Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1147 PM EDT Tue May 7 2024
Day 1
Valid 0338Z Wed May 08 2024 - 12Z Thu May 09 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE OHIO VALLEY...

...04Z Outlook Update...
A fairly focused band of convection has developed and began to
train along an axis from near Bloomington, IN to near Cincinnati,
OH over the past hour. The storms were in a very moist, unstable
environment, supporting efficient rainfall rates and 2-3 inch/3
hour totals (estimated per MRMS) so far this evening. These rates
should exceed FFG, with some concern also evident for
sensitive/urbanized areas (i.e., Cincinnati Metro) to experience
excessive runoff over the next hour or so. Given current trends, a
Slight Risk is being introduced with the expectation that rain
rates should occasionally exceed FFGs at times through the night.
The developing band should eventually pick up a southward component
of motion, taking heavier rain rates into more of Kentucky through
12Z.

Cook

...Previous Discussion...

...Great Lakes to the Tennessee Valley...

The existing Marginal Risk area across much of Illinois and into
northern Indiana was removed with this update since the main line
of storms has moved into central Indiana and western Ohio. The
latest CAM guidance suite suggests little in the way of additional
convection behind this line of storms. The best signal for locally
enhanced rainfall through 12Z will be across portions of central
and western Tennessee as the low-mid level flow becomes parallel to
an expected stalled frontal boundary across Arkansas and into
southeast Missouri. Some guidance has indicated a threat of
training near and ahead of the boundary during a nocturnal
convective pattern. Another area of concern is the ongoing
convection approaching the Ohio River, with some instances of
short-term convective training with high sub-hourly rainfall rates
across portions of southern Indiana into central/southern Ohio
within an axis of higher instability (MPD #237 is valid here until
430Z). Scattered areas of moderate to locally heavy rain are
expected to continue across portions of Wisconsin into Michigan,
but the hourly rainfall rates here should be lower than those areas
across the Ohio Valley.


...Northern Plains/Rockies...

The closing mid/upper level low over the Northern High Plains will
linger through the period, with embedded vort energy
pivoting/retrograding westward across the region. This should
continue the forcing/lift across the region and with the anomalous
moisture in place and orographic enhancement, an additional 0.5-1"
is expected and this could cause additional nuisance level
flooding concerns. The existing Marginal Risk area across Montana
was trimmed back on the eastern side of the outlook area to account
for the latest radar and CAM guidance trends.

Hamrick