November 14th, 2025: Wet Weather Late Saturday Through Monday Morning

Synopsis

An upper level trough/closed low off the coast of Southern California will lift northeastward across the Southwest US this weekend bringing  precipitation chances to Arizona. Rainfall amounts will be somewhat light with a trace to 0.25 inches in the lower deserts and 0.50 to 1 inch across the higher terrain of Northern Arizona. Snow levels will remain above 7000 feet with a dusting to a couple of inches of accumulation possible over the tallest mountain peaks. In addition, a few thunderstorms are possible mainly west of Phoenix due to weak instability. 

Models show another upper level trough/closed low impacting the region mid to late next week for another chance of precipitation. 

Current Conditions

As of 7:30AM MST this morning, mid level water vapor imagery displays a plume of deep tropical moisture being transported into Southern California.

GOES-19 mid level water vapor imagery as of 7:30AM MST courtesy of College of Dupage.

This atmospheric river is due to a deepening upper level trough off the coast of California.

06z GFS 500mb Analysis this morning.

The amount of deep tropical moisture being transported into Southern California is quite impressive as indicated by the 12z NKX (San Diego) sounding which measured 1.36 inches of precipitable water.

12z NKX observed sounding courtesy of SPC.

In fact, I checked NKX sounding climatology, and this breaks the daily record for precipitable water!

NKX sounding climatology courtesy of SPC.

This Weekend

Synoptics/Dynamics

The aforementioned upper level trough/closed low is expected to deepen over the next 24 hours due to an area of cyclonic shear vorticity (jet max) upstream of the trough axis moving into the base of the trough. It is expected to be a closed circulation by tomorrow morning with 500mb height anomalies 3 to 4 standard deviations below climatology for this time of year.

06z GFS 500mb cyclonic vorticity valid for tomorrow morning at 11AM MST courtesy of Tropical Tidbits.

  

06z GFS 500mb normalized height anomaly valid for tomorrow morning at 11AM MST courtesy of Tropical Tidbits.

By Sunday morning the area of cyclonic shear vorticity (jet max) will move upstream of the trough axis which will act to weaken and lift the wave northeastward.

06z GFS 500mb cyclonic vorticity valid for Sunday morning at 5AM MST courtesy of Tropical Tidbits.

This is the main reason why models have backed off QPF the last few days, especially in Southern Arizona. However, there still will be enough synoptic scale support for showers across much of the state but mainly focused in western and Northern Arizona.

Moisture and Instability

Moisture will be well above normal for this time of year with the UA WRF-HRRR showing precipitable water between 1 to 1.25 inches in Maricopa, Pima, Pinal, and Yuma Counties late Saturday through Sunday evening. These pwat values are above the 90th percentile for this time of year based on TUS sounding climatology. 

12z UA WRF-HRRR total precipitable water valid for 12AM MST Sunday.

Instability is forecast to be minimal due to poor laps rates in the lower half of the troposphere. The 12z UA WRF-HRRR KPHX sounding only shows around 200 J/kg of CAPE, but some areas in the lower Colorado River Valley could see CAPE on the order of 250 to 500 J/kg late tomorrow afternoon.

12z UA WRF-HRRR KPHX sounding valid for Sunday at 4AM MST.

12z UA WRF-HRRR maximum CAPE valid for tomorrow at 5PM MST.

The greatest instability in Tucson is expected around late morning, but the WRF-HRRR only forecasts around 100 J/kg of maximum CAPE.

12z UA WRF-HRRR KTUS sounding valid Sunday at 11AM MST.

Timing and Precipitation Amounts

Models are in relatively good agreement regarding timing and precipitation amounts across the state. Both the UA WRF-HRRR and WRF-GFS forecast light precipitation to begin in western Arizona during the afternoon hours tomorrow with coverage and intensity increasing around sunset.

12z UA WRF-HRRR simulated reflectivity valid for tomorrow at 6PM MST.

The best chance for the Phoenix area will be late Saturday into early Sunday morning, and the best chance for the Tucson area will be late Sunday morning into the early afternoon hours.

12z UA WRF-HRRR simulated reflectivity valid for Sunday at 2AM MST.

12z UA WRF-HRRR simulated reflectivity valid for Sunday at 10AM MST.

Total precipitation amounts will be light in the lower deserts due to weaker and brief dynamic support from the upper level trough. I'm only expecting a trace to 0.25 inches in these areas with locally higher amounts possible in Yuma and western Maricopa County due to the greater risk for thunderstorms. The greatest rainfall amounts will be mainly over the higher terrain of Northwestern Arizona due to the closer proximity of the trough dynamics. Total accumulations in that area is expected to be between 0.5 and 1 inch.

12z UA WRF-HRRR 72-hour accumulated precipitation from 5AM MST today through 5AM MST Monday.

Lastly, snow levels will remain above 7000 feet through the weekend with only a dusting to a couple of inches of accumulated snow over the tallest mountain peaks.

Isolated light showers will be possible into Sunday evening but should taper off by midnight.

Next Week

The aforementioned trough will lift northeastward into the Plains late Sunday night with anticyclonic vorticity advection (mechanism for sinking motion) dominating the synoptic scale pattern Monday due to transitory ridging moving in from the west. Models show another upper level trough digging southeastward along the California coast on Tuesday which will likely bring another round of precipitation to Arizona. At this time, there's too much uncertainty for me to provide any specific details with high confidence.

06z GFS 500mb cyclonic vorticity valid for Monday at 5AM MST courtesy of Tropical Tidbits.