Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
859 PM EDT Tue Sep 1 2026
Day 1
Valid 01Z Wed Sep 02 2026 - 12Z Wed Sep 02 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE UPPER
TEXAS COAST AND FAR SOUTHWEST LOUISIANA...
01Z Update...
Maintained the Moderate risk area without change as Edouard
continues to track inland. Weakening is still expected overnight
but remaining a threat for heavy to excessive rainfall.
In the Northeast US...most of the focus for heavy rainfall was in
the eastern portion of Pennsylvania southward into the northern
Delmarva region. Removed areas farther north from the Marginal risk
area. In the areas that remain in the Marginal risk area...the
atmosphere was characterized by precipitable water values around
1.75 inches and CAPE values generally 2500 J per kg. This often
supports rainfall rates in the 1.5 to 1.75 inch per hour
range...although locally higher rates can occur allowing for
rainfall totals of 2.5 to 3.5 inches before the enough
stabilization in the low-levels leads to a decreased risk of
flooding. Reference Mesoscale Precipitation Discussion 1168 for
additional mesoscale details.
In the Southwest...cells remained isolated to widely scattered for
much of the day into the early evening. However...slow cell motion
could still result in localized flooding. The loss of daytime
heating should lead to decreasing coverage of convection and
diminishing rainfall rates as the evening continues.
Plains...
Low-end risk of excessive rainfall exists across portions of
northeast Nebraska and a small portion of nearby South
Dakota/Minnesota/Iowa through 02/05Z. A cluster of storms formed
earlier and had a history of producing 1 inch of rainfall in less
than 30 minutes. The expectation is that convection will continue
to produce heavy rainfall rates/amounts for a few more hours in a
region where dewpoints were in the lower- to middle-70s. The Flash
Flood Guidance is high in the area which suggests flash flooding
would be isolated to widely scatter and/or urban area. Reference
WPC Mesoscale Precipitation Discussion 1170 for additional
mesoscale details .
16z Update:
Upgraded to a MDT risk for portions of the upper TX coast into the
Piney Woods region of southeast TX. Some urban flash flooding
appears likely near landfall point along the upper TX coast into
the Port Arthur to Beaumont corridor with hourly rainfall of 2-3"
and total rainfall locally exceeding 6". The system should rapidly
weaken as it moves inland, however the remnant low level vorticity
center will remain well defined. This should support periodic
convective bursts this afternoon/evening along it's track, with a
likelihood of a nocturnal convective uptick near and south of the
center late tonight into Wednesday morning. This should impact the
Piney Woods region, and localized rainfall over 6" appears likely.
Overall this axis of flash flood potential is very narrow, with
higher confidence in at least some flood impacts near landfall
today, and a conditional threat for locally significant flash
flooding tonight with the nocturnal flare up over the Piney Woods
region.
Chenard
...Previous Discussion...
...Central Gulf Coast...
NHC has forecast Tropical Storm Edouard to make landfall along the
Upper Texas Coast early in the period with a general consensus of
moving onshore very close to Galveston Bay before lifting slowly
NW through the afternoon and evening hours. The system is expected
to remain compact as it organizes and comes onshore, leading to a
narrow corridor of heavy rainfall thanks to PWs of over 2.25" in
the accompanying tropical moisture plume. While the heaviest rain
may occur along the coast and just NE of the center/track, there is
potential for some inflow convergence to maintain a corridor of
heavy rain even behind the system as it lifts into east-central
Texas. Additionally, the forecast movement (using latest NHC
forecast positions) is progged to only be around the 20th
percentile of Gulf Coast systems, suggesting the potential for
locally excessive rainfall where training is most pronounced and
prolonged.
Both the HREF and REFS ensemble suites indicate a high chance
(>70%) of at least 5" in a NW oriented stripe from Galveston Bay
through near College Station, with 8"/24hr probabilities exceeding
40% near the coast. This will continue to be monitored as the
storm evolves.
...Four Corners and Southwest...
After several days of heavy rain and substantial impacts across
the Four Corners and Southwest, activity is likely to wane
considerable today. Sufficient forcing and moisture for another
day of local impacts will be present, especially atop the
vulnerable soils impacted the last few days, thus maintaining a
Marginal Risk for much of the Four Corners.
