Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sun Oct 12 2025
Day 1
Valid 01Z Mon Oct 13 2025 - 12Z Mon Oct 13 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTHERN ARIZONA AND THE COASTAL PLAIN OF THE CAROLINAS...
0100Z Excessive Rainfall Discussion Update...
Maintained the Slight Risk across parts of the Coastal Plain in
northeast SC and far southern NC -- essentially the area that has
already received 3-5+ inches in spots with banding persisting into
the area (pivoting very little). Rainfall rates are not as much of
a concern (limited deep-layer instability); however, considering
the rain already fallen along with the persistent banding, have
kept the Slight going.
Across AZ -- the latest observational and mesoanalysis trends,
along with recent ensemble exceedance probabilities (HREF and
RRFS), was able to trim a bit of the Slight Risk from parts of
central and southwest AZ, along with southwest NM.
Hurley
0830Z Excessive Rainfall Discussion...
...Southwest...
Deep moisture, fortified with the remnants of Tropical Cyclone
Raymond, will remain in place over portions of southern Arizona and
New Mexico. This morning's mesoanalysis shows PWs of 1.25-1.6
inches (3-4 std dev above normal) covering much of region. This
moisture along with increasing large-scale ascent, provided by an
approaching upper trough, will support another day of widespread
showers and storms capable of producing moderate to heavy amounts.
Maintained a Slight Risk covering much of southern Arizona and a
small portion of southwestern New Mexico. Both the HREF and RRFS
neighborhood probabilities indicate locally heavy amounts
exceeding 2 inches are likely within this region, with some
potential for amounts over 3 inches, especially across parts of
southern Arizona.
...Eastern Southern Carolina and Southeastern North Carolina...
The initial low of what is expected to evolve into a two feature
system is forecast to linger along the coast in the vicinity of the
North and South Carolina border today. Deeper moisture will remain
as well, with many of the 00Z models, including the globals,
showing a notable signal for locally heavy amounts developing later
today. While instability will be limited, deep saturation through
the column, and tall, skinny CAPEs are expected to support very
efficient rains, promoting heavy amounts. Both the HREF and RRFS
showing high probabilities for additional amounts over 3 inches
today across parts of the region. These amounts may raise runoff
concerns, especially for those areas where significant rains have
already occurred. Therefore a Marginal Risk was introduced for
areas where the hi-res ensembles indicate the heaviest amounts are
most likely to fall.
...Northern Mid Atlantic to Southern New England Coasts...
North of its parent, a secondary, triple-point low is forecast to
develop near the northern Mid Atlantic coast. There remains some
model uncertainty regarding if and to what degree this low will
become the dominant surface feature. Despite the differences,
there is broad agreement that strong, low level easterly winds, in
combination with strong mid-to-upper level forcing, will support
widespread precipitation from the northern Mid Atlantic coastal
region to central New England, with heavy amounts expected along
the coast. These heavy rains may compound what are likely to be
poor ground conditions attributed to ongoing coastal flooding.
Pereira
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sun Oct 12 2025
Day 2
Valid 12Z Mon Oct 13 2025 - 12Z Tue Oct 14 2025
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEASTERN ARIZONA, SOUTHWESTERN NEW MEXICO, AND SOUTHERN
COLORADO...
2030Z Excessive Rainfall Discussion Update...
Expanded the Marginal and Slight risk areas across portions of
Arizona in response to an uptick in the deterministic QPF from WPC
and in response to an increase in the areal footprint of QPF from
the ensembles compared with the overnight guidance. In
general...the uptick was modest and the overall forecast reasoning
was similar to the previous outlook.
Bann
0830Z Excessive Rainfall Discussion...
...Southwest to the Central Rockies...
Lingering deep moisture over southern Arizona and New Mexico will
be drawn north ahead of an upper trough amplifying over California.
This moisture along with the broad-scale ascent afforded by the
upper trough will support one more day of showers and storms across
the Southwest, but this time shifting a bit further east while
extending north across New Mexico into the central Rockies. With
drier air working into southwestern Arizona, the potential for
heavy rain and the threat for flash flooding will become more
limited across that area. However, further to the north and east, a
Slight Risk was maintained along eastern portions of the Mogollon
Rim into southeastern Arizona and southwestern New Mexico. There
remains a notable signal for additional moderate to locally heavy
amounts across that area. Also remaining is a Slight Risk in a
portion of the San Juan Mountains, where models show deep
persistent southerly winds, along with favorable upper forcing,
supporting heavy totals as well.
...Northern and Central California....
Models remain in generally good agreement, showing an anonymously
deep upper developing and dropping south along the West Coast from
the Pacific Northwest to Northern California this period. Moisture
with this system will be relatively modest initially, but enough
to raise moisture anomalies to 1-2 std dev above normal along its
axis of strong onshore flow. This along with strong forcing may be
sufficient to produce locally heavy amounts, with isolated runoff
concerns, especially in the upslope regions of the coastal ranges
and the Sierra foothills below the snow line.
....Northeast...
Questions remain as to how the low developing along the Northeast
coast will continue to evolve, but most agree on at least a
localized threat for heavy rain spreading north from southern New
England up along the coast to areas perhaps as far north as coastal
Maine. Given the uncertainty, kept the Marginal Risk centered to
the area where the GEFS and ECENS both indicate that amounts
exceeding an inch are most likely.
