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Tuesday, October 5, 2021

SPC Oct 5, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1224 AM CDT Tue Oct 05 2021 Valid 051200Z - 061200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHWESTERN US AND OVER PORTIONS OF THE CENTRAL GULF STATES... ...SUMMARY... Isolated severe thunderstorms with large hail and damaging wind are possible across most of Arizona this afternoon and early evening. A risk for marginally severe hail and gusty winds are also possible over parts of Mississippi/Alabama this afternoon. ...Southwestern US... Upper low off the northern Baja Peninsula is forecast to continue moving northeast and this feature will track along the CA/Baja border early before deamplifying and ejecting across AZ during the overnight period. Low-level flow is not expected to be particularly responsive ahead of this feature but a weak surface low should progress into southwestern AZ during the late afternoon. This will ensure moist, south-easterly flow across much of the state prior to convective development. Notably cool mid-level temperatures will spread across AZ during the day and this will aid destabilization for scattered thunderstorms. While wind profiles are not forecast to be that strong, NAM forecast sounding at 20z for PRC exhibits adequate shear for perhaps weak supercells, and cloud bases will be fairly low over higher terrain. Have introduced 2 percent tornado probabilities for the outside chance of a weak tornado in this more moist/sheared environment; otherwise, isolated large hail/damaging winds are the primary threat with the most robust storms later this afternoon/evening. ...Gulf States... Upper low is forecast to move very little during the day1 period with a slow northwest migration expected into central AR by 06/12z. Primary low-level confluence zone will remain near the MS/AL border and deeper moisture/poorer lapse rates will be maintained across AL/GA/FL Panhandle, along with stronger shear. However, strongest boundary-layer heating will be in closer proximity to the upper low where 500mb temperatures will range from minus 14-16C across the northern two-thirds of MS. While convection that develops beneath the upper low will be weakly sheared, stronger buoyancy and steeper lapse rates may be adequate for some hail/wind with the most robust updrafts. ..Darrow/Bentley.. 10/05/2021 Read more LIVE: spc.noaa.gov