Although PWs do come down, the drier air which has been progged to
push east has slowed down, leaving PW anomalies of +0.5 to +1
sigma in place on Tuesday. With significant forcing remaining in
place as a trough approaches from the west (leading to height
falls and jet level diffluence for synoptic ascent), this will
result in another day of at least scattered thunderstorm
development during peak heating, or within any enhanced lift
beneath weak impulses embedded within the flow. Mean 0-6km winds
will remain progressive at around 25 kts, but aligned propagation
vectors and continued elevated bulk shear magnitudes above 40 kts
will support organization into clusters and potentially repeating
cells. Hourly rainfall of 0.5 to 0.75 inches may occur.
...Great Lakes to the Northeast...
Mid-level impulses tracking atop the ridge and along a wavering
frontal boundary will continue to produce rounds of scattered
convection from the Great Lakes through New England and the
northern Mid- Atlantic states. As is typical with this convective
cluster setups, there is a lot of spread in both timing and
placement of the heaviest rain signatures from the available CAMs.
While the guidance is in good agreement that many areas will
receive periods of heavy rainfall exceeding 1"/hr as storms track
steadily WNW to ESE, the duration of any of this rain may be modest
due to the progressive nature of cells. However, short duration
training is likely at times thanks to aligned propagation
vectors/mean winds to the front, which could enhance rainfall
amounts locally.
In general, rainfall should be 1-2" which will only be sufficient
to create isolated impacts related to flash flooding, but if any
significant training/repeating could occur, locally higher rainfall
is possible. This is reflected by both HREF and REFS probabilities
for 3" that peak above 25%, especially across far southern New
England, Long Island, and northern PA/southern NY. However, due to
uncertainty in timing and placement, combined with generally
elevated FFG outside of the Catskills and Tri-State area, the
Marginal Risk was maintained.
...Florida...
Easterly flow will draw tropical moisture onshore helping to fuel
scattered afternoon convection. PW values will be nearing 2.25
inches and the mean flow across the Peninsula will be very weak
suggesting cells will drift west from the sea breeze, but may
converge just inland from the Gulf as the gulf breeze also pushes
inland. Some short term training will be possible (limited in
duration by the pulse nature of the cells) but with rainfall rates
expected to be 2-3"/hr, this could create isolated flash flood
impacts, especially within urban areas.
Campbell/Weiss
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
859 PM EDT Tue Sep 1 2026
Day 2
Valid 12Z Wed Sep 02 2026 - 12Z Thu Sep 03 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS...
20z Update:
Upgraded to a focused MDT risk for portions of southeast TX with
this update. This accounts for the nocturnal uptick in convection
near/south of the remnant circulation of Edouard that should still
be ongoing at 12z Wednesday. Training/backbuilding with high
rainfall rates should be ongoing to start the period. We should see
some weakening by late in the morning, but periodic backbuilding
clusters will remain a possibility. We may see another uptick late
Wednesday night into Thursday morning as the low level vorticity
should remain fairly well defined. However, more uncertainty with
these details and the broader Slight risk also covers this
potential.
The Slight risk over NY was realigned a bit and shifted southwest
based on model trends and the expected instability axis. Portions
of northern PA into southern NY still look in line to see multiple
convective rounds Wednesday, with some training potential.
A small Marginal risk was added over southern AZ, where convective
coverage has trended up a bit with the 12z high res models. Should
be enough instability and moisture to support localized flash
flooding.
Chenard
...Previous Discussion...
...Northern Mid Atlantic & Southern New England...
A Slight Risk remains in effect for much of central and eastern
new York. A stronger shortwave tracking atop the region to
interact with a slowly northeast advancing warm front will result
in scattered to widespread convection across the region. While the
exact location of the heaviest rainfall remains uncertain, there
should be amble support of training of clusters of thunderstorms
with 1-2"/hr rain rates. The guidance focuses this heaviest
rainfall across portions of Upstate New York, and while soil
moisture is generally below normal according to NASA SPoRT, this
should support up to 3" of rain in some areas leading to scattered
instances of flash flooding, with more isolated responses
elsewhere.
...Eastern Texas and Southwest Louisiana...
