Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EST Thu Feb 25 2021
 
Day 3
Valid 12Z Sat Feb 27 2021 - 12Z Sun Feb 28 2021 

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE 
SOUTHERN PLAINS INTO PORTIONS OF THE LOWER-MID MISSISSIPPI VALLEY, 
THE NORTHERN TENNESSEE VALLEY, SOUTHERN OHIO VALLEY, AND WESTERN 
SLOPES OF THE CENTRAL APPALACHIANS...

2030 UTC Update -- Nudged the bottom portion of the Marginal Risk 
area a bit farther northward based on the latest trends in the 
guidance, while expanding the outlook area slightly downstream to 
include more of the lower OH Valley and western WV. Elevated 
instability north of the warm front at this appears modest at 
best, averaging ~250-500 j/kg over the outlook area, with pockets 
closer to 1000 j/kg. This should be more than sufficient to 
support 1.5+ inches of rainfall within a 3 hour period, especially 
with some training likely Sat night given the uptick in 
southwesterly 1000-850 mb flow into a strengthening low-level 
frontogenetic zone within the right entrance region of an upper 
level jet streak. 

Previous discussion below...

Scattered to widespread rain will persist during the day 3 period 
after spreading 1 to 2 inches across the region the day prior. 
This antecedent moisture will have likely lowered flash flood 
guidance across the Lower Mississippi and Tennessee Valleys where 
an additional 1 to 3 inches are forecast. Although the hourly 
rates across this region are expected to be less than 0.50 
inch/hour, precipitation of this magnitude will lead to an 
increased threat for flash flooding to develop. In coordination 
with the local forecast offices from far northeast Texas to 
eastern Kentucky/Tennessee a Marginal Risk area was hoisted. This 
area will continue to be monitored as the threat of moderate to 
heavy rainfall continues into the day 4 period.

Hurley/Campbell

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