Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Sep 21 2026
Day 1
Valid 16Z Mon Sep 21 2026 - 12Z Tue Sep 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL APPALACHIANS...
...Central Appalachians and the Mid-Atlantic...
16Z update... Very minor tweaks were made to the southern bounds of
the Marginal where hi-res guidance depicts a few hours of rain
rates exceeding 0.50-1.5 inches/hour outside of the inherited
Marginal area over areas of elevated terrain. The Slight Risk was
brought a little further south across northern North Carolina
where the MCV is expected to sink southward later on across
southern Virginia where cells could produce 3 to 6 inches of rain
in a short time.
Campbell
The Slight risk has been expanded to include a larger portion of WV
and southwest VA. The primary driver of heavy rainfall will be
embedded shortwave energy interacting with a backdoor cold front
and inverted surface trough.
Model guidance indicates a moderately to highly unstable airmass
will develop near the boundary over WV, with 2000-3000 J/kg of
CAPE expected. As a distinct shortwave/MCV currently positioned
over IL/IN progresses into the region, robust convective
development is anticipated. While most model solutions keep these
cells moving steadily across WV, a quick 1-3" of rain over
increasingly saturated soils should result in an additional flash
flood threat.
By this afternoon convection should propagate into southwest VA
along/near the backdoor front. In this region more persistent low
level convergence should increase the duration of convective
elements and locally enhance rainfall totals. While some guidance
pushes the front and best convective focus slightly further south
into northern NC, current model consensus supports southwest VA as
the primary axis for heavy rain. Recent high res models highlight
the potential for localized excessive totals. Both the 00z and 06z
HRRR depict a small but impressive swath of rainfall as high as
3-6". Given the available instability, mesoscale forcing, and
favorable convergence near the front, these elevated totals appear
plausible, justifying the expansion of the Slight risk.
...New Mexico and Nearby Southern High Plains...
Both the HREF and REFS indicate the potential for rainfall locally
exceeding 3" as isolated convection develops this afternoon over
eastern NM and west TX. A widely isolated flash flood risk is
possible.
...South Florida...
A Marginal Risk has been maintained for portions of South Florida
as a plume of anomalous moisture will help to fuel heavy downpours
and potentially lead to some isolated flooding/ponding in urban
areas.
...CA/NV...
Convection underneath a closed low may pose a localized flash
flood risk today across portions of eastern CA into NV.
Instability is forecast to be weak, but with cold air aloft under
the low and PWs forecast to increase over the climatological 90th
percentile, an isolated flash flood risk could evolve.
Chenard
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Sep 21 2026
Day 2
Valid 12Z Tue Sep 22 2026 - 12Z Wed Sep 23 2026
..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN NEW MEXICO...
...New Mexico and West Texas...
21Z update... The latest suite of guidance had a notable westward
shift of with heaviest QPF footprint, which now favors southwest
New Mexico. This shift triggered the need to adjust the western
boundaries of the Slight Risk area now into eastern Arizona and the
high-end Slight and the Moderate Risk areas further west across
southwest New Mexico.
Campbell
A potent, multi-day heavy rainfall event is set to begin across NM
and far southwest TX Tuesday. An upper level trough approaching
from the west will help strengthen an upper level jet,
persistently placing the region in the favorable right entrance
region. Deep southerly flow will transport tropical moisture
northward, while embedded mid level shortwave energy advances north
out of Mexico and into NM by Tuesday night. Low level easterly
upslope flow will also enhance lift in this setup.
PW values are forecast to approach mid to late Sep. record levels.
With sufficient instability expected, this deep moisture profile
will support heavy rainfall rates. Scattered flash flooding is
expected across much of NM and far southwest TX, with a more
concentrated area of slow moving convection possible over southern
NM.
Guidance is in pretty good agreement regarding high QPF potential
over southern NM. The 00z RRFS and 3km NAM depict swaths of 3"
rainfall totals, with the GFS/AIGFS/Gem reg depicting higher QPF
across a similar axis. With a day 3 Moderate risk already in
effect, and the flash flood threat expected to ramp up by Tuesday
night, we opted to upgrade the day 2 to a Moderate as well.
Scattered to numerous instances of flash flooding are anticipated,
some of which could be locally significant. This threat includes
the sensitive burn scar areas within the Sacramento Mountains.
...Ohio Valley and Mid-Atlantic...
21Z update... Mentioned as a sweet spot in the previous discussion,
below portions of central Virginia and North Carolina will be
quite favorable for heavy precipitation during this period. This
part of the region will have tall skinny CAPE near a frontal
boundary as a wave approaching the mountains along with slow storm
motion and training to increase the threat for localized flash
flooding. A Slight Risk was raised for northern/central Virginia
and northern North Carolina.
Campbell
An approaching mid-level trough and favorable positioning within
the right entrance region of an upper level jet will support
widespread rainfall across portions of the OH Valley and Mid-
Atlantic. At the surface, a backdoor cold front with strong
easterly flow will enhance low level convergence, further amplified
by a developing inverted surface trough.
