Mesoscale Discussion 2390 NWS Storm Prediction Center Norman OK 0605 PM CDT Wed Oct 21 2026 Areas affected...Central and Eastern Arizona Concerning...Tornado Watch 688... Valid 212305Z - 220100Z The severe weather threat for Tornado Watch 688 continues. SUMMARY...Large hail, severe wind gusts and a tornado threat will be possible across parts of central and eastern Arizona this evening. DISCUSSION...The latest surface analysis has a 1006 mb low over the Lower Colorado River Valley, with a trough extending east-northeastward across south-central Arizona. Low-level convergence is maximized near this surface trough and will be a potential location for cell initiation. Further to the north, low-level convergence is maximized along the Mogollon Rim due to upslope flow. To the south of the rim, surface dewpoints across much of central Arizona are in the upper 50s to lower 60s F, with the RAP showing SBCAPE from 1000 to 2000 J/kg. Over the top of this moist and unstable airmass, a mid-level jet is analyzed by the RAP over west-central Arizona. Large-scale ascent is likely maximized to the east of this feature over central Arizona, which will support continued scattered convective development this evening. This mid-level jet is creating strong deep-layer shear over much of Arizona, which will be favorable for supercells this evening. The latest RAP forecast soundings early this evening between Phoenix and Flagstaff have 0-6 km shear of 50 to 60 knots. Hodographs are long and straight, which will be favorable for supercells with large hail. In addition, forecast soundings have 0-3 km storm-relative helicity in the 250 to 300 m2/s2 range, suggesting that supercells will also have tornado potential. Isolated severe wind gusts will also be possible. ..Broyles.. 10/21/2026 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TWC...FGZ...PSR... LAT...LON 33691270 34151287 34651300 34901306 35251305 35621294 35861272 36021245 36111195 36141118 36031059 35771002 35150964 34270941 33590947 32930990 32711047 32801152 33051225 33691270 MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
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