Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
750 PM EDT Tue May 19 2026
Day 1
Valid 01Z Wed May 20 2026 - 12Z Wed May 20 2026

...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

01Z Update...
Few large-scale changes needed to the previously-issued Excessive
Rainfall Outlook. Some changes were made in West Texas based on
satellite imagery showing cells that were producing 1 to 2.5+ inch
per hour rainfall rates just outside the Marginal Risk area. Given
the amount of instability in the area...at or slightly above 3000
J per kg of CAPE) and slow cell motions...felt the threat of
excessive rainfall will linger into the evening even if these
particular cells weaken and dissipate. See the Mesoscale
Precipitation Discussion 0193 valid until 20/0530Z for latest
details.

Farther north...trimmed parts of the Ohio Valley out of the
Marginal Risk area that were post-frontal and reshaped the Slight
risk area based on radar and the overlap with lowest 1- and 3-hour
flash flood guidance. Thinking is that the threat will be
diminishing with loss of CAPE and but moisture flux convergence
along the front/outflow boundary may still be enough to support
locally heavy rainfall rates for a time this evening.

Bann

..16Z Update..

A line of convection is ongoing and continuing to push southward
in eastern OK and northern AR. The inherited SLGT area in TX was
expanded northward into parts of southern OK and southwestern AR,
to account for an expected round of convection along an outflow
boundary, along with convection along the progressing cold front
thereafter. While the system is expected to be fairly progressive,
rainfall rates will remain quite high. Latest HREF neighborhood
probabilities suggest there is a greater-than 70% likelihood of
rainfall exceeding an inch per hour, and a greater-than 40%
likelihood of rainfall exceeding 2 inches per hour in the early
afternoon hours. The SLGT area was also expanded into the Texas
Gulf Coast to account for an expected development of a low- level
convergence axis along the coast ahead of the cold front this
evening and overnight. Latest deterministic guidance suggests a
solid low-level jet developing overnight, bringing in rich Gulf
moisture, with PWATs potentially exceeding 2 inches. Meanwhile, the
SLGT risk area over southern IN and IL was largely unchanged.
While some CAM QPF disagreement remains over the amount of rainfall
expected, and where the main QPF core is expected to occur,
antecedent rainfall over prior days and very low FFGs justify the
SLGT being maintained.

Blanco-Alcala

..Previous Discussion..

...Texas...

A line of intense showers and thunderstorms currently expanding
south across northern and western Oklahoma will continue south and
east through the early morning into northeast Texas. With peak
solar heating around midday, the line of storms will encounter an
increasingly unstable, and increasingly moist air mass situated
across much of Texas. Guidance suggests that several lines of
storms will develop in north Texas through the early afternoon.
Cold pools and lift ahead of the lines should allow individual
cells to develop out ahead of the lines, which will locally
increase the duration of heavy rains in those areas hit by first
the cells, and then the line shortly thereafter. This could cause
local flash flooding, especially should that occur over the
Metroplex or other urban areas in north Texas. By mid to late
afternoon, upper level energy may support areas of convection
across central and south Texas that will be separate from any lines
to the north. Mergers with the lines as they press south across the
state and any individual cell mergers within the clusters of storms
may also pose a localized flash flooding threat. By evening, the
storms will continue pushing into south Texas, potentially
impacting the San Antonio and Houston metros before they push into
the Gulf and deep south Texas through the predawn hours.

Overall the above-described scenario should keep flash flooding
instances mostly to localized, widely scattered occasions. However,
since the storms will cover much of the state, it's probable that
in flood prone areas, the flash flooding threat could be greater.
Unsurprisingly with so many clusters of storms expected, the CAMs
are not having a great handle on them, so the Slight was expanded
to cover the Texas Triangle. Despite the antecedent dry soil
conditions over most of the state, PWATs will likely exceed 2
inches along the Gulf Coast for when the storms reach there
tonight. Thus, any and all storms will be capable of heavy rainfall
rates that could cause flash flooding.

...Southern Illinois and Indiana...

After rounds of showers and storms caused flash flooding in
portions of Illinois and Indiana yesterday, the soils in the area
are generally saturated due to widespread multiple-inch totals from
yesterday/Monday. Much of the day today will be dry. Towards
evening however, renewed rounds of showers and thunderstorms will
develop with the approach of a strong cold front, significant
moisture and instability advection ahead of the front, and upper
level disturbances helping add to the overall environmental
forcing. Thus, overnight, expect multiple rounds of training
showers and thunderstorms tracking up the Ohio River Valley. With a
robust LLJ supporting the storms, they should have no trouble
maintaining their organization despite the lack of solar heating.
Since the soils are fully saturated, most, if not all the rainfall
will convert to runoff. Thus, the inherited Slight Risk was
expanded southwest to include much of southern Illinois with this
update.

Wegman

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt