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FOUS30 KWBC 231551
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1051 AM EST Sun Feb 23 2025

Day 1
Valid 16Z Sun Feb 23 2025 - 12Z Mon Feb 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE OREGON
COAST INTO THE OLYMPIC RANGE AND OVER PORTIONS OF THE SOUTHERN
WASHINGTON AND NORTHERN OREGON CASCADES...

16Z Update...

Some very minor adjustments were made locally to the Marginal and
Slight Risk areas across the Northwest U.S. for this update to
account for the current radar trends and the new 12Z HREF guidance.
On the larger scale, no real change in the previous thinking as the
new guidance continues to support a continuation of moderate to
strong atmospheric river conditions across the region that will
support locally several inches of additional rain for the
orographically favored upslope regions this period.

Orrison

Previous discussion...

...Pacific Northwest into the Northern Rockies...
The ongoing atmospheric river event across the Pac NW will continue
during the upcoming day 1 period as additional height falls
embedded in the broad west southwest mid to upper level flow across
the northeast Pacific move toward the Pacific Northwest. The next
surge of high IVT values, 600-800 kg/m/s and anomalous PW and
850-700 mb moisture flux values, 2-4+ standard deviations above the
mean will push back into the coastal Pac NW during the first half
of day 1.  This will support another day of widespread heavy
rainfall totals of 1.5-2.5"+ 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 1 with much of the precip again
falling as rain. This will bring 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 and increasing the
risk of flooding. No significant changes were made to the slight
risk along the OR coast range, northward into the Olympic Range and
over the southern WA Cascades into much of the OR Cascades.

No significant changes to the marginal risk area inland across far
northeast OR, far eastern WA state into northern ID and northwest
MT. The anomalous PW values that pushed into the Pac NW over the
past 24 hours will move into the Northern Rockies day 1, with
values 2-3+ standard deviations above the mean. Similar to areas
across the Pac NW, snow levels will be very high day 1 with much
of the precip falling as rain. Precip totals of 1-2" possible day
1 across northern Idaho into northwest Montana, combined with snow
melt will support isolated runoff conditions developing.

Oravec


Day 2
Valid 12Z Mon Feb 24 2025 - 12Z Tue Feb 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE NORTHERN
OREGON COAST RANGE INTO THE OLYMPIC RANGE AND OVER THE SOUTHERN
WASHINGTON CASCADES...

...Pacific Northwest...
The next in the series of strong height falls in the broad west
southwesterly mid to upper level flow across the northeast Pacific
will push an amplifying trof into the Pac NW Monday. This third in
the series will be stronger than the previous two and support a
stronger surface low moving into the Olympic Peninsula/eastern
Vancouver Island area Monday evening. 850-700 mb moisture flux
values will again be anomalous..2-3+ standard deviations above the
mean, but PW values not expected to be as anomalous as the two
previous events, generally around 1 standard deviation above the
mean. This will result in slightly lower max IVT values, 500-600
kg/m/s impacting the coastal Pac NW day 2. Additional widespread
heavy rains of 1-2" likely from the Olympics, south along the
Oregon Coast Range and into the WA Cascades and northern OR
Cascades. This will bring totals beginning Sat through the day 2
period in the 7-10 inch range from the northern OR Coast Range into
the Olympic Range and through much of the WA Cascades. Increasing
soil moistures and stream flows will continue a flooding threat
into day 2. Slight risks were maintained day 2 across the southern
WA Cascades and from the northern OR Coast Range and Olympic Range.

...Southeast Florida...
Similar to the past few model cycles, there are some timing
differences among the latest suite of guidance with the amplifying
upper trof moving across the western to central Gulf Monday and
into the eastern Gulf by early Tuesday. Strengthening southerly to
southwesterly low level flow off the Gulf will push anomalous PW
and 850-700 mb moisture flux values, 2 to 3+ standard deviations
above the mean, across South Florida early day 2. Well defined
upper diffluence ahead of the amplifying upper trof will support
the potential for one or more areas of heavy rains to push across
South Florida Monday into Monday evening/early Tuesday. There seems
to be some consensus in the hi res runs for an initial area of
heavy rains to impact South Florida Monday afternoon, followed by a
second round sometime between 0000 and 1200 UTC Tue. With each
round of heavy rain, there may be localized hourly amounts of 1-2",
supporting isolated runoff issues in the urban portions of
Southeast Florida. No changes made to the previous marginal risk
area from Miami to West Palm Beach.

Oravec


Day 3
Valid 12Z Tue Feb 25 2025 - 12Z Wed Feb 26 2025

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

Oravec


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