Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
851 PM EDT Fri Apr 17 2026

Day 1
Valid 01Z Sat Apr 18 2026 - 12Z Sat Apr 18 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM OKLAHOMA
THROUGH PORTIONS OF THE MIDWEST INTO UPPER GREAT LAKES...

01Z Update: Minimal changes were made from the previous outlook.
The primary change was to remove outlook areas where a well defined
front has already passed while few changes were needed to the
northern or eastern periphery. A Slight Risk area remains from
Oklahoma northeastward into the western Great Lakes region...with
the area from northeast Oklahoma into parts of Missouri being
considered as a higher-end Slight Risk.

The convection continued to be focused along and ahead of a well
defined cold front making its way eastward at the surface and
enhanced upper level divergence due to jet coupling in the Central
Plains and the re-formation of a robust southerly low level jet
later tonight across the Southern and Central Plains. Latest
numerical guidance still pegs the precipitable water anomalies
around +3 standard deviations helping to increase the excessive
rainfall risk.

Bann

..Previous Discussion..

A strong cold front tracking southeast across the Plains will run
into a moist and unstable air mass driven by a robust low level jet
streaming north off the western Gulf and into the Great Lakes.
Meanwhile, a strengthening upper level jet across Texas and
Oklahoma will further enhance lift across the Slight Risk region,
particularly the southern part of it. The result will be a series
of waves of strong thunderstorms that will feed on the influx of
moisture and instability to allow for frequent redevelopment and
training as the entire complex of storms pushes southeast. The
strongest storms and most persistent rainfall will occur over areas
hard-hit in recent days with prior heavy rainfall, so soils in
areas from southern Oklahoma to western Missouri are already near
saturation and well above normal for soil moisture content for this
time of year. Urban areas from Kansas City to Tulsa will be
especially vulnerable should persistent heavy rains set up over
those metro areas. Meanwhile, a portion of the Ozarks could also
introduce a topographic factor to any flooding potential. A higher-
end Slight (25-40% chance of flash flooding) is in effect from
northwestern Oklahoma through central Missouri.

Meanwhile, further north into the Midwest, the storms are more
likely to organize into a single line of storms more quickly.
However, these areas have even more saturated soils due to more
recent rains. When added the urban factor in cities such as St.
Louis, Chicago, and Milwaukee, even a shortened period of heavy
rainfall could still result in widely scattered instances of flash
flooding. The Slight Risk in this area was expanded north up Lake
Michigan to Green Bay, but elsewhere remains little changed.

Wegman

Day 2
Valid 12Z Sat Apr 18 2026 - 12Z Sun Apr 19 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE GULF COAST AND LOWER MISSISSIPPI VALLEY...

20Z Update: The MRGL Risk area remains mostly unchanged from the
previous forecast. The main exception being a removal of the
northern portions of the area including parts of central MS, which
has seen a decrease in neighborhood probs. New probs suggest a
moderate possibility (40%) of over 1", with little to no chance of
an excess of 2". The progressive nature of the cold front and the
slightly decrease QPF and further justified the removal of the
area.

Blanco-Alcala


..Previous Discussion

A strong cold front sweeping south down the Plains will provide the
primary forcing for a line of strong thunderstorms to form as the
front uplifts a warm and moisture-laden air mass from the Gulf. Due
to close proximity to the Gulf, PWATs are likely to spike to
between 1.5 and 1.75 inches Saturday evening. This will support
thunderstorms capable of very heavy rainfall. The line will
generally be progressive, moving south. Further, the Marginal Risk
area is generally covering some of the highest FFG areas in the
country. Thus, the flash flooding threat is largely focused on the
urban factor in areas such as Houston, Beaumont, and Alexandria.
Most of the convective activity is expected at or after sunset, so
any flooding that occurs will be more dangerous.

Wegman

Day 3
Valid 12Z Sun Apr 19 2026 - 12Z Mon Apr 20 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR DEEP SOUTH
TEXAS...


Remnants of the previously mentioned cold front set to impact the
Gulf Coast on Saturday will continue to feed in moisture to the
deep south of Texas on Sunday. Upon reaching and entering the Gulf,
the tail-end of the front will stall just offshore of the southern
Gulf Coast. This will produce a low-level inverted trough just off
the east coast of Texas, with the low-level wind regime shifting
to a more easterly flow. PWATs will approach and exceed 2 inches
off the coast, which with the aforementioned easterlies will
result in moist onshore flow from the Gulf. This will result in
showers and thunderstorms in the Deep South of Texas, and will have
the possibility of bringing heavy rain. Currently, any higher end
flash flooding impacts will be inhibited by a variety of factors.
The low-level flow appears to be on the weaker side, with a suite
of global ensembles suggesting 15kt onshore flow. Additionally, FFG
guidance remains high, and with unfavorable upper-level forcing by
way of subtle ridge, any flash flooding would need to come by way
of training setup. At this point, any instance of this appears to
remain quite isolated.


Blanco-Alcala/Wegman


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt