textproduct: Portland

SYNOPSIS

A rather active weather pattern continues steer a series of frontal systems into the Pacific Northwest into the middle of next week with rainy conditions continuing. High surf, sneaker waves, and breezy winds impacts continue through the weekend. Snow levels fluctuate between 5000-7000ft the next couple of days before falling near 4000 ft in the Cascades late Sunday into Monday and 3000-4000 ft Tuesday into Wednesday.

DISCUSSION...through Thursday

Satellite imagery and surface observations around 1:30 PM PST Friday indicate the surface cold front that has been impacting the West Coast is situated along and east of the Cascades. Radar imagery shows widespread stratiform rain has mainly pushed east of I-5 in NW OR and SW WA with scattered showers forming along the coast and over the coastal waters where high clouds have cleared behind the front. As the front continues moving to the east, those high clouds and showers will move inland through the afternoon and evening hours. The upper trough associated with this weather system will push east into and through the region this afternoon and evening, which short term models indicate will produce a more organized band of showers pushing east through the area in the later hours of this evening. Instability is increasing along the coast behind the front with SPC's Mesoscale Analysis indicating around 100-250 J/kg of CAPE along the OR coast, locally between 250-500 J/kg south of Tillamook, and over 500 J/kg over the coastal waters. Additionally, some pockets of 0-1 km SRH over 100 m2/s2 that have developed along the coast and over the coastal waters as surface winds have turned more southeasterly while 850 mb winds remain southwesterly. With these conditions combined, can't rule out the potential for spinning storms over the waters and possibly right along the coast through late this evening. However, instability isn't expected in increase much more through today, so chances for any thunderstorms are low. The main impacts of this storm system will be another round of high surf along the coast late today into early Saturday. See the beach hazards section below for more information.

Scattered showers will continue during the day Saturday as the next weather system moves east through the Pacific hot on the heels of the current system, pushing the next front inland Saturday night into early Sunday. This system is expected to be fairly similar to the current system, though a bit more rain is expected for the coast and terrain in far northern OR and SW WA, and less for the rest of the coast and Coast Range. Also, the heaviest rain is expected in the overnight hours ahead of the frontal passage. Winds will be breezy along the coast once again in the late afternoon through late evening hours, though there's only a 10-30% chance for a High Wind event (gusts of 58 mph or higher). Can't rule out a stray gust or two this high at the typical breezy locations (Cape Disappointment, Clatsop Spit, etc), but most locations are expected to see peak wind gusts of 35-45 mph between 8 PM and midnight.

Showers continue through the day Sunday, mainly over the Cascades, behind the surface front as the associated low pressure system continues spinning in the NE Pacific. Ensembles indicate this low elongates through the eastern Pacific Sunday, pushing east inland Sunday night into Monday. This pattern produces high chances of rain continuing along the coast and Cascades into Monday (80-95+%) with lower chances for the interior lowlands (20-40%). Additionally, colder air funnels into the region Sunday into Monday, which will cause snow levels to fall from above 5500-6500 ft Sunday morning to 4000-4500 ft Sunday night. At this point, forecasted precipitation amounts are very low over the Cascades Sunday night into Monday morning with less than 10% chance of even 2 inches of accumulating snow anywhere except for the higher peaks above 6000 ft. However, given unmaintained mountain roads are free of snow and remain open, will need to at least explore Winter Weather product for the Cascades if the precipitation forecast increases even a little bit and only a few inches of snow fall Sunday night into Monday.

Ensemble members suggest inland locations could see a brief break in the active weather pattern Monday night into Tuesday afternoon, though light rain chances continue along the coast. The next weather system is then slated to approach the PacNW coast later Tuesday into Wednesday, though ensemble clusters still indicate quite a bit of uncertainty in the track and therefore potential impacts of this weather system. However, NBM's probability of at least 1 inch of precipitation between 4 AM Tuesday through 4 AM Thursday is only 30-50% along the coast, 20-30% along the terrain, and 10-15% for the interior lowlands, so chances are higher that rain impacts will be limited. The airmass will still be on the cooler side when this system hits, and snow levels are forecast to be around 3000-4000 ft Tuesday into Wednesday. Even with the lower precipitation forecast, NBM indicates a 20-30% chance of at least 6 inches of snow at pass level and higher in the 48 hours ending at 4 AM Thursday. This increases to 45-60% chance at pass level and up to 70% chance for higher elevations for at least 3 inches of rain. Once again, may have to consider Winter Weather Advisories for this weather system even if only a few inches of snow fall. Will be keeping an eye on how the forecast evolves. -03

AVIATION...Through 00Z Sunday

A north-south oriented frontal boundary was draped over the Oregon and Washington Cascades as of 22:30Z Friday. Radar and surface weather observations depicted a band of mainly light to moderate stratiform rain along and east of the frontal boundary, with scattered rain showers behind the front impacting both coastal and inland TAF sites. Expect occasional showers to continue impacting each TAF site through 15-18Z Saturday. Breezy south to southeast winds are expected throughout the 00Z TAF period with gusts up to 20-25 kt, except up to 30 kt at KONP, KAST, and KSLE.

Ceilings are expected to fluctuate between high-end MVFR and low- end VFR thresholds both inland and at the coast, with low-end VFR being most predominant through 06Z Saturday. MVFR thresholds are most likely to occur with passing showers Friday afternoon and evening. After 06-08Z Saturday, chances for MVFR ceilings increase to 30-50% at all TAF sites.

