Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
329 PM EDT Sun Apr 6 2025

Day 1
Valid 16Z Sun Apr 06 2025 - 12Z Mon Apr 07 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
THE SOUTHERN UNITED STATES...

...16Z Outlook Update...
Main changes to the ongoing outlook were dictated by latest
convective trends. Biggest change is to confine the Moderate Risk
area to locations of central and southern Alabama that will
experience the greatest risk of training deep convection. MCSs
across that area are likely to slow and/or stall eastward
progression as mid-level forcing/ascent remain well west of the
region. Additionally, instability/moisture and deep convergence
will be maximized across the Moderate Risk area for much of the
afternoon and evening. At least one recent CAM suggests potential
for 5-7+ inches of rainfall near/south of Montgomery through the
early evening, which could cause locally significant flash flood
potential despite relatively dry antecedent conditions.

Outside of the Moderate Risk area, widespread clouds/showers and
the presence of a weak front across southeastern Kentucky and
vicinity has limited instability across Kentucky and West Virginia.
Rainfall is expected to occur in these areas and soils are
wet/susceptible to supporting efficient runoff. Limited instability
appears to be a mitigating factor for a larger flash flood risk.
The Slight Risk area has been reduced in size based on these
factors.

Lastly, a broad Marginal Risk area has been retained across
portions of the Mid-South into western/central Kentucky for this
outlook. While deeper convection and heavy rainfall potential has
shifted well to the east of the region, critical/sensitive ground
conditions exist as a result of the 8-14 inches of rainfall that
have occurred over the past 3-4 days. Widespread impacts from
excessive runoff continue currently. In environments like these,
even light rainfall (i.e., a quick 0.25 inch) can result in
exacerbation of flood impacts, and this could occur on at least an
isolated basis as forcing associated with an upper low centered
over western Oklahoma gradually approaches the region.

See the previous discussion below for more details.

Cook

...Previous Discussion...

Introduced a Moderate risk mainly across central and parts of
southwest Alabama today. Even though the synoptic-scale forcing
has finally dislodged the focus mechanism for heavy
rainfall...expectation is for storms initially in Mississippi and
far northern Alabama at the start of the period to slow in forward
motion as they pushes across parts of Alabama later today...leading
to some 3 to 5 inch totals with isolated higher totals. Confidence
in these amounts was boosted as more high- resolution CAMS in the
06/00Z model production cycle continued to depict focused, training
bands of convection from central Alabama with a few of them
showing localized amounts exceeding 6-8 inches. Of note was that
the 06/00Z guidance tended to favor higher amounts extending
southward rather than northeastward toward Georgia. The 00Z HREF
neighborhood probabilities tended to show a risk of 1 inch and 2
inch per hour rates at the start of the outlook period gradually
slow down later this morning with occasional upticks/downturns in
the probabilities across into the afternoon. This is still
conditional on when/where cloud cover allows for best instability
to form and on any lingering convective outflows that can serve as
a focus for renewed convection.

Bann

Day 2
Valid 12Z Mon Apr 07 2025 - 12Z Tue Apr 08 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHEAST US ON MONDAY...

19Z Update: Upon examination of the 12Z model and CAM guidance
suite, the inherited Marginal Risk area was expanded a little to
the north to include the greater Richmond, VA metro area and all of
Hampton Roads, and a modest extension to the west to include the
foothills of the southern Appalachians. The ARW has a slower exit
of some of the heavier rainfall through midday Monday, with the
potential for some 1-2 inch totals along and just northwest of the
Interstate 85 corridor. There may also be a second area of enhanced
rainfall across the coastal plain of North Carolina and extending
into southeast Virginia where higher PWs and instability will exist
ahead of the cold front, mainly south of Interstate 64. Depending
on how much convective training occurs, some instances of 2-3+ inch
totals will be possible on Monday before things taper off Monday
evening, with some lingering lighter rains after sunset and ending
overnight. One of the mitigating factors here is recent dry weather
and higher flash flood guidance, so the threshold of flooding is
higher and therefore this precludes the need for any Slight Risk
areas at this time.

Hamrick

...Previous Discussion...

Overall...the ongoing forecast remained on track and only some
minor adjustments were needed to account for a few pieces of
guidance which still favored a slower solution and, consequently,
higher rainfall amounts over a somewhat larger territory than in
the previous outlook. Still think that any lingering moderate to
heavy rainfall will continue to shift eastward on Monday as the
large scale flow pattern remains progressive. Current model QPF
generally remained in the 1.5 inch to 2.5 inch range with isolated
higher totals possible from far northern Florida northward into
the eastern portions of the Carolinas. The plume of 1.75+ inch
precipitable water values slowly decreases with time before being
shunted entirely off the Carolina coast Monday evening (and across
the central Florida peninsula late Monday night/early Tuesday
morning. Until that happens...moisture transport of deeper moisture
remains favorable to support a low- end risk of excessive rainfall
(especially in regions of poor drainage),

Bann

Day 3
Valid 12Z Tue Apr 08 2025 - 12Z Wed Apr 09 2025

The probability of rainfall exceeding Flash Flood Guidance is less
than 5 percent.

Bann


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt