February 9th, 2024: Colder Storm to Impact Southeastern AZ Tomorrow

 Synopsis

An upper level trough will rapidly dig southward into Arizona late tonight into tomorrow bringing another round of precipitation to primarily SE AZ (including Tucson). This system is much colder than the previous storms this week which means much lower snow levels. Current guidance suggests snow levels above 3000 feet, but cannot completely rule out some wet flurries in the Tucson vicinity. Rainfall amounts expected to be between 0.10 and 0.50 inch across valley locations. Snowfall will range between a trace and 3 inches between 3000 and 5000 feet, 3 to 6 inches between 5000 and 7000 feet, and  6 to 12 inches above 7000 feet with greatest amounts over the tallest peaks of the Sky Islands. As the system moves rapidly eastward Sunday morning, a cold airmass will be left in place with morning frost likely across valley floors Sunday through the middle of next week. 



 Current Conditions

SPC 500mb analysis this morning displays a broad trough over the intermountain west. 


SPC 500mb analysis as of 17:00Z this morning.


Chilly this morning with current temps at 10:00AM MST in the mid 40s to low 50s across the lower deserts and temps in the 20s and 30s over the higher terrain.


Current obs as of 10:30AM MST courtesy of the NWS.


Tranquil weather is expected today, but will be on the chilly side with high temps in the upper 50s and low 60s across the lower deserts. 

12z WRF-HRRR 2-meter temps for today at 3:00 PM MST.


Clouds will also slowly increase from west to east throughout this afternoon and early evening as the trough amplifies over the state.



 Tonight into Sunday Morning


Synoptics 

Throughout the day today and into tonight the aforementioned trough over the intermountain west will rapidly dig southward and amplify over Arizona. By tomorrow morning and into the late afternoon, the eastern half of the state will be under the influence of PVA ahead of the trough axis inducing synoptic scale ascent.


12z GFS 500mb absolute vorticity for tomorrow at 5:00 AM MST.




12z GFS 500mb absolute vorticity for tomorrow at 5:00 PM MST.


The 12z GFS forecasting 850mb temps around 0 degC and 925mb temps around 5 degC tomorrow as shown below. 


12z GFS 850mb temps (degC) for tomorrow at 5:00PM MST.


12z GFS 925mb temps (degC) for tomorrow at 5:00PM MST.


Timing 

Precipitation will begin late tonight and early tomorrow morning across Central AZ (including Phoenix) and persist in this region through mid morning. In SE AZ (including Tucson) precipitation will begin around sunrise and will continue into the middle of the afternoon.


12z WRF-HRRR simulated reflectivity for tomorrow at 2AM MST.


12z WRF-HRRR simulated reflectivity for tomorrow at 5AM MST.


12z WRF-HRRR simulated reflectivity for tomorrow at 8AM MST.


12z WRF-HRRR simulated reflectivity for tomorrow at 11AM MST.


12z WRF-HRRR simulated reflectivity for tomorrow at 2PM MST.


Late Afternoon/Early Evening Convection

After the main rain band has moved east of Tucson by mid afternoon, low to mid level lapse rates will steepen due to colder mid level temps associated with the closer proximity of the 500mb vort max/trough axis. The 12z KTUS WRF-HRRR sounding indicating around 300 J/kg of CAPE late tomorrow afternoon which should be enough to promote a chance for scattered convective showers and maybe even an isolated thunderstorm or two. 


12z KTUS WRF-HRRR sounding for tomorrow at 4:00PM MST.


The primary hazard from these convective showers will be hail and/or graupel. 


Snow Chances in Tucson Vicinity

Over the past 48 hours have noticed models trending slightly colder and colder with this system. Even with this trend, model consensus still suggests Tucson to be just below (and I really mean just below) the rain/snow threshold. The most likely scenario is snow above 3000 feet with an outside chance of rain/snow mix and/or snow flurries across the valley. Wouldn't be surprised to even see some very light accumulations in Oro Valley and along the Catalina Foothills. The best chance for any snow in Tucson would be tomorrow morning when 2-meter temps are forecast to be in the mid to upper 30s combined with a nearly moist adiabatic profile in the low and mid levels across the Tucson vicinity. 


12z WRF-HRRR 2-meter temps for tomorrow morning at 11:00AM MST.

 

12z KTUS WRF-HRRR sounding for tomorrow at 11:00AM MST.


Rain and Snow QPF


Should get some better precipitation totals in SE AZ compared to yesterday's storm. Rainfall amounts will range from a trace to 0.10 inch in the Phoenix vicinity with rainfall totals between 0.25 and 0.50 inch in valley locations below the freezing height in SE AZ (including Tucson). 



12z WRF-HRRR 48-hour liquid QPF from 12z this morning to 12z Sunday morning


Regarding snow totals, expect anywhere from a trace to 3 inches for locations between 3000 and 5000 feet which includes the Tucson Mountains, Sierra Vista, Benson, Willcox, Oracle, and possibly even Catalina. 3 to 6 inches is forecast for between 5000 and 7000 feet with 6 to 12 inches expected above 7000 feet with greatest amounts expected over the highest peaks of the Sky Islands. 


12z WRF-HRRR 48-hour total snowfall forecast between 12z this morning and 12z Sunday morning.



Snow accumulation is not likely across the Tucson metro as mentioned above, but definitely still a chance for a rain/snow mix and/or wet snow flurries in the Tucson vicinity with an outside chance of a light dusting in Oro Valley and along the Catalina Foothills. 


Travel conditions will be extremely hazardous especially along I10 between far eastern Tucson and the AZ/NM border where snow accumulation is expected. 



 Sunday into Next Week

The trough will move rapidly eastward late Saturday into early Sunday morning leaving behind a very cold airmass leading to widespread frost across valley floors (including Tucson) with morning frost likely continuing into the middle of the work week. Some lingering isolated light snow showers will be possible near the AZ/NM Border and over the White Mountains early Sunday morning, but otherwise it will be a dry and chilly Sunday across the state. 


GEFS and EPS 500mb height anomalies indicating broad, low amplitude ridging over the Southwest for next week which means drier and more tranquil weather for AZ through at least next weekend. 










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