Tule fog (IPA: /ˈtuːli/) is a thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of California's Great Central Valley. Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground The San Joaquin Valley (ˌsæn wɑːˈkiːn refers to the area of the Central Valley of California that lies south of the Sacramento-San Joaquin Delta The Sacramento Valley is the portion of the California Central Valley that lies to the north of the San Joaquin-Sacramento Delta in the U California ( is a US state on the West Coast of the United States, along the Pacific Ocean. The Central Valley is a large flat valley that dominates the central portion of the U Tule fog forms during the late autumn and winter (California's rainy season) after the first significant rainfall. Autumn (also known as fall in North American English) is one of the four Temperate Seasons Autumn marks the transition from Summer Winter is one of the four Seasons of Temperate zones Calculated astronomically, it begins on the Solstice and ends on the Equinox A wet season or rainy season is a Season in which the average Rainfall in a region is significantly increased The official time frame for tule fog to form is from November 1 to March 31. Events 996 - Emperor Otto III issues a deed to Gottschalk Bishop of Freising which is the oldest known document using the name Ostarrîchi Events 307 - After divorcing his wife Minervina, Constantine marries Fausta, the daughter of the retired Roman Emperor This phenomenon is named after the tule grass wetlands (tulares) of the Central Valley. The Tule ( Schoenoplectus acutus, syn Scirpus acutus Schoenoplectus lacustris Scirpus lacustris subsp Accidents caused by the tule fog are the leading cause of weather-related casualties in California.
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Formation
Tule fog is a radiation fog, which condenses when there is a high relative humidity — typically after a heavy rain — calm winds, and rapid cooling during the night. Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground Relative humidity is a measurement of the amount of Water vapor that exists in a gaseous mixture of air and water The nights are longer in the winter months, which creates rapid ground cooling, and thereby a pronounced temperature inversion at a low altitude.
In California, tule fog can extend from Bakersfield to Red Bluff. Red Bluff is the County seat of Tehama County California. As of the 2000 census the incorporated city had a total Population of 13147 but it is currently Tule fog occasionally drifts as far west as the San Francisco Bay Area, even drifting westward out the Golden Gate, opposite to the usual course of summertime ocean fog. The San Francisco Bay Area, commonly known as the Bay Area, or the Bay, is a geographically and ethnically diverse metropolitan region that surrounds the The Golden Gate is the North American Strait connecting San Francisco Bay to the Pacific Ocean.
It is formed when cold mountain air flows downslope into the valley during the night, pooling in the low areas until it fills the valley to the "brim" formed by the Coast Ranges and the Sierra Nevada. This occurs because most areas in the Great Central Valley have little or no air drainage below the level of mountain passes. Because of the density of the cold air in the winter, winds are not able to dislodge the fog and the high pressure of the warmer air above the mountaintops presses down on the cold air trapped in the valley, resulting in a dense, immobile fog that can last for days undisturbed.
Tule fog is a low cloud, usually below 1,000 feet in altitude and can be seen from above by driving up into the foothills of the Sierra Nevada to the east or the Coast Ranges to the west. Altitude is the Elevation of a point or object from a known level or datum (plural data Foothills are geographically defined as gradual increases in hilly areas at the base of a Mountain range. The Sierra Nevada ( Spanish for "Snowy Range" is a Mountain range located in the U The Pacific Coast Ranges are the series of Mountain ranges that stretch along the west coast of North America from Alaska to northern and central Mexico Above the cold, foggy layer, the air is typically warm, dry and clear. Once tule fog is formed, turbulent air is necessary to break through the temperature inversion layer. Daytime heating sometimes evaporates the fog in some areas, although the air remains chilly and hazy below the inversion. Tule fog usually remains longer in the southern and eastern parts of the Central Valley.
Visibility
There is not much one can see in tule fog. Visibility is usually less than an eighth of a mile (about 600 feet), but can be less than 10 feet. A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit Visibility can vary rapidly; in only a few feet visibility can go from 10 feet to near zero. Satellite and overhead photos of the San Joaquin Valley show the fog where agriculture and cities like Sacramento can be seen. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Agriculture refers to the production of goods through the growing of plants and fungi and the raising of domesticated Animals The study of agriculture The picture shown would be considered VERY mild fog in the San Joaquin Valley.
