481
FOUS30 KWBC 142021
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 PM EDT Mon Jul 14 2025

Day 1
Valid 16Z Mon Jul 14 2025 - 12Z Tue Jul 15 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MID-ATLANTIC STATES AND SOUTH-CENTRAL TEXAS...

...16Z Update...

The main change to the previous ERO issuance was to add a Moderate
Risk for central and south-central Texas. The ongoing convection
is persistent with several Flash Flood Warnings this morning, and
even as storms weaken through the afternoon, the MCV could be left
behind to maintain forcing. Tonight this MCV combined with a low
level jet including PWs 2.25" persisting or returning will provide
the ingredients for additional convection on what is likely
saturated ground, so a Moderate Risk seems warranted given the
multiple rounds of heavy rain.

Elsewhere, the Moderate and Slight Risks in the Mid-
Atlantic/Northeast look on track per the 12Z CAMs and HREF, albeit
with spread including some CAMs not initializing well with the
current Ohio/WV convection. This lowers confidence on many
changes, but nudged the Slight Risk east on the northern side to
include NYC per recent CAMs. Best HREF probabilities for multiple
inches of rain and for FFG exceedance are in northern New Jersey
stretching southwest.

See the previous discussion for more details and discussion of
other excessive rainfall areas.


Tate


...Previous Discussion...

...Mid-Atlantic Through Northeast...
A cold front slowly advancing from the Ohio Valley will advance
into New England and the Mid- Atlantic states during the evening.
The guidance is in good agreement that convection will develop on a
pre-frontal trough downstream of the front and become numerous
during the afternoon. This will be in response to the accompanying
ascent (through height falls, a potent vort max swinging out of the
Ohio Valley, and low- level convergence) acting upon impressive
thermodynamics characterized by PWs that will exceed 2.25 inches (a
daily record) and MUCAPE of 1000-2000 J/kg. With warm cloud depths
also progged to reach 14,000 ft, efficient warm-rain processes
should dominate all convection this afternoon.

Although storm motions may remain progressive today as 0-6km mean
winds are progged to be angled sharply to the front (some better
training potential farther north into New England), intense rain
rates are expected as reflected by HREF 2"/hr probabilities that
reach 30-50%, suggesting locally 3+"/hr rates are possible. During
storm initiation, motions could be a little slower than once they
become more organized, which would lengthen the duration of any
heavy rain rates, and bulk shear of 20-25 kts could organized cells
into multi-cells, leading to subtly longer and more enhanced
rainfall as well. With extreme rain rates expected everywhere that
develops convection, rainfall could reach 2-4" with locally higher
amounts above 5" possible (HREF/REFS 40-50% chance).

While the CAMS are in good agreement with storms along the pre-
frontal trough pushing eastward, there remains some uncertainty into
pre-trough convective development. If the solutions of the ARW/ARW2
verify, which appear reasonable depicting scattered air-mass type
storms in the region of broad large scale ascent, then these slow
moving storms ahead of the line would enhance the flash flood risk,
and develop the greater potential for the 5+ inches of rain
progged by the neighborhood probabilities. Additionally, the CSU
First- Guess field (both UFVS and non UFVS versions) indicate a 25%
risk area across the I-95 corridor from near Richmond, VA to near
New York City, which is aligned with the highest ECMWF EFI
probabilities as well. Since this heavy rain signature is
consistent among the various ensembles, and will likely occur atop
primed soils from recent heavy rain, an upgrade to a MDT risk was
coordinated with the affected WFOs.


...Florida...
A westward advancing inverted mid-level trough accompanying a
slowly intensifying tropical wave will continue to push westward
today, reaching the east coast of the Florida Peninsula by the end
of D1. Although the primary trough axis will just clip Florida
today, downstream vorticity lobes swinging out ahead of it will
cross the peninsula, leading to robust ascent which will otherwise
be enhanced by upper divergence and a westward advancing sea
breeze. This lift will occur into intense thermodynamics as PWs
surge towards 2.25 inches, which is above the 90th percentile
according to the SPC sounding climatology, collocated with MUCAPE
of more than 2000 J/kg. As the trough axis shifts west, low-level
flow will veer more to the east, leading to enhanced moisture
advection onshore while additionally producing low- level
convergence axes in a region already experiencing impressive deep
layer lift. The result of all of this will be widespread showers
and thunderstorms today, with rainfall rates of 2-3+"/hr.

