Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Sun Jul 13 2025
Day 1
Valid 12Z Sun Jul 13 2025 - 12Z Mon Jul 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF NEW
MEXICO, THE SOUTHERN PLAINS, AND THE MID- ATLANTIC...

...Southern Plains...
Sunday morning begins and it is likely that convection, some of
which will be strong with heavy rainfall rates, will be ongoing
across parts of Texas. This will be in response to a potent and
convectively enhanced shortwave/vorticity maxima that will be
pivoting across the state. This shortwave will be embedded within a
weakness in the mid-level pattern between ridges both to the west
and east, basically becoming trapped within a weak col across
Texas. As the day progresses, this vorticity maxima should become
strung out and aligned more SW to NE as the mid-level trough axis
tries to swing eastward. While this will likely push some PVA
northeast into Oklahoma and the Ozarks, a ribbon of vorticity may
remain trapped back across Texas, leading to a corridor of enhanced
ascent, aided by at least modest upper diffluence during the
afternoon as a weak jet streak pivots across the middle of the
country.

At the surface, this trough axis will attempt to push a surface cold
front beneath it steadily to the east. However, it is likely this
front will oscillate a bit north and south in response to varying
and increasing low-level flow. Low-level return flow out of the Gulf
will gradually veer from SE to SW, reaching 15-25 kts, and pushing
PWs to as high as 2 inches. This anomalous moisture (PW anomalies
+1.5 to +2 sigma according to the GFS) will merge into the wavering
front, causing its oscillatory behavior, while additionally
transporting more impressive MUCAPE northward through the day and
night (reaching above 2000 J/kg at times).

With forcing for ascent remaining robust through the period, this
will result in waves of convection generally along the front, but
the CAMs are generally scattered as to where the heaviest rainfall
will occur due to differences in frontal placement and the weak
mid- level impulses. However, the impressive thermodynamics in
place will support heavy rain rates that will likely (>50% chance)
exceed 1"/hr, with short term rates of 3-4"/hr possible at times.
Utilizing both the HREF and REFS ensembles, the greatest chance for
more than 3" of rain appears to be focused from the Hill Country
of Texas northeast into the St. Louis, MO metro area, and the
slight risks have been adjusted from inherited in these areas.

There continues to be a signal in the guidance leading to a
somewhat higher potential for flash flooding across portions of
the Texas Hill Country northeast towards the Dallas metroplex. HREF
and REFS probabilities for 5"/24hrs peak around 30-40% in this
region, and this will be on top of heavy rain that is occurring
overnight (before 12Z Sunday). Briefly considered a MDT risk but
uncertainty in coverage and placement prevents that at this time.
However, there could be some locally significant impacts across
this area if slow moving convection can move effectively across the
more vulnerable areas, and it is possible a D1 upgrade to a MDT
risk may be needed depending on how convection evolves through the
early morning hours.


...New Mexico...
Farther to the west, the westward periphery of the
PW plume emerging from the Gulf will spread into New Mexico,
spreading PWs above 1" (+1 sigma) into the High Plains and into the
terrain of the central part of the state. This PW will overlap with
a ribbon of MUCAPE around 2000 J/kg to support scattered to numerous
thunderstorms developing during peak heating over the higher
terrain. These storms will initially move slowly on 0-6km mean winds
of just 5 kts,  but the presence of 20-25 kts of bulk shear will
help drive modest organization as storms come off the terrain and
drift southward on Corfidi vectors around 10 kts. With rain rates
above 1"/hr likely, this could result in instances of flash
flooding, especially over sensitive terrain features, urban areas,
or burn scars.


...Mid-Atlantic into the Northeast...
Mid-level ridge gradually pulsing northward from the Gulf Coast
will interact with a broad and slow moving trough advecting across
the Great Lakes to produce pinched SWly flow across much of the
eastern CONUS. This will manifest as impressive thermodynamics
being drawn northward from the Mid-Atlantic into interior portions
of the Northeast. These thermodynamics will be characterized by PWs
of 1.75 to 2.0 inches (90th - 99th percentile according to NAEFS)
and collocated MUCAPE of 1000-2000 J/kg to produce an environment
favorable for heavy rain. Into this environment, a cold front,
pushed slowly eastward by the mid-level trough to the west, will
combine with slow height falls to drive pronounced ascent, creating
scattered to numerous thunderstorms from the eastern Ohio Valley
into Northern New England.

These storms will contain heavy rain rates that have a 30-50% chance
of exceeding 1"/hr with brief 2+"/hr rates also possible. Although
bulk shear is progged to be minimal such that convection will
generally remain of the pulse variety, brief training as 0-6 km mean
winds aligns to the front will allow for some longer duration of
this heavy rainfall in a few areas, leading to HREF and REFS 24-hr
probabilities that peak above 70% for 3". While it is difficult even
at this time range to identify the areas most at-risk to flash
flooding due to uncertainty in exact convective placement, 0-10cm
soil moisture is above the 90th percentile according to NASA SPoRT
from central VA through Upstate NY, which is also collocated with
the locally higher ensemble probabilities. This suggests that the
inherited SLGT risk is warranted, and only adjusted cosmetically
for new guidance, although there is a signal in the guidance for
some locally heavier rainfall across the Finger Lakes region of NY
due to repeating/backbuilding cells which could result in some
locally more substantial impacts.


...Florida...
Slow moving 500mb trough east of Florida will strengthen gradually
as it drifts W/SW today. The accompanying vorticity maxima will
provide some locally enhanced forcing to the eastern side of FL,
while the entire peninsula remains sandwiched between this and a
ridge to the west, producing northerly flow across the area. As the
vort swings westward, some locally enhanced diffluence will
develop aloft as well, and as this occurs in the presence of PWs
above 2 inches collocated with MUCAPE of 2000-3000 J/kg, widespread
convection with heavy rain will result. CAMs suggest storms will
fire on the E/NE side of the peninsula and then drift SW, with some
locally enhanced organization possible into clusters thanks to
20-30 kts of bulk shear. With rain rates progged by the HREF to
have a 30-50% chance of exceeding 2"/hr, this could result in total
rainfall of 3-4", locally higher, as suggested by 24- HREF/REFS
probabilities and PMM. Where this rain occurs over more urban
areas, local flash flooding could result.

Weiss

Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt