to 30-35 kt at KTTD and up to 20-25 kt at KPDX to develop by 06z Friday. Winds will be out of the north from KSLE to KEUG, albeit weaker at around 5-10 kt. However, this will result in an ideal setup for KEUG to maintain fog through the day as persistent upslope flow will be in place.

KPDX AND APPROACHES...Expect low stratus with occasional fog to maintain LIFR to IFR flight conditions through approximately 18-21z Thursday before low clouds finally scatter out, giving way to clear skies and increasing easterly winds. Wind gusts up to 20-25 kt at expected to develop at the terminal by 06z Friday. -23

MARINE

High pressure over the area will maintain more settled conditions through the next week. On Thursday, a thermal trough will build up the Oregon coast, bringing increasing northeast winds with small craft advisory level wind gusts up to 20-30 kt. Due to the location of the ridge, the inner waters are less likely to experience gusts greater than 25 kt.

On Friday, winds will become easterly as the thermal trough moves slightly offshore. Expect winds around 10 to 20 kt with gusts up to 25 kt during that time, strongest downwind of gaps in the coastal terrain.

Winds remain easterly over the weekend, albeit much weaker in strength. Seas should stay below 10 ft this afternoon through early next week, bringing a very quiet sea state for this time of year. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until noon PST today for ORZ104-109-110- 114>118.

Air Stagnation Advisory until 4 AM PST Friday for ORZ109>111- 114>118.

WA...Air Stagnation Advisory until 4 AM PST Friday for WAZ205-206.

PZ...Small Craft Advisory from 7 PM this evening to 4 PM PST Friday for PZZ251.

Small Craft Advisory until 4 AM PST Friday for PZZ252-253-272- 273.

Small Craft Advisory from 10 AM this morning to 4 PM PST Friday for PZZ271.