Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1155 AM EDT Sun May 19 2024
Day 3
Valid 12Z Tue May 21 2024 - 12Z Wed May 22 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST...

Robust southern stream shortwave over eastern CO Tuesday morning
will head northeastward into southwestern MN by early evening as
surface low pressure deepens below 990mb over northeastern MN at
the end of the period. Strong southerly flow in the BL (850mb winds
to 50kts) will help surge moisture northward into and around the
low, with precipitable water values climbing to over 1.50" which is
about +2 sigma and 850-700mb moisture flux anomalies > +5 sigma
from MO northward to MN/WI. QPF mode will be deformation-driven on
the NW side of the wrapped-up/occluded low where rates will be
modest but perhaps exceeding longer-time FFG values vs warm-sector
QPF (MO northward/northeastward) where instability will be present
(CAPE > 2000 J/kg as far north as northern IA). The entire system
will be rather progressive, but expansive. Focused the Slight Risk
on the warm sector rainfall and nosed back toward eastern SD where
FFG values are lower than points farther west (covered by the
Slight Risk). Models show various axes of QPF tied to different
forcings in the evolution of the system, which is covered by the
broad Marginal Risk outline eastward to Lake Michigan. AI guidance
was displaced a bit to the east of the dynamical parent models, but
this was also reflected in the ensemble systems as well
(GEFS/ECMWF/GEPS). QPF spread was largest well into the warm
sector (MO into the Ozarks) where the flash flood threat may be
more isolated depending on the convective evolution.


Fracasso