FOUS30 KWBC 230714
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
314 AM EDT Thu Jul 23 2026

Day 1  Valid 12Z Thu Jul 23 2026 - 12Z Fri Jul 24 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL TO NORTHEASTERN NORTH CAROLINA INTO FAR SOUTHEASTERN VIRGINIA...

...Southeast...

Very few changes were needed with this morning's update across the
Southeast, and the forecast remains on track. Unfortunately what
also remains on track are these very persistent lines of showers
and thunderstorms tracking across central North Carolina and into
the Hampton Roads area of Virginia. This is being driven by a
strong but essentially stalled out front over Virginia. Anomalous
moisture streaming northeastward along the front is originating out
of the Gulf and T.S. Bertha. Thus, the constant moisture supply is
effectively replacing any moisture lost to heavy rain, so the
storms can persist. The front could make a bit more southward
progress down the Piedmont of southern Virginia and central North
Carolina. This should gradually diminish areal rainfall totals with
increasing longitude. Thus, the inherited Moderate Risk targeting
northeastern NC and nearby areas remains in place, since the rain
is likely to persist into that area right through the day today and
the night tonight. Urban concerns into Virginia Beach, Norfolk,
Chesapeake, and Portsmouth will remain front and center for the
risk of potential impacts from flash flooding. Thus, despite some
agreement that most of the heaviest rains eventually push south of
those cities tonight, the urban areas lowering FFGs could still
result in numerous flash floods today into tonight.

The western extension of the front into the western Carolinas
through northern Georgia, Alabama, and Mississippi will continue to
promote localized instances of flash flooding due to training
storms, following the exact same mechanisms as described above. The
only difference is the storms are likely to struggle a bit more to
organize, so fewer extreme rainfall amounts are expected from the
Atlanta Metro west. The Slight Risk is primarily for urban areas.

...Central Plains...

The inherited pair of Slight Risks were only tweaked to match with
the latest guidance around the edge of the risk areas with this
update. Across the east, an MCS will impact portions of Nebraska
into Kansas early this morning, but should generally be fast moving
and the rain will fall over dry soils. The primary concern for the
Slight Risk is for tonight as a new MCS develops. This one will be
significantly slower-moving. The MCS will have a robust LLJ
tracking due north up the Plains to replenish all rain lost to
rainfall. Thus, expect more instances of flash flooding tonight.
Across the west, over eastern Colorado, the flash-flood risk will
be in the late afternoon and evening during peak heating, as the
upper level support and monsoonal moisture will promote more
widespread but less organized convection as compared to the MCS
impacting areas further east. Guidance has been consistent on the
location of the heaviest rains, with little change in the
magnitudes as well. Thus, few changes were needed.

...Bertha/South Texas...

T.S. Bertha will continue tracking west into Texas. There is
expected to be a period of time where the center remains over water
over the far northwestern Gulf. This should allow the associated
convection, which has always been displaced well southwest of
center due to strong northeasterly shear, to eventually move into
portions of south Texas. Therefore, the heaviest rains with the
entire storm are likely to impact south Texas. There remains some
potential that coastal areas such as around Corpus Christi could
eventually need a Slight, or locally see Slight level impacts. But
since most of south Texas remains dry, much of Bertha's rains in
the area will be beneficial, with only isolated instances of flash
flooding. Thus, the Marginal Risk in this area was left little
changed with this update.

...Southwest...

Both available monsoonal moisture and forcings will diminish today
as compared to the scattered convection seen on Wednesday. Thus, a
Marginal Risk was left in the areas where convection will be most
prevalent, generally for Colorado, Wyoming, and Utah. While some
showers and storms may impact areas further west, into Arizona,
Nevada, and into Idaho, both coverage and intensity there will be
much less, so the threat should be less than 5% for most areas of
those states.

Wegman
 

Day 2  Valid 12Z Fri Jul 24 2026 - 12Z Sat Jul 25 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST AS WELL AS FOR MISSOURI AND NORTHEASTERN KANSAS...

...Southeast...

The front impacting the Carolinas remains solidly in place on
Friday as steadily training bands of showers and storms track along
the front along the coast of the Carolinas. The heaviest rainfall
totals do shift a bit from Thursday, focusing right along the coast
from central South Carolina through much of the Outer Banks to
Albemarle Sound. Hopefully, that southward shift allows for areas
to the north very hard hit both now and on Thursday to get far less
rainfall by Friday, albeit not quite none. Localized intrusions of
warmer air over southern Virginia may allow for brief showers and
storms to impact some of the hard-hit areas, but total rainfall
does not look to be impactful, especially as those hard hit areas
will still be recovering from today's rainfall. This general lack
of overlap of the heaviest rainfall from Wednesday to Thursday, and
the focus over generally flood-resistant areas of the Low Country
to the Outer Banks allowed for the risk area to remain at a Slight,
and a Moderate upgrade was not considered. Once again, the front
extends back to the west over northern Georgia, Alabama, and
Mississippi, so the Slight was continued a second day from
Birmingham through Atlanta.

