Thursday, February 5, 2009

Sierra Madre Issues Yellow Flag Alert

Yellow Flag Alert

The County has issued a Phase 1 mud and debris flow alert. National Weather Service is forecasting 70% to 80% chance of precipitation today through Friday evening. The NWS is also forecasting the heaviest rains for today may reach 0.7” between the hours of 4:00PM and 10:00PM. A Phase 1 indicates that small isolated debris and mudflows are possible at specific locations. Streets may be flooded or blocked by debris. Reports of debris on private property may be received. Few, if any, structures may be endangered.

Parking restrictions are in effect in the Upper and Lower Canyon during Yellow or Red Flag alerts. Vehicles may be towed at owner’s expense.

Green-Yellow-Red Flag Warning System Explanation
The City is acutely aware of the inconvenience that the yellow and red flag warning system and its accompanying parking restrictions cause our residents. We are truly sorry for that inconvenience and we thank our residents for their continued patience.

Thus, we do not take lightly the posting of yellow and red flag warnings. We have developed the warning system using the best, most accurate information available regarding rainfall amounts, hydrology, and local geology. For that information, we rely strictly on the National Weather Service (NWS) and the Los Angeles County Department of Public Works (LACDPW). For consistency and to avoid arbitrarily inconveniencing our residents the City issues our warnings based on recommendations from those agencies.
Condition Green is called upon receipt of a NWS forecast calling for 80% or greater chance of rain.
Condition Yellow is called upon receipt of an LACDPW Phase 1 Debris and Mudflow Forecast. LACDPW develops their forecast utilizing NWS rainfall intensity data, geologic data specific to the mountains above Sierra Madre, and LACDPW’s own empirical data on local hydrology and debris flow characteristics.
Condition Red is called upon receipt of an LACDPW Phase 2 or 3 Debris and Mudflow Forecast.

Finally, the City issues the warnings as quickly as possible following receipt of NWS and LACDPW forecasts. While it appears counterintuitive to call a Yellow Flag warning while the sun is still shining, the City must err on the side of caution. Again, thank you for your continued patience.

Yellow Flag Condition is now in effect. For more information, please visit

posted by James