FOUS30 KWBC 220903
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
403 AM EST Sat Feb 22 2025

Day 1
Valid 12Z Sat Feb 22 2025 - 12Z Sun Feb 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF
WESTERN WASHINGTON STATE AND COASTAL OREGON...

No significant changes made to the previous marginal risk across
coastal sections of Oregon, Washington and in the upslope of the
Washington Cascades and northern Oregon Cascades. The beginning of
a multi day atmospheric river/heavy rainfall event on tap as broad
west southwesterly mid to upper level flow is established across
the northeast Pacific toward the Pacific Northwest. PW anomalies
expected to rise to 2 to 3+ standard deviations above the mean by
Saturday afternoon with the lead shortwave moving toward the Pac NW
coast and continue at that level into Sunday morning. Strong
850-700 mb moisture flux, anomalies 2 to 4+ standard deviations
above the mean expected in the anomalous PW axis, WITH max IVT
values 600-800 kg/m/s. This will support max hourly rainfall rates
of .50"+ and widespread totals of 1.5-2.5"+ and max totals of 3-5"+
in favored terrain regions. The marginal risk area fits well with
where the HREF neighborhood are high for 3"+ totals day 1.

The greatest HREF neighborhood probabilities for .50"+/hr rates
are through the Olympic Range into the southern WA Coast Range from
2100 UTC Sat to 0200 UTC Sun, with probabilities in the 60-90%
range and across portions of the WA Cascades from 2300 UTC Sat to
0400 UTC Sun where probabilities peak in the 60-80% range. Snow
levels will be very high day 1 across the Pac NW, with much of the
precipitation falling as rain. This heavy rain, combined with snow
melt will support isolated runoff issues. The higher hourly rates
do not last for more than a few hours day 1 across the NW. This
combined with been below average precipitation amounts over the
past month over the Pac NW, should mitigate any widespread runoff
issues day 1.


Day 2
Valid 12Z Sun Feb 23 2025 - 12Z Mon Feb 24 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...

The atmospheric river event that started day 1 into the Pacific
Northwest will continue into day 2 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 second
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 Sunday morning. 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 2 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. Given this, slight
risk areas were added from the northern OR coast range, northward
into the Olympic Range and over the southern WA 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 pushing into the Pac NW day 1 will
move into the Northern Rockies day 2, with values 2-3+ standard
deviations above the mean. Similar to areas across the Pac NW, snow
levels will be very high day 2 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
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...

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 days 1
and 2 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 3. 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 3 day totals into 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 3. Slight risks introduced day 2 were
maintained day 3 across the southern WA Cascades and from the
northern OR Coast Range and Olympic Range.

...Southeast Florida...
While there are some timing differences among the latest suite of
guidance, there is agreement on an amplifying upper trof 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 3. This will support the potential for an
area of heavy rains to push across South Florida Monday into Monday
evening, with timing differences evident between the 00Z EC, GFS
and NAM which have detail differences with the amplitude of the
upper trof. While confidence is not great with the details of the
upper trof amplitude and resultant timing of the strongest UVVS,
there is consensus for heavy rains to push across South Florida day
3. A marginal risk area was added for the urban areas of southeast
coastal Florida from Miami to West Palm for the potential for
isolated urban runoff issues.

Oravec

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