Weather Discussion for 02/17/2017

Weather Discussion for 02/17/2017

Analysis: A few light rain showers are occurring this morning over eastern portions of Texas. These showers are occurring in response to an upper-level low moving across Texas. While moisture is limited across most of the state, enough moisture was noted on the coastal sounding sites at Brownsville and Corpus Christi to get these showers going.

Surface analysis valid February 17, 2017 at 1600Z.
500 mb analysis valid February 17, 2017 at 1200Z.

Forecast: The upper-level low should exit the state by Saturday morning, leading to riding aloft. This ridging will bring warm and dry conditions to the area tomorrow. The big story during the next week continues to be the potent, high-amplitude upper-level trough that will dig into the region beginning Sunday morning. This trough should lead to abundant lift across the region. A developing surface low over Montana will allow for warm, moist air to move north from the Gulf of Mexico. This will lead to widespread rain and thunderstorm development across much of Central and East Texas by Sunday afternoon. Model runs this morning have been more aggressive with convective instability. Both the GFS and 4 km NAM show a corridor of 1000+ J/kg surface-based CAPE reaching as far north as I-20 in North Texas, with values of over 2,000 J/kg reaching as far inland as Austin. The NAM forecast sounding for Austin shows large CAPE of over 2,000 J/kg, and 0-1 km storm relative helicity of near 200 m2/s2. This environment should be favorable for at least a marginal severe weather threat (which has been highlighted by the Storm Prediction Center in their Day 3 Outlook). The caveat on the forecast sounding is that the mean wind is parallel to the approaching Pacific cold front (the primary forcing mechanism). This means that thunderstorms would likely grow upscale into a squall line quickly. Still, given the favorable parameters, damaging wind gusts and hail will be possible. In addition to the severe weather threat, precipitable water values will increase to well over 1.50 inches across much of Southeast Texas, which will likely lead to heavy rainfall. The models have backed off a bit during the past 24 hours on the amount of precipitable water, as well as shifted the largest amounts east, but 2+ inches of rainfall will still be likely across much of Southeast and East Texas on Sunday night and Monday.

4 km NAM forecast sounding for Austin, TX valid February 20, 2017 at 0000Z (Sunday at 6:00 PM CST). Image source: Pivotal Weather.
4 km NAM forecast surface-based CAPE valid February 20, 2017 at 0000Z. Image source: Pivotal Weather.

Beyond Monday, ridging will build back in over Texas through the middle of the week, bringing warm and dry conditions.

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