Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
409 AM EDT Wed Sep 2 2026
Day 1
Valid 12Z Wed Sep 02 2026 - 12Z Thu Sep 03 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHEAST TEXAS...
...Eastern Texas and Southwest Louisiana...
Raining/backbuilding with high rainfall rates from tropical
cyclone Edouard are ongoing although there should be some
weakening by late in the morning, but periodic backbuilding
clusters will remain a possibility. Another uptick late Wednesday
night into Thursday morning likely as the low level vorticity
should remain fairly well defined. PWs of 2-2.25 inches will
support continued heavy rain with hourly rates of 2-3 inches/hour.
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 Moderate Risk was expanded to include
Freeston, Anderson and Henderson counties as well more of Polk
county. The eastern boundary of the Slight Risk was adjusted
eastward a bit to reflect the latest QPF guidance and WPC forecast.
...Northern Mid Atlantic & Southern New England...
A stronger shortwave will interact with the slow-moving warm front
over the Northeast to trigger scattered to widespread showers and
thunderstorms across the region. There continues to be ample
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.
...Florida...
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.
...Arizona...
Monsoonal moisture will return to southern Arizona to trigger
diurnal convection. Locally excessive rainfall may be possible
therefore a Marginal Risk is in effect.
Campbell
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
907 PM EDT Thu Sep 3 2026
Day 1
Valid 01Z Fri Sep 04 2026 - 12Z Fri Sep 04 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER OHIO VALLEY TO THE CENTRAL APPALACHIANS AND OVER
SOUTHEASTERN ARIZONA...
01Z Update...
...Southern Plains...
The Moderate and Slight Risks for excessive rainfall associated
with the remnants of Edouard over eastern Texas were removed. While
the hi-res models, including recent runs of the HRRR, indicate some
isolated activity may develop overnight -- any heavy amounts are
expected to be very isolated and centered west of where the
heaviest amounts previously occurred.
...Upper Ohio Valley, Central Appalachians, Mid Atlantic, and
Northeast...
Following radar trends and recent runs of the HRRR,
shifted the Slight Risk centered over the upper Ohio Valley and
central Appalachians farther south to extend from eastern Ohio to
western Maryland and the eastern West Virginia Panhandle.
Repeating convection centered over the western extent of the Slight
Risk area is expected to continue, with some guidance indicating
storms may propagate east all the way to the Delmarva overnight.
Refer to WPC MPD 1190 for additional details regarding the near-
term heavy rainfall and flash flooding threat across this region.
Farther north, extended the Marginal Risk slightly north to
include a greater portion of New York. There is some indication
that a narrow training band that has developed over western New
York may extend eastward into central New York and perhaps into
northeastern Pennsylvania, and southeastern New York.
...Upper Midwest and Great Lakes...
Adjusted the previous Marginal Risk farther north across Minnesota
into the upper Great Lakes. Storms moving across northern Minnesota
and out of eastern North Dakota and expected to track east --
remaining mostly over northern Minnesota. These storms are expected
to remain fairly progressive -- limiting the flash flooding threat.
There has been indication in several of the hi-res model runs that
storms currently to the south over northern Wisconsin will become
better organized with a period of training storms producing an axis
of heavy amounts from near Green Bay southeastward across Lake
Michigan. However, the latest HRRR (23Z) has backed away some from
this signal.
...Southwest U.S....
Made mostly minor adjustments to the outlook areas over the
Southwest, maintaining the Slight Risk over Southeastern Arizona
where convection is expected to continue to produce areas of flash
flooding into the evening. Refer to WPC MPD 1188 for additional
details.
...Northwest...
Rain is expected to continue across portions of eastern Oregon into
Idaho this evening. While limited instability is expected to hamper
rainfall rates, they may be sufficient enough to cause runoff
concerns across burn scar areas.
Pereira
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
907 PM EDT Thu Sep 3 2026
Day 2
Valid 12Z Fri Sep 04 2026 - 12Z Sat Sep 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
ARIZONA AND NEW MEXICO...
...Southwest...
20z Update:Anomalous moisture will continue to stream in across
the Southwest due to broad southerly flow ahead of a trough in the
West, as well as a tongue of moisture from the tropical Pacific.
Around 1000 J/Kg will support enough instability for the
development of afternoon thunderstorms across Arizona and New
Mexico. These ingredients will support Isolated to scattered flash
flooding, particularly over complex terrain and desert soils. The
Slight Risk was expanded farther north into central New Mexico to
match a higher QPF signal in model guidance.The Slight Risk matches
well with the 50-70% contours of 24hr HREF QPF exceeding an inch
and 15-30% 3 hourly flash flood guidance exceedance.
