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FOUS30 KWBC 131600
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Mon May 13 2024

Day 1
Valid 16Z Mon May 13 2024 - 12Z Tue May 14 2024

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE CENTRAL GULF COAST...

16Z Update...
Stretched Moderate, Slight, and Marginal outlooks
east-west along the Gulf Coast into south Texas and north Florida
based on radar trends and 12Z CAM consensus.

An mid-level low over central KS this morning will drift east to MO
through tonight with an open Gulf of Mexico bringing moisture north
across frontal boundaries near the Gulf Coast up into the Midwest.


...Gulf Coast...

A powerful MCS continues to work east along a stationary front over the
central Gulf Coast this morning with particularly heavy rain as
noted in MPD 264 which is out until 18Z. This MCS will push the
frontal boundary to or south of the Gulf Coast, but there is still
confidence on more scattered activity to continue along the Gulf
Coast this afternoon ahead of a cold front from the central US low
that sweeps east from Texas tonight. The Moderate Risk was shrunk
toward the central Gulf Coast while also expanding east a bit more
over the FL Panhandle on account of radar trends and the 12Z CAM
consensus.

Convective activity ahead of this cold front has initiated over
south-central TX east of Del Rio with a now organized multi- cell
cluster of heavy thunderstorms that are moving east over the San
Antonio metro as noted in MPD 265 which is out until 2130Z.

This south-central TX activity will push east to the Houston metro
this afternoon along with other development along the stationary
boundary just inland from the Gulf Coast. The Marginal and Slight
Risks in TX were stretched east to account for this activity and
12Z CAM consensus for its development.

...Mid-South and Southeast...

The Marginal Risk was able to be trimmed based on update
positioning of the prefrontal activity on the west side and the 12Z
CAM consensus for heavier rain over the Southeast. Much of the Day
1 Marginal over the southeast was removed based on increased
confidence on less rainfall this afternoon over the far southern
Appalachians as well as with timing for overnight activity
approaching the TN Valley overnight.

The cold frontal convection will have a fast forward speed across
Arkansas and southern Missouri. Should the convection move over a
particularly sensitive area, isolated flash flooding is possible.


...Portions of the Midwest...

Maintained the Slight from KC to Chicago though this is certainly
low end given 12Z CAM QPF progs of generally 1-2" with local 3"
through this swath which follows the warm frontal interface ahead
of the developing low over Kansas and eventually southern Missouri.
Convection in the warm sector will collide into the warm front,
which will remain largely stationary. This in turn may result in
localized training along that boundary.

Further monitoring of localized flash flood concerns for sensitive
areas such as the St. Louis metro area.


Jackson

Day 2
Valid 12Z Tue May 14 2024 - 12Z Wed May 15 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
FLORIDA PANHANDLE...

...Florida Panhandle...

Storms will be ongoing across the Florida Panhandle to start the
period Tuesday morning. They are likely to be progressive, moving
along to the east across north Florida through the morning. The
uncertainty is how much convection develops behind the first line
of storms. The broad unidirectional southwesterly flow would bring
any additional convection into the Florida Panhandle through the
day Tuesday. When added to any rainfall the area gets Monday night,
this could lead to widely scattered instances of flash flooding,
particularly between Pensacola and Tallahassee. The area has very
high FFGs, even though soils are wetter than normal. Due to the
unusually high PWATs associated with the Gulf moisture streaming
into the Panhandle ahead of a cold front which will clear out the
convection to the east by Tuesday night, any storms that form will
be capable of rates of 2 inches per hour.

...Portions of the Southeast, Mid-Atlantic, and Ohio and Tennessee
Valleys...

North of the Florida Panhandle, the cold front will be racing
eastward more quickly than previous model runs had indicated. Thus,
now most of the heaviest convection is expected to be largely
offshore of the Carolinas and Georgia, and therefore are much less
likely to cause flooding. The greatest threat of flooding from
these storms would be along the immediate coast, but given the
sandy soils, are unlikely to result in flash flooding. Thus, the
inherited Slight for Georgia and the Carolinas was downgraded with
this update.

Further north and west, the parent low and associated upper level
cold air will result in widely scattered convection Tuesday and
Tuesday night for the Ohio/Tennessee Valleys and over to the Mid-
Atlantic. Instability will be modest, but non-zero along with
modest atmospheric moisture. Thus, any storms that form, especially
those that undergo cell mergers or training, have the potential to
produce isolated instances of flash flooding. The inherited
Marginal risk was kept largely the same, but was expanded a bit to
include the DC and Baltimore metros due to low FFGs from recent
heavy rainfall.

Wegman

Day 3
Valid 12Z Wed May 15 2024 - 12Z Thu May 16 2024

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR MUCH OF THE
SOUTHERN PLAINS AS WELL AS FOR PORTIONS OF NORTHEAST FLORIDA...

...Southern Plains...

Convection that develops on the leading edge of return flow
associated with an LLJ that will move north along the west Texas
dryline is expected to be isolated to widely scattered in coverage
Wednesday afternoon, becoming more numerous by Wednesday night.
There remains considerable uncertainty as to how this convection
will organize...and given the highly variable nature of the soils
across north Texas and western Oklahoma, confidence is not yet
there for more than a Marginal Risk at this time. However, with
better confidence a Slight may be needed, particularly in north
Texas. For western Oklahoma, while similar coverage and severity of
convection is expected...very dry soils there will be better able
to absorb any rainfall, and so upgrades here are much less likely.

...Northeast Florida...

The trailing end of a cold front will stall across Northeast
Florida on Wednesday. South of the front, abundant Gulf moisture
will stream eastward along the boundary, providing a focus for
convection to develop and move. Thus, a small Marginal remains for
northeast Florida, as this area is difficult to flood due to flat
and largely swampy terrain, but any training convection in this
area could result in flash flooding, particularly in any urban
areas impacted.

Wegman


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