FOUS30 KWBC 210757
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Tue Apr 21 2026

Day 1
Valid 12Z Tue Apr 21 2026 - 12Z Wed Apr 22 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
CALIFORNIA AND TEXAS...

...California...

A cutoff large upper level low moving into California this morning
will continue to spread low-elevation rain and high elevation snow
into much of the West Coast states through tonight. Southwesterly
onshore flow ahead of this low is driving a plume of rainfall
northward up the coast. Some instability will allow for convective
elements to support cells with heavier rainfall within the broader
rain plume. This instability may allow the heavier rains to impact
urban areas such as San Francisco, Sacramento on up towards
Seattle. In addition to these urban concerns, steep upslope against
the Sierra Nevada range will support multiple inches of
precipitation into the mountains. While the highest elevations
could see as much as 2 feet of snow, much of the lower elevations
could pick up 2-4 inches of new rainfall, which will quickly flow
into the Central Valley. The inherited Marginal captures the
isolated potential for flash flooding due to both urban concerns
and heavy rainfall being quickly directed into steep valleys
draining the Sierra Nevada. No changes were needed to the inherited
Marginal Risk area.

...Texas...

A plume of rain moving across eastern Texas is the result of deep
Gulf moisture advecting northward off the western Gulf ahead of a
series of weak upper level disturbances moving across Texas. These
disturbances are supporting the broader plume of light rain and
where the forcing is greatest, supporting locally heavier rainfall
rates. Guidance has come into enough agreement about the potential
for locally heavy rain associated with slow-moving cells impacting
portions of eastern Texas as far north as the Metroplex. Thus,
given the lower FFGs associated with the large urban area
constituting the Metroplex, the Marginal has been expanded north to
cover the Triangle to include the Dallas-Fort Worth metro.
Nonetheless, with more moisture and a bit more instability, the
threat for heavy rain capable of producing isolated instances of
flash flooding should hold closer to I-10.

Wegman


Day 2
Valid 12Z Wed Apr 22 2026 - 12Z Thu Apr 23 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER TEXAS COAST AND SOUTHWESTERN LOUISIANA...

Only minor tweaks were made to the inherited Marginal Risk area
across far southeastern Texas (upper Texas Coast) and southwestern
Louisiana. Steady southerly flow off the Gulf will continue to
advect a plume of Gulf moisture northward across the Marginal Risk
area. The flow will not be much to write home about, generally
between 5-15 kts at 850 mb. In addition to the rather weak
advection, it's notable that unlike Day 1/Tuesday, the upper levels
will become decidedly less favorable for widespread rain across the
region as ridging and associated subsidence builds in. Thus, there
is good agreement that any heavy rains will be disorganized and
widely scattered in nature, as compared with the rains further west
across Texas the past couple days. Urban concerns remain a driving
factor for maintaining the Marginal, which appears to be a lower-
end risk.

Wegman


Day 3
Valid 12Z Thu Apr 23 2026 - 12Z Fri Apr 24 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSOURI AND MID-MISSISSIPPI VALLEYS...

A plume of moisture originating from the Gulf will advect moisture
and instability northward into the Missouri and Mississippi Valleys
on Thursday. Meanwhile, a strong cold front emanating from a deep
low over the northern Plains will sweep eastward across the same
region. Where these two competing air masses meet, most likely in
the Marginal Risk area, expect widespread development of showers
and thunderstorms. The greatest clashes are expected after sunset
Thursday night, as the low level jet advecting the moisture and
instability strengthens with the normal diurnal cycle. As that
warm, moist air collides with the cold front, it will stall the
latter's southward progress, creating an east-west boundary, likely
starting around the Kansas/Missouri border well south of Kansas
City, then expanding eastward with the front. Ozarks topography
will likely also support locally heavier rainfall on the south-
facing slopes as well. Guidance is in very poor agreement as to
exactly where and when this clash of air masses will occur, with
the above-described scenario seemingly the most likely solution
based on an ensemble of the guidance. Should the guidance come into
better agreement with strength and timing of the heaviest rainfall
with future updates, a Slight Risk may need to be considered. The
still full rivers and saturated soils across southeast Kansas and
southwest Missouri from recent heavy rainfall events will
contribute to more widely scattered instances of flash flooding
should the heaviest rainfall occur over this region.

Wegman
$$

--- ScorpioBBS/QWK v0.31a (Linux/x86_64)
* Origin: Project Scorpio TEST (618:250/6)

FOUS30 KWBC 250751
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Apr 25 2026

Day 1
Valid 12Z Sat Apr 25 2026 - 12Z Sun Apr 26 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE ARKLATEX
REGION INTO EASTERN OKLAHOMA AND SOUTHEAST KANSAS...

Very strong instability is likely to develop later today across the
southern Plains as a consequence of considerable northward moisture
advection. Convective initiation may be delayed until around or
after 00Z as it will take time to erode an inversion. Eventually
this is expected to give way to scattered supercells, which should
then grow into convective clusters and progress to the southeast
during the overnight hours. The environment will be supportive of
heavy rain rates to around 2 inches per hour with PW values around
1.5 inches (90th percentile for late April in the region). Flash
flooding would be possible where these rain rates can be sustained
for a couple hours; that would be most likely to occur via cell
mergers leading to brief periods of training.

A targeted upgrade to a Slight Risk may be needed later today, as
there is a chance for more focused training and backbuilding along
a composite outflow boundary and warm front that will gradually be
pushing north into southeast Oklahoma and southwest Arkansas. While
models have come into better agreement on the location of this
boundary, and the relatively strong low-level convergence
associated with it, many models also show somewhat limited
convective coverage, which would reduce opportunities for training
and a focused corridor of heavy rainfall. If greater development
along and near the boundary becomes apparent, the alignment of
shear vectors with the boundary orientation would increase the risk
of flash flooding and may warrant an upgrade.

Another area of higher QPF values (1-2 inches) is forecast from
the Poconos into the greater New York City area today and tonight.
This area was not outlooked in the ERO as the rain is expected via
steady light-moderate rain for much of the day, with a lack of
instability and chances of even 0.5 inch per hour rain rates
negligible to nil. Therefore, any impacts from the rain would not
be expected to be of the flash flood variety.

Lamers


Day 2
Valid 12Z Sun Apr 26 2026 - 12Z Mon Apr 27 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS...

Strong cyclogenesis in the central Plains on Sunday will facilitate
significant northward moisture transport and a more expansive area
of thunderstorm activity in the region. The most notable change to
the existing outlook was to reduce the size of the Marginal Risk
and focus it more directly in the Central Plains. That is where the
forcing is expected to be strongest: the left exit region of an
upper level jet and strong positive vorticity advection. Further
south, in Oklahoma and Arkansas, the trend in QPF guidance has been
drier, with expectations for weaker forcing and less favorable
low-level lapse rates associated with a warm nose. Some models keep
areas that far south almost completely dry now; therefore the
Marginal Risk has been removed and focused further north. Where the
risk area still exists, the primary question at this point will be
the amount of available instability. More unstable scenarios could
support convective clusters with higher rain rates (in excess of 1
inch per hour) that could lead to isolated flash flooding.
Scenarios with less instability could limit rain rates. Given these uncertainties, expect further refinement of the outlook in
subsequent updates. Although some potential for heavy rain exists
from central Nebraska into central South Dakota in some guidance,
flash flood guidance is much higher in those locations, so the
northwest extent of the Marginal Risk was constrained by the
presence of less favorable soil conditions.

Lamers


Day 3
Valid 12Z Mon Apr 27 2026 - 12Z Tue Apr 28 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER NORTHERN
ILLINOIS AND FAR SOUTHERN WISCONSIN...

A deep cyclone will continue to make steady progress northeastward
on Monday from the central Plains into the western Great Lakes. A
broad 50-60 knot low-level jet to the east of the cyclone and
accompanying cold front will continue significant northward
moisture transport with 1 inch PW likely to extend to the Canadian
border and 1.5 inch PW potentially reaching to southern Wisconsin.
This would place most of the Mississippi Valley firmly in the
90-95th percentile for PW in late April. This will support
relatively high rain rates in the abundant convection expected
along and ahead of the aforementioned cold front. This is reflected
in a broad Marginal Risk over much of the Middle and Upper
Mississippi Valley. The risk is held at that level for most of the
region due to the expectation for relatively narrow squall lines
forced by the cold front as the primary contributer to rainfall
over the 24-hour period. Those squall lines should steadily (or
even rapidly) advance eastward and that would limit the duration
of heavy rainfall at any one location. Rain rates will be high
enough that isolated flash flooding is still possible.

A Slight Risk was introduced in a small area of northern Illinois
and far southern Wisconsin where there is an overlap of higher
probabilities of 2+ inch rainfall (25-40 percent per NBM v5.0) and
anomalously high streamflow and soil moisture due to significant
rainfall over the past couple weeks. While the risk of flash
flooding is slightly higher in these areas, the same limitation of
relatively fast progression of thunderstorms described above still
applies. Additionally, there is some uncertainty about the degree
of instability this far north; an easterly component to the low-
level flow may advect more stable air from the cool Lake Michigan
into adjacent land areas. Models that embrace that scenario tend to
show a rapid decay of convection as it progresses east into
southern Wisconsin and northern Illinois, so this will need to be
monitored as details come into focus. Nevertheless, enough signal
for heavy rainfall exists in an area of increased vulnerability to
justify higher ERO probabilities with this update.

Lamers
$$

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

FOUS30 KWBC 260802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Sun Apr 26 2026

Day 1
Valid 12Z Sun Apr 26 2026 - 12Z Mon Apr 27 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE CENTRAL PLAINS...

The latest hi-res model guidance has trended substantially toward
a corridor of heavy rainfall in the Central Plains this evening and
tonight. Therefore, confidence has increased in a heavy rain event,
but considerable uncertainty still remains on the location. Some
guidance places the heaviest rain almost wholly into Iowa, while
other guidance is further south in the vicinity of the I-70
corridor in Kansas and Missouri -- almost 200 miles of variability
with approximately 18 hours of lead time. Given the consistent
signal for significant rainfall, we have upgraded to a Slight Risk,
and drawn it broadly to account for positional uncertainty. The
contours were largely based on EAS probabilities from the 00Z HREF;
and the major axis of the Slight Risk area intersects the QPF
maximum on the AI versions of the GFS and GEFS.

Convection is expected to develop this afternoon on the nose of a
strengthening low-level jet (LLJ) and plume of instability, likely
in northern Kansas or southeast Nebraska initially. The convective
evolution in the approx. 6 hours after initiation will be
important. In general, all models show a west-to-east progression
of thunderstorm clusters, consistent with the bulk shear vectors,
and along a focused area of low-level convergence near the nose of
the LLJ. Some models show scattered clusters progressing over
similar areas, but with intermittent breaks and not precise
training; others show a more continuous band of convection training
in a specific corridor (sustaining 1-2 inch per hour rain rates for
several hours in a given location). Comparing QPFs from those
scenarios suggests the latter scenario could double rainfall, with
amounts potentially high enough to lead to significant flash
flooding. Therefore, this will need to be monitored closely.

A Marginal Risk was considered in the Arklatex region as ongoing
convection will likely persist in some form beyond 12Z. However, a
squall line in southern Arkansas appears to be forward propagating
and accelerating, if anything. And other thunderstorm activity is
more isolated and generally less intense. Therefore, a non-zero
excessive rainfall risk does exist in the region, but no Marginal
Risk was outlined at this time.

Lamers


Day 2
Valid 12Z Mon Apr 27 2026 - 12Z Tue Apr 28 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL PRIMARILY OVER
SOUTHEAST IOWA AND NORTHERN ILLINOIS...

The training band of convection from Sunday Night is likely to
progress eastward into the Midwest on Monday; placement
uncertainties grow on Day 2, but there has been a general southward
shift in the location of the heaviest rainfall in model guidance
over the last couple cycles. Some guidance now shows the corridor
of heaviest rainfall on Monday and Monday Night as far south as the
I-70 corridor from St. Louis to Indianapolis, while other guidance
remains closer to the Illinois-Wisconsin border, where the existing
Slight Risk area was concentrated. This is about a 200 mile spread.
So while heavy rainfall is expected, confidence remains somewhat
low on the location. Given the overall trends, the main change was
to shift the axis of the Slight Risk southward, albeit only about
70 miles out of deference to continuity.

The overall environment will be very supportive of heavy rain
rates. A plume of 1.2 to 1.7 inch PWs (above the 95th percentile
for late April) and moderate to strong instability will support 1
to 2 inch rain rates in organized convective clusters and lines.
Although training convection may continue into Monday morning,
convective lines should become oriented more in a north-south
fashion later in the day as forcing along an accelerating cold
front increases. The best opportunity for training convection, and
therefore a longer duration of heavy rain rates, should be in or
near the Slight Risk area. Areas further south should not only see
steady progression to any convective lines, but have also been much
drier lately, so the risk of flash flooding is lower despite some
similar QPF from the latest model guidance.

Lamers


Day 3
Valid 12Z Tue Apr 28 2026 - 12Z Wed Apr 29 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER MUCH OF THE
INTERIOR SOUTH...

Fairly widespread convection is expected on Tuesday and Tuesday
Night over much of the interior South, in a broad plume of
anomalously high PWs between 1.5 and 1.8 inches with strong
instability. Organized convective clusters and lines should be
capable of producing rain rates up to 2 inches per hour, and any
training could lead to localized flash flooding. Much of the region
has been very dry lately; over the past 60 days most of Kentucky,
Tennessee, and eastern Arkansas have seen less than half of their
average precipitation. Therefore, the region is generally not
primed for impacts from heavy rainfall, even though flash flooding
can occur given sufficiently high rain rates sustained for a long
enough duration. Given low confidence in mesoscale details, the
risk level has been held at Marginal over the entire region for
now. It's possible an upgrade to Slight Risk may be needed
eventually, and may be more likely in Arkansas, eastern Oklahoma,
or northeast Texas where there has been some rainfall in the past
couple weeks, including earlier today.

Lamers
$$

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

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)