FOUS30 KWBC 040824
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
424 AM EDT Wed Sep 4 2024

Day 1
Valid 12Z Wed Sep 04 2024 - 12Z Thu Sep 05 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR THE MISSISSIPPI
DELTA REGION AND ADJACENT GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The surface front will continue to be draped west to east across
the South provide focus for convection to spread from south Texas 
to Florida Peninsula. The latest guidance has continued to favor a 
less progressive eastward advancement with the precipitation 
shield. A blend of CAMs/global guidance has shifted the focus for 
heavier rainfall to be along the Upper Texas coast where they will 
be located closest to an organizing and elongated area of low 
pressure in the western Gulf of Mexico. General consensus has 2 to
5 inches along the coast between Corpus Christi and Lake Charles. Southeast
TX also still sports >80% soil moisture percentiles within the 
0-40cm layer according to NASA SPoRT-LIS, suggesting soils there 
would be more sensitive to 2-3"/hr rainfall rates.

Onshore flow across southeast Louisiana and southern Mississippi
could yield 1 to 2 inches as well. Locally heavy rains are likely,
especially from New Orleans east to Mobile. For the Florida 
Panhandle there will be an influx of anomalous PWs and modest 
instability along the stalled frontal boundary that may trigger 
additional thunderstorms capable of producing torrential downpours.
Areas most at risk for possible flash flooding will be areas whose
soils are more saturated following Tuesday's thunderstorm activity
and as far east as the Jacksonville metro area.

Campbell


Day 2
Valid 12Z Thu Sep 05 2024 - 12Z Fri Sep 06 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ALONG THE CENTRAL
GULF COAST...

...Gulf Coast and Lower Mississippi Valley...

The latest guidance keeps a slower progression of the QPF 
associated with an elongated area of low pressure in the northwest 
Gulf of Mexico. As such, the Slight Risk area was expanded further
west along the Gulf Coast, between Houston and Corpus Christi, to 
account for the westward trend. While dispersion is on the higher 
side on Day 2, there is a better consensus for heavier rainfall 
along the central Gulf Coast given the bulk of PWs >99th 
climatological percentile residing along the Gulf Coast. The region
is also closer to the surface-850mb southeasterly flow that will 
sustain a steadfast regime of low level theta-e advection into the 
nearby stationary frontal boundary. Additional forecast changes are
likely given so much of this setup lies with the development of 
low pressure along the Gulf Coast.

...New Mexico and Colorado...

Convection is expected to fire up ahead of an approaching cold
front thanks to PWs topping 0.75" and up to 500 J/kg of MUCAPE.
Soils across this part of the region are sensitive given recent
moisture and burn scars. The Marginal Risk area was maintained for
the localized flash flood potential for the afternoon and evening.

Campbell/Mullinax


Day 3
Valid 12Z Fri Sep 06 2024 - 12Z Sat Sep 07 2024

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE CENTRAL AND EASTERN GULF COAST...

...Gulf states and Southeast...

The frontal boundary is expected to slowly progress eastward during
this period will draped along the Gulf Coast and the Southeast.
Deep moisture will continue to override the boundary helping to
concentrate the heaviest QPF along the central and eastern Gulf 
coast. A Slight Risk remains in effect from southeast Louisiana to
the Florida Panhandle while a Marginal Risk area spans from south-
central Louisiana to northeast Florida and northward to South
Carolina. Areal averages of 1 to 2 inches will be common across the
region with the possibility of very isolated maxes of 3 to 5 
inches, especially along the coastline.

Campbell
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