Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
250 PM EST Fri Nov 27 2020
 
Day 2
Valid 12Z Sat Nov 28 2020 - 12Z Sun Nov 29 2020 

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF 
THE WESTERN GULF COAST...

...West/Central Gulf Coast...

At the start of the forecast period (Sat-28.12z), ongoing activity 
from today into tonight will be lingering in the vicinity of the 
Western Gulf coast, along a well defined surface frontal zone.  
Strong southerly flow (West Gulf LLJ) along  responding to the 
approach of strong closed low height falls out of the Southern 
High Plains, but become increasingly weaker but still confluent 
along the frontal boundary toward the LA coast.  The LLJ will be 
pumping deep tropical moisture (1.75 to near 2" Total PWats) 
providing even 1000-1250 J/kg of instability at 12z within the 
axis of the LLJ toward the boundary.  As such ongoing activity may 
back-build and regenerate across the Northwest Gulf of Mexico and 
adjacent coastal SE Texas.  Uncertainty remains in the precise 
location of the frontal zone due to strength of outflow boundary 
today, yet the response for increased convection will pose another 
round as the surface wave develops and deepens throughout the day 
into Sunday morning, as it nears SW LA.  Hi-Res CAMs and global 
guidance remain trending a bit more off-shore with the most 
vigorous/surface rooted convection, however, there is ample signal 
particularly from the slower guidance (12z ECMWF) for stronger 
more northward shift and increased rainfall rates and totals 
potentially over areas affected by today's rainfall.  As such, 
very little has changed with the placement of the Slight Risk of 
Excessive Rainfall covering much of Southeast Texas into 
Southwest/South-Central LA to account for the continued model 
spread; although highest confidence/greater risk appears to be 
within the coastal counties in TX/parishes in LA.

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