Conventional satellite imagery depicted an upper low digging slowly southeast into the Central Rockies. Meanwhile, an active subtropical jet was focused farther south underneath it lifting northeast across northern Mexico and downstream across the wind across the Gulf Coast states.
GOES Sounder Air Mass RGB animation showing the evolution of heavy thunderstorms over the Gulf Coast centered near Houston (0600 UTC 04/16/15 – 0600 UTC 04/17/15).
While there was broad warm air advection, instability and a very moist airmass focused across the western Gulf Coast region, there were no identifiable features on the larger scale in conventional satellite imagery that suggested a forcing mechanism for organized convection to initiate. However, upon closer inspection of morning GOES-RGB airmass imagery, a subtle and small scale, but identifiable feature appeared that reflected a shortwave impulse. This impulse was tracked crossing the Rio Grande river at 12Z/16, and in conjunction with deep moisture and diurnal instability proved to be the catalyst for increasingly organized convection after 18Z/16 that continued past 00Z/17 along the Upper Texas coast and coastal areas of southern Louisiana. The result was 4 to 8 inches of rain, and flash flooding in the suburbs of Houston, TX.
GOES Sounder Air Mass RGB valid at 1200 UTC on 04/16/15. The red circle denotes the subtle shortwave that initiates downstream convection.
GOES-13 Water Vapor image valid at 1215 UTC on 04/16/15. The red circle denotes the same shortwave identified in the Air Mass RGB image.
GOES Sounder Air Mass RGB image valid at 1800 UTC on 04/16/15.
GOES-13 Water Vapor image valid at 1815 UTC on 04/16/15.
GOES Sounder Air Mass RGB valid at 0000 UTC on 04/17/15.
GOES-13 Water Vapor image valid at 0015 UTC on 04/17/15.
The NSSL 24-hour QPE product valid at 1200 UTC on 04/17/15.
Thanks for reading!
~ Andrew Orrison (WPC)
Satellite Liaison Blog 