Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
843 PM EDT Wed Sep 23 2026
Day 1
Valid 01Z Thu Sep 24 2026 - 12Z Thu Sep 24 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE TEXAS AND OKLAHOMA PANHANDLES, CENTRAL AND EASTERN NEW
MEXICO, AS WELL AS THE CENTRAL AND SOUTHERN APPALACHIANS...
...New Mexico and West Texas...
Prevailing southerly flow aloft will maintain itself for the
overnight period with a continued threat of flash flooding for the
eastern half of NM up into portions of the TX and OK Panhandles as
the remnant mid-level shortwave lifts north-northeast with
increasing convergent flow in-of a surface trough positioned across
the NM High Plains. PWAT anomalies remain on the order of +2
deviations across much of the region that has been plagued by heavy
rainfall the last 36 hrs with one last round forecast tonight. One
of the positives for this setup is the heaviest precipitation is
likely away from the areas impacted last evening with the best
signal for 2+ inches of rain located further northeast into
northeastern NM into those adjacent Southern High Plains areas of
TX/OK. 18z HREF probabilities signaled a more prominent threat
within that particular zone as convergence is maximized within that
zone as the mid-level energy over central NM drifts northeast and
becomes a bigger factor away from the terrain for the first time in
a while.
Further southeast into far west TX and southeastern NM, there is
some discrepancy in guidance for a secondary shortwave to lift
across the Rio Grande and traverse the area with another localized
convergence signature materializing across the Guadalupe Mountains
up through the Upper Trans Pecos. Some of the earlier CAMs were
quite bullish in the signature with less of an extent from the
latest HRRR/RRFS outputs this evening that are less robust with the
threat. The shortwave perturbation is noted via WV satellite across
Chihuahua, so it will come down to its general evolution and
whether the models that lift the disturbance northeastward have the
most merit, or if the disturbance gets sheared and doesn't have a
significant role in the forecast. As of now, the trends are for
this setup to yield less of a threat for those aforementioned
areas, but will bear watching as this could spur up some
significant rainfall prospects in areas that are more flash flood
prone in the terrain and Pecos River Valley.
Given the current setup this evening, had enough confidence to drop
the previous MDT risk back down to a SLGT, but maintained a broad
high-end SLGT in its place considering the sensitivities at play,
as well as some questions handling the shortwave ejection from MX.
Highest confidence in heavy precip is over that area of eastern to
northeast NM up through the northwest TX Panhandle, through the OK
Panhandle, with a northern inflection into southwestern KS.
Scattered flash flood potential within this zone with the best
threat overlapping any areas that were impacted greatly last
evening, and urban footprints that are prone to run off.
...Central to Southern Appalachians...
A stubborn upper level low continues to churn over the Ohio Valley
with a persistent convective threat situated within the terrain of
WV, eastern KY, down through the Southern Appalachian front.
Surface trough analyzed along and west of the Piedmont maintains a
suitable convergent axis caused by the the overall synoptic setup
pushing a deep CAD wedge all the way down east of the Appalachian
front. Localized convergent pattern in-of the mountain chain and
points west where instability remains prevalent outside the CAD
wedge will continue to impact the terrain for at least the next few
hours before conditions improve and we finally see a return of
nocturnal stabilization with the development of a boundary layer
cap that will finally put an end to the convective threat. Several
flash flood warnings remain in effect over southwestern WV into
eastern KY and TN which led to a continuation of the SLGT risk for
those areas while they are still being impacted. Look for less of a
threat after 06z for basically everywhere east of the Mississippi
as the surface ridge and nocturnal stabilization will finally put
the threat to rest with just some lingering light rain/showers
across the region.
Kleebauer
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
843 PM EDT Wed Sep 23 2026
Day 2
Valid 12Z Thu Sep 24 2026 - 12Z Fri Sep 25 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
NEW MEXICO INTO SOUTHWEST KANSAS...
20Z Update...
Much of the previous forecast rationale remains on track after
evaluating the latest WPC QPF and 12Z guidance. There is slightly
greater concerns for flash flooding in southeast NM, which includes
the Sacramento Mountains, given their soils will continue to
saturate in wake of Wednesday's heavy rainfall. Otherwise, the
Slight Risk that stretches from southwest NM to as far north and
east as southern KS remains in good standing.
Mullinax
---Previous Discussion---
...Southwest and Southern Plains...
Heading into Thursday the strongest mid level forcing and highest
PW anomalies will shift northward out of NM and into Colorado and
the Central Plains. However, in the wake of this exiting system,
daytime instability is actually forecast to increase over NM
compared to previous days. While PW values decrease some, they will
remain above the climatological 75th percentile. Additionally,
broad troughing will remain overhead, with embedded shortwave
energy continuing to traverse the region.
With less concentrated forcing and somewhat reduced moisture, the
overall areal coverage of heavy rainfall across NM should diminish
relative to prior days. However, the combination of stronger
instability and sufficient moisture will still support intense
localized convective rainfall rates capable of producing
significant rainfall totals. Given the hydrologic sensitivity built
up from preceding days of heavy rain, an additional flash flood
threat appears likely. While the threat may not be as widespread
as previous days, a Slight risk is maintained, as locally
significant and impactful flash flooding will still be possible.
The Slight risk also extends eastward across the TX and OK
Panhandles and into southwest KS. Convection may be ongoing across
this corridor at the start of the period. Later in the day, in the
wake of the lifting shortwave and surface low, a corridor of
enhanced low level convergence and instability may develop, which
could result in additional rounds of locally heavy convection.
Further west, isolated flash flooding will also be possible across
portions of AZ, southern UT and CO as the trough moves across
these areas.
...Central Plains...
The highest PW anomalies and strongest synoptic forcing will
overlap across KS and NE. This forcing aligns well withe a 1-3"
consensus QPF swath depicted by a majority of the model guidance.
The primary limiting factor for a greater flash flood threat will
be the degree of available instability. Thus rainfall may take the
form of a broad stratiform rain shield with only embedded heavier
convective elements. Therefore, the risk level will be maintained
at Marginal for now, with trends continuing to be closely monitored
for any needed upgrades in subsequent forecast cycles.
Chenard
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
843 PM EDT Wed Sep 23 2026
Day 3
Valid 12Z Fri Sep 25 2026 - 12Z Sat Sep 26 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM NEW MEXICO
INTO THE PLAINS, AND OVER SOUTHEAST NEW ENGLAND...
20Z Update...
Not much change with regards to the Marginal Risk area in the
Central U.S.. The Marginal was adjusted a little farther east in
the MO River Valley, but otherwise, the Marginal's Central and
Southern Plains areas were kept that same from overnight.
There remains a fair amount of model spread on the potential
placement of the developing coastal storm Friday night. The
ECMWF/EC- AIFS suite remains slower and farther west, while
GEFS/CMCE ensembles are a little more progressive and farther east.
The 12Z GEFS has been continuing a trend over the last 24 hours of
its members gradually coming west by 06Z Saturday, which suggests
a move towards the ECMWF suite. When accounting for all ensemble
members, there has generally been an increase in QPF across
southern New England and as far south and west and Long Island.
With that being the case on the latest WPC QPF, I did decide to
expand the Marginal Risk into eastern CT and eastern LI this cycle.
No Slight Risk was proposed for the time being, given the heaviest
rainfall arrives late Friday night and any longer duration heavy
rainfall would be more likely to unfold by Day 4 (Saturday).
Mullinax
---Previous Discussion---
...NM into the Central Plains...
A broad axis of anomalous PWs, low level moisture transport, and
CAPE will persist from portions of eastern NM northeastward through
NE and IA on Friday. The strongest and most persistent mid to
upper level forcing, coupled with the primary moisture transport
axis, is forecast to focus across the northern extent of this
corridor. Conversely, the most robust instability is expected to
pool further south, stretching from eastern NM into southern KS.
The spatial offset between the best large scale forcing and
greatest instability introduces uncertainty regarding exactly how
the flash flood threat will evolve. While it will undoubtedly be a
wet period across this corridor, the magnitude and extent of the
flash flood threat will depend on whether sufficient rainfall rates
can materialize further north, or if convection can organize and
become widespread enough further south where the instability is
more firmly established.
Given these lingering questions, a broad Marginal risk has been
maintained across the region. However, the available environmental
ingredients certainly support the potential for an embedded Slight
risk. Upgrades may be necessary in subsequent forecast cycles as
the event draws closer and confidence in mesoscale details
increase.
...Northeast...
A Marginal risk has been maintained from RI into eastern MA as
uncertainty lingers regarding the exact track and evolution of a
developing coastal low. While the better chance for more
widespread heavy rainfall is likely to hold of until day 4, the
northern edge of the rain shield could push into coastal areas by
later Friday.
Current indications suggest that the best instability and any
convective elements should remain offshore through the day 3
period, keeping rainfall rates predominately stratiform over land.
Consequently, the overall flash flood threat is expected to remain
relatively low. However, with 1-3 inches of rain possible and
ongoing uncertainty regarding the precise behavior of the coastal
low, continuity with the previous forecast is preferred for now,
and the Marginal risk remains in place.
Chenard
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
843 PM EDT Wed Sep 23 2026
Day 4 and Day 5
Valid 12Z Sat Sep 26 2026 - 12Z Mon Sep 28 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN US/WESTERN PLAINS AS WELL AS EASTERN NEW ENGLAND...
