Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
349 PM EDT Sun Jun 8 2025
Day 1
Valid 16Z Sun Jun 08 2025 - 12Z Mon Jun 09 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN PLAINS...GULF COAST...AND MID-ATLANTIC...

...Mid-Atlantic and Central Appalachians...
Very few changes were made to the existing Day 1 outlook over this
region, with observational trends generally matching earlier
forecasts fairly well. The initial round of rain has moved through
much of the Slight Risk area as of 15 UTC, and has produced a
fairly widespread 0.5 to 1.0 inches of rain in much of the area. As
cloud cover partially clears in the wake of the area of stratiform
rain, rapid destabilization is occurring, and this is already
beginning to support convective initiation. Although the PWs may be
slightly lower in this area of clearing, they are still relatively
high (around 1.4 to 1.5 inches) around the 90th percentile for
early June. The combination of the increasingly strong instability
and relatively deep moisture should support hourly rain rates of 1
to 2 inches per hour in the most vigorous and organized convection.
This may lead to flash flooding, particularly in situations where
the rain rates can be sustained for more than an hour, and either
in the mountainous areas of N WV, W MD, SW PA that have been very
wet lately, or in urbanized areas in the coastal plain.

...Gulf Coast...
Training and backbuilding thunderstorm activity has been far more
persistent this morning in portions of E MS and C AL than models
have been indicating. However, 12 UTC hi-res guidance appears to
generally have a better handle on the current mesoscale environment
and state of the convection. There is good agreement that the
convective line itself and/or the associated gust front will make
steady progress toward the coast today, and then begin to stall
later this afternoon or early tonight. This may focus additional
convective clusters and lines later today and tonight, with a
favorable configuration for backbuilding (southwesterly inflow with
an upstream reservoir of strong instability). The combination of
the very high CAPE values, and anomalously high PWs around 2
inches, will support very heavy hourly rain rates approaching or
exceeding 2 inches in the most organized convective clusters. If
the gust front interacts with the coastal convergence zone and
anchors convection somewhere near the coastline, heavy rain rates
could persist for several hours and lead to a locally extreme
rainfall event with potential for significant flash flooding.

...Southern Plains...
The heavy rainfall and associated flash flooding threat in this
region is more conditional, given excellent hi-res model agreement
in a very organized, rapidly forward propagating bowing line late
this afternoon and this evening. Although the instantaneous rain
rates in the line itself would be likely to be high, the fast
forward speed would likely mitigate that factor a bit. Corridors of
heavy rainfall in these cases tend to occur either:

1. Near the poleward bookend vortex, which can tend to move slower
and still have relatively high rain rates. In this case, that would
be most likely over portions of SC OK, although the fast forward
motion of the line makes it uncertain how impactful this would be
from a rainfall perspective.

2. Or along the upshear flank of the cold pool. That seems
plausible in this case, and would be most likely either in far
SW OK or in western N TX. In particular, a corridor of locally
heavy rainfall and flash flooding would seem more likely if
convective development occurs near a lingering front in advance of
the main forward propagating MCS, thereby increasing the duration
of the heavy rainfall. However, it's unclear whether this
antecedent development and the eventual gust front location will be
co-located.

Therefore, the Slight Risk was maintained given these
uncertainties, and was only nudged slightly to the southwest to
account for latest observational data trends and hi-res guidance.

Lamers


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