The average high and low temperature chart below serves as a useful measure of climate. Weather Risk suggests the risk of certain weather events occurring in this community as compared to the national average. The national average for each type of event equals a score of 100, so a score of 200 would represent twice the risk as the national average, and a score of 50 would represent half the risk of the national average.
Below are the charts for ZIP code 78209 in San Antonio Texas.
Weather risks define the relative chance, based on historical occurrence, of specific, potentially damaging, weather events. Weather event data is publicly available from government sources. This data specifies the origin point, and in some cases, the path of these events. To determine risk, a spacial analysis i s performed based on the location, frequency and strength of events within a proximity to an area.
Why is there a high risk if there have never been any hurricanes (tornados, wind events, damaging hail) in this area?
Risk values are tied to areas larger than single zip codes. For example, if a hurricane has never landed in a particular county but has crossed all of the neighboring counties at some point, then a relatively high risk might be determined. Weather events are unpredictable and at a micro level (such as zip codes, towns, and residential neighborhoods) the occurrence of such events appears random. However, if one looks at a larger area - such as a county or region - patterns become more obvious and evident.
What are the sources for hurricane risk?
Hurricane track data was obtained from publicly available USGS records. Atlantic hurricane coverage is from 1896 to the late 1990's, covering a total of 950+ storms. Pacific hurricane coverage is from 1949 to the late 1990's, covering a total of 660+ storms. Storm locations are tracked every six hours while the storm maintains the minimum wind speed required to be classified as a tropical storm. Along with location, the database includes information on wind speed and barometric pressure. The risk indexes are calculated using an area of decreasing severity along the path of the storm track and a width 100 miles to each side.
What are the sources for tornado risk?
Tornado records have been collected and published by the USGS since 1950. Unlike hurricanes, which are always presented as a hurricane path, tornadoes are presented either as a path or as a single touchdown point. Nearly 40,000 individual tornado events have been recorded and were used in the risk analysis. Each tornado point and path was assigned an area of decreasing influence which was then applied in aggregate to each community location.
What are the sources for damaging hail risk?
Damaging hail records are available from the USGS from 1955 and include over 85,000 individual events. Damaging hail is defined as hail of at least 3/4 inch in diameter. Filters were applied to this database to derive relative frequency and intensity measures which were then applied to the community locations.
What are the sources for damaging wind risk?
Wind risk events have been recorded by various agencies since 1955, and include over 115,000 separate events. A damaging event has winds of over 50 knots. Wind events do not include tornados and hurricanes.
What are the sources for earthquake risk?
Quake risk is derived from two primary sources:
- The epicenter locations of significant earthquakes during this century. The quality of the additional information is significantly improved in recent years. Quakes in the 3.0 range are included only for the very recent past, while large quakes are tracked back to the turn of the century.
- An area analysis of earthquake risk and damage derived from USGS models.
These influence areas of these sources are then applied to the community locations.
How is total weather risk calculated?
The total weather risk value represents a single index combining damaging wind, hail, hurricane and tornado events. Earthquake risk is not included. This index is based on the relative damage expected from each of the four types of events. The relative influence of each of the four weather event types is not equal and was derived by weighting estimates of total annual damage caused by each type of storm.