...Southern Rockies to Central and High Plains...
20Z Update: Little change in the previous forecast. The ECMWF
remains the more aggressive of the solutions with widespread
convective potential from northwest IA down through northern MO.
The EC-AIFS continues to pinpoint the area of central IA down into
northern and western MO as a target, a bit south of the
deterministic ECMWF, and closer to the deterministic GFS solution.
In any case, overall magnitude is closer to a higher risk, but with
some variations in where the heaviest will occur, went with general
continuity and nudged the risk area a touch south to account for ML
trends.
Kleebauer
..Previous Discussion..
The main focus of attention for possible heavy to excessive
rainfall remains over the Midwest/Central Plains on Saturday as a
shortwave energy ejects northeastward from the Rockies. The
envelope of solutions span the EC on the north side and the GFS
favoring a more southerly solution corresponding to Iowa and
Missouri/Kansas respectively. Maintained the Marginal in Iowa
where flash flood guidance is lowest after the recent rainfall
although confidence is waning about the need for one based on the
latest QPF. If the ECMWF verifies...the flash flood numbers are
higher with a correspondingly reduced threat of excessive rainfall.
A broadening mid/upper level trough to the east shunts deepest
moisture out of the Midwest by Sunday.
...New England...
General consensus is for heavy rainfall to plague much of southern
New England with the maxima centered right over eastern MA,
including the Boston metro for both D4 and D5 periods. Multi-day
heavy rain threat is due to a slow-moving coastal low as the mid
and upper height fields note a stacked 850-300mb low presentation
as we move into Sunday with a weakening expectation occurring the
back half of D4 into the D5 time frame. The prevailing southeast
to easterly flow around the low center positioned near LI will aid
in copious amounts of moisture being thrown back into the northern
Mid Atlantic into southern New England as the main axis of heaviest
precip will likely promote widespread 2-4" with locally as high as
5" with the current forecast over the 48-60 time frame of impact.
Limited instability over the region will limit the upper threshold
of flash flood capabilities, however, the significant amount of
rainfall over the long period into the urban corridor of eastern MA
will likely cause widespread hydrologic concerns, including some
flooding in poor drainage locations. The previous SLGT risks were
maintained as a result.
Kleebauer
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
843 PM EDT Wed Sep 23 2026
Day 4 and Day 5
Valid 12Z Sat Sep 26 2026 - 12Z Mon Sep 28 2026
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHERN US/WESTERN PLAINS AS WELL AS EASTERN NEW ENGLAND...
...Southern Rockies to Central and High Plains...
20Z Update: Little change in the previous forecast. The ECMWF
remains the more aggressive of the solutions with widespread
convective potential from northwest IA down through northern MO.
The EC-AIFS continues to pinpoint the area of central IA down into
northern and western MO as a target, a bit south of the
deterministic ECMWF, and closer to the deterministic GFS solution.
In any case, overall magnitude is closer to a higher risk, but with
some variations in where the heaviest will occur, went with general
continuity and nudged the risk area a touch south to account for ML
trends.
Kleebauer
..Previous Discussion..
The main focus of attention for possible heavy to excessive
rainfall remains over the Midwest/Central Plains on Saturday as a
shortwave energy ejects northeastward from the Rockies. The
envelope of solutions span the EC on the north side and the GFS
favoring a more southerly solution corresponding to Iowa and
Missouri/Kansas respectively. Maintained the Marginal in Iowa
where flash flood guidance is lowest after the recent rainfall
although confidence is waning about the need for one based on the
latest QPF. If the ECMWF verifies...the flash flood numbers are
higher with a correspondingly reduced threat of excessive rainfall.
A broadening mid/upper level trough to the east shunts deepest
moisture out of the Midwest by Sunday.
...New England...
General consensus is for heavy rainfall to plague much of southern
New England with the maxima centered right over eastern MA,
including the Boston metro for both D4 and D5 periods. Multi-day
heavy rain threat is due to a slow-moving coastal low as the mid
and upper height fields note a stacked 850-300mb low presentation
as we move into Sunday with a weakening expectation occurring the
back half of D4 into the D5 time frame. The prevailing southeast
to easterly flow around the low center positioned near LI will aid
in copious amounts of moisture being thrown back into the northern
Mid Atlantic into southern New England as the main axis of heaviest
precip will likely promote widespread 2-4" with locally as high as
5" with the current forecast over the 48-60 time frame of impact.
Limited instability over the region will limit the upper threshold
of flash flood capabilities, however, the significant amount of
rainfall over the long period into the urban corridor of eastern MA
will likely cause widespread hydrologic concerns, including some
flooding in poor drainage locations. The previous SLGT risks were
maintained as a result.
Kleebauer
