Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Thu Mar 12 2026

Day 1
Valid 16Z Thu Mar 12 2026 - 12Z Fri Mar 13 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

16z Update: The ongoing Marginal risk looks in good shape, with the
incoming model guidance and observational trends remaining
consistent.

Chenard

...Previous Discussion...

An axis of anomalous PW and 850-700 mb moisture flux
values...1.5-2.5+ and 2 to 4+ standard deviations above the mean,
respectively, will continue to impact southern WA state into
northern Oregon from the Cascades westward to the Coast Ranges.
Hourly rainfall rates are not expected to be very impressive, at
most .10-.25"+. However, there is not expected to be a lot of
movement, overall with this anomalous onshore flow, which will
support rain for nearly all of the day 1 period in this axis.
Heaviest precip likely in the upslope of the southern WA Cascades
and far northern OR Cascades, where HREF and RRFS neighborhood
probabilities are high for 2 and 3"+ amounts day 1. Changes to the
previous outlook were to trim the marginal risk southward out of
coastal southern WA, and through the Willamette Valley to better
match the latest model qpf consensus.

Oravec

Day 2
Valid 12Z Fri Mar 13 2026 - 12Z Sat Mar 14 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE PACIFIC NORTHWEST...

Not a lot of changes expected overall to the large scale flow
pattern off the northeast Pacific into portions of the Pacific
Northwest day 2. The ongoing atmospheric river event will continue
through much of the day 2 period, with the axis of anomalous PW
and 850-700 mb moisture flux values...1.5-2.5+ and 2 to 4+
standard deviations above the mean, respectively, again impacting
areas from southern WA state into northern Oregon from the Cascades
westward to the Coast Ranges. Similar to the day 1 period, the
hourly rainfall rates are not expected to be very impressive, at
most .10-.25"+. However, there will continue to be little overall
movement with this anomalous onshore flow axis, which will support
additional heavy rainfall amounts in the upslope of the northern
OR/southern WA Cascades and the northern OR Coast Range. Changes to
the previous outlook were to trim the marginal risk area over
southern WA and remove it from the Willamette Valley to better
match the latest model qpf consensus.

Oravec


Day 3
Valid 12Z Sat Mar 14 2026 - 12Z Sun Mar 15 2026

The probability of rainfall exceeding flash flood guidance values
is less than 5 percent.

Oravec

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt