Significant severe weather outbreak likely on Saturday across east TX and LA including the potential for large damaging tornadoes.
Strong to severe thunderstorms possible over SE TX N of US 59 on Saturday.
Surface cold front has pushed into the Gulf of Mexico this morning allowing a much drier air mass to filter into the region. SW flow aloft is starting to overrun the cool and dry air at the surface and radar is showing a few showers around Matagorda Bay. A potent storm system over the SW US will eject across TX on Saturday and result in a significant severe weather outbreak.
Surface front over the Gulf will begin to back northward this afternoon as a warm front as surface pressure fall over NW TX ahead of the approaching upper level trough. Not expecting much shower activity today, but increasing lift tonight will likely result in showers developing and moving northward off the Gulf. Surface warm front placement will be critical on Saturday for severe weather. Currently expect the warm front to move northward and reach US 59 by early Saturday and then a line from College Station to Lake Livingston by early afternoon. Low level winds will be backed out of the E/ESE near the warm front and then overrun by WSW/SW winds around 5000 ft resulting in significant wind shear through the lowest part of the air column. Instability rapidly increases Saturday with CAPES values of 1000-2000 J/kg over the region. As lift increases from the approaching upper level trough and focuses along the retreating warm front severe thunderstorms will develop. Wind shear supports updraft rotation and think the primary mode will be supercells along the warm front with a very large hail and tornado risk. Will focus the highest risk along and N of HWY 105 and really more toward Lake Livingston with the best chances for tornadoes.
South of the warm front, the warm sector air mass will be unstable, but a weak capping inversion will advect into the region from the SW resulting in a fairly sharp cut off in the rain and thunderstorm chances. Severe thunderstorms will be possible in the warm sector south of the warm front and ahead of an afternoon cold frontal passage…mainly along and N of US 59. South of US 59, think the air mass will remain capped and only showers will be possible across Jackson, Matagorda, and Brazoria Counties. Severe threat in the warm sector is more conditional on Saturday and will require ingredients to come together at the right time. A review of the short range models show a line of storms, and line segments moving across the area from WNW to ESE Saturday afternoon and think some of these storms could become severe with large hail and damaging winds the main threats. Any isolated discrete cell that can develop in the warm sector could become tornadic, but think the highest tornado threat will focus along the warm front which by Saturday afternoon will be NE of our area.
As far as rainfall…fast overall system and cell motions should negate much of a flood threat. Maximum totals of 1-2 inches N of HWY 105 with amounts of .50 to 1 inch south of HWY 105 to US 59 and then less than .50 of an inch S of US 59 across the coastal counties.
NOTE: should the surface warm front be slower in lifting northward early Saturday, a much greater severe and tornado risk would encompass a larger area of SE TX. The movement of the warm front will need to be monitored closely for any refinements of the risks over our area.
SPC Saturday Severe Weather Outlook:
