FOUS30 KWBC 291137
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
737 AM EDT Wed Jul 29 2026

Day 1  Valid 12Z Wed Jul 29 2026 - 12Z Thu Jul 30 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE NORTHEAST...

11z Update: We expanded the MDT risk westward into eastern NY given
observational and model trends. A stationary convergence axis is
focusing a band of intense rainfall over far eastern NY...a bit
west of earlier forecasts. Not much instability along this axis,
but strong convergence is overcoming this and supporting low
topped convection with efficient warm rain processes. As the low
over Long Island moves northward expect the rainfall axis to pivot
and persist over eastern NY, and portions of far western CT/MA.
Areas of significant flash flooding are likely through the
morning, with high end life-threatneing impacts possible across the
mid to upper Hudson Valley and point just east towards the CT/MA border.

Chenard

...Previous Discussion...

...Northeast...
Intense rainfall will be on-going over portions of the Northeast as
the Day 1 period begins at 29/12Z, with some training of cells and
some places experiencing multiple rounds of heavy rainfall--particularly
across western Massachusetts, far southern Vermont, and broadly
across southern New England. Rainfall rates between 1-2"/hr at
times will be possible through late morning/early afternoon and
totals of 2-4" (with localized higher amounts possible) are expected.

HREF/RRFS neighborhood probabilities from the 29/00Z runs remained
high (greater than 80 percent) for 3" totals across
western/central MA into far southern VT. Probabilities are moderate
(30-50 percent) for 5" totals.

Given the setup and risk of significant flash flooding continuing
from the day 1 period, a Moderate Risk was maintained with few
changes given the cumulative rainfall amounts. After 30/00Z...the
intensity of rainfall should subside while also shifting eastward.

...Four Corners States into the Central/Northern Plains...
Monsoonal flow persists with isolated to widely scattered
convection extending from the Four Corners region northward and
eastward...perhaps extending as far east as the plains of Colorado.
Some of this rain could fall atop soils saturated from heavy rain
prior to the start of the Day 1 period at 29/12Z. Persistence in
the pattern and moisture distribution leaves the risk area in good
shape with the Slight Risk focused on eastern Colorado.

...Central Gulf Coast Region into parts of the Southeast...
A cold front stalling along the Gulf Coast will be a focus for slow
moving and training thunderstorms today into tonight. Guidance
continues to indicate a low-probability threat for at least 3" of
rain due to training of 1-2"/hr rain rates within favorable
thermodynamics. This region can generally tolerate significant rain
rates and this amount of rainfall, but any more pronounced
training could result in isolated flash flood related impacts.

Taylor/Bann
 

Day 2  Valid 12Z Thu Jul 30 2026 - 12Z Fri Jul 31 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE LOWER MISSOURI AND MID TO UPPER MISSISSIPPI VALLEY...

...Lower Missouri Valley into the Mid-Upper Mississippi Valley...
Shortwave energy will be progressing east southeast as it tracks
across parts of the central and northern plains on Thursday into
Thursday night/early Friday morning. The shortwave energy will be
encountering an increasingly moist and unstable airmass with
precipitable water values in excess of 2 inches being drawn into
the region ahead of the shortwave. Given the MCS/upscale growth
potential with this system, concentrated areas of heavy rain are
expected given the potential for training and repeat-convection. The
Slight Risk remained in good shape and only minor adjustments were
needed to covers the 29/00Z ensemble guidance and to account for
the uncertainty/spread among the models.

...Four Corners States into the Central/Northern Plains...
Monsoonal flow and anomalous deep-layer moisture will maintain an
isolated excessive rainfall risk extending from eastern Arizona
northeastward across much of western and northern New Mexico into
parts of Colorado. The expanding mid/upper level ridge will likely
limit the coverage compared to recent days.

...Central Gulf Coast Region into parts of the Southeast...
Heavy rainfall is expected along a front associated with a low
pressure system which will be pulling away from New England.
Heavy rainfall with some potential of flooding will be focused
along and near the front...especially over parts of Florida and
Georgia near the state line.

...New England...
The departing low pressure is expected to be across eastern MA at
the start of the period and transition off the coast during the
period. Locally heavy rainfall will remain possible across the
region given its proximity and ample moisture to work with. While
the instability will likely be less compared to Tuesday/Wednesday,
the stronger dynamics at play and potential for training rainfall
could lead to a localized threat, particularly if over areas more
saturated from previous rainfall. A Marginal Risk was maintained.

Taylor/Bann
$$
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