Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 PM EDT Wed Apr 16 2025

Day 1
Valid 16Z Wed Apr 16 2025 - 12Z Thu Apr 17 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann

Day 2
Valid 12Z Thu Apr 17 2025 - 12Z Fri Apr 18 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Fri Apr 18 2025 - 12Z Sat Apr 19 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL AND NORTHEASTERN OKLAHOMA INTO SOUTHWESTERN MISSOURI...

2030Z Excessive Rainfall Update...
Expanded the Slight and Marginal Risk areas a bit eastward to cover
more of the possible solutions suggested by the 12Z suite of
numerical guidance QPF. The expansion covers the possible rainfall
enhancement from any interaction between the low level jet and the
complex terrain of the Ozarks/Boston Mountains should the placement
of the low level jet shift a bit in future model runs. Also
expanded the Marginal risk a bit closer to the ArkLaTex region
given the QPF amounts shown by the GFS/ENSQPF. Overall...the
changes were fairly small (from a national perspective) and did
not reflect a significant shift in forecast reasoning.

Previous Excessive Rainfall Discussion...

A large and very positively tilted longwave trough extending from
the Northern Plains down into the Southwest/4 Corners Region will
slowly press eastward towards the Southern Plains on Friday. As
this forcing encroaches across the Plains, it will run into a very
well established southwesterly LLJ extending from the far western
Gulf (and really the Caribbean before that) northward across
central Texas and then northeast into the Midwest. For much of the
day Friday, the forcing to the west and the LLJ will be
sufficiently separated so as to not result in much precipitation
over the Slight Risk area. However, come late Friday afternoon
through the overnight, that will change as the longwave trough
moves east and an embedded shortwave rides the base of the trough
and digs eastward, locally increasing the upper level divergence
(and therefore forcing), needed to initiate and maintain both
convection and a broader rainfall shield around it. Thus, expect
thunderstorms to break out along and ahead of the jet with a
supporting surface cold front slowly pushing southeastward.

As the LLJ runs into the front, storms will rapidly develop
northeastward along the front, then train northeastward one after
another as the LLJ restores the moisture used up by the storms in
the form of heavy rainfall. There is good agreement that the I-44
corridor from Tulsa to Joplin will be the area at greatest risk for
heavy rainfall through Friday night, though storms may continue to
backbuild down to the Oklahoma City metro, and will persist
eastward towards St. Louis. There is good agreement in the guidance
that this scenario will unfold, but less agreement on where this
corridor of training storms will set up, with the I-44 corridor
being the broader consensus. Thus, expect the Slight Risk area to
shift with future updates. Should this corridor shift
southeastward, the heaviest rain will align better with the area
hard hit by the historic rainfall just 2 weeks ago, and while
conditions have significantly improved due to the recent dry
weather, a repeat hit may cause worsened impacts with recovery
still occurring in the area. It's possible a further upgrade to a
Moderate Risk may be necessary with future updates. However, should
the corridor remain along I-44, urban concerns in Tulsa, Joplin,
and the Fayetteville/Bentonville area may locally increase the
impacts from the heavy rain.

Wegman


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt