What each layer shows, what can be inferred from it, and which combinations answer which question.
[1.1] Layers are grouped by the question being asked rather than by who publishes them. The five group headings are those five questions.
What is happening this minute. Radar, satellite, warnings, watches, river gauges, flood inundation. These refresh on their own while the page is open.
What is on the way. Severe weather outlooks and tropical systems. Use these the day before to decide where to pre-position.
What happened, and to whom. Rainfall totals, storm reports, past warnings, damage reports, shelters, night lights, flood extent, fire and earthquakes.
Where damage is likely before anything happens. Hazard risk by county, FEMA flood zones, storm surge. None of these changes with the weather. They are for the months before an activation rather than the week of one.
Context under and over everything else. Basemaps, aerial imagery, roads, terrain, county lines, labels, and the congregation list.
[1.2] Most layers start switched off. Radar, warnings, watches, storm reports and damage reports are on when the page loads, because those five answer "is anything happening" without a click.
[1.3] A small triangle beside a layer opens its options. Anything set there travels in the link the copy button produces, so a view can be sent to somebody else exactly as it was read.
[2.1] The national reflectivity mosaic, looping. The options behind the triangle switch between reflectivity and velocity. Opacity starts at 55% so town names and highways read through a line of storms. The play button on the radar readout, bottom left of the map, pauses the loop.
[2.1a] Reflectivity shows where the rain is. Velocity shows which way it is moving, and that is how rotation becomes visible. Switch to it behind the radar triangle when a storm looks capable of producing a tornado.
[2.1b] Green is motion toward the radar, red is motion away from it. Neither color means wind direction on the ground. Both are measured along the line between the radar and the storm.
[2.1c] What you are looking for is a tight green and red pair sitting directly against each other. Air moving toward the radar right beside air moving away from it is air turning in a circle. That couplet is the rotation signature, and the smaller and sharper it is, the more concentrated the rotation. Reflectivity alone cannot show you this.
[2.1d] It is one radar, not the national mosaic. Velocity is only published per site, so the map follows the WSR-88D nearest the center of your view and switches sites as you pan. The readout in the bottom-left corner names the site currently in use.
[2.1e] Distance from that site matters. The radar beam climbs as it travels. Close to the site you see the bottom of the storm. Far away you see its middle. Past roughly 60 miles, low-level rotation can be happening under a beam that passes over it. If a storm sits at the edge of one radar's range, pan toward it so the map picks up a closer site.
[2.2] GOES-East color imagery, refreshed every ten minutes. Useful for the shape of a system when radar only shows you its edge.
[2.2a] Lightning is not drawn on this map. The networks that track individual strikes do not permit their data to be used operationally. lightningmaps.org shows live strikes in a browser and is worth keeping open beside this map when you want to judge how active a storm is.
[2.3] Two separate checkboxes, because they answer different questions. A warning means the hazard is happening or about to. A watch means conditions favor it over a wider area and a longer window. Watches draw underneath warnings, and each has its own opacity slider and fade setting.
[2.4] "Fade in close" is on by default. Warning polygons carry the message at national zoom, where one may be a few pixels across. Zoomed to a county they are context for the roads and towns underneath, so the fill eases back as you go in. Turn it off if you want a constant fill.
[2.5] Tornado, severe thunderstorm, flood and flash flood have their own colors, warning and watch each. Everything else draws gray, so a colored polygon means damage-causing weather.
[2.6] Only gauges at or above action stage, which is a couple of dozen points nationally rather than twelve thousand. A filled dot is the stage observed now. A ring around it is the highest stage forecast over the next several days. A gauge rising toward flood shows a ring before it shows a dot, so the ring is the early warning. Colors run yellow through purple as the stage climbs.
[2.7] Modeled water, drawn street by street, from the National Water Prediction Service. Three guidance options sit behind the triangle. They are the latest analysis, a five-day river forecast, and a five-day weather-driven forecast. Radar tells you the storm and rainfall totals tell you where the water fell. This tells you which streets it reached.
[3.1] The Storm Prediction Center's categorical severe risk, in their own colors, for today, tomorrow or the day after. Use it to decide where to pre-position before anything has happened.
[3.2] The National Hurricane Center package: forecast cone, track past and future, forecast points, and the coastal watches and warnings that go with each storm. Hovering a storm opens its details.
