FOUS30 KWBC 190023
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
823 PM EDT Mon May 18 2026

Day 1
Valid 01Z Tue May 19 2026 - 12Z Tue May 19 2026

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
MISSOURI, IOWA, NEBRASKA, AND KANSAS...

01Z Update...

The overall setup for a significant round of rainfall is still very
much in-tact with the current radar/sat composite indicating a
large complex of thunderstorms growing upscale across the Central
Plains with a modest forward propagation to the east-northeast
under the guide of mean southwesterly flow aloft. A strong mid-
level shortwave trough is analyzed over the KS/NE border with a
broad axis of diffluent flow oriented over the Southern Plains to
mid-Mississippi Valley providing sufficient large scale forcing and
favorable upper dynamics to help ignite the current convective
posture. Quasi-stationary front is analyzed over central KS up
through far southeastern NE into IA with two lows situated within
the front; one located over northeast KS and the other still
positioned back into the High Plains of northeast NM. The coupling
of large scale ascent and a broad axis of prevalent deep layer
moisture imposed along and ahead of the front will aid in the
convective regime maintaining itself overnight with rainfall rates
embedded in the expected QLCS to reach between 1-3"/hr at peak
intensities. Budding 40-50kt LLJ will become oriented a bit more
parallel to the front as we move through the evening allowing for
low-level flow to become favorable for back-building and/or
training convective pulses across portions of KS into western MO.
This signal is prevalent in pretty much all the CAMs leading to a
strong neighborhood probability for >3" (40-70%) located across a
corridor extending from Wichita Falls, KS and points northeast
into northwestern MO, including the Kansas City Metro. The
Missouri River basin and surrounds continues to be the focal point
for the heaviest precip opportunities which would be the second or
even third day of impact for some of these locales. Local FFG's
have fallen considerably as a result leading to a heightened risk
of flash flooding which allowed for a general maintenance of the
inherited MDT risk.

Further southeast, remnant outflow boundary positioned just north
of the MO Ozarks extending into the western Ohio River basin near
IL/KY/IN continues to be a focal point for convection this evening
with training causing a myriad of hydrologic issues for places
along the boundary. Additional 1-2" will be possible for the
initial few hours of the 01z update before finally dissipating
overnight, however the eastern expanse of the convective
development and evolution tonight will still extend eastward into
the Mississippi River area of eastern MO into IL. This will leave
the door open for additional flash flood concerns given the greater
sensitivity posed by the recent rainfall. SLGT risk still extends
into these above areas as a result.

Kleebauer


Day 2
Valid 12Z Tue May 19 2026 - 12Z Wed May 20 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
CENTRAL TEXAS HILL COUNTRY AND OHIO RIVER VALLEY...

The main changes to the overnight forecast include a broadening of
the Marginal Risk, and introduction of embedded Slight Risk areas
over the Texas Hill Country and Ohio Valley. A relatively stagnant
synoptic pattern will continue through Day 2 as a positively
tilted mean trough slowly evolves over the Western U.S. This
configuration should maintain modest southwest flow over the
Central/Eastern U.S. to support a corridor of heavy rainfall ahead
of a northeast to southwest oriented cold front.

Toward the beginning of Day 2, thunderstorms are expected to
develop along the cold front as it enters the Southern Plains and
interacts with a moist and unstable airmass characterized by
2000-3000 J/kg and 1.6-1.8" PW. Fairly weak and unidirectional
cloud layer wind profiles atop a lingering 20-30 kt nocturnal low-
level jet suggest this convection along the front will have a
tendency to train before propagating southward with the initiating
boundary. The HREF and RRFS suggest hourly rainfall rates will
eclipse 2"/hr at times in the main axis of convection, which should
initially support isolated flash flooding during the day. The
greatest concern for excessive rainfall, however, will materialize
late tomorrow afternoon as the cold front enters the Texas Hill
Country and bisects a well-defined dryline. The resultant east-
west axis of thunderstorms will eventually grow upscale and train
within the very unstable and modestly sheared airmass. From late
Tuesday into early Wednesday, the HREF and RRFS are in good
agreement for increasing probabilities of 2-3"/hr rainfall rates,
which could lead to rainfall totals upwards of 3-5" by Wednesday
morning. When combined with the sensitive nature of the Hill
Country and urban areas in the Texas Triangle, a Slight Risk was
introduced in this update.


Otherwise, a separate Slight Risk area was introduced over portions
of the Ohio Valley as thunderstorms develop along the slow moving
front tomorrow afternoon. While weak height rises forecast in the
vicinity of the front could limit thunderstorm coverage somewhat,
forecast soundings featuring moist vertical profiles (1.8-2.0" PW),
3000-4000 J/kg of MUCAPE, and unidirectional flow suggest the
storms that develop should be quite efficient and slow to propagate
in the new Slight Risk area. This scenario is supported by the
HREF and RRFS, which depict increasing chances of hourly rainfall
rates eclipsing 2-3"/hr by late tomorrow afternoon. As this
activity overlaps with ongoing heavy rainfall in the region,
scattered flash flooding could result.

Asherman


Day 3
Valid 12Z Wed May 20 2026 - 12Z Thu May 21 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
SOUTH-CENTRAL TEXAS INCLUDING THE HILL COUNTRY AND EDWARDS
PLATEAU...

The Day 3 excessive rainfall risk is really just a translation
slightly southward of the Day 2 risk area due to a slowly evolving
synoptic pattern.

A large positively tilted trough positioned across the
Intermountain West and back into the Great Basin will gradually
amplify but maintain its NE to SW orientation. Gradually pinching
mid-level flow will help funnel additional moisture northeast from
the Pacific across the Southern Plains and into the Ohio
Valley/Central Appalachians. Within this flow, subtle shortwave
impulses lifting through the flow will help enhance ascent, aiding
low-level convergence along a nearly stalled front draped from Ohio
through Texas. At the same time, locally backing low-level flow
from the south at 850mb will converge into the front, producing
impressive moisture convergence along the front in a region of PWs
that are progged to be 1.5 to 1.75 inches. Although inflow may be
somewhat modest (850mb winds around 20 kts), this will be
sufficient within the moist column to provide plentiful advection
to support widespread convection with rainfall rates above 1"/hr
nearly certain.

Although there continues to be uncertainty into the exact
placement of the heaviest rainfall due to prior-day convection
which will cause wavering of the surface boundary, 0-6km mean winds
becoming increasingly boundary-parallel will support training of
these rainfall rates, and the SREF/ECENS/GEFS all suggest at least
a low-end risk (5-10%) of 3"/24 hrs around the updated SLGT risk
region. While this in itself may not force widespread FFG
exceedance, much of this rainfall D3 will fall atop areas that are
expected to receive significant rainfall as well D2, so the SLGT
risk was drawn to account for compounding impacts potential over
already vulnerable terrain features.

Farther northeast, the MRGL risk was cosmetically adjusted for new
guidance as convection with heavy rainfall will likely repeat from
SW to NE along the front as it slowly sags southward through the
Tennessee and Ohio River Valleys.

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