Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Fri Sep 11 2026
Day 1
Valid 16Z Fri Sep 11 2026 - 12Z Sat Sep 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN FAR SOUTHERN
ARIZONA & NORTHERN MINNESOTA...

16Z update... The latest guidance is depicting an increase in QPF
coverage and amounts across the Florida Panhandle for the remainder
of this period. Local rainfall rates of 1-2+ inches may be possible along
the coast. The Marginal Risk area was expanded eastward to
encompass more of the Florida Panhandle. Elsewhere, the highlighted
areas of elevated risk for excessive rainfall and flash flooding
potential remain in good order with no adjustments needed at this
time.

Campbell

Previous Discussion...

...Southern Arizona...

The upper level ridge over southern AZ will direct embedded 500mb
vorticity maxima westward along the US/Mexico border on Friday.
Much of AZ, southern UT, and western CO will continue to contend
with anomalous moisture content with PWs >1.5" throughout much of
southern AZ. Latest 00Z REFS/HREF probabilistic guidance does show
a section of far southern Arizona particularly at-risk for flash
flooding. The latest 00Z HREF shows moderate-to-high chances
(50-70%) for 3-hr QPF surpassing 3-hr FFGs around Santa Cruz
county Friday afternoon. For these reasons, the Slight Risk remains
on track for far south-central AZ.

...Upper Midwest...

A 500mb shortwave trough and an accompanying frontal boundary will
track through the Upper Midwest at the same time a plume of >90th
climatological percentile PWs manifests over the region. Storm
motions should be progressive, although some training thunderstorm
activity closer to the warm front is becoming inc as low pressure
heads for the MN Arrowhead. Rainfall totals could range between
1-2" (locally higher amounts up to 3") in northern MN, while
rainfall rates could approach 1.5"/hr as storms track across the
region Friday afternoon and evening.

...Lower MS Valley, TN Valley, Central Gulf Coast, and the
Southern Appalachians...

A 500mb shortwave trough tracking towards the Mid-MS Valley and a
sharp 200mb trough axis aloft will generate healthy divergence
over the Mid-South, while copious amounts of moisture reside over
much of the Southeast. A nearby frontal boundary will trigger
widespread thunderstorms that are likely to contain >2"/hr rainfall
rates within the more intense storms. Model guidance remains in
fairly good agreement on the widely scattered t-storm activity
before storms dissipate for most areas by late evening. PWs >2.0"
will be common from the central Gulf Coast to the mid-MS Valley,
while PWs in the OH/TN Valleys range between 1.75-2.0", which are
still above the 90th climatological percentile. Storms are likely
to form as far east as the Southern Appalachians and Carolinas,
although the flash flood threat is less likely along the Southeast
coast. Localized flash flooding is possible, especially in poor
drainage areas and within more urbanized communities.

Mullinax


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