Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Fri Jul 10 2026

Day 1
Valid 16Z Fri Jul 10 2026 - 12Z Sat Jul 11 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID MISSISSIPPI VALLEY...

...Mid MS Valley to the Central Appalachians...

16Z Update...
Guidance still in general agreement that heavy rainfall will
overspread much of the Mid-Mississippi Valley into the Tennessee
Valley and parts of the Ohio Valley/Central Appalachians today.
Evaluation of 12Z guidance suggests that the potential remains for
locally very heavy rainfall (HREF 24-hr probabilities for 5"
over 20%) which is depicted via most high- res CAMs. However, the
placement remains quite uncertain as there is virtually no overlap
in the footprint between the available high-res models. After
coordination with the local WFOs, a targeted MDT risk was added
basically to overlap the area that had significant rainfall
overnight leading to extremely vulnerable soils with 3-hr FFG less
than 1".

Elevated PWs above +1.5 sigma combined with 1000-3000 J/kg will
support heavy rain producing convection anywhere across this region
today, with the wavering front and any weak mid-level impulses
providing the locally enhanced ascent for stronger convection. This
will likely cause at least scattered instances of flash flooding
due to compromised FFG from recent rainfall. The focus for the
heaviest rainfall (and accompanying flash flooding) should be
downstream of a potent (especially for July) shortwave dropping
across MO which will additionally interact with the stationary
front and the relatively higher moisture along and to its south. A
potent LLJ progged to reach 30-35 kts will draw impressive
thermodynamics into the boundary as well, supporting a situation
with impressive training (weak and anti-parallel Corfidi vectors)
with rainfall rates of 2-3"/hr thanks to more than 4000m of warm
cloud depth. Training of these intense rain rates will likely
produce stripes of heavy rainfall for which nearly all high-res
CAMs indicate will reach 5-7+" in localized areas. Despite that,
the probabilities are only marginally supportive of a higher ERO
category, but at least locally significant impacts are becoming
more likely from near southeast MO through western KY and central
TN where the 0-10cm RSM from NASA SPoRT is above 70% due to recent
heavy rainfall, creating enhanced vulnerability across the region.

Previous Discussion:
The Slight risk has been expanded northward across portions of MO,
IL, IN and OH to account for multiple evolving convective threats.
Otherwise the broad Slight risk remains similar to the previous
forecast.

Convection will be ongoing at 12z this morning across southern MO
into portions of KY and TN, with areas of flash flooding already
underway across portions of this region. While the activity across
KY and TN today is forecast to become primarily forward
propagating, which should limit the overall magnitude of the flash
flood risk, strong low level westerly moisture transport will help
maintain weak Corfidi vectors. Thus, upwind propagation and periods
of backbuilding/training are possible as the convection tracks
across KY and TN today. This introduces the potential that
localized rainfall totals will exceed high res model guidance, a
trend that will be monitored closely.

A Slight risk area also covers slow moving convection that should
develop near a frontal boundary across portions of IN/OH and
southwest PA. PWs are slightly lower here than past days events,
but still remain well above climatological averages. When combined
with upwards of 2000 J/kg of CAPE, this environment supports
intense rainfall rates locally around 2" per hour. Slow cell
motions and periodic mergers should result in isolated to scattered
instances of flash flooding. The 00z HREF FFG exceedance
probabilities exceed 25%, with REFS values over 40% (noting a
typical high bias for the REFS in this type of regime).

The northward expansion of the Slight risk across portions of
MO/IL/IN covers the convective threat associated with a
shortwave/MCV ejecting eastward from the ongoing Plains
convection. Thunderstorms should become increasingly organized by
this afternoon and evening across this region. While the storm
mode may lean forward propagating, some cell mergers appear likely
and should drive a flash flood threat. Both the 00z HREF and REFS
highlight this corridor with FFG exceedance probabilities of 15-30%
and depict a 10-30% chance of hourly rainfall exceeding 3".

Heading into tonight, convection from the aforementioned
shortwave/MCV is forecast to dive southeastward from IL/IN into KY
and TN. High res model simulated reflectivity suggest a forward
propagating convective line. However, persistent low level
westerly moisture transport will keep Corfidi vectors weak,
offering further opportunities for upwind propagation and
backbuilding into the westerly flow. Should this occur, rainfall
totals and the flash flood risk could end up higher than currently
forecast by the models. Thus while FFG exceedance probabilities
from both the HREF and REFS are generally under 15% across this
area, the Slight risk remains fully warranted due to the potential
for multiple convective rounds and backbuilding. However, we will
hold off any any MDT risk upgrade due to the modest model QPF
blends and lower confidence on the exact convective mode.

...Arizona...
A similar mesoscale setup to Thursday is expected, though
potentially with slightly higher instability. Convection is
forecast to develop over the higher terrain during the afternoon
before propagating southwest into the desert valleys. Just like
yesterday, localized cell mergers could enhance rainfall and
result in a localized flash flood risk. While models suggest
overall storm coverage may be slightly greater today, the threat
remains isolated enough to maintain a Marginal risk, and the risk
area was cosmetically adjusted slightly to account for new
probabilities and the plume of highest instability.

...High Plains...
Additional shortwave energy ejecting out of the Rockies will lead
to convective development this afternoon from CO into KS and south
to the TX Panhandle. This activity is expected to be less robust
than yesterday due to generally weaker low level inflow, lower
instability, and weaker large scale forcing. Nonetheless, one or
two organized convective clusters should develop and push
eastward, posing a localized flash flood threat.

Chenard/Weiss


Day 2
Valid 12Z Sat Jul 11 2026 - 12Z Sun Jul 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MS VALLEY TO THE CENTRAL APPALACHIANS...

...MS/OH/TN Valleys...
Concerning excessive rainfall forecast continues for portions of
the MS/TN/OH Valleys on Saturday as the pattern evolves very little
from Friday into Saturday. A cold front will shift slowly
southward through the Mid-Mississippi Valley and Tennessee Valley,
but will become stalled in a west-east orientation by Sunday
morning in response to flattening mid-level flow. This evolution
will be driven primarily by the downstream evolution to a
pronounced ridge blossoming over the Four Corners, with an
extension of that ridge pushing over the Gulf Coast to slow
troughing digging from the Great Lakes. Within this trough, several
shortwaves, including those convectively reinforced my prior
thunderstorms, will try to dig southeast along the front, but will
generally be squashed to move west to east. However, each of these
could spawn waves of low pressure along the boundary to enhance
local ascent.

This will result in an elongated area of enhanced ascent from
generally the Southern Plains eastward along the boundary through
the Mid-Atlantic states, leading to areas of heavy rainfall. The
concern for Saturday will be that this ascent is acting upon robust
thermodynamics characterized by PWs exceeding 2 inches in many
areas (above the 90th percentile and more than +1.5 sigma from the
climatological mean) overlapped with plentiful CAPE of 2000-3000
J/kg. Together, these will drive scattered to numerous
thunderstorms capable of producing hourly rainfall exceeding 2"
(20-40% chance from the HREF) which by itself could be sufficient
to cause excessive rainfall in some areas.

However, more concerning is the focused convective threat and
training potential leading to prolonged duration of these heavy
rain rates. While the exact placement of these focused areas
remains uncertain due to tracking of any mid-level impulses and
accompanying MCVs/boundaries leftover from remnant convection,
there is strong agreement in the CAMs that axes of intense rainfall
will occur associated with these features, with some of this
rainfall occurring atop extremely vulnerable soils from recent
rains and flash flooding.

While the exact placement of the heaviest rainfall is uncertain,
there have been some trends slightly west and even north as
reflected by the AIGFS/ECMWF-AIFS/high-res, likely related to a
stronger (and anomalous) shortwave diving out of Missouri. With
convection blossoming downstream of this feature and within a warm
(warm cloud depths above 4000m) and highly sheared (25-40 kts of
bulk shear) environment, clusters of storms are likely, with slow
and chaotic motion reflected by Corfidi vectors falling to around 5
kts Saturday evening as the LLJ ramps up and draws impressive
thermodynamics northward.

The inherited ERO was cosmetically adjusted, but a higher risk area
to MDT was not added at this time due to uncertainty. In fact,
there has been an increasing divergence between the HREF and REFS
neighborhood probabilities, with the HREF leaning a bit north
(which aligns with some of the AI guidance actually) while the REFS
remains south. The farther south solutions usually verify in these
scenarios, so have hedged the elevated slight risk area a bit SW to
match better both the REFS guidance but also the EAS probabilities
from both the HREF and REFS. However, the SLGT was expanded
north and east into the Ohio Valley and Mid-Atlantic to account for
the potential of the farther north heavy rainfall footprint. At
this time there was not enough confidence for a MDT risk area, but
a targeted MDT risk may be needed with later updates where D2
rainfall overlaps D1 rainfall, especially from southeast MO through
central TN.

