scholarly journals The Synoptic and Mesoscale Evolution Accompanying the 2018 Camp Fire of Northern California

2020 ◽  
pp. 1-45
Author(s):  
Clifford F. Mass ◽  
David Ovens
Keyword(s):  
Sierra Nevada ◽  
Northern California ◽  
Wind Event ◽  
Downslope Wind

CapsuleThe Camp Fire of November 2018 was associated with a strong, well-forecast, downslope wind event over the western slopes of the Sierra Nevada near Paradise, California.

The Strong, Dry Winds of Central and Northern California: Climatology and Synoptic Evolution

2020 ◽  
Vol 35 (5) ◽  
pp. 2163-2178
Author(s):  
Brandon McClung ◽  
Clifford F. Mass
Keyword(s):  
Sea Level ◽  
Sierra Nevada ◽  
Critical Role ◽  
Northern California ◽  
Maximum Frequency ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
Bay Area ◽  
Downslope Wind ◽  
Wind Events

AbstractStrong, dry downslope winds over Northern and central California have played a critical role in regional wildfires. These events, sometimes called Diablo or North winds, are more frequent over the Bay Area and nearby coastal terrain than along the western slopes of the Sierra Nevada, where the highest frequency occurs over the midslopes of the barrier. For the Bay Area, there is a frequency minimum during midsummer, a maximum in October, and a declining trend from November to June. The Sierra Nevada locations have their minimum frequency from February to August, and a maximum from October to January. There is little trend in event frequency during the past two decades over either region. For the Bay Area sites, there is a maximum frequency during the early morning hours and a large decline midday, while the Sierra Nevada locations have a maximum frequency approximately three hours earlier. Before the onset of these downslope wind events, there is substantial amplification of upper-level ridging over the eastern Pacific, with sea level pressure increasing first over the Pacific Northwest and then over the Intermountain West. The coincident development of a coastal sea level pressure trough leads to a large pressure gradient over the Sierra Nevada and Northern California. Diablo–North wind events are associated with below-normal temperatures east of the Sierra Nevada, with rapid warming of the air as it subsides into coastal California. The large horizontal variability in the frequency and magnitude of these events suggests the importance of exposure, elevation, and mountain-wave-related downslope acceleration.

Late Ordovician rugose corals of the northern Sierra Nevada, California

1994 ◽  
Vol 68 (1) ◽  
pp. 164-168 ◽  
Author(s):  
Robert J. Elias ◽  
A. W. Potter ◽  
Rodney Watkins
Keyword(s):  
Sierra Nevada ◽  
Late Ordovician ◽  
Late Devonian ◽  
Northern California ◽  
Rugose Corals

The shoo fly Complex of Late Devonian and older Paleozoic age is a regionally extensive rock assemblage in the northern Sierra Nevada of northern California. It consists chiefly of a coherent unit of phyllite, quartzose sandstone, and chert, and a melange unit (Hannah and Moores, 1986). Several limestone lenses in the Taylorsville area comprise the Montgomery Limestone (Diller, 1892, 1908; McMath, 1958; Figure 1). The Montgomery was long considered to be Silurian, largely on the basis of corals, brachiopods, and cephalopods (Diller, 1892, 1908; McMath, 1958; Berry and Boucot, 1970; Merriam, 1972). However, recent analyses of the biota indicate an Ashgill (middle Maysvillian–Gamachian) age (Boucot and Potter, 1977; Harris, personal commun. cited in Hannah and Moores, 1986, p. 790; Potter et al., 1990b; present study).

Forcing Mechanisms for Washoe Zephyr—A Daytime Downslope Wind System in the Lee of the Sierra Nevada

2008 ◽  
Vol 47 (1) ◽  
pp. 339-350 ◽  
Author(s):  
Shiyuan Zhong ◽  
Ju Li ◽  
Craig B. Clements ◽  
Stephan F. J. De Wekker ◽  
Xindi Bian
Keyword(s):  
Pressure Gradient ◽  
Sierra Nevada ◽  
Great Basin ◽  
Regional Scale ◽  
Surface Wind ◽  
Formation Mechanisms ◽  
Climate Data ◽  
Local Pressure ◽  
Interesting Phenomenon ◽  
Downslope Wind

Abstract This paper investigates the formation mechanisms for a local wind phenomenon known as Washoe Zephyr that occurs frequently in the lee of the Sierra Nevada. Unlike the typical thermally driven slope flows with upslope wind during daytime and downslope at night, the Washoe Zephyr winds blow down the lee slopes of the Sierra Nevada in the afternoon against the local pressure gradient. Long-term hourly surface wind data from several stations on the eastern slope of the Sierra Nevada and rawinsonde sounding data in the region are analyzed and numerical simulations are performed to test the suggested hypotheses on the formation mechanisms for this interesting phenomenon. The results from surface and upper-air climate data analyses and numerical modeling indicate that the Washoe Zephyr is primarily a result of a regional-scale pressure gradient that develops because of asymmetric heating of the atmosphere between the western side of the Sierra Nevada and the elevated, semiarid central Nevada and Great Basin on the eastern side of the Sierra Nevada. The frequent influence of the Pacific high on California in the summer season helps to enhance this pressure gradient and therefore strengthen the flow. Westerly synoptic-scale winds over the Sierra Nevada and the associated downward momentum transfer are not necessary for its development, but strong westerly winds aloft work in concert with the regional-scale pressure gradient to produce the strongest Washoe Zephyr events.

scholarly journals Diurnal Variation of Downslope Winds in Owens Valley during the Sierra Rotor Experiment

2008 ◽  
Vol 136 (10) ◽  
pp. 3760-3780 ◽  
Author(s):  
Qingfang Jiang ◽  
James D. Doyle
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Western Slope ◽  
Owens Valley ◽  
Mountain Waves ◽  
Downslope Winds ◽  
Wind Event ◽  
Downslope Wind ◽  
Rotor Experiment ◽  
The Impact

The impact of diurnal forcing on a downslope wind event that occurred in Owens Valley in California during the Sierra Rotors Project (SRP) in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations. The observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross-valley winds in Owens Valley exhibited strong diurnal variation. The numerical simulations using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) capture many of the observed salient features and indicate that the in-valley flow evolved among three states during a diurnal cycle. Before sunrise, moderate downslope winds were confined to the western slope of Owens Valley (shallow penetration state). Surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well-mixed valley air from the westerlies aloft around local noon (decoupled state). The westerlies plunged into the valley in the afternoon and propagated across the valley floor (in-valley westerly state). After sunset, the westerlies within the valley retreated toward the western slope, where the downslope winds persisted throughout the night.

scholarly journals The Intense Lee-Wave Rotor Event of Sierra Rotors IOP 8

2007 ◽  
Vol 64 (12) ◽  
pp. 4178-4201 ◽  
Author(s):  
Vanda Grubišić ◽  
Brian J. Billings
Keyword(s):  
Sierra Nevada ◽  
Large Amplitude ◽  
Forced Flow ◽  
Mountain Range ◽  
Wave Rotor ◽  
Owens Valley ◽  
Mountain Waves ◽  
Downslope Wind ◽  
Lee Wave ◽  
Strong Control

Abstract A large-amplitude lee-wave rotor event observationally documented during Sierra Rotors Project Intensive Observing Period (IOP) 8 on 24–26 March 2004 in the lee of the southern Sierra Nevada is examined. Mountain waves and rotors occurred over Owens Valley in a pre-cold-frontal environment. In this study, the evolution and structure of the observed and numerically simulated mountain waves and rotors during the event on 25 March, in which the horizontal circulation associated with the rotor was observed as an opposing, easterly flow by the mesonetwork of surface stations in Owens Valley, are analyzed. The high-resolution numerical simulations of this case, performed with the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) run with multiple nested-grid domains, the finest grid having 333-m horizontal spacing, reproduced many of the observed features of this event. These include small-amplitude waves above the Sierra ridge decoupled from thermally forced flow within the valley, and a large-amplitude mountain wave, turbulent rotor, and strong westerlies on the Sierra Nevada lee slopes during the period of the observed surface easterly flow. The sequence of the observed and simulated events shows a pronounced diurnal variation with the maximum wave and rotor activity occurring in the early evening hours during both days of IOP 8. The lee-wave response, and thus indirectly the appearance of lee-wave rotor during the core IOP 8 period, is found to be strongly controlled by temporal changes in the upstream ambient wind and stability profiles. The downstream mountain range exerts strong control over the lee-wave horizontal wavelength during the strongest part of this event, thus exhibiting the control over the cross-valley position of the rotor and the degree of strong downslope wind penetration into the valley.

scholarly journals Hourly Analyses of the Large Storms and Atmospheric Rivers that Provide Most of California’s Precipitation in Only 10 to 100 Hours per Year

2018 ◽  
Vol 16 (4) ◽  
Author(s):  
Maryam Lamjiri ◽  
Michael Dettinger ◽  
F. Martin Ralph ◽  
Nina Oakley ◽  
Jonathan Rutz
Keyword(s):  
San Francisco ◽  
Sierra Nevada ◽  
Southern California ◽  
Extreme Rainfall ◽  
Annual Rainfall ◽  
North Coast ◽  
Northern California ◽  
Rainfall Events ◽  
Atmospheric Rivers ◽  
The North

California is regularly impacted by floods and droughts, primarily as a result of too many or too few atmospheric rivers (ARs). This study analyzes a two-decade-long hourly precipitation dataset from 176 California weather stations and a 3-hourly AR chronology to report variations in rainfall events across California and their association with ARs. On average, 10-40 and 60-120 hours of rainfall in southern and northern California, respectively, are responsible for more than half of annual rainfall accumulations. Approximately 10-30% of annual precipitation at locations across the state is from only one large storm. On average, northern California receives 25-45 rainfall events annually (40-50% of which are AR-related). These events typically have longer durations and higher event-precipitation totals than those in southern California. Northern California also receives more AR landfalls with longer durations and stronger Integrated Vapor Transport (IVT). On average, ARs contribute 79%, 76%, and 68% of extreme-rainfall accumulations (i.e., top 5% events annually) in the north coast, northern Sierra, and Transverse Ranges of southern California, respectively. The San Francisco Bay Area terrain gap in the California Coast Range allows more AR water vapor to reach inland over the Delta and Sacramento Valley, and thus, influences precipitation in the Delta’s catchment. This is particularly important for extreme precipitation in the northern Sierra Nevada, including river basins above Oroville Dam and Shasta Dam. This study highlights differences between rainfall and AR characteristics in coastal versus inland northern California, differences that largely determine the regional geography of flood risks and water-reliability. These analyses support water resource, flood, levee, wetland, and ecosystem management within the catchment of the San Francisco estuary system by describing regional characteristics of ARs and their influence on rainfall on an hourly timescale.

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