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 06Z Monday

Currently widespread VFR conditions inland and LIFR conditions at most coastal terminals as marine stratus pushes into the coastline. The one exception, KAST, has been staying clear and VFR as marine stratus pushes southeastward just south of the terminal. Looking ahead, stratus will likely continue to build along the coast and may bring deteriorated conditions to KAST by 12Z Sun (20-30% chance of LIFR conditions between 13-17Z Sun). While chances of VFR then improve after 17Z Sun at KAST, conditions will likely remain deteriorated at KONP through much of the TAF period. Guidance continues to suggest that KONP will stay LIFR through at least 21Z Sunday and may improve to IFR thereafter. As for inland terminals, expect VFR conditions through the period, with just a 10-20% chance of LIFR conditions between 12-17Z Sun. KEUG is the one exception with a 20-40% chance of LIFR between the aforementioned time.

Winds continue to ease overnight. Expect generally north to northwesterly winds of 3-6 kt through the period, with the exception of gusts up to 20 kt possible at KONP in the afternoon.

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

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 until noon PDT Sunday for PZZ252-253-273.