Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
307 PM EDT Sat Jun 27 2026
Day 3
Valid 12Z Mon Jun 29 2026 - 12Z Tue Jun 30 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM MONTANA INTO
THE NORTHERN PLAINS AND UPPER MISSISSIPPI VALLEY, AS WELL AS ACROSS
WEST TEXAS...

...Montana into the Northern Plains and Upper MS Valley...
Main change was an expansion of the Marginal risk across this
region. Convection should be ongoing Monday morning across
portions of the Dakotas within a highly unstable airmass with very
strong low level moisture transport. This activity should then
push into central/northern MN through the day. Main uncertainty
deals with the latitude of the convective axis and mode/movement.
Will note that the environment is quite impressive...with extreme
CAPE, very strong moisture transport, high PWs and weak Corfidi
vectors. Thus the potential is certainly there for an axis of
backbuilding convection and a locally significant flash flood risk.
However, it's also a possibility that the strong mean flow and
somewhat progressive forcing help move storms along and limit the
coverage/magnitude of the flash flood risk. So we will just need to
continue to monitor trends over the coming days.

While mostly stratiform rain by this time, event total rainfall of
2-4" is expected across portions of central and western MT. Even
though rainfall rates by this time should be low enough to preclude
much of a flash flood risk, this is an impressive amount of rain
for late June over this area, and thus some areal/stream flood
impacts appear probable. Thus we will include them within the
Marginal risk.

...Southwest Texas...
Increasing instability should lead to late day convective
development along and near the dry line in west Texas. Isolated
flash flooding is again possible

Chenard

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