Late Season Heavy Rainstorm Strikes Northern California
A rare late June rainstorm brought widespread precipitation to Northern and Central California this past Sunday- Tuesday. Precipitation totals were modest at coastal and low elevation sites but impressive in the Sierra Nevada and northern mountain ranges where up to 9” of rain fell.
A very moist sub-tropical stream of air originating from a dissipating tropical storm off the Japanese coast made its way across the Pacific and to the American west coast Sunday through Tuesday. Orographic lifting brought excessive rainfall to the mountains of northern and central California north of a line from Yosemite to Monterrey. A 72-hour total of 8.76” was measured at Stouts Meadow in Shasta County and 4.88” fell in 24 hours ending at 7 a.m. PST today (June 26th) at Hirz (with 2.68” of this falling in just a single 6-hour period yesterday). The Sierra Nevada mountain range received widespread totals of 2”-5” (north of Yosemite) with Blue Canyon, (elev. 5,000’) recording an impressive 3.58” total. Amounts in the Sacramento Valley and the Bay Area were spotty and mostly light: Sacramento itself had only .15” and downtown San Francisco .18”. Santa Rosa and Napa Valley saw general 1-2” totals. Any measurable rainfall at this time of the year is exceedingly rare, about once every 10 years (although an even more intense late June storm impacted the same area in 2011!).
For the central and northern Sierra and northern California mountains, the rainfall will hopefully alleviate the extreme fire danger those areas have been experiencing the past month or so. The fire danger, however, remains critical in the southern half of the state and southern Sierra Nevada.METARS for San Ramon, a San Francisco suburb, the past hour. I can never recall seeing such high dew points associated with high temperatures as well.
NWS- Monterrey office data.
Very high dew points are making it feel like an East Coast summer day this Wednesday (June 26th) with sunshine having returned but the moist air still in place. For instance, at this hour (around 1 p.m. PST), the temperature in San Ramon, 20 miles east of San Francisco, is sitting at 87° but with a 67° dew point. High dew points combined with high temperatures are extremely rare in the Bay Area. An intense heat wave is forecast to develop for inland California (and much of the Southwest) this weekend with near record temperatures expected in Las Vegas among other areas. The NWS forecast highs in Death Valley to reach 126-129°F by Monday:
Christopher C. Burt