Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1148 AM EDT Sun Aug 9 2026
Day 2
Valid 12Z Mon Aug 10 2026 - 12Z Tue Aug 11 2026

...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
MIDWEST AS WELL AS SOUTHERN ARIZONA...

...Midwest...

The MCS that will be moving across Ohio at the start of the day is
likely to persist as it traverses the state and moves into
southwestern Pennsylvania and West Virginia. By Monday morning,
the MCS should be fast enough moving that flash flooding resulting
from it, especially during this most hostile period of the day for
MCS sustenance. Nonetheless, the storms will prime the soils in PA
and WV for later rounds of rain. During peak heating in the late
afternoon, additional storms are likely to form in Indiana and
Ohio, which will continue southeastward into West Virginia during
the evening hours. Behind this complex of storms, the persistent
LLJ advecting additional moisture and instability into the large
collective cold pool will lay down a pseudo-cold front from
northeastern Indiana into western and southern Ohio.

The primary flooding threat will come Monday night as the LLJ
running into the cold pool results in numerous additional storms
forming along the slowly retreating cold pool boundary. The storms
could reform as far back/west as Chicago, but appears most likely
from northern Indiana and into western Ohio. The storms will track
southeastward across those states, but due to the cold pool setup,
the environment will be very favorable for training and
backbuilding. Considering the rain in some areas of northern
Illinois and northern Indiana could be hitting the same areas for
the second consecutive day, a Moderate Risk upgrade can't be ruled
out, as well as anywhere the storms could be most persistent into
Ohio with a more short-range update.

...Southern Arizona...

Monsoonal moisture will peak across southwestern Arizona on
Monday. Storms are expected to initiate along the Mogollon Rim, and
the numerous ranges of southeastern Arizona as normal during the
afternoon hours. Unlike prior days, enough easterly flow,
especially in the upper levels, will successfully push those
showers and storms off the mountains and towards the lower
elevations and valleys of southwestern Arizona. As the storms track
westward, they are expected to backbuild given the impressive
amounts of moisture and instability they will run into as they move
westward. Thus, the bigger cities such as Tucson and possibly
Phoenix may see periods of showers and storms that will persist
into the evening hours, since the ample moisture and instability in
southwestern Arizona will sustain the storms past peak heating.
The inherited Slight Risk is little changed, and the I-19 corridor
from Nogales to Tucson remains the primary area that could be
affected by the storms and their flash flooding.

Wegman


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