Marine Weather Net

Cape Flattery to Cape Shoalwater WA between 60 and 150 NM Offshore Forecast


TODAY

N
WINDS
5 - 15
KNOTS

TONIGHT

NNW
WINDS
10 - 15
KNOTS

SAT

W
WINDS
5 - 10
KNOTS

SAT NIGHT

S
WINDS
10 - 20
KNOTS

The Marine Weather Forecast In Detail:
PZZ800 Forecast Issued: 224 AM PDT Fri Sep 24 2021

Today...N Winds 5 To 15 Kt. Seas 4 To 6 Ft.
Tonight...N To Nw Winds 10 To 15 Kt. Seas 6 To 7 Ft.
Sat...W Winds 5 To 10 Kt, Becoming Sw 5 To 15 Kt. Seas 6 To 7 Ft.
Sat Night...S Winds 10 To 20 Kt. Seas 7 To 8 Ft.
Sun...S Winds 15 To 25 Kt. Seas 7 To 9 Ft.
Sun Night...S Winds 20 To 30 Kt, Becoming Sw. Seas 7 To 13 Ft.
Mon...S To Sw Winds 20 To 30 Kt. Seas 11 To 19 Ft.
Mon Night...W To Sw Winds 20 To 30 Kt. Seas 15 To 20 Ft.
Tue...Nw Winds 20 To 30 Kt, Becoming W To Nw 10 To 20 Kt. Seas 14 To 19 Ft.
Tue Night...W Winds 10 To 15 Kt, Becoming S To Sw 15 To 25 Kt. Seas 9 To 14 Ft.
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813 AM PST Tue Nov 30 2021
Northern and Central Washington Coastal and Inland Waters - PZZ100
Winds will increase today into Wednesday as a warm front stalls over the region. The trailing cold front will cross western Washington Wednesday night with the flow turning onshore. High pressure will build into the interior of British Columbia Thursday and Friday before another front arrives over the weekend.
Area Forecast Discussion
National Weather Service Seattle WA
901am PST Tuesday Nov 30 2021

Rather steady rain across much of the area this morning, with the heaviest located across northern areas of the Olympics and Cascades. Rain today will shift a bit northward into Wednesday for the heaviest precipitation along the border. Breezy winds with gusts of 30-35 MPH possible, with winds breezy into Wednesday before tapering off for drier weather later Thursday.

Synopsis
Rain across the area through today. Areas of flooding across through Thursday, with the focus on river flooding across northern areas. Rain will taper off on Thursday with a front moving through the area. Drier weather Friday with another system possible on Saturday with a cooler weather pattern.

Short Term - Today through Thursday
The next round of persistent rainfall has reached Western Washington this morning and is expected to persist through Thursday morning before drier conditions return to the region. Not much in the way of forecast details have changed tonight. This system is expected to yield less rainfall accumulation than the weekend system, as rainfall totals look to be more on the order of 1-1.5 inches in the Whatcom/Skagit County lowlands, with 2-4 inches in the North Cascades and in northwest portions of the Olympic Peninsula. That said, many of these areas have not had a chance to dry out from the last system, as nuisance showers persisted through most of Monday across these areas. Expect river response in these areas to be quick, with the Nooksack, Skagit, Bogachiel and Skokomish being the basins to keep an eye on over the next several days. In addition to potential continued river flooding, aerial flooding will be a concern once again along with the threat of landslides. One factor that will be worth keeping an eye on - some HREF guidance members pull the band of rain northward late tonight/Wednesday morning. In the event that most of the heavy rain lifts north of Clallam and Whatcom Counties for any significant period of time (i.e. 3+ hours), this would cause river rises to be lower. At this time, confidence is low in this scenario coming to fruition, as most HREF guidance members keep some rainfall across these areas through Wednesday morning before the band of rainfall sags southward across the area. Nonetheless, this scenario is worth keeping an eye on throughout the day as new data gets ingested into the models. See the hydrology section for further details.

As was the case with the weekend system, a period of rain shadowing looks likely across the central and northern Puget Sound, which will promote gusty southerly winds on Tuesday. Wind gusts look weaker at this time with frequent gusts generally remaining in the 25 to 35 mph range, which would keep wind impact potential fairly limited.

Temperatures through the period will remain in the mid to upper 50s with a similar airmass (snow levels rising back to 9-10k ft) in place through the end of the period.

