Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
825 PM EDT Sat Aug 1 2026
Day 2
Valid 12Z Sun Aug 02 2026 - 12Z Mon Aug 03 2026

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA BIG
BEND REGION AND THE EASTERN GREAT LAKES...

...East Coast States...
Widespread showers and thunderstorms are expected from the Gulf
Coast of Florida through the Mid-Atlantic States, and into the
interior Northeast on Sunday.

An anomalously strong upper closed low (NAEFS 500mb heights down to
the 1st climatological percentile and 850mb heights below the
climatological minimum) will be positioned over IN Sunday morning.
This feature will begin to open during D2 as a piece of vorticity
energy swings through the base, but this will result in a still
highly amplified/short wavelength trough digging all the way to the
Gulf Coast. This evolution will help strengthen a meridionally
arcing jet streak into the Northeast and Canada such that the
favorable diffluent RRQ will overlap the broad height falls
downstream of the opening trough. Together, this will create a
large expanse of impressive synoptic ascent from the Gulf Coast
all the way into New England.

This ascent will act upon impressive thermodynamics as tropical
moisture gets drawn northward ahead of the system. PWs as high as
2.25" are progged to flood northward as far as Massachusetts, with
still impressive PWs above 1.75" as far west as the St. Lawrence
River Valley. Together with a collocated plume of 1000+ J/kg
MUCAPE, this will provide an environment for which thunderstorms
will be widespread, and create numerous 1-2"/hr rain rates.
Generally fast 0-6km mean winds of 20-30 kts should limit the
duration of any individual cell in most areas, but this flow will
additionally be aligned to an approaching cold front beneath the
upper trough, suggesting the potential for repeating/training of
cells. This has prompted a large MRGL risk expansion to encompass
most of the eastern states, with isolated flash flood potential
beneath any of these heavier rain rates.

However, there appear to be two area of a more focused threat. The
first is across the Florida Gulf Coast/Big Bend and just inland
where heavy rain will occur again after heavy rain that is
currently falling during D1. An additional 3-5" of rain is possible
(30-50% chance of at least 5") due to backbuilding of cells across
the Gulf repeating onshore with 2-3"/hr rates. Within this region,
an enhanced slight risk was added for Taylor, Dixie, and Lafayette
counties which is where the 2-day rainfall is expected to be
heaviest.

Another area of locally higher excessive rainfall risk exists along
the eastern Great Lakes from around Cleveland, OH through Buffalo,
NY and into the Northern Adirondacks. While instability may be a
bit less here, this is also the region where a pivoting
deformation axis and accompanying mid-level TROWAL may exist north
of the closed low. This will produce some higher thermodynamics
into which storms, which will be slow moving and training, can
repeat with 1-2"/hr rain rates. The inherited SLGT risk was
cosmetically adjusted for new guidance, and the urban areas will be
most susceptible to impacts on Sunday.

..Southwest...
The monsoon ridge begins to expand back to the east once again on
Sunday, but activity is still expected to be suppressed to just
southern AZ/NM. This will be partially due to a shortwave rotating
anticyclonically around the base of the ridge to enhance ascent,
impinging into areas with favorable thermodynamics characterized by
PWs of 1,25 to 1.5 inches, and MUCAPE above 1000 J/kg. The
challenge Sunday is that it appears there will be some drying that
occurs from NE to SW as a decaying front drops across Texas,
followed by a weak surface trough as well. This suggests that
during peak heating, there will actually be somewhat of a
deterioration of the environment, further limiting convective
coverage. Still, scattered thunderstorms are likely for the
southeast portion of AZ, with some more isolated activity as far
east as the Sacramento Mountains of NM. With sufficient bulk shear
of 20-25 kts for modest organization, any of these storms could
produce locally 1"/hr rain rates and instances of flash flooding.

Weiss


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