FOUS30 KWBC 300826
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Fri Aug 30 2024

Day 1
Valid 12Z Fri Aug 30 2024 - 12Z Sat Aug 31 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG THE IMMEDIATE
GULF COASTAL AREAS OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

...Gulf Coast...
 
Moderate to heavy rainfall expected along the Gulf coast as deep
moisture advects northwards as a tropical low drifts in the
northwest portions of the Gulf of Mexico. Repeated rounds of slow-
moving heavy rain cells from the Gulf into the Texas/Louisiana 
border area east of Houston. Guidance depict 1 to 4 inches for 
areal average along the coast with isolated higher amounts 
possible. Some of the hi-res guidance have very isolated maximums 
of 6 to 11 inches. Areal averages of The focus for any potential 
flooding in this small area will be mainly in the urban areas 
around Beaumont/Port Arthur and points east. A Slight Risk is in 
effect from the Houston area east to Vermillion Bay. The 
surrounding Marginal risk was expanded to include areas near/west 
of Mobile.

...Great Lakes to Southern Rockies/Southern High Plains...

Convection will continue to be driven by deep gulf moisture that 
is streaming into the north/northeast towards the Great Lakes 
ahead of a well defined cold front pushing southward and eastward.
Precipitable water values of 2 to 2.25 inches are widespread from 
eastern Texas into Louisiana and Arkansas with an axis then 
extending north and east ahead of the front being some 2 to 2.5 
standard anomalies above climatology being an indication of the 
moisture-laden atmosphere still in place. There continues to be
some variance on where the deepest moisture gets funneled... with 
the above- mentioned upper level feature playing a key role.
Although the overall upper forcing still does not appear to be 
terribly robust, the diurnal instability supports at least the 
potential for locally excessive rainfall. A broad Marginal Risk was
maintained for this period from New Mexico/Texas to Wisconsin/New
York.

...Mid-Atlantic...

Portions of the region will have PW values greater than 2 inches
along with slow moving storms near the front. This environment
looks to be quite favorable for localized heavy rain with some of
the guidance showing probabilities of 3 inches/3 hour 30-50% 
across Northeast North Carolina. A Marginal Risk area was raised
for portions of southeast Virginia and northeast North Carolina.

Campbell


Day 2
Valid 12Z Sat Aug 31 2024 - 12Z Sun Sep 01 2024

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ALONG A SMALL
PORTION OF THE UPPER TEXAS COAST AND ADJACENT COASTAL LOUISIANA...

...New Mexico and Texas...

Showers and thunderstorms are expected to fire across portions of
New Mexico and Texas as the trailing cold front slows its
progression over the region. Some of these storms will be capable 
of producing hourly rain rates greater than 0.50/1 inch per hour. 
A Marginal Risk area was maintained for this part of the country.

...Gulf Coast...

Showers and thunderstorms will persist along the Gulf coast along
the nearly stationary tropical low and frontal boundary. The Slight
Risk area that was in effect has bee maintained as well as expanded
eastward to just east of Vermillion Bay. A broad Marginal risk area
extends northward and eastward as gulf moisture streams northward 
ahead of...and eventually intersects with...a cold front. Guidance
shows the highest amounts occurring from Saturday into early 
Sunday over portions of the Upper Texas coast and nearby Louisiana 
where a moisture plume with precipitable water values in excess of 
2.25 inches should be positioned at the start of the period (a 
nearly 2.5 standardized anomaly greater than climatology for this 
time of year and above the 90th climatological percentile along the
gulf coastline shown by both the ECENS and GEFS). 

...Lower Mississippi Valley to New England...

Two inch precipitable water values are forecast to extend from 
eastern Texas northeastward in a corridor to far southern Indiana. 
During the ensuing 24 hours...the northern portion of the front 
reaches portions of New England and the Mid-Atlantic region but the
southern portion of the front makes little progress into Texas and
Arkansas. Moderate to heavy rain will be possible for areas along
and ahead of the advecting boundary.

Given the amount of moisture and weaker steering flow, though, the
southern portion of the Marginal area has a better chance for 
excessive rainfall while storms to the north should be more 
progressive leading to a nominally low/more isolated excessive 
rainfall risk. The question remains whether or ot the stronger 
dynamics farther north will enhance amounts/rates. Some of the
guidance do signal a concentration of QPF and increasing threat for
excessive rainfall over portions of central pennsylvania.
Antecedent conditions will have lowered FFGs across this part of
the region thus becoming more favorable for growing flooding
concerns. After coordination with the local forecast office decided
to hold off for another cycle to reassess the need for a possible
upgrade to a Slight Risk for central portions of Pennsylvania.

Campbell/Bann


Day 3
Valid 12Z Sun Sep 01 2024 - 12Z Mon Sep 02 2024

...New Mexico and Texas...

Showers and thunderstorm activity is expected to linger with the
capability of producing excessive rainfall. The threat for
localized flood concerns will remain elevated thus a Marginal Risk
was maintained for this period.

...Gulf Coast...

The highest rainfall in this multi-day heavy rain event will have
likely already occurred however showers and thunderstorms are
expected to linger over the region near the coastline. A Marginal
Risk remains in affect from the southeast Texas coastline to
eastern Louisiana coastline.

...Eastern Tennessee Valley and Mid-Atlantic region...

Moderate to locally heavy rainfall will persist across portions of
the Mid-Atlantic as a cold front approaches the region. Some of
these areas will have lowered FFGs by this period and may be more
susceptible for additional rainfall to increase the threat for 
local flooding concerns. A Marginal Risk area was maintained from 
eastern Tennessee Valley to the Mid-Atlantic region.

Campbell
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