Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
901 PM EDT Fri Sep 4 2026
Day 1
Valid 01Z Sat Sep 05 2026 - 12Z Sat Sep 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHWEST AND THE OHIO VALLEY INTO THE CENTRAL APPALACHIANS...
01Z Update...
...Great Lakes to the Central Appalachians and Mid Atlantic...
Shortwave energy originating over the upper Midwest is expected to
support convective development, with storms propagating southeast
along an axis of deeper moisture and instability centered along the
outlook areas. Both the Marginal and Slight Risk areas were
adjusted further south, reflecting recent runs of the HRRR,
mesoanalysis, and HREF guidance. While individual cells are
generally expected to propagate steadily to the southeast, training
storms could contribute to heavier totals and a localized threat
for flash flooding. The 18Z HREF indicates totals of 1-2 inches are
likely with some potential for heavier amounts, especially from
northeastern Indiana to southeastern Ohio.
While much of the Mid Atlantic was removed from the outlook, did
maintain a narrow Marginal Risk from central Pennsylvania
southeastward to southern New Jersey and Delaware. Storms now
forming over northwestern to central Pennsylvania are expected to
further develop through the remainder of the evening, with some of
the guidance indicating heavy amounts accumulating around southern
New Jersey and northern Delaware.
...Southwest...
Trimmed the western extent of the previous outlook areas, but
maintained a Slight Risk from far southeastern Arizona into west-
central New Mexico, surrounded by a broader Marginal Risk where
storms that developed earlier in the day continue to fire. However,
expect the threat for additional heavy rain and flash flooding to
be short-lived, with storm coverage likely to decrease with the
loss of daytime heating.
...Southern Plains to the Southeast...
Maintained a Marginal Risk from portions of the Concho Valley
westward to the Texas Big Bend, where ongoing north-south
propagating storms are expected to continue for at least a couple
moisture hours. These storms will be fueled by deepening moisture,
supported by low level southeasterly flow into the region. Some
north-south training may accentuate the threat for localized heavy
amounts and isolated flash flooding.
Elsewhere, across the Southern Plains into the Southeast, the
Marginal Risk was dropped. While an axis of very deep moisture
remains, the combination of diminishing storm coverage with the
loss of daytime heating, fairly steady westerly storm motions, and
high FFGs, suggest a limited threat for flash flooding through the
remainder of the evening into the overnight.
Pereira
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Sep 5 2026
Day 1
Valid 01Z Sat Sep 05 2026 - 12Z Sat Sep 05 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR EASTERN NORTH
CAROLINA INTO THE VIRGINIA TIDEWATER...
...Southern Ohio Valley through Carolinas...
Persistent west-northwesterly flow regime aloft will see a change
starting today as large scale closed low/trough over northeastern
North America retrogrades today with stronger north to south push
of drier Canadian air crosses the Great Lakes into the Ohio Valley
by the end of the day. The lingering deep layer moisture plume and
conditionally unstable air mass will start to shift through the
Upper Ohio Valley and through the Central Appalachians with some
ongoing WAA convective line SE OH, E KY and WV at the start of the
forecast period. This 'back-door' cold front will also continue a
southward push through the Mid-Altantic and interact with the Ohio
Valley wave toward peak diurnal period in the afternoon across VA
into N NC interacting with the higher theta-E air and higher
moisture over the Carolina coastal Plains.
Total PWats to 1.75-2" will support hourly rates of similar range
though forward propagation and interaction with the sea-breeze
boundary will likely result in the greatest scattered totals
ranging from 2-5". HREF probs of 3"/24hrs (mainly coastal) are
around 50% but also across sandier, higher FFG values. So scattered
incidents of flash/rapid inundation flooding are possible. Overall little
change was made for the low-end Slight Risk for this cycle.
...Eastern South Dakota/Southwest Minnesota/Northwest Iowa...
A complex of elevated thunderstorms will be ongoing across eastern
South Dakota at the start of the forecast period. Strengthening
large scale ridging eastward across the central MN through the
Mississippi River Valley accompanied by distant passing of a
shortwave through the northern High Plains of Montana has resulted
in increased diffluent flow along the northwest side of the ridge
over the Dakotas. Low level jet has responded with strengthened
S to SSWly warm advective flow in proximity to a surface front
across the Upper Midwest toward the deepening surface reflection
associated with the wave moving through MT. Conditionally unstable
air with MUCAPE to 3500 J/kg resides across the Sand Hills of N NEB
and Missouri Valley; with deep layer moisture/TPW around 1.5"
pooled across the boundary. The strengthening and slight veering of
the WAA flow should help to maintain a NNW to SSE convective line
that will be slow moving eastward due to downstream ridging
building in. Scattered cells capable of 1.5"/hr and increased
residency suggests isolated additional totals after 12z may be in
the vicinity of the higher FFG values (2-3"/3hrs) in the area. The
area is very hard due to prolonged drought with 0-40cm relative
soil moisture values below 10%. So, overall totals and lesser rates
that may slowly absorb into the dry soils may limit overall
coverage for flash flooding potential. However, with ARW/ARW2/RRFS
solutions suggesting 2-3", a small Marginal Risk will be introduced
for the isolated to widely scattered nature of FFG exceedance
expected.
...Gulf Coast...
Return flow along the southern edge of the synoptic ridge with weak
embedded waves will continue to support enhanced regions of
convective activity at diurnal peak. Broad zone of 2-2.25" total
PWats and narrow, skinny profiles supporting 1500-2000 J/kg of
MLCAPE will be sufficient to support stronger cells with intense
rates over 2"/hr. Guidance is in fairly good agreement for a few
areas of enhanced confidence for increased coverage and
organization. The larger/broader shortwave will be progressing
westward from S MS to SE TX with enhanced 2-3"/24hr probabilities
across the saturated areas of SE TX into SW/S LA, as well as, a
secondary maxima expected across S AL and western Panhandle of
Florida. Model trends show some isolated to scattered activity
between across northern Florida, but minor enough to remove from
the Marginal Risk.
Overall coverage and increased easterly flow across the Bahamas
into Southeast Florida should also see an increase in convective
activity with increased probabilities through much of the southern
half of the peninsula, favoring the eastern side due to the
slightly increased convergence.
...Upper Rio Grande Valley through Central High Plains...
Day 1 period will see a lull in available moisture and convective
convergence relative to prior and future days. However, the return
flow around the western edge of the synoptic ridge. Low level
flow/upslope through the Rio Grande/Pecos River Valleys will
overlap with weak southwesterly flow across NW Mexico. Mountain
circulation will likely drive initial convection and pose a risk
mainly for known/prone burn scars across much of NM. However,
deeper layer flow will continue to transport moisture northward
through the Central High Plains. Weak convective clusters are
expected to grow upscale after 00z across NE CO/SW NEB/W KS, where
increasing pooled moisture could support slower clusters with
internal cell mergers. HREF probs of 40-50% for 2" and 20% spots of
3" in an area of similar FFG values. As such, have expanded the
Marginal Risk of Excessive Rainfall north-northeast to encompass
the area up to the southern SandHills of NEB.
Gallina
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Sep 5 2026
Day 2
Valid 12Z Sun Sep 06 2026 - 12Z Mon Sep 07 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHERN
NEVADA AND NORTHWESTERN ARIZONA TO CENTRAL UTAH AND OVER PORTIONS
OF SOUTH CAROLINA AND GEORGIA...
...Western U.S....
An upper low centered along the Pacific Northwest coast early in
the period is expected move inland, reaching the northern
Intermountain West by the close of the period. Meanwhile, a series
of shortwaves moving along the base of the associated trough will
track across southern California before lifting northeast through
the Great Basin. In addition to this energy, southwesterly flow
will tap tropical moisture associated with Maria, supporting an
impressive PW anomaly axis (+3 std dev) extending from southern
California to central Utah. This moisture along with large-scale
ascent afforded by the aforementioned shortwaves and upper jet
forcing is expected to set the stage for widespread shower and
thunderstorm activity. However, limited instability remains a
potentially factor with regards to rainfall rates. A Slight Risk
remains where models continue to signal where moisture, lift, along
with orographic effects will support an enhanced threat for
heavier amounts. Only minor adjustments were made to the previous
Slight Risk area extending from southern Nevada and northwestern
Arizona to central Utah, including a small shift to the north that
reflects the latest trend in the guidance. Remaining in this area
are some of the more flash flood prone areas in southwestern Utah.
