FOUS30 KWBC 222029
QPFERD
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 PM EDT Thu Oct 22 2026
Day 1
Valid 16Z Thu Oct 22 2026 - 12Z Fri Oct 23 2026
...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
SOUTHWEST COLORADO AND SOUTHERN UTAH...
...16Z update...
The biggest change with this update was the introduction of a
Slight Risk across a small portion of the interior Northwest
including southeastern Oregon into northwestern Nevada and far
northeastern California. While it appears instability will be
limited with the recent model consensus showing MLCAPE of only a
few hundred J/kg and MUCAPE locally over 500 J/kg later this
afternoon, 24 hour rainfall values of 1 to 2+ inches appear likely
based on the 12Z HREF/REFS through 12Z Friday. Some of the 24 hr
QPF will be in the form of snow toward the end of the period but
most will fall as liquid. Regarding timing, the 18-06Z window will
favor increasing upper level diffluence and divergence ahead of a
90-110 kt upper level jet max located ahead of an advancing closed
low/trough forecast to move across California and Nevada through
tonight. Slow movement of heavy rain cores could allow for hourly
rainfall locally exceeding 0.5 inches at times. While 100 year
recurrence intervals may not indicate the most representative
values for this region of the U.S., both the HREF and REFS show
fairly high probabilities of exceeding the 100 year ARI with 40-60
percent (12Z HREF) and 60-90 percent (12Z REFS). Again, the
concern for flooding impacts may be more of a longer duration
concern, rather than occurring on a 1 or 3 hour time scale.
Elsewhere, the Marginal Risk was expanded across portions of
central California given the potential for slow moving cells
beneath the core of the upper low as it moves eastward this
afternoon. MLCAPE is forecast to rise into the 500-1000 J/kg range
across portions of the San Joaquin Valley with cell motions less
than 10 kt among precipitable water values approaching 1 inch.
Hourly rainfall may exceed 1 inch locally across the Great Valley
through the early evening.
Otto
...previous discussion follows...
...Southwest...
A broad Slight risk remains in place across the Southwest as a deep
mid to upper level low tracking into the West Coast provides robust
large scale scent. Dynamic forcing is further enhanced by strong
upper level divergence within the favorable right entrance region
of an upper jet streak at the base of the trough. Ahead of the
trough deep southerly flow will continue to advect anomalous
tropical moisture northward, resulting in a broad footprint of near
to record PW values for the time of year to go along with near record
IVT values as well.
Instability will be maximized from southern to central AZ into
west central NM, where MUCAPE value upwards of 2000 J/kg are
expected. This corridor of greater instability is where the
greatest potential for intense convective rainfall rates exists,
with rates locally as high as 1-2"/hr likely. Several CAMs signal
the potential for brief cell training within the unidirectional
southerly flow this morning across central AZ, with the corridor
between Phoenix and Flagstaff favored along the nose of the low
level moisture transport axis. This higher rainfall rate potential
will gradually shift eastward across central AZ and into west
central NM later today into this evening. Scattered instances of
flash flooding are expected along his corridor, with locally
significant impacts possible.
Further north, the MDT risk centered over the San Juan Mountains
has been expanded westward into south central and southeastern UT.
Instability will be comparatively lower over this northern flank,
but portions of southern UT have already received heavy rainfall
yesterday, leaving hydrologic sensitivity elevated. A prolonged
duration of scattered showers and thunderstorms is expected today.
While quick cell motions and marginal instability will generally
cap hourly rates around 0.5"/hr, the higher CAPE axis (~1000 J/kg)
is forecast to nudge northward towards southern UT by later this
morning and afternoon. This destabilization, combined with brief
cell training, should support localized swaths of 1"/hr rain rates
over sensitive terrain, slot canyons and washes, leading to
scattered to numerous instances of flash flooding.
The San Juan Mountains will see the heaviest rainfall accumulations
from this event, with model consensus supporting around 3-4", and
localized totals potentially exceeding 5". Rainfall of this
magnitude generally equates ot a 10-50yr ARI for 24hr totals.
Instability will struggle to reach this far northeast, keeping
high res ensemble neighborhood probabilities for 1"/hr rain
subdued at roughly 10-15%. However, strong orographic ascent
within the deep moisture plume will generate persistent moderate
to at times heavy rainfall, with rates periodically reaching
0.5"/hr. While some snowmelt is expected to enhance runoff and the
flood threat, temperature at higher elevations should remain in
the 30s and 40s, allowing existing snowpack to absorb some of the
rain. Overall this event is a solid MDT risk, with numerous
instances of flooding likely, some of which may produce significant
impacts. The lack of higher convective rates and storm totals
largely holding under 5 inches keep this just below High risk levels...nonetheless, this is still expected ot be a high impact
hydrologic event for the region.
...CA into ID...
Along the CA coast, the initial band of heavier rainfall should
have weakened by 12z. However, with the main mid to upper level low
still offshore, additional isolated to scattered convective cells
are likely to redevelop through the day, supporting a localized
flash flood risk.
Further inland, modest destabilization at or below 500 J/kg is
expected into portions of NV/OR/UT. This weak instability paired
with quick cell motions off to the north northeast should keep any
flash flood threat localized and primarily over sensitive terrain
and burn scars.
A localized corridor of higher rainfall (1 to 2", locally up to 3")
is expected from far northwest NV into far northeast CA and
portions of southeast OR. Totals of this magnitude represent a
10-25yr ARI for this region and may be sufficient to induce
hydrologic concerns. A Slight risk was considered given the
anomalous rainfall magnitudes for the local climatology, but
limited instability should result in an increasingly stratiform
character of the rain following a period of initial convection.
This may help keep the hydrologic impacts more isolated in nature.
...Southeast Florida...
A Marginal risk continues for the southeast FL urban corridor. Low
level coastal convergence within prevailing northeasterly flow
will remain the primary focus for convection, with the potential
to anchor slow moving cell either along the immediate coast or
just offshore. Several CAMs highlight localized swaths of 5"+ of
rain. However, uncertainty remains whether these heavy cores will
make it onshore or stay just offshore. In addition, PW values are
currently around 1.4", and while these values may increase some
today, a significant increase is not expected. Thus some of the
more aggressive high res guidance could very well be a bit
overdone with peak rainfall magnitudes. A Marginal risk remains
appropriate to cover the localized conditional flash flood risk.
Chenard
Day 2
Valid 12Z Fri Oct 23 2026 - 12Z Sat Oct 24 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE SACRAMENTO
MOUNTAINS SOUTH THROUGH THE EL PASO METRO...
...21Z update...
...NM and southern CO...
Model agreement remains good concerning the track and timing of a
mid to upper-level trough axis moving east across the Southwest
through Saturday morning. As the main energy over Arizona/Utah from
Thursday night lifts northeastward, the trough is reinforced on
Friday over California/Nevada/Arizona, resulting in the formation
of a new closed low. The net result downstream is only a minor
eastward push of heights into New Mexico and Colorado which will be
a hindrance for forcing. However, precipitable water values are
forecast to remain anomalous (2 to 4+ standardized anomalies from
the 12Z GFS) from far western Texas into central/eastern New Mexico
and southeastern Colorado including a middle and upper level
connection to moisture related to remnant tropical systems west of
the central Mexican coast.
The mean steering flow will be from the SSW, ranging from 20 to 40
kt and 850-700 mb winds remain fairly strong at 15 to 30+ kt.
Therefore, while individual cells should remain progressive, there
will be high potential for repeating and training of heavy rain.
The 12Z HREF/REFS showed that the probabilities for 0.5 to 1.0+
in/hr rainfall ramp up in the 18-21Z time frame and diminish after
06Z Saturday. Total rainfall of 1 to 2 inches is likely across
portions of central/eastern New Mexico into southern Colorado for
the 24 hour period with localized totals between 2 to 3 inches.
Thinking from the previous shift remains valid (see below),
including the higher potential for higher rates/instability across
far western Texas into southern New Mexico despite the QPF signal
in the models lowering the existing Slight Risk area.
...East Coast of Florida...
A Marginal Risk remains in place across southeastern Florida but
was expanded northward to include Cape Canaveral where similar
potential for slow moving cells will exist. Some of the 12Z model
guidance showed the potential for higher instability farther north
with 500 to 1000 J/kg in place at times throughout the 24 hour
period near the Cape Canaveral region. While precipitable water
values are lower into the Space Coast (at or less than 1 inch),
there are some modest probabilities for 3, 5 and 8 inches over the
24 hour period ending Saturday morning near or just offshore of the
coast according to the 12Z HREF/REFS.
Otto
...previous discussion follows...
...NM and southern CO...
Scattered convection is expected to develop across portions of NM
into southern CO downstream of a mid to upper level trough
tracking eastward from CA into AZ. In the broader evolution of the
system, day 2 (Friday) appears to represent a relative minimum in
convective coverage and overall intensity compared to more active
periods expected on both Thursday and Saturday. Nonetheless, PWs
will remain anomalous and collocated with 500-1500 J/kg of CAPE.
This environment will support scattered convection capable of
locally high rainfall rates and an isolated flash flood threat.
While the latest QPF guidance remains modest and generally
supportive of a Marginal risk, the presence of better instability
over southern NM could yield an uptick in convective rainfall as we
get more into the high res model timeframe. Considering the
hydrologic vulnerability, the inherited Slight risk was maintained
across the terrain and burn scars of the Sacramento Mountains into
adjacent urban corridors.
...Southeast FL...
A setup similar to day 1 will persist across southeast FL, where
low level northeasterly flow and coastal convergence could focus
slow moving cells along the immediate coast. The heavy rainfall
threat remains conditional, with a possibility the heaviest cores
remain just offshore. Model differences also introduce some
uncertainty regarding the moisture profile, with the GFS showing
notably higher PW values than the ECMWF. Given the lingering
uncertainty with these details the inherited Marginal risk was left
unchanged.
Chenard
Day 3
Valid 12Z Sat Oct 24 2026 - 12Z Sun Oct 25 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN NEW
MEXICO INTO SOUTHEASTERN COLORADO, AND OVER SOUTHEAST FLORIDA...
...21Z update...
...Eastern NM into southeast CO...
Minor timing differences existed in the 12Z models regarding the
eastward progression of a mid to upper-level closed low over the
Southwest with the 12Z GFS a bit faster than the consensus by
Sunday morning. Despite these differences, the models are
unanimous with the potential for heavy rainfall, especially over
eastern New Mexico, with broad support for 1 to 3 inches over the
24 hour period. Anomalous precipitable water values from Friday
will remain over eastern New Mexico/eastern Colorado into the
adjacent High Plains containing 2 to 4+ standardized anomalies in
the 12Z GFS. The increased forcing/instability mentioned in the
previous discussion continues to look valid which will likely
support higher potential for heavy rain. Hourly rainfall locally
exceeding 1 inch appears likely and when combining with antecedent
heavy rainfall from the previous couple of days, a higher end
Slight Risk remains focused from the southern Sacramento Mountains
into far southeastern Colorado.
...Four Corners Region
While better moisture will have shifted well east of the Four
Corners region by Saturday morning, there will continue a localized
concern for heavy rainfall near and just east of the approaching
closed low aloft over Arizona/Utah. Snow levels should remain high
enough (9000+ feet above MSL) across the region to allow for heavy
rainfall from slow moving or repeating cells. Model forecast
instability is weak across the region but where pockets of at least
a few hundred J/kg are expected to set up, there will be support
for localized rainfall of 0.5 to 1.0+ inches in 3 hours. Given the
preceding days of heavy rainfall leading up to Saturday, the
region will be more hydrologically sensitive than average to
additional, albiet localized, heavy rainfall.
...East Coast of Florida...
Similar to Friday/Friday night, the previous Marginal Risk was
extended northward to include the Space Coast given similar
potential for instability and heavy rain from slow moving cells.
There is better model agreement today, regarding a mid-level low
that is forecast to drop southward near the east coast of Florida
late Saturday into Sunday, associated with a surge in moisture and
low level easterly flow into the central and southern Peninsula.
While model QPF for southeastern Florida are mixed, cannot rule out
some locally enhanced threat for flash flooding across the urban
southeastern corridor given the setup, so the Slight Risk was left
in place for now. Once the forecast is more within the hires
window, a better depiction of the flash flood potential should
hopefully emerge with possible changes to the ERO.
Otto
...previous discussion follows...
...Eastern NM into southeast CO...
An uptick in the flash flood threat compared to day 2 is
anticipated across eastern NM into southeastern CO on Saturday.
Synoptic scale ascent will strengthen as the mid to upper level
trough and associated jet streak approach the region, which will
also help amplify the low level moisture transport axis. PWs will
remain anomalous, holding well above normal and near climatological
max values for late October. Model guidance also indicates upwards
of 500-1500 J/kg of CAPE within this moisture plume. Deep
unidirectional southerly flow will favor some cell training and
backbuilding potential. Given the favorable ingredients, not
surprising that model QPF values are notably higher compared to
day 2.
The combination of strong forcing, deep and anomalous moisture,
and sufficient instability, will support convective rain rates
locally as high as 1-2"/hr. Overall model agreement on the axis of
heaviest rainfall is above average for a day 3 forecast. Higher
end Slight risk probabilities are justified across much of eastern
NM with scattered flash flooding expected.
