Marine Weather and Tide Forecast for Scappoose, OR

SHORT TERM
Now through Wednesday...
A broad low pressure system will continue to bring cool and unsettled weather through the first half of the week. Showers began early this morning and will continue through the day, gradually spreading inland. Although the flow pattern is not especially favorable, cooler air aloft will boost instability, resulting in around 200 J/kg of CAPE expected. This supports a 10-20% chance of thunderstorms continuing through this afternoon. So far have only seen a brief thunderstorm near Kelso WA around noon today. Total rainfall today will generally range from 0.15 to 0.30 inches in the valleys, with higher totals of 0.25 to 0.50 inches along the coast and in the Cascades.

A second round of showers and isolated thunderstorms are expected tomorrow as the low pressure system continues eastward.
Cold temperatures aloft will promote additional instability, with CAPE values potentially reaching 400 J/kg. Thunderstorm probabilities will increase to 15-30% across the area (highest chances near Eugene), especially in the afternoon and evening.
Additionally, there is the possibility to see pea- sized hail from stronger thunderstorms that may develop. Precipitation totals for tomorrow should range from 0.10 to 0.25 inches for most areas, with localized amounts up to 0.50 inches in the Cascades.

On Tuesday, shower activity will gradually taper off as the upper low shifts southeast. A weak shortwave ridge will follow, ushering in a slightly drier and more stable pattern. Still, a few light showers may linger, with up to 0.05 inches of additional precipitation possible in the interior valley. By Wednesday, the ridge pattern will continue and lead to further drying.
~Hall/42

LONG TERM
Thursday through Sunday...Precipitation chances diminish toward the end of the week as a shortwave ridge builds in, bringing a return to drier and warmer weather by Friday.
Interior valley temperatures could warm into the upper 60s by Friday. Model guidance suggests a 50% chance of hitting 70 degrees. Another low pressure system may move in Saturday, setting the stage for a renewed round of wet conditions. With current guidance suggesting a somewhat zonal pattern on Friday and a trough pattern with poor model agreement on Saturday, there is low confidence on timing and how prominent these wet conditions may be.
~Hall

AVIATION
South to southwest flow continues through tonight as an upper-level low approaches the region. Expect south winds around 10 kt with gusts up to 15-20 kt this afternoon and evening.
Gusts up to 25 kt are likely along the central OR coast, including KONP. Winds become light again tonight.

Radar and surface weather observations from 20z showed scattered rain showers increasing in coverage as expected. With these showers, there are isolated pockets of MVFR cigs and/or surface visibilities. That said, most locations are observing VFR cigs.
Expect this trend to continue through this evening as predominately VFR cigs continue aside from isolated pockets of MVFR cigs with passing showers or thunderstorms. Note the probability for thunderstorms this afternoon and evening is only 10-15%, suggesting the vast majority of today's convection will be in the form of light to moderate rain showers with no lightning concerns. Thunderstorm chances remain too low to justify PROB30 groups at this time. Instead, will amend TAF sites as needed if thunderstorms develop over or near the terminal.

Chances for MVFR cigs increase to 30-50% or higher after 06-09z Monday as a renewed round of steadier light rain spreads northward over the area.

PDX AND APPROACHES...Predominately VFR flying conditions expected through 06z Monday, aside from occasional drops to high-end MVFR cigs with passing rain showers or thunderstorms. Chances for MVFR cigs below 3000 ft increase to 30% by 09z Monday and to 60% by 12z Monday. This is also when a round of steadier light rain spreads northward over the terminal. -TK

MARINE
Buoy observations from early Sunday afternoon showed increasing southerly winds over the coastal waters ahead of an incoming surface low, especially over the central and southern waters where gusts up to 30 kt are occurring. Expect winds of this magnitude to remain in place through Sunday evening, with isolated gale force gusts up to 35 kt possible over the southern waters through approximately 7 PM PDT Sunday. Since gale force gusts are expected to be isolated and short-lived, have decided not to upgrade the current Small Craft Advisory to a Gale Warning.
However, have decided to include the northern waters in a Small Craft Advisory for gusts up to 25 kt through 8 PM Sunday, mainly to the south of the Columbia River Bar from the coastline out to 60 nm. Meanwhile, a Small Craft Advisory remains in effect until 11 PM Sunday for the central and southern waters to the south of Cape Falcon.

Seas are not expected to respond much to the brief period of increased winds, with significant wave heights rising to 6-9 ft by Sunday evening. Behind the low, high pressure building well west of Cape Mendocino will bring persistent northwest flow. Gusts of 20-25 kt will develop beyond 30 NM, with northwest swells rising to 9-11 ft at 10 seconds Monday night into Tuesday. -TK

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ251-271.

Small Craft Advisory until 11 PM PDT this evening for PZZ252-253- 272-273.