Marine Weather and Tide Forecast for Minnehaha, WA

DISCUSSION
Tonight through Sunday...The upper level ridge, which has been keep the CWA dry this weekend as well as easterly winds through the Columbia River Gorge will slowly flatten as a weak, shortwave trough moves across the Pac NW late tonight through Monday. High pressure briefly returns on Tuesday which will bring warm and dry conditions. However, a significant pattern change is on the horizon as a series of systems are expected to bring widespread precipitation, onshore flow and cooler temperatures through next Sunday.

Tonight, easterly winds will continue to slowly subside through the overnight hours. Current observations have easterly gusts at KTTD (Troutdale) around 30-35 mph with gusts of 40-50 mph at exposed ridgetops within the Columbia River Gorge (Three Corner Rock, Crown Point/Vista House). As the ridge of high pressure weakens, the pressure gradient from Portland International Airport to The Dalles (KPDX- KDLS) will gradually ease towards -3 to -5 mb tonight. As these pressure gradients ease, easterly winds will also weaken through the Gorge and along the coast, with more southerly winds expected late tonight.

Late tonight into Monday, a shortwave trough pushes into southern British Columbia and far northwest Washington. High-res ensemble guidance suggests that the front associated with this upper level shortwave will be very weak as it quickly brushes our CWA This scenario is shaping up to be a mod/high PoP event with low QPF. There is high confidence (70-80%) that 24-36 hour rain amounts starting 8 PM Sunday will remain less than 0.10" for most places. Currently, the highest chances for rain are along the coast and southwest Washington (50-70%) as this weak front is tracking further north, while chances for rain are lower (15-30%) across interior northwest Oregon.

Tuesday, another shortwave upper level ridge builds over the Pacific Northwest and will bring a brief return of dry weather.
However, by Wednesday, the first in a series of robust lows will take aim at the Pac NW. This stronger system will bring rain and cooler air back into the forecast. The first system will bring widespread rain across the CWA Wednesday through Thursday with the mean precipitation total across the CWA between 0.30-1.30" with higher totals along the coast, the 90th percentile range from 0.80-2.50" and the 10th percentile range from Trace to 0.30 inches.

As this first system pushes eastward, it will bring cooler temperatures into the region. Models have 850 mb temperatures dropping towards -1 to -3 C, which will result in snow levels falling towards to pass-level in the Cascades Thursday evening/ Friday. Mean precipitation totals for low elevation, inland locations from Friday afternoon through Saturday afternoon is between 0.30-0.75" with higher totals along the coast, the 90th percentile range from 0.70-2.00" and the 10th percentile range from Trace to 0.15 inches. Current guidance also suggests a 40-60% chance that 48-hour snow totals between 10 PM Thursday to 10 PM Saturday exceeds 6 inches through the passes, with the highest chances at the Santiam and Willamette Passes. As Saturday approaches, warmer air will be introduced as the next system moves into the region and this will result in continued, widespread precipitation through the remainder of the weekend and into Sunday. /42

AVIATION
High SCT/BKN clouds continue to stream over NW Oregon and SW Washington as a weak frontal system approaches the region from the Pacific. East gusts up to 20-30 kts continue through the western Columbia River Gorge into KTTD today, beginning to weaken later this afternoon into the evening. Expecting gusts to fall below 20 kts after 00-03z Mon. Ahead of the frontal passage tonight, there's a 10-30% chance of IFR/LIFR CIGs and VIS developing for the central to southern Willamette Valley anywhere between 03-10z Mon as long as high clouds remain on the thinner side. If high clouds become more OVC, then fog/low stratus development probabilities decrease even more. Confidence is too low to include in TAFs at the moment, but will continue evaluating.

Then as the frontal system approaches and moves through the region late tonight/early tomorrow, CIGs begin to trend downward across the entire region. There's a 60-80% chance for IFR/MVFR CIGs developing along the coast around 05-08z Mon and MVFR CIGs inland around 12-16z Mon. Conditions are expected to remain lowered through the TAF period, though inland locations could fluctuate between MVFR and low-end VFR after 21z Mon. Light rain will also accompany the front, ending by 00-03z Tue for most terminals.

KPDX AND APPROACHES...VFR conditions expected through tonight with SCT/BKN high clouds. Ceilings expected to fall below 3-4kft around 12-15z Mon as an approaching weak front brings chances of light showers. Easterly winds around 10-12 kt through 00-03z Mon, weakening to 2-5 kts after. -03

MARINE
A weak frontal system approaching the waters Sunday afternoon has shifted winds southerly. Winds generally expected to remain below 15 kts with gusts below 20 kts as the front passes through the waters tonight except for the outer waters beyond 30 NM in zone PZZ271 where wind gusts could briefly reach 21-25 kts through 8 PM PST. Seas will generally remain 6-9 ft at 10-12 seconds in Monday.

Wind direction varies through the first half of next week, but wind speeds look to remain at 5-10 kt through Tuesday night.
There is also high confidence (greater than 95% chance) that seas remain below 10 ft through midweek as well. An area of low pressure strengthening well offshore will return breezy southerly winds and building seas Wednesday into Thursday, increasing the chances (60-80% chance) for another period of conditions hazardous to small craft. There is also a 40-70% chance for Gale- force wind gusts greater than 34 kt during this period, with the highest chances across the outer waters beyond 20-30 NM. -10/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...Small Craft Advisory from 4 PM this afternoon to 10 PM PST this evening for PZZ210.