...Missouri and Kansas...

An ongoing MCS at the start of the Friday period will be the
primary animus for flash flooding across northeastern Kansas and
extending across much of northern and central Missouri on Friday.
The MCS is likely to persist through midday, diminishing through
the afternoon. Comparatively very little convection is expected
Friday night over this area, so the flooding focus will be almost
entirely Friday morning. Urban concerns in Kansas City and
eventually into St. Louis will pose the biggest impact concerns.

...Southwest...

Convection remains very widely scattered across the 4 Corners
region on Friday. Nominally higher flash flooding threat will exist
over eastern New Mexico and into the Texas Panhandle. The area is
very dry going in, so most of the rain will be beneficial for
impacted areas. An isolated flash flooding threat will remain.

Wegman
 

Day 3  Valid 12Z Sat Jul 25 2026 - 12Z Sun Jul 26 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE COASTAL CAROLINAS...

...Southeast through the Tennessee Valley...

A deepening longwave trough pushing south down the East Coast on
Saturday will finally provide a push to the stalled out front over
the Carolinas to allow it to push through the coast and offshore by
Saturday night. Thus, Saturday will be the last day where heavy
rainfall will threaten the coastal Carolinas. However, given prior
days' rains, especially the rain expected on Friday, a Slight Risk
upgrade was introduced with this update. Fortunately, outside of
urban areas such as Wilmington, Myrtle Beach, and perhaps
Charleston, SC on the south side, flat terrain, sandy soils, and
vegetation should all help to suppress the flooding risk a good
bit, despite the heavy rainfall from Friday continuing into Saturday.

Further west across the Tennessee Valley, the front will remain
stuck, as the aforementioned longwave trough only advances east of
the Appalachians, so the Tennessee Valley will remain in a warm
advection regime, allowing for periodic showers and thunderstorms
to move over cities such as Nashville, Chattanooga, and Huntsville
again on Saturday. In addition to topographic concerns, it's
probable this area may also need a Slight Risk upgrade in coming
days once the events move into CAMs range and amounts (typically) rise.

...Southwest...

The monsoon recharges and resets across the 4 Corners region on
Saturday. A westward moving shortwave moves up the Rio Grande,
which when added to renewed monsoonal moisture, will make for a
renewed round of afternoon showers and thunderstorms capable of
flash flood producing amounts of rain across central and western
New Mexico and into southeastern Arizona. Given the recent wet
weather and the expected intensity and organization of the storms
in this region on Saturday, here too appears probable to need a
Slight Risk upgrade for some areas as the event moves into the CAMs range.

Wegman
 

Day 4 and Day 5  Valid 12Z Sun Jul 26 2026 - 12Z Tue Jul 28 2026

...THERE ARE MARGINAL RISKS OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE WESTERN U.S. AND ACROSS THE UPPER MIDWEST AND GREAT LAKES
REGION INTO THE OHIO VALLEY AND CENTRAL APPALACHIANS SUNDAY
THROUGH TUESDAY...

...Southwest to the northern Rockies...
Monsoonal flow through the Intermountain West continues into early
next week. EC/GFS PW anomalies are highest (closer to 2 standard
deviations above normal) across AZ, especially southern AZ on Day 4
(12Z Sun-12Z Mon) with PWs between 1.75-2.00". Suspect southern AZ
could eventually see a Slight Risk area during this period,
especially considering the higher likelihood of more vigorous
shortwave activity rotating westward south of the mid/upper level
ridge. For now however will maintain the Marginal Risk, given the
spread in the global guidance and current low probabilities of
greater than 1-2" of QPF within the 24hr period.

For Day 5 (12Z Mon-12Z Tue), essentially minor adjustments to the
broad Marginal Risk area across the 4-Corners, Southwest, central
Rockies, and central High Plains. The globals (ECMWF, GFS, and
CMC) all show convectively-aided shortwave activity traversing W-E
overtop the flattening mid-upper ridge, into the central High
Plains, which would explain the eastward expansion of the Marginal
Risk area from the Day 4 ERO. Global ensembles also show an uptick
in PW anomalies into the central High Plains as well during this
time, along with an increase in areal-average QPF.

...Upper Midwest-Great Lakes-Ohio Valley-Central Appalachians...
Global guidance, to varying degrees, continues to show
convectively-aided shortwave activity riding down the top side of
the upper ridge. The guidance shows these ridge crawlers becoming a
bit better organized through the day 4-5 period, with an uptick in
deep-layer QG forcing (Qs convergence) and increasing low-level
moisture transport. For now, have maintained the relatively compact
Marginal Risk on Day 4, while introducing a broader Marginal Risk
on Day 5 stretching through the Great Lakes, OH Valley, and Central
Appalachians. At this point, given the spread in the guidance QPFs,
along with the strong low-mid level shear with the deep northwest
flow and progressive north-northwest MBE/Corfidi Vectors, will cap
the ERO risk at Marginal.

Hurley
$$

--- Scorpio BBS
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