Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
933 PM EDT Thu Oct 29 2026
Day 1
Valid 0130Z Fri Oct 30 2026 - 12Z Fri Oct 30 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WEST AND CENTRAL TEXAS AND SOUTHEASTERN NEW MEXICO...
0130Z Update...
Issued special ERO to better match convective trends in portions of
the Southwest in light of the full suite of upper air observation
for 30/00Z.
...Texas & New Mexico...
Confidence remains high in a heavy rainfall event unfolding through
tonight across portions of Texas and New Mexico as a mid- level
disturbance previously associated with Vance moves into the region
this evening. Southeasterly low-level flow will prime the
atmosphere ahead of the system, increasing PWATs to 1.5-2 inches
across much of Texas, which is well above normal for this time of
year. 00Z soundings showed precipitable water values of 1.35 inches
at Midland TX and 1.02 inches at El Paso. Effective bulk shear
remained near 30 kts, which should continue to organize
convection while a southern stream jet lifts across the southern
Plains, placing Texas under the favorable right entrance region
with enhanced upper level divergence. This combination of
ingredients should result in a prolonged period of large scale
ascent across the region that should support numerous showers and
thunderstorms across Texas and southern New Mexico. MU CAPE is
forecast to remain near 500-1000 J/kg across in and near portions
of the Slight Risk area.
The available ingredients support the concept of hourly rain
amounts to 2", which could occur with cell mergers, cell training,
or where a random mesocyclone occurs. A combination of the 18Z
REFS/HREF indicates that local totals of 5" are possible very near
the TX/MX border. The highest event totals should focus on the
southern side of the Slight Risk area where the highest moisture
values are expected to pool and will likely produce a high-end
Slight Risk scenario. The more widespread risk of flooding will
come from the prolonged nature of this event, with moderate to
locally heavy rain expected across much of West and Central Texas
and into southeastern New Mexico into Friday morning. Some of the
eastern portion of the risk areas has minimal, if any, top soil,
which would aid the flash flooding potential due to increased
runoff. The risk areas from this issuance strongly resemble
continuity.
MO/KS/IA/NE irregular border junction...
A warm front at 850 hPa lifts northward, with a pool of instability
in its wake. 12Z models suggested that precipitable water values
would rise to values around 1.25" or so...and the 30/00Z sounding
at Topeka observed a value of 1.20 inches and 2000 J per kg of
Cape. The 18Z HREF continued to show a backbuilding convective
scenario unfolding from 04z onward, and had probabilities of 3"+
maximize in a point near the NE/MO/KS border junction. There's
enough factors to maintain the Marginal Risk area issued earlier
today. Flash flooding would be most likely in urban areas, where
1.5" in an hour is possible.
Bann
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
933 PM EDT Thu Oct 29 2026
Day 2
Valid 12Z Fri Oct 30 2026 - 12Z Sat Oct 31 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST...
...Southwest...
Broad troughing will develop over the West with embedded shortwaves
moving across portions of the area on Friday. Meanwhile, a strong
southern stream jet will approach Baja California, placing Arizona
under the favorable left exit region with enhanced upper level
divergence Friday afternoon. Southerly low-level flow will direct
Pacific moisture into the area as well, bringing PWATs up to 1-1.4
inches across the southern half of Arizona (2-3 standard deviations
above normal), more typical of values during their summer monsoon.
This warm, moist air mass will also increase instability, with
MUCAPE values forecast to reach 1000 J/kg across much of southern
Arizona. With favorable conditions throughout the atmospheric
column, scattered to widespread convection is expected to develop
with the passing of the upper shortwave Friday afternoon and
evening.
The available ingredients support 2" an hour amounts. Given the
sensitive terrain in the area, urban areas, dry washes/arroyos,
burn scars, slot/box canyons, and relatively moist soils, this
setup will likely produce scattered instances of flash flooding. A
broader Marginal Risk area surrounds the Slight and includes
portions of the Great Basin and New Mexico where there will also be
scattered convection, but the flash flood risk will be more
isolated as rainfall rates are less likely to exceed FFGs.
