textproduct: Portland

SYNOPSIS

High pressure will result in dry conditions for the most locations through Thursday. An exception is the north Oregon and south Washington coast, where some light showers may clip those areas. The next storm system arrives Thursday night into Friday, returning widespread rain and gusty winds along the coast. Expect lingering showers on Saturday before the next system arrives on Sunday. A cooler and wet pattern continues into early next week. Make sure to clear storm drains and gutters of leaves and debris. If you are along the coast, beware of high surf at the end of the week.

DISCUSSION...Now through Tuesday

Radar imagery and surface observations as of early Wednesday afternoon depicts mostly dry conditions across northwest Oregon and southwest Washington while a continuous band of light rain associated with an atmospheric river moves into the Olympic Peninsula and western British Columbia. The backside of an upper-level ridge centered over the Rockies is keeping the bulk of the precipitation north of our area and keeping us dry today and Thursday. An exception could be the Pacific County and Clatsop County coast, where there remains a 20-40% chance for light showers clipping these area. High temperatures across interior valleys are on track to the reach the mid to upper 60s this afternoon, which is several degrees above normal and could potentially break some records. Thursday will be slightly cooler as ridging gradually breaks down over our area, but highs remain forecast to peak in the low 60s across interior valleys.

Late Thursday night into Friday, the next upper-level trough will approach the Pacific Northwest, pushing the first of a series of surface fronts through the region. This front on Friday will bring a return of widespread rain and cooler temperatures by Friday morning, with high confidence (80% chance) that the majority of places will receive at least 0.25" of rain by early Saturday morning. Chances for 24 hour rain totals exceeding 1 inch from early Friday morning to early Saturday morning are around 15-25% along the I-5 corridor, and 30-60% along the coast, with the highest chances from Tillamook southward. This system will also bring breezy winds from the south along the coast with gusts to around 30-40 mph. Chances for wind gusts exceeding 55 mph along the coast have fallen to 10-20%, so widespread power outages or downed trees along the coast appear unlikely. However, it would still be good to secure any loose outdoor items. Winds are also trending weaker along the I-5 corridor, where chances for wind gusts exceeding 40 mph have also fallen to 5-10%. Across the Cascades, snow levels around 5500 to 6500 will keep Cascade passes snow-free on Friday. This system exits the region by Friday night, with showers lingering across the area on Saturday as we receive a brief break before the next system. Snow levels briefly drop to 5000-5500 on Saturday, so there could be some light snow along Willamette Pass.

The next storm system arrives Saturday night into Sunday, bringing another round of widespread rain and gusty coastal winds. There is still uncertainty with specific rain amounts from this system, but for now, chances for 24 hour rain totals exceeding 1 inch from Saturday evening to Sunday evening are around 40-60% along the coast and 5-10% along the I-5 corridor. Snow levels rise back above 5500 feet, keeping the passes snow- free again. Looking at early next week, ensemble guidance continues to favor a general troughing pattern across the West Coast. While the specific timing, placement, and strength of the troughing remains uncertain, this would maintain cool and unsettled pattern for our area with additional chances for precipitation.

With several rounds of rain through next week, soils will become increasingly saturated through the weekend, potentially increasing runoff into area rivers and streams. At this time, the probability of widespread river flooding remains below 5%, though isolated flooding cannot being ruled out. In addition, any heavy rainfall could lead to ponding over roads as well as urban and small stream flooding of low-lying and poor drainage areas. While it is too early to determine specific hourly rainfall rates to assess the risk of urban flooding, residents can prepare by clearing gutters and storm drains of leaves and other debris. -10

AVIATION...Through 18Z Thursday

Southwest flow aloft continues today as a frontal band offshore gradually weakens maintaining dry conditions over the forecast area. Predominately VFR conditions are expected through this afternoon with persistent high clouds. A few spotty showers are possible near KAST so will maintain low chances of MVFR to low-end VFR CIGs at the north OR coast. Chances for MVFR stratus increase at KAST again after 02z Thursday as CIGs lower overnight. With similar conditions expected inland later this evening and overnight, chances for LIFR to IFR increase across the more wind protected Tualatin and southern/central Willamette Valleys. Highest chances for fog and low CIGs include KEUG (50-60%), as well as KHIO, KSLE, and KUAO (30-40%), generally developing after 08-12z Thu.

Breezy south winds are expected along the coast today with gusts up to 25 kt. Mostly light winds inland, except for easterly winds around 8-14 kt within the eastern Portland Metro, including KTTD.

KPDX AND APPROACHES...Broken high clouds continue to stream overhead with VFR conditions expected through the TAF period. East to southeast winds expected around 6-12 kt, with gusts up to 25 kt near KTTD, through this afternoon. /DH

MARINE

A stalled frontal boundary offshore will continue to weaken through this evening into Thursday morning. Southerly winds are expected to gradually ease across the waters with gusts dropping below 30 kt by this evening. Seas of around 12 to 16 ft with a period of around 12-14 seconds are also expected to linger through Thursday morning, maintain marginal hazardous seas across the coastal waters. By Thursday afternoon, southerlies again ramp up ahead of the next low pressure system that will approach the area later Thursday into Friday. A strong Gale Force front is expected to peak early Friday morning, with south to southeasterly winds gusting over 33 kt potentially over a 24 hour period. There is also a 40-50% chance for Storm Force wind gusts to occur across the outer coastal waters during the peak timing, but probabilities remain too low to upgrade to a Storm Watch. Therefore, will maintain and extend the Gale Watch that is in effect for all coastal marine zones from Thu evening through Fri afternoon.

Seas are expected to become very steep and hazardous by Friday as a fresh south-southwesterly swell likely develops, building seas to around 14 to 18 ft with a dominant period of around 10-11 seconds. This will be followed by a strong, long-period westerly swell that is expected to build seas above 20 ft Friday afternoon, with a 40-70% chance of seas greater than 25 ft. There is also a 10-30% chance for significant wave heights reaching 30 ft in the outer waters, with highest chances to the south. Another strong front is expected to move across the waters later Saturday into Sunday with high chances for another round of strong southerly Gales, while seas remain elevated through the weekend. /DH

BEACH HAZARDS

A moderate to high sneaker wave threat continues along the coast through this week as a westerly swell of 12 to 16 ft at 14 seconds continues through Thursday. This will result in waves running up significantly farther on a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning.

Additionally, confidence is increasing that a stronger westerly swell of 18 to 24 ft with a dominant period at 16-18 seconds will impact the coast later Friday into Saturday for dangerous surf conditions. Destructive waves may wash over beaches, jetties, and other structures unexpectedly.

Extreme caution should be used if you plan to visit beaches this week. The large wave runup may dislodge logs on area beaches and result in them rolling up and down area beaches, which have historically killed or seriously injured unsuspecting people, so there will be much more of a threat than just getting wet from a rogue wave.

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Gale Warning until 4 PM PST this afternoon for PZZ210-251-252- 271-272.

Small Craft Advisory from 4 PM this afternoon to 10 PM PST Thursday for PZZ210.

Gale Watch from Thursday evening through Friday afternoon for PZZ210.

Hazardous Seas Warning from 4 PM this afternoon to 7 AM PST Thursday for PZZ251-252-271-272.

Gale Watch from Thursday evening through Friday afternoon for PZZ251-272-273.

Gale Watch from late Thursday night through Friday afternoon for PZZ252-253.

Hazardous Seas Warning until 7 AM PST Thursday for PZZ253-273.

Gale Watch from Thursday afternoon through Friday afternoon for PZZ271.