Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
331 AM EDT Wed May 8 2024
Day 2
Valid 12Z Thu May 09 2024 - 12Z Fri May 10 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM EASTERN TEXAS
TO THE LOWER MISSISSIPPI VALLEY...

...Eastern Texas to Lower Mid-MS Valley...
The strong spring system over the Central U.S. will begin to
elongate/stretch in a lengthy, positively tilted shortwave trough
by the start of the forecast period and sink southward toward the
region. Earlier convection from the previous day is likely to push
outflow boundaries through the region while another embedded
shortwave trough is expected to move through in the southern
stream. Altogether, this should put the region in a favorable
region of forcing for ascent. Deeper moisture is expected to pool
along/ahead of the surface boundaries and will be characterized by
PWs greater than 1.5", which is around 2 std above the
climatological normal for this time of year. With sufficient
instability developing that will overlap with the better forcing
and moisture, rounds of thunderstorms are expected to develop along
the boundary initially over eastern TX before slipping
south/southeast toward the Gulf Coast across portions of LA/MS/AL.
By this point in the storm system evolution, the flow is likely to
be more parallel to the overall storm motions and this could favor
some repeating rounds or training convection particularly over
portions of MS/AL. The environmental ingredients will support
intense rain rates over 1-2"/hr at times and the latest
probabilistic data shows potential for isolated 2-4" totals in a
relatively short period of time. While there remains some
uncertainty in the placement of the heaviest, no significant
changes were made to the Slight Risk area and the message for
scattered instances of flash flooding.

...Central Appalachians to the Mid-Atlantic...
Low pressure is expected to track from the lower Ohio Valley to
the eastern Great Lakes over the forecast period as shortwave
trough energy aloft and height falls over the region. A strong
southwesterly flow in the low levels will bring higher moisture,
characterized by dewpoints in the upper 50s to lower 60s and PWs
above 1", especially from the Central Appalachians and southern
areas of the Northeast. With the uncapped and warm/moist
environment, there should be scattered to numerous showers and
thunderstorms that develop that will be capable of producing
isolated/localized rain rates in excess of 1-1.5"/hr at times. This
could cause isolated flash flooding, particularly for some of the
areas that have seen recent heavy rainfall and more saturated
ground conditions as well as urban locations.

...Midwest to Western Great Lakes...
Deeper moisture pooled along an inverted trough / TROWAL slowly
moving through the region will be the primary focus for embedded
heavy rain cores that may lead to flash flooding. Tall/skinny CAPE
profiles, an axis of higher/deeper moisture, and warm cloud depths
will promote efficient rain producing showers and thunderstorms
that could total 1-2" in spots and a Marginal Risk was introduced
for portions of this region.