Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
807 PM EDT Fri Jul 26 2024
Day 3
Valid 12Z Sun Jul 28 2024 - 12Z Mon Jul 29 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF
NORTHERN MINNESOTA AS WELL AS MUCH OF THE TENNESSEE VALLEY...

...20Z Update...

...Northern Minnesota...

Rain associated with a slow moving front will be ongoing across
northern Minnesota Sunday morning. It is likely to diminish in
intensity from mid-morning through early afternoon. Then much
stronger showers and storms will move into the area following along
the front Sunday afternoon, with multiple rounds of storms likely
to follow through much of Sunday night. The storms will be capable
of heavy rainfall as PWATs rise as high as 1.75 inches. Since the
front will be slow-moving, the storms are likely to train along the
same areas, likely in a southwest to northeast swath across much of
northern Minnesota, but possibly starting in the eastern Dakotas.
Portions of Minnesota remain with wetter than normal soils, so
multiple rounds of heavy rainfall are likely to cause widely
scattered instances of flash flooding.

...Tennessee Valley and Surrounding Areas...

A stationary front turned warm front will track northeastward up
the Tennessee Valley on Sunday through Sunday night. Increasing
atmospheric moisture associated with the advance of an airmass
originating off the Gulf will allow for potential training and
backbuilding of strong storms capable of increasingly heavy
rainfall. The surface warm front will likely slow as it approaches
the southern Appalachians Sunday night. This will support slower
moving storms that with interactions with the terrain will be
capable of flash flooding. Further, some of these areas, especially
the mountains along the NC/TN border have seen heavy rain in
recent days. The advection of increasing moisture will support
storms capable of very efficient warm rain processes which could
result in multiple inch per hour rainfall rates. Urban areas are at
a higher risk for localized flash flooding with any repeating
storms.

Wegman

...Previous Discussion...

...Gulf Coast to parts of the Tennessee Valley...
A closed mid- and upper-level low that started to take shape late
Saturday night/early Sunday morning should begin to lift northward
during the day on Sunday and then become an open wave again by
Sunday evening. Lowering mid-level heights should help increase the
coverage of convection within an an atmosphere sufficiently moist
to support isolated downpours in a corridor from the middle Gulf
coast to the Tennessee valley during the afternoon and evening,

...Southwest US...
The risk of excessive rainfall continues to get less conducive with
time and gets shunted eastward as mid-level westerly flow
strengthens over much of the West outside of Arizona and New
Mexico. Maintained a Marginal Risk here given the lingering
moisture.

...Upper Midwest...
Scattered convection should develop along a cold front extending
into the northern tier of the US from a system in Canada. With
increasing precipitable water and instability values increasing as
a result of southerly flow ahead of the front...isolated downpours
could result in isolated flooding or run off problems in regions of
poor drainage.

Bann

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