Marine Weather and Tide Forecast for Chinook, WA

SHORT TERM
Friday through Monday...Satellite and surface weather observations from early Friday morning depicted clearing skies along the coast with mostly cloudy conditions over the Willamette Valley, Cowlitz Valley and Cascades. Winds remain light and variable with high pressure in place. Radar observations show isolated rain showers have now dissipated. Expect a mild and dry day with increasing sunshine after 9-10 AM. High temperatures will likely top out in the lower 60s at the coast and lower 70s for inland valleys.

Temperatures will warm more noticeably on Saturday as 500 mb heights begin to rise with a transient shortwave ridge. The deterministic NBM suggests high temps will be in the mid to upper 70s across the lowlands, except mid 60s at the coast. However, cannot rule out high temps of 80 degrees of warmer in Salem (45% chance), Eugene-Springfield (25% chance), and the greater Portland/Vancouver metro (40-60% chance, except 75% from Beaverton to Tigard to Tualatin). The outcome will partly depend on how thick high clouds will be during the morning and early afternoon hours. With high pressure remaining in place, conditions will stay dry.

Dry conditions will likely hold Sunday morning and afternoon, except along the Cascades where there is a 15-25% chance of rain showers in the afternoon, increasing to 40-50% in the evening. There is also a 15% chance of thunderstorms along the Cascade crest as SBCAPE values build to 100-500 J/kg, however a slight westerly component to upper level flow will favor convection mainly to the east of the crest.
Sunday will also feature increasing high clouds, which will result in slightly cooler temps with highs in the low to mid 70s, except low to mid 60s at the coast. The increase in high clouds will be in response to an income shortwave trough and attendant surface cold front.
Models and their ensembles seem to agree well on the timing of this front, showing it push inland Sunday night into Monday morning.
Although this front looks weak, it will bring some moisture back to the area. Chances for rain increase to 30-60% across all of southwest WA and northwest OR with this front, with the highest chances at the coast and in the Cascades. Rain totals with this front look light, with most locations receiving anywhere from a trace to 0.10 inches of rain. That said, there are a handful of ensemble members from the GEFS/ENS/GEPS showing slightly heavier rain amounts around 0.25". The NBM backs this up, showing a 5-15% chance for 0.25" of rain or more, except 30-40% in the Cascades. -TK

LONG TERM
Monday night through Thursday night...After light rain showers come to an end late Monday afternoon into the evening, expect a period of dry weather from Monday night through at least Wednesday morning. Temps will likely top out in the mid to upper 70s Tuesday afternoon, except mid to upper 60s at the coast. The forecast becomes more uncertain Wednesday afternoon onward as models and their ensembles struggle to agree on the degree of upper level ridging over the region. WPC's cluster analysis for 500 mb heights and anomalies suggests heights will be above average to some degree, but each cluster differs considerably regarding how much above average. EOF patterns suggest the majority of model variance (60%) can be explained by uncertainty regarding the amplification of this ridge.
If model solutions showing a weaker ridge materialize, temps will likely match the 10-25th percentile NBM guidance (highs in the low 70s to low 80s). If solutions showing a strong ridge materialize, temps will likely match the 50-75th percentile (highs in the mid 80s to mid 90s). Note the 90th percentile is in the mid to upper 90s, meaning there is a 10% chance for temps this hot to occur. While temps this hot are unlikely to occur, it is worth mentioning as we have not observed a day with temps in the 90s yet this year.
Given the degree of uncertainty, have decided to maintain the deterministic NBM which suggests highs ranging from 82-88 degrees, except low 70s at the coast. If temps do wind up in the 80s or 90s, some may chose to seek relief by swimming in rivers and lakes, however this is not a smart idea this time of year as water temps are still cold enough to result in cold water shock for individuals not wearing a proper wetsuit.

Models and their ensembles do agree temps will cool a bit on Thursday with highs most likely back into the 70s for inland valleys. This is in response to increasing cloud cover and chances for rain showers with an incoming Pacific cold front. Guidance varies significantly regarding the strength of this front and the exact timing. Some model ensemble guidance shows the front decaying as soon as it pushes inland, resulting in very little to no rain at all. Meanwhile, some models show a relatively stronger front with widespread rain amounts upwards of 0.1-0.2 inches. The NBM is showing a 50-60% chance for measurable rain to occur with this front (e.g. 0.01" or more), and a 10-25% chance for more substantial rain amounts of 0.2" or more. Note if the dry model solutions verify, temps would likely overperform the current deterministic forecast and wind up topping out in the 80s rather than the 70s. -TK

AVIATION
As of 17Z Friday, VFR conditions (with ceilings around FL045) throughout the airspace and northerly to northwesterly flow below 10 kt. Expect these conditions to continue through the TAF period. The only exception will be the northwesterly winds along the coast, which may reach 10 kt and gust up to 18 kt during the afternoon and evening.

Looking ahead into tomorrow morning, probabilities for MVFR CIGs at coastal terminals begin to increase (to 30-40% chances) by 12Z Saturday as winds become calm. Low stratus development looks possible, but as of now, expect potential for at least MVFR CIG development around 12-14Z Saturday.

PDX AND APPROACHES...VFR conditions expected through the TAF period with mid-level clouds dissipating into the afternoon.
Expect northwesterly winds around 4-7 kts through the period.
~Hall

MARINE
Weak high pressure offshore will maintain north to northwesterly breezes across the coastal waters into the weekend.
Winds generally remain below 10-15 kt, though inland daytime heating could drive the diurnal strengthening of the pressure gradient, allowing winds to gust up to 20 kt along the nearshore waters. Seas will persist around 3 to 4 ft through Saturday. By early Sunday, winds turn southerly ahead of a weak front, increasing through the day, but expected to remain below 20 kt. A northwest swell will also build seas to around 6 to 7 ft. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...None.