Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Tue Sep 22 2026
Day 1
Valid 16Z Tue Sep 22 2026 - 12Z Wed Sep 23 2026
..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF SOUTHERN NEW MEXICO...
16Z Update:
A potentially significant and high impact flooding event is
expected over the next few days across New Mexico and far southwest
Texas. The risk of heavy rainfall will increase later today,
ramping up considerably later this evening and overnight through
Wednesday. This afternoon, expect scattered thunderstorms capable
of producing intense rain rates of 1-2"/hr (locally higher). By
tonight, most of the guidance shows the activity focusing into
south to north oriented bands, leading to the potential for
training / repeating rounds of thunderstorms and heavy rainfall.
The 12Z HREF and other hi-res guidance followed previous cycles
showing potential for several inches through early Wednesday. HREF
neighborhood probabilities are moderate for at least 3 inches
(40-60 percent) with at least a low chance (10-20 percent chance)
of at least 5 inches.
Given the sensitivity and potential vulnerability of the area,
potential significant and higher end impacts are possible and this
likely leans toward the higher end of the MDT probabilistic range.
Elsewhere, the Slight Risk was adjusted to the latest radar trends
and recent hi-res runs. The 12Z guidance shows the greatest
concern focusing on portions of central to southeast VA where low-
topped tropical showers will be capable of producing
localized/isolated 2-4"+ totals. See MPD 1354 for more details.
Taylor
...New Mexico and West Texas...
A potentially high impact multi-day heavy rainfall event is set to
begin across NM and far southwest TX today into tonight. 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, driving PW values toward mid to late September
record levels by later today into Wednesday.
Lift will be further augmented by low level easterly upslope flow
and well defined mid level shortwave energy lifting north out of
Mexico by later tonight into Wednesday. Daytime hours today will
see scattered thunderstorm activity and at least some flash flood
potential. Large scale forcing intensifies overnight allowing for
a more concentrated rain shield with embedded heavier convective
cores to impact southern NM.
Neighborhood probabilities from both the 00z HREF and REFS show a
40-70% chance of rainfall exceeding 3" across NM today, though 5"
probabilities drop off significantly. This suggests a reasonable
max rainfall footprint of 2-4" through early Wednesday. Minimal
changes were made to the inherited Slight and Moderate risk areas,
as they still look in good shape. 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...
A setup for heavy rainfall will unfold across the Mid-Atlantic
today into tonight as an approaching mid level trough aligns with
the favorable right entrance region of an upper level jet. At the
surface, strong high pressure to the north will drive a backdoor
front southward, with strong easterly flow providing enhanced low
level convergence. The 00z HREF and REFS show generally good
agreement on two primary axes of elevated FFG exceedance
probabilities.
The first axis is from southeast VA into SC. Positioned along a
coastal convergence zone and the backdoor front, this corridor
will feature greater instability and support efficient warm rain
processes. High neighborhood probabilities exist in both ensemble
suites for 3" of rain. While 5" exceedance probabilities in the
REFS are likely inflated due to its known high convective QPF
bias, the HREF still depicts low to medium probabilities,
indicating a few localized 5" totals are possible. FFG neighborhood
exceedance probabilities of 15-40% justify a Slight risk, though
overall coverage may end up on the lower end of Slight risk
criteria.
The second axis is across WV into southwest VA. Focused along an
inverted trough, this area should see lower overall QPF magnitudes
than the farther southeast axis mentioned above. However,
antecedent conditions are wetter, resulting in much lower FFG
thresholds. Strong convergence along the inverted trough combined
with sufficient instability will allow for convective development,
with FFG neighborhood exceedance probabilities over 25% in both
the HREF and REFS. A Slight risk is warranted to cover this
threat, with at least a few instances of flash flooding
anticipated.
Farther north into the Mid-Atlantic, insufficient instability will
keep rainfall predominately stratiform, keeping rain rates below
flash flood thresholds. Although strong low level forcing over top
the backdoor front will still support a broad area of rainfall,
with some areas receiving 1-2" of rain.
...South Florida...
A Marginal Risk has been maintained for portions of South Florida.
PWs remain elevated and well above average, supporting heavy
rainfall rates and a localized urban flash flood risk today.
Neighborhood probabilities of exceeding 5" of rain in the HREF and
REFS are around 20-40%.
Chenard
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Tue Sep 22 2026
Day 2
Valid 12Z Wed Sep 23 2026 - 12Z Thu Sep 24 2026
..THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF CENTRAL AND EASTERN NEW MEXICO...
...New Mexico and West Texas...
The heavy rainfall threat established on day 1 will be ongoing and
continue and peak over NM on day 2 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 and the likely development of a surface low. 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 likely.
The most recent guidance still points toward totals of 2 to 4
inches during the 24-hr period, potentially higher up to 5 inches.
