Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
838 PM EDT Wed Jul 22 2026
Day 2
Valid 12Z Thu Jul 23 2026 - 12Z Fri Jul 24 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
FAR SOUTHEAST VIRGINIA AND EASTERN NORTH CAROLINA...

...Southeast...

Convection may be ongoing at the start of the period along or just
south of a slow-moving cold front. Hi-res guidance has slowed the
southward progression slightly relative to previous model cycles,
and the main change with the outlook was to pull the risk contours
north to account for where there may be active flash flooding
around 12Z Thursday. This is most likely from far northeast North
Carolina into the Hampton Roads area of southeast Virginia, as well
as the southern Appalachians from southeast Tennessee into
southwest North Carolina, and perhaps far northern Georgia. Low-mid
level flow parallel to the front, with PWATs over 2 inches, should
be conducive to backbuilding and training, and the potential for
narrow corridors with persistent hourly rain rates reaching 2
inches per hour.

As diurnal heating commences, and especially toward the 18-00Z
period, convection is likely to refocus a bit further south where
more instability will be building, and perhaps along outflow
boundaries that will push away from the synoptic front. This would
likely shift the flash flooding threat into the remainder of the
Carolinas, north Georgia, and northern Alabama for the remainder of
the period, especially during the afternoon and evening. PWATs will
generally be around or just over 2 inches, and should continue to
support high rain rates at least approaching 2 inches per hour at
times. This should lead to scattered instances of flash flooding,
and could include some of the larger urban areas in the Southeast.

...Eastern Colorado...

A Slight Risk was introduced in Eastern Colorado, as there is
emerging signal in guidance for an area of more concentrated
convection on Thursday afternoon and evening. HREF and REFS
probabilities of rain rates over 1 inch per hour increase to around
30-50 percent between 20Z and 04Z, and probabilities of exceeding
1hr FFG are around 10-20 percent. Precipitable water values above
the 95th pecentile for July would be conducive to those higher rain
rates in areas where instablity builds. Although convection is
likely to steadily progress to the east, rain rates are likely to
be high enough to pose a risk for some flash flooding.

...Central Plains...

Multiple MCSs will develop across the Central Plains over the next
40 hours -- one late tonight (Day 1 period) into Thursday morning
(beginning of the Day 2 period), and another one Thursday Night
into Friday (late in the Day 2 period into the Day 3 period). EAS
probabilities from the HREF and REFS show much better agreement
that the first MCS is most likely from south-central Nebraska into
east-central Kansas, and this is where the Slight Risk was
maintained. For the second MCS, EAS probabilities are lower,
indicating lower confidence and more spread on placement.
Therefore, it's not certain that the rainfall footprints of both
will overlap to a considerable degree; if that does happen, it
would make flash flooding more likely. However, rain rates in the
first MCS may be sufficiently high (1-2 inches per hour) to pose a
flash flooding threat on its own.

...Bertha/South Texas...

16Z UPDATE: No major changes were made to the outlook with this
update, other than small tweaks to account for the latest
observational trends and new 12Z hi-res model runs. A slow-moving
front will continue to act as a focus for training convective rain
bands and thunderstorms from the Upper Tennessee Valley into North
Carolina, southeast Virginia, and the far southern Delmarva
Peninsula. Although hi-res guidance now indicates less persistence
and focus to the convective activity overnight, with somewhat lower
rain threshold and FFG exceedance probabilities, the Moderate Risk
was maintained for continuity and a favorable pattern for training
convection. Within the Moderate Risk area, signals remain strongest
in the Hampton Roads area.

Meanwhile, the level of concern is increasing for later tonight for
the southern Appalachians, in particular the mountainous areas of
eastern Tennessee and western North Carolina, and perhaps far
northern Georgia. Deep moisture is expected to increase over the
next 12 hours as a more direct connection is made with some of the
low-mid level moisture associated with Bertha along the Gulf Coast.
This can be seen in the CIRA layer precipitable water products from
the Surface to 850mb, as well as 850-700mb. There has already been
a concerted northward push of anomalous moisture, and the PWAT at
BMX increased from 1.86 inches to 2.10 inches between the 06 UTC
and 12 UTC balloon launches. As this reaches the stalling front
tonight, with increasing westerly low-level flow parallel to that
front, ingredients will become favorable for reinvigoration of a
training and backbuilding convective band in the vicinity of the
southern Appalachians. QPF signals in the hi-res models have
increased, with some chances of rain rates reaching 2 inches per
hour if organized thunderstorms can become established. Therefore,
although the risk level is being held at Slight, this area will be
monitored closely in case a targeted upgrade is needed.

Models continue to show a coherent signal for heavy rainfall
through South Texas, related to a convective cluster well displaced
from Bertha's center. A Slight Risk upgrade was considered given
the deep tropical moisture that is likely to be present, however
this is also mitigated by extremely dry antecedent conditions
(rainfall less than 25 percent of normal in the past month). FFG in
South Texas is among the highest in the country at the moment.
Finally, all models show a steady westward progression of the
convection, such that it doesn't linger in any one spot for more
than a few hours. Considering that, and in collaboration with WFOs
in Corpus Christi and Brownsville, the risk level was held at a
Marginal Risk for now.

Lamers


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