Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
728 PM EDT Sat Oct 10 2026
Day 1
Valid 01Z Sun Oct 11 2026 - 12Z Sun Oct 11 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN APPALACHIANS & PORTIONS OF SOUTHERN CALIFORNIA...
Southeast/Mid-Atlantic/Southern Appalachians...
Widespread heavy rains are likely to continue with Post-Tropical
Cyclone Isaias through tonight/early Sunday morning. Heaviest
rains likely into the upslope regions of the Southern Appalachians
from northeast Georgia into the Upstate of South Carolina and
western North Carolina. Strong upslope flow will support heavy
precip totals in the 3-5"+ range across these areas, with maximum
totals in the 6-10 inch range across far western NC into the
Upstate of SC. Changes to the risk areas were confined to their
western sides to account for areas where the heavy rain threat is
waning.
To the south of the maximum upslope precip area...there continues
to be potential for organized convection in the developing cold
frontal band southeast of the surface center across northwestern
FL as enough moisture, effective bulk shear, and instability
remains to fuel organized convection. Hourly rain amounts to 3" are
possible, though the thunderstorm area should be somewhat
progressive. Additional 5" totals are possible.
Frictional convergence along the coast favors the potential for
very heavy totals along the immediate northeast SC and NC coastal
regions. Both the HREF and RRFS neighborhood probabilities are high
for 2 and 3"+ totals, with isolated maximum values in excess of 5"
possible.
...Southwest...
PW values will be increasing towards 2" as moisture associated
with Rachel is drawn northeastward. More concentrated precip
areas likely after 0300 UTC as Rachel approaches the northern
Baja/Southern CA coast and a more favorable right entrance jet
region develops northeastward into the Great Basin. Probabilities
of 2"+ through early Sunday morning are highest in far southern CA,
where a Moderate Risk of flash flooding/excessive rainfall remains.
Burn scars, dry washes/arroyos, and urban areas would be most at
risk from the heavy rainfall expected.
Roth
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Oct 11 2026
Day 1
Valid 12Z Sun Oct 11 2026 - 12Z Mon Oct 12 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS THE
GREAT BASIN AND PORTIONS OF THE SOUTHWEST...
..Great Basin and Southwest...
There is good model continuity with the widespread heavy rainfall
threat across a large region across the Great Basin and portions
of the Southwest on day 1. The combination of the remnants of
Rachel and the continued very favorable right entrance region jet
dynamics over the Great Basin will keep PW anomalies very high for
the upcoming day 1 period with values 2 to 4+ standard deviations
above the mean. Model consensus is for widespread heavy precip
totals across these areas, with a moderate risk maintained from
Southern CA into southern NV, including the Las Vegas region, far
northwest AZ and far southwest UT. HREF and RRFS neighborhood
probabilities are high for 1 and 2"+ amounts inside the slight risk
area, with high probabilities for 3"+ amounts across much of the
moderate risk area.
...Mid-Atlantic...
The extra-tropical remnants of Isaias will produce widespread
moderate to heavy precipitation from the Upper OH Valley, Central
Appalachians, Mid- Atlantic, Northeast and coastal NC day 1. HREF
neighborhood probabilities are high for 2 and 3"+ amounts in the
upslope of the Blue Ridge across northwest Virginia, far eastern
West Virginia and central Maryland. A small slight risk area was
drawn for these higher probabilities . Elsewhere, no big changes to
the marginal risk, with isolated primarily urban runoff issues
possible.
....Central Florida...
Above average PW values will persist along and ahead of the cold
front pressing south day 1 across central Florida. Scattered
convection likely ahead of this front with locally heavy precip
likely. Not a lot of confidence with details, but HREF and RRFS
neighborhood probabilities are fairly high for 1 and 2"+ totals
which may produce isolated runoff issues, especially in urbanized
regions.
Oravec
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Oct 11 2026
Day 2
Valid 12Z Mon Oct 12 2026 - 12Z Tue Oct 13 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE GREAT BASIN AND THE SOUTHWEST...
...Great Basin into the Southwest...
While the remnants of Rachel will have accelerated rapidly
northeast day 1 away from the Southwest and Great Basin, a closed
low will settle southeastward day 2 across the Great Basin. This
will help maintain above average PW values to the east and
southeast of this closed low from Southern California into the
Southwest and Great Basin, although values will be lower than the
day 1 period. Model consensus is for additional moderate to heavy
precip totals from northwest Arizona into eastern Nevada and much
of Utah. While precip totals are much lower than the day 1 period,
a slight risk was maintained from northwest Arizona into much of
Utah along the Wasatch as there will likely be overlap of heavy
rain areas on day 1 with the potential day 2 moderate to heavy
totals.
