Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
730 PM EDT Thu Jul 23 2026
Day 2
Valid 12Z Fri Jul 24 2026 - 12Z Sat Jul 25 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST INTO THE OZARKS AND LOWER MISSOURI VALLEY...

...Southeast...

A stalled front will continue to snake across the Southeast,
extending from northern Mississippi, into north-central Alabama and
north-central Georgia, and then into the eastern Carolinas. This
will be the focus for renewed convective activity on Friday. Subtle
changes over the next 24 hours may actually make the atmosphere
more supportive of heavy rain rates by Friday afternoon. First,
precipitable water values are projected to increase, largely due to
a steady increase in moisture in the 850-500mb layer. By Friday
afternoon, most of the area along the stalled front should see
PWATs in the 2.1 to 2.4 inch range. Second, the deep layer mean
winds are expected to decrease from around 15-25 knots today, to
around 10-15 knots by Friday afternoon, as an upper level ridge
axis builds in and reduces upper level winds. This should create an
enviornment that favors very high instantaneous rain rates and
slow-moving, backbuilding, and training clusters near the front.

This may be compensated by a weaker front and low-level
convergence, which would tend to favor clusters and line segments
that are more scattered across the region, rather than aligned in a
specific corridor. Nevertheless, there will still be localized
opportunities for periods of training convection that could result
in flash flooding. The chances (based on hi-res ensemble data) of
rain rates in excess of 2 inches per hour, and for 24-hour rainfall
totals in excess of 5 inches, are highest about 40mi either side of
a line from Birmingham AL, to Atlanta GA, to Aiken SC, to Myrtle
Beach SC, to Morehead City NC. In fact, the 12Z HREF even shows
potential for rain rates to exceed 3 inches per hour in this same
corridor, especially in South Carolina (neighborhood probabilities
as high as 30 percent in SC), so the potential for locally
significant flash flooding remains. An upgrade to Moderate Risk
cannot be ruled out if enough observational evidence and model
guidance suggests a corridor of sustained training convection is
becoming more likely.

...Ozarks and Lower Missouri Valley...

An MCS may be ongoing at the start of the period somewhere in the
vicinity of eastern Kansas and Missouri, near the nose of the low-
level jet. The biggest change with this outlook update was to trim
the Slight Risk out of eastern Missouri in collaboration with WFO
St. Louis. A limited number of models still progress heavy rainfall
further east in Missouri, but the consensus now points more clearly
to eastern Kansas and western and central Missouri. This also
aligns with a typical bias in modeled MCS activity in the central
Plains -- it often ends up further into the inflow than models
would suggest.

There is more uncertainty about what happens later in the forecast
period, from late Friday afternoon into Friday Night. Most hi-res
models suggest the convective cluster will progress southeast into
the Ozarks and potentially Mid-Mississippi Valley by 12Z Saturday.
However, they increasingly disagree on placement of the heaviest
rainfall, the convective evolution, and magnitude of the rainfall.

From a pattern recognition standpoint, there is some concern about
an increasingly favorable setup for a backbuilding MCS on Friday
Night. The low-level jet will veer to be more westerly, and the
20-30 knot low-level inflow will exceed the strength of the
increasingly weak 15-20 knot deep layer mean flow. In these
situations, you will occasionally see a convective line backbuild
into the unstable inflow for hours, on the periphery of the cold
pool. The 12Z HRRR is the model that shows this scenario most
clearly, and it generates a maximum of about 6 inches of rain in 6
hours near the AR-MO border late in the forecast period.
Conversely, other hi-res models show scattered convection that is
far less focused. To put it another way, the synoptic evolution
would favor potential for backbuilding storms on Friday Night, but
whether it happens will ultimately come down to specific convective
evolution from the Central Plains over the 24 hours prior, and
probably whether a stronger, more concentrated cold pool can
develop. This area will be monitored closely in future updates.

Lamers


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