FOUS30 KWBC 230745
QPFERD

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 2
Valid 12Z Fri Oct 24 2025 - 12Z Sat Oct 25 2025

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

...Southern Plains...
At the start of the Day 2 period (24.12z), strong LLJ from 
overnight will likely have one or more WAA convective clusters 
ongoing with a higher based/elevated convection across the KS/OK 
border moving toward the Ozark Plateau as left exit ascent region 
of a broadening diffluent upper-level jet crosses Oklahoma prior to
the upstream mid-level cyclone exiting the Four Corners into the 
southern High Plains on Friday morning. Surface cyclogenesis and 
strength of moisture flux convergence within confluent return 
moisture stream out of the Western Gulf across central OK will 
likely help to maintain a favorable environment for further 
upstream redevelopment across portions of central Oklahoma. The 
mid-level low is also expected to strengthen slightly with heights 
reaching 1-1.5 standard anomalies from bi- weekly means. Strong 
DPVA and steepening lapse rates from advection of EML across OK 
will allow for quick replenishment of unstable environment with 
1000-2000 J/kg of MUCAPE along the upstream environment of the 
older WAA induced convection for another bout of stronger 
thunderstorms by afternoon/early evening from west-central OK south
into the Permian Basin and perhaps through the Pecos River Valley 
with 1.25-1.75"/hr rates possible. Localized streak or two of 2-4" 
totals with isolated total of 5"+ through late evening into early 
overnight hours. 

Toward midday, an upstream kicker shortwave and upper-level jet
speed max rounds the base of the closed low and ejects into the
southern High Plains providing strong mid-level ascent forcing and
strengthening low level winds and therefore, moisture/instability 
flux. The stream of warm, moist Western Gulf air will continue to 
compile across central TX into the Red River Valley with total 
Pwats starting to exceed 1.75" nearing 2". Strong directional and
speed convergence will further expand/strengthen updrafts along 
the cold front/dry line, but also quickly advance eastward allowing
for strong scattered thunderstorms with 2"+/hr rates across western
into central TX. Though stronger moisture flux convergence will
allow for higher rates, the faster cell motions will likely limit
overall totals. Yet, scattered incidents of 2-4" in short-duration
is likely to result in scattered incidents of flash flooding, given
limited infiltration even in drier soil conditions/higher FFG environment.

00z guidance trends suggest a bit greater rainfall at the
beginning of the period toward northeast OK, a slightly higher 
alignment of higher QPF maxima across central to northeast OK, 
especially with the longer range CAM guidance. However, the general
consensus of QPF maxima also aligns nicely with the core of the 
highest FFG values in the region, as well. Given the tendency of 
the remaining Hi-Res CAMs to be biased toward the wetter solutions 
and alignment with the FFG max, a higher confidence Slight Risk 
remains in place, though if trends continue, an upgrade is not out 
of the question. Further south, the run to run trends continue to 
show a slow southward shift of QPF clusters supporting a small 
adjustment of the Slight Risk in that direction as well. 

...Pacific Northwest into Northwest California...
Only small localized adjustments were made to the old Day 3
Marginal Risk for the new Day 2 (24.12z-25.12z). The modest
Atmospheric River (AR) will push across the coastal and Cascade 
ranges of WA/OR early through the period and relatively quickly the
cold front/AR plume will slide southward with respect to the 
coastline into northwest CA by the end of the forecast period. 
Strong broad closed low over the northeast Pacific will result in 
strong height-falls nearly 2-2.5 standard anomalies from bi-weekly 
mean, which is fairly impressive as it is a normal time of year for
the arrival of AR/deep lows. The low's influence provides the 
strong draw of the moisture out of the central sub-tropical Pacific
with well over 1" total PWats into the coastal range and up to 
.75-1" through the Columbia Valley into central WA; all while 
values up to 1.5" remain offshore in the narrowing plume. Winds of
45-50kts through 850-700mb will result in peak IVT values of 
700-750 kg/m/s. However, while strong, the duration is going to be 
very limited given the strength of the height-falls and forward 
propagation of the cold front. QPF signals remain at the 2-4" 
range within the favored southwest facing orography with an 
occasional rate up to .5" though fleeting; all in line with a broad
Marginal Risk of excessive rainfall. 

