Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
316 AM EST Sun Nov 15 2026

Day 1
Valid 12Z Sun Nov 15 2026 - 12Z Mon Nov 16 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
COASTAL TEXAS ON SUNDAY...

The overall synoptic set-up remains fairly well handled by the
15/00Z suite of numerical guidance. Even so...some questions remain
concerning whether enough rain falls on land areas to result in
flooding concerns. Some guidance had backed away from that idea and
kept heaviest rainfall completely over the Gulf while the ensembles
still suggested some flooding concerns persist. To account for the
range of possibilities...the Marginal was maintained with only some
trimming of inland territory. The expansion of the Slight and
Marginal risk areas still looks good without much change needed.

An upper trough responsible for storms over north-central Texas
overnight prior to the start of the Day 1 period will continue to
dig southeastward toward the Gulf Coast. Convection is expected to
reignite later this afernoon as instability builds over the area.
The heaviest rainfall should wrap up by midnight Monday.

The 15/00Z guidance has shifted the inland axis of greatest PF
axis to between Houston and Corpus Christie and nudged a bit closer
to the coast. 24 hr 5" 40km RRFS exceedance probabilities are
between 20-60%, while 3" EAS probabilities are between 10-25%.

Bann


Day 2
Valid 12Z Mon Nov 16 2026 - 12Z Tue Nov 17 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 3
Valid 12Z Tue Nov 17 2026 - 12Z Wed Nov 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE FLORIDA EAST COAST AND THE SOUTHWEST U.S....

West...
An upper-trough and accompanying cold front will progress eastward
from the West Coast into the Interior West on Tuesday. Increasing
moisture along and with the frontal passage will lead to scattered
showers and thunderstorms at lower elevations across the Desert
Southwest given precipitable water values on the order of 1 inch in
the Lower Deserts. The fact that the system being progressive is
one factor against the potential for floooding. Despite that...a
Marginal Risk was introduced mainly in the west facing terrain of
northern Arizona...generally at or below 6500 feet (with
precipitation more likely to fall as snow at elevations above 7000
ft). Present indications are that hourly rainfall rates of 1.25
inches are possible whenever/wherever cells can align or merge or
mesocyclones manage to form. Rainfall this intense could lead to
issues in dry washes/arroyos or burn scars.

Eastern Florida...
Surface high pressure parked over the central Appalachians will
keep persistent eastly low-level flow in place across much of the
eastern Florida peninsula on Tuesday into early Wednesday morning
from the Geogia line to Lake Okeechobee (in broad geographic
terms), Precipitable water values of 1.25-1.5" are forecast, and
the low- level flow should bring instability off the warmer than
average Gulf Stream. Effective bulk shear should be sufficient for
organized convection. Hourly rain amounts as high as 1.75" would
be possible wherever short, training bands manage to materialize.
Maintained the Marginal Risk area introduced on Saturday for
portions of Eastern Florida with few changes needed.

Bann


Day 4 and Day 5

Valid 12Z Wed Nov 18 2026 - 12Z Fri Nov 20 2026

...THERE IS SLIGHT RISK OF EXCESSIVE RAINFALL FOR CENTRAL COASTAL
CALIFORNIA WEDNESDAY...

...California...

An upper-trough is expected to dig southward along the West Coast
and move inland across the western U.S. early this week. Additional
upper-energy upstream will help to reinforce the upper-trough
along the West Coast by day 4/Wednesday and day 5/Thursday, with a
secondary plume of Pacific moisture/Atmospheric River (AR)
accompanying the associated surface system/Pacific front. The
forecast strength of the AR has trended up over the last 24 hours,
now rated as Moderate through central coastal California as IVT
values reach and maintain values of 500-750 KG/ms through the day
4/Wednesday period. The deterministic guidance continues to
maintain areal average rainfall totals in the 1-2" range and
locally higher totals of 3-5", with much of this rain likely
falling in a 3-6 hour period with the passage of the Pacific front.
This would be more than sufficient for scattered flooding
concerns, and thus have introduced a Slight Risk along the central
Coastal Ranges and through the Bay Area. Additional rainfall is
expected further inland through the central Valley and along the
foothills of the Sierra. However, despite the influx of warmer,
moist Pacific air, colder air will still be in place overall given
the upper-troughing already over the western U.S., limiting snow-
level rises to around 4000 feet. This should keep the flooding
threat lower along the foothills as the heaviest precipitation
occurs as snow into the higher elevations of the Sierra.

Heavy rainfall will continue into the day 5/Thursday period
through portions of central California while spreading into
southern California. Uncertainty with where the heaviest rainfall
will occur is a bit higher compared to Wednesday as the
deterministic guidance begins to disagree more on the
orientation/progression of the Pacific front/AR, particularly into
southern California along the Transverse Ranges and southward
through the LA basin. Therefore, have opted to only introduce a
Marginal Risk along the central/southern California coast and
inland along the southern extent of the Sierra for now. However,
given that the deterministic guidance remains bullish into this
timeframe with totals of 1-3"+ possible, another Slight Risk will
likely be needed once there is greater confidence in location.

...Eastern Florida...

A situation with nearly antiparallel flow (low-level easterlies
and upper level westerlies) will continue through mid- to late week
across eastern Florida. Precipitable water values of 1.25-1.5" are
forecast, and the low-level flow should bring instability off the
warmer than average Gulf Stream. Effective bulk shear should be
sufficient for organized convection. Hourly rain amounts to 1.75"
would be possible wherever short, training bands manage to
materialize. An approaching upper level system closes off into an
upper level low which will help prolong the chances for localized
heavy rainfall through the period. A Marginal Risk has been
maintained for day 4/Wednesday with another Risk area introduced
for day 5/Thursday for portions of Eastern FL as global guidance
continues to suggest heavy rain potential.

Putnam/Roth


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