Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
230 PM EDT Wed May 28 2025
Day 1
Valid 16Z Wed May 28 2025 - 12Z Thu May 29 2025
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
CENTRAL AND COASTAL TEXAS AS WELL AS CENTRAL AND SOUTHERN KANSAS...
...16Z Update...
...Kansas...
A new Slight Risk upgrade was introduced with this update for
portions of Kansas and far northwestern Oklahoma. This evening, a
southeastward moving vigorous shortwave trough will force
thunderstorms to form, likely in a line based on CAMs guidance, but
could evolve as multiple line segments. Meanwhile, an LLJ, though
not a particularly robust one, will stream Gulf moisture into the
region from the south. This LLJ will support backbuilding and
stronger storms capable of heavy rainfall. While individual storms
should be quite progressive as they track southeastward, any
backbuilding along the southern end of the line as well as
potential for new segments to form could increase the flash
flooding instances to more widely scattered frequency. Further,
NASA Sport soil moisture maps show that soils in the Slight Risk
area are at or above normal for moisture, which will convert more
rainfall to runoff.
...Texas...
The Slight Risk area inherited from the previous forecast remains
in place from the upper Texas Gulf Coast and Houston northeastward
into portions of central Texas. While the complex of storms further
south as moved into the Gulf, a remnant boundary on the eastern
edge of the return flow/LLJ off the Gulf will support renewed
widely scattered thunderstorm activity across this region this
afternoon into this evening. Soils here, like in Kansas, are also
at or above normal for moisture levels due to recent rainfall
activity. Thus, expect the storms, especially where they train, to
pose a widely scattered flash flooding risk.
Elsewhere, the Slight Risk was removed from the lower and much of
the middle Texas Gulf Coast as the complex of storms that caused
flash flooding in these areas earlier this morning has moved east
into the Gulf and no longer pose a flash flooding risk. Any further
convective development this afternoon should be isolated enough to
support only a Marginal Risk in this area.
...Mid-Atlantic...
The inherited Marginal Risk area was trimmed out of most of
Virginia with the exception of the Hampton Roads area. Instability
north of Hampton Roads is at or near zero, and therefore does not
support strong convective development. However, further south where
the Marginal remains for the Outer Banks and eastern North
Carolina, afternoon instability is expected to increase enough to
support convective development along a stalled stationary frontal
boundary draped over eastern North Carolina.
...New Mexico and West Texas...
The Marginal Risk area was removed with this update for this
region. CAMs guidance is showing only a mediocre signal in this
area, suggesting most areas see only convective showers at most. A
lack of moisture should preclude flash flooding. A stray instance
or two can't be ruled out, but was determined to be sub-Marginal.
Wegman
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
230 PM EDT Wed May 28 2025
Day 2
Valid 12Z Thu May 29 2025 - 12Z Fri May 30 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHEAST...
...19Z Update...
The inherited Slight Risk area was removed with this update. The
latest CAMs guidance for the period shows that the shortwave
driving expected convection through the period will weaken, and
struggle to organize the convection ahead of the surface cold front
in such a way as to promote a greater than isolated flash flooding
threat. FFGs across much of the Southeast, while slightly depressed
from earlier rainfall, have largely recovered and while soils are a
bit wetter than normal, the lack of organization should hold any
flash flooding to isolated instances. Thus, the combination of high
FFGs and no consistent signal of heavy rainfall should preclude
more widespread Slight Risk impacts. For the Gulf Coast, the urban
centers in the area will have the greatest threat for flash
flooding, but that assumes the storms linger over those urban areas
long enough to cause flash flooding.
Conversely, the surrounding Marginal Risk was expanded to include
more of the harder hit areas of Texas and the portions of the Mid-
Atlantic that got a good soaking rain this morning. The
disorganized nature of the afternoon convection could cause
isolated flash flooding in these areas should the storms form over
particularly sensitive areas.
A secondary area of convection that begins its life in Kansas
tonight will move across Missouri and eventually move into Kentucky
and Indiana Thursday night. This more organized convection will
locally increase the flash flooding threat compared to many other
parts of the Marginal Risk area. However, these storms will be
quite progressive, so defining where a potential Slight Risk with
these storms is also not possible at this time, but the area will
be monitored. Instability on the northern side of the complex will
likely further hamper the storms' ability to produce rainfall
amounts needed to cause flash flooding.
Throughout the Marginal Risk area, it's probable, if not likely
that locally storms will organize enough to cause Slight Risk
impacts, but where that will occur is highly uncertain at this
time.
Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
230 PM EDT Wed May 28 2025
Day 3
Valid 12Z Fri May 30 2025 - 12Z Sat May 31 2025
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE MID ATLANTIC, OHIO VALLEY, AND SOUTHEAST...
...19Z Update...
No major changes were made to the inherited Marginal Risk area
along the Mid-Atlantic and Southeast. The Marginal was expanded a
bit due to convective uncertainty across the Southeast, while in
the Mid-Atlantic the complex of storms from the Ohio Valley will
continue across the area through the period. Once again, the storms
should be moving fast enough to preclude anything other than
isolated flash flooding, with the urban centers at a bit higher
risk for flooding.