Wilder
..Previous Discussion:PW anomalies raise back to 2-2.5 standard
deviations above normal during this period. 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 PW anomaly). A Slight Risk was
maintained for Arizona while a broad Marginal covers southeast
California the Four Corner as this is where the signal for better
moisture/instability axis aligns. Isolated to scattered flash
flooding is expected.
Campbell/Chenard
...Gulf states...
20z Update: The Marginal Risk was maintained across eastern Texas
and even extended a little more northward in the Piney Woods region south
of Dallas.This was to account for the possibility of thunderstorm
regeneration in the afternoon from the remnants of Edouard and the
antecedent wet soils. For the rest of the Gulf Coast from Louisiana
to Florida, the Marginal Risk remains on track. A mid-level
disturbance moving across the Gulf, combined with high PWATS and
daytime heating, should foster plentiful thunderstorms that could
drop 1-2 inches of rainfall per hour. Southern Louisiana in
particular had higher probabilities, 20-40%, of hourly rainfall
rates exceeding 2 inches per hour and 24 hour QPF greater than 3
inches. Urban areas, such as New Orleans, could see water ponding
and localized flash flooding in this weather pattern.
Wilder
..Previous Discussion:Lingering moisture and
instability along this corridor could result in a continued
localized flash flood risk. A Marginal Risk was maintained from
eastern Texas to southern Georgia and Florida.
Campbell/Chenard
...Upper Midwest/Ohio Valley/Central Appalachians...
20z Update: The Marginal Risk across the Great Lakes, Ohio Valley,
and Mid- Atlantic remains on track. Complexes of storms should
continue to propagate northwest to southeast along a stationary
front. Model guidance is in good agreement for storms capable of
dropping 1-2 inches of rain with local maxima upwards to 3 inches.
The progressive storm motions and the relatively high hourly flash
flood exceedance guidance should limit flash flooding to an
isolated basis. The one exception may be eastern Ohio and
Pennsylvania where rainfall this week has saturated soils and
increased susceptibility to flash flooding. The flash flood signal
was not strong enough to increase confidence for a Slight Risk
introduction for this region, but there remains greater potential
to see flash flooding. The forecast will continue to be monitored.
Wilder
..Previous Discussion:Additional organized/widespread convection
to develop downwind of the upper ridge axis today. Precipitable
water values are high enough with sufficient instability that
embedded cells could produce local downpours and isolated flooding.
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. A
Marginal Risk is in effect from Wisconsin to Virginia and eastern
North Carolina.
Campbell/Chenard
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
907 PM EDT Thu Sep 3 2026
Day 3
Valid 12Z Sat Sep 05 2026 - 12Z Sun Sep 06 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
THE SOUTHWEST,APPALACHIANS AND MID ATLANTIC, AND THE GULF COAST...
...SOUTHWEST...
20Z Update: The main changes to the forecast were to remove the
Marginal across Southern California and much of Arizona due to the
expected lag of moisture advection into the area that will limit
the convective coverage for the central and western half of the
previous risk issuance. The Marginal risk was also extended
northward into southern Colorado where trends in QPF show an
increase from the previous forecast issuance. Synoptically, the
forecast rationale remains unchanged as a moisture plume partly
related to Hurricane Marie in the East Pacific moves into the
Southwest and may support localized flash flooding across the
terrain.
Wilder
..Previous Discussion: Moisture southwesterly flow will be
directed into the Southwest between a deep upper low/trough over
the Pacific Northwest and a strong upper high centered over the
Southern Plains. A suppressed moisture and instability axis will
likely be positioned from southern California through central New
Mexico. There is connection to a tropical moisture plume from Marie
so this area will continue to be closely monitored. For now, a
Marginal Risk covers the level of threat for excessive rainfall and
spans from southern California across southern Nevada, Arizona and
New Mexico.
Campbell/Jackson
...APPALACHIANS/MID-ATLANTIC...
A Marginal ERO was introduced from eastern Kentucky to the
southern Mid-Atlantic as rounds of storms, perhaps an MCS, move
northwest to southeast. The storms will be fueled by anomalous
moisture and ample surface instability. Model QPF of 1-2 inches,
locally higher, was in general agreement with some uncertainty in
the heaviest rainfall placement. The addition of an approaching
cold front the north will lead to a sharp northern fringe of
instability leading to a majority of thunderstorm activity along
and ahead of the approaching front where instability maxima is most
prevalent. Any convective activtity should remain relatively
progressive leading to more of a Marginal Risk of excessive
rainfall for the period.
Wilder
...GULF COAST...
A Marginal risk was introduced across the Florida Peninsula and
along the Gulf Coast extending into eastern Texas. The mid-level
feature should remain across the region on Saturday and enhance
storm coverage. Additionally, a tropical Gulf atmosphere will
support 1-3 inch hourly rainfall rates capable of producing
localized flooding.
