Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
856 PM EDT Tue Mar 10 2026

Day 1
Valid 01Z Wed Mar 11 2026 - 12Z Wed Mar 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN PLAINS AND THE SOUTHERN GREAT LAKES...

01Z Update...

Recent runs of the HRRR as well as the latest HREF and RRFS did not
suggest any large-scale changes to the previous outlook were
necessary. Therefore, made only only minor adjustments based on
that guidance and observation trends.

Pereira

16Z Update...

Changes to continuity include some expansion of the Marginal Risk
across the OH Valley and locally across the central and southern
Plains given what should be a relatively complex evolution of
multiple convective clusters/MCSs going through tonight. The upper
OH Valley in particular remains rather sensitive fairly low FFGs
and at least scattered areas of convection capable of producing 1
to 1.5 inch/hour rainfall rates may be possible over some of these
areas. For areas of the central and southern Plains, the Marginal
Risk generally follows the overall convective footprint in the warm
sector ahead of the approaching upstream height falls/frontal
system.

More specifically, the latest guidance continues to support
multiple areas of well-organized convection extending from the TX
Hill Country northeastward to near the Red River. Multiple linear
bands of convection with high rainfall rates locally exceeding 2
inches/hour are expected as ejecting shortwave energy interacts
with an increasingly moist and unstable boundary layer. MLCAPE
values exceeding 2000 J/kg along with PWs of 1.5 to 1.75 inches and
a strongly sheared kinematic profile will support organized
convective segments including supercells. Some localized mesoscale
boundary interactions will support areas of convection becoming
locally focused with at least some cell-training concerns possible.
As such, the Slight Risk over the southern Plains has been adjusted
a bit south and east to accommodate the 12Z HREF/06Z REFS, 06Z EC-
AIFS and recent HRRR/RRFS solutions. This includes some trimming
of it the northern portion of it closer to the Red River. The end-
result is expected to be a concern for locally several inches of
rain and scattered areas of flash flooding including an urban
flooding threat.

For areas of northern IL, northern IN, southern Lower MI and
northwest OH, the Slight Risk here has been only modestly tweaked
as the setup here favors a well-organized convective impact with
thunderstorms this evening and into a part of the overnight period
capable of producing 1 to 2+ inch/hour rainfall rates. An ejecting
wave of low pressure along a strong front coupled with a moist,
unstable warm-sector airmass should yield strong MCS activity with
a concern for areas of cell-training. The low-level jet this
evening is forecasting to increase to locally 50+ kts, and this
will being aimed into a strong front oriented west to east
downwind from the approaching low center. Locally several inches of
rain will be possible and this will drive concerns for flash
flooding.

Orrison

Previous discussion...

The signal for potentially two heavy precip axes persists in the
guidance..in the very favorable coupled jet entrance/exit regions
expected between the southern stream closed low moving into the
Southern Plains and the northern stream jet across Mid Mississippi
Valley and the Midwest region.

Gulf moisture gets drawn northward over parts of the central U.S.
from Texas into the central portion of the Mid-Mississippi Valley
during the day. There has been a trend in the model guidance over
the past 24 hours for the core of the higher precipitable water
values to get shunted more eastward than northeastward...resulting
in lower model QPF despite the upper support and mid-level
mesoscale forcing remaining favorable. Consequently...trimmed the
Slight Risk area to cover only portions of Illinois and Indiana
where QPF exceeded an inch and which overlapped areas that
experienced moderate to heavy rainfall a few days ago and have
suppressed flash flood guidance.

The better instability...and associated higher rainfall
rates...still look to be over portions of Texas into southeast of
Oklahoma as flow aloft becomes increasingly diffluent in response
to an approaching upper low. .Mixed layer CAPE values of 1500 to
around 2500 J per kg develop ahead of the low where precipitable
water values will have risen into the 1.25 to 1.5 inch range
resulting in the potential for 1+ inch per hour rates. The axis of
model QPF and WPC deterministic QPF align well with modestly-
lowered flash flood guidance from rainfall several days ago.

Bann

Day 2
Valid 12Z Wed Mar 11 2026 - 12Z Thu Mar 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER PARTS OF THE
SOUTHERN US...

19z Update: As the closed low moves across TX there is a good
setup for an axis of training convection from east TX into the
lower MS Valley. With very strong synoptic forcing and increasing
moisture transport we should see convection expand in coverage and
intensity over east TX by late morning. During the development
phase cell training/backbuilding is probable over east TX, and
while convection should grow upscale and forward propagate during
the afternoon, some west to east training is possible near the
southward dropping cold front. The inherited Slight risk was
expanded off to the south and east to account for model trends.

The Marginal risk was expanded northward across the OH Valley and
into western NY where rainfall rate driven localized flash
flooding is possible. Areal averaged rainfall is only 0.5"-1.5",
but given the 500-1000 j/kg and convective nature of rainfall, do
expect localized swaths over 2". This should be enough to at least
locally exceed FFG across this region. Over western NY, snow melt
and locally heavy rain may combine to result in areas of excessive
runoff.

Chenard

...Previous Discussion...

The upper low over the southern states will continue to translate
eastward on Wednesday. The upper support will be weakening as the
system weakens/fills with time. Model run to run consistency has
been poor and another round of changes were made this cycle. The
changes included introduction of a Slight Risk over parts of
eastern Texas and western Louisiana where model QPF exceeded two
inches. In addition...there was some overlap between locally heavy
rainfall a couple of days ago and the QPF.

...Pacific Northwest...
Persistent on-shore flow of deep moisture into parts of coastal
Washington and northern Oregon should result in occasional moderate
rainfall...mainly in the west face of the coastal ranges. Amounts
on the order of 2.5 inches to 3.5 inches in 24 hours is forecast
which could result in isolated flooding ot run off problems in
areas of poor drainage.

Bann


Day 3
Valid 12Z Thu Mar 12 2026 - 12Z Fri Mar 13 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHWEST UNITED STATES...

19z Update: Only change was to expand the Marginal risk farther
into the Cascades given high snow levels allowing for greater
coverage of heavy rainfall.

Chenard

...Previous Discussion...

...Pacific Northwest...
On-shore flow of deep moisture into parts of coastal Washington
and northern Oregon persists into the Day 3 period that results in
occasional moderate to locally heavy rainfall continuing along the
coastal ranges. An additional 1 to 3 inches in 24 hours are
possible...which could result in isolated flooding ot run off
problems in areas of poor drainage.

Bann


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