August 6
New Feature: Flash Flood Potential Index Maps
As we are in the middle of the summer Monsoon season, this week I added a few additional maps to the “Weather Maps” menu on the main DesertWeather site. These map will assist in determining thunderstorm development in our area and more importantly flash flooding potential.
You will see 3 links at the bottom labeled: “Flash Flood Potential Day 1″, “Day 2″, and “Day 3″. You will see a date at the bottom of each map to identify its date. These maps are explained by the National Weather Service in San Diego… “The Flash Flood Potential Index is intended to indicated the potential for flash flooding to develop. It is not strictly a rainfall rate product. In addition to heavy rainfall, terrain and antecedent conditions such as whether an area has had recent rainfall or has been recently burned also influence the potential for flash flooding to develop should heavy rainfall develop” -source: NWS
These maps are color coded Green, Yellow, and Red.
- No Color: No Flash Flooding is Expected.
- Green / Low: The Risk of Flash Flooding is Minimal.
- Yellow / Moderate: Thunderstorms are Expected to Develop and Isolated Flash Flooding is Possible.
- Red / High: Thunderstorms with Areas of Heavy Rain are Expected and the Threat of Flash Flooding is Significant.
Click here for today’s map
The factors that the National Weather Service uses to determine the risk are as follows:
Precipitable Water - Higher values will result in higher values of the index, lower values in lower values of the index.
600 mb Wind Speed - Attempts to indicate storm movement. Slower speeds will result in higher values of the index, faster speeds in lower values of the index.
Topography and 900-700 mb mean Relative Humidity - Attempts to indicate the potential for drier air at lower levels to reduce rainfall at lower elevations due to subcloud evaporation. Drier mean relative humidity will result in lower values of the index with higher subcloud mean relative humidities resulting in higher values of the index. With drier mean subcloud relative humidities, values of the index for lower elevations will be less than for higher elevations. The difference of values for higher and lower elevations will be less when the mean subcloud layer is more moist (greater values of mean relative humidity).
700 mb Wind Direction - Assesses the potential of storms that develop over the mountains to move west of the mountains into the valleys and coastal areas. Directions without an easterly component will set the index to low values for areas west of the mountains.-source: NWS
These map are only available through September 30th. Also these maps only cover the National Weather Service for San Diego’s coverage area. Which does not include the San Bernardino Mountains.
Comment on this post - (3) Posts