Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
819 PM EDT Tue Mar 24 2026

Day 1
Valid 01Z Wed Mar 25 2026 - 12Z Wed Mar 25 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 2
Valid 12Z Wed Mar 25 2026 - 12Z Thu Mar 26 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Hurley


Day 3
Valid 12Z Thu Mar 26 2026 - 12Z Fri Mar 27 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST AND OHIO VALLEY...

...1930 UTC Update...

We have expanded the Marginal Risk area, notably a little farther
west (into eastern IL) as well as south (into northern KY and
central WV), based on the latest guidance trends (including machine
learning).

Always a bit tricker with these more zonal, frontogenetic setups
vs. a more amplified upper trough. Strong right-entrance region
forcing south of a 150+ kt northern stream jet streak will result
in a quasi west-east ribbon of robust deep layer lift and moisture,
with 850-700 mb moisture flux anomalies getting close to 4 standard
deviations above normal as low-level trajectories originate over
the western Gulf. As such, the attendant pre-frontal, west-east
axes of anomalous TPWs (around 1.5") and IVTs (around 800 kg/m-s)
are both 2.5 to 3 standard deviations above normal for late March.
Meanwhile, current guidance (non-CAM) shows MUCAPEs averaging 1,000
J/Kg Thursday night along and ahead (south) of the front, which
along with with robust deep layer shear (0-6km bulk shear 50-70
kts), would be plenty supportive of widespread, organized
convection along and ahead of the front.

Given this degree of dynamic and thermodynamic support, along with
the low-level flow in near alignment with the mean 850-300 mb
flow, believe short term rainfall rates will be quite prolific for
a while before the the front pushes south -- likely to the tune of 1
to 1.5+" within an hour within the strongest cores. After talking
with the OHRFC, we toyed with the idea of including a targeted
Slight Risk within the now broader Marginal Risk area, however we
opted no to for now given the spread in the model QPFs. Expect to
get more clarity on this as the event gets into the high-res CAM
windows.

Hurley

...Previous Discussion...

A strong cold front will move southward across the Midwest Thursday
night. The front will run into a marginally unstable and warm air
mass, but with limited moisture with surface dew points on either
side of 60 degrees. Nonetheless, with some upper level support and
significant shear, organized thunderstorms are likely to form
Thursday evening. The storms could then train over many of the
same areas that saw some heavy rain from a very similar-behaving
front yesterday. This is a lower-end Marginal Risk as upper level
support and instability will both not be quite as favorable to the
storms as yesterday. This will be somewhat offset by a bit wetter
soils by then than they were before yesterday's rainfall event. The
areas most likely to see an instance or two of flash flooding are
the urban centers. Should forecast rainfall decrease, which appears
possible, the Marginal may be able to be dropped with future
updates.


Wegman


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt