Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Mon Oct 13 2025
Day 1
Valid 01Z Tue Oct 14 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 AS WELL AS PORTIONS OF SOUTHERN CALIFORNIA...
...California...
As a strong mid-level closed low (-4 standardized height anomaly
at 500 mb) drops southward just off the coast of central California
tonight, an occluded/cold front will follow suit, reaching southern
California's Transverse Ranges between 06-12Z. An anomalous
moisture plume, with PWAT values between 0.9 and 1.2 inches, will
focus along the coast ahead of the cold front and be directed
inland via 20-35 kt of wind at 850 mb.
An inland flash flood threat will remain where weak instability
(generally less than 500 J/kg CAPE) will align with 20-30 kt of
cyclonically curved low level flow to the east of the mid-level low
to support localized hourly rainfall of 0.5 to 1.0 inches.
Along the coast, and especially the Transverse Ranges later
tonight, low level flow of 20-30 kt becomes aligned perpendicular
to the terrain, increasing rainfall via orographic influences.
Recent RAP forecasts have shown pockets of MLCAPE in the 250-750
J/kg range just offshore with inland values up to a few hundred
J/kg which will combine with left-exit region jet divergence to
allow for higher intensity rainfall potential. A frontal
convergence axis of showers and thunderstorms appears likely to
form and steadily translate southward with the cold front. While
the front will be progressive, brief training with the front along
with pre-frontal activity could support localized 2 to 3 inch
rainfall totals through 12Z for the Transverse Ranges.
The main flash flood concern across California for the overnight
period will be urban and burn scar overlap of heavy rain, with the
threat carrying over into the Day 2 ERO period beginning 12Z
Tuesday.
...Southwest to the Central Rockies...
South-central Arizona remained convectively active as of 00Z with
a bubble of 500-1500 J/kg MLCAPE remaining with little to no
inhibition. Strong right entrance region upper level jet divergence
was also present across a good portion of Arizona, helping with
ascent. PWAT standardized anomalies of +2 to +4 above the mean
remained over the eastern half of Arizona into Utah, Colorado and
New Mexico as of 00Z tonight, but drier air will be pushing into
Utah and Arizona through 12Z from the west out ahead of a lead
impulse located ahead of a large closed low along the coast of
California. 25 to 45 kt of 700 mb flow and unidirectional SSW flow
will be supportive of repeating and training rounds of heavy rain
with the best potential for higher rates remaining co-located with
remaining instability pockets. A second area of instability is
expected to support locally higher rain rates later tonight from
near El Paso into portions of southern/central New Mexico, although
this region's flash flood concern is a bit lower than locations to
the west due to drier antecedent conditions and weaker forcing for
ascent.
Very wet antecedent conditions exist across southwestern Colorado/San
Juan Mountains and portions of central Arizona due to 3 to 4 day
rainfall totals of 2 to 6 inches. Additional totals of 2-3 inches
may occur in localized portions of the San Juan Mountains due to
upslope enhancement with 1-2 inch maxima forecast elsewhere.
The main change for the 01Z update include the removal of the
Slight Risk for southeastern Arizona into far southwestern New
Mexico where a lack of instability and better forcing is expected
to suppress convective coverage in the overnight. A portion of the
Marginal Risk was also removed from the northern California coast
where the heavy rainfall threat has ended with the movement of the
closed low.
Otto
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Mon Oct 13 2025
Day 2
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...
Few changes needed to the previously-issued ERD. Present thinking
is that the main threat for excessive rainfall across California
will be in the first 12 hours of so given the progressive nature of
the anomalous upper low dropping southward along the coast.
Elsewhere...the large scale features were handled similarly
amongst the various models.
Bann
0830Z Excessive Rainfall Discussion...
...Central to Southern California...
Our western disturbance will continue its progression slowly inland
with a steady south-southwesterly component situated over the
terrain of southern CA. Expect a continuance from the D1 to bleed
into the first half of D2 with heavy rainfall aligned within the
eastern Transverse Range and the northern Peninsular Range to the
north and northeast of Los Angeles. PWAT anomalies on the order of
1-2 deviations above normal are sufficient for a deep layer
moisture regime capable for heavy rainfall rates between 0.5-1"/hr
with a chance for a few stronger cores to exceed 1"/hr, a signal
more than capable of producing flash flooding in-of the area most
susceptible given the burn scar remnants positioned in the
Peninsular Range. Additional totals of 1-3" are forecast with
locally higher possible in those areas northeast of Los Angeles in
the terrain. Totals for the event will run between 1-4", plentiful
over a span of 12-24 hrs. to cause issues in what is a sensitive
locale for flash flooding and debris flow. The previous SLGT risk
was linked together and spans the eastern Transverse into the
northern Peninsular Range. MRGL risk is in place surrounding,
including an extension into parts of the Central Valley and
adjacent Sierra Foothills as locally heavy rainfall is still
forecast through the first 6-12 hrs. of the period which could spur
some isolated flash flood signals.
