FOUS30 KWBC 151955
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
355 PM EDT Fri May 15 2026

Day 1
Valid 16Z Fri May 15 2026 - 12Z Sat May 16 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Wegman

..16z Update..

A progressive frontal system is expected to bring a linear complex
of thunderstorms through most of Iowa this evening through the
overnight. Updated 12Z HREF neighborhood probabilities have
increased over the last couple of cycles, with now moderate
chances (50%) of rainfall exceeding 2 inches. 12Z HREF also shows
an isolated risk 3hr FFG exceedance (~40%) throughout northern
Iowa. However, due to antecedent dry conditions, and an
expectation for the system to move fairly progressively, the nil
ERO has been maintained. There is however a non-zero chance of
isolated urban flash flooding in northern Iowa.


Blanco-Alcala

Day 2
Valid 12Z Sat May 16 2026 - 12Z Sun May 17 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE CENTRAL PLAINS, MID-MISSISSIPPI VALLEY, AND OHIO VALLEY...

A series of mid-level shortwaves will eject downwind of an
amplifying trough, with its axis over the Northern/Central
Rockies. Robust southerly flow from the Gulf will advect a solid
stream of moisture, with PWATs approaching 1.75 inches. This will
allow for heavy convection to develop along a frontal boundary
across the Plains and into the Ohio Valley in the
afternoon/evening. HREF neighborhood probs suggest pockets of ~50%
probabilities of at least 2 inches of rainfall. Additionally, there
are prolonged periods of neighborhood probs exceeding 1 inch/hr
rates over the period particularly in the NE/IA. There also exists
a possibility of potential training near the urban center of Kansas
City. Soils across the Ohio Valley have sufficiently dried out
from the last round of organized heavy rain, so any flash flood
threat would likely be tied to more urbanized areas. This system
is expected to develop quickly and become fairly progressive, and
with drier antecedent conditions, any flash flooding that occurs
should remain fairly isolated.


Blanco-Alcala/Wegman

Day 3
Valid 12Z Sun May 17 2026 - 12Z Mon May 18 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE UPPER MIDWEST/UPPER MISSISSIPPI VALLEY, AND CENTRAL PLAINS...

..21Z Update..

The Marginal Risk area was expanded farther south to include parts
of Nebraska and eastern Kansas, and trimmed over the northwest
region of the risk area. A surface cold front interacting with a
dryline, along with a persistent influx of low-level moisture will
support a renewed round of convection in the Central Plains. Storm
motion should be fairly slow-moving, bringing a potential for
training thunderstorms. Further north in the upper Midwest, AI/ML
guidance suggests a slightly eastward trend, resulting in the
removal of the northwest portion of the risk area. As the QPF core
becomes less uncertain and hi-res guidance becomes available in the
shorter term, an upgrade to a Slight may be considered.


Blanco-Alcala


..Previous Discussion..

A digging longwave upper level trough will eject several rounds of
shortwave energy northeastward ahead of the trough from the central
Plains and into the Upper Midwest on Sunday. The nose of a stout
low-level jet will provide ample moisture for any storms that
develop to feed on. Morning rain will douse the area as the dying
remnants of an MCS move across the Marginal Risk area. There will
likely be a break in any rainfall for much of the day as the
atmosphere recharges and instability advects north ahead of an
approaching area of low pressure. Numerous showers and
thunderstorms will form in a line very late in the day, near
sunset, with the storms moving sufficiently parallel/along the line
to introduce a training threat across the Marginal Risk area. Much
of the heaviest rain and the greatest flash flooding threat will
occur Sunday evening before the surface low pressure propagates
into Minnesota and allows the convection to have a faster push
towards the east. The increasing forward speed of the line will
diminish the flooding threat somewhat after midnight, through
convection ahead of the low could still affect portions of northern
Minnesota well into the overnight. Dry antecedent soil conditions
should generally mitigate the flooding risk, so the inherited
Marginal Risk was left largely unchanged. Some trimming on both the
west and east sides were done to highlight the increasing
confidence that the axis of heaviest rainfall will occur generally
across Minnesota, potentially spilling over to adjacent areas of
the neighboring states.


Wegman


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