SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0310 PM CDT Sat Jul 10 2021 Valid 102000Z - 111200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF OKLAHOMA...SOUTHEAST KANSAS...SOUTHWEST MISSOURI AND NORTHWEST ARKANSAS... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHERN ARIZONA... ...SUMMARY... Severe thunderstorms with wind damage, isolated large hail, and perhaps a tornado or two are expected to develop this afternoon and tonight from parts of the southern and central Plains east-northeastward into the Ozarks. Additional severe storms with isolated wind damage and hail may also develop in parts of the mid Mississippi Valley and the Desert Southwest. ...20Z Update... The following primary changes have been made for the 20Z outlook: 1. A small 5% tornado area has been added from northeast OK/southeast KS into southwest MO. The primary threat is still expected to be severe wind and hail, but sufficient low-level shear will support the potential for a couple of tornadoes with initial semi-discrete development. 2. 2% tornado probabilities have been expanded into central IL, where a couple brief tornadoes have been noted with low-topped supercells. See MCD 1242 for more information. 3. Probabilities have been trimmed across portions of Nebraska, in the wake of ongoing convection. Otherwise, the previous forecast reasoning remains valid. See the previous discussion below for more information. ..Dean.. 07/10/2021 .PREV DISCUSSION... /ISSUED 1129 AM CDT Sat Jul 10 2021/ ...OK/southeast KS east to mid-Mississippi Valley... Late morning satellite imagery shows a midlevel shortwave trough over NE/SD moving southeast, with a convectively-reinforced cold front extending from southwest KS into northern/central MO. Associated large-scale lift with the shortwave trough will contribute to development/intensification of thunderstorms this afternoon, including supercells and linear segments/clusters. Steep midlevel lapse rates and ample westerly shear will result in a risk for damaging winds and large hail, and perhaps a tornado, with supercell structures early in the development phase. With time, upscale growth will result in a more widespread risk for damaging winds this evening across the ENH area. Farther east into the mid-Mississippi Valley, at least two MCVs were noted on morning water vapor imagery embedded within stronger midlevel flow, and thunderstorms will intensify in the vicinity of these features as boundary-layer heating/destabilization takes place. Effective shear values of 20-30 kts will support multicell clusters with a risk for damaging winds this afternoon and evening. Isolated instances of large hail are also possible. ...Southeast NE/northeast KS/northwest MO/southwest IA... Thunderstorms are expected to intensify in association with a midlevel shortwave trough this afternoon and evening. Moderate MLCAPE and cool midlevel temperatures will result in a risk for large hail, with damaging winds becoming more of a concern as storms merge into a couple of southeast-moving clusters this evening. ...AZ... Relatively strong easterly mid-level flow of 25-35 kts will be present this afternoon and evening over central and southern AZ. This, combined with sufficient low-level moisture/heating over the Mogollon Rim and Gila mountains will help to organize storms that will then track westward into the lower deserts this evening. HREF 12z guidance shows the potential again today for severe gusts in association with these storms. Read more LIVE: spc.noaa.gov
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