Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Tue May 19 2026
Day 1
Valid 12Z Tue May 19 2026 - 12Z Wed May 20 2026
...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL FOR PORTIONS OF
TEXAS AS WELL AS FOR SOUTHERN ILLINOIS AND INDIANA...
...Texas...
A line of intense showers and thunderstorms currently expanding
south across northern and western Oklahoma will continue south and
east through the early morning into northeast Texas. With peak
solar heating around midday, the line of storms will encounter an
increasingly unstable, and increasingly moist air mass situated
across much of Texas. Guidance suggests that several lines of
storms will develop in north Texas through the early afternoon.
Cold pools and lift ahead of the lines should allow individual
cells to develop out ahead of the lines, which will locally
increase the duration of heavy rains in those areas hit by first
the cells, and then the line shortly thereafter. This could cause
local flash flooding, especially should that occur over the
Metroplex or other urban areas in north Texas. By mid to late
afternoon, upper level energy may support areas of convection
across central and south Texas that will be separate from any lines
to the north. Mergers with the lines as they press south across the
state and any individual cell mergers within the clusters of storms
may also pose a localized flash flooding threat. By evening, the
storms will continue pushing into south Texas, potentially
impacting the San Antonio and Houston metros before they push into
the Gulf and deep south Texas through the predawn hours.
Overall the above-described scenario should keep flash flooding
instances mostly to localized, widely scattered occasions. However,
since the storms will cover much of the state, it's probable that
in flood prone areas, the flash flooding threat could be greater.
Unsurprisingly with so many clusters of storms expected, the CAMs
are not having a great handle on them, so the Slight was expanded
to cover the Texas Triangle. Despite the antecedent dry soil
conditions over most of the state, PWATs will likely exceed 2
inches along the Gulf Coast for when the storms reach there
tonight. Thus, any and all storms will be capable of heavy rainfall
rates that could cause flash flooding.
...Southern Illinois and Indiana...
After rounds of showers and storms caused flash flooding in
portions of Illinois and Indiana yesterday, the soils in the area
are generally saturated due to widespread multiple-inch totals from
yesterday/Monday. Much of the day today will be dry. Towards
evening however, renewed rounds of showers and thunderstorms will
develop with the approach of a strong cold front, significant
moisture and instability advection ahead of the front, and upper
level disturbances helping add to the overall environmental
forcing. Thus, overnight, expect multiple rounds of training
showers and thunderstorms tracking up the Ohio River Valley. With a
robust LLJ supporting the storms, they should have no trouble
maintaining their organization despite the lack of solar heating.
Since the soils are fully saturated, most, if not all the rainfall
will convert to runoff. Thus, the inherited Slight Risk was
expanded southwest to include much of southern Illinois with this
update.
Wegman
Day 1 threat area:
www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Tue May 19 2026
Day 2
Valid 12Z Wed May 20 2026 - 12Z Thu May 21 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE EDWARDS
PLATEAU REGION OF SOUTHWEST TEXAS...
A developing low level jet of deep Gulf moisture will advect
northwestward up the Rio Grande in south and southwest Texas in
response to height falls and an approaching shortwave moving
towards that area from Mexico. Numerous showers and thunderstorms
will develop late afternoon across the Edwards Plateau as a dry
line pushes east from the Big Bend area. The storms feeding off
PWATs of 1-1.5 inches, which is 2-2.5 sigma above normal for this
time of year in that part of the country are expected to become
plenty capable of producing heavy rain in an otherwise dry part of
the country. More susceptibility and plenty of topography in the
area will reduce the amount of rainfall needed to develop flash
flooding concerns. A general 1.5 to 2 inches of rain are expected
in the Edwards Plateau along the Rio Grande, likely falling in a
1-3 hour period as the storms track eastward down the plateau.
Thus, a higher-end Slight is in effect from Eagle Pass north and
west. As the storms move off the Rio Grande into central Texas,
generally towards San Antonio, they should weaken with time as they
separate from the dry line and the upper level shortwave rapidly
races away by the predawn hours Thursday. This should diminish the
flash flooding threat further east for this period.
Another area of more concentrated shower and thunderstorm activity
will impact the lower Mississippi Valley along the
Louisiana/Mississippi border Wednesday afternoon and evening. Due
to high FFGs and a lack of agreement in the guidance as to the
convective evolution, the area remains in a Marginal for now, but
should heavy rain producing storms move over an urban area such as
Baton Rouge, then flash flooding could occur. This area will need
to be monitored for a Slight Risk upgrade with future updates.
Wegman
Day 2 threat area:
www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
345 AM EDT Tue May 19 2026
Day 3
Valid 12Z Thu May 21 2026 - 12Z Fri May 22 2026
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHERN PLAINS THROUGH THE OZARKS...
