767
FOUS30 KWBC 140802
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
402 AM EDT Mon Jul 14 2025

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

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

...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, AND
SOUTHEAST ARIZONA...

...Florida...
Mid-level trough and possibly an accompanying surface reflection
will move across the FL Peninsula Tuesday and emerge back over the
northern Gulf by Wednesday morning. This feature will provide
sufficient ascent for widespread convection across the state, and
with PWs likely hovering around 2.25 inches combined with tall-
skinny CAPE profiles and MUCAPE above 1000 J/kg, rainfall rates of
2-3"/hr are likely (>50% chance from the HREF). In the presence of
the strong forcing accompanying this wave, and within the robust
thermodynamics, convection will once again be widespread across the
area, both near the mid-level center, but also in surrounding
convergence bands as 850mb flow of 10-15 kts pivots to become more
E/NE through the day, before eventually shifting again to the south
as the vorticity swings into the Gulf. Storm motions will generally
be slow and chaotic, driven by storm interactions and boundary
collisions, leading to total rainfall on D2 that could reach 3-4",
highest along the W and SW coast, and the inherited SLGT risk was
only adjusted cosmetically for the recent guidance.


...Northern Rockies through the Upper Midwest...
A compact but potent shortwave and associated vorticity maxima will
drop across Montana Tuesday while it becomes embedded in pinched
westerlies draped from MT into the Great Lakes. This increasingly
progressive flow will shed spokes of vorticity eastward across the
region, helping to push broad height falls into the Northern Plains
and driving a cold front south and east. The interaction of these
vorticity spokes with the low-level baroclinic gradient will yield
waves of low pressure developing along the boundary, to enhance the
slowly intensifying synoptic ascent. Additionally, as the front
drifts southward, it will gradually encounter a more intense LLJ at
850mb, with speeds rising to 20-25 kts from NE/SD into MN, leading
to modest isentropic ascent but 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 NE into MN,
MUCAPE surges Tuesday night which will support the more intense
rain rates, and the excessive rainfall risk is enhanced by 0-6km
mean winds that are aligned parallel to the front, and in a region
of 25-35 kts of bulk shear. This suggests that storms will become
more organized in this region, with some training likely from SW to
NE to enhance the rainfall potential. FFG exceedance probabilities
are modest from the HREF, likely due to still temporal and spatial
variation among the various high-res CAMs, but the inherited SLGT
risk remains with just some cosmetic adjustments to match the
higher 24-hr neighborhood rainfall probabilities.


...Northeast, Mid-Atlantic and Southeast...
A moist and unstable environment will persist from New England
southward along most of the Atlantic Seaboard downstream of a
decaying front that is expected to weaken and dissipate 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, although a sharp gradient will exist along and
north of the front into New England, with MUCAPE during peak
afternoon heating cresting over 1000 J/kg.

The front and the multiple shortwaves traversing the flow and
impinging into the favorable thermodynamics will support widespread
convective development which is reflected by the simulated
reflectivity in the available guidance. A lack of bulk shear will
keep storms generally of the pulse variety with limited temporal
lifespans, but local enhancements are expected along storm
mergers/boundary collisions, which will support rainfall rates of
2-3"/hr at times as warm-rain processes dominate within warm cloud
depths above 15,000 ft. Storm motions will be slow and chaotic,
additionally enhancing the temporal duration of heavy rain, and
some short duration training or locally enhanced organization is
possible from the Southern Appalachians into the Mid-Atlantic
states due to upslope flow/isentropic ascent. This region is also
the most vulnerable to rapid runoff due to recent rainfall pushing
0-10cm soil moisture to above the 95th percentile according to NASA
SPoRT. Any slow moving or repeating storms across this area will
enhance the flash flood risk, and a SLGT risk has been added where
24-hr probabilities for 3" maximize from the SREF, and 1-hr FFG
exceedance probabilities peak above 25%.


...Southwest...
A more active monsoon day is likely 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. With rain rates potentially
exceeding 1"/hr at times leading to short-duration rainfall of
0.5-0.75 inches in less than 1 hour, the flash flood risk appears
to be increasing across southern AZ, which is also where the HREF
1-hr FFG exceedance probabilities are highest (20-40% through
00Z/Wednesday). After coordination with WFO TWC, a targeted SLGT
risk was added, embedded within a broader MRGL risk area.


...Mid-Mississippi Valley...
Weak impulses 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.


Weiss

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

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THE GULF
COAST AS WELL AS A LARGE PORTION OF THE COUNTRY FROM THE DESERT
SOUTHWEST THROUGH THE MID-ATLANTIC STATES...

...Gulf Coast...
A tropical wave (30% chance of development from NHC) will drift
slowly westward across the northern Gulf on Wednesday. There
continues to be quite a bit of uncertainty as to both the timing of
this feature as well as its latitudinal placement, making
confidence in the accompanying rainfall modest at this time range.
However, 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. The
SREF/GEFS/ECENS 24-hr probabilities are all at least 10% for 1 inch
of rainfall across the coast from the western Florida peninsula
through southeast Louisiana, but probabilities for 3 inches are
less than 5% at this time. The MRGL risk was adjusted cosmetically
for new guidance, and while it is possible a SLGT risk may be
needed eventually, more confidence in intensity and placement of
rainfall is needed before any upgrades can be made.


...Desert Southwest through the Mid-Atlantic States...
Broad and expansive ridging centered off the coast of the Carolinas
will maintain an axis westward into the Southern Plains. Around the
periphery of this feature, return flow will maintain an environment
favorable for convection with heavy rain across a broad swath of
the country. A persistent and elongated moisture plume
characterized by PWs above the 90th percentile (NAEFS) will extend
from the High Plains of CO east-northeast through New England, and
overlap with a broad swath of MUCAPE above 1000 J/kg across much of
the same area. Into this environment, a front draped from the Great
Lakes into the Southern High Plains will translate slowly
southeast, providing focus for ascent, aided by weak impulses
embedded within the flow. This will support scattered thunderstorms
with heavy rain rates above 1"/hr across many areas on Wednesday.

Despite the broad region within the MRGL risk, there may be two
focused areas of heavier rainfall, and upgrades to targeted SLGT
risks may be needed with later issuances.

Once of these will be across parts of the Desert Southwest (AZ/NM)
where a shortwave moving beneath the ridge will interact with
increasing PWs on southerly low-level flow emerging from the Rio
Grande and Mexico. The best ascent appears to be deflected north of
the greatest instability/moisture at this time, so after
coordination with WFO TWC the MRGL risk was maintained rather than
upgrade a category at this time.

Farther northeast, there is a heavy rainfall signature from
Nebraska into Wisconsin and Michigan where training of echoes along
the front may be most pronounced. The 24-hr GEFS and ECENS
probabilities peak at 30-40% for 1 inch across this region, which
suggests that higher totals will likely be realized. However, at
this time, the confidence in sufficient rainfall to cause more than
just isolated impacts is below threshold for an upgrade.


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