DISCUSSION
Despite having a deep slug of lower level moisture across Southeast Arizona over the past 24-hours, it was been relatively quiet with only a few showers/thunderstorms that have tracked across the region. The weak storms that were moving NE across Graham and Greenlee county earlier this morning have since weakened and moved off into west central New Mexico.

I know what you are thinking. What about the poor diamondback rattlesnakes, large chuckwallas and gila monsters that have been patiently and eagerly awaiting rainfall to begin. Little fellas awkwardly standing there in the desert with their shower caps on, holding their miniature bars of soap. Well, their wait will finally be over as it is shaping up to be a wet 24-36 hours across Southeast Arizona.

Lets take a look at the favorable ingredients that we are working with today. First, the larger scale pattern aloft if defined by a trough of low pressure digging south along the California coastline. As this feature moves south today, the flow over SE AZ becomes more diffluent aloft assisting convection that does develop with a larger scale lift aloft.

Second, GOES satellite imagery continues to show the deeper moisture spread across all of Southeast Arizona, with the northern extent of the plume axis (precipitable water values ranging from 1.25-1.40 inches) extending across the eastern portions of the Tohono O'odham Nation and eastern Pima county. It is the instability associated with this moisture that will be the primary reason we will see shower and thunderstorm development this afternoon. I would expect to see storms develop today along the gradient of the best moisture convergence in the lower levels which would be across Santa Cruz and eastern Pima county including the eastern portions of the Tohono O'odham Nation. The SPC Mesoscale Analysis page indicates a sharp gradient of the maximum Theta-e vertical difference in the lowest 3km extending across the same area.

The 15/12Z KTWC upper air sounding indicated plenty of dry air above 550 mb which can be seen on WV satellite imagery rotating along the southern and southeast periphery of the upper trough.
This will mean that updrafts will entrain dry air into the upper portions of the storms assisting evaporation and thus increase the strong downdraft/outflow potential. Although we are moist in the lower portions of the sounding, it is not quite the ideal profile for wet microbursts because is it just a little to moist in the mid-levels of the storm but we can still expect some strong outflows to 45 mph. Additionally, the sounding also showed 30 knots of 0-6 km shear which should produce an isolated hail potential with the storms today.

Given all of these ingredients, it looks like the next 24-36 hours will be a decent rainmaker. The 15/12Z HRRR indicated the valleys east of a Nogales-Three Points-Eloy line have a 10-20 percent chance of total rainfall with this event above 0.50 inches, with a 40-60 percent chance in the higher terrain. In addition, there are scattered locations across Santa Cruz/western Cochise/eastern Pima and eastern Pinal counties with a 10-20 percent chance of over an inch of rain.

Given the synoptic assist from the upper trough, expect showers and thunderstorms to persist overnight into Monday morning.
Strong dynamic support with shortwaves rotating around the base of the upper trough will likely intensify thunderstorms re- development Monday afternoon. After that, we will see the moisture scour out Tuesday as a strong westerly flow ushers in dry air.
The upper trough will position itself over the Desert Southwest into next weekend. This will keep afternoon temperatures in check across the entire forecast area, with Tucson experiencing those awesome temperatures in the upper 80s to near 90.

AVIATION
Valid through 17/00Z. SCT 9k-12k clouds becoming SCT-BKN 6k-9k this afternoon and persisting into Monday. Isolated to scattered thunderstorms should develop today with brief visibility restrictions, mountain obscurations, localized heavy rain, and gusts to 45 kts. Thunderstorm coverage will increase during the evening, and may persist overnight and again Monday, especially to the east of Tucson. Outside of thunderstorm wind gusts, SFC wind will be 12 kts or less and SWLY/WLY in direction during the afternoon/early evening hours and variable in direction at other times. Aviation discussion not updated for TAF amendments.

FIRE WEATHER
There will be a chance of showers and thunderstorms through Monday, beginning this afternoon and continuing overnight tonight. Dry conditions return Tuesday and persist through the remainder of the week with valley minimum relative humidities in the 15 to 25 percent range, and higher elevations 20 to 30 percent. Winds outside of thunderstorms generally remain under 12 mph today, then south to southwest winds of 15-20 mph and higher gusts will occur for much of this coming week, mainly during the afternoon and early evening hours.

TWC WATCHES/WARNINGS/ADVISORIES
None.