How A Productive Burst Of Winter Moisture May (Or May Not) Impact Drought In The Southwest

Recently Arizona Water News asked Arizona State Climatologist Erinanne Saffell, as well as Mark O’Malley, lead forecaster for the National Weather Service, to provide some expert analysis of the spate of early-to-mid-winter storms that have made for a surprisingly wet winter in the West thus far.

We asked O’Malley for some perspective regarding the recent series of storms and their potential long-term impact on moisture conditions in the Southwest, especially the Colorado River system. Our discussion with Lead Meteorologist O’Malley appeared in the Jan. 27 issue of Arizona Water News.

Our questions for Dr. Saffell, meanwhile, focused primarily on the effect of the storms in Arizona. In addition to precipitation, Dr. Saffell addressed several other factors that ultimately impact the amount of moisture that makes its way into state reservoirs. That discussion follows below.

ADWR Water News: While the recent West Coast storms appear to be helping stabilize California drought conditions, what impacts, if any, are these "atmospheric rivers" having here in Arizona? Are snowpack conditions in Arizona dramatically improved, too? We're getting indications that they are, but is it a given that a healthy snowpack this early in the winter season will result in an equally healthy runoff? 

Dr. Saffell: The status of Water Year 2023 is in good shape so far. Arizona started the water year with a wet October, a very cold November, and continued with a wet December and January (the 17th wettest January on record). At the end of January, precipitation for the water year was above average for most counties in the state.

Arizona relies on its snowpack, and the snowpack (“Snow-water equivalent,” or SWE) in Arizona is looking very good for mid-February. SWE is the ratio of how much water is in the snow, and the average SWE is 10:1, where 10 inches of snow melts to 1 inch of water.

SWE is measured automatically by the SNOTEL network using a weather instrument called a snow pillow. A snow pillow essentially measures the weight of the snow on the pillow and equates that to how much water is in the snow, or SWE.

The Verde River basin has done exceptionally well so far this winter, with SWE currently over 250 percent of median levels. The Salt River basin is well over 100 percent of SWE. As of February 1, the Lower Colorado River basin ranked 6th for snow water equivalent since 1981.

ADWR Water News: Even if snowpack is above average, what factors may affect runoff? 

Dr. Saffell: Runoff in the upper Colorado River basin works much the same as in Arizona’s basins, meaning soil moisture plays an important role. Soil moisture is the water found in the dirt and rocks of the ground (soil moisture is the water used by plants). If the soil is dry, snowmelt will first move into the soil. If the soil is fairly moist, then runoff efficiencies improve.

With a very wet monsoon, a fairly wet fall, and a wet and cold January, soil moisture conditions in Arizona are near 80 percent to 100 percent of normal conditions in many locations. If everything continues like this, runoff efficiencies should be fairly strong, and this may result in small releases, particularly in the Verde River system.

However, a lot can still happen between February and Arizona’s usual peak runoff in March, and one thing known for sure is that winter precipitation in Arizona is highly variable. The 2nd wettest February on record for Arizona happened in 1980. Six tropical storms ravaged central Arizona, causing snowpack to melt and Salt River reservoirs to reach capacities. The Salt River had its highest flood levels since 1905, and only two Salt River bridge crossings could be used that February. Governor Babbitt called up the famous “Hattie B” passenger train to transport people across the flooded river in 1980.

ADWR Water News: Overall, how do in-state moisture conditions strike you at this point in the winter season as compared to recent years?

Dr. Saffell: Compared to the last two years, 2023’s short-term drought is looking much better. Only 21 percent of the state is currently in some measure of short-term drought (Moderate D1 or Severe D2), with 79 percent of the state in no drought or Abnormally Dry (D0) conditions.  

Two years ago (February 2021), 85 percent of Arizona was covered in Extreme (D3) or Exceptional (D4) drought.  Last winter was in better shape than in 2021, but 57 percent of the state was still in short-term drought (D1-D4) in February 2022.

With winter storm activity picking up mid-February, the short-term outlook shows Arizona leaning toward additional precipitation by the end of February. Colder temperatures also appear likely, so it’s helpful if any February precipitation comes in the form of snow for the high country. The goal is to add snow and not rain on the higher elevation basins at least through the end of February.

The seasonal outlook shows the likelihood of below-average precipitation through April. While it’s not unusual for Arizona to start drying out in March, it would be helpful if the state doesn’t dry out as mu

ch as last year.

Last March-May was the 9th driest March-May on record, and last year had the driest May on record, with no measurable precipitation anywhere in the state last May.

The dry spring of 2022 expanded Arizona’s short-term drought last year, with Extreme (D3) and Exceptional (D4) short-term drought returning to the state by June. Fortunately, the wet Monsoon 2022 helped mitigate much of the short-term drought last year. While it’s too early for Monsoon 2023 outlooks right now, we’ll be closely watching those outlooks starting in May. 

Overall, Arizona is sitting with its 24th wettest October-January on record, with statewide precipitation at 132 percent of average. While the water year still has much more to go, it’s a good start!