Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1142 AM EDT Sun Jun 15 2025
Day 3
Valid 12Z Tue Jun 17 2025 - 12Z Wed Jun 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST STATESâ€

...Midwest states...

A well organized mid-upper level shortwave trough will eject
eastward from the Rockies to the central Plains Tuesday afternoon
into the early hours of Wednesday morning, and this will sustain
the development of a surface low that will develop along a frontal
boundary. Upper level dynamics will be favorable as the region will
be place under the right entrance region of the main upper level
jet, and incoming mid-level positive vorticity advection will
further aid ascent. Precipitable water values in the warm sector of
this surface low are expected to rise into the 1.75 to 2 inch
range and an increasing southwesterly low level jet that will
advect copious moisture into the system.

Model guidance has trended a little to the south over the past few
model cycles, with the greatest consensus for the heaviest QPF
across the southern half of Iowa and over the northern third of
Missouri, and extending to northeast Kansas and west- central
Illinois. Most model solutions have a broad corridor of 1-2 inches
with embedded 3-4 inch maxima within this region, with the majority
of this happening within the 18Z Tuesday to 6Z Wednesday time
period. The heavy rain that fell across portions of the Upper
Midwest is generally north of where this expected rainfall will be,
so grounds will not be saturated in most cases leading up to this
event. The inherited Slight Risk from the previous Day 4 outlook
will be maintained with a southward expansion to it, and a broader
Marginal Risk extending across South Dakota and eastward to include
the greater Chicago metro area.

...Appalachians...

The stationary front that will be lingering across the Mid-Atlantic
will start to slowly move back north as a warm front on Tuesday
with anomalous PW values remaining in place. Scattered to numerous
showers and storms, some of which will likely be slow moving, are
forecast to develop during the afternoon and evening hours, mainly
in the 18Z-00Z time period. Parts of the central Appalachians have
been hammered with multiple heavy rainfall events and this has
served to lower flash flood guidance values, and additional heavy
rainfall in the Day 1 and Day 1 periods will only make the ground
more saturated. Therefore, a Marginal Risk is valid from western
North Carolina to western Pennsylvania.

Hamrick

Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt