Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Tue Jun 9 2026
Day 2
Valid 12Z Wed Jun 10 2026 - 12Z Thu Jun 11 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL PLAINS UP THROUGH THE MIDWEST...
.Midwest and Central Plains...
20Z Update: A larger change was implemented for the D2 period, but
much of the synoptic scale evolution described in the previous
forecast was maintained. 12z CAMs were finally able to depict the
full D2 window with a broader scope of heavy rainfall potential
within the budding warm sector across the Midwest. Strengthening
theta_E ridge across the Central U.S. east of I-35 will be one of
the more important aspects of the forecast as the meridional push
of unstable air ahead of the maturing front will aid in a
moderately buoyant environment with increasing large scale ascent
aligned from southwest to northeast from KS up through WI. Shear
levels will be highest further north into IA/IL/WI leading to more
organized cell clusters propagating east/southeast through the
region. Models are struggling with specific convective placements,
so we have a few camps on positioning of the heavier rainfall for
the period. Recent ML output aligns the heaviest precip over
southeast NE up through the Mississippi River Valley between IA/IL
with a northern expanse into WI. HREF neighborhood prob fields for
>2" is highest across north-central WI between Eau Claire to Green
Bay with several other "bullseyes" situated between northern MO
through eastern IA, northern IL, and southern WI. Rates between
2-3"/hr are forecast in the strongest cell cores with the highest
rates correlated over the area where CAPE can breach 3000 J/kg.
This leads to a southern tail in heavier precip potential arcing
back towards southeast NE to eastern KS where greatest instability
is forecast. Considering the more widespread modest neighborhood
probs and expected environment across a very large area ahead of
the maturing synoptic pattern, a SLGT risk was expanded northeast
to include much of the Midwest situated east of the Mississippi
River, tailing back through portions of IA/NE/KS/MO.
Kleebauer
..Previous Discussion..
On Wednesday, the northern Plains cyclone will move into south-
central Canada and push a trailing cold front across the Midwest.
Showers and storms will be ongoing Wednesday morning ahead of the
system over northern Minnesota, then another round of convection is
expected across the Midwest and Central Plains Wednesday afternoon
and evening ahead of and along the cold front. Deep southerly flow
ahead of the system will increase PWAT values to 1.5-2 inches,
with the higher values focused between northern Missouri and
southern Wisconsin. Instability should increase through the
afternoon as daytime heating kicks in, but the best instability
(3000-4000 J/kg) looks like it will focus from eastern Kansas and
southeastern Nebraska into northern Missouri and southern Iowa,
where there is a Slight Risk of excessive rainfall. This area will
likely experience a period of enhanced convection Wednesday night
as a frontal wave develops at the intersection of the cold front
and a dryline. A secondary wave of moisture and instability will
surge into the central Plains as a low level jet strengthens
Wednesday night, which should support efficient rainfall rates,
potentially exceeding 2 inches per hour, that could lead to
scattered instances of flash flooding.
Dolan
.Tennessee Valley and Southern Appalachians...
20Z Update: Only minor changes were necessary across the Tennessee
Valley to Southern Appalachian front with the changes more
reflected in the change in CAMs QPF output and positioning of
convection on Wednesday morning. The MRGL risk remains with best
potential over eastern KY/TN over into southwest VA and down
through the western Carolina's.
Kleebauer
..Previous Discussion..
Convection should be ongoing across portions of the Tennessee
Valley and southern Appalachians at the start of the period. A
quick-moving upper level wave will round the top of the ridge
positioned over the Gulf and support a period of enhanced
convection late Tuesday night into Wednesday morning. Anomalous
moisture and sufficient instability will be in place to support
efficient rainfall rates, and slow storm motions will contribute to
high rainfall totals. There will also be some potential for back-
building storms along a surface boundary extending from the
northern Plains/southern Canada cyclone into the Tennessee Valley,
mainly focusing over Kentucky. Showers and storms will also be
enhanced by upslope flow along the southern Appalachians.
Convection should start to weaken Wednesday morning and wane by
Wednesday afternoon, but there will at least be enough rainfall
over saturated soils to continue a Marginal Risk of excessive
rainfall into Wednesday morning.
Dolan
.Northeast U.S...
20Z Update: The MRGL risk remains for portions of the Northeastern
U.S. with the primary area of interest likely across Upstate NY
down through eastern PA. The main change was an expansion of the
risk down through much of eastern PA, northwest of the metro
corridors as recent CAMs have been highlighting a secondary area of
focus within an expected developing surface trough bisecting the
central Mid Atlantic up towards the Pocono's. Increased convergence
signature within a maturing instability axis across the Mid
Atlantic will lead to a period of heavy rainfall prospects within
the confines of the boundary as it evolves during the afternoon
Wednesday. 12z HREF probs are quite bullish over the Lower
Susquehanna Valley between US15 to US422 in PA with modest probs
for >3" locally in that region of southeastern PA. This area was
highlighted in various CAMs which typically is a signal for at
least a low-end threat given the overlap. Will be something to
monitor over the next 24 hours for the potential.
Kleebauer
..Previous Discussion..
A Marginal Risk of excessive rainfall was introduced for portions
of the Interior Northeast. An upper level trough will cross over
the Great Lakes into southeastern Canada accompanied by a surface
low pressure system that will bring precipitation chances to much
of the Northeast. The warm sector of this system will be
characterized by an anomalously moist air mass with PWAT values up
to 2 inches. There should be enough moisture and synoptic forcing
to support locally heavy rainfall in stronger convection near the
low pressure center over southeastern Canada and the Interior
Northeast. Rainfall totals and flash flood potential may also be
increased by terrain and upslope flow Wednesday afternoon.
Dolan
.Southwest Florida...
Sea breeze pattern with convergent winds around the southern
periphery of high pressure to the north will create a period of
heavy convective potential across southwest FL by Wednesday
afternoon. HREF probs for >3" along the coast between Port
Charlotte to Naples are between 60-90%, but do fall back to lower
probs between 15-30% for the >5" threshold meaning forecasts
consistently show a range between 3-5" in the hardest hit
locations. Area FFG's remain high, however the urban zones along
I-75 will be the most susceptible to localized flash flood chances.
This setup is likely to materialize between 18z Wed and 02z Thu
before dissipating. A MRGL risk was added to the aforementioned
area to cover for the low-end threat.
Kleebauer
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
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