Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
650 PM EDT Thu Sep 10 2026
Day 2
Valid 12Z Fri Sep 11 2026 - 12Z Sat Sep 12 2026

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

21Z update... The latest deterministic and CAMs guidance show an
uptick in QPF further east than previous cycles for eastern
portions of Virginia and North Carolina. Given the expected
location of the frontal boundary, instability and more than
adequate moisture pool convection capable of producing heavier rain
will like materialize. The Marginal Risk area was expanded to cover
more of southeast Virginia and Northeast North Carolina. Elsewhere
across the country remains in good shape and the inherit risk
areas remain unchanged.

Campbell

Previous discussion...

...Southern Arizona...

The ridge over southern AZ will be remain in place, although small
lobes of 500mb vorticity will move east to west 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"
likely throughout much of southern AZ that supports a localized
flash flood threat. REFS/HREF probabilistic guidance does show a
section of far southern Arizona particularly at-risk for flash
flooding. The HREF most notably shows moderate chances (40-50%) for
3-hr QPF surpassing 3-hr FFGs around Santa Cruz county Friday
afternoon. These signals in guidance support an upgrade to a Slight
Risk in far southern AZ.

...Lower MS Valley, TN Valley into the Southern Appalachians...

A 500mb shortwave trough tracking towards the Mid-MS Valley and a
sharp 200mb trough axis aloft is set to generate healthy divergence
aloft over the Mid-South, while copious amounts of moisture
continue to 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. 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.

...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 manifest over the region. Storm
motions should be progressive, although some training thunderstorm
activity closer to the warm front is possible as low pressure
heads for the MN Arrowhead. Rainfall totals could range between
1-2" (locally higher) in northern MN, while rainfall rates could
approach 1.5"/hr as storms track across the region Friday afternoon
and evening.

Mullinax


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt