FOUS30 KWBC 210835
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
435 AM EDT Sat Sep 21 2024

Day 1
Valid 12Z Sat Sep 21 2024 - 12Z Sun Sep 22 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN HIGH PLAINS...

...New Mexico into Texas/Oklahoma Panhandles...
The large-scale flow across the southern Great Basin will continue
to draw moisture northward at the low levels while becoming increasingly
diffluent aloft in response to the approach of an upper low moving
across the southern Great Basin today. Precipitable water values
are forecast to exceed 1.5 inches across parts of West Texas by
late afternoon while the right entrance region of an upper level
jet rounds the base of an upper trough and tracks over the region.
This combination should help support multi-cell storms capable of
producing isolated rainfall rates of an inch or more and storms
total rainfall amounts in excess of 2 inches over portions of
northeastern New Mexico into the Texas panhandle during the
afternoon or evening hours with an associated risk of flash
flooding. There was one round of showers and thunderstorms 
that developed on Friday evening over southeast Kansas and 
weakened as it moved into southwest Missouri...followed by a second
flare up of convection in the overnight hours on a track a bit to 
the south of the first round. There was some concern is more about
the cumulative effect of multiple rounds lowering the flash flood 
guidance here ahead of anything developing later in the day...but 
warming cloud tops and limited coverage of 1 inch amounts was 
enough to keep the area in the Marginal risk category for the time 
being.

Bann


Day 2
Valid 12Z Sun Sep 22 2024 - 12Z Mon Sep 23 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE MID MISSISSIPPI VALLEY TO THE SOUTHERN HIGH PLAINS...

The focus for areas of heavy rainfall will continue to be along a
plume of deeper moisture...precipitable water values generally at
or above 1,75 inches...from the western portion of Texas
northeastward to where it begins to encounter a cold front moving 
in from the northern United States. An upper level shortwave trough
over the central and southern Rockies on Sunday morning will eject
eastward during the day...aiding the formation of storms over parts
of western Texas capable of heavy downpours around the time of 
maximum heating. Farther to the east...model guidance tends to
generate at least some convection capable of producing isolated 2
to 3 inch rainfall amounts over portions of Missouri as moisture
flux convergence occurs ahead of a cold front pushing southward.
Mesoscale guidance...available through the first 12 hours of the
Day 2 period for the overnight EROs...does show low-end potential
for 2 inch per hour rates embedded within a broader area where
probabilities of 1 inch per hour rates are on the order of 10 to 25
pct. There was already a Slight Risk introduced here and only
needed a bit of realignment to fit the latest guidance. 

Bann


Day 3
Valid 12Z Mon Sep 23 2024 - 12Z Tue Sep 24 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER A PORTION OF
THE MISSISSIPPI VALLEY EASTWARD INTO THE OHIO VALLEY...

As the large scale upper trough continues to move eastward on
Monday...the plume of available moisture gets elongated and the
moisture flux along the front becomes less well defined. There will
be some broader upper support along the front which will have taken
on a more east-west orientation...so there is at least some
potential for problems from run off with 1 to 2 inches or rainfall
over portions of Illinois into Indiana. But with convection
expected to become increasingly elevated and with flash flood
guidance tending to be 2.5 inches per hour or greater...will
maintain a Marginal Risk area for now and evaluate the need for an
upgrade if rates/amounts pick up in later model cycles. 

Bann
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