7:08AM:
Much advertised powerful storm system arrives today.
Moderate risk for severe thunderstorms today including strong tornadoes.
Will start off with the current wind event in progress. Getting frequent gusts at or above 40mph across SE TX this morning including 42 mph at Sugar Land in the past hour. Surface pressures continue to fall and are now lowering through the 29.60’s. Very strong pressure gradient will tighten a little more this morning and expect winds to come up even more. Already seeing 45-50mph across S TX up to about Rockport and 40-45mph from BPT east into LA. May see winds gust to 45mph across SE TX ahead of rapidly deepening surface low late this morning.
Severe Weather Threat:
Major outbreak of severe weather today across TX into the mid south.
Surface low pressure continues to deepen over SW TX ahead of powerful/very deep upper trough just S of Big Bend. Surface pressures have fallen to 29.40’s along the Rio Grande and this fast deepening surface low will move NE toward College Station and NE TX by late today. Very strong lift from the upper trough will come to bear across the very moist and increasingly unstable warm sector. Moisture flow off the Gulf has boasted dewpoints into the near 70 degree range with PWS climbing through the 1.8 in toward 2.0 in by early afternoon. Wind energy is very healthy with 0-1km helicity of 200-300 m^2/s^2 and 0-3km helicity up to 450 m^2/s^2. 60-70kt low level jet at 925-850mb with 125kt jet streak right over SE TX by early afternoon yielding strong speed and directional shear. NAM shows cap eroding by late morning with surface based instability growing to near 1500 J/kg.
Expect showers and thunderstorms to begin to develop by mid morning as lift overspreads the region. Strong shear will help promote updraft rotation and discrete nature of warm sector cells will yield high tornado potential late morning into early afternoon. Linear forcing along cold front arrives this afternoon as deep surface low tracks just N of SE TX. Expect explosive squall line development along I-35 this morning and this will move eastward this afternoon. 125kt jet streak and strong low level jet point to high end wind damage threat along this line. Near surface flow will back ahead of surface low pressure especially north of I-10 leading to the greatest tornado threat in that region. Also very moist air mass will lead to low LCL’s (cloud bases). Expect mixed convective modes with supercells developing in the warm sector ahead of the line and LEWPS, bows, and embedded supercells along and in the line. Corridors of wind damage will be possible especially near bowing line segments and near the apex of bows where mid level winds will be transported toward the surface. As mid levels cool large hail threat will also accompany many of the cells.
Timing remains generally from mid morning through early evening. I must say the models have done a very good job with this system pointing toward a large severe outbreak as early as last Wednesday.
Hydro/Flood Threat:
Upper trough is fairly slow moving and extremely high PW air mass is cause for at least some concern this morning with PWS over 200% above normal. Given rich inflow of tropical moisture off the Gulf and potential for slow moving lines of training thunderstorms flash flooding will be possible. Expect HP supercells to produce rainfall rates of 2-3 inches per hour. Will go with basin wide totals of 2-3 inches and isolated amounts up to 5 inches across the region. This will produce run-off into local bayous and rivers with some rises.
Extended:
Once we get through today nice mild weather on tap through the weekend with a slight chance of thunderstorms Saturday and Sunday.
Severe Weather Safety:
Tornado/High winds:
Seek strong shelter on the lowest floor of a house or building away from outside facing walls and windows…an interior closet or bathroom. If in an office building move to an interior hallway or stairway. Cover your body with pillows and blankets to protect from flying debris. Do NOT open windows in the event of a tornado…houses are not built air tight and the pressure differences will not cause your house to explode…it is the wind driven debris and wind loading on a structure that causes the damage. Abandon a vehicle for sturdy structure…if no structure is available find a low spot such as a ditch and lie as flat as possible….Do NOT hide under freeway overpasses as winds are funneled through such features resulting in wind tunneling and increased wind speeds.
8:31 AM:
Tornado Watch may be needed shortly.
Initiation of supercells with tornado potential is growing per recently issued SPC mesodisc. Strong height falls are spreading into SC TX ahead of powerful upper air storm system helping to erode capping over the region. Incredible low level helicity values noted over Matagorda, Brazoria, Fort Bend, and Wharton counties with 0-1km values upwards of 500 m^2/s^2. Per SPC strong damaging tornadoes will be possible as early at 1000am in the region bounded by Victoria, Austin, College Station to Galveston. Expect western zone of low level jet at convergent of 850mb jet streak to be the initiation point of rapid supercell development late this morning. Given highly shear low levels and very low LCL’s the tornado threat is high in supercells rooted on the western edge of the low level jet.
