Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1151 AM EDT Thu Apr 24 2025

Day 1
Valid 12Z Thu Apr 24 2025 - 12Z Fri Apr 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN
LOUISIANA, NORTHEAST TEXAS, AND NORTHEASTERN KANSAS THROUGH CENTRAL
IOWA...

...16Z Update...

The inherited Slight Risk across much of the Plains was divided
into two much smaller risk areas with this update, with the middle
carved out back down to a Marginal. The CAMs guidance has been in
poor agreement regarding how these MCSs, as well as any new
convection later this afternoon, will behave through tonight. Where
there is at least some consensus among the guidance is for greater
amounts of convection in the new, smaller Slight Risk areas and
less in the middle, which was the catalyst behind dividing the
Slight.

...Eastern Louisiana...

The newly issued Slight in eastern Louisiana is in place for an
ongoing MCS that has a history of producing rainfall rates of 2-4
inches per hour, along with training and backbuilding that has
allowed this heavy rainfall to occur over a small area for an
extended period of time. On the whole the MCS has been weakening,
but local cores with rates that high continue this morning. CAMs
guidance is in reasonable agreement that some level of heavy rain
from convection will continue in this area, likely north of Lake
Pontchartrain, through 18Z. It appears likely that this Slight
will be able to be downgraded this afternoon with higher confidence
in the convective trends.

...Northeast Texas...

The southern end of the previous Slight has been expanded south and
east in response to a much more robust MCS (compared to the one in
Louisiana) across northern Texas this morning. Individual cores of
heavy rain have been far more persistent into the late morning, and
have developed into an east-west oriented line that is now
generally south of the I-20 corridor, and fortunately well south
and west of the Dallas-Fort Worth Metroplex. While urban concerns
remain heightened in the Metroplex for the possibility of
additional storm development this afternoon, the greatest near term
concerns will be between I-20 and I-35 in central Texas. With peak
heating, expect additional storms to develop south of the current
storms in the area of greatest inflow of moisture and instability.

...Kansas to Iowa...

Multiple small clusters of storms from northern Kansas through
central Iowa are largely weakening this morning. However, there is
some CAMs consensus that additional strong convection will break
out in southeast Nebraska this afternoon. This convection will
advect northeast into Iowa, where previous rounds of heavy rain
have depressed FFGs. Thus, despite a lower likelihood of training
and faster moving cells, the low-confidence Slight remains in place
with a small expansion northeast further into central Iowa based on
the trends in the guidance. There remains some possibility tonight
that additional convection will fire along remnant outflow
boundaries in northern Kansas where the current line of showers has
already cleared, which is why for now the Slight remains for that
area.

...Marginal Risk...

Elsewhere, as mentioned above expect a relative minimum of
convection over most of Oklahoma and southern Kansas today and
tonight, though isolated cells remain very possible. For the
Southeast, no changes were made, with expected individual cells or
small clusters of storms developing this afternoon with peak
heating. The coverage of storms in this area is unlikely to be very
robust, precluded the need for a Slight Risk upgrade for now.

Wegman


Day 2
Valid 12Z Fri Apr 25 2025 - 12Z Sat Apr 26 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS, MID-MISSISSIPPI VALLEY, OHIO VALLEY, AND
PORTIONS OF THE NORTHEAST...

A strengthening surface low developing ahead of a strengthening
upper level shortwave trough will drive the storms from a forcing
standpoint through the period. Starting in the Plains it will track
northeast into the Great Lakes Friday evening, with showers and
storms forming along the cold front to the south and east of the
low center. This will bring periodically heavy rainfall to
portions of the Northeast, which has been in a drier period the
past week. Gulf moisture continuing to advect in from the south
will lead to shower and thunderstorm activity starting Friday
afternoon across the Tennessee and Ohio Valleys, and continuing
into Friday night as the front lags behind (south and west) of the
surface low. Meanwhile, the trailing (western) end of the cold
front may be the trigger for additional thunderstorms into southern
Oklahoma, north Texas, and the southern Texas Panhandle.

In coordination will the offices in the Northeast the Marginal Risk
was removed from New Hampshire, Vermont, much of New York and
northeast Pennsylvania. This area has been drier of late and with
green up already in progress, much of the rain will be absorbed
with minimal if any flooding possible. Elsewhere, the Marginal had
minor reshaping to reflect the latest WPC QPF and model trends.

Campbell/Wegman


Day 3
Valid 12Z Sat Apr 26 2025 - 12Z Sun Apr 27 2025

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND FOR PORTIONS OF NEW ENGLAND...

...New England...

Showers and thunderstorms are expected to pass through New England
thanks to upper level shortwave energy and wavy surface fronts.
The flow is expected to be fairly progressive so it will help limit
the potential for flash flood. Given the recent QPF trends and
placement, the inherited Marginal Risk area was significantly
modified to only include northeast Vermont, northern New Hampshire
and the majority of the state of Maine.

...Southern Plains...

The steady influx of rich moisture ahead of a deeply strengthening
storm system ejecting into the Plains will fuel rounds of heavy
rain and thunderstorms across portions of the central U.S. from the
weekend into next week. Guidance has improved its focus on where
the higher QPF will occur. The old Day 4 Marginal Risk was reduced
out of Nebraska and Kansas, now spanning from Texas to western
Arkansas as the new Marginal Risk area for this period. Heavy rain
will be favorable with the upper trough diffluence combined with
front/dryline instabilities.

Campbell


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt