FOUS30 KWBC 270813
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
413 AM EDT Tue Oct 27 2026

Day 1
Valid 12Z Tue Oct 27 2026 - 12Z Wed Oct 28 2026

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

...Southeast Florida...

An area of low pressure will linger over the Bahamas while
gradually moving northwards, resulting in persistent northeasterly
flow across much of Florida. Moisture wrapping around the
circulation will be directed into Southeast Florida, bringing PWAT
values up to 1.7-2 inches. The low will trigger scattered showers
and storms over the Atlantic that will migrate into the Southeast
Florida coast. Instability will be fairly limited, but there should
be enough MUCAPE (400-800 J/kg) over the Atlantic waters and the
immediate Southeast Florida coast to support a some storms with
locally heavy rainfall (rates 1-2 inches per hour). These rainfall
rates will generally fall below FFGs, but persistent showers
throughout the day and into tonight will allow for isolated higher
rainfall amounts that could lead to flash flooding. Hi-res model
guidance shows the highest rainfall totals (generally 1-2 inches,
locally up to 4 inches) focusing along the Southeast Florida coast,
impacting the I-95 corridor, an area that has received several
rounds of rainfall over the past few days. Given recent heavy rains
and the urban environment, there is a Marginal Risk of excessive
rainfall leading to isolated instances of flash flooding in
Southeast Florida.

Dolan
 

Day 2
Valid 12Z Wed Oct 28 2026 - 12Z Thu Oct 29 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR EAST-CENTRAL
AND SOUTHEAST FLORIDA...

...East Coast of Florida...

The area of low pressure near the Bahamas will gain momentum on
Wednesday as the upper level energy splits, with a portion of the
energy being swept into the Atlantic while another portions shifts
southeast across South Florida. This will result in another day of
northeasterly flow with showers and storms moving onshore along the
Florida East Coast. The band of moisture on the northern side of
the system will shift north and increase PWATs to around 2 inches
across much of Central and South Florida. The environment will also
become more unstable as the surface reflection of the low shifts
southeast towards South Florida. MUCAPE values are expected to rise
to around 800-1200 J/kg in Central and South Florida, which will
support deeper convection capable of producing high rainfall rates
(1.5-2.5 inches per hour) at times. Hi-res and global models are in
agreement that the highest rainfall totals should materialize near
the East-Central Florida Coast, with some earlier convection
capable of producing locally heavy rainfall over portions of
Southeast Florida as well. Given recent heavy rainfall and the
sensitivity of the urban I-95 corridor, there is a Marginal Risk of
excessive rainfall for portions of East-Central and Southeast
Florida where isolated instances of flash flooding will be possible.

Dolan
 

Day 3
Valid 12Z Thu Oct 29 2026 - 12Z Fri Oct 30 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
WEST AND CENTRAL TEXAS...

...Texas and New Mexico...

Conditions will be favorable for widespread convection across
portions of Texas and New Mexico on Thursday as mid-level energy
associated with the remnants of TC Vance move into the region. As
the wave approaches, southeasterly low-level flow will bring
anomalous Gulf moisture into the south-central U.S., increasing
PWATs across Texas to 1.5-2 inches, which is 3 standard deviations
above normal and well above the climatological 90th percentile. In
addition to mid-level destabilization from the wave, enhanced upper
level divergence in the right entrance region of a southern stream
jet will support a broad region of ascent across Texas. These
ingredients combined with at least modest CAPE (slightly limited
due to widespread cloud cover) are expected to support an organized
heavy rainfall event.

Model guidance has been trending north and west with the QPF
footprint of this event during the Day 3 time frame. This has
resulted in shifting the Slight Risk area to include more of West
and Central Texas. There is good agreement among the deterministic
(physical and AI) and ensemble guidance that the highest rainfall
amounts will focus between the Edwards Plateau/western Hill Country
and the Midland area, which is facing a high-end Slight Risk on
Thursday. There is still quite a bit of uncertainty in QPF to the
west and north of this region, with some models showing a faster
and further north spread with the heavier totals and some showing
elevated amounts in the terrain of West Texas. The rest of West
Texas and portions of west-Central Texas up to the Panhandle have
been included in a Marginal Risk to account for this QPF
uncertainty. An isolated flash flood/Marginal risk will likely
extend into southern New Mexico as well where locally heavy
rainfall over sensitive terrain and burn scars could cause flash
flooding, especially considering how saturated soils are after
recent heavy rains.

