FOUS30 KWBC 290802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Wed Apr 29 2026

Day 1
Valid 12Z Wed Apr 29 2026 - 12Z Thu Apr 30 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM CENTRAL AND
SOUTHEAST TEXAS TO THE CENTRAL GULF COAST...

The Marginal Risk area was maintained with very few changes. A
threat of isolated flash flooding from heavy rainfall is still
expected, largely due to an environment that will favor very high
instantaneous rain rates. Strong instability with highly anomalous
PWs (above the 99th percentile for late April) would support rain
rates in excess of 2 inches per hour. Hi-res guidance does, in
fact, show rain rates that high, particularly in far eastern
Texas, central Louisiana, and south-central Mississippi.

However, two key limiting factors may keep any higher rainfall
totals and flash flooding impacts relatively isolated. First, much
of the Marginal Risk area is in a severe to extreme drought with
1-hour flash flood guidance in the 3 to 4 inch range; so flash
flooding would tend to require high rain rates sustaining for
multiple hours or intersecting urban areas. Second, most hi-res
guidance indicates a steady progression to convective clusters and
lines with limited backbuilding or training, which would tend to
reduce the potential for sustained heavy rain for multiple hours.

We will continue to monitor for areas in which more concentrated
heavy rainfall may occur, given the overall environment. However,
confidence is not currently high enough to increase probabilities
in any specific area.

Lamers


Day 2
Valid 12Z Thu Apr 30 2026 - 12Z Fri May 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL TEXAS...

The risk areas for Thursday and Thursday Night were generally
maintained from previous outlooks with minimal changes, refining
for better consistency with the latest rainfall guidance.
Increasing mid-upper level height falls, due to a strong shortwave
pushing through northern Mexico, should lead to a low-level mass
field response with increasing south to southeast inflow across
southern and central Texas. In general, the arrival of the better
synoptic forcing should be later in the period, which should
concentrate the main heavy rain and flash flood threat into
Thursday Night across the region.

By Thursday Night, strong low-level convergence and frontogenesis
is expected near the nose of the developing low-level jet. This is
depicted consistently across model guidance, despite some
variability in the positioning. This will coincide with anomalous,
deep moisture with PWs of 1.5 to 1.8 inches (around the 99th
percentile for late April) and narrowing CAPE profiles with lower
equilibrium levels. This fits a conceptual model for low-topped,
convective rain bands that have a more efficient warm rain process,
and could train and backbuild along the strong convergence axis.
The result could be several hours of persistent heavy rainfall in a
region of Texas that is less affected by the broader drought
conditions across the region, and with much more achievable flash
flood guidance benchmarks (around 3.5 inches in 3 hours).

We are concerned that the overall setup could merit a further risk
upgrade, but that may be more likely to occur the following day
(12Z Friday to 12Z Saturday) as the convective rain bands may not
get organized until very late in the forecast period, especially
after 06Z Friday. Therefore, while the event will get underway on
Thursday Night, impacts would be more likely to be realized in the
following forecast period, and the risk was held at the Slight
level for now in Central Texas.

Lamers


Day 3
Valid 12Z Fri May 01 2026 - 12Z Sat May 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL AND
SOUTHEAST TEXAS AND THE CENTRAL GULF COAST...

Organized heavy rain bands may be ongoing at the start of the
forecast period (Friday morning) across Central Texas, described in
the Day 2 portion of this discussion. The Slight Risk area was
pulled back to the west to account for the possibility of ongoing
impacts; the rainfall may be split between the two forecast
periods, so the QPF for 12Z Friday to 12Z Saturday, viewed in
isolation, would tend to undersell the flash flood risk on Friday
morning in central Texas.

That was the main adjustment made to the outlook at this time. We
continue to see a strong signal for heavy rainfall from Texas into
the central Gulf Coast region. The rainfall forecast has increased
a bit with the major axis shifting south about 80 miles over the
past four forecast cycles. Models show a very strong low-level
convergence signal with a strong frontogenetic circulation shifting
east along the Gulf Coast during the period. This will be situated
in an environment with anomalously high PWs (above the 90th
percentile for late April; generally 1.5 to 1.8 inches) and narrow
CAPE profiles. The strong convergence should help focus efficient
convective rain bands and could lead to training of heavy rain
rates for multiple hours.

We will continue to monitor guidance trends for possible increases
in probabilities (and risk levels) if confidence grows in the
placement of the heaviest rainfall. Training rain bands in that
environment could easily lead to several inches of rain in just a
few hours. While much of the Slight Risk area is experiencing
drought conditions, that can be overcome for flash flooding impacts
if heavy rain rates are prolonged enough in a given location.
Therefore, the key to any increases in ERO probabilities would be
much greater confidence in placement of training rain bands. For
now, the Slight Risk highlights the general area where this is
possible, given available guidance and the overall parameter space.

Lamers
$$
d

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS30 KWBC 300806
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
406 AM EDT Thu Apr 30 2026

Day 1
Valid 12Z Thu Apr 30 2026 - 12Z Fri May 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL TEXAS...

A two part setup for heavy rainfall will materialize over the
Lower Mississippi Valley back into Southwest and Central TX during
the period. Weak mid-level perturbations will ripple out of the
Southern Plains into the Lower Mississippi Valley by late Thursday
morning, encountering a generally favorable airmass positioned
across central and southern LA into southern MS. Moisture
anomalies hovering between 2-3 deviations above normal will reside
within that corridor between Baton Rouge to the southeastern corner
of LA with a general instability maximum located over the same
area. A round of convection will develop across the southern half
of the state with the latest CAMs all in agreement on the heaviest
rainfall occurring along the I-10 corridor down to around the New
Orleans metro, an area more viable for flash flooding due to the
urban footprint. Rainfall rates between 2-3"/hr at peak intensity
are anticipated in the forecast environment located over southern
LA, more than capable for localized flash flood concerns especially
when you couple with some of the recent priming from rainfall that
occurred the past 24hrs. 00z HREF neighborhood probs for >3" are
running hot between 40-60% located directly over the New Orleans
metro and neighboring areas around Lake Pontchartrain. The overlap
of CAMs signaling heavy rainfall in this vicinity prompted an
addition of a MRGL risk for the region which generally extends back
along I-10/12, aligning with the position of a quasi-stationary
front in the region.

Further west into west TX and the Southwestern U.S, a more
formidable large scale synoptic evolution will enhance ascent over
a broad area of the Southwest US into the southwest portions of TX
leading to a rapid development of convective initiation that will
lead to scattered flash flood prospects in wake of their
development. A strong mid-level shortwave trough will eject out of
Chihuahua with sights on the southwest reaches of TX by Friday
evening. A moist, unstable airmass will preclude the trough
approach with an amplifying mid-level evolution allowing for a
strengthening nocturnal LLJ developing across west-central TX down
the Rio Grande. At the surface, a weak quasi-stationary front will
be positioned across Central TX which will be a key component for
maximizing low-level convergence in the areas it resides. Models
are consistent in the development of convection across southwest TX
by late-afternoon due to the arrival of the mid-level ascent and
diurnal instability coupling that will develop during peak heating.
As we begin to integrate the LLJ into the pattern, this, combined
with the increased forcing and shear provided by the trough
approach will enhance a broad convective initiation with the
highest coverage likely to ensue over the terrain of southwest TX
over into the Edwards Plateau and neighboring Hill Country. 00z
HREF neighborhood probs for >2" are pretty robust (50-90%) over the
entire area referenced with the highest probs centered over the
Lower Trans Pecos into the neighboring Edwards Plateau and Hill
Country along and north of I-10. The evolution of the upper pattern
inspires a prolonged nocturnal convective regime that will promote
hours of heavy rainfall prospects with some places likely to breach
3" where cell training and/or repeated cells occur. This has been
very consistent within the means of the QPF distribution the last
few days with a solid output promoted via the ML, which has been
rock steady on its presentation the last several cycles.

The SLGT risk inherited was maintained, but shifted a bit south to
account for trends in heavier QPF orientation of the CAMs, trending
closer to the ML axis of heaviest precip from the past few days.
The overlap of the CAMs and ML provides higher confidence in the
setup, thus expectations for scattered flash flood instances are
warranted.

Kleebauer


Day 2
Valid 12Z Fri May 01 2026 - 12Z Sat May 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN CENTRAL AND
SOUTHEAST TEXAS AND THE CENTRAL GULF COAST...

A prolific upper level evolution coupled with a broad axis of
formidable moisture anomalies and instability will stand to produce
a widespread axis of heavy rainfall across the Southern Plains in
TX over through the Lower Mississippi Valley on Friday into
Saturday morning. At the surface, a slow-moving quasi-stationary
front will orient itself across south-central TX down to around the
Gulf coast with a wave of low pressure riding along the boundary
during the forecast period. PWAT's will run between the 95-99th
percentile (NAEFS climatology) across Hill Country over into
Southeast TX and neighboring LA. These PWATs (1.7-2.1") are
notable for producing more efficient warm rain processes, noted
very well by the warm cloud layer depths presented in various point
soundings in the 00z deterministic suite. Thunderstorms will be
ongoing the night prior as large scale ascent is maximized with the
approach of a strong mid-level shortwave ejecting out of Chihuahua
with a well-defined axis of diffluence located downstream of the
mean trough. These storms will continue through the morning as the
nocturnal LLJ will maintain some of its muster through the evolving
synoptic scale process leading to enhanced convergence over Hill
Country, eventually migrating eastward into Southeast TX by the
late-morning and afternoon.

The primary shortwave and attendant surface reflection will quickly
advance eastward with the aid of a digging mean trough shoving
through the Central US, acting a bit as a "kicker" in the overall
upper level synopsis. This will provide a period of enhancement as
cells re-ignite across Southeast TX and LA, especially in the confines
of the quasi-stationary front positioned over the southeast
portion of TX. Where this boundary bisects will be important in the
location of convective development and the prospects of training
as the mean flow will run relatively parallel to the boundary which
typically promotes better training episodes and/or repeated rounds
of convection in a given area. Rainfall rates are likely to be
between 1-3"/hr in the heavier cells, and multiple rounds of these
rates would easily prompt localized totals greater than 3" with a
potential for greater than 5" as inferred by the 90th and 95th
percentile of the 01z NBM 24hr QPF prob fields. The 00z HREF
currently only covers the first half of the period, but it is
notable the probs for >3" are very high (50-80%) for a large
portion of Central TX, including the I-35 corridor between
Austin/San Antonio and along I-10 as you move east between San
Antonio and the Houston metro. Heaviest rainfall for these areas
will likely materialize for southeast TX after 18z Friday with an
ongoing heavy rain threat well into the evening before the large
scale pattern shunts east with dry air advection occurring in wake
of the shortwave trough passage.

This setup is conducive for more widespread flash flood prospects
with even some locally significant flood impacts for areas hit the
hardest. The current setup likely puts places along I-10 from San
Antonio over to Houston, especially the northern suburbs and exurbs
in the cross-hairs with the northern extension up towards the Piney
Woods area. This is the area with an areal average QPF between 2-3"
and local maxima likely to exceed 5" in spots. This axis of heavier
rain will expand eastward along I-10 into LA by late-Friday into
early Saturday morning putting places from Baton Rouge over into
far east TX as the secondary area of interest. A high-end SLGT is
currently forecast for this entire corridor referenced above with a
potential for a targeted upgrade as we move closer to the period as
CAMs come into better focus and we monitor trends in the expected
upper evolution. This scenario has a history of a trail of flash
flood warnings stretching hundreds of miles, so this is a period to
watch very closely.

Kleebauer


Day 3
Valid 12Z Sat May 02 2026 - 12Z Sun May 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST U.S...

Progressive upper pattern will lead to a fast-moving convective
episode across the Southeast with the primary focus likely
occurring over the Florida Panhandle up through southern GA and the
Low Country of SC. The setup promotes a relatively favorable
environment suitable for heavy rainfall with the stronger cell
cores capable of producing rainfall rates between 1-2"/hr. Regional
FFG's remain elevated across this portion of the CONUS, however
there's enough of a signal for the potential of some urban flooding
across the aforementioned areas with the best opportunities in
those larger urban footprints in FL and GA. Deterministic outputs
range from scattered 1" totals to more bullish 2-3" areal averages,
all pending on the propagation speed and magnitude of the
anticipated line of convection moving out of AL. Maintained general
continuity in the MRGL risk from the previous forecast, but removed
the areas near Tampa as rates likely remain insufficient for
anything appreciable to trigger flash flooding.

Kleebauer
$$

--- Scorpio BBS
* Origin: (618:250/6)

FOUS30 KWBC 020817
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Sat May 2 2026

Day 1
Valid 12Z Sat May 02 2026 - 12Z Sun May 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST U.S....

A progressive upper trough is expected to help focus and sustain
additional showers and thunderstorms across portions of northern
Florida into southeast Georgia today into day into the early
morning hours of Sunday. The atmospheric setup still promotes a
relatively favorable environment suitable for localized heavy
rainfall. Flash Flood Guidance values may come down just a bit
given the rainfall moving across the region prior to the start of
the Day 1 period at 12/02 but the expectation is that the FFG
values should not come down significantly. As a result...even if rainfall
rates on the order of 1- to 2-inch per hour occurs the impact may
only prove to be short-lived run off problems or ponding in
regions of poor drainage and/or urban areas.

Bann


Day 2
Valid 12Z Sun May 03 2026 - 12Z Mon May 04 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THEM SOUTHEAST FLORIDA PENINSULA ON SUNDAY...

Maintained the Marginal Risk area for a portion of the southeastern
Florida peninsula on Sunday. The area was along and south of a
southward advancing front where the airmass was characterized by
CAPE on the order of 500 to 1000 J per kg and precipitable water
values are forecast to be around 1.5 inches. Given the recent
dry spell, it appears that the greatest risk of excessive rainfall
will be in urban areas where the surface is largely impervious to
water. With the front progressing farther south with each model
run...the amount of territory at risk keeps shrinking and there may
be little to no need for an excessive rainfall area shortly.

Bann


Day 3
Valid 12Z Mon May 04 2026 - 12Z Tue May 05 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann
$$

--- ScorpioBBS/QWK v0.32a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS30 KWBC 180800
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 AM EDT Mon May 18 2026

Day 1
Valid 12Z Mon May 18 2026 - 12Z Tue May 19 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF MISSOURI...

In coordination with SGF/Springfield, MO; EAX/Pleasant Hill, MO;
and LSX/St Louis, MO forecast offices, a Moderate Risk upgrade was
introduced with this update. Much of the CAMs guidance has made a
rather drastic shift south of the current line of convection
tracking across Kansas and Missouri. There is reasonably good
agreement that the line of storms will move into west-central
Missouri over the next few hours, then stall out. Corfidi vectors
across this part of Missouri essentially drop to light and
variable over the next few hours. This combined with an influx of
atmospheric moisture, with PWATs increasing up to 1.75 inches, will
give the storms additional "juice" to work with in the form of
heavy rain. Once the storms stall, the 40 kt southwesterly LLJ will
allow for efficient backbuilding of storms along a narrow axis. An
ensemble of models highlight the new Moderate Risk area for the
most likely axis where the backbuilding will be most efficient. The
result is several models highlighting extreme rainfall amounts,
with the RRFS the highest at over 9 inches. On average, most peak
the heaviest rainfall amounts between 5 and 7 inches. Despite dry
soils in the area, this amount of rain over a 6 hour period,
combined with topographic effects, will lead to numerous instances
of flash flooding, resulting in the Moderate Risk upgrade.

The Moderate Risk is a double upgrade (from Marginal) in all areas
from the inherited forecast, with the southern sliver of the
Moderate perhaps a triple upgrade. This extreme shift in the
forecast unfortunately has much to do with the CAMs struggling to
resolve rapidly evolving convective patterns well. The heavy rain
is likely to begin in the Moderate Risk area over the next few
hours, with the early period (between 12-18Z/7am to 1pm CDT) being
the period with the most likely chances of seeing multiple inch per
hour rates, and the Moderate Risk getting the most rainfall of the
day. There should be a break in the rainfall during the evening and
most of the overnight, before a second much more progressive line
of storms possibly impacts this same area for a much shorter time
in the 09Z to 12Z time frame tonight. This second line of storms
will impact the hard-hit areas from northeast Kansas to southwest
Iowa during the late afternoon and evening before shifting
southeast across Missouri. Some training will also be possible here
before the storms organize, and given the more favorable hydrology,
the higher-end Slight remains in place from Kansas City north and
west through the southeastern corner of Nebraska.

