Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
850 PM EDT Mon Jun 30 2025
Day 1
Valid 01Z Tue Jul 01 2025 - 12Z Tue Jul 01 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL/SOUTHERN PLAINS AND THE NEW MEXICO AND WESTERN
TEXAS...

...01Z Update...
Biggest adjustment at 01Z was to shift the Slight Risk area
further south across the Southern Plains. Recent runs of the HRRR
and the 18Z HREF generally agree that convection will continue
along a southwest-northeast axis from the Permian Basin in western
Texas to the Ouachita Mountains in southeastern Oklahoma and
western Arkansas. Neighborhood probabilities from the 18Z HREF
indicate that localized amounts of 2-3 inches are likely along this
axis during the remainder of the evening and overnight. Further to
the north, the Marginal Risk was removed from the Central Plains.

Elsewhere, made mostly minor adjustments based on radar trends and
recent hi-res guidance.

Pereira

...16Z Update...
Main changes to the overnight forecast include the introduction of
a Slight Risk over portions of the eastern Ohio Valley, Central
Appalachians, and Upper Mid-Atlantic. 12Z sounding data across the
region highlights a very moist and unstable airmass (PWATS at or
above the daily max for PIT and IAD) in the vicinity of a slow
moving warm front. Showers and thunderstorms are forecast to expand
in coverage today with continued heating, which will be capable of
very efficient subhourly rainfall rates which could breach flash
flood guidance in spite of generally progressive storm motions.

Otherwise, the Slight Risk was trimmed in the Central/Southern
Plains in the wake of an overnight MCS which has sent a strong cold
pool southward. The main area of concern will focus along this
boundary later today, over portions of Central Oklahoma and Eastern
Arkansas into the Red River.

Asherman


Previous Discussion...
A Slight Risk was maintained across New Mexico and into western
Texas given the presence of a front dropping southward into the
Southern Plains and Southern Rockies...with moist easterly flow
into the complex terrain of the southern Rockies and provide
greater coverage of thunderstorms by the afternoon due to diurnal
heating, increasing lapse rates and instability. Precipitable water
values of 1 inch to 1.5 inches are forecast and will near the 90th
climatological percentile and support rainfall rates of 1-2 inches
per hour. Additionally, widespread coverage of thunderstorm
activity over parts of the Central and High Plains overnight was
accounted for by the introduction of a Slight Risk mainly from
Kansas into Oklahoma this morning before another round of
convection forms over the Southern High Plains along the associated
frontal boundary within an area of very weak mid- level flow later
today. Storms will likely be slow- moving across western Texas and
eastern New Mexico before becoming outflow dependent unless a
large enough cold pool can organize a larger thunderstorm complex.

Elsewhere...convection is expected to develop within a region of
decent CAPE and precipitable water values in excess of 2 standard
deviations above climatology. Except for some mid-level westerly
flow around the Great Lakes to provide some shear there...the flow
farther south should be fairly meager (but offset by steeper low-
level lapse rates). This sets up the potential for some local
rainfall rates in excess of 1 inch per hour that results in
excessive rainfall from the southern Plains east/northeastward into
the Ohio Valley and parts of the Mid- Atlantic region today and
tonight.

Some details are coming into focus, which includes the
likelihood of overnight convection lingering into the early-morning
hours across parts of the central Plains and Mid- Mississippi
Valley. Meanwhile, an upper trough lingering across the Southeast
will continue to foster an area of convergence on the
southern/southwestern periphery which could lead to locally heavy
rainfall along the eastern Gulf Coast and much of the northern
Florida Gulf Coast. There is some potential for extremely heavy
rainfall within this tropical airmass and precipitable water values
between 2.25 inches and 2.5 inches, but the signal from the
numerical guidance is that most rainfall to occur over the Gulf
waters at this time.

Farther north into the Ohio Valley, Appalachians and Northeast, a
weakening surface boundary will help focus some of the threat for
heavier rainfall with its placement remaining quite uncertain. The
synoptic setup with a stationary/warm front stretching across
southern PA and an approaching cold front from the west should help
foster greater coverage in showers/storms within a moist
environment, but storm motions within a mean column wind of 30kts
could limit the flooding threat even though this area remains
sensitive to intense rainfall.

Snell/Bann

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