SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1125 AM CST Sat Feb 27 2021 Valid 281200Z - 011200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY AND OHIO VALLEY... ...SUMMARY... Isolated strong to severe thunderstorms appear possible from parts of Texas into the Ohio Valley on Sunday. Damaging wind gusts should be the main hazard, but some hail and a couple tornadoes may also occur. ...Southern Plains into the Lower Mississippi and Ohio Valleys... Multiple mid-level shortwave troughs will move eastward across the CONUS on Sunday. One such shortwave trough is forecast to advance from the northern Plains and Upper Midwest to the Great Lakes by Sunday evening. Another shortwave trough should develop slowly southeastward from the Great Basin to the Southwest, eventually closing off over AZ/NM late Sunday night. The primary surface low is expected to develop northeastward across the Upper Midwest/Great Lakes and into southern Ontario by Sunday evening, in tandem with the previously mentioned shortwave trough. A cold front extending southward from this low should be located over parts of the lower OH Valley into the Mid-South and southern Plains Sunday morning. This cold front will shift slowly southeastward through the period across these regions, and it will likely provide a focus for convection. A fairly broad swath of enhanced mid-level southwesterly winds should overlie the frontal zone, but stronger forcing associated with both shortwave troughs is likely to remain north of the warm sector. Still, forecast soundings from northeast TX into the lower MS Valley/Mid-South and continuing into parts of KY indicate a veering and strengthening wind profile with height through mid levels. Upwards of 50-60+ kt of effective bulk shear appears likely, which is clearly sufficient for organized storms, including supercells. However, two potentially limiting factors remain apparent. One is the orientation of the front nearly parallel with the southwesterly mid-level flow. Tendency may be for storms to form along the front and then get quickly undercut while becoming elevated. The other limitation may be generally weak low/mid-level lapse rates and related modest instability. Even so, the presence of surface dewpoints generally in the 62-68 F range coupled with some diurnal heating south of the front should support MLCAPE around 250-1000 J/kg by Sunday afternoon. Current expectations are for mainly elevated storms to be ongoing across parts of the lower OH Valley Sunday morning in a strong low-level warm advection regime. Additional convective development appears likely along much of the length of the cold front by late Sunday morning or early afternoon. Short bowing line segments may pose an isolated damaging wind threat as they move east-northeastward. Even though low-level flow should tend to veer to southwesterly across much of the warm sector through the day, enough low-level shear may remain to pose a threat for a couple tornadoes with either semi-discrete storms or circulations embedded within the line segments. Eventually, this isolated severe threat should wane across the lower MS Valley and TN Valley Sunday evening as storms become mainly elevated behind the front. Finally, some hail threat may exist with elevated storms both Sunday morning and Sunday night across parts of TX into the ArkLaTex vicinity. Mid-level lapse rates should be modestly steepened across this region in advance of the shortwave trough over the Southwest, and deep-layer shear will likely be rather strong and uni-directional, potentially supporting elevated supercells. ..Gleason.. 02/27/2021
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