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Excessive Rainfall
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Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
405 AM EDT Mon May 20 2024
Day 1
Valid 12Z Mon May 20 2024 - 12Z Tue May 21 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM FAR
NORTHEAST COLORADO, ACROSS SOUTHERN AND EASTERN NEBRASKA INTO
NORTHWEST IOWA AND ACROSS SOUTHEAST WISCONSIN INTO NORTHEASTERN
ILLINOIS...

...Central Plains into the Mid Missouri Valley...
The amplifying mid to upper level trof pushing east across the
Central to Northern Rockies will ignite the next round of active
Central Plains convection late Monday afternoon, continuing into
the early hours of Tuesday. Overall favorable conditions for active
convection with strengthening of the low level flow, strengthening
boundary layer convergence and favorable upper difluence in the
vicinity of the frontal boundary forecast to stretch from the lee
of the Central Rockies, east northeastward into the Upper
Mississippi Valley. There is spread among the latest hi res
guidance as to whether this next round of convection will
consolidate into one distinct line as per the ARW, or have more
than one round of convection moving along the frontal zone as per
the NAMNEST, FV3LAM and ARW2. However, there is consensus that
either way, the convection will be fairly progressive to the east-
northeast, and continue to be a detriment to very heavy rainfall
amounts. We have kept the risk level at marginal given the expected
quick movement. This is reflected in HREF neighborhood
probabilities for 1"/hr amounts that are in the 20-45% range in the
marginal risk area, but much lower, mostly less than 15% and more
geographically spotty for 2"/hr amounts.

...Southeast Wisconsin into northeast Illinois...
The well defined MCV moving into the Lower Missouri Valley early
this morning is expected to remain intact as it pushes
northeastward into the Upper Mississippi Valley and Upper Lakes
region Monday into Monday night. While there may be weakening to
the current organized convection associated with this MCV early day
1, there is the possibility for additional convective enhancement
ahead of the MCV late Monday morning into afternoon across
southeast Wisconsin into northeast Illinois. No significant changes
made to the previous marginal risk area with concerns primarily
for urbanized runoff issues from Chicago, north through Milwaukee
and Green Bay.


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