Wilder
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
907 PM EDT Thu Sep 3 2026
Day 4 and Day 5
Valid 12Z Sun Sep 06 2026 - 12Z Tue Sep 08 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ON DAY 4 ACROSS
PORTIONS OF SOUTHERN AND CENTRAL UTAH...
Daytime update...
The biggest adjustment from the previous issuance was the addition
of a Slight Risk extending from southwestern into central Utah on
Day 4. The daytime guidance remained consistent -- indicating
widespread convection fueled by tropical moisture extending from
portions of Southern California northeastward. It also showed a
growing signal for some of the heavier Day 4 totals centering
across southwestern to central Utah. This along with the natural
vulnerability of the area to rapid runoffs spurred the upgrade to
a Slight Risk. Additional expansions of this area may be warranted
if model signals remain consistent.
Elsewhere, minor adjustments were made to the previous outlook
areas based on the 12Z guidance.
Pereira
Previous Discussion...
...Southern California/Southwest, Great Basin into the Northern
Rockies... The anomalously strong western mid to upper level trof
will continue to be very slow moving during the upcoming day 4 and
5 period. There is consensus that this trof will be able to
transport anomalous PW values in the vicinity of Marie
northeastward from Southern CA/Southwest, into portions of the
Great Basin, and Northern Rockies. Widespread scattered convection,
locally heavy rains and localized flash flooding possible across
this area. A more widespread qpf and excessive rainfall footprint
expected day 4, with a decrease in threat area day 5, confined to
eastern AZ/western to central NM into southwest CO. A slight risk
area is possible in future updates when confidence in details of
potential heavy rain axes increases.
...Northern Plains into the Upper Mississippi Valley...
Shortwave energy moving northeastward in the broadly diffluent
upper flow pattern across the Northern Plains/Upper MS Valley
region will also support potential for organized convection along
and to the northeast of the northwest to southeast oriented frontal
zone across the Northern Plains. Anomalous PW values, 2-3+
standard deviations above the mean, expected across this region,
supporting potential for heavy rains and isolated runoff issues
both day 4 and day 5.
...Southeast/North Florida...
Widespread scattered convection likely both day 4 and 5 in the
vicinity of the slowly southward moving frontal boundary across
the Southeast/North Florida. Low confidence in qpf details in the
vicinity of this front, but with PW values 1.75-2.00", locally
heavy rains and isolated runoff issues possible.
Oravec
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
907 PM EDT Thu Sep 3 2026
Day 4 and Day 5
Valid 12Z Sun Sep 06 2026 - 12Z Tue Sep 08 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ON DAY 4 ACROSS
PORTIONS OF SOUTHERN AND CENTRAL UTAH...
Daytime update...
The biggest adjustment from the previous issuance was the addition
of a Slight Risk extending from southwestern into central Utah on
Day 4. The daytime guidance remained consistent -- indicating
widespread convection fueled by tropical moisture extending from
portions of Southern California northeastward. It also showed a
growing signal for some of the heavier Day 4 totals centering
across southwestern to central Utah. This along with the natural
vulnerability of the area to rapid runoffs spurred the upgrade to
a Slight Risk. Additional expansions of this area may be warranted
if model signals remain consistent.
Elsewhere, minor adjustments were made to the previous outlook
areas based on the 12Z guidance.
Pereira
Previous Discussion...
...Southern California/Southwest, Great Basin into the Northern
Rockies... The anomalously strong western mid to upper level trof
will continue to be very slow moving during the upcoming day 4 and
5 period. There is consensus that this trof will be able to
transport anomalous PW values in the vicinity of Marie
northeastward from Southern CA/Southwest, into portions of the
Great Basin, and Northern Rockies. Widespread scattered convection,
locally heavy rains and localized flash flooding possible across
this area. A more widespread qpf and excessive rainfall footprint
expected day 4, with a decrease in threat area day 5, confined to
eastern AZ/western to central NM into southwest CO. A slight risk
area is possible in future updates when confidence in details of
potential heavy rain axes increases.
...Northern Plains into the Upper Mississippi Valley...
Shortwave energy moving northeastward in the broadly diffluent
upper flow pattern across the Northern Plains/Upper MS Valley
region will also support potential for organized convection along
and to the northeast of the northwest to southeast oriented frontal
zone across the Northern Plains. Anomalous PW values, 2-3+
standard deviations above the mean, expected across this region,
supporting potential for heavy rains and isolated runoff issues
both day 4 and day 5.
...Southeast/North Florida...
Widespread scattered convection likely both day 4 and 5 in the
vicinity of the slowly southward moving frontal boundary across
the Southeast/North Florida. Low confidence in qpf details in the
vicinity of this front, but with PW values 1.75-2.00", locally
heavy rains and isolated runoff issues possible.
Oravec