Wegman
...Previous Discussion...
A potent mid-latitude trough will pivot through the Ohio Valley on
Friday morning with a broad axis of diffluence downstream of the
mean trough leading to a large scale forcing regime that will
enhance regional precip field across the Mid Atlantic. At the
surface, low pressure will navigate into the Mid Atlantic with a
trailing cold front migrating eastward through much of the Eastern
CONUS, interacting with a wedge of low to mid-level instability
situated over the Central/Southern Appalachians and points east.
Greatest thermodynamic alignment will likely be closer to the
coastal plain, but elevated MUCAPE signatures can be found within
the Mid Atlantic Piedmont and under the primary trough. The
tandem of increased sfc-500mb forcing from the trough/front combo
will lead to a scattered to widespread convective pattern that will
induce locally heavy rainfall and potential for flash flooding.
Timing of the ascent pattern and frontal progression will be key in
determining the logistics of where the main axis of convection will
occur. As of now, the best chances for convectively driven heavy
rain are within the Central and Southern Appalachians, Southern VA
through the NC Piedmont, and the Eastern Carolinas up to the VA
Tidewater. These are the areas conducive for flash flooding at this
time with localized amounts reaching 2-3" in the places hit the
hardest. 1-2" is more likely out in the terrain of the Apps, but
that is a signal sufficient for flashier responses due to the
complexity of the topography. Despite the questions of timing, the
threat remains leading to a broad MRGL risk over much of the Mid
Atlantic with a southern inflection down towards FL as the trailing
front will move through the region and interact with a deeper
moisture layer and plentiful instability to induce some heavier
convective cores capable of flash flooding in more urbanized zones.
Kleebauer
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Wed May 28 2025
The flow pattern across the Continental U.S. will transition from
progressive to more amplified this weekend into early next week. A
series of leading shortwaves and secondary systems will dig into an
amplified upper trough over a cooled and unsettled East. This
occurs as a trailing, rainfall-focusing front works offshore into
the western Atlantic, Florida, and the Gulf where some heavy
downpours may linger into next week with deepened moisture to
monitor. The bulk of the energy associated with the upper trough
lifts out early next week. Prior to its exit, a trailing,
deepening, surface low will lift from New England into eastern
Canada this weekend. While instability is generally lacking, the
QPF footprint is certainly enough to maintain and even expand the
marginal risk ERO across northern New England for Day 4/Saturday.
Meanwhile, upper ridging will prevail over much of the West into
the weekend, supporting anomalous heat and temperatures rising
upwards of 10 to 20 degrees above normal. This potentially
hazardous heat will focus across the California Central Valley into
the Desert Southwest. Parts of the West that will be spared from
the heat include the Pacific Northwest, where upper trough energy
with modest rain will keep temperatures cooler. Despite some timing
differences, guidance continues to trend in favor of significant
upper trough amplification into the West early next week, along
with the ejection of the lead southern stream closed system from
offshore Baja. This transition will then act to provide relief from
the heat over the West with the building of a much more unsettled
and increasingly wet flow pattern farther inland and downstream to
the Intermountain West and especially the northern Rockies through
midweek. Despite the calendar flipping into June, this pattern will
support at least a minor threat for mountain snow in the highest
elevations.
Miller/Schichtel
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
235 PM EDT Wed May 28 2025
The flow pattern across the Continental U.S. will transition from
progressive to more amplified this weekend into early next week. A
series of leading shortwaves and secondary systems will dig into an
amplified upper trough over a cooled and unsettled East. This
occurs as a trailing, rainfall-focusing front works offshore into
the western Atlantic, Florida, and the Gulf where some heavy
downpours may linger into next week with deepened moisture to
monitor. The bulk of the energy associated with the upper trough
lifts out early next week. Prior to its exit, a trailing,
deepening, surface low will lift from New England into eastern
Canada this weekend. While instability is generally lacking, the
QPF footprint is certainly enough to maintain and even expand the
marginal risk ERO across northern New England for Day 4/Saturday.
Meanwhile, upper ridging will prevail over much of the West into
the weekend, supporting anomalous heat and temperatures rising
upwards of 10 to 20 degrees above normal. This potentially
hazardous heat will focus across the California Central Valley into
the Desert Southwest. Parts of the West that will be spared from
the heat include the Pacific Northwest, where upper trough energy
with modest rain will keep temperatures cooler. Despite some timing
differences, guidance continues to trend in favor of significant
upper trough amplification into the West early next week, along
with the ejection of the lead southern stream closed system from
offshore Baja. This transition will then act to provide relief from
the heat over the West with the building of a much more unsettled
and increasingly wet flow pattern farther inland and downstream to
the Intermountain West and especially the northern Rockies through
midweek. Despite the calendar flipping into June, this pattern will
support at least a minor threat for mountain snow in the highest
elevations.
Miller/Schichtel