Coverage across the peninsula will vary considerably based on time
of day today. Overnight (before 12z Monday) and early on Monday,
storms will likely be confined along the Atlantic coast. However, as
instability climbs through the day, convection will spread across
the area and then move S/SW on 0-6km mean winds of 15 kts. While
this will keep cells generally progressive, some short duration
training is possible along convergence axes and where any
organization can occur through 20-25 kts of bulk shear. Then late
tonight, generally after 03Z Tuesday, as the trough axis moves
onshore, a secondary enhancement of convection may accompany a
developing surface wave and move back onto the Atlantic coast. Where
repeating rounds or any training can occur, total rainfall of 3-5"
with locally higher amounts (40-60% chance of 5+ inches from the
HREF) possible. This will produce at least scattered flash flood
impacts today, especially across any urban areas.


...Desert Southwest through the Mid-Mississippi Valley...
Complex upper level pattern will lead to another day of scattered
but intense convection, with clusters of locally more organized
activity, from the Desert Southwest through the Mid-Mississippi
Valley. The driver of this activity will be a strung out mid-level
ridge which will maintain a west-to-east oriented axis from Nevada
into Oklahoma, and a secondary ridge over the Southeast. Between
these features, a shortwave trough will be trapped within a col and
move slowly over the Ozarks, while additional shortwave impulses
rotate westward around the equatorward side of the ridge from West
Texas through New Mexico and Arizona. Ascent accompanying these
features will act upon robust thermodynamics to support heavy
rainfall, as PWs rise to 1.75-2.0 inches from the Gulf Coast of
Texas into the Mid-Mississippi Valley, with a secondary maximum
approaching 1.25-1.5 inches in southern Arizona. Additionally,
MUCAPE, especially during peak aftn/eve heating, will rise to 1000-
2000 J/kg across much of the area.

In this environment, the CAMs suggest generally scattered
thunderstorm development, but with locally enhanced coverage and
intensity. Regardless, any cells that develop will likely contain
rainfall rates of at least 1"/hr (generally 30-60% chance), with
local rates of 2-3"/hr likely, especially from Texas into the
Ozarks. Despite the scattered nature of thunderstorms, there may be
two focused areas today:

1) Across the Desert Southwest a potent shortwave undercutting the
ridge will drift southwest into southern NM and AZ, overlapping a
surge of elevated PWs drawing northward from the Rio Grande Valley
this evening. Rainfall rates may touch 1"/hr at times as CAPE
increases, especially where any storms can organize into clusters
through 0-6km bulk shear of 20-25 kts and storms drop SW off the
terrain. The HREF and REFS 24-hr probabilities for 1+" rise above
60%, highest in SE AZ/SW NM, with the HREF indicating a low end
potential (10% chance) for 3" in this same vicinity. Briefly
considered a SLGT risk for this region, but current satellite
suggests cloud cover will be expansive this morning and CAPE may
struggle to regenerate, so the MRGL risk was left although
isolated impacts are likely.

2) The other area will be from the TX Hill Country northeast into
the Ozarks along a decaying stationary front which will help to
focus slow-moving thunderstorms with the aforementioned intense rain
rates this afternoon/evening. Additionally, an MCV noted in
satellite imagery lifting northward from Coahuila, Mexico this
morning, is likely to provide additional focus for ascent across
south-central Texas. Although the CAMs feature a large variation in
QPF amounts and spatial footprint, there is an increasing signal
for heavy rainfall across the Hill Country, which is additionally
supported by low-level PW (from CIRA LPW products) reaching above
the 95th and even 99th percentile between 850-700mb which will be
supported by strengthening winds within that layer (actually the
strongest winds of the column) providing additional lift through
convergence. This region has been exceptionally wet recently as
well (AHPS 7-day rainfall more than 600% of normal) leading to
extremely vulnerable soils and FFG of just 0.25-1.5"/3hrs. This is
also where the ECMWF EFI is 0.6 to 0.7, indicating an increasing
threat for a heavy rain event, which overlaps a SLGT risk forecast
from the CSU first guess field. After coordination with WFO
SJT/EWX, a SLGT risk was added, focused across the TX Hill Country.


...Northern Plains...
Generally flat/zonal 500mb flow aligned along the Canada/United
States border will gradually amplify into a broad trough this
aftn/tonight as a potent shortwave digs out of Alberta. This
evolution will push a wavy cold front southeastward into an airmass
with PWs above the 90th (locally 97th) percentile according to
NAEFS. A piece of this shortwave and its accompanying vorticity
will swing eastward along the front as the low-level baroclinic
gradient strengthens due to a surging southerly LLJ reaching 25-35
kts to enhanced warm air advection. This will draw even more
favorable PWs northward, and where the most impressive ascent
overlaps the favorable thermodynamics, convection with heavy
rainfall will result. 0-6km mean winds of 20-30 kts suggest storms
will be progressive, but also track parallel to the front which
indicates a training potential. Additionally, some modest
organization is possible which could help enhance rain rates to 1-
2"/hr, especially later this evening. 6hr/5yr RI exceedances peak
this evening as the LLJ ramps upward, suggesting at least an
isolated excessive rainfall/flash flood risk later today.


Weiss


Day 2
Valid 12Z Tue Jul 15 2025 - 12Z Wed Jul 16 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE FLORIDA
PENINSULA, PARTS OF THE MID-ATLANTIC, THE UPPER MIDWEST, SOUTHEAST
ARIZONA, AND CENTRAL TEXAS...

...Florida...
Mid-level trough and an accompanying surface low of tropical origin
will move across the FL Peninsula Tuesday and emerge back over the
northern Gulf overnight. Expect sufficient ascent for widespread
convection across the state, and with PWs peaking around 2.25
inches and tall- skinny CAPE profiles (MUCAPE above 1000 J/kg)
promoting rainfall rates of 2-3"/hr. Convection will once again be
widespread across the area, both near the mid-level center and in
surrounding convergence bands as 850mb flow of 10-15 kts pivots to
become more E/NE through the day, before shifting again to the
south as the feature swings into the Gulf. Storm motions will
generally be slow and chaotic, driven by storm interactions and
boundary collisions, leading to additional rainfall of 2-3",
highest along the W and SW coast. The SLGT risk is maintained with
the Keys removed per coordination with WFO KEY.

...Northern Rockies through the Upper Midwest...
A potent shortwave trough will shift across Montana Tuesday while
a leading impulse shifts from Wyoming to southern Minnesota. An
existing stationary front draped over MT/ND will be driven south
over the northern Plains through Tuesday night with a surface low
forming over MN which will provide a focus for ascent. An intense
LLJ, with speeds rising to 20-25 kts from Neb/SD into MN is
expected to develop Tuesday night, leading to modest isentropic
ascent and stronger convergence as post-frontal winds surge out of
the N/NE at 25 kts as well. This will result in widespread showers
and thunderstorms from MT all the way to MN, with rainfall rates
of 1-2"/hr likely at times within the anomalous PWs (broadly above
the 90th percentile from NAEFS) and increasing MUCAPE, especially
Tuesday night when it eclipses 2000 J/kg across MN. While there
will be widespread rain and thunderstorms across much of this area,
the excessive rainfall risk appears higher across
eastern/downstream portions of the region. While the ECMWF EFI
across MT is impressive (>0.9 in many areas), instability there is
quite weak, suggesting more widespread stratiform rain with just
modest embedded convective elements. Downstream from Neb into MN,
MUCAPE surges Tuesday night with 0-6km mean winds that are aligned
parallel to the front, and in a region of 25-35 kts of bulk shear,
allowing storms to become more organized with some training from
SW to NE to further enhance the rainfall potential. A Slight Risk
is maintained for central Neb through north-central MN to the
southern shore of Lake Superior.

...Mid-Atlantic and Southeast... A moist and unstable environment
will persist from southern New England southward along most of the
Atlantic Seaboard downstream of a decaying front that is expected
to weaken and stall Tuesday from New England into the Central
Appalachians. This front will provide a focus for convective
development, with ascent across the region aided by subtle
impulses/ripples moving within the flow and around a ridge centered
off the coast. Broad SW return flow around this ridge will pump
plentiful moisture (PWs above 2 inches) into much of the area which
will converge on the frontal zone which should feature further MCV
activity from upstream/the Ohio Valley.
While 12Z guidance is rather suppressed for central Mid-Atlantic
QPF (suppressed farther south than previous consensus), the
presence of the front and MCV risk warrants maintaining the Slight
Risk at least for now. The Marginal Risk was trimmed from central
PA which is particularly active today and should be again on
Wednesday (so Tuesday will be generally a reprieve day for the
northern Mid- Atlantic).

...Southwest...
A more active monsoon day is still expected Tuesday as mid-level
ridging weakens a bit and shortwaves traverse east to west beneath
the ridge. This will occur in tandem with a PW surge to 1.25-1.5
inches (+1 standard deviation above the climo mean) as 850mb winds
surge to 20-25 kts from the south, advecting moisture northward up
the Rio Grande and out of Mexico. These anomalous PWs will combine
with SBCAPE of 1000-2000 J/kg, which has been shown to be the best
discriminator for significant monsoon days, to produce an
environment favorable for widespread showers and thunderstorms,
especially in southern Arizona. Storms will likely fire in the
higher terrain and then drift slowly southward on mean winds of
just 5-10 kts, with some organization into clusters supported by
0-6km bulk shear of 20-30 kts. Rain rates potentially exceeding
1"/hr at times with a higher flash flood risk with the Slight Risk
maintained.

...Central Texas...
A LLJ develops again tonight and should allow overnight activity to
continue past 12Z again as has happened in recent days. Therefore,
a Slight Risk is needed to account for this in spite of CAM
guidance once again generally suppressed. New develop over the
Serranias del Burro suggests further MCV development/tracking
tonight. The location of where the repeating rain risk is for
tonight into Tuesday remains uncertain, so this Slight Risk is
likely to need refinement.

...Mid-Mississippi Valley...
Weak impulses/MCVs lifting northeast out of Texas will interact
with a weakening stationary front over the Mid-Mississippi Valley.
While forcing for ascent will remain generally modest, enough lift
into robust thermodynamics (PWs 1.5 to 2.0 inches overlapped with
MUCAPE of 1000 J/kg) will support scattered thunderstorms with rain
rates of 1-2"/hr. 0-6km mean winds of 15 kts suggest cells will
remain generally progressive, but some weak organization in the
vicinity of any mid-level impulse combined with some training along
the weakening boundary could produce some excessive rainfall
related impacts. The Marginal Risk is maintained.


Jackson/Weiss


Day 3
Valid 12Z Wed Jul 16 2025 - 12Z Thu Jul 17 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR NORTHERN KANSAS
AND MUCH OF PENNSYLVANIA...

...Gulf Coast...
A tropical wave (still 30% chance of development from NHC) will
drift westward across the northern Gulf on Wednesday. There
continues to be quite a bit of uncertainty with how much rainfall
occurs on the northern side of this feature. That said, PWs will
likely be over 2.25 inches in the vicinity of this wave, with at
least modest instability spreading onshore, but tempered by what
could be expansive cloud cover. This could limit the northward
progression onshore of rainfall, but in the deeply saturated
column, rainfall rates of 2"/hr still appear likely, with training
from east to west possible along the coast. A Marginal Risk is
maintained for now, but further investigation into this feature
should allow better modeling/confidence in what this feature will
do rain wise for the Gulf Coast through Wednesday night.

...Great Lakes through Appalachians/Mid-Atlantic...
Broad and expansive ridging centered off the Carolinas will
maintain a return flow and push the stalled frontal boundary back
north as a warm front, expanding the environment favorable for
convection with heavy rain compared to Tuesday. The frontal zone is
currently progged to lift over PA which should allow enhanced
convergence and there will likely be further MCV propagation along
the frontal zone. 12Z Canadian Region and experimental RRFS
highlight much of PA with heavy rain, so a Slight Risk is raised
for much of the state. This risk area should see refinement as the
number of CAMs reaching its time period increases. As of now the
broad Marginal from the Great Lakes, along the Appalachians, and to
the Mid-Atlantic Coast is warranted given the aforementioned
moist/unstable environment.

...Desert Southwest through the Central Plains...
Increasing PWs on southerly low-level flow emerging from the Rio
Grande and Mexico is expected Wednesday. Greater PW over southeast
AZ is progged for Wednesday than Tuesday. However, overnight
convection should promote more stratiform activity on Wednesday, so
a Marginal Risk is maintained for now in coordination with WFO TWC.
The shortwave trough crossing MT Tuesday night shifts across the
northern Plains through Wednesday night. Associated surface low
development looks to be over western Kansas with a frontal zone
extending ENE into Neb/Iowa. Convergence in the warm sector ahead
should allow for organized convection to develop Wednesday night.
Based on agreement in the 12Z Canadian Regional and the
experimental RRFS, a Day 3 Slight is raised for much of northern
KS. This area may need refinement as more CAMs get into range.


Jackson/Weiss


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt