Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jun 17 2026
Day 1
Valid 16Z Wed Jun 17 2026 - 12Z Thu Jun 18 2026
...THERE ARE MODERATE RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF
ILLINOIS/INDIANA AS WELL AS THE MISSISSIPPI DELTA...
...1600 UTC Update...
The Moderate Risk in the Midwest has been shifted south based on
current observational trends and the latest 12Z hi-res guidance
with regards to an ongoing MCS over northern Illinois. This will
likely limit the northward progression of the warm front/effective
outflow into the afternoon hours bringing the greatest threat for
heavy rainfall/flash flooding along a west-northwest to east-
southeast axis through central Illinois into central Indiana. This
includes both the more intense storms on the southern/southwest end
of the ongoing MCS able to tap into greater moisture/instability
along the warm front as well as for additional storm development
that will focus along the warm front/effective outlfow. Repeated
development/potential training of robust, heavy rainfall producing
storms (rainfall rates ~ 2 inches/hour) leading to totals of 3-5",
locally as high as 6-7", will pose a threat for scattered to
widespread incidents of flash flooding.
Further south, the Moderate/Slight Risk areas have also been
minimally adjusted based on the latest 12Z guidance along and east
of the track of what is now Tropical Storm Arthur. Plentiful
tropical moisture will support additional rainfall totals of 3-5"
with localized amounts as high as 6-10". The highest totals look to
focus along a corridor within southeastern Louisiana generally
between Baton Rouge and New Orleans where the greatest threat for
more widespread instances of flash flooding will exist.
Putnam
...Previous Discussion...
...Chicagoland...
A potent low racing out of the Plains and across the Great Lakes
today will run into an increasingly moist air mass in place ahead
of the low over the Midwest. As the low approaches the Chicagoland
region late morning, convection will break out along the low's warm
front extending east of the low center. The initial hit of rain
with the warm front is unlikely to feature too much heavy rain,
though embedded elevated convection could make for brief heavier
downpours. Immediately behind the warm front, however, a surge of
moisture and instability will fuel backbuilding thunderstorms
during the afternoon ahead of a strong cold front trailing behind
the low. These storms are progged by many of the CAMs to generate
into several broken lines of storms as they cross northern Illinois
and into northern Indiana and southern Michigan through the late
afternoon/early evening. These storms will have ample forcing
allowing them to organize into severe clusters of storms. They are
likely to produce localy heavy rainfall rates of up to 2 inches
per hour where they backbuild. However, since the series of line
segments will be sufficiently separated by much lighter or no rain,
it seems any flash flooding that results from these storms will be
more localized and less widespread. Further, as mentioned, the
storms will be racing very quickly, likely moving at 40+ mph. This
will greatly reduce the time any one area sees heavy rain, but
since the lines are expected to align parallel to the windflow,
those areas may see a bit longer time of heavy rainfall.
Hydrologically, the Chicagoland area has seen several bouts of
heavy rain in recent weeks that have left the soils above normal
for moisture content as well as prone to flash flooding with
sufficiently heavy rain. Of course, the large urban area of Chicago
will also help to worsen any flash flooding that develops, so in
those local areas where heavy rain overlaps with urban areas,
locally considerable flash flooding is possible. Further east into
Indiana, eastern Michigan, and eventually northwestern Ohio, the
lines of storms this evening should align with the cold front and
largely orthogonal to the flow. This should lower the flash
flooding risk in these areas, despite similarly favorable
hydrology.
...Mississippi Delta...
The moisture plume of Potential Tropical Cyclone 1 (PTC1) will
continue to slowly advect northeast across the northwestern Gulf
and into southern Louisiana today into tonight. For much of the
day, the heaviest rains will remain offshore, and except for
occasional showers and an isolated storm or 2, much of the area
should not contend with much heavy rain. That changes tonight as
the center of circulation of what may be Tropical Storm Arthur
moves ashore near the TX/LA border. All of the deep moisture will
be east of the center of circulation, so that will direct the
fire-hose of heavy rain into south-central Louisiana, from the
Abbeville/New Iberia area northeast near Baton Rouge and into
southern Mississippi after midnight. By that point, the diurnal
strengthening of the nocturnal jet will function as the the primary
driver of heavy rain as northeastward moving storms backbuild into
the jet. The area from around Baton Rouge northeast to the north of
Lake Pontchartrain and into far southern Mississippi is likely to
be the corridor with the heaviest rain.
There is considerable uncertainty first of the eastern extent of
the axis of heaviest rain, particularly in relation to the New
Orleans Metro. For now most of the guidance makes a very tight
gradient of moisture, which most of the city remains on the drier
side of. However, this axis of heaviest rain has been shifting
east from model run to model run over the last couple days, which
any further eastward drift would bring New Orleans right into the
corridor of multiple-inch per hour rainfall for multiple hours.
