National Weather ServicePennsylvaniaDense Fog AdvisoryArchive to October 1, 2026
Dense Fog Advisories in Pennsylvania
The National Weather Service issued 46 dense fog advisories for Pennsylvania in 2025 and 27 a year on average in 2008-2025; in 2021-2025 it had the 30th most of any state. 2026 through September: 56, 215% above the average of 18 for those months in 2008-2025. Delaware was covered most often (112 times since 2008).
How many dense fog advisories does Pennsylvania get?
Every dense fog advisory that covered part of Pennsylvania. 2026 is an outline: the year is not over.
The numbers
| Year | Count |
|---|---|
| 2026 (through September) | 56 |
| 2025 | 46 |
| 2024 | 44 |
| 2023 | 32 |
| 2022 | 29 |
| 2021 | 22 |
| 2020 | 24 |
| 2019 | 24 |
| 2018 | 39 |
| 2017 | 25 |
| 2016 | 15 |
| 2015 | 38 |
| 2014 | 22 |
| 2013 | 31 |
| 2012 | 23 |
| 2011 | 16 |
| 2010 | 12 |
| 2009 | 21 |
| 2008 | 20 |
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 Pennsylvania 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 Pennsylvania?
| County or forecast zone | Since 2008 | Since 2023 | Last issued |
|---|---|---|---|
| Delaware | 112 | 28 | March 21, 2026 |
| Lancaster | 112 | 27 | May 26, 2026 |
| Schuylkill | 112 | 39 | May 26, 2026 |
| Philadelphia | 110 | 26 | May 10, 2026 |
| Western Chester | 109 | 32 | May 26, 2026 |
| Eastern Chester | 108 | 32 | May 26, 2026 |
| Upper Bucks | 107 | 31 | May 26, 2026 |
| York | 107 | 24 | May 26, 2026 |
| Eastern Montgomery | 105 | 31 | May 10, 2026 |
| Lebanon | 105 | 27 | May 26, 2026 |
| Southern Centre | 105 | 27 | August 21, 2026 |
| Lower Bucks | 104 | 30 | May 10, 2026 |
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 Pennsylvania.