Gallina


Day 3
Valid 12Z Sat Oct 25 2025 - 12Z Sun Oct 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHEAST TEXAS/WESTERN LOUISIANA...

...Southern Plains into Lower western Mississippi River...
At the start of forecast period (25.12z), the combined
shortwave/closed low energy will remain progressing eastward across
the Southern Plains with strong DPVA and solid diffluence
downstream as the upstream shortwave ridge is slower to budge,
slightly amplifying across the lower Ohio and eastern Mississippi
River Valley. As such, ongoing convective activity along the cold
front will continue intersect strong moisture flux and higher
theta-E air out of the Western Gulf. Even with the approaching
upper-low, the southeastern low level ridge has remained strong
with a tight gradient supporting this strong return flow through
east Texas. The confluence of the return flow and the western Gulf
jet will remain strong across eastern TX with 35-45kts of 850mb
flow and total PWat values of 1.75 to 2".

The warm conveyor belt and thunderstorms will press eastward 
through the Piney Woods while a strong TROWAL will continue to 
advect above average moisture along/back west into the developing 
comma head across OK into far southern KS. Instability will be 
limited further north to around 250-500 J/kg suggesting some 
scattered cells, but limited elevated cells will likely be limited 
in overall coverage. Yet, rainfall over the two prior days may 
saturate grounds and bring FFG values into a range of these cells.
As such have pulled the Marginal Risk of Excessive Rainfall across
much of eastern OK where there is supportive overlap of current day
1 & 2 forecast QPF and the TROWAL activity. 

While there is likely to be a progressive squall line with intense
rainfall rates tracking through eastern TX into LA through the 
morning period, generally aligned with the deeper warm conveyor 
belt, lingering surface to boundary layer moisture will be
reinforced by the Western Gulf LLJ pumping higher theta-E air
northward post-WCB but ahead of the front. Solid EML will provide
lapse rates to support increasingly unstable air northward across E
TX into the afternoon/evening with CAPE values of 1500-2000 J/kg
expected, though some guidance suggests 2000-3000 J/kg across the
Coastal Plain. As such, another round of strong thunderstorms is
expected across the recovering areas from the morning line across
SE TX into W LA. As such, broad areas of 3-6" 24hr totals with 
some suggestions to localized 8". There are hints of localized
training environments with the second round to support some of
these higher localized possible totals. All in all, the inherited
Slight Risk of Excessive Rainfall remains solid, though have backed
up the western edge and trimmed the southeast edge a bit, 
resulting in a more SSW to NNE oblong risk area across SE TX and 
much of western LA. If trends continue to tick upward, an upgrade 
in category is not out of the realm of possibility going forward 
into the Hi-Res CAM cycles. 

...Pacific Northwest...
The core of the broad long wave/deep cyclone remains anchored
across the Gulf of Alaska though the leading height-falls/ 
shortwave rotated through into the Interior Northwest leaving the
lingering cold front and sub-tropical moisture plume to slowly fade
across northwest California nearing San Francisco Bay with weak
onshore winds below 30kts. Its slower progression will allow for
some localized 1-3" totals along the NW California Ranges, but 
given it is over the boreal rain forest, it will likely be 
beneficial. However, as large scale cyclone broadens, mid to upper-
level zonal flow will promote onshore flow of modest moisture but 
also CAA aloft providing steeper lapse rates for widely scattered 
showers capable of quick bursts of heavy rainfall/small hail ahead 
of the next strong shortwave. This wave will bring strengthening 
winds, but with the moisture axis shunted south, IVT values will 
remain in the 300 kg/m/s range. This will bring another 1-3" totals
across the coastal range and some scattered 1-2" totals in the 
lower foothills of the Cascades, so given this and prior activity 
will hold onto the low-end Marginal Risk though have further 
trimmed out shadowed areas of the Willamette Valley. 

Gallina
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