Well to the north of the frontal boundary, limited instability
will keep rainfall primarily stratiform, with rain rates remaining
below flash flood thresholds. Considerable model spread remains
regarding where the strongest convergence and sufficient
instability will overlap, complicated by dry air advecting in from
the northeast. While the 12z EC and 00z GFS were previously in
agreement with a heavy QPF axis along the coastal plain from
eastern VA into the Delmarva, the 00z EC has trended further
inland. Meanwhile, the 00z RRFS and REFS favor a further inland
and southward axis stretching from south central VA into central
NC.
Ultimately, the forecast hinges on far south cold air damming
forces the instability axis and also how far inland the surface
trough gets nudged. A localized sweet spot may emerge where
persistent convergence intersects sufficient instability to drive
a heavy rainfall and flash flood threat. Where these ingredients
overlap, the environment will be conducive for some low topped
convective cores and efficient warm rain processes. However given
the current uncertainty, we will keep the risk level at Marginal
for this update, and we will reevaluate later today when we have
the full suite of high res guidance available.
...South Florida...
21Z update... A minor adjustment was made to include the Keys in
the Marginal Risk.
Campbell
A Marginal Risk has been maintained for portions of South Florida.
Locally heavy downpours will remain possible with anomalously high
moisture in place, which could lead to some isolated
flooding/ponding in urban areas.
Chenard
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Sep 21 2026
Day 3
Valid 12Z Wed Sep 23 2026 - 12Z Thu Sep 24 2026
..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF EASTERN NEW MEXICO...
...New Mexico and West Texas...
21Z update... For this period the latest guidance shifted the focus
toward northeast New Mexico. This necessitated adjustments to all
risk levels. The Marginal Risk was nudged northward across Arizona,
southern Colorado and western Nebraska. The Slight was nudged
northward across north-central New Mexico and the northern boundary
of the Moderate was was expanded a bit to the west and east to
cover the new WPC QPF footprint.
Campbell
The heavy rainfall threat established on day 2 will continue and
potentially peak over NM on day 3 as large scale forcing gets even
stronger. A well defined mid level shortwave is forecast to lift
northward across the state, accompanied by robust upper level
divergence. PW values will remain near record levels for this time
of year, with an anomalously deep moisture profile.
With such strong forcing and widespread moisture in place, the
primary limiting factor for heavy convective rates will be the
extent of cloud cover and its impact on destabilization. While
widespread clouds are a concern, daytime heating should allow at
least the eastern edge of the rainfall shield to sufficiently
destabilize, aided by broad easterly upslope flow. Thus while some
areaS may see predominately stratiform rain, a concentrated swath
of intense convective rainfall remains probable.
Guidance continues to show some spread regarding the placement of
this heaviest rainfall axis. The 00z EC remains the furthest west
solution, with the GFS, AIGFS, AIFS and RRFS clustered a bit
further east. The current forecast favors this eastern consensus,
though given we are still three days out, additional spatial
adjustments are probable.
Based on this setup the inherited Moderate risk remains justified,
and it was expanded to encompass a larger portion of eastern NM.
Scattered to numerous instances of flash flooding are
anticipated, some of which could be locally significant. This
threat includes the sensitive burn scar areas within the
Sacramento Mountains.
...Mid-Atlantic...
21Z update... Higher QPF amounts have modestly trended higher
across northern/eastern Virginia during this Period. Given the
expected antecedent moisture from the Day 1 and Day 2 period,
soils will be more sensitive to additional heavy rainfall. The
Marginal Risk area are expanded northward for portions of Virginia.
Campbell
A complex and somewhat disjointed synoptic pattern will be present
over the Mid-Atlantic on day 3. A mid to upper trough will will
drift slowly eastward from the OH Valley into the Mid-Atlantic
while a separate coastal low develops offshore. Meanwhile, surface
high pressure to the north will advect drier and more stable air
into the corridor between these two systems.
While some instability may materialize directly beneath the cold
core of the mid level low, PW values will have generally decreased
by this time. The bulk of the deeper moisture and instability may
remain offshore with the coastal low.
Despite the intrusion of dry air, there remains enough
uncertainty regarding the exact evolution of these features to
warrant a continuation of the Marginal risk. An embedded Slight
risk may be needed in subsequent updates, contingent upon the exact
track of the upper low, position of the moisture/instability axis,
and the state of antecedent soil conditions from previous days
rainfall.
...Florida...
A Marginal risk continues across south FL where above normal PWs
and instability will continue to pose a localized flash flood
risk.
Chenard
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Sep 21 2026
Day 4 and Day 5
Valid 12Z Thu Sep 24 2026 - 12Z Sat Sep 26 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO, SOUTHEAST ARIZONA, AND THE TEXAS PANHANDLE ON DAY 4...
20Z Update...
For Day 4, while the footprint of heavy amounts is expected to be
less than the previous day, models indicate that moisture anomalies
will remain high -- supporting the potential for additional
localized heavy amounts, which are likely to exacerbate runoff
concerns given the heavy amounts that are expected earlier in the
week. Therefore, expanded the Slight Risk farther south to include
southern New Mexico and a small portion of southeastern Arizona.
