SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1158 PM CST Tue Jan 05 2021 Valid 061200Z - 071200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE TEXAS COASTAL PLAIN... ...SUMMARY... A few severe storms are possible today into tonight along the western Gulf Coastline. Primary hazards are expected to be damaging wind gusts and a couple tornadoes. ...Synopsis... A mid-level trough is expected to become more negatively tilted as it amplifies and crosses the southern Plains region. Immediately ahead of the trough, a surface low is also expected to intensify across central Texas, with a 40+ kt 850 mb jet advecting a seasonably moist low-level airmass across eastern Texas. Elevated convection is expected to develop along the nose of the low-level jet shortly after 12Z and traverses the OK/AR/KS/MO border area. By early afternoon, as the trough takes on a more positive tilt, a 55-75 kt westerly mid-level jet is expected to rapidly overspread the warm sector across eastern TX. Deep forcing for ascent will encourage new thunderstorm development along and south of a warm front across east-central TX, and ahead of a cold front poised to be sweeping across the TX Hill Country. The strong westerly mid-level flow bisecting the south-southwesterly low-level jet will promote ample veering with height for organized thunderstorm updrafts, with a few severe storms likely. Meanwhile, another trough aloft, with multiple embedded mid-level impulses, will approach the West Coast. The first impulse is expected to reach northern California and southwest Oregon by morning. Despite deep-layer ascent, buoyancy is expected to be on the more marginal end, but should support a few lightning flashes. Later in the afternoon, a second impulse will approach the Pacific northwest, supporting a couple lightning flashes as well. ...TX Coastal Plain... A warm front will slowly drift northward across east-central Texas through the day, with modest destabilization expected across the warm sector. Surface temperatures are expected to peak into the mid 60s to near 70F, with lower 60s F dewpoints advecting northward from the Gulf of Mexico. With up to 6-7 C/km mid-level lapse rates expected to overspread the warm sector by mid-afternoon, resulting in up to 800 J/kg MLCAPE by afternoon peak heating. As the mid-level trough and associated deep-layer ascent approaches, the development of relatively more intense convection is expected around the 18-20Z time frame. While strong forcing along the cold front suggests that a squall line may develop through the afternoon along the Texas Coastal Plain, ample veering with height in the lowest 3 km suggests that semi-discrete supercells are possible, with at least transient low-level rotation expected. Any supercell structure that can become sustained and anchor to the warm front may ingest 150-300 m2/s2 effective SRH, with a couple tornadoes possible. Given the aforementioned strong flow fields aloft, adequate downward momentum transport within the squall may foster multiple instances of damaging winds. A Slight risk has been introduced to account for the wind/tornado threat. Towards the end of the period (roughly 07-12Z), modest buoyancy may advect inland along portions of the southeast LA/MS coastline, where deep-layer and low-level shear would support storm organization/rotation. Any storms that can manage to root in the boundary layer and become surface based may also pose a risk of a couple damaging gusts and perhaps a tornado. ..Squitieri/Darrow.. 01/06/2021
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