Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
257 PM EST Sun Nov 15 2026

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

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF EASTERN TEXAS...

16Z Update: Based on the latest (12Z) guidance, including the REFS
QPF exceedance probabilities, along with the current mesoanalysis
(CAPE trends), expect the heaviest rain rates to reside off the TX
coast through the remainder of the Day 1 period (through 12Z Mon).
This includes the next batch of widespread rain out ahead of the
main shortwave, which again is traversing across a more stable (or
much less 'unstable') environment with higher FFGs.

Because of this, and per collaboration with WFOs HGX, CRP, and
LCH, have dropped the Slight Risk while retaining the Marginal
Risk.

B. Hurley


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.

Hurley


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

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE FLORIDA EAST COAST....

...Eastern Florida...
2000Z Update: Based on the latest guidance, including the 12Z AI
ECMWF and GFS, have hoisted a Slight Risk (Level 2/4) across east-
southeast parts of the FL Peninsula, including the Gold Coast,
Treasure Coast, and parts of the Space Coast up to Cape Canaveral.
Positively-tilted mid-upper level trough across the eastern Gulf on
Tue-Wed will slowly track across the Peninsula during the rest of
the week, setting up a multi-day rainfall event. PWs are expected
to climb to 1.75-2.00", while the strengthening low-level easterly
flow off the Atlantic (20-30kts at 850 mb) opposes the mean 850-300
mb flow. Deep-layer instability will be a limiting factor across
this area, north of the surface front which will drop south of the
Keys. MUCAPEs are expected to remain below 1000 J/Kg, generally
peaking around 500-750 J/Kg. However given the persistence (longer
duration), expect there could be a few more runoff issues towards
the tail end of the Day 3 period (Tuesday night into Wednesday
morning), likely carrying over into Day 4. We confined the Slight
Risk to the areas that had the highest 3" probabilities on Day 3
per the GEFS/ECENS/CMC.

Hurley

Previous Discussion...

Surface high pressure parked over the central Appalachians will
keep persistent easterly low-level flow in place across much of
the eastern Florida peninsula on Tuesday into early Wednesday
morning from the Georgia 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

...Parts of the Southwest and Lower Great Basin...
2000Z Update: Expanded the Marginal Risk across central-northern AZ
into southeast NV and southern UT based on the 12Z guidance trends.
These are the areas where the guidance shows MUCAPEs peaking
between 250-500 J/Kg during the day Tuesday. The QPF signal is
highest across southwest into south-central UT (southern Wasatch);
however, that is also the region devoid of instability and where
a good portion of the precipitation is expected to fall as snow.

Hurley

Previous Discussion...

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 flooding. 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.

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, with
additional reinforcements to the longwave trough coming in mid-week.
Guidance trends have been quicker/more southerly with this system
over the past couple of days. A plume of Pacific moisture/
moderately strong Atmospheric River (AR) accompanies the
associated surface system/Pacific front.  The deterministic
guidance shows areal average amounts in the 2-4" range and locally
higher totals anticipated. Much of this rain is likely to fall in
a 3-6 hour period with the passage of the Pacific front. Given the
hilliness of the coastal range, including the cities in the Bay
Area, kept the Slight Risk going as there are bound to be scattered
instances of localized flooding/ponding of water in low spots.
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 of the Sierra Nevada as the heaviest precipitation
occurs as snow into its higher elevations.

Heavy rainfall will continue into Thursday, increasingly impacting
the Transverse Ranges of southern California. As the guidance shows
reasonable agreement, extended the Slight Risk for Wednesday into
the western Transverse Ranges and introduced a Slight Risk on
Thursday for the Transverse & Peninsular Ranges, including the
larger metro areas near the coast (Los Angeles & its suburbs as
well as San Diego).

...Eastern Florida...
A synoptic pattern with vague similarity to the one that
materialized on October 31-November 3 appears to be setting up by
mid week. Nearly antiparallel flow (low- level easterlies and
upper level westerlies) will continue through mid- to late week
across eastern Florida as a positively tilted upper level trough
cuts off a cold low near the northwestern Peninsula which then
remains quasi-stationary. Precipitable water values of 1.5-1.75"
are forecast near the East Coast of FL, 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 2" would be possible wherever short,
training bands or mesocyclones manage to materialize. As the GFS
has a strong signal for heavy rainfall (10"+ local amounts
Wednesday and 6"+ local amounts Thursday), and the heavy rain
pattern in eastern FL has expanded in the 12z ECMWF run when
compared to its older run, added Slight Risk areas for areas
between Cocoa Beach and coastal Palm Beach County, areas that
received very heavy rainfall two weeks ago. Localized Moderate Risk
impacts cannot be ruled out.

Roth/Putnam


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