Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Tue May 7 2024
Day 1
Valid 12Z Tue May 07 2024 - 12Z Wed May 08 2024

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

...Ohio Valley...
The strong spring system will evolve into a large closed upper low
over the Northern High Plains while a piece of embedded shortwave
energy quickly lifts through the Midwest and lower Great Lakes.
Initial decaying line of convection will move into the region later
this morning which will likely be fast-moving and have diminishing
intensity in rain rates. This will likely set up an outflow
boundary across parts of Indiana and Ohio that will then be the
focus for additional thunderstorm development in the afternoon/evening
hours once convective temperatures and maximum destabilization
occurs. Meanwhile, a zone of higher PWs is forecast to develop,
characterized by PWs of 1.5+", along the Ohio River. As storms
develop later today, they will be moving generally along/parallel
to the mean flow with some south/southeast component and the
latest hi-res guidance shows some support for training/repeating
rounds and the latest HREF neighborhood probabilities indicate
hourly totals of 1-2" appear possible. Some of this rainfall may
fall over more saturated areas of southern Ohio and northern
Kentucky. Given the environmental ingredients, possible 1-2 rounds
of convection, and some greater sensitivity in ground conditions, a
Slight Risk was introduced across parts of Indiana, Ohio, and
Kentucky.

...Upper Midwest and Great Lakes...
The impressive line of thunderstorms currently moving eastward
across the Plains and Midwest will continue to lift north/northeast
this morning into the Upper Midwest, generally working along the
leading edge of the warm frontal passage and best isentropic lift.
Moisture in the low levels will continue to rise through the
period, with an axis of PWs > 1.25" expected from Minnesota
southward into Illinois which will support isolated/embedded cores
producing heavier rain rates. The latest hi-res guidance does
suggest potential for some repeating/redeveloping convection as
the flow becomes parallel to the storm motions over Wisconsin,
which could produce isolated/streaks of higher rain totals.
Altogether, the risk for flash flooding lies in the lower end of
the range and the Marginal Risk looks good for this forecast
update.

...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 flooding concerns.

Taylor