Farther northeast, moisture and shortwave energy lifting out of the
southwest are expected to reach into the Central Plains -- raising
the threat for heavy amounts and isolated flash flooding concerns.
A Marginal Risk was extended from the southern High Plains into
parts of Nebraska, where PW anomalies are expected to surge up to
2-3 std dev above normal on Thursday.
For Day 5, the only notable change was to add a Marginal Risk to
portions of eastern Massachusetts and Rhode Island. Although there
is still significant spread with regards to the track of a strong
coastal low that is forecast to move along the Northeast coast at
this time, there was enough of a model signal indicating the
potential for heavy rains to impact portions of southeastern New
England to warrant the introduction of a Marginal Risk.
Pereira
Previous Forecast...
...Southern Rockies/High Plains...
The threat of additional flooding lingers into Thursday given a
favorable upper level pattern for additional showers.Even though rainfall
rates should be diminishing and the bulk of the rainfall will be
shifting into the Texas and Oklahoma panhandles, but the concern in
New Mexico is that any additional rainfall will be falling on wet
to saturated soils. Consequently, introduced a Slight Risk area
within the Marginal Risk area. At the same, refrained from
expanding the Marginal Risk area too far eastward in order to
better assess the potential rainfall amounts/rates that move over
considerably drier ground.
By Friday...some of the convection will be moving into parts of the
central Plains which should also have lowered flash flood guidance
due to rainfall in the preceding days. Introduced a Marginal Risk
area there due to the antecedent conditions and given the low
level feed of moisture being drawn northward from the Gulf. At the
same time, maintained a Marginal Risk in parts of New Mexico.
...Ohio Valley/Appalachians to Mid-Atlantic...
By Thursday, a coastal low will likely be developing in the
Atlantic. Depending on the low position, some guidance shows heavy
rainfall reaching onshore in the Mid-Atlantic on Thursday then spreading
towards southeastern New England on Friday. Models continue to show
the heaviest rain could remain offshore, and because that region
is not very sensitive to heavy rain given the sandy soils if there
are moderate amounts onshore. But this should continue to be
monitored.
Bann
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
400 PM EDT Mon Sep 21 2026
Day 4 and Day 5
Valid 12Z Thu Sep 24 2026 - 12Z Sat Sep 26 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO, SOUTHEAST ARIZONA, AND THE TEXAS PANHANDLE ON DAY 4...
20Z Update...
For Day 4, while the footprint of heavy amounts is expected to be
less than the previous day, models indicate that moisture anomalies
will remain high -- supporting the potential for additional
localized heavy amounts, which are likely to exacerbate runoff
concerns given the heavy amounts that are expected earlier in the
week. Therefore, expanded the Slight Risk farther south to include
southern New Mexico and a small portion of southeastern Arizona.
Farther northeast, moisture and shortwave energy lifting out of the
southwest are expected to reach into the Central Plains -- raising
the threat for heavy amounts and isolated flash flooding concerns.
A Marginal Risk was extended from the southern High Plains into
parts of Nebraska, where PW anomalies are expected to surge up to
2-3 std dev above normal on Thursday.
For Day 5, the only notable change was to add a Marginal Risk to
portions of eastern Massachusetts and Rhode Island. Although there
is still significant spread with regards to the track of a strong
coastal low that is forecast to move along the Northeast coast at
this time, there was enough of a model signal indicating the
potential for heavy rains to impact portions of southeastern New
England to warrant the introduction of a Marginal Risk.
Pereira
Previous Forecast...
...Southern Rockies/High Plains...
The threat of additional flooding lingers into Thursday given a
favorable upper level pattern for additional showers.Even though rainfall
rates should be diminishing and the bulk of the rainfall will be
shifting into the Texas and Oklahoma panhandles, but the concern in
New Mexico is that any additional rainfall will be falling on wet
to saturated soils. Consequently, introduced a Slight Risk area
within the Marginal Risk area. At the same, refrained from
expanding the Marginal Risk area too far eastward in order to
better assess the potential rainfall amounts/rates that move over
considerably drier ground.
By Friday...some of the convection will be moving into parts of the
central Plains which should also have lowered flash flood guidance
due to rainfall in the preceding days. Introduced a Marginal Risk
area there due to the antecedent conditions and given the low
level feed of moisture being drawn northward from the Gulf. At the
same time, maintained a Marginal Risk in parts of New Mexico.
...Ohio Valley/Appalachians to Mid-Atlantic...
By Thursday, a coastal low will likely be developing in the
Atlantic. Depending on the low position, some guidance shows heavy
rainfall reaching onshore in the Mid-Atlantic on Thursday then spreading
towards southeastern New England on Friday. Models continue to show
the heaviest rain could remain offshore, and because that region
is not very sensitive to heavy rain given the sandy soils if there
are moderate amounts onshore. But this should continue to be
monitored.
Bann
