textproduct: Portland

SYNOPSIS

A brief period of drier and warmer weather is expected today and Thursday before a more active pattern returns Friday. Multiple frontal systems will bring renewed chances for widespread rain and breezy winds through the weekend and into early next week. Sneaker waves remain a concern along the coast, with another round of high surf increasingly likely Friday night into Saturday.

DISCUSSION...Now through Monday

Upper-level ridging will build over the Pacific Northwest today, supporting mostly dry conditions and unseasonably warm temperatures. Interior valley highs are expected to reach the mid to upper 60s, with a few locations potentially challenging daily record highs. Portland and Hillsboro both have a record high of 64 degrees for today, while Vancouver's record of 66 degrees could also be within reach. A 20-30% chance for showers will persist along the north Oregon coast and in Pacific County.

The ridge begins to shift eastward Thursday, allowing a more onshore pattern to develop. Most locations should remain dry, although a few showers may linger along the north Oregon and south Washington coasts. Interior temperatures will cool slightly, with highs generally in the low 60s, but will remain above seasonal averages. By Thursday night, the next upper-level trough will begin approaching the northeast Pacific, setting the stage for a much more unsettled pattern.

Confidence is increasing that a deep trough will remain over the northeast Pacific from Friday into the weekend, directing a series of frontal systems toward the Pacific Northwest. This will bring repeated opportunities for widespread rainfall and breezy winds across the forecast area. There is still considerable uncertainty regarding the timing and intensity of individual systems, along with eventual rainfall and wind values. However, the overall signal for a wet and increasingly windy period is becoming more consistent. Ensemble guidance suggests high confidence for an integrated vapor transport exceeding 500 kg/m s near the Oregon coast Friday and then moderate confidence Saturday night. This could support another atmospheric river, although the exact placement and duration of the heaviest precipitation remain uncertain.

With several rounds of rain expected, soils may 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. Locally heavy rainfall could also lead to ponding in urban areas, poor- drainage locations, and smaller streams. While it is too early to determine specific rainfall rates, residents can reduce localized flooding issues by checking that gutters and storm drains are clear of leaves and other debris.

Snow levels will initially be quite high with the first incoming system, generally around 5500 to 6000 feet Friday, keeping the Cascade passes largely snow-free. Levels are expected to lower toward 5000 feet Saturday, which could allow some light snowfall near Willamette Pass. With that said, from Friday to Sunday, probabilities for at least 1 inch of snow are less than 5% for the passes, including near Government Camp along Highway 26. Higher elevations above 6000 to 6500 feet are likely to see considerably greater snow fall accumulations.

Wind impacts will also be worth monitoring as the frontal systems move through. Along the coast, there is a 10-20% chance of maximum gusts exceeding 55 mph Friday and Saturday, with the greatest potential Friday. Gusts of this magnitude could result in scattered or widespread tree damage and/or power outages. Farther inland along the I-5 corridor, the probability of gusts exceeding 40 mph is lower, around 5-15%, though isolated impacts remain possible. To prepare, make sure to secure loose outdoor items.

Looking toward early next week, ensemble guidance continues to favor a degree of troughing across the West Coast. This would maintain a generally cool and unsettled pattern, with additional precipitation opportunities likely. The specific timing and strength of any systems remain uncertain at this range. ~12

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 6-10 kt through this afternoon. /DH

MARINE

A frontal boundary draped across the waters is supporting hazardous conditions to some degree for all zones. Currently, a Gale Warning is in effect for waters north of Cape Foulweather, including the Columbia River Bar while Hazardous Seas Warnings are in place south of Cape Foulweather to Florence. Wind gusts around 40 kt are expected through this afternoon before headlines transition to Hazardous Seas Warnings for all zones. A building west swell will increase seas to 13-16 ft around 14 seconds through Wednesday. Hazardous Seas conditions are expected to continue through tonight before possibly dropping down to Small Craft Advisory conditions.

A brief lull in activity is expected on Thursday before ramping back up late Thursday evening. Another strong front is expected to move into the waters, likely bringing at least Gales with a 70-80% chance and a 10-30% chance for storm force winds (highest in the outer waters). As a result, a Gale Watch has been issued beginning at 4 PM Thursday for the waters north of Cape Falcon and then expanded to all the waters by 10 PM Thursday. Seas are again expected to rise above 20 ft by Friday afternoon with a 30-60% chance for greater than 25 ft and a 10-20% chance for 30 ft or greater in the outer waters. Another strong front is expected during the latter half of Saturday, continuing the active pattern for the waters. ~12/19

BEACH HAZARDS

A moderate to high sneaker wave threat continues along the coast through this week as a westerly swell of 10-12 ft at 13-15 seconds increases to 14-16 ft midweek. 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 18-22 ft with a dominant period at 16-18 seconds will impact the coast on 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.

Hazardous Seas Warning from 4 PM this afternoon to 4 AM PST Thursday for PZZ210.

Gale Watch from Thursday afternoon through late Thursday night for PZZ210-251-271.

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

Gale Watch from Thursday evening through late Thursday night for PZZ252-253-272-273.

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