Elsewhere, the Slight Risk was also expanded well to the east into
western Indiana, where a separate area of training thunderstorms is
also coming into better agreement in the CAMs guidance. These
storms are also most likely to impact the area from about
Evansville/Terre Haute north and east to the Indianapolis metro.
While amounts won't be nearly as high as areas in the Moderate Risk
further west, the proclivity of training convection here should
result in widespread 1-3 inch rainfall amounts, requiring the
Slight Risk upgrade. Confidence is decreasing into southern
Minnesota for significant heavy rain, instead favoring either fast
moving storms or a more long-duration light rain. Thus, the Slight
Risk was trimmed south out of the Twin Cities metro area.

Wegman


Day 2
Valid 12Z Tue May 19 2026 - 12Z Wed May 20 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE SOUTHERN
PLAINS TO THE LOWER OHIO VALLEY...

Relatively few changes were needed for the Day 2 outlook as
compared to the changes to the Day 1/Monday period. As the day 2
period enters the CAMs coverage period, there is an unsurprising
spread in the guidance as to how the convection will evolve,
especially moving just beyond the CAMs period Tuesday night. An
axis of heavier rainfall tracking along with the low level jet,
will persist from south Texas northeast into the Ohio Valley.
Depending on how the rainfall develops this evening in the lower
Ohio Valley, and where the areas of heaviest rainfall move in the
guidance, a few Slight Risk upgrades may be needed with future
updates. Should the storms D1 in Indiana outperform, then the
additional rainfall, while far from major, may be able to team up
with the newly favorable hydrology to result in more widely
scattered instances of flash flooding. The greater threat for a
Slight Risk upgrade will be in central Texas, where a maximum of
rainfall extends across the Texas Triangle (the area between the
Metroplex, San Antonio, and Houston). Given the urban concerns,
should there be better agreement in the CAMs as they move to
resolve the entire Day 2 period later today, a Slight Risk upgrade
may also be needed there.

Wegman


Day 3
Valid 12Z Wed May 20 2026 - 12Z Thu May 21 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
THE TEXAS HILL COUNTRY...

The heavy rain footprint not just across Texas but all across the
Marginal Risk area is a real mess by the Day 3/Wednesday period.
It's likely that the final flooding forecast will be determined by
the behaviors of prior convective regions both across Texas and
northeast to the mid-Appalachians. Thus, there remains a large
Marginal Risk from the southern Plains to the mid-Appalachians. The
inherited Slight Risk across west Texas was shrunk and shifted
south with this update. Higher rainfall totals are now expected in
the Texas Hill Country (but given the fickle nature of convection,
this is likely to change a lot over the coming days). This area is
particularly flood-prone should heavy rain occur over small and
topographically steep river channels common in the Texas Hill
Country. Thus, the Slight Risk highlights this higher flooding
risk, even though the heavy rainfall footprint in this area remains
highly uncertain.

Further east, an additional heavy rain area in the ensembles is
noted from east Texas, north of Houston east into northern
Louisiana. This area is relatively dry with no recent heavy
rainfall events, though that could change in some areas after the
Day 2/Tuesday period. The heaviest rainfall looks to occur over the
Piney Woods, and relatively sparsely populated areas of east Texas
and northern Louisiana, so for now, the Marginal Risk covers the
flooding threat, but a Slight may be needed if the heavy rainfall
shifts into urban areas such as Houston, or if the rainfall
forecast increases further in these lesser populated areas. The
moisture and instability plume will extend northeast from there,
where training storms are possible at times through the Tennessee
Valley and into the mountains of West Virginia. Given low FFGs and
the flood prone nature of the valleys of WV, the Marginal Risk was
expanded there to cover that potential flooding threat.

Wegman
$$

--- Scorpio BBS
* Origin: (618:250/6)