From Mike Powell@618:250/1 to All on Friday, September 06, 2024 08:11:00
AWUS01 KWNH 061154
FFGMPD
LAZ000-061501-
Mesoscale Precipitation Discussion 0981
NWS Weather Prediction Center College Park MD
753 AM EDT Fri Sep 06 2024
Areas affected...Central LA coastline
Concerning...Heavy rainfall...Flash flooding possible
Valid 061153Z - 061501Z
Summary...Periods of 3-3.5"/hr rainfall rates along the eastern
flank of a meso-low will drive a risk of additional flash flooding
along the Central LA coastline through 15z.
Discussion...Recent radar mosaic depicts an emerging mesoscale
circulation near Vermilion Bay with a slow northeastward track,
attached to a stationary front analyzed along the Gulf Coast. East
of this low, periods of 3-3.5"/hr rainfall rates are noted within
the warm sector of the front along the coastline.
RAP forecasts suggest this boundary will slowly lift inland over
the next several hours, ushering in 1000-2000 J/kg MUCAPE to
maintain periods of very heavy rainfall close to the coastline in
the presence of 1) 2.5-2.6" PWATS and 2) enhanced deep moisture
convergence east of the low. The last 3-4 runs of the HRRR appear
to have initialized the location of the and strength of the
circulation better, and suggest very localized rainfall totals
upwards of 4-6" are possible through 15z. Given 1-3 hour FFGs
generally in the 2-3" range, additional flash flooding may result
along the immediate coastline.