textproduct: Portland

SYNOPSIS

A rather active weather pattern continues to steer a series of frontal systems into the Pacific Northwest through the middle of next week with rainy conditions persisting at times. High surf, sneaker waves, and breezy winds impacts continue through this weekend as well. Snow levels fluctuate between 5000-7000ft through Sunday before falling near 4000 ft in the Cascades Sunday night into Monday and 3000-4000 ft Tuesday into Wednesday with potential for pass-level snowfall concerns.

DISCUSSION...Now through Friday

Water vapor satellite imagery reveals the next low pressure system wrapping up in the NE Pacific this afternoon. The 960 mb surface low will remain north as it drifts into the Gulf of Alaska. But, the associated cold front racing across the Pacific today will push across the Pacific NW tonight bringing breezy winds and increasing rainfall across the area later this evening into Sunday. NBM and hi-res guidance suggest rain likely arrives at the coast by 6-8 pm and spreads inland quickly thereafter. A strong southwesterly upper level jet will push into western Oregon associated with IVT values peaking between 500- 750 kg/m2. With the orientation and speed of the frontal system, expect the highest rainfall rates and accumulations to occur along the coast and southwest facing slopes of the Coast Range, as well as into the SW Washington Cascades. Here, probabilities for exceeding 1 inch of rainfall over 24-hours is highest, generally between 30-70% at the coast (highest along the central OR coast), and 50-80% in the Coast Range. The interior lowlands along the I-5 corridor are more likely to see around 0.25 inch total (60-80% chances), where more of a rain-shadow effect is expected. Steady rain transitions to showers on Sunday behind the frontal passage. South to southeast winds increase today ahead of the approaching front. The strongest winds are expected at the coast, likely peaking later this evening (between 8 PM and midnight) with gusts up to 40- 50 mph. There remains around a 10% chance for high wind gusts exceeding 58 mph. Breezy winds inland should max out with gusts around 25-35 mph.

Post-frontal showers continue through Sunday, while snow levels gradually drop from around 6000 ft Sunday morning to around 4000- 4500 ft Sunday night. Snow showers may occur down to pass level in the Cascades, but probs for even 1 inch of accumulation remain low (25% or less) through Sunday night. By Monday, the upper level trough becomes stretched and elongated offshore, pushing south of California before sliding inland across the West Coast. This will maintain chances for light showers across the area through the day, while temperatures trend cooler back toward seasonal norms.

Ensemble members show increasing confidence in a brief break in the active weather pattern late Monday night through Tuesday afternoon. 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 of the low pressure system and therefore potential weather impacts. However, NBM's probability of at least 1 inch of precipitation between 4 AM Tuesday through 4 AM Thursday is only 10-40% along the coast, 10-20% along the terrain, and 1-10% for the interior lowlands, so the trend is for rain impacts to 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 5-10% chance of at least 6 inches of snow at pass level. This increases to 10-20% chance at pass level and up to 50% chance for higher elevations for at least 3 inches of snow. Highest probabilities near Willamette Pass. DH/99

AVIATION...Through 18Z Sunday

VFR conditions are being observed Saturday afternoon across NW OR and SW WA with very light rain showers over locations north of KTMK and KSLE. The next frontal system is approaching the region Saturday afternoon, causing southerly winds to increase along the coast. Gusts of 25-30 kts will increase through Sunday night, peaking around 04-08z Sun with gusts up to 35-40 kts possible (40-70% chance), and winds shift from southeast to southwest after 07-08z Sun. Winds inland are south to southeast around 7-10 kts with occasional gusts to 20-25 kts. More widespread gusts up to 20-25 kts expected between 05-12z Sun, then winds shift to the south to southwest after 09-12z Sun. Another round of widespread rainfall will push into the coast around 01-03z Sun then move east to inland terminals by 04-06z Sun. Conditions along the coast deteriorate to MVFR after 05z Sun with heavier rain showers causing occasional IFR conditions at times. Conditions improve to VFR after 12-14z Sun as rain transitions to showers along the coast. There's a 30-50% chance of MVFR conditions for inland terminals at any given hour between 09-16z Sun, so expect mainly VFR conditions with heavier showers causing occasional MVFR conditions.

KPDX AND APPROACHES...Predominately VFR conditions with dry weather through early Saturday evening, though can't rule out a stray light rain shower or two. Southeast winds around 10 kts. The next frontal system brings widespread rain around 04-05z Sun. Expect mainly VFR conditions with heavier showers producing MVFR conditions at times between 09-16z (20-40% chance). Wind gusts increase to 20-25 kts between 06-12z Sun, shifting from southeast to south around 08-11z Sun. -03

MARINE

Rather treacherous marine conditions are expected to continue into Sunday. Seas are forecast to remain above 20 ft around 20-25 ft at 14-18 seconds through Sunday night. This is due to a combination of an exiting strong westerly swell, increasing westerly winds today, and a fresh westerly swell moving into the waters on Sunday. A Hazardous Seas Warning is in effect through 4pm this afternoon. In addition to these elevated seas, another deep low pressure system in the NE Pacific is pushing a strong front east and will move through the coastal waters tonight into Sunday morning. Confidence is high for storm force wind gusts of 48-55 kt across our waters accompanying this front, especially beyond 10-20 NM offshore, starting late this afternoon and continuing through around 10 PM PST. Thus, a Storm Warning is in effect for the inner/outer waters including the Columbia River Bar during this time period, followed by another Hazardous Seas Warning through Sunday for the elevated seas. Wind gusts will quickly fall down to 30-39 kts behind the frontal passage after 10 PM PST, then lowering to 25-30 kts Sunday morning.

Seas are forecast to gradually diminish below 20 ft Monday towards the 10-15 ft range by Tuesday morning, and wind gusts decrease below 20 kts by Monday morning. However, 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 14-16 ft at 14-15 seconds through Wednesday night. There's a 50-60% chance that seas could reach at least 17 ft beyond 40 NM from the coast. Looking further ahead, there is decent model agreement for seas to slowly decrease through the end of next week, dropping below 10 ft by Friday as the weather pattern briefly calms. -03

BEACH HAZARDS

Hazardous high surf conditions will continue along the Oregon and southern Washington beaches through Monday morning. Even though the westerly swell from overnight is slowly decreasing today, the swell still remains higher than normal around 16-18 ft at 15-16 seconds, which still translates to breakers of 20-25 ft. The sneaker wave threat still remains extremely high during this period. Then, another large westerly swell around 20 ft with dominant wave periods of 15-18 seconds arrives Sunday afternoon and lasts into Monday, resulting in breakers up to 25 to 30 ft. A High Surf Advisory is in effect through 10 AM Monday. 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. 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. All in all, please remain extremely vigilant if you insist on visiting area beaches the next several days - your life may depend on it.

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 4 PM PST this afternoon for PZZ210- 251>253.

Hazardous Seas Warning from 4 AM Sunday to 4 AM PST Monday for PZZ210-251>253-271>273.

Storm Warning until 4 AM PST Sunday for PZZ210-251>253.

Storm Warning until 4 AM PST Sunday for PZZ271>273.