PlainHazard

Dense Fog

NOAA Storm Events type · 17,881 records since 1996 · 46 states and territories

The National Weather Service defines dense fog as: "Water droplets suspended in the air just above the Earth’s surface reducing visibility to values equal to or below locally/regionally established values for dense fog (usually 1/4 mile or less) and impacting transportation or commerce." NOAA's Storm Events Database holds 17,881 dense fog records from 1996 through June 30, 2026, the most in California (2,441), with 292 deaths recorded.

How the National Weather Service files dense fog

Water droplets suspended in the air just above the Earth’s surface reducing visibility to values equal to or below locally/regionally established values for dense fog (usually 1/4 mile or less) and impacting transportation or commerce. If the event that occurred is considered significant, even though it affected a small area, it should be entered into Storm Data.
National Weather Service Instruction 10-1605, Storm Data Preparation (July 26, 2021), Appendix A, entry 7

Source: National Weather Service Instruction 10-1605. Read the instruction (PDF).

Dense Fog, 1996 to 2026

Records per year (2026 to June 30, 2026).

  • recorded, no damage figure
  • under $10 million
  • $10 million or more
  • $100 million or more
  • $1 billion or more, or 100 deaths
  • $10 billion or more, or 1,000 deaths
  • a year's colour: its recorded damage or deaths
  • a year with a death
Records
17,8811996 to June 30, 2026
Deaths
2921,817 injuries
Damage, 2025 dollars
$66Mas filed (scale steps before 1993)
Counties with a record
1,133of 3,266

Source: NOAA NCEI Storm Events Database, records through June 30, 2026. Search the record at NCEI.

Where do dense fog records happen?

States

  1. California 2,441
  2. Illinois 2,188
  3. Kentucky 1,882
  4. Virginia 1,707
  5. Wisconsin 1,612
  6. Maryland 1,086
  7. Missouri 1,043
  8. Florida 751
  9. New Jersey 737
  10. West Virginia 545
  11. Indiana 512
  12. Pennsylvania 466
  13. Colorado 409
  14. Kansas 311
  15. Oklahoma 306

Counties

  1. Fresno County, CA 1,057
  2. Kern County, CA 671
  3. Tulare County, CA 661
  4. Merced County, CA 626
  5. Kings County, CA 577
  6. Madera County, CA 456
  7. Mariposa County, CA 333
  8. San Diego County, CA 225
  9. Fauquier County, VA 178
  10. Saline County, IL 150

Source: NOAA NCEI Storm Events Database (forecast-zone records count on every county the zone covers).

When do dense fog records happen?

40% of its dense fog records since 1996 fell in December and January. The busiest month is December.

The values, month by month

Jan 3,338 · Feb 2,233 · Mar 1,412 · Apr 596 · May 772 · Jun 268 · Jul 414 · Aug 710 · Sep 853 · Oct 1,199 · Nov 2,256 · Dec 3,830 (records).

Source: NOAA NCEI Storm Events Database, records by the month they began.

The deadliest dense fog records

The dense fog records with the most deaths
DateRecordCharacterKilledInjuredDamage
2002-10-11 Dense FogSheboygan County, WI · forecast zone Sheboygan Shallow dense fog developed over parts of Sheboygan and Ozaukee counties during the overnight hours, and persisted to about 0830CST. The dense fog, reducing visibilities to zero to 1/4 mile, was a factor in three closely-spaced, but separate multi-vehicle accidents in Sheboygan County (total of 50 vehicles), and one ... 10 0 –
2023-10-23 Dense FogSt. John the Baptist Parish, LA · forecast zone St. John The Baptist A chain reaction event of car accidents occurred on I-55 near mile marker 14 as dense fog reduced visibility to near zero. The pile up that took place included 158 vehicles and resulted in dozens of injuries and several fatalities. Many vehicles caught fire and one toppled over the interstate guard rail and ended up ... 7 55 $3.9M
2008-01-09 Dense FogPolk County, FL · forecast zone Polk A controlled burn from the previous afternoon was still producing smoke as patches of dense fog began to develop around 4AM. The smoke and fog interacted to produce super-fog in about a 2 mile area encompassing Interstate 4 near Polk City between US 27 and the Polk Parkway. The super-fog caused zero visibility for ... 5 38 –
1997-12-11 Dense FogPlacer County and 4 more, CA · forecast zone Yolo T W/Ne Solano/Sacramento T X Sw/X W Placer/X W Amador/S Sutter Patchy dense fog was a main contributing factor in a major chain reaction collision on northbound Interstate 5 near Lambert, CA, 17 miles south of downtown Sacramento. The crash involved 8 tractor trailers, 1 tanker truck, and 28 automobiles and small trucks. The five fatalities were burn victims caught in the fires ... 5 26 $2.8M
2022-03-17 Dense FogMississippi County, MO · forecast zone Mississippi Dense fog along portions of Interstate 57 between the Mississippi River and Interstate 55 resulted in several fatalities (indirect) in a massive pile-up. The pile-up occurred on both sides of the interstate near Charleston, Missouri in Mississippi County. Approximately 50 vehicles were involved, including multiple ... 5 14 –
2015-01-13 Dense FogCalaveras County and 2 more, CA · forecast zone Northern San Joaquin Valley A 2 vehicle car crash occurred on Highway 4 off Van Allen Rd., east of the city of Stockton, resulting in 5 fatalities and 3 injuries. The accident occurred at approximately 6:30 am PST and is thought to be related to poor visibility from fog. First responders reported visibility less than 100 feet when they arrived ... 5 3 $50K
2007-03-13 Dense FogOsceola County, FL · forecast zone Osceola A total of five people were killed, including a sheriff's deputy, in a series of three accidents on the Florida Turnpike in southern Osceola County. 5 3 $185K
2020-11-14 Dense FogButte County and 4 more, CA · forecast zone Central Sacramento Valley The California Highway Patrol (CHP) reported a 10 vehicle pile up in Butte County, along highway 99 between Gridley and Biggs Saturday morning. The report noted 5 big rigs and 5 passenger vehicles were involved, which forced the highway to be closed for several hours. 5 fatalities were reported with this event, with 2 ... 5 0 –

Source: NOAA NCEI Storm Events Database, deaths direct and indirect as filed.

The most recent dense fog records

To June 30, 2026
DateRecordCharacterKilledInjuredDamage
2026-06-28 Dense FogBucks County, PA · forecast zone Upper Bucks 0 0 –
2026-06-28 Dense FogMontgomery County, PA · forecast zone Eastern Montgomery 0 0 –
2026-06-28 Dense FogChester County, PA · forecast zone Western Chester 0 0 –
2026-06-28 Dense FogChester County, PA · forecast zone Eastern Chester 0 0 –
2026-05-31 Dense FogMoffat County and 2 more, CO · forecast zone Central Yampa River Basin 0 0 –
2026-05-25 Dense FogLehigh County, PA · forecast zone Lehigh 0 0 –
2026-05-25 Dense FogCarbon County, PA · forecast zone Carbon 0 0 –
2026-05-25 Dense FogBerks County, PA · forecast zone Berks 0 0 –

Source: NOAA NCEI Storm Events Database.

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