FOUS30 KWBC 290829
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
429 AM EDT Fri May 29 2026

Day 1
Valid 12Z Fri May 29 2026 - 12Z Sat May 30 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHEAST...

Largely maintained the previous Slight Risk area that was introduced
in the Southeast US. A sheared 500mb vorticity maximum approaching
from the west will be encountering a moist airmass with increasing
amount of instability later during the day and evening. The latest
numerical guidance kept expected precipitable water values in the
2 to 2.25 inch range along and south of a quasi-stationary front
draped across the region from the TN Valley to the SC coast.
Instability will be highest over AL on east into central and
southern GA with MUCAPE between 1,000-2,000 J/kg most often. MUCAPE
up to 1,000 J/kg will be available later tonight from the Savannah
River to coastal SC. This combination should be enough to support
and sustain localized rainfall rates in excess of 2 inches per hour
where warm rain processes predominate from eastern AL eastward to
the Savannah River this afternoon and tonight.

...Middle Mississippi Valley to the Southeast...

The western portion of the front affecting the Southeast US will
extend into portions of the Middle Mississippi Valley and provide
the focus for showers and thunderstorms...some of which may produce
locally heavy rainfall from the Tennessee Valley into the Middle
Mississippi Valley into tonight.

...Eastern Washington to Northern Rockies...

A marginal risk remained in place across far northeast Washington
to northwest Montana due to an increase in the heavy rainfall
signal for this period as an upper low over the West on Day 1
places this region in an area with better upper forcing and
advection of moisture. The presence of anomalous moisture and some
instability may present a threat for localized heavy rainfall and
flash flooding, especially for burn scar locations within this region.

Bann


Day 2
Valid 12Z Sat May 30 2026 - 12Z Sun May 31 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS THE
NORTHERN ROCKIES TO HIGH PLAINS AND THE SOUTHEAST...

...Southeast...

Latest numerical guidance has shifted a majority of the rainfall
eastward enough compared with previous runs to preclude an upgrade
to a Slight risk. In addition...the spread of model
guidance both in terms of placement and amounts precluded an
upgrade. As mentioned previously...some of the region, especially
western parts of South Carolina and into the Appalachians, has
been very wet as of late and is well primed, so may by more
vulnerable to flooding concerns.

...Northern Rockies to High Plains...

The upper level low over the West during the Day 1 period will
weaken and shift northeastward, moving over the Northern Rockies to
High Plains region on Saturday. Moisture anomalies will continue
to be in the 90-90th percentile, supporting moderate to heavy
rainfall, with widespread QPF greater than 0.5-1" likely across
western and central Montana. There may not be a lot of instability
to work with, so any flood or flash flood threats should be mainly
localized with particular attention to burn scar locations. A
fairly broad marginal risk remained in place across much of
western and central Montana, into parts of northern Wyoming as well.

Bann


Day 3
Valid 12Z Sun May 31 2026 - 12Z Mon Jun 01 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE NORTHERN ROCKIES AND THE SOUTHEAST UNITED STATES...

...Northern Rockies and Adjacent High Plains...
The upper level low which has been supporting the prolonged wet
period over the Northern Rockies will continue to move northward
across Montana slowly on Sunday. This results in surface low
pressure and associated surface front to makes its way out over the
Plains and gradually weaken while the mid and upper level
circulation keeps precipitation lingering over Montana and far
northern Wyoming. Moisture remains anomalously high but instability
still looks to be dependent upon cloud cover. As in the Day 2
period...any flood or flash flood threats should be mainly
localized with particular attention to burn scar locations.

...Southeast...

Until surface high pressure builds far enough southward into the
Southeast states to decrease coverage of lingering convection on
Sunday evening...the antecedent conditions keep a risk of flooding
concerns over the area.

Bann
$$
--- MultiMail/DOS
 * Origin: Project Scorpio TEST (618:250/6)