Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
836 PM EDT Sun Jun 28 2026
Day 2
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 Mississippi
Valley...

21Z update... In general, the area identified for having an
elevated threat for excessive rainfall and isolated areas of flash
flooding remain in good order. Small adjustments were made with the
southern boundary across central Nebraska to reflect the latest WPC
QPF and model trends. A modest southern expansion was made into
eastern Idaho and northwest Wyoming to account for the
precipitation occurring during the Day 1 period and a southern
shift in QPF placement in the latest guidance.

Campbell

Saw little reason to make major changes in this region. On-going
convection at the start of the outlook period on Monday morning
will be occurring in a highly unstable airmass with very strong
low level moisture transport. 00Z model runs did little to settle
the latitudinal of the convective axis and mode/movement. Given the
impressive CAPE, very strong moisture transport, high PWs and weak
Corfidi vectors...there is the potential for 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
continue 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 Montana.
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

Bann


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