textproduct: Portland

SYNOPSIS

Dry weather under higher pressure continues through late Saturday with another round of fog and frost development expected tonight into Saturday morning. A pattern shift early next week will favor a wet week for the upcoming holiday.

DISCUSSION...Today through Friday

Visible satellite imagery along with ground observations shows dense fog across the Willamette Valley this morning. Much like yesterday, expect this fog to lift and become low level clouds. Saturday overall is expected to be mostly a rinse and repeat of Friday. A weak weather system slowly approaches the region today which will bring increasing precipitation chances along the north Oregon and SW Washington coast. As Saturday progresses, the cold frontal system will bring a widespread band of precipitation inland by Saturday evening through Sunday, precipitation will become showery Sunday afternoon/evening and continuing through Monday afternoon. Rain amounts with the Saturday through Monday system will be around 0.25-0.95 inches along the coast and Coast Range, 0.15-0.35 inches for inland locations, and 0.25-1.00 inches over the Cascades. Snow levels remain above Cascade pass level through Sunday, then they will begin falling Sunday night behind the cold front, falling to 2500-3000 ft by Monday morning. However, as conditions will be showery by this point, limited snow accumulation is expected at pass level, generally less than 2 inches. Winds are not expected to increase much with this system with gusts up to 30 mph along the coast Sunday during the day and over the Cascades Sunday night, remaining less than 20 mph for inland valleys. The start of next week, mornings again are expected to be on the cooler side even with widespread cloud cover. Monday night into early Tuesday is expected to be dry with another night of colder temperatures in the 30s across the interior lowlands. By midday Tuesday, widespread precipitation chances increase again as ensemble guidance members indicate the first in a series of back to back frontal systems move through the region. Current guidance has an active weather pattern continuing through the remainder of the week. Exact timing details remain uncertain this far out, but limited impacts are expected at this time.

Probability for 2 inches of rain in the 72 hour period from 4 AM Tuesday to 4 AM Friday is 5-10% for inland lowlands, 15-30% chance south of Highway 20 in Oregon, and 40-75% chance north of Highway 20. 3 inches of rain over the same 72 hour period are less than 10% for inland lowlands, 10-20% chance south of Highway 20 in Oregon, and 20-45% chance north of Highway 20. Given that these system will be warm, snow levels will rise above pass level. Looking beyond Thursday, ensembles indicate yet another weather system could bring additional rain on Friday into Saturday. Keep an eye on the forecast if you have holiday travel plans! /42

AVIATION

The influence of high pressure persists resulting in fog continuing to develop across much of the Willamette Valley and portions of SW Washington. This is resulting in widespread IFR/LIFR conditions. These conditions are expected to persist through at least 18Z Saturday. However, it will be challenging to forecast when/if these conditions could improve. In general, guidance is showing general improvement towards IFR/MVFR conditions from 18Z-20Z Saturday, but at this point, there is around a 60% probability of improvement. If there is any improvement, expect it to be rather short lived as conditions are expected to deteriorate back towards IFR/LIFR around 00Z-03Z Sunday.

KPDX AND APPROACHES..LIFR conditions currently in place at and near the terminal. Expecting conditions to improve around 18Z-20Z Saturday with a return to MVFR/VFR conditions by 20Z-22Z Saturday. However, there is around a 40% probability of conditions only improving to IFR. If there is any improvement, expect it to be rather short lived as conditions are expected to deteriorate back towards IFR/LIFR around 00Z-03Z Sunday. /42

MARINE

High pressure over the area is maintaining fairly stable conditions with minimal change expected through Monday. Seas currently range from 10-15 ft at 12-16 seconds and are expected to slowly subside towards 9-12 ft by Monday. Seas are expected to fall below 10 ft around Monday afternoon and will persist through at least the middle of the upcoming week. On Sunday a frontal system will make it's way over the waters causing winds to increase from the south with gusts up to 25 kt. The low will move inland by late Sunday into Monday and winds will shift to the northwest. /42

BEACH HAZARDS

An energetic westerly swell is expected along the northwestern Oregon and southwestern Washington coasts through Monday. Seas 9-14 ft at 13-16 seconds are forecast through the the weekend. These energetic waves can run significantly farther up a beach than normal, including over rocks and jetties, creating potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters.

A Beach Hazards Statement has therefore been issued through 10 AM Monday. Caution should be used when in or near the water, and beachgoers with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. Those participating in razor clam digs should additionally exercise caution. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until 11 AM PST this morning for ORZ108>111- 114>118.

WA...Dense Fog Advisory until 11 AM PST this morning for WAZ204>206.

PZ...Small Craft Advisory until 10 AM PST Monday for PZZ210-251>253- 271>273.