SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0158 PM CST Sun Feb 28 2021 Valid 282000Z - 011200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF NORTHEAST TEXAS INTO THE MID-SOUTH AND TENNESSEE VALLEY... ...SUMMARY... Damaging thunderstorm wind gusts, a few tornadoes, and large hail will remain possible through tonight from northeast Texas into the Mid-South and Tennessee Valley. ...20Z Update... Severe probabilities have been reduced behind a southeastward-moving cold front across parts of north-central/northeast TX and southeastern OK. Convection is still expected to increase in both coverage and intensity across AR into western/middle TN and northern MS this afternoon and evening, with all severe hazards possible. For more meteorological information on the short-term severe threat across this region, see Mesoscale Discussion 136. Farther east into central/northern AL and eastern TN, probabilities for damaging winds and a couple tornadoes have been modestly expanded to account for a line of storms along the cold front overnight that may still pose an isolated severe risk. ..Gleason.. 02/28/2021 .PREV DISCUSSION... /ISSUED 1015 AM CST Sun Feb 28 2021/ ...Synopsis... A positively-tilted upper-level trough within the Four Corners region will continue to sag southeastward today with a closed low aloft eventually developing across AZ/NM. A broad swatch of strong mid-level flow will exist from the Texas Big Bend into the Ohio Valley and lower Great Lakes. At the surface, a cold front extends from a central WI surface low southeastward into MO/OK and west TX. The front will be the main focus for severe weather this afternoon. ...ARKLATEX into the Mid-South... Upper 60s to around 70 F dewpoints are situated to the south of the southeastward moving cold front. Broken cloud cover, particularly in the ARKLATEX region has allowed temperatures to rise to the low 70s F. Areas that continue to see broken cloud cover will support 1500-2000 J/kg of MLCAPE this afternoon. Effective shear values of 50-70 kts will support organized storm structures. Deep-layer shear is generally parallel to the front and will generally favor linear storm mode, though supercells ahead of and embedded within the line are possible. Large hail will be possible, particularly early in the convective cycle. An area of greater hail risk is evident within the ARKLATEX given this morning's observed upstream mid-level lapse rates. Very large hail will be possible in this region. Damaging wind gusts will generally be the primary threat as convection evolves and grows upscale along the boundary. Low-level hodographs are supportive of a risk for tornadoes. Again, the linear storm mode and the weakness in the flow around 700 mb in both observed and forecast soundings should limit the overall potential. However, a few embedded supercell and mesovortex tornadoes within the convective line may occur. ...South TX... A conditional threat for large hail will exist from the Edwards Plateau into parts of South Texas. There is continuing uncertainty with whether storms will develop based on the latest guidance. However, deep-layer shear will be strong and forecast soundings indicate very long hodographs. Should storms develop, they will likely be elevated supercells behind the front.
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