textproduct: Portland

SYNOPSIS

After a storm system clips the area today, expect drier weather Wednesday and Thursday before another storm system brings widespread rain and breezy conditions to the area Friday into the weekend. Sneaker waves will be a threat through the week with another round of high surf conditions appearing increasingly likely Saturday. A cool and wet pattern continues early next week.

DISCUSSION...Now through Monday

Radar imagery and surface observations as of early Tuesday afternoon depicts a band of rain over far northwest Oregon and southwest Washington as an atmospheric river pushes into the Pacific Northwest and British Columbia. Moisture that is being squeezed between upper-level troughing over the Gulf of Alaska and upper-level ridging over the Great Basin and southwestern U.S. has become an atmospheric river aimed towards our area. High pressure to our south is resulting in a pretty distinct line between rain and dry conditions. Most of the rain over the past 12 hours has been north of a line from Newport, OR to The Dalles, OR. Surface observations have shown rain amounts between 0-0.10" for locations along this line and southward, while areas to the north have received anywhere from 0.25 to 1 inch in the last 12 hours. The heaviest rain amounts have been further north over the Olympic Peninsula. Breezy southerly winds continue along the coast through this afternoon with gusts to 30-40 mph. Inland, winds are generally coming out of the southeast but remaining under 10 mph. Tonight, upper-level ridging will build over the area, gradually decreasing rain and returning drier conditions.

Upper-level ridging will reach its peak amplitude on Wednesday, supporting dry and unseasonably warm temperatures across interior valleys with high temperatures forecast in the mid to upper 60s. Daily record high temperatures could be broken tomorrow, including the 64F record at Portland (PDX) and Hillsboro (HIO) set in 1989, and 66F at Vancouver (VUO) set in 1904, 1907, and 1930 may be in jeopardy. However, a 20-40% chance for showers will continue in Pacific County and along the coast north of Tillamook. Thursday is also looking to be a mostly dry day with similar chances for showers along the north Oregon and south Washington coast. Daytime temperatures will lower a few degrees, though will still be unseasonably warm in the low 60s across interior valleys. By Thursday night, upper- level ridging will begin to shift eastward as upper-level troughing begins pushing into the northeast Pacific.

There is high confidence that a deep upper-level trough 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. There is still uncertainty with specific rainfall amounts and peak wind gusts; however, we can say for certain that it will be wet. 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 similar probabilities of vapor transport values remaining above 250 kg/(ms) into Sunday. Increasingly saturated soils from multiple weather systems could allow for greater runoff into area rivers, meaning at least isolated flooding cannot be ruled out. However, chances for widespread flooding of rivers remains <5% at this time. It's still too far out to determine hourly rainfall rates, but if rain is heavy enough, we could also see some urban and small stream flooding of low-lying and poor drainage areas. People should make sure to clear gutters and storm drains of any leaves or debris.

Across the Cascades, it appears that this system will be warm enough to keep snow levels between 5500-6500 feet on Friday, keeping the passes snow-free. By Saturday, snow levels drop to around 5000 ft, potentially bringing some light snow to Willamette Pass. From Friday afternoon to Sunday afternoon, there is a 30% chance for total snowfall amounts of 1 inch or greater along Santiam and Willamette Passes, and a 10% chance along Highway 26 at Government Camp. Much higher snowfall amounts expected above 6000-6500 feet.

When it comes to winds, there is a 20-40% chance for maximum wind gusts exceeding 55 mph along the coast Friday and Saturday, with the highest chances on Friday. Wind gusts of this magnitude could result in scattered or widespread power outages or tree damage. Along the I-5 corridor, there is a 5-15% chance for maximum wind gusts exceeding 40 mph, which could result in isolated power outages or tree damage. To prepare, make sure to secure loose outdoor items.

Heading into early next week, the vast majority of ensemble members show some degree of troughing over the West Coast, maintaining a generally cool and wet pattern. -10/03

AVIATION...Through 00Z Thursday

A warm front has shifted northward into Washington late this afternoon and evening where most of the rain has now shifted. South of the warm front, conditions have trended VFR except along portions of the coast, which are still stuck in IFR conditions. Elsewhere skies have mostly cleared or at least clouds have thinned. With light winds and dewpoints in the mid 50s, and models suggesting only passing high clouds overnight, it seems the probability for fog development is growing rapidly, particularly along and west of Interstate 5. Despite only 10-20% of the high resolution ensembles suggesting fog development in the Willamette Valley, have opted to include it in the TAFs for KEUG, KSLE, KUAO and KHIO for now. May need to add IFR conditions into KPDX, but low level easterly winds should help to keep conditions VFR. Fog and low clouds will be more stubborn than normal to scatter out on Wednesday, particularly across the western and southern portions of the Willamette Valley given weak pressure gradients and winds aloft so will not be surprised if some sites stay stuck in IFR conditions into Wednesday evening. Meanwhile, gusty southerly winds along the coast will continue through the taf period with gusts generally hovering between 20-30 kt.

KPDX AND APPROACHES...A warm front has lifted north of the region with thinning cloud cover over the terminal. Easterly winds continue at the surface, which should help to keep conditions VFR overnight. With that said, not super confident we won't see those winds weaken with fog either developing or pushing upriver into the terminal as a result. For now will plan to keep the TAF VFR, but will be monitoring trends to see if any adjustments towards IFR conditions is needed.

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 Falcon, including the Columbia River Bar while Hazardous Seas Warnings are in place south of Cape Falcon to Florence. The Gale Warning expands southward to zones PZZ272 and PZZ252 later this evening. Wind gusts around 40 kt are expected through Wednesday afternoon before headlines transition to Hazardous Seas Warnings for all zones. A building west swell will increase seas to 14-17 ft around 14 seconds through Wednesday. Hazardous Seas conditions are expected to continue through Wednesday night 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 Storms (highest in the outer waters). Seas are again expected to rise above 20 ft by Friday afternoon with a 30-50% chance for greater than 25 ft and a 10-15% 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. -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.

There is also the potential for tidal overflow flooding Wednesday as the tide plus anomaly are forecasted between 10 and 11 ft (MLLW). This could lead to further water inundation and coastal erosion.

Additionally, confidence is increasing that a stronger westerly swell of 20-24 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. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Gale Warning until 4 PM PST Wednesday for PZZ210-251-271.

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

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

Hazardous Seas Warning until 7 PM PST this evening for PZZ252- 272.

Gale Warning from 7 PM this evening to 4 PM PST Wednesday for PZZ252-272.

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