textproduct: Portland

SYNOPSIS

High pressure will maintain dry and sunny conditions across the area today. The next frontal system arrives Saturday, returning widespread rain through Sunday. Sunday night to Tuesday, rain transitions to post-frontal showers with cooler temperatures and sub-advisory snow showers through the Cascade passes. Relatively drier conditions return mid-week with chances for light showers before chances for rain increase by the end of the week.

SHORT TERM...Today through Sunday night

High pressure over the Pacific Northwest will bring one more day of dry and sunny conditions. High temperatures this afternoon are forecast similar to the previous couple days, running around 10 degrees above normal. Some locations may even come close to breaking their daily record high. See the climate section below for current daily records across the region.

Easterly winds through the Columbia River Gorge have now weakened as pressure gradients between Troutdale (KTTD) and The Dalles (KDLS) have eased to -3 mb. Expect light winds across the forecast area today. These light winds in combination with low mixing heights will remain favorable for stagnant air. The Air Stagnation Advisory for portions of the Willamette Valley and southwest WA lowlands remains in effect through 10 PM this evening. Stagnant air may lead to deteriorating air quality. Fortunately, it looks like this won't last much longer since the next system will be arriving on Saturday, returning well-mixed conditions. Tonight will see increasing cloud cover as the next system approaches the Pacific Northwest, minimizing concerns for fog and frost.

A cold front and associated moderate atmospheric river will bring widespread rain to the region through this weekend. Rainfall initially looks to arrive at the coast Saturday morning before pushing inland through Saturday afternoon. Mild temperatures from southwesterly flow will keep snow levels above 6000-7000 ft, meaning even Cascade passes will see all rain through at least Saturday night. As the front progresses inland, there is a potential for it to stall, supporting higher rainfall totals. At this time, this is most likely to occur over southwestern or west-central Oregon, although it cannot be ruled out that the front instead stalls to the north over northwestern Oregon or southwestern Washington. By the time rainfall diminishes Sunday night, there is high confidence (>90% chance) of rainfall amounts greater than 0.5 inches along the I-5 corridor and greater than 0.75 inches along the coast. Most likely rainfall amounts vary from 0.75-1.25 inches along the I-5 corridor and 1-2 inches along the coast. Amounts of up to 2-3 inches are most likely (50-70% chance) over the Coast Range and Cascades, however, there is a 5-10% chance the lowlands could see these higher end amounts if the front stalls over a particular location. Given dry weather observed through much of January across the region, even the longer duration rain event is unlikely to produce enough precipitation to cause flooding. Sustained heavy rain rates over a particular location may yield isolated flooding in urban or poor-drainage areas, but more widespread areal or river flooding is not anticipated. -10/36

LONG TERM...Monday through Thursday

Behind the front, cooler and more seasonable temperatures arrive for the workweek. Lingering post-frontal showers and snow levels dropping to 3000-4000 ft early in the week will support pass-level snow accumulations in the Cascades. By this time, precipitation amounts will be much lower with sub-advisory snow. Chances for 6 inches of snow within a 48 hour period ending 4 PM Tuesday remains only around 5-10% at the Cascade passes. By mid-week, the majority of long-range ensemble members suggest drier conditions, through some members maintain chances for light showers. Greater uncertainty in the forecast follows for the end of the week, but 80% of ensemble members are suggesting a drop in 500 mb heights as a trough approaches the Pacific Northwest. Most of the uncertainty remains in exact timing and amounts of precipitation, as well as how cool we'd get. -10/36

AVIATION

At 20z Friday, light winds and mostly clear skies were being observed across northwest OR and southwest WA, aside from continued easterly winds at KTTD around 10 kt with gusts up to 20 kt. However, easterly winds should weaken even more at KTTD through Friday evening as the surface pressure gradient from KTTD to KDLS weakens. Note satellite and surface weather observations depicted lingering low stratus and patchy fog over the Willamette Valley between KSLE and KEUG, but with no impacts at the KSLE and KEUG terminals. In addition, expect this area of low stratus to scatter out completely by 21-22z Friday.

High clouds will increase from west to east tonight into Saturday morning ahead of an incoming Pacific frontal system. This system will bring rain and high-end MVFR cigs to the coast, beginning between 13-17z Saturday. Conditions will deteriorate on the south WA/north OR coast first, before spreading down the central OR coast last. Rain will likely begin for inland terminals sometime between 18-20z Saturday. With light winds continuing over the Willamette Valley tonight, patchy fog and low stratus cannot be ruled out, especially if high clouds hold off until the late overnight hours. All inland terminals have a 15-35% chance for fog or low stratus between 06-16z Saturday, except KPDX and KTTD where light offshore should be enough to maintain VFR flight conditions. Confidence in fog and low stratus development is not high enough to reflect in the TAFs, except at KEUG where confidence is high enough to at least hint at potential fog development.

KPDX AND APPROACHES...Expect VFR flight conditions to most likely continue through 00z Sunday with relatively light winds. High clouds will increase between 10-18z Saturday ahead of an incoming frontal system, which will bring light rain to the terminal shortly after 18z Saturday. By 00z Sunday, chances for MVFR cigs around 3000 ft increase to 45%. -23

MARINE

Weakening high pressure inland will support southerly winds around 10 to 20 kt over the coastal waters, strengthening to 20 to 30 kt Friday night as a frontal system nears the coast. This frontal system will bring a 60-90% chance for intermittent gale force wind gusts up to 35 kt beyond 10 NM between 6am-Noon Saturday and 50-80% chance within 10 NM. Gale force wind gusts are expected to be too brief and isolated to warrant a Gale Warning, likely impacting any given location for a few hours as the frontal boundary moves eastward towards the coast. Therefore, have decided to maintain a strongly worded Small Craft Advisory for all marine zones, including the Columbia River Bar. These advisories remain in effect through 4 AM PST Sunday, except through 1 AM PST Sunday for the Columbia River Bar.

For seas, expect a persistent southwesterly to westerly swell to maintain significant wave heights within the 9-13 foot range through the weekend and into early next week. Note seas should be highest on Saturday behind the frontal passage. Note there is a 5-10% chance seas will peak as high as 14-15 ft.

It appears seas will decrease to 5 to 7 ft on Wednesday with relatively light north to northeast winds. More active weather is possible late in the week, but confidence in forecast details remains low at this time. -23

CLIMATE

Daily record high temperatures for Friday, February 6:

Site Record Temp

Astoria, OR 65F (1954) Vancouver, WA61F (1907) Portland Downtown62F (1963, 1998) Portland Airport59F (1998, 2020) Hillsboro, OR63F (1998) McMinnville, OR 61F (1984) Salem, OR 67F (1998) Eugene, OR 66F (1963)

PQR WATCHES/WARNINGS/ADVISORIES

OR...Air Stagnation Advisory until 10 PM PST this evening for ORZ108- 115>118-123>125.

WA...Air Stagnation Advisory until 10 PM PST this evening for WAZ204- 205.

PZ...Small Craft Advisory until 1 AM PST Sunday for PZZ210.

Small Craft Advisory until 4 AM PST Sunday for PZZ251>253- 271>273.