Farther east, more typical monsoon moisture will support diurnal
activity, with the potential for isolated flash flooding across
southeastern Arizona, New Mexico, and southern Colorado.
Elsewhere, a broad Marginal Risk was maintained to the north,
covering portions of the Northwest, northern Rockies, and High
Plains. The previously noted upper low/trough is expected to
support widespread activity. Instability west of the Rockies will
remain quite limited, however rates may become sufficient to raise
isolated concerns, especially across recent burn scars.
...Northern Plains to the lower Missouri Valley...
While the models are showing plenty of differences in the details,
there is a growing signal for heavy amounts impacting at least a
portion of the area as energy spills off of the top of a
persistent ridge centered over the Plains. This energy is forecast
to interact with a strengthening low level jet and axis of
deepening moisture (PWs ~1.75 inches). There is indication in some
of the models, including the ARW, NAM, and RGEM, that heavy rains
may be ongoing or developing near the start of the period across
portions of the eastern Dakotas and western Minnesota. This
activity will eventually drop south, followed by additional storms
developing late in the period and possibly impacting some of the
same areas. Model spread did not offer enough confidence to go
higher than a Marginal Risk. However, this is an area where a
potential upgrade may be necessary, especially if the hi-res
guidance begins to show a more unified signal.
...Southeast...
Energy dropping into the base of a broader-scale trough centered
along the East Coast is expected to support a weak wave developing
along a slow-moving, moisture-laden front extending from the coast
near the South Carolina-Georgia border back across the Southeast.
Models continue to signal heavy amounts near the coast, but also
some potential for heavy rains and potential flash flooding
extending as far north as Upstate South Carolina and western North
Carolina as deep moisture is drawn northwest by the developing
wave. Reflecting the overnight model trends, the Slight Risk was
shifted a little farther south, but also extended northwest along
the South Carolina-Georgia border.
Pereira
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Sep 5 2026
Day 3
Valid 12Z Mon Sep 07 2026 - 12Z Tue Sep 08 2026
...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST, NORTHERN ROCKIES, NORTHERN PLAINS, UPPER MIDWEST, AND
THE SOUTHEAST...
...Northern Rockies to the High Plains...
An upper low/trough will continue to translate east, reaching the
northern High Plains/southern Canadian Prairie by Tuesday morning.
Mid-level energy and upper jet forcing interacting with notable PW
anomalies (+2 std dev) will contribute to widespread precipitation,
with some orographically-focused heavier amounts. Rainfall rates
will likely be checked by limited instability, but may be
sufficient to cause isolated runoff concerns, especially in
vulnerable areas.
...Northern Plains into the Upper Mississippi Valley...
Moisture will continue to deepen across the region as southerly
flow intensifies ahead of the previously noted upper trough moving
out of the West. This is expected to fuel showers and storms
developing ahead of a strong cold front moving across the northern
Plains, with heavy amounts possible, especially across portions of
northern Minnesota.
...Southwest...
Additional showers and storms along an axis similar to the previous
day are expected across portions of eastern Arizona, western to
central New Mexico, and southern Colorado - where PW anomalies will
remain around 2 std dev above normal.
...Southeast...
Deep moisture will remain centered along a front that will continue
to sink slowly south across the Southeast. PWs around 2 inches,
along with weak mid-to-upper level forcing, will help accentuate
diurnal activity -- raising the potential for heavy amounts and
possible flash flooding across parts of the South Carolina
Lowcountry, southern Georgia, and North Florida.
Pereira
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Sep 5 2026
Day 4 and Day 5
Valid 12Z Tue Sep 08 2026 - 12Z Thu Sep 10 2026
Day 4
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHWEST AND OVER PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND
UPPER LAKES...
...Southwest...
An axis of above average PW values will stretch from the Southwest,
northeastward through the Central Plains and into the Upper
Mississippi Valley and Upper Lakes region. Scattered monsoonal
convection likely to continue across the Southwest day 4,
supporting locally heavy rains and isolated runoff issues.
...Upper Mississippi Valley into the Upper Lakes...
Farther to the northeast, while the frontal boundary overall is
expected to be progressive day 4 moving from the Upper Mississippi
Valley into the Upper Lakes, the southwestern portion of the front
will become 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.
Day 5...
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS EASTERN
CALIFORNIA, THE SOUTHWEST, THE CENTRAL PLAINS INTO THE MID
MISSISSIPPI VALLEY AND OVER NORTHERN NEW YORK STATE INTO NORTHERN
NEW ENGLAND...
