Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
410 AM EDT Fri Apr 03 2020
 
Day 3
Valid 12Z Sun Apr 05 2020 - 12Z Mon Apr 06 2020 

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS 
OF SOUTHWEST CALIFORNIA...

...Southwest California... 
A deepening closed mid level low approaching the north central CA 
coast during Day 3 interacts with a deepening moisture plume to 
produce heavy to locally excessive rainfall across upslope region 
of southwest CA. A 20/30 knot low level southwest flow focuses 
0.75 inch precipitable water air (which is between two and three 
standard deviations above the mean) on the upslope areas of Santa 
Barbara, Ventura and far western Los Angeles counties ahead of 
surface cold front in the 06/06z to 06/12z time frame. This timing 
is nearly coincident with the best synoptic scale lift in advance 
of the closing mid level low. 

At this point, model soundings are not showing much in the way of 
instability (with 00z GFS model soundings indicating 100 J/KG of 
less of MUCAPE) ahead of the front, which is not unusual this far 
out. Steepening mid level lapse rates could allow for instability 
rooted above the surface to develop just ahead of the front. Model 
soundings did show a moist column through at least 400 mb, which 
may support more efficient rain makers in the cells that do 
develop ahead of the front.

This could support hourly rainfall rates approaching 0.50 inches, 
especially toward 06/12z. Rainfall rates this high could result in 
flood issues over burn scars in Santa Barbara and western Ventura 
counties. After collaborating with WFO LOX, a Marginal Risk was 
placed over the upslope region of the abovementioned counties for 
Day 3.

Hayes
 
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt