Subj : HVYRAIN: Excessive Rainfall Discussion
To   : wx-storm@lists.illinois.edu
From : COD Weather Processor
Date : Wed Jan 17 2024 08:17:12

FOUS30 KWBC 170817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Wed Jan 17 2024

Day 1
Valid 12Z Wed Jan 17 2024 - 12Z Thu Jan 18 2024

....THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
FAR NORTHWEST CALIFORNIA INTO SOUTHWEST OREGON...

No changes to the inherited Marginal risk across portions of far
northwest CA and southwest OR. A strong mid level low is moving
into western OR early this morning which is resulting in an uptick
in rainfall intensity. After 12z onshore upslope flow will
continue to be directed into this region to the south of a surface
low expected to gradually move into western WA. This is not the
strongest core of IVT, but it is persistent enough to result in up
to a 12 hr period where 0.25"+/hr rainfall will be possible within
the favorable western facing terrain. The consensus of current
guidance still suggests now through 21z today as the most favored
time for these heavier rainfall rates. Localized 0.5"/hr rainfall
is still a possibility, with high res ensembles showing
probabilities up to ~35%, but unlikely to see rates much higher
than that in this setup. Given the prolonged nature of steady
rain, event totals today may locally get as high as 4-7", with the
00z HREF neighborhood probabilities of exceeding 5" between
60-70%. Rainfall of this magnitude may begin to cause some mainly
minor runoff concerns.

Chenard


Day 2
Valid 12Z Thu Jan 18 2024 - 12Z Fri Jan 19 2024

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

We opted to remove the Marginal risk over western WA with this
update. It still looks like a rainy day across the region, with a
pretty widespread 1-2" expected. Localized 3" totals are still
probable over the favored south to southwest facing slopes of the
Olympics. However this appears like a light to steady rain,
generally lacking the rates needed to pose much of a flood risk.
The 00z GFS and ECMWF keep 3 hourly rainfall below 0.5" during the
event, so this looks like a longer duration 1-3" event...with
neither the magnitude or rates appearing to support a Marginal
risk at this time.

Chenard

Day 3

The Day 3 outlook will be updated by 0830Z.


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!5nAOgTMo7THbMrGoOdqZSbVZrPTVmzB6aedJD5cZ2Uy-=
FDXENbItfMH2UknHIxwgLKz9auctGNewKJzS7aMkNPyJHdY$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!5nAOgTMo7THbMrGoOdqZSbVZrPTVmzB6aedJD5cZ2Uy-=
FDXENbItfMH2UknHIxwgLKz9auctGNewKJzS7aMkj6JsdDs$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!5nAOgTMo7THbMrGoOdqZSbVZrPTVmzB6aedJD5cZ2Uy-=
FDXENbItfMH2UknHIxwgLKz9auctGNewKJzS7aMkmAWKKFE$=20


$$



=3D =3D =3D
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