Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
408 AM EDT Thu May 21 2026

Day 1
Valid 12Z Thu May 21 2026 - 12Z Fri May 22 2026

...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS AS WELL AS FOR THE UPPER TEXAS COAST INTO
SOUTHWEST LOUISIANA...

...Southern Plains...

The combination of several ingredients coming together across
eastern Oklahoma and north Texas will be the driver for rounds of
training convection expected across the area. At the surface, the
nose of a low level jet will advance northward over Oklahoma,
spiking the PWATs over 1.5 inches this morning. Surface convergence
around a trough will support low level lift and thunderstorm
formation. An approaching upper level trough will increase the
divergence and lift in the upper levels. The result will be a
rather narrow corridor at first with mostly showers but some
thunderstorms by early afternoon, as the day is approaching peak
heating. Cold pools and speed convergence will focus the
convection, allowing training to become more likely as the storms
track northeastward. A secondary wave of thunderstorms will move
northward across north Texas, which will increase the areal
coverage of convection into the early evening hours. The
strengthening upper level shortwave driving this secondary wave
will become the primary forcing, allowing the complex of weakening
storms tonight to push northward and end the rainfall threat from
south to north. While the greatest flash flooding threat may be in
a rather narrow corridor from north Texas north and east through
Tulsa, sufficient Gulf moisture could still allow for flash
flooding in other areas as well.

The inherited Slight Risk was split with this update owing to
better CAMs agreement that from north Texas through Oklahoma will
be the best area for flash flooding risk, but less rainfall is
expected across east central Texas, between Houston and the
Metroplex, allowing for a downgrade to the risk in that area.

...Upper Texas Coast into Southwest Louisiana...

A large complex of storms currently over South Texas will push
northeast up the Texas Coast through the day today. The area will
have abundant Gulf moisture, instability, and some limited support
from the upper levels. Thus, any storms will be capable of very
heavy rainfall, but the time of the heavy rainfall in any one area
may be limited as the complex progresses northeastward. The area
was hit hard with very heavy rain yesterday, resulting in rainfall
totals over 5 inches near Freeport. As this second round of storms
moves through this morning, convergence into the storms, sea breeze
effects, and the saturated soils from yesterday's rains could
result in additional instances of flash flooding. The storms
continue into the Houston Metro around midday, introducing an urban
factor to the flash flooding threat. The storms then turn more
northward through the afternoon, ending the flash flooding threat
for the day along the coast. To summarize, the Slight Risk, albeit
a low- end one, remains in place mostly for the potential for very
heavy rains with PWATs approaching 2 inches and the favorably wet
soils overcoming the fast movement of the storms to result in flash
flooding.

Wegman

Day 2
Valid 12Z Fri May 22 2026 - 12Z Sat May 23 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE EASTERN U.S....

The inherited Marginal Risk was left largely unchanged for many
areas with this update, save some trimming across both Oklahoma and
Missouri due to reduced signal for heavy rainfall in those areas.
Two areas in particular stand out as higher-end Marginal Risks,
where a Slight may be needed with future updates:

Across a portion of the Ohio Valley from northern Kentucky through
southern Ohio, efficient moisture advection will spike PWATs from
around 1.25 inches early in the day Friday to 1.75 inches by the
afternoon. With this added moisture, so too will instability
increase. Rain in the form of showers and thunderstorms following a
warm front, the same wave that will impact the Slight Risk areas on
D1/Thu will increase in coverage at peak heating Friday afternoon.
Mostly stratiform rain will lead the convection in the morning,
helping saturate the soils that in some areas of the Ohio Valley
remain nearly saturated from prior days' rains. Then during the
afternoon as instability and moisture rapidly increase and the
cloud cover and relative stability push north into northern Ohio
and Pennsylvania, areas of showers and storms will impact northern
Kentucky into southern Ohio. There remains considerable uncertainty
as to how much instability can develop given the short time frame
between the morning's stabilizing rains with the warm front and the
following convection. Further, there is uncertainty as to how the
storms will organize, with some training needed to produce anything
more than isolated instances of flash flooding. Thus, for now, the
Marginal was maintained, but is likely the higher of the two areas
for a potential Slight risk upgrade with future updates.

The other area of the large Marginal that is drawing additional
scrutiny is the area from north Georgia into the Carolinas. Here
moisture and instability will be plentiful, supporting clusters of
heavy-rain-producing thunderstorms. Winds are generally
unidirectional which may support training. However, lack of forcing
with upper level ridging in place will act as a counter to allowing
the storms that form to organize. Thus, clusters of disorganized
convection will be unlikely to produce much in the way of flash
flooding. Further, much of this area is in severe drought, and
soils are extremely dry. Sandy soils would work against flooding as
well into the Piedmont, so that highly unfavorable hydrology should
also work to effectively keep any flooding threat in check.

Wegman

Day 3
Valid 12Z Sat May 23 2026 - 12Z Sun May 24 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF EASTERN
TEXAS AND WESTERN LOUISIANA...

Perhaps the most active day of the Days 1-3 period will be on
Saturday across eastern Texas into Louisiana. Plentiful moisture
and instability will be drawn north off the Gulf, spiking PWATs to
around 2 inches in some areas, and instability could peak over
4,000 J/kg right at convective initiation midday/early afternoon
Saturday. Lines of intense thunderstorms will develop in this
extremely favorable air mass during the afternoon. The storms will
generally track northeastward. However, as they move north,
additional clusters are likely to form as both moisture and
instability rapidly recover. In the upper levels a series of small
shortwaves, but nonetheless potent ones given the highly favorable
atmosphere will allow for new clusters of storms to form across
southeast Texas soon after the prior rounds move off to the north.

Once daytime heating wanes in the evening, it appears likely that
additional storms that form will predominantly move southeastward
towards the Gulf as they follow the instability. This could lead to
additional periods of heavy rainfall over many of the same areas
hit with heavy rains Saturday afternoon. Further, these storms
moving against the prevailing windflow could slow down the storm
movement, increasing both interaction potential between cells as
well as the duration of the heavy rainfall, this threat appears
particularly probable in the Houston metro area. With CAMs input
over the next day or so, a Moderate Risk may need to be considered
in and around the Houston metro, perhaps extending southwest along
the Texas coast with future updates.

Elsewhere, the Marginal across portions of the Northeast was
removed with this update as the warm front over the area will have
zero instability to work with, resulting in a long duration
stratiform rain. Some elevated convective elements may sneak their
way that far north, but the otherwise light rainfall should allow
any rain to soak into the soils with no flash flooding expected.
Conversely, a Marginal Risk was introduced for a portion of north
Georgia into the Carolinas. Following likely rain from storms on
D2/Friday, additional widespread storms are expected again Saturday
afternoon into the evening over many of the same areas. As on
Friday, forcing in this area will be very limited. The storms will
generally track east-southeast towards the coast, with enough
movement that interactions are generally unlikely to initiate
additional convection. Any lines of storms should align
perpendicular to the flow reducing the training risk. Finally,
despite any rains on Friday, the ongoing severe drought should
still greatly mitigate most of the flash flooding threat. Given the
plentiful moisture and instability the storms will have to work
with, they will still likely produce very heavy rain in their
cores, raising resultant flooding potential into the Marginal
category.

Wegman


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