UPDATE
Water vapor imagery shows a closed low moving through southern California with high pressure centered over Texas. The low will progress eastward today into Arizona and will help produce gusty southwest winds with speeds 15-25 mph and gusts 25-35 mph. High temperatures will be right around normal with Tucson likely seeing its 127th straight 90 degree or higher day.
It's possible this streak is broken tomorrow thanks to cooler air in the wake of the trough. Please see the previous discussion for longer term details.

PREV DISCUSSION
/issued 220 AM MST Fri Sep 20 2024/ A dry weather system will be moving into the region today to bring breezy conditions. As of the 0840Z water vapor imagery, a low pressure center is along the Los Angeles coast and moving southeast into the deserts of southern California. The low pressure center axis will push into central Arizona and the resulting pressure gradient will bring those breezy conditions. M The 00Z HRRR wind probabilities show at least 20% to 30% chance of exceeding 20 mph and higher chances in the more wind prone or exposed areas that are susceptible to southwest winds. Chances for exceeding 25 mph is less than 10 percent and mainly confined to the west facing slopes of the Sky Islands. Therefore, majority of Southeast Arizona will likely experience at least 15 mph with several locations can experience closer to 20 mph and up to around 25 mph. Also, with the tightening of the pressure gradient, it will be enough to squeeze some moisture to form of clouds later this evening. Cloud coverage will generally be low across the region, but enough to block a few stars.

The system will exit our area by late Friday and into Saturday which will keep temperatures near to slightly below normal.
Saturday morning lows is forecasted to be one of the coolest mornings that most locations haven't experience for a long time.
Winds will lessen but can be breezy at times on Saturday.

Next change in the pattern starts on Sunday. A ridge of high pressure will build over the region. Ensemble models have been consistently showing this ridge building across the region and lasting through all week and possibly into the new weekend. This means temperatures are back on the rise to remind us that summer hasn't quite finish. (We got a taste of fall today and tomorrow.)
100 degrees temperatures will start to move from the west to the east, starting in Ajo and reaching to Tucson by midweek. Tucson has a 25 percent chance of hitting 100 on Thursday and those chances will increase to 50% through weekend. This broad ridge appears to stick around for a little over a week. A small wrinkle to the forecast is the 15 to 25 percent chances for thunderstorms in the White Mountains and down into Greenlee County. These are low chances due to the fact not all of the ensemble models agree on the placement of the high pressure center, but it is a non- zero chance for a thunderstorm to form over the higher terrain in the late Wednesday. Something to keep an eye out over the next several days. Any way, the main story next week is the hot temperatures across the region.

AVIATION
Valid through 21/12Z.
SKC through majority of the forecast period with FEW low level clouds at or around 10-12k ft AGL developing after 21/03 to the end of the forecast period. Light SFC winds this morning and becoming southwesterly by 20/16z at speeds 12-18 kts and gusts to around 30 kts. After 21/04z, SFC winds return to variable and less than 10 kts to the end of the period. Aviation discussion not updated for TAF amendments.

FIRE WEATHER
Dry conditions with temperatures within a few degrees of normal through Saturday. Today, breezy 20-foot south- southwesterly winds at speeds of 15 to 20 mph with gusts up to around 25 mph and locally higher in wind prone areas. Tomorrow's winds will lessen down to 10 to 15 mph. Min RHs will generally be 15 to 20 percent in the lower locations and 20 to 30 percent in the higher locations. Starting Sunday, high pressure ridge will bring warmer temperatures and lighter winds through the new week.

TWC WATCHES/WARNINGS/ADVISORIES
None.