FOUS30 KWBC 301943
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 PM EDT Mon Mar 30 2026

Day 1
Valid 16Z Mon Mar 30 2026 - 12Z Tue Mar 31 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

General pattern will induce areas of moderate to locally heavy
rainfall across MI to areas downwind of Lake Erie and Ontario.
Guidance has trended north from the previous runs leaving an axis
of higher QPF more likely off Ontario with increasing convergent
flow mainly north of I-90 beginning later this afternoon through
the overnight. CAMs are in relatively good agreement on an area of
0.75-1.5" of rainfall across areas of western NY state with
neighborhood probabilities of >1" running between 60-90% over the
entire area from the NY/PA border off Lake Erie to off the southern
portion of Lake Ontario. The key in this setup is the lack of
sufficient buoyancy with rates being capped below 1"/hr as prob
fields indicate <1% chance of rates exceeding the threshold.
Urbanized zones will have a non-zero potential across eastern MI
near and over Detroit proper and any larger urbanized zones in
western NY. First guess fields remain un-enthused for this
particular period as well with a nil remaining over the
aforementioned areas. Will hold off on any introductions of a risk
area, but will reiterate that the setup is non-zero, but the risk
is below standard thresholds.

Kleebauer


Day 2
Valid 12Z Tue Mar 31 2026 - 12Z Wed Apr 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
WESTERN NEW YORK AND SOUTHEAST MICHIGAN...

20Z Update: Overall upper pattern will become slowly backed as a
deep longwave trough out west begins to pump the mid-level ridge
downstream from the Mississippi River to the Eastern CONUS. At the
surface, a quasi-stationary front will bisect areas west to east
from the Midwest the Northeast with a weak surface low migrating
along the frontal positioning. Shortwave associated with the area
of low pressure will eject through the Great Lakes leading to a
period of convective development downstream into MI and points
east. This initial round of rainfall will occur in the morning
hours with some moderate to locally heavy rainfall forecast to
impact southeast MI to areas downwind of Lake Erie. There's pretty
good agreement within the precip fields that some lake enhancement
off Erie is probable in this setup leading to streaming bands of
heavier rainfall focused across Buffalo into the Southtowns leading
to totals likely exceeding 1" in many areas with as much as 2"
plausible in just the first round of precip that begins the end of
D1, bleeding into the front end of D2.

As the low migrates eastward into the neighboring Ontario province
in Canada, flow returns out of the north on the backside of the
cyclone allowing for the front to sink south across MI, entering
into the northern Ohio Valley bisecting more of northern IN/OH back
into northern IL by the second half of Tuesday. This sets the
stage for a second shortwave ejection to materialize within the
increasingly diffluent pattern upstream with another round of
convection breaking out across the northern Missouri Valley, moving
northeast along the front. Locally heavy rain will impact that
area of the northern Ohio Valley back into IL where relatively
modest theta_E presence will dictate a suitable convective
environment capable of localized flash flood concerns as rates
trend closer to 1-1.5"/hr at peak intensity as noted via modest
HREF probabilities of 20-40% for exceeding 1"/hr. This setup will
align back across the I-90 corridor into northeast OH into western
NY state before the front finally sags south of the region to
alleviate some concerns for that area. Coupled with the heavy
rainfall threat in the morning, western NY areas downwind of Lake
Erie will see widespread totals of 1.5-3" leading to a more
elevated flash flood concerns, especially when combined with river
flood concerns as stream flows across the region have been elevated
since the previous events over the area. Flood Watches will be in
effect for portions of western NY given the signal of both the
river and flash flood threat aligning well with a targeted SLGT
risk across the area.

The SLGT extends back into Detroit due to the urbanization factors
and expected heavy rainfall the front half of D2 into the metro
which creates a better opportunity for flash flooding considering
the setup. A MRGL risk encompasses the northeastern portion of IL
through southern MI, northern IN/OH, and extends well east and
northeast to include Upstate NY, Northern New England, and the
northern Hudson Valley as combination rainfall and snow melt will
allow for elevated stream flows and any locally heavy rainfall
could induce flash flood prospects.

Kleebauer


Day 3
Valid 12Z Wed Apr 01 2026 - 12Z Thu Apr 02 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL STRETCHING FROM
TEXAS TO THE MIDWEST/UPPER MIDWEST...

20Z Update: Broad MRGL risk was maintained for D3, but did extend
the risk further southwest as indications for a line of convection
reaching as far south as western Hill Country and the lower Concho
Valley have increased within the latest global deterministic and
ensembles. Frontal progression timing and magnitude of the
meridional regime anticipated with the longwave setup will be the
largest players for the D3 prospects as a long axis of convection
is very likely at this juncture. A prominent warm-sector will
materialize from west-central TX into MO with a surface low
forecast to be positioned over the Central Plains by Wednesday
afternoon. Several shortwaves will eject northeast within ahead of
the mean trough leading to multiple waves of rainfall across parts
of KS into MO. The area of increasing interest is within a triple-
point centered over the KS/MO line with most guidance highlighting
the KC metro and surrounds as the primary area where multiple waves
of heavier rain of convective origin could impact the area. Despite
the antecedent dry conditions in place, prolonged rainfall within
the urban corridor with slower cell motions could lead to a greater
threat for scattered flash flooding before the system finally moves
eastward and the area sees the frontal passage. Areal average of
1.5-2.5" of rain area forecast already in the means, and that's not
including some of the global deterministic outlining totals >3" in
their outputs as of the 12z model suite. There is still some
discrepancy on the magnitude and placement, and since we have time
and are outside CAMs range, will allow for a few more model cycles
before adding any higher risk categories. For now, maintained
continuity of a MRGL over the aforementioned area.

Kleebauer

...Previous Discussion...

The central portion of the country is shaping up for heavy rainfall
as a frontal system extending from the Northeast to the Mid-South
taps into Gulf moisture advecting northward. Multiple rounds of convection
are expected to fire up across central and eastern CONUS given the
upper level support for sustained rainfall potential. Local
flooding may arise over portions of the Southern Plains, Lower and
Mid-Mississippi Valley. The general footprint of the rainfall
shield has trended a bit west from the previous cycle thus
requiring a western adjustment of the Marginal Risk area.
Consensus continues to favor the highest QPF to focus over eastern
Oklahoma, southeast Kansas and into central Missouri.

The timing of the incoming shortwave/lifting warm front has
remained a trickier part of the forecast, and convection south
along the cold front may also limit instability further
north/become the higher threat. At this time a Slight Risk was not
raised but may be needed with future updates.

Campbell/Tate


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