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Last (for now) in series of 3 atmospheric river systems expected over Whatcom County tonight

WHATCOM COUNTY, Wash. — The third of 3 nearly back-to-back atmospheric river weather systems forecast last week is expected to arrive over Whatcom County late tonight, Monday, November 29th. When making the forecast last Wednesday, National Weather Service (NWS) Seattle office forecasters noted, “While none of these events by themselves would likely result in widespread flooding, the cumulative effects of these storms will increase flooding concerns over the next week.”

Rain is forecast to begin late tonight and continue through Thursday morning.

The next round of persistent rainfall will reach Western Washington late tonight into Tuesday as a weaker AR affects the area once again. Current ensemble guidance suggests lighter rainfall accumulations than what we experienced over the weekend.

National Weather Service Seattle office forecasters (November 29, 2021)

The previous 2 weather systems resulted in 3 to 6 inches of rainfall accumulation. Forecasters said today they expect this next system to result in about 1 to 1.5 inches in the lowlands and 2 to 4 inches in the north Cascade Mountains.

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Plot of vertically integrated water vapor transport analysis forecast for 10am, November 30, 2021.

Nooksack River level forecasts at the key locations of the Saxson bridge, Cedarville and Ferndale show the river rising before reaching seasonably normal levels and cresting Wednesday 3 to 4 feet below the highest levels reached over the past 2 days.

Potential impacts from these river levels may be compounded by not only by the saturated soil and existing puddling created by the recent weather systems but also levee damage caused during the mid-November flooding event.

It remains unclear how rivers in these areas will respond to additional rainfall over the next 2 days. One hazard that will persist is the threat for additional landslides. Soils will not have adequate time to fully dry out, therefore they will remain unstable.

National Weather Service Seattle office forecasters (November 29, 2021)

Besides rain, a typical component of atmospheric rivers is wind and forecasters say to expect gusty southerly winds Tuesday through Wednesday with the strongest gusts reaching as high as 45mph on Tuesday.

Looking further ahead than most forecasters are typically confident in doing, computer weather forecast models are showing potential for another atmospheric river aimed at Whatcom County and arriving sometime around Sunday, December 5th.

Plot of vertically integrated water vapor transport analysis forecast for 4pm, December 5, 2021.

Whatcom News readers are encouraged to stay informed by monitoring the latest Nooksack River level forecasts on Whatcom-News.com.

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