Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1211 PM EDT Sat Oct 10 2026

Day 1
Valid 16Z Sat Oct 10 2026 - 12Z Sun Oct 11 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS THE
SOUTHERN APPALACHIANS AND OVER FOR PORTIONS OF SOUTHERN
CALIFORNIA...

16Z Update...

Given the latest few runs of the HRRR, expanded the Slight risk
area a bit northward into southwest Virginia...although the
footprint of the expansion is fairly limited although the terrain.
The main focus for heavy rainfall will remain in the warm sector of
the system...especially along and east of a cold front from Georgia
into northern Florida as well as in portions of the Carolinas where
rainfall amounts look to be enhanced in the upslope region of the
terrain and along the immediate coastal regions. The expectation is
that there will be an uptick in the rainfall rates later today as
instability increases. The previous outlook had these areas well
covered and changes were minor.

Across the Southwest...moisture streaming ahead of Rachel will lead
to increasing coverage of rainfall across the Southwest US during
the day..with an increasing potential for significant flash and
urban flooding. This has remained consistent despite some small
variations in the forecast track.  Changes were minor.

Bann

Previous Excessive Rainfall Discussion...

Widespread heavy rains are likely day 1 across much of the
Southeast, Southern Appalachians, into the Tennessee Valley with
the extra-tropical remnants of Isaias. 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. The HREF
and RRFS neighborhood probabilities are in good agreement and show
high probabilities for 2, 3, 5"+ amounts in the upslope regions of
the Southern Appalachians where a moderate risk is maintained from
the previous outlook. Both the HREF and RRFS means also show a
defined region of 8"+ probabilities, albeit smaller than the 1, 3
and 5"+ amounts in the upslope regions of the Southern Appalachians.

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. Training of cells parallel to this developing front will be
possible day 1, supporting 2-3"+ precip totals and isolated 5"+
totals where max training occurs.

In the comma head/deformation precip band on the northwest side of
the circulation, the slight risk area from the previous issuance
was removed across northern MS,Northern AL into central to western
TN. While there may be heavy precip totals day 1 in this comma head
region, hourly rates will likely be less than 1" and remain below
FFG values, with only isolated runoff issues possible. HREF and
RRFS probabilities of 3 hour precip totals exceeding FFG values are
zero in this comma head/deformation band region.

No changes made to the risk area along the coastal Carolinas.
Strong coastal convergence will favor potential for very heavy
totals along the immediate upper SC and lower 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 to very anomalous levels day 1, 2 to
5+ standard deviations above the mean, from Southern CA, into the
Great Basin and portions of the Southwest as moisture associated
with Rachel is drawn northeastward. Initially day 1, convection
should be widely scattered across the Southwest into the Great
Basin. 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. Both the HREF and RRFS probabilities of 3 hour
precip exceeding FFG values increase after 0300 UTC, with the
greatest values over Southern CA into far southern NV and far
northwest AZ. Overall, not a lot of changes from the previous
issuance. The slight risk was extended farther northeast into
southern UT to cover the slot canyon regions. Otherwise, no
changes made to the moderate risk area over Southern CA.

Oravec


Day 2
Valid 12Z Sun Oct 11 2026 - 12Z Mon Oct 12 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL IN THE
SOUTHWEST...

A widespread heavy rainfall threat will continue across a large
region from Southern California, into the Great Basin and portions
of the Southwest on day 2. 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 day
2, 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. A broad slight risk area continues northeastward into the
Great Basin, with a northeastward extension of this slight risk
area made from the previous issuance into far northeast NV,
northern UT and far southeast ID to match the model consensus heavy
qpf axis.

The remnants of Isaias will produce widespread moderate to heavy
precipitation from the Upper OH Valley, Central Appalachians, Mid-
Atlantic, Northeast and coastal NC day 2. Aside from isolated
urban runoff issues, believe there will not be any excessive
rainfall issues across these areas. There may be some convection
along the immediate NC coast Sunday, with isolated runoff issues
possible.

Oravec


Day 3
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...

While the remnants of Rachel will have accelerated rapidly
northeast day 2 away from the Southwest and Great Basin, a strong
amplified mid to upper level trof will continue across the Great
Basin into central to southern California. This will maintain
above average PW values to the east of this upper trof from
Southern California into the Southwest and Great Basin, although
values will be lower than the day 1 and 2 time 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 2 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 day 2
with the potential day 3 moderate to heavy totals.

Oravec


Day 4 and Day 5

Valid 12Z Tue Oct 13 2026 - 12Z Thu Oct 15 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
ARIZONA INTO UTAH MONDAY INTO EARLY WEDNESDAY...

...Western U.S...

Remnants from Rachel plus the influence of a mature upper level low
centered over the Great Basin will maintain another active period
with convection centered over the Mogollon Rim in AZ up through UT
where the model consensus continues to depict scattered heavy
convective prospects in-of the terrain and the valley areas to the
north. The good news compared to previous periods is the remaining
energy from Rachel will be diffuse by this juncture of the
forecast, however the upper level progression just to the east will
be plentiful in providing a continued ascent regime capable of
maintaining a broad convective threat with locally heavy rainfall
thanks to PWATs lingering between 1-2 standard deviations above
normal. Considering the environment prior, this is progress to
waining the worst of the flash flood threat that will ensue over
the weekend. That said, antecedent soils may be pretty well-
saturated by this point leading to perhaps a bit of an easier
chance for flash flooding despite rates and expected rainfall
accumulations being lower than previous periods. A broad MRGL risk
remains over the interior west with an embedded SLGT still
lingering over northwest AZ up through much of UT where the best
mid and upper level forcing is progged for much of Tuesday before
the threat finally ends heading into mid-week.

...Southern High Plains into the Central Plains...

An increasing threat of heavy rainfall will be brought into the
Central and Southern Plains by D4 thanks to the introduction of
remnant energy and moisture advection from now Hurricane Simon in
the Eastern Pacific off Mexico. The current upper pattern depicts
Simon taking a turn and moving due north through Mexico with its
primary energy becoming sheared as it migrates poleward across
northern Mexico and eventually makes headway into the CONUS.
Current ensembles are in agreement for the energy of Simon to
maneuver through Coahuila and up through southwest TX before
pivoting north-northeast around a broad ridge centered over the
Southeast U.S. This will bring the main energy, albeit sheared and
weaker than the prior 72 hrs, across the Central and Southern
Plains leading to a focused area of ascent to couple with elevated
PWATs bring brought into the area. A surface ridge to the north
will only act to increase low-level convergence in tandem with the
primary energy ejection leading to an area of convection spawning
after 00z with the introduction of a budding nocturnal LLJ. Models
are consistent with a signal for 1-3" of rainfall in areas where
convection develops with a few pockets with higher totals. Ensemble
mean QPF is much lower overall, so the maxima is more in line with
the deterministic output from the global suite. In any case, this
signal is reputable for a broad MRGL risk with the alignment of the
risk basically right within the expected path of the mid-level
energy as it moves north-northeast into the CONUS. The best
potential will likely be over OK/KS into MO thanks to the added
benefit of the low-level convergence regime being introduced with
the combination LLJ and surface ridge to the north.

As we move into D5, the threat blossoms into some more appreciable
with sights on the Central and Southern Plains, perhaps expanding
as far north as the Northern Plains as the upstream pattern evolves
further with a strong ULL disturbance migrating through the Inter-
Mountain West leading to lee cyclogenesis over the Front Range. The
addition of the low and upper low into the pattern will only
benefit a more pronounced convergence pattern and favorable upper
support to maintain a broader, more intense precipitation shield
over the Central U.S. come Wednesday afternoon and beyond. This is
fairly classic in the evolution the surface ridge to the north and
now maturing lee cyclone will only set the stage for a more
prototypical synoptic evolution that typically correlates to more
widespread convection within a budding warm sector and the
migration of a cold front that materializes along the base of the
surface low. Ample moisture noted via widespread PWAT anomalies
between 2-3 standard deviations above normal coupled with
increasingly favorable jet and kinematic ascent will lead to quite
a resurgence of convection over the Central Plains into the Mid-
Mississippi Valley by Wednesday night creating a broad area of
potentially heavy rainfall and flash flood concerns. The greatest
threat based on recent NBM and global ensemble probabilities, as
well as the latest First Guess Fields center the risk over eastern
KS into MO with an already robust 2+ inch forecast being depicted
within the means. At this lead time, that's fairly impressive, but
makes sense synoptically. Another broad MRGL risk was added for the
new D5 period, but a SLGT is also forecast within that
aforementioned area where probabilities for >2" are highest across
the Central Plain into the Mid-Mississippi Valley.

Kleebauer


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt