Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
657 PM EDT Sat May 18 2024
Day 3
Valid 12Z Mon May 20 2024 - 12Z Tue May 21 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL PLAINS/CORN BELT...

...20Z Update...

The MRGL risk was maintained, but the orientation was changed
from the previous forecast issuance considering the latest trends
within the QPF fields in the bias corrected ensemble and ML
guidance. The premise for the heaviest rainfall over the Sandhills
of NE remains the same with that area mostly void of the risk area
due to very high FFGs. Further to the south, models are beginning
to focus an initiation for heavy rainfall across northeast CO into
southwest NE where the FFG indices are more favorable, albeit not
significantly to favor a flash flood potential with the current
precip forecast. We still reside outside of the CAMs window, but
the pattern is ripe for elevated convective concerns and locally
enhanced rates within the diffluent side of the sharpening
shortwave trough entering the high plains. The MRGL was maneuvered
towards the eastern fringes of the Sandhill's down towards the
KS/CO/NE border where the latest ML guidance continues to hint a
QPF maximum where the frontal boundary will be focused. This
extends back into northeast CO where the convective initiation is
being depicted, as well as north of the Sandhill's in southern SD
where the best QPF footprint outside the higher FFG areas is
located.

Kleebauer


...Previous Discussion...

Upper pattern remains fairly similar to D2 across the Plains, with
broad SW flow over the region. One wave will exit through the
Upper Midwest as troughing over the West deepens via northern and
incoming southern stream vorticity. Upper diffluence east of the
Rockies will support widespread showers/storms over the central
Plains Monday into Monday night along the stalled surface boundary,
with sufficient moisture in place and sfc CAPE 500-1500J/kg.
Heaviest rainfall per the ensembles lie over western Nebraska (Sand
Hills) where FFG values are highest, so focused the area to the
southeast and east into Iowa where rainfall on D2 may lower FFG
values a bit (from already somewhat lower numbers).

Fracasso