Oravec
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Oct 11 2026
Day 3
Valid 12Z Tue Oct 13 2026 - 12Z Wed Oct 14 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE GREAT BASIN AND FROM THE SOUTHERN HIGH PLAINS INTO THE
CENTRAL PLAINS AND LOWER MISSOURI VALLEY...
...Great Basin...
The closed low over the Great Basin day 2 will be pushing east
toward the four corners region by the end of day 3. Additional
moderate to isolated heavy precip totals possible in the comma
head/deformation band to the north of the closed low center across
the Great Basin into the Central Rockies. Snow level will be
dropping day 3 in the Wasatch/Uinta with rain primarily over
northwestern Utah. A marginal risk is depicted here where isolated
runoff issues may occur, especially after heavy rain totals days 1
and 2.
...Southern High Plains, Central Plains, Lower Missouri Valley...
Across the Southern High Plains into the Central Plains/Lower
Missouri Valley region, PW values expected to rise to 2-4+ standard
deviations above the mean in the broad southwesterly mid to upper
level flow on the east side of the Great Basin closed low. Some
moisture, likely mid to upper level, from the remnants of Simon
moving into the west coast of Mexico late Monday into Tuesday may
push northeastward in this broad mid to upper level southwesterly
flow. This should support increasing coverage of precip across
these areas, especially Tuesday night into early Wednesday when
overall favorable right entrance region jet dynamics will be
present in this above average PW axis. There still is a lot of
spread in the latest guidance with details of where the heaviest
precip will fall, keeping the threat level, at the moment. to
marginal.
Oravec
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Oct 11 2026
Day 4 and Day 5
Valid 12Z Wed Oct 14 2026 - 12Z Fri Oct 16 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHERN AND CENTRAL PLAINS TO MID-MISSISSIPPI VALLEY ON DAY 4 AND
DAY 5...
...Southern & Central Plains...
Day 4...
Longwave pattern across the west begins to shift eastward with an
increasingly diffluent pattern downstream of the mean trough over
the Central and Southern Plains. The current progs are textbook
synoptic evolutions for lee cyclogenesis within the Front Range of
CO which will help translate into quite an active setup for both
the D4 and D5 time frames. Remnant moisture from now Hurricane
Simon is expected to pull northward the beginning of the week as
the moisture flux and energy from what is left of Simon pivots
around the western periphery of a ridge positioned across the
Southeast CONUS. PWAT anomalies across the Southern High Plains all
the way up into portions of the Midwest will run between +2 to +3
sigma according to both the ECENS and NAEFS anomaly outputs for
PWATs. This will place a large area of PWAT outputs between
1.75-2.3" from the Big Bend of TX up through at least the southern
half of the Midwest (IL/IA/WI) leading to a primed environment
capable for heavy rainfall in any convective environments.
Synoptic evolution will yield a surface low over the Front Range
of CO with a cold front extension down through the Southern
Rockies with an advancement eastward expected as the upstream upper
level setup continues its forward propagation into the Central U.S.
A broad warm sector regime will materialize on Wednesday afternoon
and evening with a crescendo of convective development expected
Wednesday evening with the addition of a stronger low-level jet
(LLJ) initiating around 00z Thu, lasting through the evening. Model
outputs have been increasingly favorable for widespread 2-3" totals
across portions of the Central and Southern Plains into the Mid-
Mississippi Valley with the maxima focused over OK into MO with a
southwest inflection back into north TX across the Red River. Heavy
rain is likely in any convective cores that develop thanks to the
environment in place with such a prolific deep moisture plume in
place thanks to the remnants of Simon. Given such a prominent QPF
signature and expected synoptic evolution for mid to late week, a
broad SLGT risk is in place over the aforementioned areas with only
some minor adjustments over the region from the previous forecast.
Further assessment in the coming days may lead to a higher risk, or
at least wording of a higher end SLGT with perhaps some adjustment
in the areal coverage of the risk. Until then, this will be the
start of an active period of heavy rainfall potential across a
large part of the Plains.
Day 5...
The D5 time frame is almost a repeat of the previous period with an
ongoing heavy rain threat from widespread convection along and
ahead of a slow-moving cold front out of the Rockies into the
Central and Southern High Plains. There will be quite a bit of
resistance against the front over the Southern Plains thanks to
the stout ridge axis flexing its muscle over the Southeast U.S
extending back into the Southern High Plains. This will likely
infer a slow propagation of the front and continued onslaught of
convection during the afternoon and evening portions of Thursday
into early Friday morning. Surface ridge over the Northern U.S.
will act to press the front southward from the standpoint for areas
north of I-70. Despite the assistance from the ridge to the north,
it will be difficult for the cold front trailing back into the
High Plains to make much progress until the upper pattern over the
Rockies finally opens up and kicks northeast out of the region.