Dolan
 

Day 4 and Day 5
Valid 12Z Fri Oct 30 2026 - 12Z Sun Nov 01 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN AND CENTRAL ARIZONA ON FRIDAY...

..Texas into Oklahoma...
We will maintain a Marginal risk on day 4 (Fri) across portions of
TX into OK. Some threat of flash flooding will persist as the
features responsible for the day 3 risk shift northward. However
the signal becomes a bit more muted by day 4 and uncertainty on the
details become higher. Still will have impressive synoptic support
with mid level shortwave energy, upper level divergence and a
strong low level jet/moisture transport axis. However the system
should be rather progressive by this time, and there is a more of a
question regarding the degree of destabilization by this time. So
while an area of locally heavy rainfall should be moving north
across TX and into OK, rainfall rates and the extent of the flash
flood potential become less clear with northern extent. Thus we
will stick with a Marginal for now and continue to monitor trends.

...Southwest...
Still good model agreement on day 4 with broad troughing
progressing into the western United States. While some timing
uncertainty persists regarding individual embedded shortwaves, the
overall environmental ingredients are coming together to support a
robust convective and heavy rainfall threat centered over AZ on
Friday. This is particularly true in the non-ncep models such as
the ECMWF/AIFS/UKMET.

Dynamic forcing will be impressive, featuring a very strong
southern stream upper level jet that will place AZ within its
favored left exit region, promoting strong upper level divergence.
Mid level shortwave energy ejecting east will interact with a
rather strong southerly low level jet resulting in impressive low
level moisture transport and PWs across the region. This strong low
level flow should help organize and sustain some training/backbuilding
convective cells. While thermodynamic details carry inherent
uncertainty at this lead time, current model guidance suggests that
corridors of 1000+ J/kg of CAPE are probable. Much of the region
has been anomalously west of late, which has notably increased the
hydrologic sensitivity across the area. While the exact placement
and magnitude of the heaviest rainfall axis remains subject to
adjustments as we get closer, confidence is high enough in an
isolated to scattered flash flood threat to warrant a Slight risk.

More spread and greater uncertainty exists across the Southwest on
day 5 (Sat). One thing that is certain is that there will be an
anomalous amount of deep moisture moving into much of the
Southwest. Troughing moving into the West will pull an impressive
amount of moisture northward with PWs near or even above record
values for the time of year. What is uncertain is the exact timing
of the trough axis and an area of low pressure moving towards
southern CA, and the degree of instability over the region. With
this amount of moisture there is likely to be abundant cloud cover,
and model instability fields are currently pretty meager on
Saturday. Thus we could be looking at showers and orographically
enhanced rain instead of heavier convective rates. This is
uncertain though, and even limited instability may result in flood
impacts given the saturated conditions over portions of this
region. In addition, a quicker low (like the AIFS has been
showing), could bring heavier rainfall into southern CA on day 5.
All this to say we will start with a broad Marginal risk and fine
tune as we get closer.

...Lower to Mid MS Valley...
The system responsible for the Southern Plains heavy rainfall on
day 3 and 4 will shift into the lower and mid MS Valley on day 5
(Sat). The mid level shortwave and left exit of an impressive jet
will provide plenty of synoptic ascent for convection. Limiting
factors for flooding will be a fairly quick progression of the
system, questionable instability, and very dry antecedent
conditions. However given the degree of forcing in play and PWs
forecast over the 97th percentile for the time of year, at least a
localized flash flood risk seems in play from the central Gulf
Coast into southern MO. Given the orientation/progression of
forcing, could envision a scenario where the front tries to slow
across the southern half of the Marginal risk, which is also where
the greater chances of higher instability will reside. This could
allow for some training/backbuilding component to convection over
these areas. Model preference at this time is non-GFS, which seems
too quick progressing things off to the east. The ECMWF, AIFS and
UKMET are better clustered and align with the Marginal risk area.
Given the dry antecedent conditions, this is probably only a urban
flash flood risk, where high rainfall rates and brief training
could locally result in flash flooding.

Chenard
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