textproduct: Portland

SYNOPSIS

We are entering into a period of typical winter weather here in the Pacific Northwest with a low pressure system sitting off of the coast. Will see continued rain and Cascade snow through Saturday followed by a ridge of high pressure that will keep conditions dry, cooler, with foggy mornings.

LONG TERM...Saturday night through Thursday

High pressure continues to strengthen the latter half of the weekend with clearer skies causing temperatures to drop. Overnight Saturday into Sunday, temperatures will fall around or below freezing for many of the inland valleys. Currently there is around a 90-95% chance of temperatures below freezing within the southern Willamette Valley, near 60-70% in the northern Willamette Valley and around 15-25% in the Portland-Vancouver Metro area. The coast also has a non-zero chance of seeing freezing temperatures Sunday morning as well. The probability of 25 degrees or less is a much lower probability with a 15-25% chance within the southern Willamette Valley and less than 5% chance elsewhere. Rural locations in the Battleground area, Upper Hood River Valley, etc will have the highest probability for well below freezing temperatures. During the day, conditions will be dry and mostly clear, however, we will likely have to deal with patchy overnight/morning fog which can struggle to burn off this time of year. Something to consider is that with these cold temperatures overnight and the saturation that is likely to occur, frost may have a higher probability of forming vs fog. If temperatures drop faster than saturation occurs, then frost is the more likely scenario. Similar conditions expected on Monday and Tuesday mornings but models continue to bounce between a warmer or a colder trend. Based on current guidance, Monday morning appears to be the coldest of the mornings.

Looking into the way long-term, some uncertainty remains regarding the exact breakdown of this ridge feature. Nearly all of the global ensembles show a longwave trough aloft moving in late Wednesday into early Thursday. -27/99

AVIATION

Low pressure off the southern Oregon coast will continue to influence the region today. Lingering showers along the coast may briefly impact coastal terminals. Despite showers over the area, conditions are expected to remain mainly VFR into early tonight. Southerly winds through the area but will remain light at less than 10 kt. The exception being KTTD where winds will remain easterly with gusts around 20 kt will drop off this evening. Probabilities for MVFR conditions increase from south to north after 10-12z Friday to 40-60% as the offshore low moves inland over southern Oregon and northern California. This will also bring an increase in showers across the region.

KPDX AND APPROACHES...Expect VFR conditions to prevail with CIGs remaining above 5000 feet. Southeasterly winds at less than 10 kt. Probability for MVFR conditions increase late tonight into early Friday morning around 12-15z to 40-50% before improving again in the late afternoon. /19

MARINE

A low pressure system located 200-300 NM west of Coos Bay pushed a front from south to north through the waters today. As of 12 PM PST, the front is located around Astoria, OR. Winds and seas are increasing behind the front. A Gale Warning in in effect for the waters south of Cape Falcon and beyond 10 NM from the coast for south wind gusts up to 40 kt through 10 PM PST. Elsewhere, Small Craft Advisories remain in effect through 7 PM PST for wind gusts up to 30 kt, though brief gusts up to 35 kts are possible north of Cape Falcon. A Hazardous Seas Warning replaces the Small Craft Advisory in zone PZZ721 at 7 PM PST and the Gale Warning in zones PZZ272-273 at 10 PM PST. A combination of wind waves and an increasing southerly swell will build seas through tonight. Seas within the Gale Warning may build to 17-22 ft at 10-12 sec, while other locations build to 13-16 ft at 11-12 sec. A Small Craft Advisory has been added for the Columbia River Bar due to increasing confidence of elevated winds and seas reaching the Bar.

Seas decrease briefly early Friday morning to 9-12 ft with wind gusts up to 20-25 kts. The low pressure system then moves east through the waters Friday. Winds shift northwesterly Friday morning and increase Friday afternoon with gusts to 25-30 kts through Friday night. Seas also increase to up to 11-15 ft at 10 sec. Winds begin decreasing Saturday morning, but waves remain elevated through the day, decreasing late afternoon to below 10 ft. The Hazardous Seas Warning and Small Craft Advisory remain in effect through Saturday afternoon across all waters. A ridge of high pressure builds overhead late Saturday into Sunday. Winds decrease to less than 15 kts by Saturday night and seas settle in the 4-6ft range, continuing into Sunday. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory from 4 AM Friday to 4 PM PST Saturday for ORZ126>128. WA...Winter Weather Advisory from 4 AM Friday to 4 PM PST Saturday for WAZ211. PZ...Small Craft Advisory until 3 PM PST Saturday for PZZ210. Small Craft Advisory until 3 PM PST Saturday for PZZ251>253. Small Craft Advisory until 7 PM PST this evening for PZZ271. Hazardous Seas Warning from 7 PM this evening to 3 PM PST Saturday for PZZ271. Gale Warning until 10 PM PST this evening for PZZ272-273. Hazardous Seas Warning from 10 PM this evening to 3 PM PST Saturday for PZZ272-273.