New Mexico Spring Runoff

Climatological Spring Runoff Data
New Mexico & Southern Colorado
(updated May 9, 2024)

2024 Snowmelt: Hydrologic Outlook
(updated May 9, 2024)

There are no longer any significant areas of concern for snowmelt runoff this spring. Flood advisories for the Rio Chama will continue to be monitored for the latest reservoir releases and associated hydrologic response. Snow pack is greatly reduced and nonexistent in some areas after a very warm, dry and sunny April resulted in an earlier than usual snowpack reduction. Hazards to area rivers and streams will likely shift to rain-driven or infrastructure (dam release or breach) flooding concerns only.

Median Runoff Statistics
(Current NWPS data and historical median data is available for sites with links)

Spring Snowmelt Considerations & Hazards

Snowmelt flooding occurs when the major source of water involved in a flood is caused by melting snow. The northern tier states and mountainous areas of the U.S. are particularly susceptible to snowmelt flooding. Unlike rainfall that can reach the soil almost immediately, the snowpack can store the water for an extended amount of time until temperatures rise above freezing and the snow melts. This frozen storage delays the arrival of water to the soil for days, weeks, or even months. Once it begins to melt and does reach the soil, water from snowmelt behaves much as it would if it had come from rain instead of snow by either infiltrating into the soil, running off, or both. Flooding can occur when there is more water than the soil can absorb or can be contained in storage capacities in the soil, rivers, lakes and reservoirs.

High soil moisture conditions prior to snowmelt can contribute to snowmelt flooding. Rainfall during the late fall is particularly important because there is less evapotranspiration and less time for the soil to drain and dry before it freezes. Ground frost or frozen soil is another contributor. Deep, hard ground frost prevents snowmelt from infiltrating into the soil. Cold temperatures prior to heavy snowfall and normal or above normal soil moisture contribute to this.

Deep snow cover can worsen snowmelt flooding since there is more water stored and available for snowmelt. Also, when snow cover is widespread, it usually keeps air temperatures cooler and delays spring warming, which increases the potential for more rapid snowmelt. Rain falling while snow is still on the ground contributes more water for flooding and helps to melt the snowpack, thus rain-on-snow events are watched carefully.

Most often, snowmelt is a relatively slow phenomenon. Snowmelt rates are usually comparable to light or moderate rainfall. Important exceptions to this can occur, especially during unusually warm periods with high dew point temperatures, and when nighttime temperatures remain above freezing. Snowmelt rates can be much higher than normal under these conditions, which can increase the risk of snowmelt flooding. (NWS Flood-Related Hazards)

Other river flood hazards include:

• Bank erosion and bank instability
• Channel re-routing around debris/sediment islands
• Levee breaks
• Lowland inundation
• Cold water