...New Mexico and West Texas...
Remnant elevated moisture across far west TX into NM within a
persistent axis of diffluent flow will yield a period of scattered
thunderstorms over the two areas leading to isolated flash flood
concerns, mainly in urban zones and over the complex terrain
aligned from the Sacramento's up into the Sangre de Cristos. Totals
are not very appreciable at this juncture, but environmental
conditions still support some heavier rainfall prospects over areas
that will have seen a decent amount of rain leading in. Combination
of antecedent conditions and additional rainfall place the threat
inside the MRGL risk threshold leading to general continuity from
previous forecast.
Kleebauer
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
857 PM EDT Mon Oct 13 2025
Day 3
Valid 12Z Wed Oct 15 2025 - 12Z Thu Oct 16 2025
...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL OVER PORTIONS
OF THE CENTRAL AND SOUTHERN ROCKIES...
2030Z Excessive Rainfall Discussion Update...
The forecast reasoning remained similar to the previously issued
discussion and the outlook was largely unchanged.
Bann
0830Z Excessive Rainfall Discussion...
...Rockies...
Longwave pattern out west will continue to evolve with upstream
troughing pushing east-northeast leading to a final prospect of
isolated to scattered convection over the terrain of the central
and southern Rockies. A lot of the threat stems from RER
positioning with a broad upper jet aligned over the Mountain West
with an extension into the High Plains by the end of the forecast
cycle. The main areas of concern will likely be in those complex
terrain locations in-of the Sangre de Cristos, San Juans, and down
near the Sacramento's. These areas will all have either very wet
antecedent soil moisture that would promote easier run off
capabilities, or burn scar remnants that maintain a posture for
localized flash flood opportunities with any rates >0.5"/hr. This
is still feasible with PWATs remaining ~2 deviations above normal
in this zone when assessing the latest NAEFS output. A MRGL risk
remains in place over these areas of the central and southern
Rockies as a result.
Kleebauer
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Mon Oct 13 2025
A current coastal storm is expected to be working well out to sea
across the western Atlantic by Thursday, but should still support
continued unsettled/windy conditions over New England through late
week as enhanced as impulses dig on the backside of the storm.
An upper low/amplified trough impacting the West over the next few
days will work over the Rockies to increasingly effect the north-
central U.S. mid-late week to include increasing chances of rain
with wavy surface system translation. More moisture-laden air to
the south over the central Plains and Mid-Mississippi Valley will
support a growing pattern with showers and heavier thunderstorms.
Activity may flourish as focus shifts slowly into the east-central
U.S. states into next weekend in an emerging return flow pattern to
monitor for enhanced rainfall and runoff issue potential.
Later period, the upstream signal continues to grow in support of
approach of an amplified Northeast Pacific storm system to the
Pacific Northwest/West Coast next weekend to offer unsettled flow
and enhanced precipitation threat to monitor.
Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
355 AM EDT Mon Oct 13 2025
A current coastal storm is expected to be working well out to sea
across the western Atlantic by Thursday, but should still support
continued unsettled/windy conditions over New England through late
week as enhanced as impulses dig on the backside of the storm.
An upper low/amplified trough impacting the West over the next few
days will work over the Rockies to increasingly effect the north-
central U.S. mid-late week to include increasing chances of rain
with wavy surface system translation. More moisture-laden air to
the south over the central Plains and Mid-Mississippi Valley will
support a growing pattern with showers and heavier thunderstorms.
Activity may flourish as focus shifts slowly into the east-central
U.S. states into next weekend in an emerging return flow pattern to
monitor for enhanced rainfall and runoff issue potential.
Later period, the upstream signal continues to grow in support of
approach of an amplified Northeast Pacific storm system to the
Pacific Northwest/West Coast next weekend to offer unsettled flow
and enhanced precipitation threat to monitor.
Schichtel
