Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EST Thu Feb 25 2021
 
Day 2
Valid 12Z Fri Feb 26 2021 - 12Z Sat Feb 27 2021 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF 
THE LOWER MISSISSIPPI VALLEY...TENNESSEE VALLEY...CUMBERLAND 
PLATEAU...SOUTHERN APPALACHIAN MOUNTAINS...AND THE CAROLINA 
PIEDMONT...

2030 UTC Update -- Have hoisted a Marginal Risk over the area, 
based on the latest guidance trends, particularly late in the 
period (00-12Z Sat) as the warm front lifts slowly northward 
Fri-Sat. PWs Friday night climb to 1.25+ inches, which is about 2 
standard deviations above normal. This as southwesterly low-level 
inflow increases to 50-55 knots, becoming nearly parallel while 
approaching the magnitude of the mean 850-300 mb low -- setting 
the stage for upwind propagation and cell training with elevated 
convective bands north of the surface warm front Friday night. 
Instability looks to be on the marginal side, with MUCAPEs 
generally averaging between 250-500 j/kg, which for the most part 
will cap 3 hourly rainfall rates between 1-1.5 inches.

Previous discussion..

The latest guidance continues to show Gulf moisture being 
transported northward within an increasing low level flow. The 
best mid-upper level lift will be present with the best lift 
occurring 00Z-12Z near northern Mississippi/western and central 
Tennessee as the associated front advances. Periods of moderate to 
locally heavy rainfall will be supported within this environment; 
with a couple of the hi-res guidance showing rain rates of 0.50 
inch/hour across parts of Arkansas into Mississippi and western 
Tennessee during the 12-18Z period. This is also where the swath 
of higher QPF is expected to occur, with WPC forecasting 1 to 2 
inches. During this time isolated locations may experience ponding 
or rapid runoff but the aerial coverage of flooding is not 
expected to be widespread. It will however increase soil 
saturation across the region and lower the FFG from the Southern 
Plains/Lower Mississippi Valley to the Tennessee Valley.

Hurley/Campbell

 
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt