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Tuesday, October 5, 2021

SPC Oct 5, 2021 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0737 AM CDT Tue Oct 05 2021 Valid 051300Z - 061200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF AZ... ...SUMMARY... Isolated to scattered severe thunderstorms with damaging winds and large hail are probable across most of Arizona this afternoon and early evening. A significant severe event is possible. ...AZ... A mid-level low near the southern CA/northern Baja CA coastal border will dampen as it ejects towards the Four Corners area. Low-level flow is not expected to be particularly responsive ahead of this feature, but a weak surface low remain centered across southwest AZ through late afternoon. This should help maintain a plume of mid to upper 50s surface dew points over the Gila Valley. Scattered non-severe thunderstorms are ongoing this morning, in one swath across parts of AZ within the warm conveyor and the second closer to the upper low over far southeast CA. The gap between the two regimes, currently over the Lower CO Valley into southwest AZ, is progged to be maintained as the warm theta-e advection regime shifts east/north no slower than the ejection of the mid-level low/trough. The length of robust diabatic surface heating between the two regimes will be crucial to the degree of available buoyancy this afternoon. Notably cool mid-level temperatures will favor the potential for very steep low to mid-level lapse rates. Favorable speed shear through the buoyancy profile will foster an elongated mid to upper-level hodograph with 35-45 kt effective values. This setup has the potential to produce at least a few supercells, with large hail to around 2 inches and damaging wind gusts to around 65 kts. A brief tornado is also possible near the Mogollon Rim in central AZ. The overall severe threat should subside into early evening as convection spreads northeast of the Rim. ...MS... An upper low anchored over the Ark-La-Miss should move little today before slowly shifting north early Wednesday. Boundary-layer heating beneath the mid-level cold pocket will result in a plume of moderate buoyancy this afternoon with MLCAPE of 1000-2000 J/kg becoming common. Scattered thunderstorms are expected to develop across parts of AL/MS and drift west-northwest this afternoon. While lower-level flow will be anemic (generally around 10 kts or less) and effective shear should hover around 15-20 kts, steep mid-level lapse rates will support a risk for marginally severe hail in the deepest cores. This threat will diminish after sunset as the boundary layer cools. ...Western FL Panhandle... With minimal synoptic pattern change across this area through the period, regenerative convection is expected to peak in coverage overnight into early Wednesday along the coast into the Gulf. 15-25 kt 850-mb southerlies will foster modest low-level hodograph curvature. But weak low-level instability and poor mid-level lapse rates will likely inhibit brief tornado potential. ..Grams/Mosier.. 10/05/2021 Read more LIVE: spc.noaa.gov