Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Mon Jun 8 2026
Day 2
Valid 12Z Tue Jun 09 2026 - 12Z Wed Jun 10 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
NORTHERN PLAINS AND WESTERN KENTUCKY AND TENNESSEE...

20Z Update...

The inherited threat areas in the Northern Plains and Upper
Mississippi Valley were adjusted based on latest WPC QPF and 12Z
HREF probabilistic guidance. The primary change this forecast cycle
was to expand the Slight Risk in the Mid-South farther south and
east into the TN Valley and southern Appalachians. Latest 12Z
guidance has shown a gradual southward expansion in the QPF field,
which aligns well with where the highest PWs (around 2.0" PWs) and
instability will be located. A sheared 500mb trough tracking
towards the Southeast will also promote healthy upscale ascent over
an area with very sensitive soils. The 12Z HREF/REFS probabilistic
guidance shows moderate-to-high chances (50-70%) for rainfall
totals >3" in northern GA and parts of the western Carolinas.

In addition, farther north, the same 12Z HREF/REFS guidance shows
low chance probabilities (20-40%) in central KY and northern TN.
These areas under what would be considered the "high-end Slight"
section within the larger Slight Risk area in the Mid-South. CAMs
guidance is more on the southern envelope of QPF rather than global
models which are farther north. Still, some CAMs members show some
locally significant rainfall totals where back-building and
training storms occur.

The northern Plains and Upper Mississippi Valley threat areas had
minor adjustments based on latest guidance, but otherwise no
additional threat areas were proposed this cycle.

Mullinax

---Previous Discussion---

On Tuesday, a potent upper level trough will move across the
northern Rockies and emerge into the northern Plains. This trough
will spur cyclogenesis over the northern Plains while a low level
jet increases moisture and instability ahead of the system. The
environment will be ideal for supercell development Tuesday
afternoon, and increasing shear over the region will allow storms
to evolve into an MCS Tuesday evening into Tuesday night. Deep
convection within these severe storms will be able to tap into
moisture in the atmosphere (PWAT values 1.5-2 inches) and create
very heavy rainfall. The quick nature of the MCS should somewhat
limit the risk of flash flooding, but intense rainfall rates in
excess of 2 inches per hour will exceed FFGs and could lead to
impactful flash flooding, especially in urban areas. A Slight Risk
area has been introduced for much of central and eastern North
Dakota and northwestern Minnesota.

Scattered showers and storms are forecast from the southern
Appalachians and Tennessee Valley through the Ohio Valley and Great
Lakes region, which will be supported by an upper level shortwave
lifting northeast across the Ohio Valley and Great Lakes and a slow
moving warm front extending south into the Tennessee Valley and
southern Appalachians. The air mass in place will be anomalously
moist (PWATs around 2 inches) and sufficiently unstable to support
locally heavy rainfall. Available hi-res guidance suggests higher
rainfall totals will be possible across western Kentucky and
Tennessee where convection will continue from the Day 1 period into
Tuesday morning. A mid-level shortwave will be enhancing this
convection and should allow for efficient rainfall rates over 2
inches per hour. A Slight Risk area has been introduced to cover
the elevated flash flood threat over western Kentucky and
Tennessee. Global models have also been showing locally enhanced
rainfall totals over portions of the Ohio Valley, but there is
still a significant amount of uncertainty in the location of these
higher totals. It is possible the Slight Risk area may need to be
expanded to the northeast as convective details become more clear
with additional hi-res guidance available later today.

Dolan

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