Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
804 PM EST Sun Nov 2 2025

Day 1
Valid 01Z Mon Nov 03 2025 - 12Z Mon Nov 03 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTH CAROLINA OUTER BANKS...

Opted to introduce a Marginal risk for portions of the NC Outer
Banks for the overnight period. A developing low pressure may bring
periods of heavier convection into these coastal areas resulting in
a localized flash flood risk. The last several HRRR runs have all
indicated localized rainfall amounts over 5", with some runs
depicting isolated max rainfall in excess of 7". The big question
will be whether these higher totals remain offshore, or are able to
get into the Outer Banks. Recent obs show easterly winds at
Hatteras, NC and northerly flow just west of Pamlico
Sound...suggesting an axis of convergence and possibly allowing for
an advection of instability into the Outer Banks from the
Atlantic. Thus the HRRR depiction of heavier convection getting
onshore seems plausible, and while the magnitudes may not be as
extreme...the pattern would favor slow moving convection and there
is a reasonable threat of rainfall exceeding 5". So while
confidence in the heavier convection getting onshore is only
average...we think there is enough of a conditional threat to
justify introducing a Marginal risk with localized flash flooding a
possibility.

Chenard


Day 2
Valid 12Z Mon Nov 03 2025 - 12Z Tue Nov 04 2025

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

Orrison


Day 3
Valid 12Z Tue Nov 04 2025 - 12Z Wed Nov 05 2025

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

2030Z Update...

The latest multi-model consensus continues to advertise arrival of
strong atmospheric river activity late Tuesday and into early
Wednesday morning across portions of especially southwest OR and
northwest CA. This will be driving by strong jet energy rounding
the base of a deep layer trough amplifying offshore of the West
Coast. Enhanced deep layer Pacific moisture transport and
orographic ascent along the coastal ranges will yield heavy
rainfall. Generally 2 to 4 inch rainfall totals are still
anticipated by early Wednesday morning across the southwest-facing
slopes of far southwest OR and northwest CA, but some spotty 5+
inch totals will be possible given the level of elevated IVT
magnitudes which may peak Tuesday night around 1000 kg/ms. Given
the consistent meteorological setup compared to continuity, only
very minor tweaks were made to the Marginal Risk for excessive
rainfall for this update.

Orrison

Previous discussion...

The next strong landfalling atmospheric river (IVT > 750 kg/ms)
looks to impact coastal portions of northern CA/far southwestern OR
come Tuesday afternoon, likely peaking in strength in the evening
to overnight period. Initial low-level flow earlier in the day
looks more ideally directed perpendicular to the coast/mountains,
but by the time higher IVT sets in veering to the SW-SSW may
mitigate the effectiveness of the topographic lift (with otherwise
limited instability as MUCAPE of less than 250 J/kg is forecast).
Even still, this is a relatively warm system (with the cold core
staying offshore until beyond Day 3) and PWATs of 1.2-1.4" are in
the vicinity of the 90th percentile climatologically. Rainfall
totals of 2-4" are generally expected (and may locally exceed 4"),
and much of that could occur in a 6-12 hour period. The inherited
Marginal Risk is sufficient (in-line with the latest GEFS-driven
machine learning first guess field) and has been maintained (with
only minor adjustments based on the latest models QPF footprint).
Any flash flood impacts are most likely where relatively high
rainfall rates (0.25"+/hr) coincide with sensitive burn scars.

Churchill


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