Typically the term "dry January" is reserved for discussions relating to alcohol use, but the saying can also be literal as it applies to Santa Monica weather. The city received 0.3 measurable inches of rain during the month, all concentrated within two days, Jan. 21-22, with the remainder of 2024’s first weeks parched.
As the calendar flips to February, however, a new storm in the Los Angeles area looks to drench Santa Monica with five times as much precipitation as January’s total. According to a National Weather Service forecast discussion, a low pressure system that was centered about 1,500 miles west of Seattle Monday will slide down the coast this week, bringing rain throughout California on Wednesday and Thursday. The storm will bring a 4-8 hour period of "steady moderate to occasionally heavy rain" to areas throughout Los Angeles County, with precipitation set to peak between 4 a.m. and 10 a.m. Thursday morning.
The NWS report states that peak rain rates will be between 0.33 and 0.66 inches per hour, meaning one hour of the storm will bring more rain to Santa Monica than all of January. Rainfall totals will generally end between 1.5 and 3 inches, with showers expected to dissipate by Friday.
Impacts from the rainfall include moderate flooding to roads and small creeks, however, the NWS states that "risk for significant damage is low." A report on the upcoming storm by AccuWeather Senior Meteorologist Alex Sosnowski noted that storm runoff may be "substantial and quick" with potential area-wide incidents of debris flows, rockslides and washouts.
Outside of precipitation, the truncated warm spell that ended the month will subside due to the conditions. According to a Weather Underground report using data from the Santa Monica Municipal Airport weather station, the high temperature climbed from 61 degrees Fahrenheit on Jan. 25 to 75 on Jan. 27, followed by a high of 78 on Jan. 28. After Monday and Tuesday also reached the 70s, the storm will plunge temperatures by double-digit degrees, with Thursday’s high set to be 60 degrees.
This week’s storm is classified by AccuWeather as an atmospheric river, a plume of tropical moisture in the atmosphere that can result in heavy rainfall in a narrow patch of land. A series of atmospheric rivers was the source of life-altering storms for many throughout California during the 2022-23 winter season, and the event will once again trigger precipitation in Santa Monica.
After the series of atmospheric rivers delivered 15.45 inches of measurable rainfall to the city from January-March, 2023 was relatively dry, save for an intense downpour in August from Tropical Storm Hilary. In total, the city received 21.44 inches of rain in 2023, severely outpacing a parched 2022 with just 5.22 measurable inches. March of 2023, which brought the city 7.85 inches of rainfall, outpaced the entire 2022 total.
The dried out conditions of 2022 left not only Santa Monica, but all of California, in significant drought. According to the United States Drought Monitor, in January 2023 over half of California was locked into at least moderate drought conditions, but the early 2023 storms have changed that tune. As of Jan. 23, the drought monitor shows that just under 29% of the state is in at least moderate drought, with this week’s rain aiming to further lower that number.
Snowpack throughout the state will also be impacted by the storm, with Southern California mountains like the Tejon and Cajon passes set to gain a "small, slushy accumulation" according to the AccuWeather report. Accumulations are also in store for the Sierra Nevada snowpack along the state’s eastern border, which is currently running below historical averages for late January.
