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Friday, October 15, 2021

SPC Oct 15, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0235 PM CDT Fri Oct 15 2021 Valid 152000Z - 161200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE MID-SOUTH/TN VALLEY AS WELL AS PORTIONS OF THE OH VALLEY INTO WESTERN NEW YORK... ...SUMMARY... Isolated severe gusts and hail, along with a marginal tornado threat, are expected today from parts of Arkansas across the Ohio Valley into western New York. ...20Z Update... ...Mid-South/TN Valley... Recent surface analysis places a low over the MO Bootheel/far northeast AR vicinity, with a cold front extending southwestward from the low across central AR and into northeast TX. Thunderstorms have developed along this front, as well as within the broad warm sector ahead of it. Expectation is for the front to continue eastward as the surface low moves east-northeastward and the upper trough approaches. The front will likely overtake the preceding storms later this evening, while increased large-scale forcing for ascent help form a more coherent line. This could result in a brief period of a more organized linear structure in the western TN vicinity before limited instability and nocturnal stabilization result in a more outflow dominant storm structure. However, the limited buoyancy and relatively weak/veered low-level flow should preclude robust organization and the potential for widespread severe that would merit an upgrade to ENH. ...Middle OH Valley into western New York... Recent surface analysis places a low about 20 miles southeast of TOL. A cold front extends southwestward from this back across IN, while a warm front extends northeastward along the southern coast of Lake Erie and into western NY. Showers and thunderstorms will continue to develop within the warm sector between these fronts. Instability is modest but wind profiles support supercell structures with any more robust/prolonged updrafts. As a result, the threat for isolated wind damage and/or brief tornadoes will continue through the afternoon into the early evening. ..Mosier.. 10/15/2021 .PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Oct 15 2021/ ...Lower Mississippi Valley and Tennessee Valley region... Cold front extends from a weak surface low in northeast IN southwest through southeast MO and northwest AR. A moist warm sector is in place with dewpoints around 70 F from western TN, northern MS into AR. However, morning RAOB data show a pronounced subsidence inversion near 600 mb with a substantial dry layer above. This type of profile may tend to limit updraft accelerations to some degree. Nevertheless, effective bulk shear with 45+ kt is supportive of some organized storm structures. Several MCVs are evident including one over southeast MO, and another farther west across northwest AR, and these features may tend to augment storm development as the boundary layer destabilizes. Visible imagery shows stratus beginning to erode from the southwest across AR and this trend should spread northeast with time. Storms are expected to undergo a slow but gradual increase in coverage and intensity as the atmosphere begins to destabilize with MLCAPE up to 1500 J/kg expected during the afternoon. Strong effective bulk shear will support both supercells and bowing segments with damaging wind the main threat. Low-level hodographs are expected to remain modest in size due to veered winds in the lowest 2 km. However, a couple of tornadoes cannot be ruled out, especially with any supercell structures. Activity will likely evolve into an organized line as it continues east through the TN Valley this evening. Some potential for an ENH exists for wind, and this will be re-evaluated in the upcoming 20Z outlook. ...Ohio Valley into western New York... As of mid day a warm front extends from the lower Great Lakes through western and central PA, and isolated storms have recently intensified in the warm advection zone in vicinity of this boundary across northwest PA. Farther west a cold front extends from a surface low in northeast IN southwest into southeast MO. The warm sector remains marginally unstable with 500-800 J/kg. Pockets of heating will contribute to further boundary layer destabilization, especially from northeast OH into PA with MLCAPE up to 1200 J/kg possible during the afternoon. The 12Z Raob from Pittsburgh showed minimal inhibition, and isolated storms may develop in the warm sector as surface heating continues. Farther north and west, additional storms will likely develop along the cold front from northwest OH into IN and spread east into the lower Great Lakes. An MCV is currently located along the IN/OH border and this feature may foster a relative concentration of storms along the front. Wind profiles with up to 40 kt effective bulk shear will support some supercell structures with isolated damaging wind the main threat. Low-level hodographs are rather modest, but a tornado or two cannot be ruled out especially with any isolated supercell interacting with the warm front from the lower Great Lakes region into central PA later this afternoon. Read more LIVE: spc.noaa.gov
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