Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1159 AM EDT Tue Jun 23 2026
Day 2
Valid 12Z Wed Jun 24 2026 - 12Z Thu Jun 25 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS TO LOWER MISSISSIPPI
VALLEY...

...High Plains to Lower Mississippi Valley...

Persistence in the upper level setup across the CONUS will lead to
another day of northwesterly flow over the Front Range to Lower
Mississippi leading to convection taking similar trajectories for
the period. Consensus is for the initial portion of the forecast to
focus over the Southern Plains to Lower Mississippi Valley as the
initial complex at the end of D1 will likely traverse southeast
through OK into AR/LA, eventually ending as it motions into
Mississippi by later Wednesday morning. Heavy rain threat will
follow the complex as it maneuvers southeastward with some guidance
igniting the complex over LA/MS as it enters a better environment
and we see a build-up of instability through the early daytime
hours. Progressive nature of any thunderstorm activity will likely
preclude more ominous flash flood concerns, however these areas
have seen their share of flash flooding the past week, so the areas
where any complex moves across will have some susceptibility to
hydro concerns. Initial 12hrs in the forecast period (12z Wed - 00z
Thu) have a solid signal within the CAMs for heavy rain totals
across the aforementioned corridor between eastern OK to south-
central MS, backed up by modest neighborhood probs from the
correlated HREF signaling >60% chance for at least 2" and 30-50%
for at least 3" in the above zone(s). Given the state of the soils
and lower FFG's than normal over the region, the prospects for
flash flooding a bit higher than normal which led to a maintenance
of the SLGT risk inherited over the area.

Moving further northwest, a repeat from the previous period will
ensue by the late-afternoon time frame as yet another shortwave
will eject out of the High Plains of WY and initiate another round
of organized convection over the High Plains between WY/NE,
pushing south-southeast as it maintains prevalence within the mean
northwesterly flow between the stout ridge over the Southwest U.S.
and the longwave trough centered over the Northern Plains. Heavy
rain footprint will follow a similar line to the D1 period with the
core of heaviest rain likely to fall across northeast CO,
southwest NE, and western KS during the nocturnal period between
00-12z Thursday. Totals of 1-2" will be common in wake of the
thunderstorms, however local totals will once again be pushed
closer to 3-5" in the hardest hit locations. Latest ECMWF EFI
indices are signaling anomalous QPF distributions within that
general zone, as well, which matches up with the heavier QPF
depictions we see within the global deterministic and regional
model guidance. As a result, the SLGT was kept over the area with
little deviation in the previous positioning.

...Southwest U.S...

Anomalous mid and upper level moisture will be advected over the
Southwestern U.S. as we move into Wednesday as prevailing
southwesterly flow around the western flank of the ridge over
northern Mexico will help usher in warm, moist Pacific airmass
centered off Baja. The addition of elevated moisture into the
region coupled with intense heating across the Desert Southwest
will lead to increased boundary layer instability and the ability
to generate afternoon convection for the first time in a while over
the deserts of southern CA into the Great Basin by Wednesday
afternoon. Models are not too enthused by sense of magnitude,
however with PWAT anomalies pushing +2 to +3 standard deviations
across the area by the afternoon period, it stands to reason that
some of the convection could be sufficient in causing localized
flash flood prospects over those more prone areas like slot
canyons in the interior and flashier portions of southern CA. A
MRGL risk was added for the low-end threat with emphasis on the
terrain in AZ, deserts of southern CA, and slot canyon areas within
NV/UT/AZ.

Kleebauer


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