An unusually strong storm for the time of year is affecting the Western U.S., dumping heavy rain and higher elevation snow. Many cities could double or triple their normal precipitation for May, normally a dry month, in just 24 to 48 hours, meteorologists warn. This is the first of three expected waves of rain to hit the region over the next 7 days.
A strong upper level system arriving into the Western U.S. by the morning of May 16 (LT) will bring several days of unsettled weather to much of the Northwest and into the Rockies, NWS warns.
Locally heavy to excessive rainfall is possible, especially along the favored terrain of central/northern California late May 15, and the northern Rockies on May 16.
This system will usher in much below normal temperatures (5 to 11+ °C / 10 to 20+ °F below average) which will support moderate to heavy snowfall in some of the highest elevations.
The best chance for significant snows will be in the Sierra Nevada where up to 60 cm (2 feet) of snow is possible and winter storm warnings are in effect.
"This storm will bring unusually heavy rainfall and a flooding and mudslide threat to parts of California in what is normally a dry month," said AccuWeather Senior Meteorologist Jack Boston.
San Francisco recorded 10.66 mm (0.42 inches) on May 15, nearly a month's worth of rain in just 24 hours (11.93 mm / 0.47 inches).
Normal rainfall amounts for the entire month of May range from about 8.38 mm (0.33 inches) to 38.1 mm (1.50 inches) across the Bay Area.
"Many locations can expect to approach tor even surpass these monthly normals over the next 24 hours, NWS Bay Area said May 15.
Featured image credit: NASA NOAA/Suomi NPP/VIIRS. Acquired May 15, 2019