Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
336 PM EDT Thu Aug 13 2026
Day 2
Valid 12Z Fri Aug 14 2026 - 12Z Sat Aug 15 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
MIDWEST...

...Midwest into the Mid Atlantic...

1930Z Update: Collaborated with WFOs DMX, DVN, LOT, and ILX on the
inclusion of a Moderate Risk across parts of the Corn Belt (IA
into northwest IL) on Day 2. This due in part to recent (and
current) heavy rainfall in the area, along with the additional
elevated convection expected again tonight north of the stationary
surface front. High-res CAMs show a relatively narrow band
overnight into Friday morning -- perhaps not the degree of upscale
growth compared to the previous MCS -- however the CAMs do show the
likelihood of some west-to-east cell training. Because of the
narrow width, there is some north/south areal spread in the
guidance in terms of max rainfall amounts per the CAMs tonight
(00-12Z Fri), and as such for now the Moderate Risk does not begin
until the start of Day 2 (12Z Fri).

Given the current and recent rainfall, the anticipated rainfall
Thursday night, and the expectation of a more vigorous MCV and more
numerous areas of heavy rain Friday night, felt more confident in
upgrading a portion of the Upper Midwest/Corn Belt to a Moderate
Risk. Despite the aforementioned spread in the QPF guidance, the
REFS and especially HREF exceedance probabilities -- i.e. QPF, FFG,
and ARI -- would support the placement of the Moderate. 12Z HREF
24hr probabilities of QPF exceeding 5" are up to 40-50% within the
Moderate Risk area, while probabilities of exceeding 8" are up to
20-30% over a smaller portion.

Hurley

...0830Z 08/13 Discussion below...which highlights the area now
under a Moderate Risk, along with surrounding locations...

A corridor of convection will continue to be favored near a
stalled front on the periphery of the strong upper ridge centered
over the southern U.S.. There are some larger latitudinal
differences by this time time in the models, however, the AIFS and
AIGFS have been pretty consistent with a farther south axis, and
this aligns well with the 00z 3km NAM and RRFS. Thus we leaned in
this direction with the Slight risk corridor given the good track
record of the AI guidance, and the agreement with the available
CAMs.

The strongest forcing and moisture convergence should end up
along the western end of this Slight risk area...and PWs over this
region should be even higher than what we have on day 1. While some
models have this axis farther north into WI...our current
preference keeps it across IA into IL. This may very well overlap
areas that see heavy rainfall and flash flooding on day 1. Thus we
will consider this area a higher end Slight risk, and there is the
potential for a MDT risk upgrade on future updates pending model
trends and how convection on day 1 evolves. Significant flash
flooding is certainly a possibility in this setup over portions of
IA into IL, especially if/where there is overlap from day 1
rainfall. The QPF signal is a bit less pronounced farther
southeast into IN/OH/WV...but the environment will be conducive
for heavy rainfall rates and periodic training here as well. Thus
given wet antecedent conditions stretching across this corridor the
Slight risk was expanded to the southeast.

...High Plains...

A Slight risk remains for portions of northeast CO into southwest
NE. A similar setup as Thursday, with high PWs and CAPE supporting
heavy rainfall rates. Also some model spread here...but a solid
model clustering between the AIFS/AIGFS/RRFS/Gem reg supports the
Slight risk area as having the greatest convective coverage Friday.

...Southwest...

A Slight risk was added to portions of northwest AZ, southeast NV
and southwest UT. PWs will probably be a bit lower by this time,
but still expecting sufficient CAPE, and stronger forcing given
the approaching mid level trough. The HREF members and RRFS depict
good convective coverage, and FFG exceedance probabilities similar
to day 1 (Thursday)

Chenard


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