Tropical cyclone Edouard will be well inland and slowly its
progression while spread bands of heavy rainfall to eastern Texas
and into Louisiana. Additional heavy rainfall is likely even as the
central low pressure begins to dissipate. PWs of 2-2.25" will
support continued heavy rain, and as 850mb inflow only slowly
weakens it will drive enhanced convergence to support 2-3"/hr rain
rates. While most of the rain should be around the center of the
system which will be lifting slowly northward towards north Texas,
there is potential for a locally enhanced inflow band on its south
side which could prolong and enhance the rain across areas that
receive heavy rain. The small size of the storm should limit the
footprint and potential impacts, but ECENS/GEFS probabilities still
indicate that at least an additional 3" of rain may fall, with
locally higher amounts, leading to instances of flash flooding.
Some further refinements in the Slight Risk area are expected with
future updates, both to capture the latest guidance track, but
also better resolve where any additional rainfall will occur on top
of heavy rain from Tuesday.
...Northern Plains and Midwest...
Lingering MCS activity possible early in the period across the
Upper Midwest. PWAT anomalies remain elevated at times mid- week,
with values of 1.5-2" forecast, however the spread in the
deterministic QPF is higher than average. A broad Marginal Risk
spans from Minnesota/Iowa eastward to the Great Lakes.
...Florida...
Another day where the tropical moisture plume remains entrenched
across Florida, reflected by PW anomalies of +1.5 sigma stretching
across most of the state. Both coasts could experience slow moving
storms with 2+"/hr rain rates, as well as across the inland
portions of the peninsula where storm mergers/collisions can occur.
A Marginal Risk was maintained for this period.
Campbell/Weiss
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
859 PM EDT Tue Sep 1 2026
Day 3
Valid 12Z Thu Sep 03 2026 - 12Z Fri Sep 04 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN ARIZONA...
The Marginal risk was expanded across the Gulf Coast and into
eastern TX. The remnant vort center of Edouard should be less
defined by this time, but still present over east TX. Thus it could
still help focus some organized convective clusters, and thus an
isolated flash flood risk could linger into Thursday.
The Marginal risk from the Great Lakes to Mid-Altnatic was
realigned to focus a bit farther south, which matches model
trends. Still some uncertainty on the details, but one or more
rounds of organized convection should traverse portions of this
area Thursday into Thursday night.
The Slight risk was maintained across southern AZ, where an uptick
in moisture should result in increased convective coverage and a
scattered flash flood risk. There is a little more model spread
here, with the GFS/AIGFS more aggressive with convective coverage
and the flash flood threat than the drier ECMWF/AIFS. Thus we will
need to continue to monitor trends over the coming days.
A Marginal risk also exists from northern CA into ID. A strong
synoptic system will bring an axis of heavy rainfall to the region.
Not much instability, but just enough showing up in model
forecasts to suggest some potential for localized higher rates and
an isolated flash flood potential.
Chenard
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
859 PM EDT Tue Sep 1 2026
Day 4 and Day 5
Valid 12Z Fri Sep 04 2026 - 12Z Sun Sep 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS
PORTIONS OF ARIZONA...
2030Z Discussion...
Maintained the Slight Risk area over portions of Arizona on Day 4 given
the moisture plume connection with Marie...despite Marie's recent
shift away from the coast and despite the subtle decrease in QPF.
This was done to account for the possibility of guidance shifting
back. The area can be downgraded to a Marginal in subsequent
short- range EROs as confidence in guidance grows.
In the Northwestern US and the Great Lakes region...area average
rainfall amounts are pretty modest. Even so...precipitable water
values are high enough with sufficient instability that embedded
cells could produce local downpours and isolated flooding.
The Southwest remained the only outlook area on Day 5.
Bann
Previous Outlook
...Southwest/Four Corners/Central-Southern Rockies...
The signal for the return of heavy rain areas across the Southwest
into the Four Corners and central-southern Rockies remains strong
both Friday and Saturday, especially Friday across central to
southeast AZ where a Slight Risk area remains from yesterday's Day
5 ERO. GEFS and ECENS PWAT anomalies increase back to 2-2.5
standard deviations above normal both Fri and Sat, however the
deterministic and probabilistic QPFs per the GEFS, EC, and CMC
ensembles are more supportive of the Slight Risk on Day 4 (Fri-Fri
night), with the axis of best monsoonal moisture influx shifting
slightly west next weekend. Still remains to be seen how much
influence the eventual tropical system that ultimately pulls west
of Baja will have in terms of the upper level moisture (potential
uptick in the PWAT anomaly( by Friday and over the weekend. The GFS
remains too far east with the track of this feature compared to
the rest of the global guidance, and it continues to trend towards
the ECMWF and CMC suites.
