textproduct: Portland

SYNOPSIS

Today a decaying frontal system drops southward clipping the region and bringing chances for rain through tonight with the highest probabilities along the Washington and north Oregon coast and Coast Range. Dry weather is favored again by Wednesday, likely lasting through the weekend, with temperatures trending warmer day to day as well.

DISCUSSION...Now through Monday night

Current radar and satellite imagery early this morning shows precipitation/cloud cover associated with a frontal system slowly sliding southward into the region. As it progresses throughout the day it is expected to continue weakening but there should be enough lingering moisture to facilitate light rainfall over portions of the Oregon coast and possibly the Portland Metro area and locations northward into southwest Washington. The latest NBM suggests there is still around a 45-60% chance for 0.25 inch of rainfall from Tillamook northward, with a 50-60% chance for a 0.50 inch of rain or more in the Willapa Hills. Rain will be more spotty with light amounts expected across portions of southwest WA and the Portland metro, generally only 20-25% chance for amounts to exceed 0.10 inch, while conditions Salem southward remain mostly dry.

Thanks to the quick-hitting nature of this frontal system, confidence is high widespread dry conditions return Wednesday morning, and from this point onward dry weather likely continues through the remainder of the week and weekend. The one caveat includes a weak weather system potentially brushing northern portions of our forecast area again on Thursday and Thursday night. But in-line with prior weather model cycles, most 00z ensemble members are keeping the rain pinned farther north, with only 10% or less showing rainfall locally. Temperatures remain fairly seasonable through the end of September into the first couple of days of October with highs generally in the low to mid 70s across the inland valleys.

By the weekend, models and their ensembles are in fairly good agreement of a more pronounced ridge of high pressure building over the region. This would maintain dry weather and potentially trend afternoon temperatures around 5-10 degrees above normal for early October. Clusters hint at more uncertainty though heading into early next week as ensembles struggle to handle the potential breakdown and progression of this upper-level ridge. -99/DH

AVIATION...Through 12Z Wednesday

Early this morning clouds cover continues to increase across the region with MVFR conditions along the coast while VFR CIGs/VIS prevail inland though CIGs have been steadily dropping. For inland sites, probabilities for terminals to experience MVFR conditions are highest around the Portland metro at 50-70% between 16-21z. Low clouds are likely more SCT to BKN throughout the central and southern Willamette Valley with MVFR chances at 20-40% any given hour between 14-21z. Southerly winds gradually increase to 5-10 kt as a cold front associated with the trough moves through the region. Higher speeds at KAST up to 10-15 kt with gusts up to 20-25 kt expected.

KPDX AND APPROACHES...VFR conditions likely transition to MVFR between 14-16z this morning due to lowering CIGs as a frontal system enters the region. That said, we'll likely see a switch back to low-end VFR mid to late afternoon into the evening. Expect southerly winds around 5-12 knots through the day. -99

MARINE

This morning a frontal boundary quickly approaches the waters with southerly wind gusts in the 20-30 knot range peaking north of Cape Falcon, especially right along the coastline. A Small Craft Advisory remains in effect for coastal waters north of Cape Foulweather, including the Columbia River Bar, into the late afternoon and early evening hours. Behind the front, winds are expected to abruptly shift to the northwest, transitioning to a somewhat lighter northerly wind pattern Wednesday. Another weak system may approach the northern waters from the west on Thursday, but it likely holds north as it moves toward the Washington coast then out of the region to the east. Northerly winds then return Friday, likely persisting over the weekend.

A mid-period west-northwesterly swell of 6 to 8 ft at 13-15 seconds will move through the coastal waters today through tonight, increasing significant wave heights into the 8 to 10 ft range. Seas then gradually subside to around 4 to 6 ft later in the week with no other prominent swells of note at this time. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ210. Small Craft Advisory until 5 PM PDT this afternoon for PZZ251- 271. Small Craft Advisory from 5 AM early this morning to 5 PM PDT this afternoon for PZZ252-272.