...Sierra, southeast California, the Southwest and Southern
Rockies...
PW values expected to become increasingly anomalous day
5 across the Southwest, southern to central California and into the
Great Basin. This is the result of the re-amplification of the mid
to upper level trof off the northern to central California coast
that will be capturing tropical moisture from in the vicinity of
Marie and advecting it northeastward. Scattered convection in this
anomalous PW axis, 2-3+ standard deviations above the mean, will
support locally heavy rains and isolated runoff issues from the
Sierra, into southeast California, the Desert Southwest and
portions of the Southern Rockies.
...Central Plains into the Lower Missouri and Mid Mississippi
Valley...
A surface frontal boundary is expected to become west to east
oriented along the southern edge of the westerlies from the Central
Plains into the Lower MO and Mid MS Valley region. Shortwave
energy pushing eastward along the southern edge of the westerlies
will enhance uvvs along the west to east oriented front, supporting
potential for organized convection in what is expected to be an
axis of PW values 1 to 2+ standard deviations above the mean. Heavy
rain and isolated runoff issues possible with this organized
convection.
...Northern New York State into Northern New England...
The northern and eastern extension of the front over the Central
Plains to Mid MS Valley region is expected to remain progressive
day 5 as it pushes from the Great Lakes into the Northeast. There
is the potential for organized frontal convection in an axis of PW
values 1.75-2" moving eastward across NY State into New England. A
marginal risk was depicted where FFG values are relatively low
across northern NY State into Northern New England. The very
progressive nature of the front will be a detriment to any
widespread runoff issues.
Oravec
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 AM EDT Sat Sep 5 2026
Day 4 and Day 5
Valid 12Z Tue Sep 08 2026 - 12Z Thu Sep 10 2026
Day 4
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHWEST AND OVER PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND
UPPER LAKES...
...Southwest...
An axis of above average PW values will stretch from the Southwest,
northeastward through the Central Plains and into the Upper
Mississippi Valley and Upper Lakes region. Scattered monsoonal
convection likely to continue across the Southwest day 4,
supporting locally heavy rains and isolated runoff issues.
...Upper Mississippi Valley into the Upper Lakes...
Farther to the northeast, while the frontal boundary overall is
expected to be progressive day 4 moving from the Upper Mississippi
Valley into the Upper Lakes, the southwestern portion of the front
will become 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.
Day 5...
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS EASTERN
CALIFORNIA, THE SOUTHWEST, THE CENTRAL PLAINS INTO THE MID
MISSISSIPPI VALLEY AND OVER NORTHERN NEW YORK STATE INTO NORTHERN
NEW ENGLAND...
...Sierra, southeast California, the Southwest and Southern
Rockies...
PW values expected to become increasingly anomalous day
5 across the Southwest, southern to central California and into the
Great Basin. This is the result of the re-amplification of the mid
to upper level trof off the northern to central California coast
that will be capturing tropical moisture from in the vicinity of
Marie and advecting it northeastward. Scattered convection in this
anomalous PW axis, 2-3+ standard deviations above the mean, will
support locally heavy rains and isolated runoff issues from the
Sierra, into southeast California, the Desert Southwest and
portions of the Southern Rockies.
...Central Plains into the Lower Missouri and Mid Mississippi
Valley...
A surface frontal boundary is expected to become west to east
oriented along the southern edge of the westerlies from the Central
Plains into the Lower MO and Mid MS Valley region. Shortwave
energy pushing eastward along the southern edge of the westerlies
will enhance uvvs along the west to east oriented front, supporting
potential for organized convection in what is expected to be an
axis of PW values 1 to 2+ standard deviations above the mean. Heavy
rain and isolated runoff issues possible with this organized
convection.
...Northern New York State into Northern New England...
The northern and eastern extension of the front over the Central
Plains to Mid MS Valley region is expected to remain progressive
day 5 as it pushes from the Great Lakes into the Northeast. There
is the potential for organized frontal convection in an axis of PW
values 1.75-2" moving eastward across NY State into New England. A
marginal risk was depicted where FFG values are relatively low
across northern NY State into Northern New England. The very
progressive nature of the front will be a detriment to any
widespread runoff issues.
Oravec