Numerous areas of showers and thunderstorms will impact the Slight
Risk area on Thursday through Thursday night. An ensemble of
guidance that covers the Day 3/Thursday period generally agree that
Thursday morning, the strongest storms will be across coastal Texas
through central Texas. These storms will track northeastward and
grow upscale as the impact areas from northern Louisiana, northeast
Texas, and Oklahoma. Thursday evening, a new round of storms
impacts south Texas as the rest of the storms push northeast into
Arkansas, northeast Oklahoma, and into Kansas, which then continue
northeast up the mid-Mississippi River Valley and a separate area
of storms impacts the Kansas City area. Despite this broad
evolution, there is very little confidence on how the storms will
behave/merge or track. Thus, the Slight covers likely more
saturated soils after rainfall expected in many of these areas on
Days 1 and 2. There will be no shortage of moisture and instability
across the Slight Risk area, especially the southern half, so it's
likely any limiting factor will be a generally progressive forward
speed to the storms, and cold pool interactions.
It's likely that with future updates, CAMs guidance should help
narrow down where the greatest threats for storms will be on
Thursday. This should allow the Slight to shrink a bit with better
confidence, though much of the region should see at least some
rainfall.
Wegman
Day 3 threat area:
www.wpc.ncep.noaa.gov/qpf/99epoints.txt
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
135 PM EDT Mon May 18 2026
Heavy rainfall is expected to make weather headlines going into the
latter half of the work week from central Texas to the Tennessee
River Valley. The highest QPF should be across east-central Texas
where multiple mesoscale convective systems will develop and affect
the same areas on multiple days. For the Day 4/Thursday ERO, a
Slight Risk will remain valid from near San Antonio to northeast
Texas where 1-3 inches of rainfall is likely with storms producing
high rainfall rates. This lingers going into Friday as well with a
broad Marginal Risk for the Day 5/Friday ERO, extending from the
Rio Grande to Ohio, with possible upgrades to Slight Risk in future
outlooks as timing and placement become clearer.
Elsewhere across the country, lighter precipitation is expected
farther to the east across the Carolinas into Virginia with
overrunning flow north of the frontal boundary. There should also
be corridors of moderate rainfall across portions of the
central/northern Plains to the Midwest states through Friday. The
potential exists for this region to see an upward trend in rainfall
totals in future forecasts. Mountain snow across the northern
Rockies on Thursday should abate in intensity before a drier
weather pattern ensues by Friday.
In terms of temperatures, a welcomed relief from the heat wave
across the eastern U.S. is expected to arrive on Thursday as a
strong cold front reaches the Mid-Atlantic, and then drops south
across North Carolina going into Friday before stalling. A cold
air damming type event will likely become established east of the
Appalachians with overcast skies and periods of mainly light rain
at times, and warm and humid conditions continuing south of the
boundary. Elsewhere, relatively cool conditions across the
central/northern Plains are expected to gradually warm through the
forecast period.
Oudit/Hamrick
Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
135 PM EDT Mon May 18 2026
Heavy rainfall is expected to make weather headlines going into the
latter half of the work week from central Texas to the Tennessee
River Valley. The highest QPF should be across east-central Texas
where multiple mesoscale convective systems will develop and affect
the same areas on multiple days. For the Day 4/Thursday ERO, a
Slight Risk will remain valid from near San Antonio to northeast
Texas where 1-3 inches of rainfall is likely with storms producing
high rainfall rates. This lingers going into Friday as well with a
broad Marginal Risk for the Day 5/Friday ERO, extending from the
Rio Grande to Ohio, with possible upgrades to Slight Risk in future
outlooks as timing and placement become clearer.
Elsewhere across the country, lighter precipitation is expected
farther to the east across the Carolinas into Virginia with
overrunning flow north of the frontal boundary. There should also
be corridors of moderate rainfall across portions of the
central/northern Plains to the Midwest states through Friday. The
potential exists for this region to see an upward trend in rainfall
totals in future forecasts. Mountain snow across the northern
Rockies on Thursday should abate in intensity before a drier
weather pattern ensues by Friday.
In terms of temperatures, a welcomed relief from the heat wave
across the eastern U.S. is expected to arrive on Thursday as a
strong cold front reaches the Mid-Atlantic, and then drops south
across North Carolina going into Friday before stalling. A cold
air damming type event will likely become established east of the
Appalachians with overcast skies and periods of mainly light rain
at times, and warm and humid conditions continuing south of the
boundary. Elsewhere, relatively cool conditions across the
central/northern Plains are expected to gradually warm through the
forecast period.
Oudit/Hamrick
