Marine Weather and Tide Forecast for Kalama, WA

DISCUSSION
Now through Sunday night...An onshore flow regime will remain in place this week. This will result in the continuation pf seasonable temperatures with highs mainly in the 70s inland and 60s at the coast, except Friday through Sunday when highs in the 60s are likely for inland areas and 50s for the coast.

Satellite and surface weather observations from early Monday morning depicted mostly clear skies and calm winds over northwest OR and southwest WA under high pressure. Over the northeast Pacific, water vapor imagery showed two areas of enhanced moisture associated with separate frontal systems. The first front is already approaching the coastal waters and will move towards the coast Monday night/Tuesday morning, bringing a 20-40% chance of light rain for coastal locations. Inland areas will likely stay dry as the first front will be decaying upon landfall. The second front arrives Tuesday night/Wednesday morning, bringing chances for light rain for coastal and inland locations. That said, PoPs are low from Salem to Eugene at around 10%, suggesting these areas will most likely stay dry.

After these two systems high pressure will build in temporarily, bringing dry and mild weather on Thursday with a mix of sun and clouds. The weather pattern will begin to change on Friday as a cool upper level low settles directly over WA/OR. This low will linger over the region through at least Saturday. During that time, widespread showers are expected across all of western WA and western OR. Models and their ensembles continue to suggest abundant moisture will accompany this low, while soundings show steepening mid-level lapse rates as cooler air aloft develops. If there are enough sun breaks on Friday and/or Saturday, there would likely be enough surface-based instability to warrant stronger showers and isolated thunderstorms capable of producing heavy rainfall. NBM 6-hour thunder probabilities currently range between 10-15% Friday to Saturday during the afternoon/evening hours. NBM 48-hr probabilities for 0.25" of rain or more have increased to 60-90% across all of northwest OR and southwest WA, with the highest probabilities in the mountains and the lowest probabilities in the Willamette Valley. Probabilities for at least 0.5" of rain range from 20-40%, except 40-60% in the mountains. Assuming this much rain falls, it would be the most significant rain amounts observed during the month thus far.

On Sunday, the exact location of the low pressure system becomes more uncertain. Most ensemble guidance from the GEPS/GEFS/CMC suggests the low will progress eastward into Idaho and Montana, resulting in cool northwest flow aloft for western WA/OR and mainly dry conditions.
However, around 20% of the total ensemble space suggests the low will remain stuck in place over eastern WA/OR, resulting in a more northerly to northeasterly flow regime aloft and higher chances for continued rain showers. -TK

AVIATION
VFR conditions currently along the coast with small patches of marine stratus beginning to show up on satellite.
Expecting stratus to become more widespread along the coast after 10-12z with MVFR/IFR CIGs , mixing out by 18z or so. Northwest winds will remain below 5 kt through the overnight period, and increase to 5-10 kt out of the west to northwest by the afternoon.
Another chance for marine stratus after 3-6z Tuesday.

Inland, VFR conditions are likely to persist throughout the period, although few-sct stratus at 2-3 kft is expected to build westward from the Cascades after 10z. There remains a 15-25% chance of coverage increasing enough to result in MVFR cigs, most likely at TTD. Cloud bases will lift as mixing deepens by 20-21Z.
Winds below 5 kt overnight will increase out of the west to northwest at 5-10 kt by Monday afternoon.

*KTTD ASOS is currently INOP except for altimeter and will be AMD NOT SKED.

PDX AND APPROACHES...Mainly VFR conditions expected. Sct stratus coverage at 2-3 kft is again expected to encroach from the west after 10-12Z Mon, with around a 10% chance of MVFR cigs if stratus coverage is higher than anticipated. Skies will trend clearer and cloud bases lift above 3-4 kft by Monday afternoon as mixing increases. Northwest winds around 5 kt overnight increase to 5-10 kt by the afternoon. -Batz/Picard

MARINE
A weak disturbance is expected to cross the region on today, supporting a wind shift from northwesterly flow to southerly flow late this evening and through Tuesday. A westerly swell is also expected to move into the waters late Monday, increasing seas from around 3 feet to around 5 ft at 10 seconds.
Combined seas still look to remain 7 ft or less through next week.
Winds remain southerly through Tuesday, gradually turning back to the west/northwest on Wednesday. -Batz

PQR WATCHES/WARNINGS/ADVISORIES

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