This type of profile supports splitting storms, which was seen Tuesday afternoon. A special 18Z sounding (weather balloon observations), launched by NWS Phoenix Tuesday, showed the shear was mostly speed shear with fairly uniform wind directions throughout the tropospheric profile and the hodograph was relatively linear. Shear magnitudes were also sufficient for supercell development, which are a type of thunderstorm more common in the Plains. This promoted tilted updrafts and more organized storm structures than the ordinary storms in low shear seen during the monsoon.

Shear (changing wind direction and/or speed with height) was high for Arizona, with effective bulk shear upwards of 40-50 kts. 5, 2021, of (clockwise from top-left): mixed-layer convective available potential energy (MLCAPE) w/ Effective Bulk Shear Effective Bulk Shear Large Hail Parameter (LHP) Effective Storm Relative Helicity (ESRH). Objective analysis fields at 3-4 PM on Oct. This supported strong thunderstorm updrafts. Mixed layer convective available potential energy (MLCAPE - a measure of buoyancy of air near the ground) was moderate around 1000-1500 J/kg in the afternoon and low- and mid-level lapse rates (change in temperature with height) were conditionally unstable around 7-8 ☌/km. Ample sunshine over the lower deserts of Arizona helped boost surface heating and instability, especially during the afternoon. Strong atmospheric dynamics played a large role in the intensity of storms and storm mode on Tuesday. SPC Day 1 Convective Outlook (left) and Severe Thunderstorm Watch (right). The primary threats were wind and hail with a low probability threat of a few tornadoes.įig. At 11:45 AM MST the SPC in coordination with NWS offices in Phoenix, Tucson, Flagstaff, and Las Vegas issued a Severe Thunderstorm Watch for most of Arizona. 6, 2021.Īt 5:40 AM MST on October 5, the Storm Prediction Center (SPC) upgraded their Day 1 Convective Outlook to include a Slight Risk for severe thunderstorms in Central Arizona. In addition to the hail, some thunderstorms produced damaging winds and heavy rainfall with localized flash flooding.įig. With cold air aloft and unstable conditions, most thunderstorms produced at least small hail and the strongest thunderstorms produced large hail up to 1.5 to 2 inches in diameter (ping-pong ball to lime sized). The most notable and attention-grabbing impact from thunderstorms on Tuesday was hail. Initially showers and thunderstorms were relatively weak, but increased in intensity through the day Tuesday as the upper level low gradually progressed through the region.

Credit: Spike Davis (left) & William Pitts (right).Ī strong low pressure system led to the development of scattered showers and thunderstorms across Arizona and southern California beginning on Monday October 4th and lasting through the evening of Tuesday October 5th. Images of the supercell that moved through Phoenix and estimated ping-pong ball sized hail that fell between Phoenix Sky Harbor Airport and South Mountain. Impacts: Supercells with large hail, strong winds, and heavy rainįig. Last updated at 700 PM MST on October 14, 2021

Las vegas weather in october 2021