Marine Weather and Tide Forecast for Scappoose, OR

SHORT TERM
Now through Tonight...High pressure over the interior west has begun to weaken as large-scale upper-level ridging shifts eastward through this weekend. The observed pressure gradient across the Cascades (PDX-DLS) has fallen to around 5 mb early this morning, easing gusty winds through the Columbia River Gorge and other gaps. Clear skies thus far overnight has supported efficient radiative cooling and the development of valley fog in sheltered locales, most notably the southern Willamette Valley. Areas away from fog and gap winds will instead see patchy frost as morning low temperatures fall into the mid 30s. Largely clear skies and abundant sunshine will see any fog or frost quickly dissipate as daytime highs again approach 60 degrees for many. Daily record high temperatures are possible at sites across the northern Willamette Valley and Portland/Vancouver Metro; see the Climate section below for current daily record temperatures across the region.

Coastal areas will see increasing marine clouds ahead of an approaching frontal system, although dry weather will continue through much of tonight before rain arrives at the coast early Saturday morning. -36


LONG TERM
Saturday through Thursday...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 pre-frontal southwesterly flow will see snow levels rise 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 possible 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 rainrates over a particular location may yield urban or poor-drainage flooding, but more widespread areal or river flooding is not anticipated.

Behind the front, cooler and more seasonable temperatures arrive for the workweek. Lingering post-frontal showers and snow levels to 3000-4000 ft early in the week may support pass-level snow accumulations in the Cascades. By this time, precipitation amounts will be much lower though, and the chance for 6 inches of snow remains only around 10% at the Cascade passes. Forecast uncertainty increases beyond midweek, with the majority of long- range ensemble members suggesting drier conditions before chances for rainfall increase again late in the workweek. -36

AVIATION
At 18z 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 around 20 kt. However, easterly winds should weaken even more at KTTD Friday afternoon and 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 20-22z 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 hold off for inland terminals until after 18z Friday. 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 18z 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 continue through 18z Saturday 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. -23

MARINE
Winds have turned southerly at around 10 kt as high pressure has begun to weaken inland, and will strengthen tonight into Saturday as a frontal system nears the coast. Intermittent and isolated gale-force gusts are likely across the outer waters (60-90% chance of maximum gusts above 35 kt on Saturday), and possible over the inner waters (25-50% chance of maximum gusts above 35 kt), but are not expected to be persistent or widespread.
These strongest gusts are most likely between 6 AM and Noon on Saturday beyond 20 NM offshore as the frontal rain band approaches the coast. Otherwise, sustained winds of 15-25 kt with gusts up to 35 kt are expected across the waters from Friday evening through early Saturday afternoon. Meanwhile, a west- southwesterly swell of 8-10 ft will maintain seas of 10-12 ft across the waters through the first half of the weekend. The Small Craft Advisory currently in effect has therefore been extended through 4 PM PST Saturday for the Columbia River Bar, and through 4 AM PST Sunday across all other coastal waters.

Behind the frontal boundary, the swell will turn more westerly, but support continued seas of 8-10 ft into next week. Further active weather is possible late in the week, but confidence in forecast details remains low at this time. -36

CLIMATE

Daily record high temperatures for Friday, February 6:

Site Record Temp

Astoria, OR 65F (1954)
Vancouver, WA 61F (1907)
Portland Downtown 62F (1963, 1998)
Portland Airport 59F (1998, 2020)
Hillsboro, OR 63F (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 4 PM PST Saturday for PZZ210.

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