FOUS30 KWBC 030830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
330 AM EST Fri Jan 3 2025

Day 1
Valid 12Z Fri Jan 03 2025 - 12Z Sat Jan 04 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR FAR
SOUTHWESTERN OREGON AND PORTIONS OF NORTHERN CALIFORNIA...

A long duration atmospheric river has resulted in 2-4" rainfall
totals over portions of far northwestern CA over the past several
days, with 1-3" occurring over the past 48 hours (extending into
portions of far southwestern OR as well). A final push of low-level
moisture transport is beginning to reach the coastline early this
morning, as a potent shortwave and associated surface cyclone
brings the most significant source of uplift yet (as well as
elevated instability with the HREF indicating MU CAPE of 250-500
J/kg in association with height falls aloft). The shortwave and=20
low will move into the coast this evening and through the=20
overnight shifting, shifting the heaviest rainfall both southward=20
and inland with time (bringing northern portions of the Sacramento
Valley, which has been largely missed with the previous days'=20
rainfall, into the Marginal risk for excessive rainfall). Areas
most at-risk for rainfall rates exceeding 0.25"/hr (which can
become problematic for particularly sensitive terrain, such as=20
burn scars) are along the upslope portions of the Coast Range,
Klamath Mountains, Cascade Range, into the northern Sierra Nevada
(per HREF Ensemble Agreement Scale, 10-100 km, neighborhood
probabilities of 60-90% for 1-hr, 0.25" exceedance). Additional
24-hr totals of 1-3" are expected (with a slight majority of the=20
rainfall occurring prior to 00z).=20

Churchill


Day 2
Valid 12Z Sat Jan 04 2025 - 12Z Sun Jan 05 2025

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

Churchill


Day 3
Valid 12Z Sun Jan 05 2025 - 12Z Mon Jan 06 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST AND CENTRAL GULF COAST...

An impressive deep layer cyclone is anticipated to develop over=20
the central US into Day 3 (originating from the aforementioned=20
shortwave impacting the Pacific Northwest on Day 1), as strong DPVA
via a digging shortwave (cutting off into an upper low) interacts
with the right-entrance region of a broad phased jet structure
(~130 kt jet streak @ 250 mb over the Mid-Atlantic). A substantial
low-level jet (850 mb of 40-50 kts) is expected to form as a
result, ushering in highly anomalous (for this time of year)
precipitable water values nearing 1.5" (near the 90th percentile to
max moving average, per JAN/BNA/BMX sounding climatology). While=20
downscaled global guidance (GFS/ECMWF) suggests only localized 1-2"
totals at this stage, the impressive dynamics of this system=20
(along with the anomalous moisture) suggest the potential for this
guidance to be exceeded (as hi-res CAMs will shed a light on as=20
the event gets closer in range). That said, both the progressive=20
nature of the system and a distinct lack of instability should be=20
limiting factors for organized heavy rainfall. Maintained an=20
inherited Marginal risk area for much of the Southeast (with some=20
expansion towards the central Gulf Coast, where instability will be
more abundant) encompassing the expected warm sector of the system
(while excluding areas farther north where more impressive broad=20
QPF exists, as this precipitation will mostly occur in the form of=20
ice and snow).=20

Churchill


Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/94epoints.txt__;!!DZ3fjg!6g3RPfbLLwpaqbq9WnlYdbegHyOlfV0OLEJWWgHRsn2l=
gRL-2j7rz5gSy5xUmCswn8s0sFrdC_hUDFbsl6XndGkGhog$=20
Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/98epoints.txt__;!!DZ3fjg!6g3RPfbLLwpaqbq9WnlYdbegHyOlfV0OLEJWWgHRsn2l=
gRL-2j7rz5gSy5xUmCswn8s0sFrdC_hUDFbsl6XnmIZLAyE$=20
Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go=
v/qpf/99epoints.txt__;!!DZ3fjg!6g3RPfbLLwpaqbq9WnlYdbegHyOlfV0OLEJWWgHRsn2l=
gRL-2j7rz5gSy5xUmCswn8s0sFrdC_hUDFbsl6XnL2Nyrx4$=20

=3D =3D =3D
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