This is the current indication with the most likely outcome leading
to yet another period of heavy rainfall extending from southwestern
TX back into the at least the southern half of MO. Models are less
consistent with the placement of the heaviest rainfall in this
period, but there is still enough of a consensus in the ensembles
to warrant another broad SLGT risk encompassing the Southern High
Plains into the Mid-Mississippi Valley. The SLGT risk outline is
fairly identical to the D4 period which notes just how slow the
evolution of the upcoming pattern will be before we finally see
progress by the end of the weekend and following weekend. As was
noted in the D4, this time frame will need to be monitored for a
potentially higher risk over anywhere within the current SLGT
forecast, so stay tuned over the next several forecast cycles for
continued updates on the threat.
Kleebauer
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sun Oct 11 2026
Day 4 and Day 5
Valid 12Z Wed Oct 14 2026 - 12Z Fri Oct 16 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHERN AND CENTRAL PLAINS TO MID-MISSISSIPPI VALLEY ON DAY 4 AND
DAY 5...
...Southern & Central Plains...
Day 4...
Longwave pattern across the west begins to shift eastward with an
increasingly diffluent pattern downstream of the mean trough over
the Central and Southern Plains. The current progs are textbook
synoptic evolutions for lee cyclogenesis within the Front Range of
CO which will help translate into quite an active setup for both
the D4 and D5 time frames. Remnant moisture from now Hurricane
Simon is expected to pull northward the beginning of the week as
the moisture flux and energy from what is left of Simon pivots
around the western periphery of a ridge positioned across the
Southeast CONUS. PWAT anomalies across the Southern High Plains all
the way up into portions of the Midwest will run between +2 to +3
sigma according to both the ECENS and NAEFS anomaly outputs for
PWATs. This will place a large area of PWAT outputs between
1.75-2.3" from the Big Bend of TX up through at least the southern
half of the Midwest (IL/IA/WI) leading to a primed environment
capable for heavy rainfall in any convective environments.
Synoptic evolution will yield a surface low over the Front Range
of CO with a cold front extension down through the Southern
Rockies with an advancement eastward expected as the upstream upper
level setup continues its forward propagation into the Central U.S.
A broad warm sector regime will materialize on Wednesday afternoon
and evening with a crescendo of convective development expected
Wednesday evening with the addition of a stronger low-level jet
(LLJ) initiating around 00z Thu, lasting through the evening. Model
outputs have been increasingly favorable for widespread 2-3" totals
across portions of the Central and Southern Plains into the Mid-
Mississippi Valley with the maxima focused over OK into MO with a
southwest inflection back into north TX across the Red River. Heavy
rain is likely in any convective cores that develop thanks to the
environment in place with such a prolific deep moisture plume in
place thanks to the remnants of Simon. Given such a prominent QPF
signature and expected synoptic evolution for mid to late week, a
broad SLGT risk is in place over the aforementioned areas with only
some minor adjustments over the region from the previous forecast.
Further assessment in the coming days may lead to a higher risk, or
at least wording of a higher end SLGT with perhaps some adjustment
in the areal coverage of the risk. Until then, this will be the
start of an active period of heavy rainfall potential across a
large part of the Plains.
Day 5...
The D5 time frame is almost a repeat of the previous period with an
ongoing heavy rain threat from widespread convection along and
ahead of a slow-moving cold front out of the Rockies into the
Central and Southern High Plains. There will be quite a bit of
resistance against the front over the Southern Plains thanks to
the stout ridge axis flexing its muscle over the Southeast U.S
extending back into the Southern High Plains. This will likely
infer a slow propagation of the front and continued onslaught of
convection during the afternoon and evening portions of Thursday
into early Friday morning. Surface ridge over the Northern U.S.
will act to press the front southward from the standpoint for areas
north of I-70. Despite the assistance from the ridge to the north,
it will be difficult for the cold front trailing back into the
High Plains to make much progress until the upper pattern over the
Rockies finally opens up and kicks northeast out of the region.
This is the current indication with the most likely outcome leading
to yet another period of heavy rainfall extending from southwestern
TX back into the at least the southern half of MO. Models are less
consistent with the placement of the heaviest rainfall in this
period, but there is still enough of a consensus in the ensembles
to warrant another broad SLGT risk encompassing the Southern High
Plains into the Mid-Mississippi Valley. The SLGT risk outline is
fairly identical to the D4 period which notes just how slow the
evolution of the upcoming pattern will be before we finally see
progress by the end of the weekend and following weekend. As was
noted in the D4, this time frame will need to be monitored for a
potentially higher risk over anywhere within the current SLGT
forecast, so stay tuned over the next several forecast cycles for
continued updates on the threat.
Kleebauer
