Looking back at this September and the first half of October, it has been dry and hot.
This September, the coastal valleys — San Luis Obispo and Santa Maria — saw their high temperatures average about 3 degrees warmer than usual, while the inland valleys — Paso Robles and Santa Ynez — were nearly 8 degrees above average!
So far, in October, it has been even worse with Santa Maria 8 degrees above average, San Luis Obispo 14 degrees above typical, and Paso Robles 15 degrees above normal!
Except for areas of drizzle along the coastline, it has been bone dry this rainy season, which runs from July 1, 2020, through June 30, 2021.
October is often a transition period between the dry and wet seasons. The average rainfall is typically between one half and one inch in San Luis Obispo, Paso Robles, and Santa Maria during October.
It is not unusual to have dry Octobers; on the other hand, we have seen some surprisingly intense autumn rainstorms.
On the 13 and 14 of October 2009, a storm slammed into the Central Coast, unlike any other October storm since records have been kept, with many 24 and 48-hour rainfall records for the month broken, especially in Monterey County and the northern part of San Luis Obispo County.
On October 11, 2009, a storm developed in the eastern Pacific and rapidly intensify to 968 millibars off the Coast of Oregon. This low-pressure system produced a steep pressure gradient along the West Coast with tightly spaced isobar lines that run perpendicular to the coastline.
On October 13, the southerly winds in many locations reached over 50 mph. A newly installed Condor Lookout weather station on Hi Mountain in the Los Padres National Forest with an elevation of 3,190 feet — wind gusts hit 85 mph.
The associated warm front arrived in the morning and produce steady rain. The rain continued over the next 24 hours as a very-slow-moving front from the west passed the Central Coast. It was hard to call this a cold front because there was not much cold air associated with this system and hardly any wind shift.
Feeding into this storm were the remnants of former super Typhoon Melor that had crashed into Japan earlier in the month. The upper-level charts indicated a powerful jet stream centered directly over the Big Sur coastline. This jet acted like a conveyor belt, bringing in tropical moisture from the eastern Pacific.
The south to southwesterly winds pushed air masses higher as they hit the coastal mountains, causing more rain to fall. Meteorologists call this “orographic enhancement.”
Farther south in the county, the rainfall totals slowly decreased.
The Santa Lucia mountains in Monterey County received over 21 inches of rain! The San Luis Obispo County Water Resources rain gauge on the top of Rocky Butte near San Simeon recorded 13.7 inches of rain.
I received emails from readers that reported between 7 and 10 inches along Highway 41 between Morro Bay and Atascadero.
I had one report of 10.5 inches in See Canyon. The SLOweather.com rain gauge in the hills near Los Osos Valley Road and Foothill Boulevard recorded 7.7 inches, while Cal Fire Station 15 — the former South Bay Fire Department in Los Osos —recorded 5.2 inches.
The Diablo Canyon Ocean Lab rain gauge recorded 2.5 inches; further south in Nipomo saw 2.4 inches. The Lompoc Airport reported 0.66 of an inch of rain on the 13th and 2.03 inches on the 14th. Oddly, the Santa Maria Airport only saw about three-quarters of an inch of precipitation. Nacimiento Lake went from 9 percent of capacity to 18 percent in just 24 hours. That is what I call a rainstorm.
Due to COVID 19 pandemic, our team has had to suspend tours of the Diablo Canyon Power Plant and the thousands of acres of pristine lands that surrounded it. While the tours are on hold, we made some short virtual tour videos of the Diablo Canyon Lands and Facilities; which can be viewed on YouTube.