Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
724 PM EST Fri Feb 21 2025
Day 3
Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND OREGON AND NORTHERN IDAHO INTO
NORTHWEST MONTANA...

19z Update: Made a modest expansion of both Marginal risk areas.
With 48 hour rainfall amounts of 3-6" (locally higher) in the
terrain, and 1-3" in valley locations, opted to broaden the
Marginal risk over western WA and OR. When combining the duration
and strength of the IVT this is approaching strong atmospheric
river levels...which verify at Slight risk levels about half the
time. However, given the broad and prolonged nature of the event,
hard to pin down a targeted Slight risk at this point, and the
drier antecedent conditions going into the event may help keep
impacts at the Marginal level. Nonetheless will continue to
monitor, and either way at least some flooding issues are expected.

Rainfall totals have trended up along the central Gulf Coast.
Strong dynamics will likely result in a swath of moderate to
locally heavy rainfall, although even the stronger and further
north GFS fails to bring notable instability inland. Thus still
thinking rainfall rates will not be high enough to justify adding a
risk area in the ERO...so will continue without an area depicted.

Chenard

...Previous Discussion...

The atmospheric river event that started day 2 into the Pacific
Northwest will continue into day 3 as additional height falls
embedded in the broad west southwest mid to upper level flow across
the northeast Pacific move toward the Pacific Northwest.
No significant changes to the plume of anomalous PW values and
anomalous 850-700 mb moisture flux anomalies impacting the Pac NW
day 3, with values 2-4+ standard deviations above the mean
persisting along with max IVT values of 600-800 kg/m/s. This will
support another day of widespread heavy rainfall totals of 1-2"+
and max totals in the 3-5"+ range in the favored terrain regions.
Snow levels again will remain high across much of the Pac NW day 3
with much of the precip again falling as rain. With widespread two
day totals in the 3-5"+ range and max totals 6-10" in favored
terrain regions, increasing soil moisture and stream flow values
will increase the risk of flooding.

A marginal risk area was added inland across portions of northern
Idaho into northwest Montana. The anomalous PW values pushing into
the Pac NW day 2 will move into the Northern Rockies day 3, with
values 2-3+ standard deviations above the mean.  Similar to areas
across the Pac NW, snow levels will be very high day 3 with much of
the precip falling as rain . Two day precip totals of 1-3"
possible across northern Idaho into northwest Montana, combined
with snow melt will support isolated runoff conditions developing.

Oravec

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