Regardless, even if New Orleans misses out on the heaviest
rainfall, feeder bands of showers and storms could still cause
localized flash flooding in the city. Thus, the Moderate Risk
remains largely unchanged and includes New Orleans. More than a
couple CAMs do bring strong cells over the city, which would very
quickly lead to flooding problems.
Wegman
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jun 17 2026
Day 2
Valid 12Z Thu Jun 18 2026 - 12Z Fri Jun 19 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHEAST...
...Southeast...
Very heavy rain associated with what will be the remnants of PTC1
will be ongoing at the start of the period over most of southern
Mississippi and likely extending into southwestern Alabama. These
storms will be fueled by a strong low level jet pumping deep
tropical moisture into a corridor that covers much of the Moderate
Risk area. By around midday, the rapidly increasing instability and
the typical weakening of the low level jet will allow the
widespread convection to transition into training lines of storms
that track east with time, as the line gradually drifts south
towards the greatest instability and moisture source that is the
Gulf. Thus, the greatest focus of heaviest rain now appears to set
up from southeastern Mississippi east across the southern tier of
Alabama and far western Georgia. 3+ inch/hour rainfall rates from
individual storms will combine with multiple hours of rain as the
storms train along the east-west oriented lines. Storm total
rainfall for the day could easily exceed 8 inches in spots. Mobile,
AL will be the biggest city in the crosshairs of the heaviest
rainfall.
With this rather dramatic southward shift in the guidance of where
the heaviest rainfall totals are expected, the Moderate Risk
inherited was trimmed significantly on the north side, while
expanded across southeast Alabama, the western Florida Panhandle,
and far southwestern Georgia. The Moderate Risk was downgraded out
of both the Birmingham and Atlanta metros as those areas see
leftover heavy rains from the much more potent and heavy rain
producing storms much closer to the Gulf Coast. Nonetheless,
periodic convection and a long duration of light to moderate rain
is still expected over those metros, so the higher-end Slight
remains in effect. Convective coverage greatly decreases Thursday
night over all of the Southeast, but isolated to widely scattered
storms could persist through the night in some areas.
...Ohio/Tennessee Valleys...
Further north from the Gulf Coast along the Ohio and Tennessee
Valleys, a cold front will start the day following roughly parallel
to the Ohio River. The front will slowly sink southward over
Kentucky through the day. Meanwhile, daytime heating and
unidirectional southwesterly flow ahead of the front is expected to
generate a long line of storms. The storms will be training and
backbuilding along the KY/TN border and extending into West
Virginia. Guidance has shifted a bit further south, especially with
the western end of the line, so the higher-end Slight now follows
the entire length of the KY/TN border, and now includes Nashville,
while the Ohio River has largely been removed from the risk area.
With nightfall and the loss of daytime heating, the flash flooding
risk from storms will also diminish.
...Arkansas/Oklahoma...
On Thursday night, the westernmost extension of the low-level jet
over Texas will run into the same stalled out front that extends
east into Kentucky. This clash of air masses is likely to result in
the development of an MCS over eastern Oklahoma, which will then
propagate southeastward into western Arkansas. Here too the soils
are wetter than normal from multiple bouts of heavy rain in recent
weeks, so a Slight Risk remains in place over the area with few
changes.
Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jun 17 2026
Day 3
Valid 12Z Fri Jun 19 2026 - 12Z Sat Jun 20 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR MUCH OF
SOUTHERN ALABAMA...
...Southeast...
Any lull in heavy rainfall across southern Alabama from Thursday
night behind the precipitation shield associated with the remnants
of Potential Tropical Cyclone 1 will end in a hurry Friday morning
as the cold front over the Tennessee Valley continues to press
southward and runs into the ongoing southerly flow and low-level
jet of deep tropical moisture from off the Gulf. The clash of these
air masses looks to maximize over southern Alabama, where storms
are likely to continue in some form or fashion for much of the day
Friday. Assuming the multiple inches of rain from Thursday occurs
in these same areas, the slightly lower storm total rain on Friday
will make little difference for the flooding risk, as multiple
inches of rain fall over the same areas very hard hit from
Thursday. This very good overlap in the storm placement from
Thursday to Friday necessitated a risk upgrade across southern
Alabama for the Day 3/Friday period. Should this overlap continue
to hold and the widespread multiple inches of rain with localized
totals to double digits from Thursday occurs as forecast, it's
entirely feasible that the hardest hit areas may need further
upgrades to the flooding risk. Unfortunately the track record with
the CAMs ensembles on maintaining continuity day to day on where
the storms will occur is not very good, so any movement breaking
the overlap will greatly improve the rather ominous flooding
outlook for southern Alabama on Friday. Convective coverage over
Alabama should diminish greatly Friday night as heavier rains to
the west and the departing system to the east should put the state
in a relative ridging pattern, allowing for a much needed break
from the rainfall.
