Oro Valley, AZ 85737 Weather

Synopsis

Scattered showers and thunderstorms this morning, becoming more numerous across the region this afternoon and persisting into the evening. Saturday will see a lull in precipitation, though slight chances (10 percent) of showers persist. Another weather system will bring 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

A busy weather pattern through the weekend for southeast Arizona. The upper air pattern currently features southwesterly flow as an active subtropical jet pattern takes hold. The first of two significant weather systems will impact southeast Arizona today. A pre-cursor disturbance has already resulted in scattered showers and thunderstorms last night, with showers and thunderstorms persisting early this morning as broader lift increases across the region under broad diffluent flow and increasing 850-700mb moisture convergence. In the last hour a round of thunderstorms moved through Tucson producing a quick localized 0.5" to 1 inch of rain and some small hail. Latest SPC mesoanalysis shows MUCAPE around 1000 J/KG helping to support elevated convection. CAMs have really struggled this morning picking up on any of this activity, so have made short term modifications to the forecast to maintain scattered showers and thunderstorms through the morning hours before more widespread shower and thunderstorm activity moves in this afternoon. This activity will be aided by the combination of broad scale lift in the left front quadrant of the 250mb jet and deep lower level moisture with strong 850-700mb moisture convergence. Still some uncertainty in terms of just how much solar insolation we'll see to increase surface based instability but should be enough warming to generate around 500-1000 J/KG of SBCAPE which combined with modest 0-6km bulk shear around 30 kts will be enough to result in the potential for a few stronger to marginally severe thunderstorms. SPC continues to outline our area in a marginal risk today for severe thunderstorms with strong wind gusts and hail the main threats. We're also in a marginal risk from WPC for excessive rain north of Tucson today. The most common additional rain amounts today through this evening will be 0.25" to 0.75", though given the convective nature of the precipitation, some areas will see less and others more. Higher precipitation amounts can be expected in areas that see repeating rounds of thunderstorms which is most likely north to northeast of Tucson. In this case, isolated areas of 1 to 2 inches of rain (with isolated flash flooding as well) are expected with the probability of 1 inch or more of rain averaging about 20 percent for any single location.

While the area remains under southwesterly flow aloft on Saturday, we'll generally be between systems with limited large scale lift. However, given the moisture still in place (0.75" to 1" PWAT), isolated shower activity is expected (10 to 20 percent chances during the day), with any precipitation short lived under individual showers. Thereafter, more widespread rain chances start to ramp up as the evening progresses Saturday night on the leading edge of the next more significant weather system.

A more potent subtropical weather system the moves into and through our region Sunday through Sunday night. This will bring near record to record levels of PWAT for this time of year (1.25" to 1.50") or about 5 standard deviations above normal. IVT values also peak at around 750 which is a level 3 on the AR scale, though this is tempered by the short residence time of the AR. What this all boils down to on Sunday is the expectation for widespread shower activity with isolated embedded thunderstorms. Given the stronger dynamics and lower level 700mb jet around 40 kts, convective activity will be capable of bringing down some stronger wind gusts. Precipitation amounts Sunday through Sunday night will average 0.50" to 1" for Pima, Santa Cruz and Cochise Counties with locales north of Tucson including Pinal, Graham and Greenlee Counties along with favored southwest flow upslope areas of our Sky Islands more likely to see rain amounts ranging from 1 to 2+ inches. A Flash Flood Watch remains in effect for 11 PM Saturday through 5 AM Monday for much of southeast Arizona. This level of rainfall will result in flowing washes, with subsequent increased flows in our river systems into early next week as well.

Thereafter, we'll get into a quieter weather regime early next week. Any lingering precipitation should come to an end Monday morning with shortwave ridging and dry conditions Tuesday and Wednesday. Thursday still looks dry as well, then more uncertainty thereafter as another system potentially impacts our area next Friday and beyond with more precipitation chances.

Daytimes temperatures will mostly be below normal through the forecast period, with the coolest highs Sunday and Monday.

Aviation

Valid through 31/12Z. SCT-BKN clouds 7-10k ft AGL through the forecast. Expect scattered to numerous SHRA and scattered -TSRA through much of the period through 31/06Z, with the most widespread precipitation this afternoon into evening. SFC winds mainly SELY/SLY 6-12 kts through the forecast period, with gusts 15- 20 kts this afternoon. Gusty and erratic winds also possible near any thunderstorm. Aviation discussion not updated for TAF amendments.

Fire weather

Scattered to numerous showers and thunderstorms today as weather system impacts the region. A brief break between weather systems Saturday with only slight chances for showers, then then widespread showers with scattered thunderstorms Sunday into Monday. Moderate intensity rainfall with pockets of heavy rain is expected today and Sunday, with locally heavy storm total rainfall amounts possible, especially in the higher terrain. Afternoon high temperatures will lower below normal through the forecast period. 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.