Mesoscale Precipitation Discussion 0850
NWS Weather Prediction Center College Park MD
134 AM EDT Tue Aug 23 2022
Areas affected...southeastern/eastern TX into northern LA and
western MS
Concerning...Heavy rainfall...Flash flooding likely
Valid 230532Z - 231015Z
SUMMARY...Periods of heavy rain with peak rainfall rates of 2-3
in/hr (locally over 3 in/hr) are likely to impact portions of
southeastern TX into western/northwestern LA through 10Z. Heavy
rain from northeastern TX into northern LA and western MS will
also be possible atop areas of saturated soils from recent heavy
rainfall. Flash flooding will remain likely for these locations.
DISCUSSION...Regional radar imagery at 05Z showed a broken axis of
heavy rain from the Piney Woods region of TX into northwestern LA,
located just ahead of a low located near LFK. Rain cooled
boundaries/effective frontal segments extended from the low,
marked by about 5 to 10 degrees of temperature/dewpoint contrast
across the boundary. MRMS-derived rainfall rates were 2 to 3+
in/hr within an anomalous plume of moisture marked by precipitable
water values between 2.2 and 2.4 inches (00Z sounding data and
recent GPS observations). 15-25 kt of 850 mb flow was converging
along the current axis of convection while aloft, placement of an
elongated ridge axis just south of the Gulf Coast was supporting
diffluent flow in the upper levels from the western and central
Gulf Coast to about 150 miles inland.
A slow moving 850-700 mb low located over northeastern TX is
forecast by the RAP to stay in roughly the same location over the
next 6 hours, while low level flow over eastern TX and western LA
increases in magnitude slightly through 12Z while expanding in
coverage. Sufficient vertical shear exists across the region to
support the development of embedded mesocyclones within the
precipitation axis which will be capable of increasing rainfall
efficiency within an already highly favorable environment for
heavy rain.
Over the next 3-5 hours, a slow eastward translation is expected
with the heavy rain axis currently over northwestern LA into
eastern TX, with peak rainfall rates of at least 2-3 in/hr and 5
hour additional rainfall totals of 3-6 inches possible. In
addition, thunderstorms are expected to expand along a west-east
low level convergence axis located near the AR/LA border in the
08-10Z time frame. Instability to the north is expected to remain
weak (< 1000 J/kg) but this region has seen 3-6 inches of rain
over the past 24 hours which has lowered flash flood guidance to 2
inches in 3 hours for a few locations.
Otto
ATTN...WFO...HGX...JAN...LCH...LZK...SHV...
ATTN...RFC...ABRFC...LMRFC...WGRFC...NWC...
LAT...LON 33579363 33529207 33389123 33209053 32959023
32439020 31949061 31689227 30949330 30079409
29549501 29469600 29919623 30409585 31139506
32109455 33169489 33569454