913
FOUS30 KWBC 150038
QPFERD

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

Day 1
Valid 01Z Tue Jul 15 2025 - 12Z Tue Jul 15 2025

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

...Mid-Atlantic Through Northeast...

...0100 UTC Update...
Changes made to the Moderate and Slight Risk ERO areas were to
account for the latest observational (radar/satellite) trends --
i.e. trimming a considerable portion on the western edges, while
maintaining the outlooks along and downstream the QLCS. Current
0-6km bulk shear values remain reasonably sufficient across
northern portions of the Mid Atlantic Region this evening as the
upper level shortwave trough and surface boundary slowly migrate
over the area. Deep-layer moisture along the Eastern Seaboard
remains quite favorable for heavy rainfall (PWs 2-2.25"), however
given the weak kinematic environment, weakening deep-layer
instability (negative dCAPE/dT) following sunset will result in
somewhat less-intensive rainfall rates as the evening wears on.

Hurley

...Florida...

...0100 UTC Update...
Convection continues to diminish in intensity this evening
following the loss of peak heating, though given the mid level
vorticity presence off the east coast of FL, the guidance continues
to show renewed convection overnight along the west coast of FL and
especially westward towards the FL Big Bend. Based on the 18Z HREF
suite (including 1/3/6/12 hr QPF exceedance probabilities), expect
any flash flood threat during the remainder of the evening and
overnight will be localized/isolated.

Hurley

...Desert Southwest through the Mid-Mississippi Valley...

...0100 UTC Update...
No new updates to the EROs in these areas. 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.

Weiss

...Northern Plains...

...0100 UTC Update...
No new updates to the EROs in these areas. 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