Rillito, AZ Weather

Synopsis

Scattered showers and thunderstorms Friday, followed by an overall lull in storm activity Saturday. Widespread showers with scattered thunderstorms Sunday into Monday. A Flood Watch has been issued for most of Pima county, Pinal county, Santa Cruz county, Graham county, and Greenlee county from 11 PM Saturday through 5 AM Monday.

Discussion

Moisture has begun to stream into the area due to southwesterly flow from the approaching trough off the coast of California. Satellite derived PWATs are around 0.5 to 0.75 inches and increasing. High clouds have moved across the region with cumulus clouds forming in western Pima county and along the Arizona/ New Mexico border with isolated showers and thunderstorms. The chance for isolated showers and thunderstorms will persist through afternoon.

A sub-tropical jet associated with the Pacific trough will push over northern Mexico and drive anomalously high moisture into the area. This will substantially raise PWATs to around 1 to 1.5 inches, increasing the chance for more isolated showers and thunderstorms Friday across the region. Ample forcing aloft combined with strong mid-level flow will provide a risk for strong and organized thunderstorms, capable of heavy rainfall rates, damaging wind gusts, and hail. With storm motions likely to be fairly quick, any flash flooding threat will likely be kept to areas that see multiple rounds of thunderstorms. Overall, total rainfall amounts for this first wave of activity will be around 0.25 to 0.5 inches with locally high amounts if a strong thunderstorm or rounds of thunderstorms were to pass over an area. Activity will wain overnight Friday through most of Saturday.

Saturday into Sunday the strong trough off the coast will move inland bringing moisture into the area pushing near climatological maximum for this time of year. This will lead to widespread chances for showers and thunderstorms. Chances for showers and thunderstorms will first increase Saturday night, though there remains some discrepancies in how early this activity will develop. An initial round of isolated to scattered showers/thunderstorms will be possible in the evening. The main wave will move in during the day Sunday with chances increasing from west to east. Though instability will be more limited, long duration moderate to locally heavy rainfall rates may bring a threat of rapid runoff and localized flash flooding. Rainfall probabilities remain generally consistent with previous shifts with around 0.5-1 inches in the valleys and 1-2 inches in the mountains. Due to terrain upsloping, it is possible the mountains could see greater than 2 inches of rainfall. A Flood Watch has been issued for most of Pima county, Pinal county, Santa Cruz county, Graham county, and Greenlee county from 11 PM Saturday through 5 AM Monday.

Chances for showers and thunderstorms linger through Monday morning but will quickly drop off into the evening. Temperatures both Sunday and Monday will be 5-10 degrees below normal, potentially even cooler on Sunday in areas that see rainfall through the afternoon. Temperatures will then likely moderate to near or just below normal by by mid- week after the system fully exits to the east.

Aviation

Valid through 31/00Z.

SCT-BKN cirrus AOA 20k ft through the day today. FEW-SCT cumulus at 7k-10k ft in areas near the New Mexico border with isolated showers/thunderstorms from 29/21Z-30/04Z. Light and terrain driven surface wind under 12 kts through the period, with gusty and erratic winds possible near any thunderstorm. Showers/ thunderstorms will move into the area after 30/18Z starting in western Pima county moving east across the area. Aviation discussion not updated for TAF amendments.

Fire weather

Scattered showers and thunderstorms will return to the region Friday, followed by a lull in storm activity Saturday, then widespread showers with scattered thunderstorms Sunday into Monday. Moderate intensity rainfall with pockets of heavy rain is expected both Friday and Sunday, with locally heavy storm total rainfall amounts possible, especially in the higher terrain. Afternoon high temperatures will lower below normal Friday into early next week. Breezy southerly winds are anticipated Friday, with breezy to locally windy southwest winds expected Sunday, turning northwest Monday. Minimum RH values will be in the 15-25 percent range today and Wednesday. Minimum RH levels will increase Friday into early next week, with values at 40+ percent.

Watches, warnings and advisories

Flood Watch from Saturday evening through late Sunday night for AZZ502>511-513>515.