< Day 2 Outlook
WPC Day 3 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2029 UTC Thu Feb 25, 2021
Valid: 12 UTC Feb 27, 2021 - 12 UTC Feb 28, 2021
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
354 PM EST Thu Feb 25 2021
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.
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt