Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Mon Sep 14 2026
Day 1
Valid 01Z Tue Sep 15 2026 - 12Z Tue Sep 15 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
IOWA...
01Z Update...
...Midwest...
In the Midwest, the biggest adjustment from the previous issuance
was the removal of the northern extent of the Marginal Risk area
from the upper Mississippi Valley and northern Great Lakes area,
where either the rainfall threat has ended, storms are
progressive, or where limited instability is likely to keep
rainfall amounts and the potential for flash flooding in check. It
still appears the greatest threat for heavy rainfall and flash
flooding through the remainder of the evening into the overnight
will center from southwestern to central Iowa. Heavy showers and
thunderstorms will continue to expand, with cell-training
supporting the potential for heavy amounts and flash flooding. A
Moderate Risk remains in place -- largely centered where recent
runs of the HRRR and the 18Z HREF suggest the greatest threat. HREF
probs indicate localized amounts exceeding 3 inches are possible
overnight within this area. Refer to WPC MPD #1284 for additional
information regarding the near-term heavy rain and flash flooding
threat in this area.
...Southwest...
In the Southwest, removed much of central to northern Arizona and
Utah from the outlook. However, a broad Slight Risk stretching from
southeastern Arizona across much of western New Mexico into
southwestern Colorado remains. Widespread convection continues to
fire across this area, producing areas of flash flooding. Storms
are expected to continue for at least a few more hours, posing
additional concerns. Refer to WPC MPD #1283 for further
information.
Pereira
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Mon Sep 14 2026
Day 2
Valid 12Z Tue Sep 15 2026 - 12Z Wed Sep 16 2026
...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, MISSOURI VALLEY, AND SOUTHWEST U.S...
...Central U.S...
The heavy rain focus over the central states will align with the
slow moving cold front over Kansas, northern Missouri, and western
Illinois where a Slight Risk persists. The Slight was trimmed from
the north, but kept for far southeast Nebraska and southern Iowa
given wet antecedent conditions despite less QPF there. Deep layer
SWly flow will remain parallel to the cold front, promoting
training convection. 12Z guidance favors this repeating rain threat
area to continue farther southwest to the Texas Panhandle where the
Slight Risk was expanded into. PW anomalies of 2 to 3 deviations
above normal can be expected with a swath of actual values around
2". QPF in the 2-4" range are in both the 12Z REFS and HREF with
the HREF favoring northeast KS while the REFS is broader across
northern MO. This area can be considered to have a more enhanced
risk than a general Slight. Scattered flash flooding is considered
likely, especially for overlap from the several inches of rain that
fell north of the KC metro this morning.
The overall risk area continues east along the front across
northern Indiana to Cleveland where the Marginal was expanded.
...Southwest U.S...
The Southwest Monsoon continues in earnest at least through
midweek as an upper high persists over the Mid-South and low
pressure tracks down the West Coast to Northern California.
Moisture anomalies of 2 to 2.5 standard deviations are expected
Tuesday for southern/central Arizona, much of New Mexico, and
over southern Utah through central Colorado. This will be the 4th
day in a row with this pattern leading to increasingly vulnerable
areas/wet antecedent surface. Expanded the Slight areas to include
all of the Slot Canyon Region of southern Utah east to the San
Juans in Colorado as well as more of the Mogollon Rim area in
central Arizona. PW anomalies are less over northern Arizona for
now, but southerly flow is across the region, so further expansion
may be eventually warranted.
Jackson
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Mon Sep 14 2026
Day 3
Valid 12Z Wed Sep 16 2026 - 12Z Thu Sep 17 2026
...THERE ARE SLIGHT RISKS OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST, CENTRAL PLAINS & SOUTHWESTERN U.S...
...Central Plains & Midwest...
High pressure in the wake of the low tracking across the Canadian
Prairies today shifts over the northern Great Lakes Wednesday.
Return flow west of the high brings the frontal zone and moisture
back north into vulnerable areas of southeast Nebraska, northeast
Kansas, northern Missouri, southern into central Iowa and northern
Illinois. Right entrance region jet dynamics are also in play from
the Upper Midwest. Expect more convective development near the
front on the strong LLJ. The higher-res 12Z RRFS/Canadian Regional
are farther south, but the 12Z ECMWF/EC-AIFS are a tick farther
north of Iowa. Some trim to the north side of the Slight Risk was
made with areas of central/southern Iowa still considered more of
an enhanced Slight. Swaths of 2-5" are given in these dynamic
models. Depending on what happens tonight and where guidance favors
the maximum going forward, further upgrades are possible.
...Southwest U.S...
Vigorous Southwest Monsoon activity on tap for Wednesday as the
West Coast low reaches far northern California with downstream
troughing pumping stronger southwest flow over the Desert
Southwest. Moisture looks to peak for the week from southern AZ
through much of NM and southern CO with PW anomalies of 3 standard
deviations above normal. 12Z RRFS and Canadian Regional (two of the
few higher res models for Day 3) are aggressive with 2-4" over much
of southeast AZ up the Mogollon Rim and western NM and southern CO.
The Slight Risk is expanded farther up the Mogollon Rim and down
over the Sacramento Mountains, with a larger area of more enhanced
Slight Risk areas over much of western NM.
Jackson
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Mon Sep 14 2026
Day 4 and Day 5
Valid 12Z Thu Sep 17 2026 - 12Z Sat Sep 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST U.S, CENTRAL PLAINS, MISSOURI VALLEY, AND INTO THE UPPER
MIDWEST...
20Z Update...
...Southwest...
Overall, no large-scale changes were made to the previous outlook.
For Day 4, confidence is increasing that parts of the Southwest --
notably southwestern to north-central New Mexico -- may be
categorized as a "high-end Slight." Following what is expected to
be a very active Wednesday, areal averages are expected to drop
off some on Thursday, but the coverage of impactful amounts still
looks to be significant. PW anomalies on Thursday are forecast to
remain 2-3+ standard deviations above normal across much of New
Mexico and eastern Arizona on Thursday. Meanwhile, mid-to-upper
level energy embedded within southerly flow between an approaching
low/trough and a downstream ridge will help produce areas of
enhanced ascent. One limiting factor may cloud cover from the
previous day's activity and reduced instability. However, even with
reduced rainfall rates, soils are likely to be remain vulnerable
to excessive runoff given the previous days' rainfall.
...Upper Midwest...
Made mostly minor adjustments here as well. While the 12Z guidance
continued to show a good signal for heavy amounts extending east
across parts of the northern Plains toward the upper Mississippi
Valley on Day 4, and then from the upper Mississippi Valley toward
the Great Lakes on Day 5, they also showed notable latitudinal
spread regarding its axis. The Slight Risk areas remains near the
middle of the envelope of solutions.
Pereira
Previous Discussion...
The Days 4-5 period (Thu. Sept 17 - Fri. Sept 18) can be
summarized by an expansive and highly anomalous upper- level ridge
of high pressure taking hold over much of the Southern U.S., while
an upper-level trough in the West makes its way from the West Coast
towards the Northern Rockies. There is also a deep upper- trough
tracking through eastern Canada, which in contrast with the upper-
ridge to the south will create tight thermal and moisture gradient
from the Great Lakes to the Northeast. The 850mb ridge will remain
positioned over the Mid- South and is ideally located to produce an
extended fetch of southerly flow over the Southern Plains. This
results in unusually strong IVTs over the Great Plains both Days 4
and 5. The ECMWF SATs show >90th climatological percentile IVTs
aimed at the Great Lakes and Northeast on Day 4, which combined
with increasing instability and a nearby frontal boundary present,
could lead to scattered thunderstorms capable of producing
localized flash flooding.
By Day 5, the Midwest becomes the focus for flash flood potential
as a pair of jet streaks; one over the Great Lakes and another
emerging from the Rockies, place their divergent jet streak
quadrants overhead. Combined with PWs >1.75", which is above the
99th climatological percentile, this serves as an ideal setup for
additional rounds of excessive rainfall. The Midwest will have also
dealt with heavy rainfall the first half of the week, making
overly saturated soils a key player in potential flash flooding
late week. A pair of Slight Risks are in place over parts of the
North Central U.S. for both Thursday and Friday to cover this
prolonged window of excessive rainfall.
Lastly, the Southwest remains mired in a steadfast monsoonal flow
regime that is pumping copious amounts of moisture into the region.
Day after day, scattered thunderstorms will produce locally
excessive rainfall rates in excess of 1"/hr, keeping the threat for
flash flooding in place through the end of the week. A Slight Risk
remains in place for Day 4 (Thursday) while a large Marginal
encompasses an area that extends from southern NM and western TX,
to northern AZ and the Central Rockies.
Mullinax
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
854 PM EDT Mon Sep 14 2026
Day 4 and Day 5
Valid 12Z Thu Sep 17 2026 - 12Z Sat Sep 19 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHWEST U.S, CENTRAL PLAINS, MISSOURI VALLEY, AND INTO THE UPPER
MIDWEST...
20Z Update...
...Southwest...
Overall, no large-scale changes were made to the previous outlook.
For Day 4, confidence is increasing that parts of the Southwest --
notably southwestern to north-central New Mexico -- may be
categorized as a "high-end Slight." Following what is expected to
be a very active Wednesday, areal averages are expected to drop
off some on Thursday, but the coverage of impactful amounts still
looks to be significant. PW anomalies on Thursday are forecast to
remain 2-3+ standard deviations above normal across much of New
Mexico and eastern Arizona on Thursday. Meanwhile, mid-to-upper
level energy embedded within southerly flow between an approaching
low/trough and a downstream ridge will help produce areas of
enhanced ascent. One limiting factor may cloud cover from the
previous day's activity and reduced instability. However, even with
reduced rainfall rates, soils are likely to be remain vulnerable
to excessive runoff given the previous days' rainfall.
...Upper Midwest...
Made mostly minor adjustments here as well. While the 12Z guidance
continued to show a good signal for heavy amounts extending east
across parts of the northern Plains toward the upper Mississippi
Valley on Day 4, and then from the upper Mississippi Valley toward
the Great Lakes on Day 5, they also showed notable latitudinal
spread regarding its axis. The Slight Risk areas remains near the
middle of the envelope of solutions.
Pereira
Previous Discussion...
The Days 4-5 period (Thu. Sept 17 - Fri. Sept 18) can be
summarized by an expansive and highly anomalous upper- level ridge
of high pressure taking hold over much of the Southern U.S., while
an upper-level trough in the West makes its way from the West Coast
towards the Northern Rockies. There is also a deep upper- trough
tracking through eastern Canada, which in contrast with the upper-
ridge to the south will create tight thermal and moisture gradient
from the Great Lakes to the Northeast. The 850mb ridge will remain
positioned over the Mid- South and is ideally located to produce an
extended fetch of southerly flow over the Southern Plains. This
results in unusually strong IVTs over the Great Plains both Days 4
and 5. The ECMWF SATs show >90th climatological percentile IVTs
aimed at the Great Lakes and Northeast on Day 4, which combined
with increasing instability and a nearby frontal boundary present,
could lead to scattered thunderstorms capable of producing
localized flash flooding.
By Day 5, the Midwest becomes the focus for flash flood potential
as a pair of jet streaks; one over the Great Lakes and another
emerging from the Rockies, place their divergent jet streak
quadrants overhead. Combined with PWs >1.75", which is above the
99th climatological percentile, this serves as an ideal setup for
additional rounds of excessive rainfall. The Midwest will have also
dealt with heavy rainfall the first half of the week, making
overly saturated soils a key player in potential flash flooding
late week. A pair of Slight Risks are in place over parts of the
North Central U.S. for both Thursday and Friday to cover this
prolonged window of excessive rainfall.
Lastly, the Southwest remains mired in a steadfast monsoonal flow
regime that is pumping copious amounts of moisture into the region.
Day after day, scattered thunderstorms will produce locally
excessive rainfall rates in excess of 1"/hr, keeping the threat for
flash flooding in place through the end of the week. A Slight Risk
remains in place for Day 4 (Thursday) while a large Marginal
encompasses an area that extends from southern NM and western TX,
to northern AZ and the Central Rockies.
Mullinax
