Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
419 AM EDT Mon Apr 15 2024

Day 1
Valid 01Z Mon Apr 15 2024 - 12Z Mon Apr 15 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE PLAINS...

A deepening low and amplifying jet will pivot into the Upper
Midwest creating broad areas of ascent while increasing low-level
southerly flow from the Gulf of Mexico. Precipitable water values
will surge to 1.25/1.5 over the Plains with moisture anomalies
peaking around 2.5 standard deviations. The environment will be
conducive for convection to develop ahead of the front that will be
capable of multiple hazards like very large hail, destructive
winds(possible tornadoes) and heavy rainfall. The nature of these
storms will be progressive which may somewhat limit the threat for
flooding however with the support of mixed-layer CAPEs of at least
1000-2000 J/Kg over the southern portion of the Marginal Risk area,
there will be a higher probability of more intense 1-3hr rainfall
rates compared to areas farther north. Higher FFGs (lower soil
moisture percentiles lower) over the southern portion of the
outlook area will maintain a Marginal or localized flash flood
risk.

Meanwhile, lower FFGs/wetter antecedent soils over the northern
portion of the outlook area, along with a better chance for more
prolonged activity along/north of the surface warm front, will be
offset by decided lower deep-layer instability (even elevated). So
even here, again the flash flood risk remains marginal.

Campbell/Hurley

Day 2
Valid 12Z Mon Apr 15 2024 - 12Z Tue Apr 16 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS EASTERN
PORTIONS OF THE NORTHERN PLAINS SOUTHWARD THROUGH MUCH OF THE
MISSISSIPPI VALLEY...

The closed low and trailing cold front will advance from the High
Plains into the Upper Mississippi Valley while an west-east
orientated warm front extends across the Upper Midwest to the Mid-
Atlantic region. An axis of anomalous precipitable water values up
to 2 standard deviations above the mean, will persist along and ahead
of the well defined cold front while pooling along the warm front.
Organized convection will likely fire up in proximity to this
anomalous moisture axis. Like the previous day, the convection is
expected to be fairly progressive that continues to limit the
potential for heavy rainfall and associated areas of localized
flooding.

Locations along and north of the warm front have the greater
potential for organized precipitation to span from the Northern
Plains to the Upper Mississippi Valley/Upper Midwest. Heavy rain
will likely spread across locations north of the warm front and
maintain for longer durations as the moisture surging
northward from the Gulf of Mexico over the frontal boundary
persists. Consensus suggests broad areal averages of 1 to 2 inches
with locally higher amounts certainly possible. This region has
been relatively dry over the past few weeks, resulting in dry soils
and below average stream flows.

Campbell

Day 3
Valid 12Z Tue Apr 16 2024 - 12Z Wed Apr 17 2024

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE GREAT LAKES, OHIO VALLEY AND WESTERN PARTS OF THE NORTHEAST...

Showers and thunderstorms will shift east as the closed low and
fronts advance through the Ohio Valley toward the Mid-Atlantic.
Much of the guidance has 1 to 2 inches for this period for parts of
the Great Lakes, eastern Ohio Valley and portions of the Northeast.
This part of the country has much lower FFG guidance from
antecedent rain thus are more sensitive to additional rainfall. A
Marginal Risk spans from Michigan/Wisconsin south to Kentucky and
east into western New York, Pennsylvania and Maryland.

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