Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Thu Oct 23 2025
Day 1
Valid 12Z Thu Oct 23 2025 - 12Z Fri Oct 24 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS...

...Southern Plains...
At the start of the forecast period, 23.12z, a southern stream
fairly concentric/symmetric mid-level cyclone continues to advance
across the Four Corners region of the Southwest. The low will
continue to consolidate and deepen slightly throughout the day as a
stronger (90+ kt) jet streak rounds the base toward 24.00z
broadening across the southern High Plains providing strengthening
left exit and diffluent larger scale ascent across the Southern
Plains thereafter.

The low levels were already responding with and open Western Gulf
return stream of enhanced theta-E air northward across central
Texas toward the Big Country and Red River Valley. As the
divergence increases aloft, the LLJ responds with 850mb increase
from 15-20kts toward 30-35kts with broad veering increasing low
level confluence/convergence after dark. Combine this with cross
northern Mexico sub-tropical moisture into the 700-500mb layer and
overall total PWat values increase from 1-1.25" toward 1.5" by late
evening. Modest lapse rates with support MUCAPE 1000-1500 J/kg and
the strong WAA/isentropic ascent across the frontal zone should
allow for scattered elevated convective activity across southern KS
and central OK throughout the evening. Hi-Res CAMs suggest there
may be some back-building potential given the strengthening LLJ
and with deep-layer flow, some short-term training may exist.

As the night progresses, core of highest theta-E, West Gulf
moisture reaches the surface front. Moisture flux convergence
increases and half of the Hi-Res CAM suite breaks out or
intensifies weaker scattered/ongoing convection across the eastern
Cap Rock/western Big Country into larger clusters, in a similar
regime; though with lower bases and greater moisture flux through
deeper cells, rainfall efficiency can increase from 1.25-1.5"/hr
toward isolated 2"/hr rates. 00z HREF continues to show a few
signals of such rates over 20% and localized spots of 3"+ (35-40%)
along/near the front near the Red River with an isolated 4" not
out of the realm of possibility.

This is a split signal within the guidance where a few (anchored
by the NAM/NAMnest) remain stable near the surface front allowing
greater flux toward the elevated WAA convection with higher totals
further north east into north-central OK and points north. However,
this is a minority of the suite but to account for this remaining
plausible solutions, have expanded the Marginal Risk north-
northeastward into southern KS, though rates will be lighter and
still grounds remain dry with higher FFG, no greater risk area
could be highlighted at this time, though highest probabilities
within the Marginal Risk lie with any near surface rooted cells
capable of 2"/hr.


...Northwest...
Elsewhere, the leading Atmospheric River plume approaches late in
the forecast period, likely after 24.06z. Strong onshore flow with
40-50kts of low level flow and PWat moisture values of 1-1.25" will
support IVT values over 600 kg/m/s into the Olympic Range. This
will be a good starter for the AR event, but not likely to rise any
flooding/stream concerns for the Day 1 period. No Excessive
Rainfall category will be necessary for this period, but solid
rains are increasing for the Day 2 period.

Gallina

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