15 Mar 2023 | 09:55 AM UTC
US: Adverse weather forecast over western regions through at least March 17
Heavy rainfall and snowfall forecast across parts of the western US through at least March 17. Possible flooding and associated disruptions.
Event
Heavy rainfall and snowfall are forecast across parts of the western US through at least March 17. Heavy snowfall is forecast across parts of the Northern Intermountain Region, the Great Basin, and the Northern Rockies before expanding into the Central Rockies and Northern Plains by late March 15. Snowfall accumulations of up to 15-25 cm (6-10 inches) are possible in elevated parts of the affected region. Strong winds could also combine with snowfall to cause blizzard conditions in parts of the affected area. Hazardous driving conditions are likely due to icy roads and reduced visibility caused by blowing snow.
Heavy rainfall is expected across parts of the Great Basin and Southwest on March 15 before moving into the Southern Rockies on March 16. The heavy downpours could trigger urban and flash flooding across parts of the affected region.
Government Advisories
As of early March 15, the National Weather Service (NWS) has issued winter storm warnings for parts of central and eastern Idaho, central, eastern, and southwestern Montana, southern and western Wyoming, northern and southern Utah, and western Colorado. Winter storm watches have been issued for parts of southern Colorado and northern New Mexico and winter weather advisories have been issued for parts of eastern Oregon, central and eastern Idaho, much of Montana, eastern and southern Wyoming, northeastern and southern Nevada, central and northeastern Utah, and central and eastern Colorado. Avalanche warnings have been issued for parts of central Idaho. High wind warnings and advisories are also in place across parts of the affected area.
Flood warnings have been issued for parts of central Nevada, central Arizona, and eastern Idaho. Flood watches have been issued for parts of central and western Arizona and far southwestern Utah and flood advisories are in place across much of central and northern Nevada and parts of eastern Idaho. The NWS's Weather Prediction Center has warned of a Slight Risk (level 2 on a four-tier scale) across parts of central and western Arizona from March 15-16.
Officials could update and possibly extend the coverage of weather alerts over the coming days.
Hazardous Conditions
Where precipitation falls as rain, flash and areal flooding is possible. Such flooding is possible in low-lying communities near watercourses and other large bodies of water and in urban areas with easily overwhelmed stormwater drainage systems. Sites located downstream of large reservoirs may be subject to flash flooding after relatively short periods of intense rainfall.
Precipitation could fall as snow especially in higher elevations over the coming days. Wind gusts could cause blowing and drifting snow; decreased visibility is likely in mountainous areas. Rain-induced landslides cannot be discounted in areas of elevated terrain; there is also the possibility of avalanches in mountainous areas where the snowpack has become unstable due to heavy snowfall. Power outages could occur throughout the affected area.
Transport
Floodwaters and related debris may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around the affected area. Flooding in urban areas could also result in significant traffic congestion. Heavy snow will likely make driving hazardous in some areas; authorities could implement temporary road closures or detours in such locations. Mountain passes and tunnels could be closed as a precautionary measure during periods of intense snowfall.
The disruptive weather will likely cause some delays and cancellations at airports in the region. Flooding or snow could block regional rail lines; freight and passenger train delays and cancellations are possible in areas that see heavy rainfall and potential track blockages.
Disruptions triggered by inclement weather and resultant hazards, such as flooding or avalanches, could persist well after conditions have improved - it could take days before any floodwaters recede and/or officials clear debris. Repair or reconstruction efforts may result in residual disruptions if there is severe damage to infrastructure.
Advice
Monitor local media for weather-related updates and advisories. Confirm all transport reservations and business arrangements before traveling in the affected area. Seek updated information on road conditions before driving or routing shipments through areas where severe weather is forecast; plan for possible supply chain disruptions throughout the affected areas. Stay away from elevated streams, creeks, and other watercourses that are prone to flash flooding. Do not attempt to navigate flooded roadways. Exercise caution in elevated terrain due to the threat of landslides, as well as mountainous regions where avalanches pose a threat. Charge battery-powered devices in the case of prolonged electricity outages.
