Arizona

How a productive flurry of winter moisture may (or may not) affect Southwest drought.

Snow water equivalent in % of the median, per basinThe news for the past few weeks has been a barrage of headlines reflecting what millions of people across the country are wondering (and hoping for):

Have the amazing storms that have been sweeping the west since mid-December finally defeated the drought?

The answer is of course complex. Yes and no. But in reality it is much more “no” than “yes”. Drought is a long-term condition that doesn’t… err… evaporate in a few very wet weeks.

For a well-informed perspective on the recent spate of “atmospheric flows” that have swept the West Coast and contributed to record snowfalls in places like Flagstaff, ADWR Water News turned to two of the Southwest’s most renowned experts in weather conditions and forecasting.

Both Mark O’Malley, senior forecaster for the National Weather Service, and Erinanne Saffell, Arizona state climate researcher, provide biennial expert analysis for the Arizona Drought Interagency Coordinating Group, which makes biennial recommendations to the Arizona Governor on whether a statewide drought emergency exists should be proclaimed.

ADWR News specifically asked O’Malley to provide an assessment of the recent series of storms and their potential long-term impact on moisture conditions in the Southwest, particularly in the Colorado River system. Our questions to Dr. Saffell, meanwhile, focused primarily on the impact of the storms specifically in Arizona.

The following is an ADWR Water News discussion of the general current moisture conditions in the Colorado River Basin with NWS Chief Meteorologist O’Malley.

Next week: Dr. Erinanne Saffell, Arizona State Climatologist, discusses the impact of recent storms on Arizona’s drought conditions.

Mark O’Malley

The US Winter Outlook 2022-2023 temperature map

ADWR Water News: While the recent storms appear to be helping to stabilize drought conditions in California, what, if any, impact are these “atmospheric fluxes” having further east? Have snowpack conditions in the Colorado Basin also improved dramatically?

O’Malley: The series of storms that have hit California helped bring beneficial moisture into inland Arizona and the Colorado Basin. The snow water equivalent (SWE) ranges from 125-150 percent of normal for that part of the winter in the headwaters of the Colorado River to 250 percent of normal in northern Arizona.

It must be noted that we are still in the midst of winter and additional snowfall will be required over the next few months to ensure increased spring runoff.

ADWR Water News: Even if snow cover is above average, what factors can affect runoff? In the recent past, hot, dry, windy conditions and the early onset of spring have resulted in a dramatic reduction in runoff in the Colorado River watershed. Does that still threaten runoff forecasts?

O’Malley: In recent years, inconsistent snowfall throughout the winter, unusually warm spring months with rapid snowmelt, and prolonged drought to deep soil moisture profiles have hampered spring runoff below expected levels.

There are early indications (based on better summer and fall 2022 rainfall to support soil moisture and more extensive snowpack) that runoff may not be as adversely affected this season as in recent years. However, it is still mid-winter and it remains to be seen how additional precipitation and spring warming will affect the runoff season.

Even if conditions remain favorable and above-average spring runoff occurs throughout the Colorado Basin, storage levels in the larger reservoirs are so low that this year’s contribution from runoff represents only a small dip in the long-term deficit.

ADWR Water News: How are you finding the humidity in the state at this point in the winter season? We suspect things are looking good, but doesn’t Arizona have the same mitigating factors as the Colorado River watershed?

O’Malley: Overall, rainfall and humidity in Arizona so far this winter have been above normal. Storm systems in the early season consisted primarily of precipitation. However, much colder storms since mid-December have resulted in more favorable snowfall that has created favorable snowpack.

Weekly average sea surface temperature for the last winter in La Nina

Even with early-season rain events, discharge into state reservoirs has been better than in recent years, so we are optimistic that spring total discharges will be very beneficial to local central Arizona reservoirs.

ADWR Water News: Last fall, you predicted that the “La Nina” condition would subside in the early months of 2023, and that appears to be the case. What do you see as a result of this turn towards a more “neutral” or “El Nino” state this spring?

O’Malley: While the Pacific Basin is still in La Nina conditions, there are strong indications that we will enter a neutral state in the spring and summer. This winter was a good example that not all La Nina years produce consistently drier than normal weather in the Southwest. While the majority of La Ninas is dry for Lower Colorado, there are a small handful (including this year) that result in normal to above-average rainfall.

The spring forecast indicates a small increase in the probability of warmer than normal temperatures, but no real tilt in the probability of precipitation. Beyond the spring and summer, it’s a little early to accurately predict the state of El Nino/La Nina, but another La Nina next fall and winter is the least likely outcome.

ADWR Water News: In relation to the current conditions in the Colorado River watershed, are these average to above average conditions evenly distributed? Or are some parts of the system still unusually dry? In the recent past, the southern slopes of the Rocky Mountains were often significantly drier than in the north.

O’Malley: Some of Utah’s headwaters are still suffering from severe and extreme drought conditions given the ongoing deficits. However, many of Colorado’s headwaters have fallen off the drought plot (as has the majority of Arizona). Snowpack in upper Colorado, however, is slightly lower (relative to normal) compared to the rest of the basin — albeit still a healthy 125-150 percent of normal. All in all, this is much better than the past two winters, although peak runoff is a few months away.

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