Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
356 PM EDT Sun Apr 21 2019
 
Day 2
Valid 12Z Mon Apr 22 2019 - 12Z Tue Apr 23 2019 

...A MARGINAL RISK FOR EXCESSIVE RAINFALL IS IN EFFECT FOR 
PORTIONS OF EASTERN NEW MEXICO, NORTHERN TEXAS AND WESTERN/CENTRAL 
OKLAHOMA...
...A MARGINAL RISK FOR EXCESSIVE RAINFALL IS IN EFFECT FOR 
PORTIONS OF THE UPPER GREAT LAKES REGION...

...Eastern NM/Northern TX/Central OK...

A surface cyclone will develop across west Texas along a residual 
cold front draped from a surface low moving into the Great Lakes 
region. Southerly winds of 30 to 40 kts will transport rich Gulf 
moisture northward pooling over the central U.S. During this time 
precipitable water values will be on the order of 1 to 1.25 
inches, equating to roughly 1.5 standard deviations above the 
seasonal average. Instability noted by surface based CAPE values 
nearing 2000 J/kg, modest shear coupled with a fairly potent jet 
streak will lead to strong forcing for ascent and organized 
convection over a portion of the Southern High Plains. As the 
surface low develops and the front slowly moves south, convection 
will develop Monday afternoon.  The greatest area of concern is 
for convection across eastern New Mexico where FFG is around 1.5 
inches per hour in some locations.  Based on the ingredients 
discussed and high resolution model output, hourly rain rates of 
over 1.5 inches/hour seems plausible with some slow moving cells 
exacerbating the flood potential.  With a bit of uncertainty with 
respect to coverage and intensity of convection, kept this area 
under a Marginal Risk.  Though FFG is lower across northern TX and 
west/central Oklahoma, there could be high rain rates (1.5+ 
inch/hour) associated with the convection that could result in 
localized flooding concerns. Given the slow movement of the front, 
training of precipitation could also be problematic.    

...Upper Great Lakes...
A stalled boundary draped across the southern shore of Lake 
Superior aided by isentropic lift north of the apparent surface 
low will result in continued rounds of moderate, to at times, 
heavy rain.  With ongoing precipitation and another couple of 
rounds over the next 36 hours, the soils will be quite sensitive, 
not to mention the vulnerability associated with runoff from 
snowmelt.  Therefore, while high rain rates are not expected 
(forecasting <0.5 inches/hour), the antecedent conditions paired 
with an additional 1-2 inches of precipitation will likely lead to 
minor flood concerns in urban areas.  For these reasons a Marginal 
Risk was issued for locations adjacent to the southern shore of 
Lake Superior.  

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