SPECIAL: Flash flood threat increasing in Austin

Weather Blog

AUSTIN (KXAN) — See the special advisory from the National Weather Service Weather Prediction Center.

Further south, another corridor of enhanced rainfall is possible in the vicinity of the Balcones Escarpment or the I-35 corridor around Austin TX.

Surface observations implied a region of enhanced low-level convergence and a psuedo-warm front from Llano County east to Burleson County. North of this boundary, surface winds were backed with temperatures in the mid-upper 60s and dense low-level cloud cover.

To the south, more mixing was occurring with southerly winds and temperatures rising into the mid-70s. In the same area, RAP analysis showed a maximum of boundary layer warm air advection and surface thetae advection.

This may increasingly focus convection in a concentrated area as it moves from Texas Hill Country into the I-35 corridor.

The inflow region near and south of San Antonio was characterized by fairly strong instability (CAPE in excess of 2000 j/kg) and a pocket of higher PWs from 1.7-1.9 inches (GPS-PW observations).

This should sustain vigorous convection into the early afternoon, with the potential for hourly rain rates exceeding 2 inches at times.

Hi-res models appear to be underestimating the organization and vigor of ongoing convection. The squall line appears to have a cold pool, with KBBD (just behind the line) reporting a 61 degree temperature at 15Z, and that should enable continued maintenance of strong updrafts on the downshear flank of the line. This area may also be more vulnerable to flash flooding given recent heavy rainfall.

Many areas from Kerrville and Killeen east to Austin and College Station have seen 6-10 inches of rain in the past couple weeks, and Flash Flood Guidance is lower in these areas (2-3 inches in 3h).

Multiple hi-res models show 3 inches of rain in 3 hours in this area, despite generally underestimating the intensity and coverage of ongoing convection.

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