textproduct: Portland

SYNOPSIS

Warming trend continues through the weekend as high pressure peaks on Sunday, with periods of offshore flow and early morning fog within sheltered valleys. Temperatures moderate but remain above normal as dry weather persists through much of the workweek. More seasonable conditions with increased chances for rain may return late in the week.

UPDATE...Saturday morning

Areas of dense fog have lifted along the south Washington coast, with surface visibilities improving. Therefore, the Dense Fog Advisory has been cancelled for this zone. Meanwhile, a Dense Fog Advisory remains in effect along the northern and central Oregon coast until 10 AM PDT Saturday; these coastal areas are still observing areas of dense fog with visibilities around 1/4 mile or less. -23

LONG TERM...Monday through Friday

By the beginning of the workweek, there remains good agreement that the upper-level ridge will shift inland over the Rockies while its amplitude decreases, resulting in nearly zonal flow over the Pacific Northwest. This pattern shift will allow onshore flow to return, supporting moderating but still above normal temperatures Monday through Thursday. The broad ridge continues to support high confidence in further dry weather. Late in the week, there is increasing agreement that upper troughing will return to the Gulf of Alaska, bringing renewed rain chances to the region from Friday into the weekend. While details in timing and amounts remain low confidence, some 60% of long-range ensemble members favor rain at some point from Friday through the weekend. -36

AVIATION...Through 12z Sunday

Broad subsidence across the airspace is compressing the shallow marine layer and producing LIFR cigs/vis along the coast and lower Columbia River as cloud bases are lowered nearly to the surface. Vis of 1SM or less is likely (70-80% chance) to persist through much of the morning at coastal terminals, until 17-19z Sat, before diurnal mixing will tend to clear skies and return to VFR vis. Low clouds near the coast will present persistent 30-50% chances for IFR cigs throughout the afternoon along the immediate coast including at KONP, while terminals even a few miles inland (KAST, KTMK) will see much lower chances (10% or less). A stagnant pattern will see a repeat of high IFR/LIFR chances again late Saturday.

At inland terminals, largely clear skies continue early this morning. Areas of low stratus are expected to develop along the Willamette Valley in the hours around sunrise, supporting 30-50% chances for MVFR cigs from 14-18z Sat. Ahead of the development of low clouds, ideal conditions for radiative cooling will allow for patchy fog or mist, most likely in the southern Willamette Valley including at KEUG, which persists through the late morning. Otherwise, VFR conditions expected to prevail throughout the period.

Diurnally varying winds expected across the region. Light offshore (easterly) flow at coastal terminals will back out of the northwest and build to around 10 kt, before easing and veering back offshore tonight. Easterly flow around 5 kt is also favored at KTTD throughout the period. Elsewhere, light winds overnight will build out of the north to northwest at around 5 kt today, then ease again this evening.

KPDX AND APPROACHES...VFR conditions expected while low stratus develops along the Cascade foothills around sunrise, supporting a 30% chance for MVFR cigs from 14-17z Sat. Otherwise, largely clear skies with diurnal northwest winds rising to around 5 kt this afternoon, then easing this evening. -36

MARINE

Persistent high pressure offshore will see northerly winds prevail through much of the next week, with speeds reaching diurnal peaks each afternoon. Chances for peak wind gusts of 20-25 kt generally increase daily through Wednesday, though the duration and coverage stronger gusts may not be sufficient to support Small Craft Advisories each day. High pressure building aloft through this weekend will also support areas of dense fog developing nightly as cloud bases are compressed down to the surface. A Dense Fog Advisory therefore remains in effect through noon Saturday for widespread visibility of 1 SM or less, especially within 40 NM of the coast. Strengthening northerly flow will see largely wind- driven seas continue at 4-6 ft through much of the week, with a modest west-northwest swell at 8-9 seconds lengthening to 10-12 seconds early in the workweek.

More active marine conditions are likely in the latter half of the week as troughing over the Gulf of Alaska generates a building northwest swell and chances for rain return to the region Friday into next weekend. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until 10 AM PDT this morning for ORZ101>103.

WA...None.

PZ...Dense Fog Advisory until noon PDT today for PZZ210-251>253- 271>273.