Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
335 PM EST Fri Feb 22 2019
 
Day 2
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 
risk.


Weiss



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