Day 2 Outlook >
WPC Day 1 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 0058 UTC Sun Oct 24, 2021
Valid: 01 UTC Oct 24, 2021 - 12 UTC Oct 24, 2021
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sat Oct 23 2021
Valid 01Z Sun Oct 24 2021 - 12Z Sun Oct 24 2021
....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN MISSOURI, SOUTHERN IOWA AND WEST CENTRAL ILLINOIS...
A strong atmospheric river is on track to impact CA later tonight
into Sunday. Heavy rains should move into northwest CA between
06-12z tonight...with as much as 2-4" falling by 12z. Rainfall
impacts through 12z should end up limited in scope...thus the
Marginal risk should be okay...although any more sensitive burn
scar areas could experience some runoff issues before 12z. The
bigger and more widespread impacts still look to be after
12z...where we have Moderate and High risks of excessive
rainfall...with significant impacts expected.
...Central Plains into mid MS Valley...
Convection should expand in coverage later this evening from
northeast KS/southeast NE...east into portions of southern IA,
central/northern MO into IL. Strong southerly flow will increase
ahead of the approaching trough, resulting in a strengthening
corridor of low level moisture convergence. Flow in the upper
levels will also become gradually more divergent...although the
real uptick in this looks to hold off until after 12z.
Nonetheless, the low level convergence, modest upper level
divergence, and plentiful upstream instability should support an
expanding region of convection. Corfidi vectors may become quite
weak overnight pointed towards the south...which should support
some backbuilding/training of convection given the persistent low
level convergence and increasing mid/upper level support with
time. Hourly rainfall approaching 2", and localized swaths of over
3" in a couple hours seems probable with this setup. It will
likely be a pretty narrow swath and some lingering uncertainty on
the exact latitude...with the most probable location somewhere
from northern MO into far southern IA into west central IL.
We will go ahead and upgrade this corridor to a Slight risk for
the remainder of the overnight hours...as some exceedance of the
1hr and/or 3hr FFG seems probable on an isolated to scattered
basis. While 2-4" amounts are most likely within the swath, there
is at least some risk of localized 4-7" totals if training ends up
a bit more robust/persistent.
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt