SUMMARY...Heavy to extreme rain rates over 3 in/hr are expected to
occur within localized pockets over portions of eastern TX and
southwestern LA over the next few hours. Areas of flash flooding
are likely to continue through 17Z.
DISCUSSION...1245Z radar imagery over the lower Sabine River
Valley showed a small cluster of thunderstorms west and northwest
of LCH with 3 Wunderground observation stations reporting 3+
inches of rain in an hour two stations showing 5 inches in an hour
through 12Z. Thunderstorm coverage was expanding NNW from
southwestern LA into portions of eastern TX along an elevated
(925-850 mb) convergence axis with low level flow intersecting the
boundary from the west. Some of the "strongest" low level flow was
located just south of the DFW Metroplex and over southwestern LA
with about 10-15 kt oriented nearly perpendicular to the elevated
convergence axis with mean layer winds directing cells slowly
toward the southeast. SPC mesoanalysis data from 12Z showed MUCAPE
values of 500-1500 J/kg coincident with PWATs of 2.1 to 2.3+ inches.
Short term forecasts from the RAP show the low level flow
maintaining over the next few hours but with gradual weakening
through 17Z which may act to disrupt organization late this
morning. However, the environment will remain supportive of highly
efficient rainfall production until then with pockets of extreme
rain rates possible (3+ in/hr) and localized storm totals in
excess of 5 inches through 17Z. Areas of flash flooding will be
likely and trends will be monitored for additional MPDs as needed
later this morning.