By Reginald Stanley. Posted February 18, 2019, 7:14 PM.

A cold, unstable air mass interacted with solar heating Monday afternoon, producing an unexpected cluster of showers which surprised many residents of the region.

The showers were largely preceded by a significant gust front where they occurred. Sustained wind gusts in the 20-30 MPH range were observed in affected areas in western Riverside County and northern San Diego County. This co-occurred with a marked, steep temperature drop of roughly ten degrees, producing near-freezing wind chill factors in the lowlands. Where rain fell, it was brief. A notable burst of showers occurred in western Riverside County, forming northeast of Hemet before 3 PM. Stretching approximately 50 miles southwest, it gained strength and marched southward into southwestern Riverside County, and eventually northern San Diego County. The burst mimicked the appearance of a weak squall line on Doppler Radar. Ominous, dark clouds shrouded all areas it passed over. The burst eventually broke up over the city of San Diego.

Similar clusters appeared over San Bernardino County, Orange County, Los Angeles County and Ventura County. In the WeatherCurrents network, the highest totals recorded Monday were in De Luz and Fallbrook, both with 0.07 inches. Anza and South Temecula both recorded 0.03 inches, and Beaumont (Cherry Valley) recorded 0.02 inches. In French Valley, East Hemet, Northwest Murrieta and Perris, 0.01 inch fell. A total of 0.02 inches was also reported in Central Murrieta (report by Reginald Stanley).

Monday's unstable weather stands in contrast to original forecasts of sunny, fair weather for Monday. Clear weather was once again expected Monday night, as the trough moves further to the east.