635
FOUS30 KWBC 251603
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1203 PM EDT Tue Jun 25 2024

Day 1 Valid 12Z Mon Jun 24 2024 - 12Z Tue Jun 25 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PARTS OF
MIDWEST...

16Z update... Due to ongoing severe comms issues graphics and other data
are largely unable to update. For the Southwest, with the peak
heating of the day showers and thunderstorms are expected to fire
up across the region this afternoon and continue through the
evening hours. These slow moving storms will increase the risk for
localized flash flooding concerns, especially over favored
sensitive terrain. For the Midwest, a west-east line of storms span
from southern Iowa to northern Ohio this morning have brought
moderate to heavy rain over some of the same areas from yesterday.
Redevelopment is anticipated roughly between 3 and 7pm across
north-central portions of the Iowa that will have the potential to
produce high rainfall rates over near/over-saturated soils, thus
aggravating any flooding over the area.

Campbell

...Southwest...
PW values will remain highly anomalous (above the
95th climatological percentile and +5 standard deviations) from
southern California into the Southwest with a continuation of weak
forcing under the upper ridge axis stretching from the
Southern/Central Plains into the Southwest. An influx of deeper
moisture throughout the mid-levels associated with a tropical
disturbance over Mexico. This added moisture when combined with
sufficient instability should create greater coverage in convection
through the afternoon and evening hours. The sensitive urban
locations in and around Tucson prompts a greater risk for scattered
flash floods and runoff issues. The trend of slow- moving
convection occurring across sensitive terrain is expected to
persist which may lead to isolated heavy rainfall and flooding
concerns across the broad region of the Southwest and Four Corners.

...Upper Mississippi Valley/Upper Great Lakes...
The surface frontal boundary oriented northwest to southeast from
the Northern Plains into the Mid Missouri Valley begin to push
back to the northeast toward the Upper Mississippi Valley/Upper
Lakes region. Strengthening south-southwesterly low level flow
into this front will raise PW values to 1.5-2" along and to the
northeast of the front. Shortwave energy pushing eastward across
the Northern Plains toward the Upper Mississippi Valley will help
strengthen isentropic lift over this front and support for
overrunning convection. There is not a lot of agreement on
placement of any heavy precip totals, but overall some potential
given the favorable MCS set up. There is potential for heavy
rains to overlap where recent heavy rains fell across southern
MN/northern IA and into northern IL.

Snell/Oravec


Day 2 Valid 12Z Tue Jun 25 2024 - 12Z Wed Jun 26 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NEW MEXICO...

In the wake of the warm front pressing northeastward across the
Upper Mississippi Valley/Upper Lakes region, the associated cold
front will be dropping southeast from the Northern Plains into the
Upper Mississippi Valley/Upper Lakes during this period.
Additional convection likely to develop in the axis of high PWs
pooling along the front that becomes more west to east oriented.
Convection may train in a west to east direction parallel to this
front as the low level flow will also be westerly along and ahead
of the boundary. There still is spread in model qpf details, but
the multi model ensemble qpf mean and latest NBM do show potential
for heavy amounts across areas of far southern WI/eastern IA and
northern IL that have received heavy rainfall recently. A broad
marginal risk spans from the central Gulf Coast, portions of the
Tennessee/Ohio Valleys and most of the Northeast.

...Southwest...
No significant large scale changes expected during this period over
the Southwest besides the gradual northward lifting of anomalous
PWs into parts of UT. PW values 3-4+ standard deviations above the
mean will persist from southern California, into the Southwest and
southern Great Basin in a region of continued weak forcing under
the building closed high over the Southwest. Widespread scattered
diurnal convection again possible across these areas, with
continued low confidence in any qpf details. There is some
elevated concern that convection could be widespread enough to
create scattered flash flooding throughout the slot canyon region
of south-central Utah. This area will likely be monitored for a
targeted upgrade over the next few days should sufficient
instability show up in CAMs and greater qpf coverage.

Snell/Oravec


Day 3 Valid 12Z Wed Jun 26 2024 - 12Z Thu Jun 27 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE NORTHERN AND CENTRAL PLAINS AND FOR PORTIONS OF NEW MEXICO,
COLORADO AND FAR SOUTHERN WYOMING...

A low pressure system and associated fronts tracking into the
Northern Plains Thursday will bring a threat for heavy rainfall
across the north-central Plains into the Upper Midwest. Some
conflicting signals remain regarding locations that may see
significant rainfall, but latest guidance is suggesting two areas
of relatively greater focus during the period. One is within the
existing Slight Risk area over parts of the Midwest with a modest
southwestward adjustment per latest guidance, and another farther
north across northern North Dakota and far northwestern Minnesota
where a Slight Risk area has been introduced. Slight Risk areas
within the broader Marginal Risk are subject to change based on
updated forecasts of convective evolution and location relative to
areas with greatest sensitivity due to prior heavy rainfall.

Santorelli/Campbell


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