...Southern/Central Plains & Midwest...
Widespread moderate to locally heavy rainfall will continue into
Friday morning across portions of Texas and Oklahoma as a shortwave
moves northeast across the southern and central Plains and
interacts with a returning front. Any lingering convective
activity from Thursday night/early Friday morning could be ongoing
in and near IA at the start of the period. The southern stream jet
should shift north, maintaining favorable conditions for convection
through Friday afternoon. Anomalous moisture will remain in place
across the southern Plains and precipitable water values of 1.25"+
broaden in scale across portions of the Midwest/Corn Belt. Cloud
cover could limit instability. With favorable dynamics, there
should still be enough support for locally heavy rainfall, up to
1.5" in an hour, which would be most problematic in urban areas.
The flood risk will mainly be a function of duration, with rainfall
impacts compounding from Thursday into Friday. The highest risk of
flash flooding is more likely materialize over portions of
Texas/Oklahoma and in/near IA which have the highest potential for
heavy rains. The flash flood risk will be relatively low, but
enough for isolated to widely scattered instances of flash
flooding and a Marginal Risk of excessive rainfall.
Roth
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
933 PM EDT Thu Oct 29 2026
Day 3
Valid 12Z Sat Oct 31 2026 - 12Z Sun Nov 01 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN AND NEAR
PORTIONS OF ARIZONA...
...Southwest...
A deep layer trough/low will move over the West Coast on Saturday,
sweeping up a potent Pacific shortwave and directing it into the
Southwest by Saturday evening. This system will be accompanied by
an amplified southern stream jet that will enhance divergence over
portions of the Southwest Saturday evening into Saturday night.
Ahead of the system, a stream of subtropical moisture will increase
PWATs above 1 inch across southern California, southern Nevada,
and Arizona, and even above 1.5 inches for portions of central and
southern Arizona. These values are highly anomalous (4-6 standard
deviations above normal) for this time of year and are more
representative of moderately active monsoon days. This should
support widespread precipitation as the shortwave moves onshore.
CAPE will be the limiting factor in this scenario, with cloud
cover keeping MUCAPE to only a few hundred J/kg over portions of
central and southern Arizona with less CAPE elsewhere. Given this
setup, locally heavy rainfall will be possible across much of the
Southwest, but high rainfall rates may be limited outside of
favorable locations in Arizona where there is a Slight Risk of
excessive rainfall. Portions of Arizona will also see heavy
rainfall on Friday, which may increase the sensitivity to flash
flooding with additional rainfall through Saturday night. This
event will continue into Sunday, and conditions are expected to
become more conducive for a widespread heavy rainfall event across
the Southwest.
...Central Gulf Coast and Lower Mississippi Valley...
There is potential for locally heavy rainfall somewhere between
the Mid-South and central Gulf Coast on Saturday. Over the Gulf
Coast, an amplified jet will create upper level divergence. Low-
level confluence is seen in the guidance and the precipitable water
values are plentiful, with values of 1.75-2" forecast. Over 1000
J/kg of MU/ML CAPE is expected/forecast. The problem will be that
the main shortwave triggering convection will be strongest to the
north in the Midwest and Ohio Valley, which is leading to lower
values of effective bulk shear, roughly 20 kts near the Gulf Coast,
implying a pulse character to convection that forms. Soils from
the Mid- Mississippi Valley to the Gulf Coast are anomalously dry,
resulting in high FFGs. Most of the area would need over 3 inches
of rainfall to cause flash flooding, which is approached in the 12z
GFS/UKMET and 00z ECMWF guidance. The ingredients support hourly
rain amounts to 2.5", likely from cell mergers or wherever random
training manages to occur, which would be more than sufficient for
issues in urban areas. While there remains some spread on
location, enough ingredients appear to be there for isolated to
widely scattered flash flooding. A Marginal Risk has been
introduced on this cycle.
...Florida Gold Coast...
An approaching shortwave aloft interacts with a moist, easterly
low- level flow off of the Gulf Stream. Precipitable water values
rise to 1.75-2". ML CAPE rises to 2000 J/kg or so. With the flow
being antiparallel with height, effective bulk shear should be
sufficient for thunderstorm organization, which could organize into
short, efficient training bands for 1-2 hours at a time. Hourly
rain amounts to 3" are possible, given the ingredients. Isolated
flash flooding is possible within the South Florida urban
landscape, so raised a Marginal Risk for this region.
Roth
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
933 PM EDT Thu Oct 29 2026
Day 4 and Day 5
Valid 12Z Sun Nov 01 2026 - 12Z Tue Nov 03 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST SUNDAY...
...Southwest to Plains/Mississippi Valley...
21Z Update...
A set up which has the potential to result in a high impact
rainfall set up remains in the realm of possibilities on Sunday
based on the latest deterministic and ensemble runs. The threat is
tied to a combination enhanced moisture transport into a region
that has been rather wet still...with some enhancement of the
amounts in region where the moisture interacts with the terrain.
The placement varied a bit but the overall picture is similar and
covered by the previously-issued outlook.]
Bann
Previous Excessive Rainfall Discussion...
A potentially high impact setup remains possible over the
Southwest on Sunday. A deep longwave upper trough will be located
over the West Coast early Sunday, while an anomalously far south
southern stream shortwave tracks toward/into southern
California/northern Mexico while carrying a surface low pressure
system, with these features merging later Sunday. The combining
features will bring strong forcing to the Southwest, including the
right entrance region of the upper jet. Moisture-wise, IVT
anomalies start to max out (for this time of year) in southern
Arizona and vicinity Sunday per the NAEFS Ensemble Situational
Awareness Tables, as strong and deep level Pacific moisture takes
aim at the region. Widespread moisture and cloud cover may limit
instability a bit, but at least a modest level of instability is
forecast to develop, given the strong troughing aloft should
steepen lapse rates. Soil moisture remains rather wet in most areas
due to heavy rain over the past days and weeks, increasing the
flooding threat hydrologically. All this, plus potential terrain
enhancements to rainfall, yields what is considered a higher-end
Slight Risk across the Southwest on Sunday. Moderate Risk level
impacts are possible and this potential will continue to be
monitored in future forecasts. A broader Marginal Risk expands west
through southern California and east across much of New Mexico.
The deep upper trough is forecast to track east across the
Intermountain West on Sunday night and Monday, with the southern
stream shortwave enhancing flow as it tracks northeast through the
eastern side of the broader trough. A strong southerly low level
jet will set up across the Plains Sunday night (tail end of Day 4)
and Monday ahead of a cold front anchored by a strengthening
surface low. Some instability will be pulled all the way north
across the Plains/Mississippi Valley toward the Upper Midwest,
allowing for some heavy rainfall rates. Will show a broad Marginal
Risk for this convective activity as a starting point for the Day 5
outlook. Thunderstorms look to have lower rain rates farther north
where there could be slower movement of convection, while higher
rates are possible farther south but could be more progressively
moving. Additionally, antecedent conditions are drier east of the
south-central High Plains for uncertainty in the impacts of heavy
rain. Do expect there could be a corridor of heavy rainfall that
could overcome drier soil conditions for flooding potential, for a
potential embedded Slight Risk in future issuances, but the
positioning is uncertain at this point.
...Florida...
21Z Update...
Few changes needed.
Bann
Previous Excessive Rainfall Discussion...
Shortwave energy spilling into Florida on Sunday and Monday could
promote increased convective coverage. PWs should be 1.5-2 standard
deviations above average while global models show MUCAPE reaching
around 1500 J/kg at times. While much/all of Florida could see
scattered thunderstorms with locally heavy rain, will show Marginal
Risks for the east coast in particular, because of easterly low
level flow for increased convergence, and the urban centers that
are more sensitive to heavy rain. Sunday looks to be the primary
day for a flash flooding threat, but the AI models in particular
maintain some higher rain totals into Monday, so kept the Marginal
going through Day 5 as well.
Tate
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
933 PM EDT Thu Oct 29 2026
Day 4 and Day 5
Valid 12Z Sun Nov 01 2026 - 12Z Tue Nov 03 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST SUNDAY...
...Southwest to Plains/Mississippi Valley...
21Z Update...
A set up which has the potential to result in a high impact
rainfall set up remains in the realm of possibilities on Sunday
based on the latest deterministic and ensemble runs. The threat is
tied to a combination enhanced moisture transport into a region
that has been rather wet still...with some enhancement of the
amounts in region where the moisture interacts with the terrain.
The placement varied a bit but the overall picture is similar and
covered by the previously-issued outlook.]
Bann
Previous Excessive Rainfall Discussion...
A potentially high impact setup remains possible over the
Southwest on Sunday. A deep longwave upper trough will be located
over the West Coast early Sunday, while an anomalously far south
southern stream shortwave tracks toward/into southern
California/northern Mexico while carrying a surface low pressure
system, with these features merging later Sunday. The combining
features will bring strong forcing to the Southwest, including the
right entrance region of the upper jet. Moisture-wise, IVT
anomalies start to max out (for this time of year) in southern
Arizona and vicinity Sunday per the NAEFS Ensemble Situational
Awareness Tables, as strong and deep level Pacific moisture takes
aim at the region. Widespread moisture and cloud cover may limit
instability a bit, but at least a modest level of instability is
forecast to develop, given the strong troughing aloft should
steepen lapse rates. Soil moisture remains rather wet in most areas
due to heavy rain over the past days and weeks, increasing the
flooding threat hydrologically. All this, plus potential terrain
enhancements to rainfall, yields what is considered a higher-end
Slight Risk across the Southwest on Sunday. Moderate Risk level
impacts are possible and this potential will continue to be
monitored in future forecasts. A broader Marginal Risk expands west
through southern California and east across much of New Mexico.
The deep upper trough is forecast to track east across the
Intermountain West on Sunday night and Monday, with the southern
stream shortwave enhancing flow as it tracks northeast through the
eastern side of the broader trough. A strong southerly low level
jet will set up across the Plains Sunday night (tail end of Day 4)
and Monday ahead of a cold front anchored by a strengthening
surface low. Some instability will be pulled all the way north
across the Plains/Mississippi Valley toward the Upper Midwest,
allowing for some heavy rainfall rates. Will show a broad Marginal
Risk for this convective activity as a starting point for the Day 5
outlook. Thunderstorms look to have lower rain rates farther north
where there could be slower movement of convection, while higher
rates are possible farther south but could be more progressively
moving. Additionally, antecedent conditions are drier east of the
south-central High Plains for uncertainty in the impacts of heavy
rain. Do expect there could be a corridor of heavy rainfall that
could overcome drier soil conditions for flooding potential, for a
potential embedded Slight Risk in future issuances, but the
positioning is uncertain at this point.
...Florida...
21Z Update...
Few changes needed.
Bann
Previous Excessive Rainfall Discussion...
Shortwave energy spilling into Florida on Sunday and Monday could
promote increased convective coverage. PWs should be 1.5-2 standard
deviations above average while global models show MUCAPE reaching
around 1500 J/kg at times. While much/all of Florida could see
scattered thunderstorms with locally heavy rain, will show Marginal
Risks for the east coast in particular, because of easterly low
level flow for increased convergence, and the urban centers that
are more sensitive to heavy rain. Sunday looks to be the primary
day for a flash flooding threat, but the AI models in particular
maintain some higher rain totals into Monday, so kept the Marginal
going through Day 5 as well.
Tate