...Northern Great Basin/Northern Rockies...
Marginal Risk area from yesterday's Day 5 ERO continues in the new
Day 4 outlook across portions of the interior Northwest,
particularly the area surrounding the northern Idaho Panhandle.
This area will be much closer to the upper level trough, so forcing
should be much better than in the Southwest. However, moisture and
instability will be much lower, resulting in more likelihood of
stratiform rainfall. Despite this, the rainfall should still have
modest amounts of instability to work with in a generally dry, and
therefore flash flood prone, area of the country.
...Upper Midwest/Ohio Valley/Central Appalachians...
Despite the current spatial and temporal spread with the current
(00Z 9/1) guidance suite, expect more organized/widespread
convection on Friday downwind of the upper ridge axis. This will
likely start over eastern portions of the Upper Midwest, where the
upper jet streak to the northeast is expected to strengthen as the
pivoting northern stream trough impinges on the broad-scale ridge
to the south. Have essentially traced the Marginal Risk area
southeast along the mean 850-300 mb thickness fields, where the
upper level forcing along/ahead of the surface front will be most
supportive of more organized activity.
Hurley
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
859 PM EDT Tue Sep 1 2026
Day 4 and Day 5
Valid 12Z Fri Sep 04 2026 - 12Z Sun Sep 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FRIDAY ACROSS
PORTIONS OF ARIZONA...
2030Z Discussion...
Maintained the Slight Risk area over portions of Arizona on Day 4 given
the moisture plume connection with Marie...despite Marie's recent
shift away from the coast and despite the subtle decrease in QPF.
This was done to account for the possibility of guidance shifting
back. The area can be downgraded to a Marginal in subsequent
short- range EROs as confidence in guidance grows.
In the Northwestern US and the Great Lakes region...area average
rainfall amounts are pretty modest. Even so...precipitable water
values are high enough with sufficient instability that embedded
cells could produce local downpours and isolated flooding.
The Southwest remained the only outlook area on Day 5.
Bann
Previous Outlook
...Southwest/Four Corners/Central-Southern Rockies...
The signal for the return of heavy rain areas across the Southwest
into the Four Corners and central-southern Rockies remains strong
both Friday and Saturday, especially Friday across central to
southeast AZ where a Slight Risk area remains from yesterday's Day
5 ERO. GEFS and ECENS PWAT anomalies increase back to 2-2.5
standard deviations above normal both Fri and Sat, however the
deterministic and probabilistic QPFs per the GEFS, EC, and CMC
ensembles are more supportive of the Slight Risk on Day 4 (Fri-Fri
night), with the axis of best monsoonal moisture influx shifting
slightly west next weekend. Still remains to be seen how much
influence the eventual tropical system that ultimately pulls west
of Baja will have in terms of the upper level moisture (potential
uptick in the PWAT anomaly( by Friday and over the weekend. The GFS
remains too far east with the track of this feature compared to
the rest of the global guidance, and it continues to trend towards
the ECMWF and CMC suites.
...Northern Great Basin/Northern Rockies...
Marginal Risk area from yesterday's Day 5 ERO continues in the new
Day 4 outlook across portions of the interior Northwest,
particularly the area surrounding the northern Idaho Panhandle.
This area will be much closer to the upper level trough, so forcing
should be much better than in the Southwest. However, moisture and
instability will be much lower, resulting in more likelihood of
stratiform rainfall. Despite this, the rainfall should still have
modest amounts of instability to work with in a generally dry, and
therefore flash flood prone, area of the country.
...Upper Midwest/Ohio Valley/Central Appalachians...
Despite the current spatial and temporal spread with the current
(00Z 9/1) guidance suite, expect more organized/widespread
convection on Friday downwind of the upper ridge axis. This will
likely start over eastern portions of the Upper Midwest, where the
upper jet streak to the northeast is expected to strengthen as the
pivoting northern stream trough impinges on the broad-scale ridge
to the south. Have essentially traced the Marginal Risk area
southeast along the mean 850-300 mb thickness fields, where the
upper level forcing along/ahead of the surface front will be most
supportive of more organized activity.
Hurley
