FOUS30 KWBC 090818
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 AM EDT Tue Jun 9 2026

Day 1
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, OHIO AND TENNESSEE VALLEYS, AND SOUTHERN APPALACHIANS...

.Northern Plains...
A potent upper level trough will push across the northern Rockies 
into the Plains today and spur cyclogenesis over the northern 
Plains. Low pressure will strengthen over the region with a cold 
front extending to the southwest and a warm front extending to the 
east. Southerly winds ahead of the trough will direct warm, moist, 
unstable air into the northern Plains, with PWAT values expected to
exceed 1.5 inches and MUCAPE expected to rise above 3000 J/kg. 
Increasing mid/low level winds on the leading edge of the trough 
will create a highly sheared environment that is conducive for 
supercell development this afternoon. By this evening, an 
intensifying low level jet oriented parallel to the surface cold 
front will support upscale convective growth into a linear MCS. 
Deep convection within supercells and eventually the more organized
MCS will be able to tap into the atmospheric moisture to produce 
very intense rainfall rates in excess of 2 inches per hour. 
Relatively fast storm motion will be a limiting factor to the flash
flood risk, but rainfall rates will be enough to overwhelm FFGs 
and cause flash flooding, especially if heavy rain occurs in urban
environments. A Slight Risk of excessive rainfall remains in effect
for the heaviest convective activity expected over central and 
eastern North Dakota and northwestern Minnesota. A broader Marginal
Risk area extends into the Midwest where convection may focus 
along a surface boundary extending from the northern Plains cyclone tonight.

.Ohio and Tennessee Valleys and southern Appalachians... 
An upper level trough will lift northeast across the Midwest and 
Great Lakes region today accompanied by a surface low over the 
Great Lakes and a slow-moving warm front extending south into the 
Ohio and Tennessee Valleys. The air mass in place across these 
regions will be anomalously moist with PWAT values around 2 inches,
2-2.5 standard deviations above normal for this time of year. 
There will also be sufficient synoptic forcing and instability to 
support scattered to potentially widespread convection from the 
Great Lakes to the Interior Southeast. Convection will be ongoing 
at the start of the period and should translate east throughout the
day as the system progresses. High moisture content in the 
atmosphere will support chances for locally heavy rainfall, and 
more intense rainfall may be possible over the Ohio and Tennessee
Valleys where convection will be enhanced by a couple quick-moving
mid-level waves rounding the top of the ridge positioned over the 
Gulf. The first wave will pass over the region early in the period,
resulting in a burst of more intense convection this morning. The 
second wave will pass over this area tonight into early Wednesday 
morning and will have the potential for back-building storms along
a surface boundary extending into the lower Ohio Valley from the 
northern Plains cyclone. Hi-res guidance suggests rainfall rates of
2-3 inches will be possible in stronger cells, and most hi-res 
CAMs are showing a swath of rainfall totals of 3-5 inches, with 
locally higher amounts, across portions of Kentucky and maybe
southern Indiana as well. The HREF and RRFS are both showing 
relatively high probabilities (50-70% and 40-50% respectively) of 
24 hr totals exceeding 5 inches in this area. Enhanced convection 
will also be possible, but to a lesser extent, under the upper 
waves over Tennessee and in upslope areas of the southern 
Appalachians. Some areas may be more susceptible to heavy rain 
today after recent heavy rains over the past few days. A Slight 
Risk of excessive rainfall covers the area of enhanced convection 
over the Ohio and Tennessee Valleys and southern Appalachians and 
a Marginal Risk area extends north through the Great Lakes. 

Dolan


Day 2
Valid 12Z Wed Jun 10 2026 - 12Z Thu Jun 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHEASTERN
KANSAS, SOUTHEASTERN NEBRASKA, NORTHERN MISSOURI, AND SOUTHERN IOWA...

.Midwest and central Plains...
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. There is still some 
uncertainty regarding rainfall totals within the Slight Risk area. 
If the frontal wave is more progressive, the risk of flash 
flooding may be limited. A broader Marginal Risk area surrounds the
Slight Risk and extends up through the Midwest where strong 
convection could result in at least isolated instances of flash flooding.

.Tennessee Valley and southern Appalachians...
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. 

.Interior Northeast...
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


Day 3
Valid 12Z Thu Jun 11 2026 - 12Z Fri Jun 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM NORTHEASTERN
MISSOURI THROUGH EASTERN IOWA AND NORTHERN ILLINOIS TO SOUTHERN WISCONSIN...

The frontal wave that developed over the central Plains Wednesday
night will progress northeast and intensify as a strong upper
trough swings into the northern and central Plains Thursday
morning. A strong low level jet will increase moisture and
instability across the central Plains Wednesday night, and this air
mass will expand towards the Upper Midwest as southerly winds surge
ahead of the surface frontal boundary. A large swath of high PWAT 
values above 2 inches will stretch from the southern Plains to the
Midwest, which will support a broad area of convection capable of 
producing locally heavy rainfall. A wave of deeper convection will 
accompany the strong frontal wave as it progresses, resulting in 
high rainfall totals over an area from northeastern Missouri 
through eastern Iowa, northern Illinois, and southern Wisconsin. 
These areas are highlighted by a Slight Risk of excessive rainfall 
to account for enhanced convection capable of producing scattered 
instances of flash flooding. A broader Marginal Risk of excessive 
rainfall surrounds the Slight and includes much of the Midwest and 
portions of the central and southern Plains. 

Dolan
$$
--- SBBSecho 3.28-Linux
 * Origin: Capitol City Online (618:250/10)