KPDX AND APPROACHES...Expect occasional rain showers to continue through 18Z Saturday. Any lingering showers should dissipate after 18Z Saturday, with dry weather expected for the remainder of the 00Z TAF period. Expect breezy southeast winds with gusts as high as 20-25 kt Friday evening through Friday night. Ceilings are expected to fluctuate between high-end MVFR and low-end VFR thresholds, with low-end VFR being most predominant through at least 06Z Saturday. MVFR thresholds are most likely to occur with passing showers Friday afternoon and evening. After 08Z Saturday, chances for MVFR ceilings increase to 30-50%. -23

MARINE

An extremely active and impactful weather pattern will keep ample marine hazards in place through the weekend and potentially beyond. A strong area of low pressure remains offshore as of Friday afternoon. Buoy observations from early Friday afternoon showed southerly winds gusting up to 30-35 kt with significant wave heights around 17-20 ft. The increase in significant wave heights is due to a combination of southerly wind waves and a building long-period westerly swell. A Gale Warning remains in effect across the inner and outer waters, including the Columbia River Bar, through 10 PM PST Friday, except through 7 PM PST for the outer waters.

Although southerly winds will weaken in strength thereafter, seas will remain extremely hazardous and will continue to increase with significant wave heights most likely peaking between 24-29 ft Friday night into early Saturday morning. There is a 10-30% chance seas will peak over 30 ft beyond 20-30 NM offshore over the central and southern outer waters. Seas likely fall back into the upper teens by late Saturday afternoon, especially over the inner waters. However, there is a 20-40% chance that seas will remain at 20 ft or higher through sunset on Saturday over the outer waters beyond 10-20 NM offshore. After sunset on Saturday, chances for seas over 20 ft increase to 45-65% beyond 10-20 NM offshore and near 10% from 0-10 NM offshore. Although seas will most likely dip slightly below 20 ft over the inner waters and Columbia River Bar by late Saturday afternoon, conditions will still be very steep and hazardous.

In addition to the elevated seas, another deep low pressure system will quickly spin up in the NE Pacific on Saturday, pushing a strong front toward the coastal waters Saturday night into Sunday morning. Confidence is high for storm force wind gusts of 48-55 kt beyond 10-20 NM offshore Saturday afternoon through Saturday night, and a Storm Warning is in effect for the outer waters during that time. A Storm Watch remains in effect from 4 PM Sat to 4 AM Sunday for the inner waters and Columbia River Bar, as confidence is lower these marine zones will observe storm force wind gusts of 48 kt or stronger (30-50% chance over the inner waters compared to an 80-90% chance over the outer waters). The reason for this is due to a slight offshore component to the wind direction along the coast, which is not a favorable set-up for a coastal jet. That said, confidence is high winds will at least gust up to 40-45 kt over the inner waters, with the highest chance for low-end storm force wind gusts during a 1-3 hour period with the frontal passage. Beyond the increase in winds, a building westerly swell likely nudges seas above the 20 ft mark again on Sunday with the swell persisting into Monday. Seas gradually diminish towards the 10-15 ft range by Tuesday. -23

BEACH HAZARDS

A very large westerly swell will facilitate dangerous high surf conditions along our beaches to end the week. A large westerly swell upwards of 18-20 ft is already pushing towards the coast as of 2 PM PST Friday, and is expected to increase to 24-27 ft by 7-10 PM PST Friday. This swell will take aim at the Washington and Oregon coast, with the largest wave heights expected along the central Oregon coast. Breakers as high as 30-35 ft are expected, and a High Surf Warning is in effect for the south Washington coast and northern/central Oregon coast between now and Noon Saturday. Given dominant wave periods will be in the 17-20 second range, these waves will have a lot of mass and momentum than the typical storm swell we see this time of year. This will result in waves running significantly farther up on area beaches and jetties than what is normally observed. More simply put, the sneaker wave threat will be extreme. Beachgoers should use extreme caution as 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. In addition, 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. Beach erosion is also expected. Avoid beaches if possible.

The large westerly swell will gradually subside Saturday afternoon and evening, albeit not by very much. The sneaker wave threat will remain high during that time despite breaker heights decreasing. Then, another large westerly swell near 20 ft with dominant wave periods of 15-18 seconds arrives Sunday afternoon and lasts into Monday. This will necessitate another High Surf product and result in another round of high surf conditions, beach erosion, and dangerous sneaker waves. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory until 4 PM PST this afternoon for ORZ101- 102.

High Surf Warning until noon PST Saturday for ORZ101>103.

WA...Coastal Flood Advisory until 4 PM PST this afternoon for WAZ201.

High Surf Warning until noon PST Saturday for WAZ201.

PZ...Gale Warning until 10 PM PST this evening for PZZ210-251>253.

Hazardous Seas Warning from 10 PM this evening to 4 PM PST Saturday for PZZ210-251>253.

Storm Watch from Saturday afternoon through late Saturday night for PZZ210-251>253.

Gale Warning until 7 PM PST this evening for PZZ271>273.

Hazardous Seas Warning from 7 PM this evening to 1 PM PST Saturday for PZZ271>273.

Storm Warning from 1 PM Saturday to 4 AM PST Sunday for PZZ271>273.