Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
847 PM EDT Sun Aug 16 2026
Day 2
Valid 12Z Mon Aug 17 2026 - 12Z Tue Aug 18 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE OHIO VALLEY AND THE CENTRAL APPALACHIANS...

20Z Update...

Felt the combination of very moist soils and the potential for
additional heavy rains was enough to warrant the upgrade to a Slight
Risk across portions of southern Ohio, West Virginia, and
southwestern Virginia. A shortwave now moving across Iowa and
northern Missouri is forecast to move through the Ohio Valley
tomorrow, interacting with a pool of deeper moisture settling south
ahead of a cold front. While, widespread additional heavy amounts
are not expected, both the HREF and REFS indicate 1-2 inch amounts
are likely, with the HREF showing some greater than 50 percent
probabilities for amounts over 2 inches within the Slight Risk
area. At 12Z, 3-hr FFGs ranged from 0.25-1 inch within much of this
area, with the HREF and REFS showing probabilities for rainfall
amounts exceeding these values climbing over 50 percent late Monday
afternoon and evening across parts of the northern West Virginia
and southwestern Virginia mountains.

Elsewhere, made only minor changes to the previous outlook.

Pereira

Previous Discussion...

...OH/TN valley into the Appalachians...
A southward dropping cold front will serve as a focus for scattered
convection on Monday. While overall storm coverage will be reduced
compared to previous days, lingering moisture and instability just
behind the boundary will maintain a heavy rainfall threat from KY
and TN into the central Appalachians, enhanced by local terrain
upslope. A Marginal risk is maintained for isolated flash
flooding. Notably, the 00z RRFS and REFS hint at an upstream MCV
moving into KY and TN that could increase convective
coverage/organization enough to warrant a Slight risk. However,
given limited global model support, the risk tier will be held at
Marginal pending a full suite of high res guidance in subsequent
cycles.

...Southwest...
A Marginal risk remains on track across much of NM and adjacent
portions of southeast AZ and southern CO. Beneath an upper level
ridge strong instability and slightly above average PWs will
interact with embedded shortwave energy trapped in the weak flow.
Terrain based initiation is expected during the afternoon, with
scattered coverage and cell mergers likely as convection drifts off
the higher elevations.

...NE to MN...
The Marginal risk has been adjusted slightly southwestward, now
extending from central NE into far southeast SD and far northwest
IA. Frontal forcing combined with a robust instability pool over
the Central Plains and a nocturnal low level jet ramp up will
support a convective cluster centered across NE by Monday
evening/night. Recent high res models, along with the AIFS and
AIGFS, show better spatial agreement focusing this activity over
NE, supporting the minor shift in the risk area.

Chenard


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