Marine Weather and Tide Forecast for Lake Shore, 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
Bkn/ovc high clouds continue to spread over NW Oregon and SW Washington as a weak frontal system approaching over the Pacific nears the coast this evening. Ahead of the boundary, east winds at 15 kt gusting to 25 kt continue west of the Columbia River Gorge at KTTD, however the east-west surface pressure gradient has finally begun to weaken, allowing winds to east below 10 kt by 12z Mon. While light southeast winds reach to KPDX as of 0530z Mon, calm to light southerly winds are in place elsewhere across the region. Ahead of the high cloud cover associated with the front, areas of fog/mist or low stratus may develop in the central/southern Willamette Valley as well as other sheltered valleys nearby. KEUG maintains the best chances to see categorical restrictions, with current MVFR vis expected to give way to IFR/LIFR conditions by 08-10z Mon. Confidence in the occurrence of fog/mist is lower at other Willamette Valley terminals (KSLE, KCVO, KUAO), with MVFR vis/cigs more likely after 10-12z Mon.

As the frontal system arrives from the northwest and progresses to the east/southeast across the region tonight into early Monday, cigs will trend downward within rain showers, most likely along the coast and from the northern Willamette Valley north into SW Washington. Rain showers are expected to arrive at KAST by 08-11z Mon, then inland to Portland-area terminals as well as southward along the coast to KONP by 11-15z Mon. While coastal terminals will have a 50-70% chance of bottoming out at LIFR cigs, inland terminals are more likely (50-70% chance) to maintain MVFR cigs during rain showers. While precipitation chances are lower to the south at KSLE/KEUG, MVFR cigs remain favored through Monday morning. Conditions look to trend upward behind the frontal passage as winds turn out of the west/northwest at 5 kt or less.

KPDX AND APPROACHES...VFR conditions continue this evening ahead of an approaching frontal system with light southeast winds at KPDX, but gusty east winds persisting closer to the Columbia Gorge at KTTD. Cigs are expected to trend down to MVFR during light rain showers, most likely from 15-21z Mon, before improving to VFR late in the period as winds shift out of the northwest. -36

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...None.