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000 ACUS01 KWNS 221256 SWODY1 SPC AC 221255 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0655 AM CST Sat Feb 22 2020 Valid 221300Z - 231200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Thunderstorms are possible across the Southwest. ...Synopsis... In mid/upper levels, rather distinct northern and southern streams will persist over the CONUS, as split flow occurs around a pronounced cyclone now centered off the southern CA coast. The associated 500-mb low is forecast to move east-northeastward across southern CA and northern AZ to the Four Corners area by the end of the period. By than time a trough should extend southwestward from the low diagonally across AZ, past the YUM area, and over northern Baja. Meanwhile, the northern stream will become less zonal as shortwave troughs amplify toward the WA coastline and over northeastern ND/northwestern MN. At the surface, a major continental/polar anticyclone will cover the southeastern CONUS, with associated ridging to northeastern MX. This pattern will substantially impede a still-incompletely modified Gulf boundary layer's moisture return to land areas east of the Rockies. ...Southwest... Isolated to widely scattered thunderstorms are possible through the period across a vast swath from southern CA to the southern Rockies. Strong thunderstorms with hail and gusts approaching severe limits are possible this afternoon across parts of western to central/ northern AZ, as the leading rim of the cyclone's cold-core region overlies a narrow plume of destabilization related to diabatic surface heating and warm advection. At this time, severe potential still appears too isolated and conditional for an outlook upgrade, though one may be needed in a succeeding update if 12Z and later models, combined with mesoscale trends, more robustly suggest buoyancy/shear parameter spaces would verify on the upper end of what has been progged. The afternoon destabilization should occur behind a plume of precip -- with isolated, embedded, brief thunderstorms -- now spreading across most of central and southern AZ, and forecast to shift northeastward in a warm-advection regime, and eastward in phase with the cyclone's translation. MLCAPE 200-400 J/kg (locally/briefly near 500 J/kg) may develop. Time series of forecast soundings indicate that destabilization of the low/middle-level air mass -- in the narrow corridor following morning clouds/precip -- generally will coincide with reduction in low-level hodograph area, though deep shear will be favorable. This offset, combined with the marginal nature of the buoyancy, support the lack of persistent supercellular convection evident in convection-allowing guidance, and suggest taking a restrained approach to outlining severe potential for this cycle. ..Edwards/Broyles.. 02/22/2020 $$