textproduct: Portland

SYNOPSIS

Abnormally warm and dry conditions will continue through Thursday with periods of offshore flow and early morning fog within sheltered valleys. The warmest temperatures will occur this weekend. A potential trough approaches the region Friday into next weekend, bringing cooler temperatures and increasing chances for rain.

LONG TERM...Tuesday through Friday night

The long term forecast starts out dry with warmer than normal temperatures, and ends with increasing chances for cooler weather and rain. The GEFS/GEPS/ENS ensembles agree well on the synoptic-scale pattern Tuesday through Thursday, suggesting broad upper-level ridging will remain in place over the Pacific Northwest. It appears weak offshore flow will also make a quick return. This pattern will favor cool mornings with areas of valley fog, giving way to sunny and warm afternoons with highs in the mid 70s to lower 80s for inland valleys and mid 60s to lower 70s at the coast. Confidence for continued above normal temperatures is very high (>90% chance). However, record high temperatures are highly unlikely (<10% chance).

Chances for rain finally return to the forecast Friday into next weekend with temperatures trending close to seasonal normals. By Friday night, around 65-85% of the total ensemble space from the GEFS/GEPS/ENS combined are showing measurable rain over southwest WA and northwest OR within the 24-hour period ending at 5 AM PDT Saturday. The highest probabilities are over southwest WA. Due to significant timing differences in the start/stop time of precipitation, 6-hourly NBM PoPs only peak between 10-30%. If rain does occur, it could start anytime between early Friday morning and late Saturday morning according to total model ensemble spread. -23

AVIATION...Through 00z Sunday

Satellite imagery and terminal observations as of early Saturday afternoon depicts VFR conditions with sunny skies across most terminals. An exception is KONP, where persistent marine stratus is resulting in LIFR CIGs and MVFR VIS. Expect these trends at each terminal to continue through this afternoon. Later this evening after 02-03z Sun, there is high confidence (>70-80% chance) for marine stratus returning to the coast. High pressure aloft will compress cloud bases down to the surface, resulting in LIFR stratus/fog. Across the Valley, VFR conditions continue overnight, but there is a 10-20% chance for IFR/MVFR stratus returning at any given hour between 11-17z Sun. Northerly to northwesterly winds generally under 7-8 kt for most terminals except 10-11 kt at KONP this afternoon. In addition, tightening offshore pressure gradients between KTTD-KDLS will result in light easterly winds at KTTD. Winds ease overnight.

KPDX AND APPROACHES...VFR conditions through the TAF period with a 10-20% chance for IFR/MVFR stratus between 12-17z. Northwesterly winds around 3-6 kt. -10

MARINE

Persistent high pressure offshore will maintain northerly winds through 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. 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.

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, especially within 40 NM of the coast. Another Dense Fog Advisory has been issued from 11 PM this evening through 12 PM Sunday for visibilities of 1 NM or less across the waters south of Cape Foulweather and the waters between Cape Falcon and Cape Foulweather. Confidence for widespread dense fog is lower in the northern waters, but will continue to monitor if the advisory needs to be expanded.

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. A longer period northwesterly swell may also bring a moderate sneaker wave threat. -10/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Dense Fog Advisory from 11 PM this evening to noon PDT Sunday for PZZ252-253-273.