...Southwest...
The monsoonal pattern begins to take shape more robustly on
Saturday as a mid-level ridge re-centers and expands across the
Four Corners with weak impulses rotating westward beneath it. A
subtle weakness in the building ridge should allow for greater
coverage of convection as it taps into elevated PWs (1.25 to 1.5
inches) and MUCAPE (~1000 J/kg) than prior days. Storms should
develop initially across higher elevations and then drop slowly
westward with some organization possible through 20-30 kts of
shear. Rainfall rates as much as 0.75"+/hr are progged via the UA
WRF, leading to a 20-40% chance of at least 3" of rainfall and
40-70% chance of exceeding hourly FFG. For this reason the
inherited SLGT risk was maintained, and just slightly adjusted
cosmetically.

Weiss


Day 3
Valid 12Z Sun Jul 12 2026 - 12Z Mon Jul 13 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST, AND FROM TEXAS INTO THE SOUTHEAST...

...Southeast Quarter of the Country...
A broad Marginal risk extends from eastern TX stretching
northeastward into portions of the TN/OH Valley, the southern Mid-
Atlantic and much of the Southeast.

A cold front will drop slowly through the Southeast and towards the
Gulf Coast states on Sunday, providing convergence for ascent
within broad mid-level trough and beneath the diffluent tail of a
departing jet streak. This will produce widespread deep layer
ascent across the region, tapping into PWs above 2 inches
overlapping MUCAPE of 2000-3000 J/kg. This will likely lead to
scattered to numerous thunderstorms, especially during peak
heating, with additional development later D3 with the onset of the
LLJ and its accompanying moisture convergence.

While the environment will support heavy rainfall rates within any
of this convection, the location of any focused areas of heavy
rainfall leading to a higher risk category remains uncertain. The
greatest threat for higher rainfall totals should be in the
vicinity of dual mid-level impulses: one over the Carolinas and one
near the ArkLaMiss where focused and more prolonged ascent could
lead to stronger and more organized convection to support training.
However, these areas have a climatologically naturally higher FFG,
and 0-40cm soil moisture from NASA SPoRT is generally below the
20th percentile reflecting the recent hot and dry conditions. A
slight risk upgrade may be needed eventually (more likely in the
Carolinas than elsewhere) but at this time, and after coordination
with the WFOs, the MRGL risk was maintained until higher confidence
in placement can be established.

...Southwest...
Expanding mid-level ridge centered over the Northern High Plains
will extend into the Four Corners, but leave a subtle weakness
along the Mexico/Arizona/New Mexico border. Within this weakness, a
shortwave may rotate cyclonically to the west to cause locally
enhanced lift into expanding favorable thermodynamics lifting
beneath the ridge. At this time there appears to be a relative lack
of overlap between the most anomalous PWs and the greatest CAPE,
leading to some uncertainty into how convection will evolve on
Sunday. For this reason the MRGL risk was maintained, but with the
shortwave aloft, any better match of the higher thermodynamics
could necessitate a SLGT risk upgrade across parts of southern AZ.

Weiss


Day 4 and Day 5

Valid 12Z Mon Jul 13 2026 - 12Z Wed Jul 15 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG PARTS OF THE
CENTRAL GULF COAST ON MONDAY...

...Southeast U.S. into Texas...

A generally stable upper pattern will lead to relative persistence
in the convective setup across the CONUS into early next week which
keeps the risk of excessive rainfall in a broad corridor on the
southern side if a sprawling upper ridge. Deep moisture will be
present in that corridor with enough embedded shortwave energy
within the larger scale flow pattern to trigger and support
thunderstorms capable of producing heavy to excessive rainfall given
the high CAPE/low shear environment. Greatest focus currently is
over the Central Gulf coast extending into eastern Texas and
Louisiana where the adage of a organized mid-level disturbance
rotating out of the Tennessee Valley will enter the picture
allowing for enhanced forcing and perhaps a surface wave. A SLGT
risk was maintained from the previous forecast across the Central
Gulf coast area for the D4 period with a broad MRGL encompassing on
D4, followed by a general MRGL D5 over similar areas on the
southern periphery of the ridge.

...Southwest U.S...

The Southwestern U.S. will lie within the western flank of the
broad ridge pattern over the Central and Eastern U.S which will
provide a dominant southerly flow over the region allowing for
continued moisture advection and enhanced surface troughing over AZ
up through the Great Basin. This pattern is a continuation of the
Monsoonal presence out west with a potential for increasing flash
flood prospects as multi-day impacts could spur targeted
opportunities for repetition of areas getting hit by convection in
consecutive periods. For now, maintained a MRGL risk throughout the
Southwestern CONUS for both the D4 and D5 time frames, however
will need to monitor the periods closely as move forward in time
for possible upgrades with the greatest potential likely over
southeastern AZ up through the Mogollon Rim where several days of
consecutive impacts are forecast beginning this weekend, carrying
forward into next week as the pattern remains stable.

Kleebauer/Bann


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