[4.1] Radar-estimated rainfall in inches, over a window you choose from one hour to 72. The service draws its own legend into the panel, which is the only way to read inches off the colors. Opacity starts at 65% because a 72-hour total covers the whole storm footprint and hides the roads under it.
[4.2] What people on the ground told the Weather Service: tornado, hail, flooding, wind damage, wildfire. Last 24, 48 or 72 hours. These are observations, so they cluster where people live and thin out where they do not.
[4.3] Warning polygons already issued and expired, over the last 24, 48 or 72 hours, filtered to tornado, tornado plus severe storm, or everything. These are the narrow wedges drawn ahead of a cell, not the county-wide products.
[4.4] This is the layer for the morning after. The live warning layer has already cleared itself. This one shows what was warned overnight, and where to start calling. Clicking a polygon links to the warning text, which carries the radar-indicated gust estimate.
[4.5] The Weather Service Damage Assessment Toolkit, last seven days. Surveyed per structure, with a degree-of-damage rating and often a photograph in the popup. This is the closest thing to a verified damage map that exists. It is human-collected, so it arrives days after the event, and only where a survey team went.
[4.6] One row, two markers. A filled dot is an open shelter, with the live head count in its popup. A diamond is a FEMA disaster recovery center, with the declaration number it belongs to.
[4.7] A shelter is a fast signal that somebody was displaced, usually before any federal declaration exists. A recovery center is slow confirmation that a declaration happened. Several open shelters are usually churches, so the layer often names buildings a coordinator already knows.
| Signal | Lag after the weather |
|---|---|
| [4.8] Storm-based warnings | minutes |
| [4.9] Shelters open | 1 to 3 days |
| [4.10] Federal declaration | about a week |
| [4.11] Recovery centers open | 2 to 3 weeks |
[4.13] Satellite measurement of light leaving the ground at night. Pick a date and a satellite. Two cross each night. Compare the night after a storm with the night before and the dark patch is where the power went.
[4.14] No public feed reports power outages nationally, so this is the available substitute. Cloud hides the ground, so if a night looks blank, try the other satellite or the night either side.
[4.14a] For a count of customers out rather than a picture of it, poweroutage.us collects utility outage reports across the country. It is free to read in a browser alongside this map. Their data is licensed, so it cannot be drawn as a layer here without paying for it. Deploy Hope can add it as a paid layer if that is worth it to you.
[4.15] Water seen from orbit as a three-day composite, by date. Observed rather than modeled, so it complements flood inundation rather than repeating it. That one is fine-grained and only draws close in. This one is coarse and draws everywhere.
[4.16] Magnitude 2.5 and above over the last day. Current wildfire perimeters from the interagency feed. Satellite hot spots from the last 24 hours, which appear before anyone has drawn a perimeter.
[5.1] These three layers do not change with the weather. They show where damage has happened before and where it is likely again. That is the question you ask when there is nothing on the radar. All three start switched off.
[5.2] FEMA's National Risk Index, county by county. The hazard picker behind the triangle covers eighteen hazards. The four radio buttons under it choose what the map shows about the one you pick.
[5.3] Click a county for its numbers. The popup answers a click rather than a hover, because counties cover the whole map. It shows the ratings straight away, then asks FEMA for the rest. That adds the population and what the county is expected to lose in an average year. Under those sits a list of the hazards the loss comes from, biggest first.
[5.4] The opacity slider starts at 45%. County polygons cover everything under them, so turn it down before reading roads, churches or warnings through it.
[5.5] Behind the funnel button, the filter panel narrows the church layer to congregations in counties rated Relatively High or Very High. It rates them on whatever the risk layer is showing. That is how you get from a picture to a list of who to call first. Each church is placed by its own coordinates, not by the county name in the file, because 269 records do not carry one.
[5.6] FEMA's regulatory floodplain, the map an insurer and a building inspector work from. Zoomed out it shades the counties where a floodplain has been mapped at all. Zoomed in to neighborhood level it draws the zones themselves. The 1% annual chance floodplain is cyan, the regulatory floodway red, the 0.2% annual chance floodplain orange. There is a zoom between the two where neither draws, and the panel hint says which of the three you are looking at.
[5.7] This is the effective map, revised monthly as changes are issued. It is not a forecast and it is not where water is now. For that, use flood inundation under Now or flood extent under Aftermath.
[5.8] The worst case from many hypothetical hurricanes of one category, at high tide, from NOAA's SLOSH model. Pick the category behind the triangle. It opens on Category 3. This is not a forecast for any storm. It is the ceiling. If a category 3 hurricane came ashore in the worst place for this spot, this is how deep the water could get.
[5.9] Coastal only. The Gulf and East coasts, Puerto Rico, Hawaii and parts of the Caribbean have data. Everywhere inland is blank, and blank here means "no surge reaches this far," not "the layer is broken."
[5.10] The color is depth above ground, not depth of water. Blue is less than 3 feet, yellow more than 3, orange more than 6, red more than 9. Three feet of moving water takes a car off a road. Areas behind a levee are drawn as gray hatching rather than a depth, because what happens there depends on the levee. Ask local officials.
[6.1] Three, and only one at a time. Positron is the pale default, which keeps weather colors readable. OpenStreetMap carries more detail. Aerial imagery is nationwide photography, one to three years old. That makes it the "before" picture. Read a damage report against it and you can see what used to be there.
[6.2] The imagery has a detail option. Standard is fast and stops resolving past about zoom 16. Fine detail switches to 30 cm aerial photography, which takes a second or two per view and only draws once you are zoomed in. The hint under the options says which state you are in.
[6.3] Roads, railways and waterways drawn over whatever basemap is showing. Pair it with aerial imagery to put a street name to what the photograph shows. Draws from about county zoom inward, with its own opacity slider.
[6.4] Shaded relief under everything else. Not a hazard layer. It is there so a flood polygon or a debris path can be read against the ground that produced it.
[6.5] County lines with names. "Labels on top" draws place names and highway shields above every other layer, so weather layers do not cover the town names underneath. Over aerial imagery it switches to light text on its own. PCA churches draw as points, with pastor, phone and presbytery in the popup, and the funnel button filters them by state.
[6.6] The search box takes a church name, a town, a county or a ZIP code.
[7.1] Most questions need more than one layer. Each combination below is a sequence: switch the layers on in the order given and read each against the one before it.
The warning polygons give you the corridor while the reports are still sparse. Churches inside a polygon are the call list. Reports confirm which polygons produced something.
The cone tells you where to pre-position. Rainfall and gauges tell you where the water went. Night lights tell you who is still dark a week later.
Gauges give you days of warning. Inundation turns a gauge reading into streets. Terrain explains why those streets and not the next ones.
Step the date back and forward one night at a time. The dark patch that persists is the one that needs generators, not just chainsaws.
Zoom to the church. The imagery is the before, the damage report popup is the after, and the roads tell a driver how to get there.
Severity, displacement and proximity are three different questions. Answer them in that order.
[7.2] Change one thing at a time. Several of these layers overlap. Comparing rainfall, flood extent and inundation one at a time tells you more than switching all three on together.
[7.3] Send the view, not a description. The copy button in the panel header produces a link that reproduces position, zoom, every layer and every option. That includes the dates on night lights and flood extent.
[8.1] These are gaps in the underlying data, not settings. An empty area on the map does not mean nothing happened there.
| Question | Where the map stands |
|---|---|
| [8.2] Who lost power? | No live outage feed exists for free. Night lights is a proxy, needs a clear night, and is read by eye. |
| [8.3] Who was told to evacuate? | No public feed covers the Southeast. Evacuation orders come from counties, and only a few western states publish them. An order relayed by the Weather Service does appear under Warnings. |
| [8.4] How bad is the damage, building by building? | Damage reports, and only where a survey team went. Automated damage assessment from imagery exists commercially and has no free equivalent. |
| [8.5] What did the peak wind gust reach? | Storm reports carry measured gusts. There is no free gridded map of radar-estimated peak gusts. The warning text behind a past-warning polygon carries the estimate the forecaster used. |
| [8.6] What does it look like right now? | Aerial imagery is one to three years old. Post-event aerial photography is flown for hurricanes and major floods, rarely for tornadoes, and is not on this map. |
| [8.7] How many households need help? | Not yet on the map. Federal assistance applicant counts by ZIP code are published during a declared disaster and are the closest public data gets to a call list. Until then, disasterassistance.gov is where to send somebody to register, and it lists the declarations currently open for applications. |
Layers draw on the National Weather Service, the National Water Prediction Service, the Storm Prediction Center, the National Hurricane Center, FEMA, the US Geological Survey, NASA, the interagency fire center, Iowa State University and OpenStreetMap. Every source is public and free. For internal use.