Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
245 AM EST Sat Dec 27 2025
Day 2
Valid 12Z Sun Dec 28 2025 - 12Z Mon Dec 29 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NORTHERN
ILLINOIS THROUGH WESTERN NEW YORK...

A Marginal Risk upgrade was introduced with this morning's forecast
update across a portion of the Great Lakes, in coordination with a
couple of the impacted forecast offices. While the atmospheric
river event in California is long over, the remnant moisture
therefrom has continued east and will be harnessed by a developing
storm system across the Midwest. The low center will track from
near Kansas City Sunday morning to over Lake Huron by Monday
morning. In that time it will deepen from around 1000 mb Sunday
morning to around 974 mb Monday morning. This rapid cyclogenesis
will allow the moisture to the tune of 5 sigma above normal for
this time of year, as well as IVT values over 750 kg/m/s will
support additional dynamic lift along the warm front which extends
east of the low, and along its cold front to the low center's
south.

Elevated convection resulting in locally heavy rainfall is
likely, despite the fast movement of any convective cells. Bare
ground is in place across most of the Marginal Risk area. Due to
lack of flora, it should take longer for the rainfall to penetrate
into the ground, resulting in more runoff. Urban areas in the rain
shield, including Chicago, Detroit, and Buffalo could see urban and
small stream flooding. Across upstate New York, at the higher
elevations some snowpack remains, especially east of the lower
lakes. This too could locally contribute to rising stream and creek
levels leading to isolated instances of flash flooding.

Wegman

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