FOUS30 KWBC 232030
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
430 PM EDT Thu Oct 23 2025
Day 1
Valid 16Z Thu Oct 23 2025 - 12Z Fri Oct 24 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS AND THE INTERMOUNTAIN WEST...
16Z Update...
A vigorous closed low and associated upper-level trough will be
traversing the Four Corners region today. Relatively strong dynamic
forcing and related DPVA coupled with orographics and modest
instability will favor scattered to locally broken coverage of
showers and thunderstorms. The main axis of relatively heavier
rainfall potential should be across far northern AZ, south-central
to southeast UT and into western CO. PWs are only slightly
anomalous, with MLCAPE forecast to increase to as much as 500 to
1000 J/kg with the diurnal heating cycle. Given the current
activity noted over southern UT, some increase in convective
coverage should tend to occur over the next several hours. Spotty
rainfall rates with the stronger storms may approach 1 inch/hour,
and some localized storm total amounts through tonight may reach
1.5 to 2 inches as the core of the upper low/trough arrives. This
may yield some isolated flash flooding concerns and primary to the
more sensitive slot canyons along with the normally dry washes and
burn scar locations. A Marginal Risk of excessive rainfall has been
introduced for this area as a result to account for this threat.
Elsewhere, the Marginal Risk area currently depicted over the
southern Plains remains largely on track from a forecast
perspective, with only modest tweaks made to it to account for the
12Z HREF/06Z REFS suites of guidance and the 06Z EC-AIFS solution.
Convection is still expected to initiate later today and especially
tonight across areas of the southern Plains and upstream
forcing/divergence aloft begins to overlap with the southerly
return flow of moisture and instability up across the Rio Grande
Valley and toward the Red River Valley.
Orrison
Previous Discussion...
...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...
2030Z Update...
A very active day for convection is still expected for especially
Friday afternoon through Saturday morning across the southern
Plains as strong height falls associated with the upstream
Southwest U.S. closed low/trough ejects out into the High Plains
along with a cold front. A substantial pool of moisture and
instability will be in place across much of central and northern TX
as the nose of a 30 to 40+ kts southerly low-level jet rides up
into the Red River Valley region. Organized convection should
develop initially across areas of west TX and advance east by later
in the afternoon/evening which will be capable of producing high
rainfall rates upwards of 2 inches/hour with the stronger cells.
However, the organized nature of the convection suggests some
forward propagation potential that could mitigate the overall storm
total amounts. In fact, most of the guidance supports a fairly
well-organized MCS evolution into southeast TX and near the
northwest Gulf Coast region by early Saturday morning.
Strong warm air advection and dynamic forcing meanwhile should=20
help foster elevated convection with locally heavy rainfall rates=20
across OK and some portions of southern KS. The Slight Risk area is
largely maintained except with some shifting of the north/south=20
axis a bit farther back to the west to account for where the axis=20
of better instability should be along with corridors of convective=20 initiation. This is also in better alignment with a consensus of=20
the 12Z HREF/06Z REFS guidance. Scattered areas of flash flooding,=20 especially for the more urbanized locations, will be a concern.
No changes to the previous forecast thinking or the Marginal Risk
area were made for the atmospheric river activity arriving across
the Pacific Northwest and northwest CA.
Orrison
Previous discussion...
...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 SOUTHEAST
TEXAS THROUGH FAR SOUTHERN ARKANSAS AND WESTERN LOUISIANA...
2030Z Update...
Multiple rounds of heavy showers and thunderstorms are expected to
impact the broader northwest Gulf Coast region this period, with
one initial axis of convection likely ongoing Saturday morning=20
across areas of southeast to east-central TX and advancing across=20
western LA and possibly southern AR. This will be the carryover of=20
organized convection from the day 2 period which should be=20
interacting at least initially with a 40+ kt southerly low-level=20
jet off the western Gulf. PWs of 1.75+ inches and MUCAPE values=20
locally of 2000+ J/kg will support high rainfall rates potentially=20
exceeding 2 inches/hour with the stronger storms.=20
This initial round of convection should advance downstream into=20
portions of the Lower MS Valley and gradually weaken given=20
downstream boundary layer stabilization on the cool side of a=20
front draped across the region. However, the arrival of an upper-
level jet streak in the subtropical stream combined with the=20
interaction with the southern stream closed low/trough axis=20
crossing the southern Plains will favor a renewed convective=20
outbreak across areas of eastern TX through portions of western and
southern LA Saturday afternoon through early Sunday. The details=20
of this will be predicated on how the mesoscale environment is=20
manipulated by the early-day convective activity, but generally the
expectation is for there to be a rather strong and sustained=20
poleward advance of moisture and instability off the western Gulf=20
working in tandem with stronger deeper layer ascent and shear for=20
organized convection with high rainfall rates. While antecedent=20
conditions are quite dry, the concern for multiple rounds of=20
convection which combined may yield some 3 to 5+ inch totals, will=20
probably be enough to support a threat for scattered areas of flash
flooding. The more sensitive urbanized locations will be at=20
greatest risk for impacts. For this update, the Slight Risk area=20
has been largely kept intact with some tweaking based on the 12Z=20
suite of hires model CAMs.
For the Pacific Northwest and northwest CA, multiple surges of
moisture transport into the coastal ranges will continue for the
period as atmospheric river activity continues. Locally a few
additional inches of rain will be possible for the windward slopes
of the terrain, but given the early-season and relatively modest
nature of this atmospheric river activity, any flooding concerns
are expected to be isolated at best. Therefore, the Marginal Risk
area is maintained with no changes for this update cycle.
Orrison
Previous discussion...
...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
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!-fqRGaEM08B0WOCVEy2be4eL2Eu5oZ0rwFyBbgmlTWIV= FJgSHRz3Ijl4RVQejO-OXVYy253jUAxY9FolxI6pqD66kOU$=20
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!-fqRGaEM08B0WOCVEy2be4eL2Eu5oZ0rwFyBbgmlTWIV= FJgSHRz3Ijl4RVQejO-OXVYy253jUAxY9FolxI6p2IVCwuQ$=20
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!-fqRGaEM08B0WOCVEy2be4eL2Eu5oZ0rwFyBbgmlTWIV= FJgSHRz3Ijl4RVQejO-OXVYy253jUAxY9FolxI6p7fOkwCc$=20
=3D =3D =3D
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