The variability in visibility is the cause of many chain-reaction pile-ups on roads and freeways. In one such accident on Interstate 5 near Elk Grove south of Sacramento, 25 cars and 12 big-rig trucks collided inside a fog bank in December 1997. Route description Southern California See also San Diego Freeway, Santa Ana Freeway, Golden State Freeway Interstate 5 starts Elk Grove is a City in Sacramento County California, located just south of the state capital of Sacramento Five people died and 28 were injured. In February 2002, two people were killed in an 80-plus car pile-up on State Route 99 between Kingsburg and Selma. State Route 99 (SR 99 commonly known as Highway 99 or 99, is a north-south State highway in the U Kingsburg is a town in Fresno County California. For much of the town's history the fields around Kingsburg were mostly grape vineyards which produce mainly Raisin Selma is a city in Fresno County California. The population was 19240 at the 2000 census The visibility at the time of the accident was zero. On the morning of November 3, 2007, heavy tule fog caused a massive pile-up that included 108 passenger vehicles and 18 big rig trucks on Northbound State Route 99 between Fowler and Fresno. State Route 99 (SR 99 commonly known as Highway 99 or 99, is a north-south State highway in the U Fowler is a small town in Fresno County, California, United States. Visibility was cut to about 200 feet at the time of the accident. There were two fatalities and 39 injuries in the crash. [1].
Freezing Drizzle and Black Ice
Lack of visibility in tule fog is hazardous enough, but these fog events are often accompanied by drizzle and freezing drizzle. Because of the lack of sunlight penetrating the fog layer, temperatures may struggle to climb above freezing, and episodes of freezing drizzle occasionally accompany tule fog events during winter. Freezing drizzle is Drizzle that freezes on contact with the ground or an object at or near the surface Such events can leave an invisible glaze of black ice on roadways, making travel especially treacherous. For the AC/DC album see Black Ice (album Black Ice is a rap group featuring Ice T and Black Silver
Safety tips
Tule fog can make driving very difficult, especially along the Interstate 5 freeway and the freeway/divided highway State Route 99, two of the main roads through the valley. Driving is the controlled operation of a land Vehicle, usually a Motor vehicle such as a Truck or a car. Route description Southern California See also San Diego Freeway, Santa Ana Freeway, Golden State Freeway Interstate 5 starts A dual carriageway or divided highway is a road or Highway in which the two directions of traffic are separated by a central barrier or strip of land known as a State Route 99 (SR 99 commonly known as Highway 99 or 99, is a north-south State highway in the U A road is an identifiable route, way or path between two or more places. With the greatly reduced visibility resulting from the tule fog, safe driving speeds are often much less than the posted speed limit. When possible, drivers should try to postpone their trip until the fog has lifted.
A driver must remember that horizontal visibility is limited just as much as vertical visibility. In Astronomy, Geography, Geometry and related sciences and contexts a plane is said to be horizontal at a given point if it is locally In Astronomy, Geography, Geometry and related sciences and contexts a direction passing by a given point is said to be vertical if A driver should use his or her car's headlights to see ahead. Using low-beam headlights is highly recommended, as the fog reflects high-beam headlights back at the driver, reducing visibility. A driver should drive at a safe speed, which is usually below the speed limit. If a deadline is to be met, a driver should leave earlier to allow time to safely get to his or her destination.
Because of the low visibility, a driver should listen for traffic that cannot be seen. A driver must stay patient. If possible, a driver should avoid intersections where cross traffic does not stop (there are many of those intersections in the Central Valley). An at-grade intersection is a junction at which two or more transport axes cross at the same Level (or grade) If there is an emergency, and a driver needs to pull his or her vehicle over, then he or she must be careful to pull the vehicle completely off the road and use flares to alert other drivers. A flare, also sometimes called a fusee, is a type of Pyrotechnic that produces a brilliant light or intense heat without an Explosion.
When pulling off the road at night and in extremely poor visibility, leaving the lights or parking lights on once the vehicle has been pulled over is dangerous as drivers often use the tail lights of the car they are following to help them determine where the road is and they may steer off the road in an attempt to stay lined up behind your car. For reasons which may be obvious to some, but not to others, it is also dangerous to remain in or in front of your car.
As always, one should be sure to heed instructions of the California Highway Patrol, especially if they are providing escorts. The California Highway Patrol (CHP is a state agency that acts as the State police force of California. One must always read and obey the overhead traffic and weather information on signs along California highways.
References
External links
- Page on tule fog from the National Oceanic and Atmospheric Administration (NOAA)
- Forecasting Radiation Fog University Corporation for Atmospheric Research
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