Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1158 AM EDT Thu Jun 25 2026
Day 2
Valid 12Z Fri Jun 26 2026 - 12Z Sat Jun 27 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN EFFECT OVER
PORTIONS OF THE MID-MISSISSIPPI AND OHIO VALLEYS...

...Mid-Mississippi and Ohio Valley's...

Shortwave ejecting out Missouri Friday morning will continue to
progress through the Ohio Valley the rest of the D2 time frame.
Quasi-stationary front will remain positioned along and just north
of the Ohio River leading to an emphasis on convection within
proximity of the boundary. The 00z HREF does not go beyond the 00z
Saturday hour, however, the 12hr period between 12z Fri - 00z Sat
is very much indicating some significant rainfall in-of that area
of the Mississippi/Ohio River confluence and surrounds. HREF
neighborhood probabilities for at least 3" in that 12hr period are
solidly between 30-60%, a signal that usually correlates to heavy
rainfall with rates sufficient for flash flood prospects.
Thermodynamically and kinematically, this setup is one that favors
locally significant rains with most guidance in agreement on areas
of 2+ inches during the back end of D1 heading through D2. The
threat will continue to extend east through southern IN and OH with
the eastward advancement likely to extend as far as western PA down
through the Central Appalachian front in PA/MD/WV. Current
indications are for the heaviest rain to likely focus west of I-79
in WV, so the SLGT risk remains situated closer to the OH/WV/KY
border and points west with a MRGL further east. A high-end SLGT is
forecast over the confluence area of the Mississippi/Ohio rivers
and surrounds, which includes: southern IL/IN, eastern MO, and
western KY where consensus for 2-4" has grown over the course of
the last 24hrs.

...Montana...

A potent shortwave trough will migrate through the interior
Northwest U.S. leading to a regionally amplified setup capable of
producing locally heavy rainfall across central and eastern MT.
Steering flow will be pretty fast overall, so any convective
activity will likely be moving relatively quickly with the flow to
the east-northeast after genesis. That said, environment for mature
mesocyclones and stronger convective cores will be capable for
periods of heavy rainfall during any of these thunderstorms as they
migrate through the High Plains of MT. Rates between 1-1.5"/hr will
be plausible at peak intensity leading to pockets of 1-2" of rain
falling in a short window as storms traverse over the area. The
previous MRGL risk was maintained to account for the threat.

...Northern ME...

Shortwave trough moving through Quebec will pivot across northern
ME as we move into Friday afternoon. Sufficient buoyancy and mid-
level forcing brought upon by the disturbance and boundary layer
priming in the afternoon will lead to a round of thunderstorms
capable of producing locally enhanced rainfall that could impact
more sensitive areas of northwest ME. As of now, the prospects for
locally 1-2" of rainfall have increased the past succession of runs
from NWP with some deterministic outputs pointing to a quick inch
or more over the northern Appalachian area of western ME advancing
into interior Aroostook county in northern ME. The previous MRGL
risk was maintained for the threat as guidance still favors the
potential.

Kleebauer


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