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Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 1537 UTC Sun Dec 3, 2023
Valid: 16 UTC Dec 03, 2023 - 12 UTC Dec 04, 2023
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1035 AM EST Sun Dec 03 2023
Day 1
Valid 12Z Sun Dec 03 2023 - 12Z Mon Dec 04 2023
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR ALL OF THE
OREGON COAST RANGES AND MUCH OF THE OREGON CASCADES...
16z update...
Timing and magnitude of moisture flux orientation into the Pacific
Northwest Ranges appears to be on target and aligned with previous
discussion(s). The cold front is about to progress through the
far NW portion of the PacNW in the next hour or so; and this will
likely diminish the lower-end risk for much of the remainder of
the forecast time period across portions. However, since it has
not fully arrived at 16z and there will be a narrow window prior
to 04.12z for additional .10-.25"/hr rates across W WA into the
Olympic Range...the thought is to retain much of the Marginal Risk
areas in WA and NW Oregon.
Further south, the central Oregon coastal Range and downstream
Oregon Cascades will remain within the core of the stronger
southwesterly onshore flow for greater than six more hours with
similar 400 to 600 kg/m/s IVT values. One-quarter to one-third
inch per hour will remain on exposed southwestern facing orography
with highest peaks perhaps reaching near .5" occasionally. Given
strong warm advection, freezing levels rise above all but the most
extreme peaks, so there may be some rain on snow melt to help with
increased run-off and rapid rise responses on some creeks/streams
in the vicinity. So no changes were made to the Slight Risk areas
across the coastal Ranges and Oregon Cascades.
Gallina
A moderately-strong atmospheric river, centered on OR, will
continue to push into the coast today through this evening. A
brief reprieve from the rain is expected tonight between impulses
of energy. On top of the rain that's already fallen, expect
another 2 to 4 inches of rain through this evening, with local
amounts as high as 6 inches for the day. More widely scattered
flash flooding impacts are likely today due to so much rain
falling in a short amount of time. NASA Sport imagery shows soil
moisture profiles about normal for this time of year across
western OR, or about 75% saturated. The additional rainfall today
should take less time than yesterday to cause flash flooding
impacts since there's rain ongoing and soil moisture levels
continue to increase.
The ERO risk areas today remain largely the same, with the only
change of note to extend the Slight Risk into the northwest corner
of CA, from Crescent City northward as the coastal ranges in that
area may see 2 to 4 inches of rain through this evening. The
Slight Risk remains in effect for much of the OR Cascades, as
rising snow levels will allow for snowmelt to contribute to rising
river levels on the west side of the range, along with most to all
of the precipitation on the foothills of the Cascades falling as
rain. Much lighter amounts of rain are expected from central WA
north today as the focus says largely over OR, with only 1 to 2
inches of rain expected. Since this too will be added to previous'
days rains, an isolated flash flooding instance can't be ruled
out, and the Marginal remains unchanged.
Wegman
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
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