This is likely to result in scattered to numerous instances of
flash flooding, some of which could be life-threatening and
significant. This would be most likely across sensitive terrain,
urban areas, and burn scars. The inherited ERO risk is in good
shape given the most recent guidance.
...Mid-Atlantic...
A complex synoptic pattern will be present over the eastern U.S. as
a mid to upper level low slowly drifts from the Ohio Valley
towards the Mid-Atlantic, while a separate coastal low develops
offshore. Meanwhile, surface high pressure positioned to the north
will advect drier and more stable air into the corridor between
these two features.
Much of the deepest moisture and instability will remain offshore
with the coastal low. The primary threat for heavy rainfall over
land should focus closer to the cold core of the upper low from
the OH Valley down through western NC and into north GA. While PW
values will have lowered across this area, model guidance still
indicates CAPE exceeding 1000 J/kg within a trough axis over the
region.
This localized axis of instability, coupled with a stationary
convergence axis, will support the development of slow moving
convective cells. Even with the reduction in deep moisture, locally
heavy rainfall rates are likely. Given that at least some of this
region will have compromised FFG and heightened hydrologic
sensitivity from previous rainfall, some flash flood risk is
expected to continue.
Based on signals from the 00z REFS and HREF members, as well as
the GFS and ECMWF, a small Slight risk has been introduced
stretching from eastern TN into eastern KY and southern WV, where
the focus for slow moving convection is expected to be greatest.
...Florida...
A Marginal risk continues across south FL where above normal PWs
and instability will continue to pose a localized flash flood
risk.
Chenard/Taylor
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Tue Sep 22 2026
Day 3
Valid 12Z Thu Sep 24 2026 - 12Z Fri Sep 25 2026
..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
NEW MEXICO AND THE TEXAS PANHANDLE...
...Southwest...
The stronger mid level forcing and highest PW anomalies will shift
northward out of NM and into Colorado and the central PLains on
Thursday. Despite the loss of stronger large scale forcing,
daytime destabilization over NM is actually forecast to increase
in the wake of the exiting system compared to prior days. While PW
values decrease some, they will remain above the climatological
75th percentile.
With less concentrated forcing and somewhat reduced moisture, the
overall areal coverage of heavy rainfall across NM should diminish
relative to days 1 and 2. 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, a Slight risk is
maintained for NM into the TX Panhandle. Locally significant flash
flood impacts will remain possible. Isolated to scattered flash
flooding will also be possible across portions of Arizona,
southeast Utah, and Colorado as shortwave energy lifts northward
across the region.
...Central Plains...
The deep moisture plume will maximize over the Central Plains on
Thursday, pushing PW values toward late September record levels.
The mid to upper pattern coupled with a robust low level moisture
transport axis supports a favorable setup for organized convection
across portions of KS and NE, with backbuilding/training a
possibility. There remains some uncertainty in the placement of the
heaviest rainfall and eventually a Slight Risk might be needed.
Chenard/Taylor
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Tue Sep 22 2026
Day 4 and Day 5
Valid 12Z Fri Sep 25 2026 - 12Z Sun Sep 27 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...
Day 4...Multiple areas of interest for the end of the week into the
weekend with a broad trough sweeping through the interior northwest
with a shortwave ejection out of the Rockies, enhancing regional
ascent within the Central High Plains into the Missouri River
Valley and adjacent Corn Belt. Model spread continues to be
relatively low with the handling of the two features leading to
better than normal confidence at range for a period of heavy rain
from widespread convection across the above area. Main axis of
heavy rainfall will likely be over central and eastern NE into
western IA and portions of northern KS and southern SD. Totals are
currently between 1-2" on areal average, but signal with
instability was sufficient for a broad MRGL risk placement
maintained over the area with only minor adjustments from the
previous forecast.
Further south over the Southern High Plains, a weak shortwave over
the Southern Rockies will advance east-northeast within the mean
mid-level flow with enough diurnal instability to couple with the
focused ascent pattern to cause a period of convective initiation
across the Southern High Plains of NM into the TX Panhandle.
Signals remains on the weaker side, but some of the areas
anticipated to be impacted will still be in recovery from the
barrage of heavy rain prospects the day prior, especially into NM.
A broad MRGL remains in effect for the above area.
Day 5...Main attention over the Midwest as the disturbance over the
northern tier of the CONUS migrates eastward and leads to a
carryover threat from the prior period. Models are less in
agreement on the overall threat, so the MRGL risk in place over the
Midwest into northern Missouri is of the lower end variety given
some of the model discrepancy. A period to monitor as there's an
equal chance of a higher risk and a removal pending the eventual
convective evolution.
...Eastern New England...
Day 4...Models remain consistent on the potential for a strong
synoptic surface low off northern Mid Atlantic coast with heavy
rain prospects in-of southeastern New England to perhaps as far
south as the northern Mid Atlantic coastal areas. As of the latest
ensemble probs and mean QPF distribution, the primary threat is
still over southern New England with southeastern MA into RI as
the areas of interest with 2+" totals plausible in the setup. The
one positive in this evolution is a limited convective footprint
leading to mainly heavy stratiform type precipitation coincident
with a Nor'Easter that tends to offer some flash flood threat, but
primarily leans more hydrological in terms of long term heavy rain
leading to swollen rivers and streams with urban flooding due to
poor drainage and consistent run off from prolonged rainfall. The
MRGL risk inherited was only adjusted a bit from the previous
issuance but maintaining the foothold over eastern MA into RI.
Day 5...There's some discrepancy in the southward push of heavy
rainfall (ML vs NWP outputs) as the upper pattern shows an
occluding low with a drift to the west or southwest over the course
of Saturday. Pending the upper level evolution, heavy rain
prospects could be felt as far south as the NJ coast, perhaps
leaking into portions of the Delmarva while still dealing more
rainfall into LI and portions of southern New England. At this
juncture, went with persistence in the forecast as higher probs
remains situated over southern New England, but will have to
monitor any trends backing more west to southwest with the
occluding low which would bring heavier rain and perhaps a shift of
the risk area further in that direction. Given the lack of
relevant instability with the setup, a MRGL risk is still the most
likely excessive outcome in the forecast, but positioning is where
there could be some changes in the coming days, pending trends in
guidance.
Kleebauer
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
326 PM EDT Tue Sep 22 2026
Day 4 and Day 5
Valid 12Z Fri Sep 25 2026 - 12Z Sun Sep 27 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...
Day 4...Multiple areas of interest for the end of the week into the
weekend with a broad trough sweeping through the interior northwest
with a shortwave ejection out of the Rockies, enhancing regional
ascent within the Central High Plains into the Missouri River
Valley and adjacent Corn Belt. Model spread continues to be
relatively low with the handling of the two features leading to
better than normal confidence at range for a period of heavy rain
from widespread convection across the above area. Main axis of
heavy rainfall will likely be over central and eastern NE into
western IA and portions of northern KS and southern SD. Totals are
currently between 1-2" on areal average, but signal with
instability was sufficient for a broad MRGL risk placement
maintained over the area with only minor adjustments from the
previous forecast.
Further south over the Southern High Plains, a weak shortwave over
the Southern Rockies will advance east-northeast within the mean
mid-level flow with enough diurnal instability to couple with the
focused ascent pattern to cause a period of convective initiation
across the Southern High Plains of NM into the TX Panhandle.
Signals remains on the weaker side, but some of the areas
anticipated to be impacted will still be in recovery from the
barrage of heavy rain prospects the day prior, especially into NM.
A broad MRGL remains in effect for the above area.
Day 5...Main attention over the Midwest as the disturbance over the
northern tier of the CONUS migrates eastward and leads to a
carryover threat from the prior period. Models are less in
agreement on the overall threat, so the MRGL risk in place over the
Midwest into northern Missouri is of the lower end variety given
some of the model discrepancy. A period to monitor as there's an
equal chance of a higher risk and a removal pending the eventual
convective evolution.
...Eastern New England...
Day 4...Models remain consistent on the potential for a strong
synoptic surface low off northern Mid Atlantic coast with heavy
rain prospects in-of southeastern New England to perhaps as far
south as the northern Mid Atlantic coastal areas. As of the latest
ensemble probs and mean QPF distribution, the primary threat is
still over southern New England with southeastern MA into RI as
the areas of interest with 2+" totals plausible in the setup. The
one positive in this evolution is a limited convective footprint
leading to mainly heavy stratiform type precipitation coincident
with a Nor'Easter that tends to offer some flash flood threat, but
primarily leans more hydrological in terms of long term heavy rain
leading to swollen rivers and streams with urban flooding due to
poor drainage and consistent run off from prolonged rainfall. The
MRGL risk inherited was only adjusted a bit from the previous
issuance but maintaining the foothold over eastern MA into RI.
Day 5...There's some discrepancy in the southward push of heavy
rainfall (ML vs NWP outputs) as the upper pattern shows an
occluding low with a drift to the west or southwest over the course
of Saturday. Pending the upper level evolution, heavy rain
prospects could be felt as far south as the NJ coast, perhaps
leaking into portions of the Delmarva while still dealing more
rainfall into LI and portions of southern New England. At this
juncture, went with persistence in the forecast as higher probs
remains situated over southern New England, but will have to
monitor any trends backing more west to southwest with the
occluding low which would bring heavier rain and perhaps a shift of
the risk area further in that direction. Given the lack of
relevant instability with the setup, a MRGL risk is still the most
likely excessive outcome in the forecast, but positioning is where
there could be some changes in the coming days, pending trends in
guidance.
Kleebauer
