textproduct: Portland

SYNOPSIS

Persistent onshore flow will bring near-average temperatures with varying degrees of morning clouds and afternoon sunshine for much of the next week. A series of weak fronts will bring notable chances for light rain and drizzle to portions of the Washington and north Oregon coasts Tuesday and next weekend, while Friday is likely to be the warmest day.

DISCUSSION...Monday afternoon through Sunday

There has been very little change to the forecast today. The large- scale pattern remains fairly steady through the next week with the region wedged between upper-level troughing over the Gulf of Alaska and upper- level ridging over the Rockies and Central Plains. In general, the weather locally will be typical for the mid-summer: morning clouds followed by increasing afternoon sunshine, seasonable temperatures, and largely dry conditions, but with some variations as the strengths of these two dominant features change relative to one another.

Upper ridging wins out today as heights aloft have risen marginally. Morning stratus has dissipated with mostly clear skies and seasonably warm high temperatures expected in the 60s to low 70s on the coast and mid 80s within the Willamette Valley. On Tuesday, an upper shortwave passing to the north will tilt the scales in favor of upper troughing, sending a weak front toward the coast resulting in cooler temperatures across the region and chances for light rain or drizzle along the coast and Coast Range. Temperatures are also forecast to be a few degrees cooler than today as cloud cover may persist across the region through the afternoon hours.

Wednesday into Thursday, the upper-level ridge strengthens slightly, increasing heights aloft locally and again tipping the balance toward dry weather, though smaller shortwaves along the flow will keep temperatures in the low 80s for the interior lowlands. On Friday, upper high pressure spreads farther west into the region, increasing heights aloft locally and allowing for warmer temperatures. Daytime temperatures are forecast to peak in the upper 60s to low 70s along the coast and upper 80s for the interior lowlands. Despite this trend, onshore flow will continue, limiting the risk for hazardous heat. Minor HeatRisk is favored for the entire region on Friday, with 20-40% chances for Moderate HeatRisk in urban and suburban areas from Salem north to Vancouver, WA.

By the weekend, there is higher uncertainty in the evolution of the upper-level pattern, but many ensemble members depict more pronounced troughing returning to the Pacific Northwest, favoring cooler temperatures and further chances for rainfall. The details of timing and potential rainfall amounts remain fuzzy at this lead time, but those near the coast or within coastal terrain will be the most likely beneficiaries of any rainfall, with chances increasing to the north. -36/03

AVIATION...Through 00Z Wednesday

Mostly clear skies and VFR flight conditions will continue at all TAF sites through the remainder of the day. Winds at the coast have increased to 7-10 kt with occasional gusts up to approximately 15 kt. Winds at the coast will ease below 5 kt and back out of the south later this evening. For inland TAF sites, a sea breeze front will bring increasing west to northwest winds between 01-06Z Tuesday, sustained between 5-10 kt. Winds become calm thereafter.

MVFR ceilings are expected to return to the coastal terminals by approximately 06Z Tuesday. There is some uncertainty regarding exactly how low ceilings will get at KONP; although low-end MVFR ceilings are the most likely outcome, there is around a 50% chance for IFR ceilings below 1000 ft. Inland TAF sites will most likely remain VFR tonight into tomorrow morning, however there is a 20-35% chance for a period of MVFR ceilings between 2000-3000 ft between 10-18Z Tuesday.

KPDX AND APPROACHES...Mostly clear skies will maintain VFR flight conditions today. Light and variable winds around 5 kt will become northwesterly around 5-10 kt around 02Z Tuesday with an incoming sea breeze. Although skies will most likely stay clear tonight, there is a 20-30% chance for a broken or overcast low stratus deck with ceilings between 2000-3000 ft between 10-18Z Tuesday. -23

MARINE

Buoy observations from early Monday afternoon showed significant wave heights of 4 to 5 ft with southerly winds generally ranging between 5 and 15 kt, strongest over the northern waters. There are two separate swells ongoing, with a short period northwest swell and a long period southwest swell dominating the current sea state. Given the low swell heights and relatively weak winds, there are no headlines in effect over the coastal waters at this time.

Very little change is expected to the overall sea state through Friday. However, the wind direction will change from southerly to northerly by late Tuesday afternoon in the wake of a weak frontal passage. North winds are then expected to continue through Friday. Winds become more northwesterly on Saturday with wind gusts increasing to around 15-20 kt, and then veer back to the north on Sunday with gusts increasing to 20-25 kt. Winds will be strongest during the afternoon and evening hours over the central and southern waters. Confidence in small craft advisory level wind gusts over 21 kt on Sunday is high, as probabilities for max gusts of this magnitude range between 70-90% over the central and southern waters. Probabilities are relatively lower over the northern waters, ranging between 50-65%. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.