textproduct: Portland

SYNOPSIS

High pressure returns dry and mostly sunny conditions today through the middle of the week. Cool nights will bring chances for morning frost across sheltered valleys and rural areas this weekend into early next week. Temperatures trend warmer late in the week as an upper-level ridge amplifies over the region.

SHORT TERM...Today through Tuesday night

Satellite imagery and surface observations as of early Sunday morning depict mostly clear skies with calm winds across northwest Oregon and southwest Washington. This is supporting efficient radiational cooling with temperatures falling into the upper 30s to low 40s. Will continue to see temperatures cool into the low to mid 30s these next few hours, mainly for sheltered valleys and rural areas outside urban cores. Frost Advisories remain in effect across the north Oregon Coast Range, Cascade foothills, Upper Hood River Valley, and southern Willamette Valley through 9 AM this morning, where temperatures of 33 to 36 degrees will support frost development. Anyone growing outdoor plants that are susceptible to frost damager should continue to cover plants or leave plants indoors if possible.

Expect dry and sunny conditions today through Tuesday as upper- level ridging amplifies offshore and extends over western OR/WA. At the same time, an upper-level low will also be in place over eastern OR/WA and the Great Basin, resulting in thermal troughing along the coast and Cascade foothills. These thermal troughs will support light offshore winds from the north/northeast today with peak wind gusts of 25-35 mph along the Columbia River Gorge and 20-25 mph across the central/southern Willamette Valley. There is a low chance (10-20%) that peak wind gusts today exceeding 30 mph across the Willamette Valley. Temperatures will warm up a few degrees compared to yesterday with afternoon highs forecast to peak in the mid to upper 60s each day. Clear skies each night through Monday night will also lead to renewed chances for frost development as morning lows drop into the low to mid 30s again. Will likely need additional Frost Advisories for the next few nights. -10

LONG TERM...Wednesday to Saturday

By mid-week, the majority of ensemble members are in agreement with upper-level ridging remaining slightly offshore of the U.S. West Coast. This will maintain mostly dry and warm conditions on Wednesday, however, we could see some increasing cloud cover as a system rides the northern periphery of the ridge and heads into British Columbia. Given that this system will track further north, precipitation is not expected for the majority of our area except for a 15% chance for light showers along the south Washington coast. Will also note that increased cloud cover will also warm our low temperatures slightly and reduce the threat for frost development.

Thursday to Friday, the aforementioned upper-level ridge will shift eastward and move over the Pacific Northwest. This will result in temperatures rebounding to the low to mid 70s across interior valleys at the end of the week. Heading into the weekend, the upper ridge gets pushed further east by upper-level troughing coming down from the Gulf of Alaska. There remains uncertainty with the timing, position, and magnitude of the troughing at this point, but what we can say with higher confidence is that this pattern would return cooler temperatures and chances for precipitation by the weekend. -10

AVIATION...Through 18Z Monday

As of 1730z Sun, observations indicate stratus has mostly dissipated across the region, only remaining in portions of the central and southern Willamette Valley and Portland area east of KPDX. Lingering stratus should continue to dissipate by 18-19z Sun. Otherwise, VFR conditions with mostly clear skies expected across NW OR and SW WA through the TAF period due to building high pressure over the region. North/northeasterly winds today, strongest along the coast and central/southern Willamette Valley at 10-13 kt with gusts to 20-25 kt. Elsewhere, winds remain around 4-7 kt. Winds decrease after 02-04z Mon, becoming light and easterly along the coast and variable inland.

Between 07-15z Mon, clear skies and calm winds will support temperatures falling towards 33-36 degrees F across much of the area outside of the Portland metro and as low as 28-32 degrees F in the Upper Hood River Valley. Locations that are able to cool down to these temperatures may see frost development on metal surfaces.

KPDX AND APPROACHES...VFR conditions expected through the TAF period. Northwesterly winds 4-7 kt today, becoming light and variable by 03-06z Mon. -03

MARINE

Small Craft Advisories remain in effect through at least early Monday morning for all waters including the Columbia River Bar for steep and choppy seas of 6-9 ft at 7-9 seconds. Thermal troughing will set-up along the coast today, resulting in northeasterly winds. These winds are expected to remain light today, as chances for widespread and frequent wind gusts exceeding 21 kt are around 5% or less.

Benign marine conditions expected for the rest of the week. Winds gradually weaken on Monday and remain northerly through early Tuesday morning. Tuesday to Wednesday, winds turn more southwesterly ahead of an approaching weak front, but return northerly by the end of the week. Seas subside to 4-6 ft with winds remaining below 15 kt. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight tonight to 8 AM PDT Monday for ORZ104-107-109-112>119-123>125.

Freeze Warning from midnight tonight to 8 AM PDT Monday for ORZ121.

WA...Frost Advisory from midnight tonight to 8 AM PDT Monday for WAZ202-204>208.

PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ210-251>253- 271>273.