NWS Weather Prediction Center College Park MD
1228 PM EDT Sat May 11 2019
Areas affected...portions of the western to central Gulf Coast
Concerning...Heavy rainfall...Flash flooding likely
Valid 111627Z - 112225Z
SUMMARY...Increasing coverage of convection is expected along
portions of the central Gulf Coast through 22Z with a few
locations picking up 2-4 inches of rain. Given wet antecedent
conditions, flash flooding is considered likely.
DISCUSSION...16Z surface observations placed a stationary boundary
from just off of the Texas coast into the lower Mississippi Valley
into a weak low near LLQ. Two weak surface waves were analyzed
along the boundary as well, one just west of GLS and the other
east of CRP. Farther east, an outflow boundary was noted just
south of Mobile Bay into far eastern LA, just north of Lake
Pontchartrain. Radar trends over the past 1-2 hours have shown a
rapid development and expansion of mostly elevated convection from
the middle Texas coast into southwestern LA. Meanwhile, scattered
showers and thunderstorms continue to develop in southern MS on
the cool side of the outflow boundary along the central Gulf Coast
into a region which has picked up 6-10 inches of rain over the
past 24 hours. 12Z soundings from CRP, BRO and LIX along with
recent GPS data show plenty of available moisture with
precipitable water values approaching or exceeding 2 inches along
and offshore of the western Gulf Coast.
Development of convection appears to be related to the advection
of low level moisture into southeastern TX from the western Gulf
and the approach of the exit region of an estimated 130 kt upper
level jet (per RAP analyses) centered over the southern Gulf of
California, with strongly diffluent flow over the TX Gulf Coast.
Flow in the 850-700 mb layer of 20-30 kt from the southwest will
mostly parallel storm motions of similar magnitude this afternoon.
This will cause training of heavy rain at times with pockets of
2-4 inches expected through 22Z. Convection is expected to
translate toward the east into Louisiana ahead of the tail end of
a weak 700 mb trough axis extending into eastern TX. Many of these
areas have seen much above average rainfall over the past few days
which will increase the likelihood of flash flooding from
additional heavy rain.
Otto
ATTN...WFO...HGX...JAN...LCH...LIX...MOB...
