Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
346 PM EDT Sat Oct 24 2026
Day 2
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...
...21Z update...
...Central and Southern High Plains...
The Slight Risk was extended southward from the TX/OK Panhandles
into southeastern NM and far western TX (just east of El Paso).
This was due to forecasts for higher instability (500-1500 J/kg
MLCAPE) over these regions which will be capable of supporting
higher rainfall rates. While better synoptic scale forcing will be
to the north with an ejecting shortwave, a lingering surface trough
axis/weak dryline will help to focus afternoon/evening
thunderstorms with potential for repeating/training due to largely
unidirectional southwesterly flow in the LFC-EL layer. There
remains some question on the coverage of cells but antecedent
rainfall from Saturday into Sunday morning will be a factor for
producing excess runoff. 12Z HREF/REFS neighborhood (40 km)
probabilities for exceeding 1 inch of rain in an hour are greatest
within the Slight Risk area extending from southeastern
CO/southwestern KS into the northwestern TX Panhandle, eastern NM
and far western TX (30-50 percent).
Farther north, forecast MUCAPE from the 12Z members of the HREF
showed values mostly below 500 J/kg throughout the 24 hour period
and more often, far less than 500 J/kg. This is reflected in the
12Z HREF/REFS neighborhood (40 km) probabilities for exceeding 1
inch per hour which are less than 15 percent where the Slight Risk
was trimmed but a Marginal Risk remains over portions of
northwestern KS. Outside of smaller maxima for exceeding 2 and 3
inches over the 24 hour period, the 12Z HREF/REFS neighborhood (40
km) probabilities showed the largest regional max for 2 and 3+
inches/24 hours to be centered from northeastern NM into the
western TX/OK Panhandles.
...East Coast of Florida...
Fairly good model agreement exists with the setup across FL with
25-35 kt of northeasterly 925-850 mb winds and a relative surge in
moisture that is in place at the start of the period. 12Z models
showed precipitable water values of 1.5 to 1.8 focused mostly over
the southeastern Peninsula along with the greatest instability
across the state, containing ~500 to 1000 J/kg MLCAPE. Moisture is
forecast to fluctuate through Monday morning along the east coast
of FL, remaining near average for late October. Repeating rounds
and brief training of showers/thunderstorms are expected to result
in isolated high rainfall totals. The 12Z HREF/REFS showed 40-60
percent neighborhood (40 km) probabilities of exceeding 3 inches
across southeastern FL over the 24 hour period ending Monday
morning along with up to 15 percent chances for exceeding 5 inches
near the coast or just offshore.
Otto
...previous discussion follows...
...Central and Southern High Plains...
The cutoff low will gradually progress northeastward, resulting in
an expanding region of precipitation ahead of the system from West
Texas through the southern and central High Plains. Similar to the
setup on Saturday, anomalous moisture will stream ahead of the
system into the Plains under favorable upper level conditions for
scattered to widespread convection. The best instability should be
focused over New Mexico and Texas, but there should be enough
instability extending into the High Plains to support deeper
convection with locally heavy rainfall.
The highest flash flood threat will likely be located over
portions of northeastern New Mexico, southeast Colorado, western
Kansas, and the Oklahoma and Texas panhandles where there is a
Slight Risk of excessive rainfall. There is still quite a bit of
uncertainty surrounding rainfall totals, but the general consensus
is for the highest amounts over the southern and central High
Plains, and this is also where the REFS is flagging the highest
probabilities for heavy rainfall. The western side of the Slight
Risk area is where there is a chance that the heavy precipitation
footprint may overlap with areas forecast to receive heavy rainfall
on Saturday, which would make the area more susceptible to flash
flooding with any additional rainfall.
The broader Marginal Risk area surrounding the Slight Risk area
was expanded in this forecast cycle to include more of southeastern
New Mexico and West Texas. This region will have the best
ingredients for heavy rainfall (CAPE greater than 1000 J/kg and
PWATs of 1-1.5 inches) but will be slightly displaced from the best
synoptic forcing with the main low. Any convection that develops
in this area will have the potential to produce locally heavy
rainfall. Given vulnerable terrain in southern New Mexico and heavy
rainfall received yesterday and expected today, the expansion of
the Marginal Risk area was justified. Soils over portions of Texas
will not be as saturated, but given the favorable setup could still
see a localized flash flood threat. The Marginal Risk area was
also trimmed on the northern side to remove some of Nebraska and
South Dakota where rainfall rates will be limited due to a lack on
instability and where rain should be more stratiform in nature.
...East Coast of Florida...
The mid/upper level low sliding down the coast will stall
southeast of Miami, which will result in a prolonged period of
moist, onshore flow across Southeast Florida. Showers and storms
will form over the Atlantic and move over the Florida coast, which
will result in heavy rainfall focused along the I-95 corridor. The
heavy rainfall threat will shift south throughout the day, with the
highest rainfall totals expected to accumulate over Southeast
Florida once the system stalls. There is a Marginal Risk of
excessive rainfall for much of the I-95 corridor south of
Jacksonville and a Slight Risk for the I-95 corridor south of
Melbourne. The Slight Risk area was expanded south to include more
of the Miami metro area based on the latest model trends in QPF.
Scattered instances of flash flooding will be possible, especially
in urban, low-lying, and poor drainage areas.
Dolan
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
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