FOUS30 KWBC 060830
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 AM EDT Wed May 6 2026

Day 1
Valid 12Z Wed May 06 2026 - 12Z Thu May 07 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE INTERIOR SOUTHEAST...

On-going convection at the start of the Day 1 period will linger
over portions of Arkansas. northern Mississippi and adjacent
portions of Tennessee as a cold front progresses into a most and
unstable atmosphere. Given the alignment of the storm motion and
the boundary...some training will continue with localized rainfall
totals of 1 to 2 inches before convection wanes. WPC Mesoscale
Precipitation Discussion was issued covering this area valid
through 1320Z.

The high-resolution guidance continued to struggle at eh 06/00Z
production cycle and continued with their earlier idea of bimodal
distribution to the heavy rainfall while coarser scale models
tended to have a more uniform distribution of rainfall but with
different orientations. Both the Latest HREF/RRFS guidance showed
some 15+ percent neighborhood probabilities of 24 hr QPF exceeding
10 year ARIs over portions of Mississippi and Alabama. This led to
a southward expansion of the Slight Risk area. Elsewhere...rainfall
amounts of 1 to 2 inches in an hour should be reachable within the
Slight Risk area but the signals as to where this happens are not
as strong. With increasing input from the convective allowing
models...further increases in expected rainfall amounts and better
agreement are possible which might result in an upgrade with future
updates.

Bann

Day 2
Valid 12Z Thu May 07 2026 - 12Z Fri May 08 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
TEXAS EASTWARD TO GULF COAST REGION AND SOUTHEAST UNITED STATES...

Abundant moisture along a stalled frontal boundary on Thursday
will support additional thunderstorm formation along the front.
Rapidly weakening forcing at the surface and aloft will greatly
diminish convective coverage and restrict the parameters favorable
for heavy to excessive rainfall along the Gulf Coast and into
central Georgia and South Carolina. Given differences in the way
numerical guidance has in terms of how fast the front is
progressing...there was some continued adjustments to the placement
of the Marginal risk area.

South TX Brush Country...
An upper low with an associated surface boundary approaching the
region should lead to increasing chances for showers and
thunderstorms. Expectations are that most of the convection in this
time frame will remain west of the international border but there
are enough models showing some storms making east of the Rio Grande
River with isolated heavier amounts and inferred rainfall rates
that could lead to isolated flooding concerns during the late
day/evening.

Bann

Day 3
Valid 12Z Fri May 08 2026 - 12Z Sat May 09 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE LOWER- AND CENTRAL TEXAS COAST ON FRIDAY...

Attention shifts to the Lower Texas coast for a risk of excessive
rainfall as shortwave energy nears the region from the southern
Great Basin and northern Mexico. Low level flow backs in response
to the approaching shortwave which results in precipitable water
values to exceed 2 inches along the immediate coastline. This
occurs at the same time flow aloft is expected to become
increasingly difluent and when the CAPE is approaching 1000 J per
kg. This should result in growing coverage of convection that will
be capable of producing rainfall rates sufficiently high to result
in isolated instances of flash flooding.

Bann




...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE GULF COAST AND SOUTHEAST UNITED STATES...

The risk of excessive rainfall will be focused along the low-level
boundary that builds into the region on Day 2 and stalls along a
west to east axis. Precipitable water values in excessive of 1.5
inches should be pooling along the boundary on Friday...with higher
precipitable water values returning northward later in the day on
Friday and through Friday night/early Saturday morning.

Southern stream shortwave energy become southerly during the day
and increases.

The Marginal risk area is conditional in the sense that a Slight
could be needed depending on observed rainfall on Day 2, the
degree of overlap with Day 3 QPF and the amount of urbanization.

Bann

Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt