Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
846 PM EDT Sun Mar 30 2025
Day 3
Valid 12Z Tue Apr 01 2025 - 12Z Wed Apr 02 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE CENTRAL PLAINS & MIDWEST...

A blocking pattern begins to emerge by Tuesday, as the
aforementioned shortwaves lift northeastward into Canada with
large-scale ridging quickly builds across the eastern United States
from the North Atlantic. Meanwhile, large-scale troughing becomes
amplified out West, with a potent upper-low expected to develop
over the Northern Rockies and Plains (translating across the
Rockies from the Pacific Northwest). While 12z global model suites
are in overall good agreement with the evolution of the synoptic
scale, the GFS/NAM are drier than the rest of the guidance with the
associated surface low (which is depicted as a sub 990 mb low from
the GFS, ECMWF, and CMC). Within the GFS/NAM guidance, the idea of
light QPF is internally inconsistent as the forecast precipitable
water values (1-1.25") combined with the 1000-500 hPa thickness
values near 5610 meters suggest a nearly saturated atmosphere, and
there appears to be sufficient instability in the vicinity and
effective bulk shear for convective organization, so the wetter
guidance was more believable. However, nearly as soon as the
necessary ingredients are in place, they take off to the east due
to system progression. Most deterministic solutions follow that
idea and depict localized totals of 2"+ (including the downscaled
ECMWF, the UKMET, and the CMC- reg) with remarkably good spatial
agreement for this range. The ingredients above suggest hourly
rainfall up to 1.75" with local amounts in the 3-4" where/when
cells have the opportunity train or backbuild, so the inherited
Marginal risk remains, though the area showed some expansion.

Roth/Churchill

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