textproduct: Portland

SYNOPSIS

Unsettled showery weather lingers through Monday while a high surf and sneaker waves threat persists across our beaches - the product of the active pattern we've seen the last several days. Snow levels drop to 4000 ft in the Cascades tonight into Monday before conditions quickly trend drier Tuesday. We'll still need to watch for some limited pass snowfall concerns on Wednesday (mainly central OR Cascades) before dry conditions return again to end the week.

DISCUSSION...Now through Saturday

Yet another frontal system has passed through the region early this morning with bands of showers currently spread across southwest Washington and Western Oregon. We'll stay in this post-frontal airmass into Monday. It's worth quickly noting while some of these cells are presenting decently on radar to start the day, model soundings show the CAPE fueling these cells largely below the temperature layer (-10 to -20c) typically needed for electrification. Thus, the probability for T-storms today is low, only around a ~10% chance, but strong cells could still produce heavy rainfall and locally gusty outflow winds. Cooler air gradually filters in aloft over the next 24 hours, allowing snow levels to drop from 6000-7000 ft early this morning to around 4000-4500 ft tonight into Monday morning. Snow showers may occur down to pass level in the Cascades, but probabilities for 2 inch of accumulation or more at pass level remain fairly low (10-35% or less) through Monday morning. By Monday evening, the upper level trough becomes stretched and elongated offshore, pushing south of California before sliding inland across the West Coast and spelling the end for any lingering showers come sunset.

Ensemble members show increasing confidence in a brief break in the active weather pattern Monday night through Tuesday afternoon thanks to a weak transient ridge of high pressure passing overhead. Areas of morning valley fog likely make a return. The next weather system is then slated to approach the PacNW coast late Tuesday into Wednesday, with ensemble clusters now showing better agreement on the general track of this system. Exploring the latest 00/06z guidance, the vast majority of models show the vertically stacked low pressure undercutting us to the south and diving into California. Still, a shortwave rotating around the larger circulation associated with this system will attempt to sling-shot northward into the region increasing chances for precipitation. While precipitation amounts don't appear particularly noteworthy, the airmass will still be on the cooler side when this system hits, and snow levels are forecast to be around 3000-3500 ft Tuesday night into Wednesday. The best chances (30-50%) for 2+ inches will the across the southern portion of our CWA across Santiam and Willamette pass. Otherwise, once we get into the Thursday through Saturday time period, there is good ensemble agreement in prevailing dry conditions with near normal temperatures, enjoy the dry window while we have it. -99/DH

AVIATION...Through 18Z Monday

The region remains under scattered post-frontal showers with mainly VFR conditions in place across the airspace. Skies are expected to slowly clear through the majority of the TAF period. However, showers are expected to linger and could result in periods of MVFR conditions through 03Z Monday. Overall shower coverage slowly decreasing after 03Z Monday, but clouds are expected to return as another round of precipitation is expected towards the end of the TAF period. Winds stay a little breezy out of the south today with gusts up to 25 kts along the coast and 10-15 kt for inland locations before decreasing this evening.

KPDX AND APPROACHES...Generally VFR conditions with intermittent showers through the majority of the TAF period. Showers could bring brief periods of MVFR conditions through 22Z Sunday, with VFR conditions around FL040 expected afterwards through at least 15Z Monday. Light precipitation expected to return towards the end of the TAF period. /42

MARINE

An aggravated seas state continues into early next week as an yet another frontal system and reinforcing swell takes aim at the region. Our latest frontal system has passed to the east early this morning with seas holding in the mid to upper teens at 12-15 seconds through a good chunk of the daytime hours - a Hazardous Seas Warning remains in effect. As alluded to, a trailing westerly well is expected to arrive late this afternoon and evening, likely pushing significant waves heights back into the 19-23ft range overnight into early Monday morning. Fortunately after this point seas are forecast to gradually diminish below 20 ft by midday Monday, bottoming out near 10-14 ft by Tuesday morning while wind gusts decrease below 20 kts as well. However the lull is fairly short-lived as another frontal system will increase winds again Tuesday afternoon through Tuesday night. There's a 60-80% chance of Gales for locations beyond 30 NM from the coast during this time and a 30-50% chance for the waters within 30 NM from the coast. Another increasing fresh westerly swell follows Wednesday morning, increasing seas to around 14-18 ft at 14-16 seconds through Wednesday night. Looking further ahead, there is decent model agreement for seas to slowly decrease through the end of the week into the first half of next weekend, likely dropping below 10 ft by Friday as the weather pattern briefly calms. Ensemble models hint at another storm system around the second half of next weekend which would bring renewed winds and swells. -99/03

BEACH HAZARDS

Hazardous high surf conditions persist the latter half of the weekend into early next week along the Oregon and southern Washington beaches. Seas currently sit in the upper teens this morning with another westerly swell around 17-22 ft accompanied by a dominant wave periods of 15-18 seconds slated to arrive this afternoon through Monday. This will translate to breakers up to 25 to 30 ft for our beaches. Thus, a High Surf Advisory is in effect through 10 AM Monday before the seas slowly diminish. In these conditions, wave will run significantly farther up on area beaches and jetties than what is normally observed. More simply put, the sneaker wave threat will be very high. 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. Never turn your back to the ocean. 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. Further beach erosion is also possible. Avoid the beaches if you can.

PQR WATCHES/WARNINGS/ADVISORIES

OR...High Surf Advisory until 10 AM PST Monday for ORZ101>103.

WA...High Surf Advisory until 10 AM PST Monday for WAZ201.

PZ...Hazardous Seas Warning until 7 PM PST Monday for PZZ210.

Hazardous Seas Warning until 10 PM PST Monday for PZZ251>253- 271>273.