Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1120 AM EDT Sat Jun 7 2025
Day 1
Valid 16Z Sat Jun 07 2025 - 12Z Sun Jun 08 2025

...THERE IS A RISK OF EXCESSIVE RAINFALL ACROSS MUCH OF THE EASTERN
UNITED STATES...WITH SLIGHT RISKS IN SOUTHERN NEW ENGLAND... THE
OHIO RIVER VALLEY...AND MID-SOUTH...

An active day of heavy rainfall and flash flooding is expected
across a large portion of the eastern United States, with the
Marginal Risk area now encompassing the majority of the land area
in the CONUS east of 95W longitude. This is due to a broad region
of near to above normal tropospheric moisture (via PW anomalies)
and sufficient instability for convective rain bands and
thunderstorms.

Generally, the broad zone of heavy rainfall risk can be divided
into three main areas of concern, all indicated by a regional-scale
Slight Risk maximum now:

1. In the Northeast, where low-topped convection has organized into
narrow bands of efficient heavy rainfall. MRMS analysis indicates
almost no ice present in these convective bands, with 30 dBZ echo
tops generally shy of the -10C level. In other words, warm rain
processes are dominant and any organized convective rain band could
produce localized heavy rainfall. The area of greatest concern is
probably from active area of flash flooding in the Hudson Valley
near Albany, NY eastward through Massachusetts and northern
Connecticut to the Boston metro area. There should naturally be
increasing low-level convergence with the existing front draped
across the region, and increasing easterly flow near the coast
around the north side of the offshore low. Aloft, a coupled jet
structure should lead to enough divergence to focus convection.

2. The Ohio River Valley region, particularly the middle and upper
Ohio Valley from late this afternoon well into the overnight hours.
This will be due to scattered convective rain bands and perhaps
some thunderstorms developing in advance of an eastward propagating
mid-upper level wave, and developing surface low by this afternoon,
currently centered over IA- MO. This should allow for some
organized convective bands in the warm air advection regime. Model
forecast soundings show increasing PWs to near or above the 90th
percentile for early June and tall, skinny CAPE profiles that are a
good match for efficient, low-topped convective flash flood events.
Of particular concern will be the potential for flash flooding
overnight in the central Appalachian region from eastern Kentucky
and southeast Ohio into West Virginia and southwest Pennsylvania.
Models show southwest low-level inflow increasing into the
mountains in a very moist environment, with the right entrance
region of an upper level jet streak providing divergence aloft. All
of this should support an organized heavy rain threat and the
structure of the instability profile will keep convection low-
topped and dominated by warm rain processes. Locally significant
flash flooding will be possible given the terrain in the area and
relatively wet antecedent conditions.

3. Across the mid-South where a forward propagating MCS has already
generated some flash flooding in central Arkansas, but appears to
begin accelerating. Renewed development and/or stalling and
training will be possible along the southern periphery of the cold
pool later today, and hi-res models do show localized corridors of
heavy rainfall that would be sufficient to cause flash flooding.
The Slight Risk was shifted south to account for observational
trends indicating the current position of the cold pool and
convective line, and the projected motion over the next few
hours.

Lamers


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt