Marine Weather and Tide Forecast for Corvallis, OR

SHORT TERM
Now through Tuesday night...The short term forecast is highlighted by chilly overnight temps with potential frost in outlying rural areas, mainly Monday night when the coldest temps are expected. This is when conditions will be clear and calm with high pressure in place, an ideal setup for radiational cooling. Trended the low temperature forecast towards the NBM 25th percentile to better reflect typical cool spots in valleys, which did lower temps a degree or two in most rural locations. The 12z iteration of the HRRR backs this decision up, showing high probabilities (70-100%) for low temps in the 33-36 degree range Monday night and early Tuesday morning for the central and southern Willamette Valley, Cascade foothills, Upper Hood River Valley, and coastal mountains. The Cowlitz Valley has slightly lower probabilities around 50-60%. Temps will likely stay above 36 degrees for the immediate coast and most of the Portland/Vancouver metro, aside from the Hillsboro and Battle Ground area. Given high confidence for temps cold enough to support frost formation, have issued a Frost Advisory Monday night for inland valleys, excluding Portland and Vancouver. The coldest temps are expected near Parkdale where lows could drop to near freezing, potentially impacting the many fruit trees budding in this area.
Those with sensitive outdoor potted plants should consider moving plants indoors if possible, or cover plants with a lightweight cotton fabric to help prevent frost damage. Another round of frost is possible Tuesday night, albeit confidence is lower as temps look to be 2-3 degrees warmer. If frost is able to form again Tuesday night, it would most likely be confined to the Upper Hood River Valley and southern Willamette Valley/adjacent Cascade foothills.

Expect high temps in the 50s to lower 60s both Monday and Tuesday, except mid 60s in the Portland/Vancouver metro on Tuesday. Light rain showers ongoing Sunday afternoon will continue through Sunday evening before diminishing Sunday night. Once any lingering showers end tonight, conditions will be dry across the region from Monday through at least Wednesday. -TK

LONG TERM
Wednesday through Saturday night...The long term forecast is highlighted by warm and dry weather Wednesday through Thursday followed by a return to cool and wet weather beginning Thursday night or Friday. The period of warmer temps expected Wednesday and Thursday will be in response to an upper level ridge that models and their ensemble continue to show building over the Pacific Northwest. The NBM 1D Viewer shows fairly minimal model spread on Wednesday, suggesting high temperatures will likely range somewhere between the upper 60s and mid 70s.

Model spread increases on Thursday, which is reflected well by the NBM 10-90th percentile. The NBM 10th percentile represents a reasonable cool scenario with highs in the upper 60s, while the 90th percentile represents a reasonable warm scenario with highs in the lower 80s. If the 90th percentile were to verify (10% chance), then several daily record high temperatures would be broken. While this isn't the most likely outcome, temps will be running above normal for time of year given average highs in mid April are in the lower 60s.
The main reason for the increased model spread on Thursday is due to uncertainty regarding the timing of an incoming upper level trough and surface frontal system. This system will bring the return of cool and wet weather to the area once it moves inland, however some model guidance shows rain moving in as early as Thursday evening while some shows rain moving in as late as Friday afternoon/evening. Aside from a few dry ENS ensemble members and a few members from the GEPS, all ensemble guidance from the ENS/GEPS/GEFS shows at least some measurable rain. NBM probabilities for 24-hr rain amounts over 0.25" from 5am Friday to 5am Saturday range between 25-50% for most locations, with the highest probabilities in the Cascades and Coast Range. -TK

AVIATION
Northwest flow aloft continues through the TAF period. A weak front is slowly pushing inland resulting in increasing clouds and chances for rain showers, mainly north of KSLE. There's a 75-90% probability of MVFR CIGs along the coast, though expecting the CIGs to bounce between MVFR and VFR. Inland locations are more likely to see a mix of VFR and MVFR conditions with about a 30-50% probability of MVFR conditions. Inland conditions expected to return to predominately VFR after 00Z Monday. Winds remain generally less than 10 kts, north to westerly along the coast and mainly variable inland, before becoming northwesterly after 00Z Monday.

PDX AND APPROACHES...Expecting generally low end VFR with periods of high end MVFR with CIGs fluctuating between FL025-FL040 through 00Z Monday. The cause will be light rain showers through the same time period. Light southwest winds, shifting northwest after 00Z Monday. /42

MARINE
Strong high pressure offshore will maintain northerly winds across the coastal waters. This will result in a surface level thermal trough developing and strengthening over the southern and central Oregon coast. This set up will maintain northerly winds across all waters through the middle of the week.
This could also result in gusty northerly winds of 25-30 kt at various times through the middle of the week. Therefore, expect Small Craft conditions at various times. Currently, conditions are favorable for SCA conditions in zone PZZ273 starting late Monday afternoon through early Tuesday morning. There are other time frames this week which could see SCA conditions, but there is still some uncertainty as to the timing and strength. Seas are expected to persist around 6 to 8 ft at 10 seconds through the middle of the week. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight Monday night to 9 AM PDT Tuesday for ORZ104>109-113>119-121-123>125.

WA...Frost Advisory from midnight Monday night to 9 AM PDT Tuesday for WAZ203>205-208.

PZ...Small Craft Advisory from 5 PM Monday to 2 AM PDT Tuesday for PZZ273.