WPC Day 2 Excessive Rainfall Outlook
Risk of 1 to 6 hour rainfall exceeding flash flood guidance at a point
Updated: 2032 UTC Fri Feb 22, 2019
Valid: 12 UTC Feb 23, 2019 - 12 UTC Feb 24, 2019
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
335 PM EST Fri Feb 22 2019
Valid 12Z Sat Feb 23 2019 - 12Z Sun Feb 24 2019
...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE LOWER MISSISSIPPI VALLEY NORTHEASTWARD INTO THE OHIO VALLEY
AND THE WESTERN MID-ATLANTIC...
A strengthening negatively tilted mid-level low will lift
northeast from near the TX Panhandle into the Great Lakes Saturday
and Saturday night. Southeast of this feature, a surface low will
lift northeast, with warm moist advection occurring ahead of it.
Anomalously high PWAT air, forecast to reach 3 standard deviations
above the mean, will spread northeast as rich dewpoint air from
the Gulf of Mexico lifts northward on a robust LLJ of 50-60 kts.
As the upper low lifts northeast, enhanced mid-level diffluence
will spread eastward from the Mississippi Valley through the
western Mid-Atlantic states. This synoptic ascent will be aided by
a brief window of SBCape up to 1000 J/kg, supportive of intense
rain rates in convection as far north as Kentucky.
While the forcing should begin to eject northeastward quickly the
latter half of Saturday, any additional rainfall will occur over
pre-saturated grounds as recent heavy rainfall has lowered 3hr FFG
values to less than 0.25 inches from N MS into eastern TN. This
supports a southern extension of the SLGT risk despite a
relatively short window for heavy rain as dry air advects quickly
from the west. SREF probabilities for 1"/3hr are modest, but with
such low FFG values even moderate rain rates may be problematic.
Further northeast into the OH Valley and the Appalachians, rain is
expected to be more widespread under stronger synoptic lift, but
instability is more limited. This suggests more areal coverage of
rainfall than further southeast, but with lower rain rates. In
this area, FFG is still only around 1"/3hr, which combined with
the sensitive terrain of the mountains still warrants the SLGT
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt