Increasing Collaboration and the Prediction of Tule Fog Impacts between the California Department of Transportation, California Highway Patrol and NWS Hanford

Over the past few years, the National Weather Service (NWS) in Hanford has been working closely with the California Department of Transportation (CalTrans) District Six in Fresno, and the California Highway Patrol (CHP) in Hanford/Ft. Tejon, to increase the exchange of timely information, that can reduce the number of fog related fatalities across the central valley of California. Dense Fog is the number one cause of weather related fatalities across the Hanford National Weather Service (NWS) County Warning Area (CWA). For the 2017-18 fog season, CalTrans specifically requested a forecast product that could assist with their decision support services with regards to planning, resource allocation, and changeable overhead digital road signs. The California Highway Patrol (CHP) could also benefit from an online, visually appealing fog map with regards to their highway pacing program. During the worst fog events, when visibility is less than 500 feet, patrol cars are dispatched to guide traffic at safe speeds through stretches of heavily traveled roadways. CHP can operate this program with more efficiency and efficacy with increased lead time if it is provided in a map based format, something that our legacy, zone based, text Dense Fog Advisory product cannot address. Model guidance sometimes performs poorly predicting visibilities in our region, and the implied deterministic nature of the dense fog advisory creates a fear of false alarm among forecasters, which can lead to missed events or little lead time. The above considerations made the development of the multi-tiered color-coded Experimental Fog Severity Index (FSI) a necessity, which merges the standard operating procedures of CalTrans, CHP and the NWS. It is important to note that the FSI is not restricted by traditional hard-coded criteria. Visibilities above the quarter mile or less requirement for a Dense Fog Advisory can cause transportation impacts on smaller, curvy mountain roads.

Aggressive collaboration and communication leading up to this past fog season, through an Integrated Warning Team and an event simulation, led to the merging of CalTrans’ Operation Fog and NWS Hanford’s Operation Ground Cloud projects. Prototype images of the FSI with roadways and changeable overhead sign locations were presented during the simulation. The FSI maps conveyed where CalTrans could display messages which alerted motorists of dangerous visibilities, miles before they were encountered. Also, an NWS Chat account was created and CalTrans Transportation Management Center (TMC) operators practiced using the application with forecasters back at the office.

An overarching goal of the project is to create a communication loop between CHP, CalTrans, the NWS, the media, and school superintendents to help the entire community be more prepared for dense fog. Ultimately one message regarding tule fog will emanate from multiple trusted sources. This is the most powerful way to inspire motorists to respond appropriately to transportation risks.

A post-season fog symposium was held to identify positives and negatives of the project over the 2017-18 season. Forecasters agreed that the National Blend of Models (NBM) visibility product usually was an improvement over the HRRR, increasing their confidence in the FSI. Some CalTrans changeable message signs, which were dormant during past extreme events, were activated with fog impacts for the first time.

After this year’s positive feedback, the FSI and Operation Ground Cloud is expected to be expanded to neighboring NWS locations, as other CalTrans Districts want to be involved. This presentation will present more details about the collaboration and the Experimental Fog Severity Index. New endeavors, such as the initialization of the FSI with GOES-East data and/or LIFR Probabilities from the Cooperative Institute for Meteorological Satellite Studies (CIMSS), will be discussed.