Administrators NorthGeorgiaWX Posted December 9, 2023 Administrators Share Posted December 9, 2023 SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0203 PM CST Sat Dec 09 2023 Valid 092000Z - 101200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER WESTERN AND MIDDLE TENNESEE...AND SMALL PARTS OF NORTHERN MISSISSIPPI AND FAR SOUTHERN KENTUCKY... ...SUMMARY... Several tornadoes, scattered large hail and areas of damaging winds are expected through the afternoon into the evening from portions of the Ohio and Tennessee Valleys southward to the Lower Mississippi Valley and middle Gulf Coast. ...Lower MS Valley into much of TN and southern KY... Tornado probabilities have been increased within an Enhanced Risk for the unfolding tornado situation over western into Middle TN and far southern KY, and extending into northern MS. Cells have remained discrete and are currently within a developing instability plume, adjacent to an area of enhanced low-level shear over Middle TN, southern KY and northern MS. The combination of favorable storm mode, and fully-effective 0-1 SRH of 150-200 m2/s2 will pose a damaging tornado risk through the late afternoon. The greatest threat area may remain relatively concentrated due to the cooler air mass to the east, but an isolated strong tornado or two is possible. For more information, see mesoscale discussion 2305. ..Jewell.. 12/09/2023 .PREV DISCUSSION... /ISSUED 1036 AM CST Sat Dec 09 2023/ ...Gulf Coast/Lower Mississippi Valley/Tennessee Valley... Region is being increasingly influenced by height falls but otherwise resides between larger scale influences of an upper trough over the Upper Midwest and a positive-tilt trough over the southern High Plains. Increasing warm-sector moisture (generally lower to some middle 60s F surface dewpoints) ahead of a southeastward-moving cold front, along with considerable deep-layer/low-level shear, will be favorable factors for a long-duration severe risk through the afternoon into tonight. However, the likelihood of a complex/mixed quasi-linear convective mode casts uncertainty regarding the magnitude of the severe risk, particularly regarding a supercell-related sustained/focused tornado risk. It is also noted that some guidance suggests that 1-3km AGL winds may somewhat weaken by late afternoon/early evening within the warm sector, while noting SRH will still remain favorable for rotating/severe storms. Storms should continue to increase in coverage through early afternoon, initially near the front across Arkansas northeastward into western portions of Tennessee/Kentucky. Sufficiently steep mid-level lapse rates will support some hail potential, especially the first part of the day, but the tendency for storm clustering will otherwise limit this overall potential, as well as limiting prospects for more consequential hail magnitudes. As the boundary layer warms this afternoon, the potential for initially semi-discrete supercells will increase along with related damaging wind risk as well as tornado potential, which will persist through the afternoon/evening even with a quasi-linear convective mode. As warm-sector inhibition further weakens later this afternoon, additional deepening convection may develop within weak pre-frontal convergence/confluence regime, mainly across Mississippi into Alabama, with this development eventually merging with or taking over as the main convective band this evening. Similarly, pre-frontal confluence may support isolated supercellular development along the Gulf Coast/Florida Panhandle vicinity through late night hours/early Sunday, within a somewhat separate regime capable of a few severe storms. Read more View the full article Quote Link to comment Share on other sites More sharing options...
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