Pereira
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
858 PM EDT Sun Oct 12 2025
Day 3
Valid 12Z Tue Oct 14 2025 - 12Z Wed Oct 15 2025
...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHERN CALIFORNIA...
2030Z Excessive Rainfall Discussion Update...
Introduced a Slight Risk over portions of southern California as a
deepening system brings increasing coverage of rain to an area with
recent burn scars that has made the ground impervious to water
infiltration. In such areas...most of the rain will immediately
run-off. Elsewhere...the large scale synoptic pattern was handled
similarly by the models and only minor modifications were needed.
Bann
0830Z Excessive Rainfall Discussion...
...Central to Southern California...
A deep upper low will continue to dig south early in the period
before turning east across California into the Great Basin this
period. Before turning inland, this system will support an ongoing
threat for heavy precipitation, with the focus shifting south along
with its associated axis of deep onshore flow across Southern
California into the southern Sierra Nevada. A Marginal Risk was
drawn south along the Southern California Transverse Ranges, where
0.75-1 inch PWs interacting with favorable upper jet dynamics and
orographic ascent are expected to support rainfall amounts of 1-2
inches along the favored terrain. These amounts may produce
isolated runoff concerns, especially over vulnerable burn scar
areas. A Marginal Risk was also maintained further to the northeast
along the southern Sierra foothills, where similar amounts are
expected below the snowline.
...New Mexico and West Texas...
As drier air continues to spread east across Arizona into eastern
New Mexico, PWs anomalies will remain high across portions of
central New Mexico and West Texas where strengthening low level
easterly winds will add to the lingering moisture. With the
increase in moisture, the GFS shows PW anomalies remaining over 3
std dev above normal across much of the highlighted areas. This
along with daytime heating will support additional shower and
thunderstorm development, with some potential for locally heavy
amounts and isolated runoff concerns.
Pereira
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Sun Oct 12 2025
A lead short range coastal storm will be working well out to sea
across the western Atlantic by midweek but still support continued
unsettled/windy conditions over New England through late week with
impulses digging behind the system bring some lingering showers.
An incoming upper low/amplified trough slated to bring rain/snow
to California early week will lift increasingly inland across the
West/Rockies mid-late week. A Day 4/Wednesday WPC Excessive
Rainfall Outlook Marginal Risk area remains over New Mexico and
southern Colorado where leading moisture levels may fuel some
lingering local downpours with runoff issues. Upper system and wavy
frontal progression will also drive organized rain/snow over the
north-central Intermountain West/Rockies Wednesday/Wednesday night.
Much of the West will see at least some rain or snow, with snow
levels lowering as colder air moves in. Temperatures will be well
below normal into Wednesday (by 10-20 deg) with some slight
moderation for the rest of the week, but still cooler than normal.
Later period, there is also some upstream guidance signal
supporting approach of another amplified Northeast Pacific storm
system toward the Pacific Northwest/Northwest next weekend that may
offer quite unsettled flow and enhanced rainfall to monitor.
Downstream for the central states, southwesterly upper flow will
increase the chances of rain for mid-late week over the Northern
Plains into the Upper Midwest closer to the jet stream with wavy
surface system translation/genesis. Mild and more moisture-laden
air to the south over the central Plains and Mid-Mississippi Valley
will support a growing pattern with showers and thunderstorms
ahead of the western/Rockies system into Thursday/Friday. Activity
may flourish as focus shifts slowly with more uncertainty into the
east-central states into next weekend in an emerging return flow
pattern to monitor for enhanced rainfall/runoff issue potential.
Santorelli/Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Sun Oct 12 2025
A lead short range coastal storm will be working well out to sea
across the western Atlantic by midweek but still support continued
unsettled/windy conditions over New England through late week with
impulses digging behind the system bring some lingering showers.
An incoming upper low/amplified trough slated to bring rain/snow
to California early week will lift increasingly inland across the
West/Rockies mid-late week. A Day 4/Wednesday WPC Excessive
Rainfall Outlook Marginal Risk area remains over New Mexico and
southern Colorado where leading moisture levels may fuel some
lingering local downpours with runoff issues. Upper system and wavy
frontal progression will also drive organized rain/snow over the
north-central Intermountain West/Rockies Wednesday/Wednesday night.
Much of the West will see at least some rain or snow, with snow
levels lowering as colder air moves in. Temperatures will be well
below normal into Wednesday (by 10-20 deg) with some slight
moderation for the rest of the week, but still cooler than normal.
Later period, there is also some upstream guidance signal
supporting approach of another amplified Northeast Pacific storm
system toward the Pacific Northwest/Northwest next weekend that may
offer quite unsettled flow and enhanced rainfall to monitor.
Downstream for the central states, southwesterly upper flow will
increase the chances of rain for mid-late week over the Northern
Plains into the Upper Midwest closer to the jet stream with wavy
surface system translation/genesis. Mild and more moisture-laden
air to the south over the central Plains and Mid-Mississippi Valley
will support a growing pattern with showers and thunderstorms
ahead of the western/Rockies system into Thursday/Friday. Activity
may flourish as focus shifts slowly with more uncertainty into the
east-central states into next weekend in an emerging return flow
pattern to monitor for enhanced rainfall/runoff issue potential.
Santorelli/Schichtel
