Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Fri Sep 4 2026
Day 1
Valid 12Z Fri Sep 04 2026 - 12Z Sat Sep 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR SOUTHEASTERN
ARIZONA AND WESTERN NEW MEXICO...
...Southwest...
A longwave trough over the Pacific Northwest will keep the jet
stream out ahead of it over the monsoon-affected areas of the
Southwest. A Slight Risk of excessive rainfall will therefore
remain in effect for the flood prone areas of southeastern Arizona
and western New Mexico. Convective coverage is unlikely to be
anything noteworthy...rather remaining widely scattered to
scattered. The storms will propagate northeastward, which should
lower the threat for metro Tucson today. Prior days' thunderstorms
in this area are keeping the soil conditions wet enough to promote
any storms' runoff causing localized flash flooding, especially in
low-lying areas, slot canyons, and over and downstream of burn
scars.
...Gulf Coast...
Abundant Gulf moisture remains along all of the Gulf Coast. A
stalled front a bit inland from the Gulf could provide some focus
for organized convection in localized areas. However, the storms
are largely expected to remain disorganized, likely following any
sea breeze fronts. High FFGs due to sandy soils and around average
moisture levels in the top soils should keep any flash flooding
localized to urbanized areas.
....Great Lakes to Mid-Atlantic...
A large ridge of high pressure over the middle of the country will
steer "ridge-riding" disturbances southeastward from the Great
Lakes to portions of the Mid-Atlantic. Many areas expected to see
storms again today were hit by storms, sometimes multiple times,
yesterday. A Marginal Risk remains over the area since the storms
are likely to be very fast moving, as they have been in recent
days. Due to abundant moisture still in place, however, any storms
will be capable of locally very heavy rainfall. This could cause
flash flooding in urban, low-lying, and other flood-prone areas
today.
Wegman
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Fri Sep 4 2026
Day 2
Valid 12Z Sat Sep 05 2026 - 12Z Sun Sep 06 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NORTH
CAROLINA...
...Ohio Valley and the Mid-Atlantic...
A lower-end Slight was introduced with this update for
eastern/coastal North Carolina. A back-door cold front will make
steady progress southward down the Delmarva Peninsula today. Ahead
of the front in eastern North Carolina, multiple rounds of storms
are possible as instability maximizes in the area ahead of the
front. Sea breeze fronts are likely to be the predominant forcing
for any storms during the early to mid-afternoon. Then as the front
approaches in the late afternoon and evening, a second much more
widespread area of storms will impact the area. While soils there
are dry currently, expect a round of storms today to help saturate
the soils ahead of this Day 2/Saturday round. This nudges the area
into the low-end Slight category.
Further west into the Ohio Valley, storms along the western
extension of the front will also push southward with time. The
front will be much slower-moving to the west of the Appalachians.
Any associated storms impacting the Ohio Valley may produce
localized flash flooding in urban areas and other low-lying and
flood prone locales.
...Gulf Coast...
Another round of typical afternoon convection may cause localized
flash flooding in urban and flood prone areas. Once again, most
forcings for the storms will be localized, such as sea breeze or
old outflow boundaries. An abundance of moisture, with PWATs over 2
inches over a large areas will support any storms being capable of
very heavy rainfall. Generally flat terrain with sandy soils should
largely hinder any flooding to any urbanized areas.
...Southwest...
A Marginal Risk covers from southeastern Arizona across much of
New Mexico and into far southern Colorado. Storms Saturday
afternoon should largely be confined to the slopes of mountain
ranges. This should keep any resultant flash flooding localized.
Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Fri Sep 4 2026
Day 3
Valid 12Z Sun Sep 06 2026 - 12Z Mon Sep 07 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE COLORADO RIVER VALLEY FROM THE ARIZONA/NEVADA BORDER NORTHEAST
INTO CENTRAL UTAH...
...West...
Sunday looks to be a particularly active day over much of the West.
Some moisture from the large plume associated with Hurricane Marie
well out into the Pacific will be drawn into the Southwest.
Meanwhile the large longwave trough over the West will capture and
fling a few disturbances around the base and across the West. The
result will be much more widespread convection, especially over the
Slight Risk area from Las Vegas northeast over much of Utah. The
Slight Risk was expanded southwestward to include more flood prone
areas near Las Vegas, the Grand Canyon, and some of the western
National Parks in Utah, including Zion and Bryce Canyon. Slot
Canyons may be a particularly dangerous place to be on Sunday
afternoon with the more widespread convection expected. Additional
expansions and a potential inclusion of a higher end Slight are
probable with future updates given the very favorable pattern.
A slow-moving front along the Canadian border will make for a wet
go over much of northern Montana and into North Dakota, then
spreading south over much of Minnesota. A Marginal Risk remains in
place, but here too it's probable a Slight may be needed with
future updates as the convective evolution in this area becomes
more clear.
...Southeast...
The Marginal Risk was expanded with this update to include some
areas where TS Edouardo just hit, another afternoon with widespread
convection over the Florida Peninsula, and some chance that
convection could spread over North Carolina's southern coast. The
area of heaviest rain could be over much of South Carolina's coast.
A Marginal was left for Charleston and adjacent areas in
coordination with the forecast office there. Better consistency
with convective behavior at the end of a front there may allow for
future upgrades, but for now given the difficulty for rain to cause
flash flooding in portions of the Low Country, the Marginal is
sufficient.
Wegman
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
416 AM EDT Fri Sep 4 2026
Day 4 and Day 5
Valid 12Z Mon Sep 07 2026 - 12Z Wed Sep 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHWEST, SOUTHERN TO CENTRAL CALIFORNIA INTO THE SOUTHERN GREAT
BASIN, ACROSS THE UPPER LAKES INTO THE UPPER MISSISSIPPI VALLEY AND
OVER THE SOUTHEAST/NORTH FLORIDA...
...SOUTHWEST,SOUTHERN-CENTRAL CALIFORNIA,SOUTHERN GREAT BASIN....
A mid to upper level trof in the mean will persist across the
western U.S days 4 abnd 5. A lead closed low will be ejecting
northeastward from the northern Great Basin into the Northern
Plains, while additional height falls reform the mid to upper level
trof along the West coast. The net effect will be to maintain an
axis of much above average PW values from Southern CA into the
Southwest day 4 and expanding northward into Central CA and the
Southern Great Basin by day 5 in response to the re- amplifying
West coast upper trof. A marginal risk is maintained day 4 over
eastern AZ into western to central NM/far southern CO in the model
consensus qpf axis. Scattered convection across this region will
support locally heavy rains and isolated runoff issues. With the
expansion of the anomalous PW farther to the north and west day 5
into Central CA and the Southern Great Basin, the marginal risk was
also expanded from day 4, stretching from southwest CO, western NM
into all of AZ, far southern NV and southeast CA. Increasingly
favorable right entrance region jet dynamics on the east side of
the re-amplifying upper trof will support locally heavy rains in
the widespread scattered convection, supporting isolated runoff
issues.
...Northern Plains into the Upper Mississippi Valley/Upper Lakes...
The above mentioned northeast ejection of the western trof from
the Northern Great Basin/Northern Rockies into the Northern Plains
at the beginning of day 4 will support potential for organized
convection along and to the northeast of the northwest to southeast
oriented frontal zone across the Northern Plains. Strengthening
low level southerly flow into this front in an axis of anomalous PW
values, 2-3+ standard deviations above the mean, expected across
this region, supporting potential for heavy rains and isolated
runoff issues day 4. By day 5, the associated surface frontal
boundary is expected to become more southwest to northeast
oriented along the southern edge of the westerlies. At this time
the low level inflow into this front is also expected to become
more parallel to the boundary, supporting potential for a period
of training along the front Tuesday night into early Wednesday.
...Southeast/North Florida...
Widespread scattered convection likely day 4 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
416 AM EDT Fri Sep 4 2026
Day 4 and Day 5
Valid 12Z Mon Sep 07 2026 - 12Z Wed Sep 09 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHWEST, SOUTHERN TO CENTRAL CALIFORNIA INTO THE SOUTHERN GREAT
BASIN, ACROSS THE UPPER LAKES INTO THE UPPER MISSISSIPPI VALLEY AND
OVER THE SOUTHEAST/NORTH FLORIDA...
...SOUTHWEST,SOUTHERN-CENTRAL CALIFORNIA,SOUTHERN GREAT BASIN....
A mid to upper level trof in the mean will persist across the
western U.S days 4 abnd 5. A lead closed low will be ejecting
northeastward from the northern Great Basin into the Northern
Plains, while additional height falls reform the mid to upper level
trof along the West coast. The net effect will be to maintain an
axis of much above average PW values from Southern CA into the
Southwest day 4 and expanding northward into Central CA and the
Southern Great Basin by day 5 in response to the re- amplifying
West coast upper trof. A marginal risk is maintained day 4 over
eastern AZ into western to central NM/far southern CO in the model
consensus qpf axis. Scattered convection across this region will
support locally heavy rains and isolated runoff issues. With the
expansion of the anomalous PW farther to the north and west day 5
into Central CA and the Southern Great Basin, the marginal risk was
also expanded from day 4, stretching from southwest CO, western NM
into all of AZ, far southern NV and southeast CA. Increasingly
favorable right entrance region jet dynamics on the east side of
the re-amplifying upper trof will support locally heavy rains in
the widespread scattered convection, supporting isolated runoff
issues.
...Northern Plains into the Upper Mississippi Valley/Upper Lakes...
The above mentioned northeast ejection of the western trof from
the Northern Great Basin/Northern Rockies into the Northern Plains
at the beginning of day 4 will support potential for organized
convection along and to the northeast of the northwest to southeast
oriented frontal zone across the Northern Plains. Strengthening
low level southerly flow into this front in an axis of anomalous PW
values, 2-3+ standard deviations above the mean, expected across
this region, supporting potential for heavy rains and isolated
runoff issues day 4. By day 5, the associated surface frontal
boundary is expected to become more southwest to northeast
oriented along the southern edge of the westerlies. At this time
the low level inflow into this front is also expected to become
more parallel to the boundary, supporting potential for a period
of training along the front Tuesday night into early Wednesday.
...Southeast/North Florida...
Widespread scattered convection likely day 4 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
