FOUS30 KWBC 170814
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
414 AM EDT Thu Jul 17 2025

Day 2
Valid 12Z Fri Jul 18 2025 - 12Z Sat Jul 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL GULF COAST, MID-ATLANTIC, AND THE UPPER MIDWEST...

...Central Gulf Coast...

The center of circulation of a tropical disturbance over south-
central Louisiana will stall out early Friday morning and turn
north through much of the Day 2/Friday period. Much of the guidance
and the official rainfall forecast have 2 distinct maxima of total
rainfall Friday and Friday night: One is over western Louisiana,
with a second into the Mississippi and Alabama Gulf Coasts. While
these are maxima, in most cases rainfall amounts will hold between
2 and 4 inches for the day. As mentioned in the Day 1/Thursday ERO
discussion, the tropical disturbance will simply be too weak and
disorganized to support sustained convection for more than a few
hours. Despite help from daytime heating and with ample atmospheric
moisture, without a well-defined source of forcing, the guidance
and the forecast generally agree that the convection will be highly
disorganized in clusters that are most likely to track over those
two aforementioned maximum areas, but could just as easily form in
other areas, rain heavily, then collapse and weaken. New storms may
form in similar areas, but once again they will remain widely
scattered. PWATs of 2.25 inches and higher will still support any
storms that can form to be capable of short bursts of very heavy
rainfall of 3+ inches per hour. The disorganized nature of the 
storms may still support multiple separate clusters moving over the
same unfortunate area, resulting in highly localized double digit 
rainfall totals. However, it is impossible at this point to
pinpoint any one area that is likely enough to see 6+ inches of
rain in a large enough area to continue to paint it in a Moderate
Risk area. Thus, while it remains likely localized areas will see
enough heavy rain to cause localized flash flooding, some of which
may be significant, the threat for numerous flash flooding has
continued decreasing due to the disorganized nature of the
disturbance as a whole. Thus, given the paltry signals for heavy
rain that are highly changeable, the inherited Moderate Risk for
western Louisiana was downgraded with this update.

Meanwhile, further east into coastal Mississippi and Alabama, 
these areas east of the center of circulation will be under a
predominant southerly flow of deep tropical moisture. With the
center of circulation drifting northward through the period, expect
nearly stationary "bands" of very heavy showers and thunderstorms
to develop as early as the predawn hours Friday. Any "bands" will
have embedded thunderstorms with much heavier rain in between
lighter showers. Given any heavy rain in these areas from the Day
1/Thursday period will likely have saturated the soils in these
largely urbanized areas, the higher likelihood for additional heavy
rainfall into Friday will only worsen the localized flash flooding
threat from Gulfport east through Pensacola, including Mobile. A
higher end Slight is in effect for this area.

...Mid-Atlantic...

A new Slight Risk area was introduced with this update from central
Virginia southeast through the Tidewater and into northeastern
North Carolina with this update. Disturbances from prior
thunderstorms over the Appalachians will track ESE across this
region on Friday. Ample moisture and instability remain in place
from multiple days of showers and thunderstorms over the past few
weeks. Thus, much of this region has very saturated soils that
cannot handle much additional rainfall. Given the front stalled
over this region will act as a focus, the storms will likely form
over western VA and WV, then track southeastward across the Slight
Risk area and into the Carolinas. Additional thunderstorms are
likely to impact eastern areas prior to that, resulting in 
multiple rounds of storms impacting the same area in some cases. 
While the storms will be fast-moving, which may limit the time of 
the heavy rain over any one area, the likelihood of training and 
backbuilding thunderstorms could still result in multiple hours of 
heavy rain over some areas, resulting in locally significant flash 
flooding, especially were this to occur over any urban area.

...Upper Midwest...

Building southerly flow into a stalled out front will result in
scattered convective development over far southern Minnesota and
northwestern Iowa Friday afternoon. While the storms are in their
formative stage...slow movement and cell mergers could result in
widely scattered instances of flash flooding. The storms are likely
to congeal into a line in eastern Iowa, which will increase in
forward speed as the line races southeast into Illinois by Friday
night. Once the line has formed, the flash flooding risk should
decrease since the line will track orthogonal (southeastward) to
its orientation (southwest to northeast). Soils are at or above
average for this time of year in the area, so the heavy rainfall
likely in this area will support any flash flooding due to
excessive runoff.

Wegman


Day 3
Valid 12Z Sat Jul 19 2025 - 12Z Sun Jul 20 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST INTO THE MID-ATLANTIC...

Multiple rounds of thunderstorms are likely to impact areas from
Iowa southeast to the VA/NC coast on Saturday. Thunderstorms
ongoing from the Friday night period may impact the Ohio Valley and
central Appalachians Saturday morning. With daytime heating
additional storms will form over much of Virginia, as lines and
other congealing storms move into the Appalachians. Meanwhile an
upper level shortwave will support repeating thunderstorms from
Iowa southeast through Indiana from Saturday afternoon through
Saturday night. All of these are likely to occur over the same
areas hit with strong thunderstorms capable of heavy rainfall on
previous days. Further, the remnants of the tropical disturbance
over the northern Gulf will further add to the moisture available
for storms to use to produce heavy rain over the Midwest. Thus, in
some instances where repeating storms occur, it may not much matter
how saturated the soils are, as the prolonged heavy rain will
result in flash flooding by overcoming the areas where soils are dry.

The Slight Risk area was expanded into southeastern VA and northern
NC with this update. While confidence isn't quite as high on
D3/Saturday as compared with D2/Friday, the signal for heavy rain,
if reduced from Friday, will still support flash flooding in these
hard hit areas.

...Lower Mississippi Valley...

The inherited Slight Risk area over northern Louisiana was
downgraded to a Marginal with this update. There is good agreement
in the guidance that any remnants of the northern Gulf tropical
disturbance will be dissipated by Saturday, with only showers and
isolated thunderstorms remaining over Louisiana, posing only a
Marginal flash flooding risk at most. The downgrade was
coordinated with SHV/Shreveport, LA forecast office.

Wegman

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