FOUS30 KWBC 250812
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
412 AM EDT Sun Oct 25 2026

Day 1
Valid 12Z Sun Oct 25 2026 - 12Z Mon Oct 26 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS AND SOUTHEAST FLORIDA...

...Central and Southern High Plains...

An upper level low will track across the Four Corners region and
central Rockies today, while shortwave energy moves north across
the southern and central High Plains ahead of the low. This setup
will bring anomalously moist air into the south-Central U.S.,
tapping into Pacific and Gulf moisture that will fuel scattered to
widespread convection on the leading edge of the system. PWAT
values are expected to rise to 1-1.5 inches (2-4 standard
deviations above normal) from West Texas through the central High
Plains. The highest instability (MUCAPE 1000-1500 J/kg) is expected
to focus across portions of West Texas and New Mexico, which will
likely support intense rainfall rates up to 1-1.5 inches per hour.
Instability will be more limited over the central High Plains, but
modest instability (MUCAPE around 500 J/kg) combined with upper
level shortwave support should allow for some deeper convection
with locally heavy rainfall. Scattered instances of flash flooding
will be possible from West Texas through portions of the southern
and central High Plains, which is highlighted with a Slight Risk of
excessive rainfall for today. Soils are already saturated from
recent heavy rainfall over portions of West Texas and eastern New
Mexico, and increased runoff may heighten flash flooding concerns.
Areas near steep terrain and burn scars will also be vulnerable to
flash flooding.

A broader Marginal Risk area extends further north into the
central Plains where soils are less susceptible to flash flooding
but locally heavy rainfall may result in isolated instances of
flash flooding. Moisture will spread even further north ahead of
the system into the northern Plains, but with little instability to
work with, it will be difficult to get rainfall rates heavy enough
to pose a risk of flash flooding.

...East Coast of Florida...

A mid-level low will gradually move south over the Atlantic
parallel to the Florida Peninsula, then stall offshore of
Southeast Florida by this afternoon. This will result in a
prolonged period of northeasterly onshore flow along the East Coast
of Florida, with an emphasis over Southeast Florida. Moisture
wrapping around the northern side of the low circulation will bring
PWATs across the Peninsula up to 1.5-1.75 inches and up to 1.75-2
inches across Southeast Florida, which will support scattered to
widespread showers and storms that will form over the Atlantic and
migrate over the coast. Coastal convergence will focus the highest
precipitation totals right along the coast, which will create a
risk of isolated instances of flash flooding along the I-95
corridor south of Jacksonville. As the system stalls, precipitation
will target Southeast Florida, which is where the highest rainfall
totals are expected today. Hi-res models show rainfall totals
reaching 1-2 inches across Southeast Florida with locally higher
amounts possible. Given the sensitivity of urban areas of Southeast
Florida, scattered instances of flash flooding will be possible
and there is a Slight Risk of excessive rainfall for much of this area.

...Pacific Northwest...

A closed upper low will gradually move onshore in the Pacific
Northwest today, accompanied by steady rainfall along a leading
cold front and scattered to numerous post-frontal showers across
western Washington and Oregon. Locally heavy rainfall may be
possible, but given the dry antecedent conditions there is not
expected to be a flood threat with this system.

Dolan
 

Day 2
Valid 12Z Mon Oct 26 2026 - 12Z Tue Oct 27 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS AND SOUTHEAST FLORIDA...

...Central and Southern High Plains...

The upper low will push past the Rockies into the Plains,
resulting in surface cyclogenesis over the central/northern Plains.
Scattered showers and storms are expected in the warm sector of
the system over the central and southern High Plains. Similar to
Sunday, anomalous moisture streaming ahead of the system will
spread along the trailing cold front up into the northern Plains,
but the best instability will be limited to the central and
southern High Plains, which is where the highest flash flood risk
is expected. Precipitation totals are forecast to be modest
compared to previous days, but there will likely be a period of
enhanced convection Monday afternoon into Monday evening as an
upper level shortwave moves north into the region. During this
period, the ingredients will be in place to support a threat of at
least isolated instances of flash flooding within the Marginal Risk area.

Widespread precipitation is also expected over the northern Plains
in the vicinity of the surface low, but with little instability,
rainfall rates should remain moderate at best. Model guidance is
showing rainfall rates and totals remaining well below current FFGs
for the area, so there will be little to no flash flood risk for this area.

...Southeast Florida...

Northeasterly onshore flow with high PWATs up to 2 inches will
continue across Southeast Florida as the mid-level low remains
stalled near the Bahamas. Eventually, the low will be absorbed by
another wave moving north over Cuba, then move northeast into the
Atlantic later this week. Meanwhile, the system will become weaker
and less organized and precipitation coverage and intensity should
decrease. Even so, scattered showers will move onshore in Southeast
Florida throughout the day on Monday, and locally heavy rainfall
will be possible. Given heavy rainfall expected on Sunday, a
Marginal Risk area was continued for Southeast Florida where there
could be isolated instances of flash flooding, especially in urban areas.

Dolan
 

Day 3
Valid 12Z Tue Oct 27 2026 - 12Z Wed Oct 28 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR SOUTHEAST FLORIDA...

...Southeast Florida...

Northeasterly flow will continue across the Florida Peninsula,
with scattered showers and storms forming over the Atlantic and
moving onshore in Southeast Florida. Model guidance shows a surge
in moisture across Central and South Florida on Tuesday, with PWATs
exceeding 2 inches. This will likely support locally heavy
rainfall along the Southeast Florida coast as showers move onshore.
Isolated flash flooding could be possible in urban areas,
especially considering the previous days of heavy rainfall, so a
Marginal Risk of excessive rainfall was introduced for portions of
Southeast Florida.

Dolan
 

Day 4 and Day 5
Valid 12Z Wed Oct 28 2026 - 12Z Fri Oct 30 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL TEXAS...

A Slight risk has been introduced on day 5 (Thu) across portions of
TX, stretching from the Stockton Plateau through parts of the
western Hill Country and into south-central TX. Large scale forcing
for ascent will be driven in part by a strong southern stream
upper jet providing divergence aloft. Embedded shortwave energy
will also eject out of the East Pacific within the deep
southwesterly flow aloft, with some potential moisture and
vorticity contribution from what is currently tropical cyclone
Vance. Mid to upper level moisture sourced from the East Pacific
will combine with a strong southeasterly low level jet bringing
moisture out of the Gulf. This combination will drive PW values
well above the climatological 90th percentile for late October.

The environmental ingredients in place will support an organized
heavy rainfall event. As expected at a day 5 lead time, exact spatial
and temporal details will change some as the event nears. However
there is enough run to run consistency and model clustering...both
among physics based and AI guidance (with preference given to the
AIFS, AIGFS and ECMWF model suites)...to justify going straight to
a day 5 Slight risk. While adjustments to the risk area are
probable in subsequent updates as model guidance evolves/converges,
the currently outlined corridor represents the area of highest
probabilities at this time. We will continue to closely monitor
trends, as certainly some chance for locally significant flood
impacts from this event.

Surrounding the Slight risk, a broader Marginal risk extends
westward across West TX and into southern NM. While this region is
currently forecast to reside west of the primary heavy rainfall
axis, elevated hydrologic sensitivity exists over some of this area
from recent rainfall. Some uptick in moisture and instability is
forecast which should be sufficient for isolated to scattered
convection and localized flash flooding.

Chenard
$$
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