SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1238 AM CDT Thu Jul 22 2021 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF MONTANA INTO THE WESTERN DAKOTAS AND ACROSS PARTS OF ARIZONA... ...SUMMARY... Thunderstorms capable of strong to potentially severe wind gusts are possible this afternoon and evening across much of Montana into parts of northeast Wyoming and the western Dakotas. Gusty winds are also possible with thunderstorms across much of Arizona. ...MT to the western Dakotas... Seasonally strong upper trough located along the Pacific Coast is forecast to eject across BC into southern AB by 23/00z, before translating to near the SK/MB border by the end of the period. Southern influence of this feature will only glance northern MT as upper ridging is flattened near the international border. Scattered convection developed off the Bitterroots and western MT higher terrain Wednesday afternoon, primarily due to strong heating and orographic forcing. In the absence of meaningful large-scale forcing for ascent, boundary-layer heating and orographic forcing will once again be responsible for convective initiation across MT and northern WY. Latest forecast soundings suggest convective temperatures will be breached by 21z across southwestern MT/northern WY. Scattered storms should develop then spread east-northeast within an environment that will favor strong/severe downdrafts. Ample mid-level flow will be present for possible storm organization but it's not entirely clear whether activity can grow upscale into clusters in the absence of large-scale support. For this reason will maintain MRGL risk, but there is some concern for a corridor of stronger winds with convection from central into northeast MT. ...Arizona... Center of upper anticyclone may weaken a bit and drift north across the Four Corners region into the day2 period. Deep-layer flow should remain marginal across AZ so any thunderstorm clusters that develop will propagate largely due to internal processes/outflow. Forecast soundings suggest locally severe wind gusts can be expected due to seasonally high PW values and favorable sub-cloud RH levels. ..Darrow/Squitieri.. 07/22/2021 Read more LIVE: spc.noaa.gov
http://dlvr.it/S4Bpxz
