Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 PM EDT Thu Oct 30 2025

Day 1
Valid 16Z Thu Oct 30 2025 - 12Z Fri Oct 31 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE NORTHEAST MID-ATLANTIC AND SOUTHERN NEW ENGLAND...

A strong deep layer trough and associated closed low will continue
to gradually take on a negative tilt today through tonight as the
energy pivots gradually out of the Mid-Atlantic region and into the
Northeast. Strong DPVA coupled with enhanced low-level moisture
transport/convergence and modest instability around the northeast
flank of a strengthening and occluded low center will drive bands
of heavy showers and a few thunderstorms up across portions of
eastern PA, NJ, southeast NY, and adjacent areas of southern New
England.

The short-term concerns will be mainly to eastern PA and NJ as a
ribbon of modest instability with MUCAPE values of ~500 J/kg nose
up across the region with a strongly forced environment. The 12Z
HREF and 06Z REFS solutions suggest some linearly oriented bands of
convection will be possible with rainfall rates potentially up to
1 inch/hour before the frontal occlusion crosses the region.

However, areas of northern NJ, far southeast NY (including the
greater NYC metro area) and into adjacent areas of southern New
England (CT/RI) will see some potential for some brief convective
cell-training concerns this evening as the low-level Atlantic
moisture transport (aided by 925/850 mb flow of 40 to 50 kts)
becomes increasingly convergent/focused near a developing triple
point low as the primary low advances well inland. Very modest
instability will keep the rainfall rates somewhat subdued, but the
level of dynamic jet-aided forcing/ascent through the column and
the moisture transport may support some spotty 1 to 1.5 inch/hour
rainfall rates.

Localized storm total amounts of 2 to 4 inches will be possible
where any cell-training ends up occurring, but with the dry
antecedent conditions, any flash flooding concerns will be isolated
and mainly confined to the urbanized corridors closer to I-95. As
such, the Marginal Risk area is maintained and just locally tweaked
to account for the latest radar trends and 12Z hires CAM solutions.

Orrison


Day 2
Valid 12Z Fri Oct 31 2025 - 12Z Sat Nov 01 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR WESTERN
WASHINGTON...

2030Z Update...

Generally no changes to the previous thinking. The latest guidance
continues to support atmospheric river conditions arriving across
western WA this period which will drive heavy rainfall into the
coastal ranges and the windward slopes of the Cascades. Snow levels
will be rather high, some there will be heavier rainfall amounts
materializing at some of the higher elevations which as previously
mentioned may reach as high as 3 to 5 inches for the period. Made
only cosmetic changes to the Marginal Risk area for this update.

Orrison

Previous discussion...

A modestly strong atmospheric river will setup across the Pacific
Northwest with an advection of high IVT (>750 Kg/ms) into the
region beginning Friday afternoon, carrying through the late
evening Friday into Saturday. Inflow at 850 hPa approaches 50 kts
out of the southwest while precipitable water values in the coastal
ranges rise into the 1.25-1.5" range. MU CAPE is forecast to
remain weak, under 250 J/kg. Precip rates should rise to between
0.5-0.75"/hr during the peak of the heavy rainfall, producing local
amounts of 3-5" in the higher terrain of western WA, which would
be particularly challenging for the Skokomish river. Considering
the consistency within guidance on totals and expectation for some
enhanced rates to generate river rises and minor flooding, a
Marginal Risk was maintained, with some expansion to the south to
account for the wetter 00z UKMET solution.

Roth


Day 3
Valid 12Z Sat Nov 01 2025 - 12Z Sun Nov 02 2025

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

Roth/Orrison


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