(- Java animation of PW images: 16-19 June 2000 -)
The second earliest start on record of the annual Arizona "monsoon" began on 19 June 2000, leading to several days of convective activity over the southwest US. NOAA GOES Sounder Precipitable Water (PW) images (above) show the northward surge of higher PW values during the 16-19 June period. PW values across Arizona on 16 June were less than 20 mm (blue enhancement), but increased to 30-40 mm (yellow to red enhancement) during the following few days.
On 22 June, GOES-10 10.7 micrometer InfraRed (IR) imagery (above, left) showed that early morning convection was decreasing across extreme southeastern California. The upper-level convective debris and other mid and high-level cloudines formed a broken band that extended north-northeastward across southern Nevada / northwestern Arizona / southwestern Utah. This cloudiness helped to create a differential heating mechanism (reduced solar heating beneath the cloudy region, strong solar heating adjacent to the edges of the cloudy region) which acted to focus convective development later in the day.
After sunrise, GOES-10 visible imagery (above, right) revealed a convectively-induced circulation near Needles, CA (station identifier KEED). The cloudiness associated with this circulation dissipated during the late morning and early afternoon hours, but the circulation likely persisted, helping to initiate convection later in the afternoon over west-central Arizona. Note the high dewpoint temperatures (50's and 60's F) across the desert regions of southern Arizona and California.