The Storm Prediction Center (SPC) has issued an Enhanced Risk for parts of the Texas Gulf Coast.
Associated with the Enhanced Risk is a 5% Tornado Threat Ring.
The SPC is basing this threat on the approaching trough, a surface front that is moving north, and an outflow boundary from an existing system. Today’s forecast is quite complex due to the ongoing Mesoscale Convective System (MCS).
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows a large, broad trough pushing through Texas, with a particularly sharp edge over eastern Texas by 0Z. Ahead of this edge will be the most likely place for severe weather.
The 500 mb NAM chart shows a little Positive Vorticity Advection (PVA) this morning. Throughout the day, this vorticity maxima will continue east, thus there will be Negative Vorticity Advection (NVA) in its wake. The sinking air may clear up some of the ongoing convection, and help diurnal heating later today.
The 700 mb NAM chart shows plenty of rapidly-rising air by 18 Z to the east of the Enhanced Risk area. This large pocket of rising air will be where storm initiation occurs.
The 850 mb NAM chart shows only weak Warm Air Advection (WAA); the winds blow across the thermal gradient from warm to cold, but the gradient itself is not very strong. Even so, this is one source of the rapidly-rising air on the 700 mb chart.
The 12Z upper air sounding from Corpus Christi, TX, shows the threat today. The sounding shows an uncapped, damp atmosphere, with a surface dewpoint of 73 F and over 2100 J/kg of Convective Available Potential Energy (CAPE) already this morning. All of this led to a morning supercell parameter of 16.4. With little to no capping inversion in place, however, this energy may be quickly expended by the left-over convection from last night, and may have to rebuild throughout the day.
The deep-layer shear was 44 kts, and the low-level shear was 19 kts. The shear profile is beautiful; directional shear in the boundary layer, and speed shear aloft. This will support rotating storms and tornadoes.
TwisterData.com shows that the CAPE is not actually expected to climb very far inland. Near the coast, the CAPE will be the highest. This chart is probably the maximum CAPE today, at 0Z.
TwisterData.com shows a heavily sheared environment. The RAP has high shear throughout the day, so storms that form will likely rotate and become severe.
Currently, the surface observations (from the SPC Mesoscale Analysis Map) show the overcast skies and high dewpoints. I am not seeing the frontal boundary, but I’ll keep looking. Unisys has it drawn south of this chart, so that may be why I can’t find it.
The Supercell Parameter will only rise to 4 over the next six hours according to the RAP. This will be limited in this time frame due to the cloud cover.
The visible satellite imagery shows the large MCS over central Texas. This may dampen diurnal heating, though it will also generate a few outflow boundaries in the Enhanced Risk area.
The enhanced infrared satellite imagery shows that this MCS has a high, cold top.
The water vapor satellite imagery shows that the dominant moisture feature is that MCS over central Texas.
Overall, I expect that there will be storms today. However, I expect that today would be a very difficult chase. I think that there will be supercells embedded in an MCS, making for a very dangerous situation. Given the existing MCS, the high dewpoints, and low LCLs, the supercells will be of High Precipitation (HP) variety.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC