National Weather ServiceIdahoDense Fog AdvisoryArchive to October 1, 2026
Dense Fog Advisories in Idaho
The National Weather Service issued 21 dense fog advisories for Idaho in 2025 and 23 a year on average in 2008-2025; in 2021-2025 it had the 35th most of any state. 2026 through September: 15, 14% above the average of 13 for those months in 2008-2025. Lower Treasure Valley was covered most often (187 times since 2008).
How many dense fog advisories does Idaho get?
Every dense fog advisory that covered part of Idaho. 2026 is an outline: the year is not over.
The numbers
| Year | Count |
|---|---|
| 2026 (through September) | 15 |
| 2025 | 21 |
| 2024 | 33 |
| 2023 | 28 |
| 2022 | 25 |
| 2021 | 17 |
| 2020 | 7 |
| 2019 | 14 |
| 2018 | 12 |
| 2017 | 17 |
| 2016 | 27 |
| 2015 | 22 |
| 2014 | 31 |
| 2013 | 42 |
| 2012 | 8 |
| 2011 | 10 |
| 2010 | 32 |
| 2009 | 43 |
| 2008 | 26 |
Source: Iowa Environmental Mesonet archive of National Weather Service watches, warnings and advisories (VTEC); National Weather Service. Data as of October 1, 2026.
When in the year does Idaho get them?
Sum of 2008-2025; the busiest month is labelled.
Source: Iowa Environmental Mesonet archive of National Weather Service watches, warnings and advisories (VTEC); National Weather Service. Data as of October 1, 2026.
Where in Idaho?
| County or forecast zone | Since 2008 | Since 2023 | Last issued |
|---|---|---|---|
| Lower Treasure Valley | 187 | 43 | January 15, 2026 |
| Upper Treasure Valley | 157 | 32 | January 15, 2026 |
| Upper Weiser River | 82 | 25 | January 15, 2026 |
| Coeur d'Alene Area | 81 | 23 | February 5, 2026 |
| Western Magic Valley | 62 | 14 | January 18, 2026 |
| Northern Panhandle | 42 | 15 | February 5, 2026 |
| Upper Snake River Plain | 41 | 5 | March 3, 2026 |
| Lower Snake River Plain | 40 | 6 | February 12, 2026 |
| Eastern Magic Valley | 30 | 5 | January 19, 2026 |
| Idaho Palouse | 28 | 9 | February 6, 2026 |
| West Central Mountains | 21 | 3 | December 20, 2024 |
| Orofino/Grangeville Region | 17 | 1 | December 24, 2025 |
The NWS issues these products for counties or forecast zones; a zone can be part of a county or a mountain range.
Source: Iowa Environmental Mesonet archive of National Weather Service watches, warnings and advisories (VTEC); National Weather Service. Data as of October 1, 2026.
What is a dense fog advisory?
A dense fog advisory means fog will cut visibility to a quarter mile or less over a wide area. An advisory is issued for a hazard less serious than a warning that can still cause inconvenience or danger if people are not careful. The national record · Every warning type in Idaho.