The figure above indicates the forecasted high in orange (with error bar denoting the range of ensemble forecast members), average high for this time of year in orange (dashed line), forecasted low in blue (with error bar), average low this time of year in blue (dashed line), and forecasted wind speed in purple. Note that the wind speed forecast is sustained wind (not gusts), and it is based on only one model (not an ensemble).
There is a very rare occurrence happening this week. The same low pressure system that moved through Arizona early last week, bringing isolated severe thunderstorms to Arizona, will move through Arizona again (déjà vu)! After moving slowly southeastward through Arizona and New Mexico last week, it drifted into northern Mexico and slowly retrograded back toward the west. The low is now currently spinning along the coast of the Baja of California and is expected to move slowly northward then northeastward across Arizona later this week.
The low will be weaker than it was last week, but it will still usher sufficient moist, unstable air across the state for another round of showers and thunderstorms Thursday – Sunday. Thunderstorms that form will likely not be severe, but will be capable of locally heavy rain or small hail. The storm will also bring cooler air, returning the unusually warm temperatures today through Wednesday back down to near normal levels by Friday.
A second weak upper-level trough may also move across Arizona next Monday and tap into any remaining moist air, continuing the chance of showers or thunderstorms through Monday. Skies will probably become clear again by next Tuesday.
Met Mail is an unofficial weather discussion and forecast transmitted once or twice a week via e-mail by the Embry-Riddle Department of Meteorology (http://meteo.pr.erau.edu/). Embry-Riddle offers an undergraduate bachelor-of-science degree program in Applied Meteorology. Please spread the word to all potential qualified candidates!
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Official National Weather Service forecast