Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
250 PM EST Sat Dec 13 2025

Day 1
Valid 16Z Sat Dec 13 2025 - 12Z Sun Dec 14 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHEASTERN FLORIDA...

A weak mid-level wave over the eastern Gulf will aid in increasing
mid-level flow/ascent across the Florida Peninsula and adjacent
Gulf Stream during the overnight hours. Meanwhile, low-level
moisture will increase across coastal areas as a weak surface
boundary/inverted trough becomes established just inland across the
Peninsula. PW values should increase into the 1.6-1.8 inch range
amid 500+ J/kg SBCAPE. Meanwhile, point forecast soundings depict
favorable kinematic profiles for relatively slow-moving cells that
could impact urban areas of southeast Florida along the I-95
corridor. Local 1+ inch/hr rates are possible. Urban flash flooding
is possible in the 03-12Z timeframe this evening/tonight.

Cook

Day 2
Valid 12Z Sun Dec 14 2025 - 12Z Mon Dec 15 2025

..THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
WESTERN WASHINGTON STATE LATE SUNDAY NIGHT/EARLY MONDAY MORNING...

2100 UTC Update -- No changes made to the Marginal Risk outlook
based on the new (12Z) guidance. 12Z HREF window runs through the
entire D2 period, and of note is the uptick in 0.50"/hr
probabilities after 06Z -- peaking over 80% across the Olympic
Ranges toward 12Z Mon, and over 40% across portions of the Cascades
in WA.

Hurley

Previous discussion...

Maintained the Marginal Risk area over parts of the Olympic and
northern Cascade Ranges in Washington as the next push of moisture
approaches late Sunday night into the early morning hours of
Monday. The models have shown some run to run differences with QPF
but no real clear trend. One consistent signal is that the
orientation of the moisture plume remained more southwest-northeast
than the event that just ended a couple of days ago. That still
points to the idea that rainfall may not increase in coverage or
intensity until late in the Day 2 period. Based on the expected IVT
plume increasing to over 600 at about the time that the flow
reaches the coast and begins to take on more of an on- shore
component...am inclined to follow the ensemble idea of 0.75 inches
to locally 1.5 inches of precipitation focused in the terrain. The
area is sensitive given the nearly week-long excessive rainfall
event...so any additional rainfall is expected to bring renewed
hydrologic concerns. Given a fairly tight window of opportunity for
rainfall during the outlook period...and at least some questions
about timing of the onset....still think a Marginal Risk is
sufficient for now although later shifts can adjust if needed.

Bann

Day 3
Valid 12Z Mon Dec 15 2025 - 12Z Tue Dec 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
WASHINGTON AND OREGON...

2100 UTC Update -- Only minor (cosmetic) changes made to the
previous D3 outlook, some of which was to pull the eastern edges of
the Slight ever so slightly westward in WA based on the latest
snowfall forecast (lowering snow levels).

Hurley

Previous discussion...

Areal coverage of rainfall expands and rain rates increase on
Monday as a well defined atmospheric river continues to direct
abundant moisture into the Washington coastal ranges and Cascades
that gradually makes its way southward into Oregon. Given
antecedent conditions from the excessive rainfall event from
earlier in the week plus whatever falls on Day 2...the concern is
for renewed flooding potential in addition to worsening on-going
flooding especially in the terrain with potential for additional
landslides or mudslides. Saw little reason to modify the Slight
risk area that propagated into the Day 3 period from yesterdays Day
4 outlook especially given the magnitude of the IVT and
precipitable water values forecast by the global models. The focus
of the heavy rainfall should gradually shift southward into an area
that did not receive as much rainfall from the previous
atmospheric river. Opted to extend a Marginal risk area along the
coast as far south as northwestern California more in deference to
uncertainty of timing as to the rainfall amounts.

Bann


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