...Texas Hill Country...
Southeasterly flow of deep moisture from off the Gulf will
continue across much of Texas through the Day 3 period.
Northwestward moving convection on the leading edge of the deep
moisture will collide with storms that form along the dry line and
the Mexican mountains Friday evening, resulting in MCS development
that turns the storms back towards the best instability to the
southeast. This should result in some areas seeing multiple rounds
of heavy rain producing storms over the historically flash flood
prone region of the Texas Hill Country. Thus, a Slight Risk area
remains in effect for the region. Lesser amounts of rain are
expected further east into north-central Texas and the Metroplex,
so the Slight Risk inherited with downgraded in that area.
Wegman
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jun 17 2026
Day 4 and Day 5
Valid 12Z Sat Jun 20 2026 - 12Z Mon Jun 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE OF CENTRAL PLAINS THROUGH THE MID MISSISSIPPI INTO THE LOWER
OHIO VALLEY...
Day 4...
A well-defined 500mb shortwave trough will move from the Great
Basin into the northern Rockies midday Saturday, reaching the
northern High Plains by Saturday night. Ahead of a southward
advancing Canadian cold front, a northward-lifting warm front
across the central Plains will lead an anomalous moisture plume
into an increasing unstable environment. While exact convective
placement varies, the deterministic models remain in generally
good agreement -- depicting a deepening surface low over the
central Plains that will help to focus moisture along the leading
edge of a strengthening low level jet. A deepening pool of
moisture (PWs increasing to 1.5-2 inches) over central
Nebraska/Kansas eastward into southwestern Iowa and western to
central Missouri will support efficient rainfall rates. This ample
moisture along with large- scale ascent afforded by mid-level
shortwave and right- entrance region jet forcing will further
encourage heavy rainfall and the potential for flash flooding
across the region. Therefore, a Slight Risk was maintained across
the region. Farther south, a weakening frontal boundary and
residual tropical moisture will trigger additional thunderstorms
from South Texas across the Gulf Coast. Localized flooding will
likely remain a threat given the increasing sensitive soils.
Day 5...
Forecast confidence lowers notably heading into the latter half of
the weekend as guidance begins to diverge on the track of the
leading wave forming over the central Plains on Day 4. Notably, the
ECMWF offers one of the more northerly solutions compared to other
guidance. Beyond the primary wave's track from the Midwest into the
East, considerable model spread exists regarding the timing of the
trailing front and subsequent wave and storm development. With the
continuation of ample moisture, instability, and strong forcing
areas of heavy rainfall and flash flooding appear likely. Given
the model spread, the outlook area, including a Slight Risk
extending from the lower Missouri to the lower Ohio Valley, relied
most heavily on a multi-model ensemble mean.
Pereira
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Wed Jun 17 2026
Day 4 and Day 5
Valid 12Z Sat Jun 20 2026 - 12Z Mon Jun 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE OF CENTRAL PLAINS THROUGH THE MID MISSISSIPPI INTO THE LOWER
OHIO VALLEY...
Day 4...
A well-defined 500mb shortwave trough will move from the Great
Basin into the northern Rockies midday Saturday, reaching the
northern High Plains by Saturday night. Ahead of a southward
advancing Canadian cold front, a northward-lifting warm front
across the central Plains will lead an anomalous moisture plume
into an increasing unstable environment. While exact convective
placement varies, the deterministic models remain in generally
good agreement -- depicting a deepening surface low over the
central Plains that will help to focus moisture along the leading
edge of a strengthening low level jet. A deepening pool of
moisture (PWs increasing to 1.5-2 inches) over central
Nebraska/Kansas eastward into southwestern Iowa and western to
central Missouri will support efficient rainfall rates. This ample
moisture along with large- scale ascent afforded by mid-level
shortwave and right- entrance region jet forcing will further
encourage heavy rainfall and the potential for flash flooding
across the region. Therefore, a Slight Risk was maintained across
the region. Farther south, a weakening frontal boundary and
residual tropical moisture will trigger additional thunderstorms
from South Texas across the Gulf Coast. Localized flooding will
likely remain a threat given the increasing sensitive soils.
Day 5...
Forecast confidence lowers notably heading into the latter half of
the weekend as guidance begins to diverge on the track of the
leading wave forming over the central Plains on Day 4. Notably, the
ECMWF offers one of the more northerly solutions compared to other
guidance. Beyond the primary wave's track from the Midwest into the
East, considerable model spread exists regarding the timing of the
trailing front and subsequent wave and storm development. With the
continuation of ample moisture, instability, and strong forcing
areas of heavy rainfall and flash flooding appear likely. Given
the model spread, the outlook area, including a Slight Risk
extending from the lower Missouri to the lower Ohio Valley, relied
most heavily on a multi-model ensemble mean.
Pereira
