Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1143 AM EDT Fri Apr 03 2020
 
Day 1
Valid 16Z Fri Apr 03 2020 - 12Z Sat Apr 04 2020 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER SOUTHERN 
TEXAS...

16z Update: A Marginal risk will be maintained for southern TX 
ahead of the southward shifting cold front. As the corridor of 
strong low level convergence near the front pushes southward, it 
enters into a higher PW/CAPE environment, and also begins to 
interact more with the exit region of the subtropical Pacific jet. 
This should allow for an expansion of convective activity by early 
this afternoon. Mean flow is parallel to the front (west to east), 
which should allow for some periodic training. Although the 
southward progression of the front should shift things southward 
and erode instability, which should limit the duration of heaviest 
rain. Thus while a few flash flood issues appear probable given 
the environment in place, the coverage of the heaviest rains (3"+) 
should stay isolated enough to keep flash flooding localized in 
nature. Thus think the Marginal risk should suffice. By this 
evening into the overnight the front should slow over far southern 
TX, which may set up the potential for training there and possibly 
an uptick in the flood risk. Although this part of the forecast 
remains a bit more uncertain and FFG is higher here...thus a 
Marginal should cover it for now.

Chenard

...Previous Discussion...

Convection is expected to become increasingly active day 1 across 
eastern and South Texas along and ahead of the strong cold front 
pressing southeast across the Southern Plains.  Widespread 
instability, mu-capes 1000-2000+ j/kg, LI's -4 to -8 expected 
along and ahead of this boundary in an axis of PW values 1.5-2.5 
standard deviations above the mean.  This will be supportive of 
locally very heavy rainfall amounts and localized flash flood 
potential.  Precipitation has been slightly below average across 
these regions over the past week, resulting in stream flows at or 
below normal as per the National Water Model.  While there are a 
lot of details differences among the latest models, there is 
strong signal for the potential of locally very heavy rainfall 
amounts.  Hourly rainfall totals from the hi res guidance are 
showing isolated 1-2"+ totals and isolated storm totals of 3-5",  
but again with large differences in details of placement.  With 
respect to changes from the previous issuance, the marginal risk 
area was expanded slightly northeastward into southwest Arkansas 
for activity across this area early in the day 1 period.  The 
marginal risk area was also extended to the central Texas Gulf 
coast and farther southward into South Texas to cover the spread 
in the latest model solutions.

Oravec
 
Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt