964
FOUS30 KWBC 132350
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
750 PM EDT Sun Jul 13 2025

Day 1
Valid 01Z Mon Jul 14 2025 - 12Z Mon Jul 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE TEXAS, THE OHIO VALLEY, & THE MID-ATLANTIC STATES...

...South-Central Texas...
A well-defined MCV, which has occasionally sported an eye feature,
is moving by Hamilton TX at the present time. Also present is an
upper level low is far southeast NM. Precipitable water values
remain north of 1.5", MU CAPE remains 2000-4000 J/kg across the
southern third of TX, and effective bulk shear is near 25 kts, but
declining as the MCV moves away. The expectation is that a more
limited round of convection is possible overnight as a small uptick
in the low-level inflow is forecast, which could keep the effective
bulk shear close enough, and possibly exceeding, 25 kts so
convective organization remains possible.

The REFS and HREF have backed off on heavy rain expectations
overnight between their last couple cycles, but given the
ingredients, a more splotchy and at least semi-organized
convective event is possible, perhaps on a smaller scale,
overnight. Hourly rain amounts to 2.5" and local amounts to 5"
remain possible, which is problematic given the compromised soils
across portions of Central and South-Central TX. The guidance and
current convective trends no longer supports a Moderate Risk, so it
was dropped on this update. However, this environment appears to
fit a higher end Slight Risk as the mesoscale guidance sometimes
has issues with this environments where convective organization
could occur but remains iffy. Higher amounts could be more splotchy
overnight than last night/earlier today, depending on convective
organization. While there is a bit of uncertainty regarding
expected evolution, it remains prudent to keep a higher end Slight
Risk going as a precaution.


...New Mexico...
Convective organization is expected to continue for several more
hours. Pared back the Slight Risk from continuity based on radar
reflectivity trends and the latest HREF/REFS guidance.


...Ohio River Valley...
Shifted the Slight Risk forward, up the Ohio River Valley, per
radar reflectivity trends. See Mesoscale Precipitation Discussion
#675 for more details on the short term threat in this area, which
is valid through 0410z. This system is expected to have the highest
chance of sputtering convection through the overnight hours, so
maintained a fairly large Marginal Risk around the Slight to
account for this.


...Mid-Atlantic into the Northeast...
Kept the Slight Risk going per trends seen in radar reflectivity
and signals seen in the 12z AIFS, 18z HREF, and 12z REFS guidance,
with activity expected to survive for at least a few hours after
sunset. There is some indication that there could be an early
morning uptick to activity near the urban centers as well.
Available moisture and instability support hourly amounts to 2.5"
where cells backbuild, merge, or train.


...Florida...
A tropical disturbance east of the state has been drifting
southward today. Moisture is high, with precipitable water values
above 2", with effective bulk shear roughly 20 kts. HREF and REFS
guidance suggest that currently activity could survive until 04-06z
before fading.

Roth


Day 2
Valid 12Z Mon Jul 14 2025 - 12Z Tue Jul 15 2025

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
MID-ATLANTIC AND NORTHEAST AS WELL AS THE FLORIDA PENINSULA...

...Mid-Atlantic Through Northeast...
There is an overnight threat of thunderstorms tracking across
southern portions of the Midwest that could still be going over
eastern KY/southern OH early Monday. The Marginal Risk was expanded
east through this area to account for this threat.
Then, diurnally driven thunderstorms develop ahead of a slow
moving cold front over the northern/central Appalachians and track
east to the I-95 Northeast urban corridor through the evening. The
front is slow to advance because the parent upper low remains
stationary into midweek. Broad return flow ahead of the front (SW
at 10-15 kts) draws a ribbon of PWs around 2 inches (above the 90th
percentile according to NAEFS), sufficient instability (MUCAPE
over 1000 J/kg into New England), deep warm cloud depths (above
15,000 ft) and light mean layer flow to support efficient and heavy
rain. Rain rates exceeding 2"/hr have a 40-60% probability from
the 12Z HREF, especially in the Mid-Atlantic.

Guidance today increased the likelihood of heavy rain up through
New England, so the Slight Risk was expanded through New Hampshire
in coordination with WFOs GYX, ALY, BGM, and PHI.

...Florida...
A westward-advancing and deepening mid-level wave approaches the FL
peninsula on Monday, providing widespread increasing ascent. In
addition to the height falls/PVA accompanying this trough, modest
upper diffluence will develop as northerly flow continues,
enhancing deep layer lift. This impressive and amplifying ascent
will impinge into intensifying thermodynamics with PWs surging
above 2.25 inches, or above the 90th percentile according to NAEFS.
There continues to be some evolutionary discrepancies among the
various models, but in general the setup will be favorable for
widespread thunderstorms with heavy rainfall, especially during
peak heating when MUCAPE climbs above 2000 J/kg. The heaviest
rainfall now looks to develop across central and southern portions
of the peninsula. With rainfall rates likely eclipsing 2"/hr, some
bulk shear 20-30 kts to help organized convection into clusters,
and chaotic/weak storm motions, total rainfall could exceed 3" in
places. The inherited SLGT risk was focused just a little.

...Desert Southwest through Texas, the Ozarks and Mid-Mississippi
Valley...
MCVs and impulses will track along the existing stationary front
over the Mid-Miss Valley down to Texas. A very favorable
environment remains to support heavy rainfall with PW nearly 2
inches into the Ozarks and above 1" as far as southern Arizona
thanks to persistent moist advection out of the Gulf leading to PW
anomalies reaching above the 90th percentile locally from West TX
into NM and near the Ozarks. These are the locations that may have
slightly higher potential for excessive rainfall on Monday, with
slow moving storms over West Texas/New Mexico (0-6km mean winds 5
kts or less) and organized convection on 20-30 kts of bulk shear
from OK into MO/AR. As of now the Marginal was expanded more over
southern Texas given the threat for further overnight activity
from central TX.

...Northern Plains...
Marginal Risk along Canadian border from MT to MN retained. Potent
but positively tilted shortwave will dig out of British Columbia
and emerge into a belt of pinched westerlies aligned to the
Canada/United States border. This will help elongate a cold front
as it drops southward into the Northern Rockies and Northern High
Plains, producing locally enhanced ascent across the area. A piece
of this vorticity lobe will swing rapidly eastward and interact
with the low-level baroclinic zone, which will intensify due to
warm advection on an 850mb LLJ surging to 30 kts Monday evening up
the Plains, drawing thermodynamics characterized by PWs of 1-1.25
inches and MUCAPE of 1000 J/kg northward. This will support
scattered thunderstorms Monday night, and although cells should
remain progressive on 0-6km mean winds of 20-25 kts, aligned
Corfidi vectors to the mean wind and the front suggests training
which could produce 1-2" of rainfall and local FFG exceedance.

Jackson/Weiss

Day 3
Valid 12Z Tue Jul 15 2025 - 12Z Wed Jul 16 2025

..THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE
SOUTHERN FLORIDA PENINSULA AS WELL AS THE UPPER MIDWEST TO CENTRAL
GREAT PLAINS...

...Florida...
The mid-level wave reaches the Florida Peninsula on Tuesday
providing ascent with PWs of 2-2.25 inches collocated with tall
skinny cape with MUCAPE above 1000 J/kg. There could also be a
surface low (please see NHC guidance) which would additionally
enhance ascent. As winds behind the wave turn back to the S/SE
across the peninsula, it will likely result in weakly convergent
boundaries upon which thunderstorms will blossom and track NW with
2+"/hr rates. Where these cells exhibit even short- term training,
especially atop urban areas or across soils moistened from rainfall
between now and then, instances of flash flooding could result
from 2-3" of rain with locally higher amounts. The Slight Risk for
the southern half of the Peninsula remains.

...Northern Rockies through the Upper Midwest...
A defined shortwave trough shifts east across MT Tuesday. This
will push a cold front, initially aligned generally west-to- east,
to become more SW to NE as it approaches the Upper Midwest the
latter half of the period. The accompanying ascent (driven by low-
level convergence, PVA, and jet- level diffluence) will produce
widespread convection on Tuesday areas with PWs above the 90th
percentile according to NAEFS. This will support rainfall rates of
1-2"/hr, with training of echoes likely due to boundary parallel
mean flow.

The greatest potential for heavy rainfall continues to be focused
from the eastern Dakotas through northern MN with additional maxes
south/southwest across eastern SD to central Nebraska where
backbuilding/regenerating cells appear likely. The Slight Risk was
expanded over central MN to align with 12Z consensus (that includes
the 12Z RRFS and Canadian Regional).

...Northeast, Mid-Atlantic and Southeast...
A generally moist and unstable environment will remain across much
of the eastern CONUS Tuesday morning as broad ridging expands from
the Atlantic. A lingering surface front over southern New England
retains an excessive rainfall threat from overnight convection. So
a Marginal risk was raised up through Boston.
850mb flow around the offshore ridge will become increasingly
S/SE, surging a ribbon of PWs above 2" from the Gulf Coast through
the Mid-Atlantic. Although forcing for ascent will be modest,
widespread showers and thunderstorms are expected, many of which
will have 1-2"/hr rain rates despite their pulse nature. Therefore,
the Marginal Risk was maintained for the Mid-Atlantic down to
Georgia.

...Mid-Mississippi Valley...
Continued risk for MCV coming out from central TX activity looks to
push through MO/IL on Tuesday. Elevated moisture and pivoting
forcing from associated impulses raise a threat for excessive rain.
A Marginal Risk is raised for much of IL, eastern MO into central
IN.

...Southwest...
Elevated moisture with light steering flow should allow diurnal
convection to be locally excessive over the Big Bend of Texas and
southeast Arizona. Targeted Marginal Risks were raised for both
areas.


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