Methodology

Flood

Peril Report looks up the FEMA National Flood Hazard Layer for the point that matches your address. The headline is the mapped flood zone, with the annual chance of flooding where FEMA publishes it. Show on Map overlays FEMA flood hazard zones on the address map and places a legend under the map. Street, satellite, and elevation views are available (OpenStreetMap streets, Esri satellite imagery, and Esri topographic elevation); a pin marks the looked-up point without an address popup.

Special Flood Hazard Areas (typically A and V zones) are the 1% annual-chance floodplain. Zone X includes areas outside that floodplain, including the 0.2% annual-chance (500-year) floodplain when FEMA maps it. A levee is noted only when FEMA’s zone subtype says the area is protected by a levee.

If the point is not in a mapped flood zone, the report shows the nearest mapped zone within 2 miles. It also names the nearest river or ocean used as a flood source, and the closest named body of water, each searched within 2 miles, from the USGS National Hydrography Dataset (rivers, streams, lakes, and reservoirs).

The Flash Flooding figure is the 1% annual-chance (100-year) 1-hour rainfall intensity from NOAA Atlas 14, queried at the address from the Precipitation Frequency Data Server. Values are partial-duration series estimates in inches per hour. The figure is omitted in regions Atlas 14 does not cover, including much of the Pacific Northwest.

Tropical Cyclones

Hurricane chances on Peril Report come from NOAA IBTrACS (International Best Track Archive for Climate Stewardship). Storms are counted from 1950 onward when the U.S. wind speed reaches hurricane force (64 knots, Category 1) or major-hurricane force (96 knots, Category 3).

A storm counts if its center passed within 50 miles of the Census county that contains the address. Unique storm IDs are used so one hurricane is not counted twice. The annual chance is a Poisson estimate from that history: 1 − exp(−count / years). The rating in that section is FEMA’s National Risk Index tropical-cyclone expected annual loss rating for the county, which is separate from the IBTrACS strike chances. The percentile bar is the tropical-cyclone expected annual loss rate compared with other U.S. counties. The text also prorates historic and modeled building-loss ratios over 30 years.

Hurricane storm surge comes from the National Hurricane Center’s National Storm Surge Risk Maps, the same public maps at https://www.nhc.noaa.gov/nationalsurge/. Those maps take SLOSH Maximum of Maximums (MOM) water levels at high tide and convert them to inundation above ground on a ~10 m DEM. Peril Report lists the NHC depth class for each hurricane category (1–5) that inundates the address, labeled as water depth from a worst-case storm of that category. Depths use NHC’s published bins (< 3 ft, 3-6 ft, 6-9 ft, and > 9 ft). A category is omitted where that storm does not flood the location. Leveed areas are shown as such. If the maps show no inundation but historic hurricane chance is at least 0.1%, the same cited box states that the location is not expected to be exposed, based on storm, tide, and elevation modelling. NHC does not cover the Pacific Northwest or Alaska.

For Gulf and East Coast counties that Colorado State University covers, Peril Report also shows that year’s Tropical Cyclone Impact forecast: the probability of a hurricane and of a major hurricane tracking within 50 miles. Those seasonal odds are adjusted from 1880–2020 climatology using CSU’s latest Atlantic forecast. They are omitted when CSU does not publish a forecast for the county.

Tropical cyclone is the generic name for a warm-core storm with a closed circulation. A tropical depression has winds below 39 mph (34 kt), with rain and flooding the main threats. At 39–73 mph (34–63 kt) it is a tropical storm and is given a name. At 74 mph (64 kt) or higher the same storm is called a hurricane in the Atlantic and Northeast Pacific, a typhoon in the Northwest Pacific, and a cyclone (or severe tropical cyclone) in the South Pacific and Indian Ocean. Super typhoon is a regional term for the strongest Northwest Pacific storms. A subtropical cyclone is a hybrid of tropical and extratropical storms; it can still bring damaging wind, rain, and surge, and may later become fully tropical.

Forecasting

The Forecasting page shows live tropical and climate outlooks alongside the address lookup. The National Hurricane Center 7-day Atlantic Graphical Tropical Weather Outlook is the official short-range product. Google Weather Lab’s WeatherNext Cyclones 1000-member ensemble (FNV3 large ensemble) is shown as a map of the probability that a tropical cyclone passes within 200 km of a 0.5° grid cell at any lead time in that run. Probability is the share of ensemble members with a track point inside that radius. The map covers the Atlantic basin. Weather Lab’s public download only pairs predicted tracks with official observed storms, so invests and ensemble genesis are not included. The forecast is experimental, not an official warning; recent cycles are subject to Weather Lab’s terms of use. ECMWF’s AIFS ENS (50 members plus a control) is shown on the same 200 km / 0.5° grid, using that model’s tropical-cyclone trajectory files, which include storms that form during the forecast. AIFS is experimental, not an official warning; ECMWF open data is CC BY 4.0.

