textproduct: Portland

SYNOPSIS

A rather active weather pattern continues steer a series of frontal systems into the Pacific Northwest ushering in periods of high surf and sneaker waves to the coast, and rain/breezy conditions areawide through at least early next week. Snow levels fluctuate between 5000-7000ft the next couple of days before falling near 4000 ft in the Cascades late Sunday into Monday.

DISCUSSION

Our focus remains on a strong but vertically stacked low pressure system off the coast of the Pacific Northwest where the latest WPC surface analysis estimates the surface pressure has slowly weakening/filling in to 965mb. Current satellite and radar depict the accompanying frontal boundary rushing into western Oregon and southwest Washington early this morning, likely making it into the I-5 corridor for the morning commute. A strong wind field of 60-70 kt at 925mb has developed along the southern and central coast of Oregon with a decent east to west pressure gradient present as well. While it likely keeps east winds pushing through the Cascade gaps, it should also keep most of the aforementioned strong winds just off the coast, particularly off the north Oregon and south Washington coast. However, the pressure gradients do open ever so slightly that some of this wind field could be realized at our most exposed locations along the central coast of Oregon. Would estimate there is a 25% chance our windiest sites meet High Wind Warning criteria (58mph+) with lower odds north of Tillamook County. Will need to monitor trends and monitor buoy observations to see how well they are tracking with modeled wind fields but so far so good. Either way, given the pressure gradients the strongest winds are unlikely to last more than 1-2 hours along any portion of the coast, which should reduce impacts. The bigger impact 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.

Models and their ensembles are in good agreement an embedded shortwave trough will swing northeastward into the area this afternoon into early evening, which should aid in creating a more organized band of showers spreading into the region around that time. Cooler sea surface temperatures near the coast may limit vigorous convection coming onto the coast, but wind fields will be supportive of some rotating storms farther offshore Friday.

The next storm system is currently south of the Aleutian Islands and will shift eastward over the first half of the weekend. As it does so, another low pressure will deepen rapidly to around 960mb and move into the place of the current existing low pressure over the northeast Pacific. This will push another front eastward into the region Saturday night bringing another round of increased winds along the coast. It appears there is a 30-40% chance for a low end High Wind event along the coast late Saturday before a cooler and more showery weather regime takes hold. Snow levels will drop from above 5000-7000 ft early Sunday to near 4000 ft by Monday morning. Given unmaintained mountain roads are free of snow and open, will need to at least explore Winter Weather product for the Cascades even if only a few inches of snow fall Sunday night into Monday - currently precipitation appears limited.

There looks to be a brief lull in the wet and breezy weather around Tuesday before most global ensemble members suggest another storm system impacts the region Wednesday into Thursday of next week. However, ensemble clusters do show a notable amount of variance in the exact track and thus potential impacts of this system. -99/Neuman

AVIATION...Through 12Z Saturday

Our next frontal boundary quickly approaches with rain already in place along the coast, likely spreading inland by 12-15z. However, this front should quickly dissipate any lingering fog and IFR/LIFR conditions in the southern Willamette Valley with a return to MVFR/VFR. For locations near the Portland metro where east winds likely persist most of the TAF period, the latter (VFR) is favored. That said, there'll still be chances for MVFR conditions once the front passes and we break to post-frontal showers this afternoon (10-35% chance each hour). Showers likely persist into Saturday morning. Southerly winds increase with the arrival of the front with gusts 25-30 kt along the coast. Inland will be a touch lower up to 15-25 knots.

KPDX AND APPROACHES...Rain is quickly approaching however easterly flow should keep CIGs/VIS mainly VFR through the period. Still, once we break to post-frontal showers there'll be a 20-25% chance for MVFR conditions this afternoon. -99

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 well off the coastline of the Pacific Northwest is pushing a frontal boundary over the coastal waters early this morning with Buoys 29/50 recording gusts between 35-40 knots. As a result, a Gale Warning remains in effect across the inner and outer waters, including the Columbia River Bar, through the afternoon today. There remains around a ~30% chance for Storm Force wind gusts up to 50 kt, likely associated with the frontal passage this morning. Gusty south winds are expected to gradually moderate tonight, albeit only temporarily.

Looking at additional observations, seas early this morning currently sit around 14-16 ft at 12-14 seconds as we await a strong, long period westerly swell slated to arrive by midday, helping to push seas above 20 ft by 2-4 PM. Significant wave heights are likely (60-85% chance) to build into the mid-20s tonight before slowly subsiding Saturday. The latest guidance even indicates a 10-15% chance for seas to push the 30ft mark tonight as wave heights peak. Seas likely fall back into the upper teens by late Sat afternoon, but there is a 20-40% chance that seas remain at 20 ft or higher through Sat night as the next frontal system arrives.

Another deep low pressure system quickly spins up in the NE Pacific on Saturday pushing a strong front toward the coastal waters Sat night into Sunday morning. At a minimum we'll likely see yet another period of strong southerly Gales while the NBM continue to hint at a 40-70% chance for Storm Force wind gusts exceeding 50 kt - highest probabilities across the outer coastal waters. A Storm Watch remains in effect from 4 PM Sat to 4 AM Sunday for the inner and outer waters. 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. Looking through the middle of next week, seas gradually diminish towards the 10-15 ft range by Wednesday. -99/DH

BEACH HAZARDS

The combination of a notable tidal anomaly and large westerly swell will facilitate impactful conditions along our beaches to end the week. A tidal anomaly from persistent southerly winds and warmer than average ocean temperatures will result in the total tide pushing ~10.2-10.5 ft at the Garibaldi tidal gauge this afternoon which historically produces flooding along Fraser-Burton Road south of Tillamook along the Tillamook River. Elsewhere, lowland and agriculture flooding will occur with total tides of ~10.6 ft and 11.2 ft at Astoria and Toke Point respectively. Small stretches of Highway 101 and other low lying areas could be impacted in Clatsop and Pacific County as well this afternoon.

However, more importantly, a large westerly swell will push towards the coast Friday afternoon and peak late Friday evening (most likely between 7-10 PM). This swell will take aim at the southern Oregon coast, but a swell of 25+ ft will still push onto the central and north Oregon coast while the swell will be closer to 20 ft along the south Washington coast. Given periods will be in the 17-20 second range, these waves will have a lot of mass and momentum than the typical Winter time storm swell we see this time of year. This will result in waves running significantly farther up on area beaches and jetties.

More simply put, the sneaker wave threat will be extreme. People 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.

The large westerly swell will gradually subside Saturday. However, another westerly swell that will be pushing 20+ ft with dominant 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 sneaker waves during this time. -99/Neuman

PQR WATCHES/WARNINGS/ADVISORIES

OR...Coastal Flood Advisory from noon today to 4 PM PST this afternoon for ORZ101-102. High Surf Warning from noon today to noon PST Saturday for ORZ101>103. WA...Coastal Flood Advisory from noon today to 4 PM PST this afternoon for WAZ201. High Surf Advisory from noon today to 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 PZZ251>253-271>273. Gale Warning until 7 PM PST this evening for PZZ271>273. Hazardous Seas Warning from 7 PM this evening to 4 PM PST Saturday for PZZ271>273.