Models Showing Strong Cap Friday Afternoon & Evening

SPC Day 2 Outlook Valid Friday, March 28, 2019

10:00 PM CDT | March 28, 2019

I just wanted to post a quick weather update this evening. Officially, the Storm Prediction Center has a marginal risk for the Red River Valley of North Texas on Friday. This is where a very conditional risk of severe weather *may* exist. It is far from certain, however. Let me explain. Yesterday, I discussed the severe weather season, watch vs warning, and the capping inversion. For storms to develop, parcels of air at the surface need to be able to lift upward and rise. When there is a layer of warm air above the surface, this prevents these parcels from rising. This is because the surrounding air is warmer than the parcels, and they stop rising. The warm air originates from the higher terrain of Mexico. When there is southwesterly flow aloft, it pulls this warm air across the state. Since the cap allows the air below to continue to warm and moisten, the potential instability increases. If the cap can break, explosive thunderstorm development can occur during the spring months. We saw this happen last weekend.

Capped Atmosphere Vs Uncapped Atmosphere

Next, I have attached a graphic from one of this evening's weather models. It is a forecast sounding valid at 7:00 PM Friday near Graham, which will not be too far from the dryline/cold front intersection. Like the first graphic, the red line is the temperature profile. I have circled the layer of warm air (the cap) that is being depicted by this model. For a cap to be breakable, there usually needs to be -50 j/kg or less of CINH (convective inhibition). This particular model shows CINH as great as -338 j/kg above the surface! To the north-northeast, this model shows CINH of -165 j/kg for Ardmore, Oklahoma. This is weaker but still fairly stout. The takeaway is that, if this strong cap verifies, it would shut down storm chances altogether late Friday afternoon and evening for Northwest/North Texas. As the cold front pushes southward Friday night, we will probably see a thin line of showers and isolated thunder develop along the boundary. Severe weather is not expected with the overnight activity.

00z NAM Graham, TX Forecast Sounding At 7:00 PM March 28, 2019

The reason for the cap strength is that the system will take a track too far to our north. If it had taken a more southerly track, the capping inversion would not be an issue. It is a double-edged sword in the spring for Texans. If you have a strong cap, you don't get severe weather. You also don't get any moisture. If you have a weak cap, you get some moisture - often with severe weather. I will keep an eye on the trends, but this is where the recent data has trended. For the latest local weather information for your area, please visit the National Weather Service website. You can also find Texas Storm Watch on Facebook. To help make sure you do not miss any updates, LIKE the Facebook page and join the Facebook group.