El Niño–Southern Oscillation status uses NOAA Climate Prediction Center’s Oceanic Niño Index and the latest ENSO Diagnostic Discussion.

Wildfires

Peril Report searches mapped wildfire perimeters within 20 miles of the address. Historic fires come from the NIFC Interagency Fire Perimeter History layer. Recent fires, including current-year perimeters, come from WFIGS Interagency Fire Perimeters. Prescribed burns are left out.

If the point sits inside a perimeter, the report says the location burned over and, when more than one unique fire is mapped there, how many times. Otherwise it names the closest mapped fire, when it burned, and its size. Beyond 20 miles, it only says the closest mapped wildfire is more than 20 miles away.

The rating is FEMA’s National Risk Index wildfire expected annual loss rating for the county. The percentile bar is the wildfire expected annual loss rate compared with other U.S. counties. The text also prorates historic and modeled building-loss ratios over 30 years. Red-flag warning counts from the past 10 years are included when that record is available, on the same line as the closest mapped wildfire.

Risk to Potential Structures comes from the USDA Forest Service Wildfire Risk to Communities 30-meter raster (USFS WRC Risk to Potential Structures). It combines wildfire likelihood and intensity with generalized consequences to a home at that pixel: the relative risk to a house if one existed there. Classes are Low, Medium, High, and Very High using national pixel percentiles from the WRC methods (below the 40th, 70th, and 90th percentiles). The Community Wildfire Risk Reduction Zone (USFS WRC CWiRRZ 4-class raster) is the exposure type at that pixel: minimal, indirect (embers and home-to-home), direct (adjacent vegetation plus embers), or wildfire transmission.

For California ZIP codes, the report also shows the CAL FIRE Fire Hazard Severity Zone at the point (CAL FIRE OSFM FHSZ maps). State Responsibility Area zones are the adopted April 2024 map. Local Responsibility Area zones use CAL FIRE’s 2025 recommended classes (Moderate, High, Very High). Points outside those polygons are reported as not in a mapped zone.

Severe Convective Storms

Hail

Hail on Peril Report uses FEMA’s National Risk Index for the county. The headline is the expected annual loss rating (for example, Relatively Low), not the composite hail risk rating that also folds in social vulnerability and community resilience.

The percentile bar is the expected annual loss rate compared with other U.S. counties. The text also reports how often hail occurs in the NRI record and prorates historic and modeled building-loss ratios over 30 years.

Tornadoes

Tornado chances use Storm Prediction Center tornado tracks from 1950 through 2017. Peril Report counts tracks that intersect the Census county containing the address, for any tornado (EF0 or above) and for strong tornadoes (EF3 or above). The annual chance is a Poisson estimate from that county history: 1 − exp(−count / years). The rating in the section is FEMA’s National Risk Index tornado expected annual loss rating, which is separate from those track-based chances. The percentile bar is the tornado expected annual loss rate compared with other U.S. counties. The text also prorates historic and modeled building-loss ratios over 30 years.

Wind

The Wind section shows the ASCE 7-22 basic wind speed at the address: the 3-second gust wind speed at 33 feet above ground for Exposure C, based on a 100-year mean recurrence interval (the serviceability wind speed under Section 26.5.2 of ASCE/SEI 7-22), from the ASCE 7 Hazard Tool. This is not a forecast or a historic wind report.

Earthquake

Earthquake results are FEMA National Risk Index values for the county, not a site-specific shaking model. The headline is the expected annual loss rating (for example, Relatively Moderate), not the composite earthquake risk rating that also folds in social vulnerability and community resilience. Frequency comes from the NRI annualized frequency field. Event counts, when present, are from the NRI record, which FEMA treats as a 100-year earthquake history for this index.

Peak ground acceleration comes from the USGS National Seismic Hazard Model at the address, for a 2% chance of exceedance in 50 years on site class BC (Vs30 = 760 m/s). Instrumental intensity and potential damage follow the USGS ShakeMap PGA ranges (Wald et al. 1999).