textproduct: Portland

SYNOPSIS

Mostly dry weather today before wetter and more active weather returns Friday. Additional chances for rain return late Saturday afternoon into Sunday, and Monday through the middle of next week. South winds become breezy later Saturday afternoon and evening.

DISCUSSION...through Wednesday

Clouds are clearing enough for the sun to peek through this afternoon as weak, transient ridging moves over NW OR and SW WA today. Expect calm and dry weather to continue through tonight, though mostly cloudy skies will return by Friday morning as the next weather system approaches the region.

Rainy season has officially arrived for the Pacific NW. The next week will be characterized by repeated weather systems producing multiple rounds of rain and occasionally breezy winds. At this point, precipitation amounts associated with each weather system will be on the lighter side, leading to limited widespread flooding concerns. The next weather system will bring rain to the coast Friday morning, spreading inland Friday afternoon through the evening. The surface low associated with this system will move farther north into British Columbia, so rain will mainly be limited to locations northwest of a line stretching from Newport to Corvallis to southern Hood River County. Highest rain amounts will be along the north OR and south WA coast, ranging from 0.25-0.75 inch of rain with anywhere from a few hundredths to 0.25 inch for inland areas.

A brief break between weather systems will bring dry conditions everywhere except the far north OR and south WA coast during the day Saturday with daytime temperatures rising into the low to mid 60s along the coast and inland valleys. However, expect skies to remain mostly cloudy as a stronger low pressure system quickly moves through the eastern Pacific towards the coast. This system will speed through the area Saturday night with most rain falling before Sunday morning, though post-frontal scattered showers will linger into the day. This rain will be more widespread, though still on the lighter side with 0.2-0.5 inch for inland valleys and 0.3-0.75 inch for the coast and terrain. Breezy winds will accompany the frontal passage with this weather system, especially along the coast and over terrain. There's a 20-40% chance of wind gusts of 55 mph for the beaches and headlands along the coast and 5-20% chance for coastal communities off of the beach. This probability increases to 35-55% for the high Cascades. Inland valleys are more likely to see peak gusts up to 25-35 mph with a 40-70% chance of wind gusts over 30 mph. Winds will increase along the coast in the afternoon, spreading inland by 8-11 pm, and decreasing by 5-8 am. Winds of this magnitude along the coast could cause some downed trees and power outages, though inland impacts would mainly be some downed tree limbs, especially as many trees still have leaves.

Ensemble guidance is in good agreement that another round of brief, dry weather returns Sunday afternoon into Monday morning before yet another weather system impacts the PacNW. High uncertainty remains with the evolution of this system, in terms of both location and intensity. Both the GEPS and EPS indicate this system could sustain IVT values between 250-500 kg/ms for a much longer duration than previous weather systems, generally around 72 hours, with a 55-70% chance that IVT values exceed 500 kg/ms for at least 48 hours of that period. This would support higher rain accumulations than previous weather systems, though NBM probabilities for even 1 inch of rain in 48 hours ending Wednesday morning is around 50-70% for the coast and 25-60% for the Cascades and inland valleys. Probabilities for 2 inches in the same 48 hour period decrease quite a bit. These probabilities are likely on the lower side due to the significant uncertainty on where in the PacNW the main plume of moisture will fall. Widespread flooding impacts are not expected at this time with only 1-2 inches in 48-72 hours, though antecedent rainfall from earlier weather systems could lead to more saturated soils and increased areal flooding in low lying or flood prone areas. Keep an eye out on the forecast for any changes. -03

AVIATION...Through 00Z Saturday

This afternoon generally VFR conditions are in place across the region as a weak ridge of high pressure moves overhead accompanied by some high clouds. Headed through the evening and overnight hours, this trend of generally VFR conditions should hold. However, we'll have to keep an eye on patchy fog formation mainly in the Tualatin Valley, and in central/southern Willamette Valley, after 09-11z through 18z Friday. Probabilities for sub-MVFR/IFR conditions are around 15-30% for most inland sites, highest in the aforementioned areas. The approaching weather system also brings chances for light rain to KAST in the morning before those chances shift inland in the afternoon. Expect winds along the coast to increase out of the south on Friday as well with gusts around 20-30 knots during the afternoon. -99

KPDX AND APPROACHES...VFR conditions likely persist through the evening hours. We'll have to keep an eye on fog/low stratus formation late overnight but the overall set-up is more marginal due to high cloud cover compared to the last several days. The probability for IFR conditions are only 15-20% locally between 09-15z. Winds gain a southerly component of Friday but stay fairly light overall. -99

MARINE

A very active and winter-like weather pattern will take hold across the coast waters headed through the weekend into next week. Expect south winds increase late tonight through Friday as our next frontal system pushes towards the waters. Confidence is high wind gusts exceed 34 knots around and north of Cape Falcon Friday morning through the afternoon so a Gale Warning is in effect during this time period. Steep and hazardous seas will also be possible later Friday as significant wave heights likely build to 14 to 18 ft prompting a Hazardous Seas Warning for the coast waters south of Cape Falcon.

Headed through Friday evening/night winds ease briefly, however, an even stronger front is expected to quickly approach the area late Saturday morning into the afternoon hours, bringing more widespread chances for Gales (85-95%) across our entire coastal waters - winds peak Saturday evening. It now appears as winds peak right along the frontal boundary, there is a decent chance (30-55%) for a period of Storm Force winds across the waters as well, with the highest probabilities Cape Falcon northward. Another westerly swell is expected to build seas into the mid to upper teens, with around a 25-45% chance of wave heights exceeding 20 ft. The active weather pattern likely continues into early next week as additional weather systems parade into the Pacific Northwest facilitating a similar array of impacts. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 7 AM PST Friday for PZZ210-251-252- 272. Gale Warning from 7 AM to 4 PM PST Friday for PZZ210-251. Hazardous Seas Warning from 7 AM Friday to 4 AM PST Saturday for PZZ252-272. Small Craft Advisory until 10 AM PST Friday for PZZ253-273. Hazardous Seas Warning from 10 AM Friday to 4 AM PST Saturday for PZZ253-273. Small Craft Advisory until 4 AM PST Friday for PZZ271. Gale Warning from 4 AM to 4 PM PST Friday for PZZ271.