Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
337 PM EDT Mon Aug 10 2026
Day 2
Valid 12Z Tue Aug 11 2026 - 12Z Wed Aug 12 2026

...THERE ARE A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE OHIO VALLEY...

...Midwest and Ohio Valley...

20Z Update: Continued active setup across the Midwest to Ohio
Valley will lead to widespread heavy rainfall from multiple
convective complexes that will also exhibit potential for training
and back-building over areas of IN/OH during the period. A growing
consensus within both the CAMs and global deterministic allowed for
a higher confidence forecast across much of southern Ohio back into
eastern Indiana to connect with the already forecast MDT risk over
portions of West Virginia. Latest HREF blended mean QPF depicted a
long axis of 2-4" totals between areas just east of Indianapolis
all the way towards Charleston, WV with some of the local maxima
actually closer to 6-8" when assessing individual deterministic.
This setup is conducive for these totals with a classic summer
convective scenario of multiple MCS propagating through a
persistent northwest to southeast aligned mean flow thanks to a
squeeze player between the northern periphery of a broad ridge
across the Southern U.S. and a deep cyclonic gyre spinning up over
east-central Canada. The combined effort between the two distinct
upper features will create a mid to upper level "highway" for
several shortwave impulses to migrate out of the High Plains and
traverse the central Midwest into the Ohio Valley. The coupling of
favored jet dynamics and increased large scale forcing from the
prevalent mid-level vorticity maxima will interact with a suitable
thermodynamic environment positioned over the Ohio and Tennessee
Valley's as noted via some prolific theta_E advection occurring
during Tuesday afternoon.

Area PWAT anomalies on the order of 1-2 standard deviations above
normal will be present across much of the Ohio Valley back into the
central and southern Midwest providing a sufficient deep, moist
profile that will be conducive for efficient rainfall processes
necessary for more formidable heavy rain accumulations.
Increasingly backed flow in the lower boundary layer will occur
over portions of IN/OH thanks to the disturbance advecting into the
area by later Tuesday leading to a period of training and/or back-
building convection after initiation, carrying through at least the
first half of the evening hours. Remnant cold pool from today's
convection will be a focal point for the training potential and the
recent CAMs have been locking in on the area extending from eastern
IN into southwestern WV as the most likely orientation and location
of the surface feature in question. This correlated to some
significant rainfall forecasts from the 12z CAMs suite within that
zone leading to enhanced neighborhood probabilities for both the
>3" (50-80%) and >5" (30-50%) thresholds during the period. 24hr
10yr-ARI exceedance probs across the same areas are fairly robust
with a bullseye of 40-60% located between Muncie, IN to Wilmington,
OH with the same area already seeing 20-35% probs for even the
100yr-ARI exceedance threshold, a testament to the anticipated
magnitude of heavy rainfall for the coming setup.

In coordination with the OHRFC and local WFO's from IN/OH/WV, the
previous MDT risk was expanded across portions of eastern Indiana,
the southern-third of Ohio, into western side of WV, mainly along
and west of the I-79 corridor. Significant flash flooding is likely
in these areas with widespread flash flood warnings and rapid
riverine responses likely to cause issues lingering through the
rest of the week as the overall setup extends beyond the D2 period.

Kleebauer

...Southern Arizona...

20Z Update: Latest CAMs and associated HREF continue to pin another
round of heavy rainfall across the southern and southeastern
portion of AZ thanks to elevated PWATs between 2-3 deviations above
normal and a very buoyant environment conducive for heavy rainfall
development. Prob fields for >1" remain very high (70-90%) over the
area extending from Cochise county over into the eastern half of
Pima, extending north towards the I-10 corridor in Tuscon. I-19
remains the focal point for heavier rainfall, however the ridge
positioning would invite more of southeast AZ into the picture for
locally heavy rains, including the Huachuca Mountains that will
likely be another focus for development as we move into Tuesday
afternoon. The previous SLGT risk forecast was maintained as the
signal remains consistent with little run-to-run variability.

Kleebauer

..Previous Discussion..

Southeast AZ remains most at risk for more persistent heavy
rainfall, so left the Slight Risk intact. Across the Great Basin,
the Marginal Risk was broadened as moisture subtly increases from
Monday to Tuesday as an upper level trough settles in to the CA
Coast and ridging near the Four Corners weakens, which should lead
to less mid-level capping and broader convective coverage.

Roth


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