textproduct: Portland

SYNOPSIS

An active weather pattern will continue through much of the next week, producing periods of rain and wind, especially along the coast. Following a midweek lull, a more potent system could affect the region late in the week.

DISCUSSION...Now through Sunday

Radar and satellite imagery early Monday morning show mostly dry conditions with mid to high level clouds over NW OR and SW WA with the next frontal system around 150-200 miles offshore speeds towards the coast. This next front will move quickly from west to east today, bringing a quick shot of rain to the area. Expect rain to begin along the coast later this morning, moving inland by midday, and tapering off from west to east through the evening hours. Latest guidance indicates higher precipitation amounts are expected today than previous forecasts with around 0.25-0.5 inch along the I-5 corridor and around 0.5-0.75 inch along the coast, Coast Range, and Cascades. Rain will be heavy at times with a 20-50% chance of rain rates of 0.1-0.15 inch for the interior lowlands and 20-40% chance of rain rates of 0.2-0.25 inch for the terrain. Expect ponding of water on roadways and in low lying areas, especially where leaves remain on the ground and could clog drains. Breezy southerly winds expected along the coast with gusts up to 35-40 mph this afternoon and gusts of 20-25 mph inland. Seasonable temperatures in the 50s also continue today.

On Tuesday, another upper-level shortwave moves into the Pacific Northwest while upper-level ridging will begin to amplify east of the Cascades. This ridging will act to limit rain to the coast, Coast Range, and inland areas north of US-20 Tuesday morning, then steadily displace rain chances to the north through the afternoon. A rather sharp gradient in rainfall totals on Tuesday is expected from south to north, with little to no rain south of US-20, less than 0.2 inch for the interior lowlands south of Longview and the coast south of Tillamook, 0.25-0.5 inches for the SW WA Cascades and Tillamook to the state line, and 0.5-1 inch for Pacific County. Heavier rain associated with this atmospheric river is expected over the Olympic Peninsula. Breezy southerly winds with gusts as highs as 30-40 mph can be expected along the coast north of Tillamook and SW WA west of I-5 through Tuesday evening.

Upper-level ridging will reach its peak amplitude on Wednesday, supporting dry and unseasonably warm temperatures in the low to mid 60s with light offshore flow. Daily record high temperatures look to remain out of reach for most locations, though the record values of 64F at Portland (PDX) set in 1989 and 66F at Vancouver (VUO) set in 1904, 1907, and 1930 may be in jeopardy. Thursday is expected to be a transition day as upper ridging begins shifting east as upper troughing begins pushing into the northeastern Pacific. Daytime temperatures will lower a few degrees, though will still be unseasonably warm in the low 60s inland. Mostly dry weather is expected through the day except for a 20-40% chance of showers along the coast, mainly due to uncertainty on specific timing of the approaching trough.

There remains good consensus amongst ensemble members that an upper-level low pressure system will become situated over the northeast Pacific west of Canada from late Thursday/Friday into the weekend, returning troughing to the Pacific Northwest. Multiple surface frontal systems are expected to move through the region during this time, bringing repeated chances for widespread rain and breezy winds. Specific details remain uncertain, but this is shaping up to be another atmospheric river event as long-range ensembles indicate a 60-70% chance for vapor transport to exceed 500 kg/(ms) at the leading edge of this trough on Friday somewhere along the Oregon coast with higher probabilities of vapor transport values remaining above 250 kg/(ms) through Saturday. NBM probabilities for 2 inches of rain from Friday morning through Sunday morning are 30-15% along the I-5 corridor and 60-80% for the coast and terrain. Additionally, the coast and terrain have a 20-50% chance of 3 inches of rain for the same time period. Increasingly saturated soils from multiple weather systems could allow for greater runoff into area rivers, meaning at least isolated flooding cannot be ruled out. -03/36

AVIATION...Through 12Z Monday

As of 12Z Monday, widespread VFR conditions are being observed, though locally low stratus/fog has developed in the past couple of hours leading to localized IFR/LIFR conditions. These could continue until after sunrise, around 14-16Z. Otherwise, CIGs are expected to slowly trend towards low-end VFR through 15Z-18Z Monday ahead of the next frontal system. Southwesterly winds along the coast and variable winds inland around 3-6 kt through around 18Z Monday.

The next system arrives Monday morning, returning rain showers to the coast and southern Valley around 16Z Monday, spreading northeastward into the rest of the Valley by 18Z Monday along with Coastal TAF sites. Showers could be heavy at times, briefly reducing visibility. As the front moves in, conditions will trend towards MVFR/IFR along the coast starting around 18Z-20Z Monday, and around 20Z-22Z Monday for inland locations. Guidance suggests a 40-70% chance for MVFR CIGs across the region at any given hour between 18Z Mon-02Z Tue, with the highest chances along the coast. Southerly winds increase after 18Z Monday with gusts up to 25-30 kt along the coast while winds generally remain under 10 kt inland. However, could see some isolated gusts up to 20 kt for locations within the Central Willamette Valley and near the mouth of the Columbia River Gorge from 18Z Monday to 02Z Tuesday. For KTTD, surface winds trend more east/southeasterly while winds aloft are westerly, which could result in some LLWS from 20Z-23Z Monday as the front passes.

KPDX AND APPROACHES...VFR conditions with mid to high clouds with ground fog or low stratus producing occasional IFR conditions through 14Z Monday. Around 18Z Monday, conditions drop towards low- end VFR/MVFR as the next system approaches and showers begin. Showers could be moderate to heavy at times, briefly reducing visibility. There's a 50-75% chance for MVFR CIGs at any given hour between 21Z Mon-02Z Tue. -03/42

MARINE

An active weather pattern will continue across the waters through the week. As of early Monday morning, wind gusts are less than 15 kts and seas have fallen to around 12-15 ft around 13-15 seconds. Seas will continue to fall to around 10-13 feet by sunrise, remaining through tonight. Winds over the waters begin to ramp up later this morning as the next frontal system approaches the waters. High resolution model guidance suggests high confidence (>80% chance) for a return of breezy southerly winds with gale force wind gusts up to 35 kt at any given hour from 0900 to 1600 Saturday.

Winds will decrease briefly Monday night, though occasional gusts up to 25 kts will be possible, before the next frontal system will bring another round of gale force wind gusts Tuesday morning, continuing into Wednesday. A Gale Warning is in effect through at least Tuesday for all of the waters. Additionally, an increasing westerly swell on Tuesday will build seas to 14-18 ft at 13-15 seconds. Conditions calm a bit on Thursday before ramping up again at the end of the week. -03/10

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 12-15 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, leading to a High Surf concern. NBM indicates a 50-70% chance of seas increasing to 20-25 ft at any given hour between 1 AM to 4 PM on Saturday. This would result in large waves and 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 10 AM PST Tuesday for PZZ210-251>253-271>273.