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< Day 1 Outlook Day 3 Outlook >
WPC Day 2 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2019 UTC Sat Jul 20, 2024
Valid: 12 UTC Jul 21, 2024 - 12 UTC Jul 22, 2024
Day 2 Excessive Rainfall Forecast
Forecast Discussion
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
746 PM EDT Sat Jul 20 2024
Day 2
Valid 12Z Sun Jul 21 2024 - 12Z Mon Jul 22 2024


...21Z Update...
Overall pattern remains largely unchanged from previous
outlook...with a corridor of anomalous moisture draped across the
Southeast US and the expectation of moderate to locally heavy
rainfall in the Southwest US. Changes in the Southwest tended to
fit adjustments made in the WPC deterministic QPF, ensemble
guidance and input from affected offices. In the southeastern
US...made only minor adjustments given the fact there were no
strong or compelling signals to latch onto.


Previous Excessive Rainfall Discussion

...Southwest and Southern Rockies...

A pattern of general persistence within the mid and upper-levels
will lead to an ongoing threat of convective development in-of the
Southern Rockies and adjacent terrain of NM due to primed
environmental destabilization coinciding with a progression of mid-
level vortices streaming down the eastern flank of the ridge
across the Western U.S. A slight weakening of the ridge will allow
for an expansion of the convective threat to migrate westward into
the Mogollon Rim with some deterministic output signaling some
formidable amounts within the terrain. The ensemble mean QPF was
not as robust compared even with the addition of the elevated
deterministic signals leading to less confidence of higher impacts
that would necessitate an expansion of a higher risk across parts
of Central AZ. The previous update does have the eastern most
confines of the Mogollon Rim within the inherited SLGT risk which
does jive with the latest NBM probability fields signaling the best
threat further east away from the ridge center. QPF mean around
0.75-1.25+" was the target precip depiction for where to outline
the SLGT risk which aligns with the lower FFG exceedance markers
across the region. The highest probabilities for those totals
within the NBM are mainly in NM with only some of AZ seeing those
types of better outputs. This solidified the SLGT risk from
previous forecast with some minor modifications based on the QPF
footprint. The primary areas of interest within the current SLGT
will reside within the complex terrain and areas surrounding the
remnant burn scars located within the Sacramentos and Sangre de
Cristos. SBCAPE between 800-1200 J/kg is forecast within the
ensemble means with some max of 1500+ J/kg showing up within the
terrain of NM and AZ. Expect a general continuity for the next
succession of updates with perhaps that westward expansion of the
SLGT into the Mogollon Rim if the short range guidance trends
upward with the heavy rain signal.

...Southeast to Southern Mid Atlantic...

Persistent surface front bisecting much of the Southeastern U.S up
through the Southern Mid Atlantic will continue the threat of
scattered thunderstorms capable of locally heavy rainfall with some
training prospects within the confines of the quasi-stationary
boundary. The QPF footprint is a shotgun of small QPF maxima
reflective of the potential with less of any organized threat and
more of a widespread convective pattern that favors some locally
greater impacts, but remaining on the low to middle grounds of the
MRGL threshold. Unlike the previous period, a lack of stronger
mid-level vorticity will negate the higher end potential as the
ascent pattern is mainly limited to boundary layer destabilization
and low-level convergence within the front. The previous MRGL risk
was maintained with some minor adjustments.

...Southern Plains...

The eastern extent of the broad ridge axis across the Western U.S
will help send down multiple mid-level perturbations that will
allow for convective development upstream over the Eastern NM High
Plains, eventually propagating south and east along expected
outflow generation and mean steering flow out of the north-
northwest. There's a growing signal for organized multi-cell
clusters to move off the Caprock and enter portions of West TX and
the nearby Upper Trans Pecos. Deterministic output is subject to
variability in the location and magnitude of any convective cluster
that materialized and enters the area. The signal for potential is
present and was enough to expand the western MRGL risk area further
southeast to account for the threat of more organized heavy
rainfall. This is within the lower end of the risk threshold for
now, but will be subject to expansion or removal based on later
trends within numerical output, especially in the hi-res window.

Further to the southeast across Central and Eastern TX, an
approaching front will become a focal point for diurnally driven
convective development in-of the boundary itself as the environment
it moves into becomes increasingly favorable for cell generation.
The convergence signal is not nearly as impressive as areas further
to the east, but the ensemble mean QPF footprint dictates a
smattering of smaller QPF maxima that would indicate some locally
enhanced rainfall potential. Mean QPF is only around 0.75-1.25" in
spatial coverage, but some deterministic output is much more robust
with 2-4+" bullseyes in portions of Hill Country, Concho Valley,
out into the I-35 corridor. This is a lower end MRGL risk
opportunity within the region, but the upper quartile of outcomes
could spell for some local flash flood concerns if everything
breaks right (or wrong depending on perspective).


Day 2 threat area:

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