Long Term - Friday Through Monday
A cold front will clear the region late Thursday night, ushering in a drier and cooler airmass across the region. As was stated in the previous AFD, Friday will be the coldest day of the week, with temperatures in the 30s Friday morning, topping out in the mid 40s for highs Friday afternoon. Quasi-zonal flow will remain in place aloft, keeping the door open for additional progressive systems through the weekend. A quick moving system will bring a chance for showers to Western Washington on Saturday, followed by a more substantial system bringing lowland rain and mountain snow to the region late Sunday into Monday. Given the colder airmass in place, flooding will not be likely with these systems. Beyond that, details remain unclear regarding the system at the end of the period.

Marine
A warm front will stall over the region today with increasing southerly winds over the waters - Small Craft Advisories remain in effect. Meanwhile, seas will also build to 10-12 feet. Southerly flow will continue.nue through Wednesday then turn onshore Wednesday night as the cold front moves through western WA. The flow will turn offshore as we move into the end of the week. A weak front will cross the area on Saturday followed by a stronger Pacific frontal system on Monday. 33

Hydrology
The third-in-a-row (and in a week) AR has moved into western Washington this morning. This one will last into Thursday morning. Thus there are renewed river flooding concerns. While the worst of the AR will focus just to our north in BC, moderate to heavy rain will once again impact the Olympic Peninsula and the northern Cascades. This system looks to produce slightly less rainfall, with totals more on the order of 1-2 inches in the Whatcom/Skagit County lowlands, with 2-4 inches in the North Cascades and in portions of the Olympic Peninsula.

There are several things exacerbating the flooding situation. The antecedent conditions are such that the runoff efficiency from the rainfall will be high. With persistent rain, heavy at times, and flooding over the last several weeks, the soils are saturated and just can't absorb any more. In addition, the temperatures will be relatively warm with snow levels over 10,000 feet. Breezy winds and high relative humidity will increase snow melt, though the availability of low to mid elevation snow is likely limited. In some areas, flooding will still be ongoing when the storm starts, despite river and stream levels being below flood stage by then.

Flood impacts along the Nooksack and around the Everson area appear to be higher than usual, likely due to the movement of river sedimentation that has altered the streambed. This change also adds uncertainty to the calculated river flows and therefore to the river forecasts.

One caveat is that with this decently strong atmospheric river just to our north, a change in its trajectory could make a huge difference given the potential of the storm. Changes in an AR's trajectory are not uncommon. Should this one slide in a little more to the south than forecast, there would be the potential for flooding on the more northerly rivers to be much higher; at least as high as yesterday's minor flood crest, if not higher. The 90 percentile Quantitative Precipitation Forecast max over the mountains of Whatcom County top out at 8 inches rather than the 4 inches in the current operational forecast. Plugging this doubling of the precipitation into the river model for the Nooksack give a crest will into the moderate flood range rather than cresting belong flood stage. That being said, this morning some of the high resolution models are hinting that later in this event there will be a longer, farther north push to the heaviest precipitation which will put the precipitation totals on the lighter side instead.

This ongoing precipitation will also provide trigger points for landslide initiation and keep the threat of landslides elevated into the weekend.

JBB

NOAA Seattle WA Office: Watches - Warnings - Advisories
WA...Flood Watch through Thursday morning for Admiralty Inlet Area- Bellevue and Vicinity-Cascades of Snohomish and King Counties-Cascades of Whatcom and Skagit Counties-East Puget Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-North Coast-Olympics-Western Skagit County-Western Strait of Juan De Fuca-Western Whatcom County.

PZ...Small Craft Advisory until 3pm PST Wednesday for
Grays Harbor Bar

Small Craft Advisory until 4pm PST Wednesday for
Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-
Coastal Waters From Cape Flattery To James Island Out 10 Nm-
Coastal Waters From James Island To Point Grenville 10 To 60 Nm-
Coastal Waters From James Island To Point Grenville Out 10 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-
Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-
West Entrance USA Waters Strait Of Juan De Fuca.

Small Craft Advisory until 10am PST Wednesday for
Admiralty Inlet
East Entrance U.S. Waters Strait Of Juan De Fuca-
Northern Inland Waters Including The San Juan Islands-
Puget Sound and Hood Canal