...Southeast FL...
The Slight risk has been maintained across the southeast FL urban
corridor. The mesoscale setup remains similar to days 1 and 2,
with northeasterly low level flow promoting coastal convergence
and possible slow moving convection. By this time, dynamic ascent
may be aided by a distinct mid level shortwave dropping southward
into the area. While model guidance is in relatively good agreement synoptically, model spread persists regarding the magnitude of
moisture present. The ECMWF and AIFS remain noticeably drier
overall, depicting an environment less conducive for heavy
rainfall. Conversely, the GFS/AIGFS/UKMET/CMC all depict a deeper
moisture profile and consistently produce a coastal heavy rain
signal. Given this lingering uncertainty and the conditional
probability for slow moving convection to anchor along the
sensitive coastal corridor, there is no reason to deviate from the
inherited Slight risk. Trends will continue to be monitored in
subsequent forecast cycles.
Chenard
Day 4 and Day 5
Valid 12Z Sun Oct 25 2026 - 12Z Tue Oct 27 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL AND SOUTHERN HIGH PLAINS, AS WELL AS SOUTHEAST FLORIDA
ON SUNDAY...
...Central to Southern High Plains...
Our western disturbance will continue to eject eastward, albeit
relatively slowly, over the course of Sunday leading to enhanced
ascent downstream of the mean trough. Elevated moisture positioned
over the Central and Southern High Plains in tandem with the
increased ascent within a defined jet coupling over the area will
allow for scattered to widespread convective development during the
course of Sunday into early Monday morning before we finally see
the pattern settle heading into the D5 time frame. Current ensemble
means remain steady with a broad axis of 1-2" of rainfall with the
individual global deterministic output showing some of the
embedded 3-4" higher amounts during the D4 period across the region
between southern NE down into the TX Panhandle and adjacent
northeastern NM. The overall pattern has been fairly consistent
run-to-run in the evolution of the upper level disturbance with
closed upper level reflection finally opening up and ejecting
northeast into the Northern Plains by the D5 time frame which will
subsequently put an end to the more prolific heavy rainfall posture
we've experienced from the Southwest to the eventual impact across
parts of the High Plains. The previous SLGT risk on D4 was adjusted
a bit to reflect the, again, slower trends in the forward
propagation of the upper low across the Four Corners which allowed
for a small shift westward in the overall threat. The main area of
interest has not changed, however, so the forecast remains in good
standing with the greatest threat likely over eastern NM up through
the TX/OK Panhandles, and into western KS.
By D5, the threat begins wind down as the primary ascent shifts
northward and the lingering elevated moisture and instability is
offset from the primary forcing. Maintained the MRGL risk across
the Southern High Plains to reflect the potential lingering into
Monday and will need to monitor a potential risk addition over the
Midwest as the main energy lifts into the area. That said,
instability to the north is meager, comparatively, so the threat
is not as prevalent over areas of SD/MN to areas south into TX/OK.
...Southeast Florida...
A relatively stagnant synoptic pattern will lead to a continuation
of heavy convective threats anchored to the immediate coast of
southeastern FL. This is likely the final day of the heavy rain
potential, although a few models do want to linger a bit into early
next week. Regardless, a bit of a hold over from what will likely
be an active D3 period leading to the threat for D4 (Sunday) before
things finally settle. Expectation is for local totals of 3-5"
additional on top of any heavy rain the previous periods will only
add to the prospects of flash flooding within the urban corridor.
Given the expected antecedent conditions and the threat of heavy
rain from any convective development, a SLGT risk remains in place
for the D4 time frame before we finally fall to a nil ERO for D5
(Monday) as the threat begins to fade.
Kleebauer
Day 1 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt__;!!DZ3fjg!8M-ZhNnWJ3HmH_guTg1cNJigdvbuAqLHae7LE-cLO0L1ZRredKYfS5GbJgELbDATsTZwdaqCoLFZi_4-_l5OLLgA_bs$
Day 2 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt__;!!DZ3fjg!8M-ZhNnWJ3HmH_guTg1cNJigdvbuAqLHae7LE-cLO0L1ZRredKYfS5GbJgELbDATsTZwdaqCoLFZi_4-_l5OYrKxVHg$
Day 3 threat area:
https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt__;!!DZ3fjg!8M-ZhNnWJ3HmH_guTg1cNJigdvbuAqLHae7LE-cLO0L1ZRredKYfS5GbJgELbDATsTZwdaqCoLFZi_4-_l5OIpMv_Sw$
$$
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