Methodology
Updated August 22, 2026
Every figure shown here includes the time it was observed and the source that reported it. The time shown is when the measurement was made, not when the page was built. This page explains where the numbers come from, how they are counted, and how often they update.
What every page has in common
- Each number on the page comes with its source and the time or date it was observed. Times appear in the state's own time zone; dates use US form.
- Local Storm Reports come from National Weather Service offices and pass through the Iowa Environmental Mesonet; they make up the live reports. The time, the person who filed it, and whether the value came from a measurement or an estimate are listed in each report. Reports are shown as filed and may be revised later by the issuing office.
- Refresh cycles run every 5 minutes for state pages, every 15 to 30 minutes for hubs and the homepage, and every 30 minutes for city pages. The timestamp on a page is the time of the newest figure, not the time the page was generated.
- A storm-mode banner appears on the state page whenever a National Weather Service warning is in force for that state. The banner names the warning. The NWS stays the official source for warnings.
- Quiet is a normal state. When no report has arrived in the last 24 hours, the page says so.
Snow
Snow totals are reported in inches to one decimal place. Live reports cover the last 24 hours; for the season total, storm log, and records, one station per city provides the numbers, using NOAA's GHCN-Daily station observations.
| Figure | Source | Lag or refresh | Note |
|---|---|---|---|
| Live reports | National Weather Service Local Storm Reports via Iowa Environmental Mesonet | State pages every 5 minutes | Snowfall in inches, last 24 hours, per state |
| Season to date | GHCN-Daily station observations from NOAA NCEI | 1 to 3 days behind | Season runs July 1 to June 30, labelled by its starting year, for example 2025-26. One station per city, named on the page. |
| Storm log and records | GHCN-Daily station observations from NOAA NCEI | 1 to 3 days behind | Values that fail NOAA quality flags are dropped. Any daily total higher than the US record of 75.8 inches gets dropped. Averages and record-lows exclude any season that logged fewer than 200 daily observations. Records are rebuilt after June 30 each year. |
| Normals | U.S. Climate Normals 1991-2020 | Static climatology | Monthly normals summed to the date for 'normal to date.' |
Rain
Rain is reported in hundredths of an inch, and a trace shows as T. Live reports show heavy rain in the last 24 hours; the official daily figure comes from the airport climate report, and the longer view comes from the station record.
| Figure | Source | Lag or refresh | Note |
|---|---|---|---|
| Live reports | National Weather Service Local Storm Reports via Iowa Environmental Mesonet | State pages every 5 minutes | Heavy rain in inches, last 24 hours, per state |
| Yesterday's official figure | The National Weather Service issues the daily climate report for the city's airport, and the Iowa Environmental Mesonet relays it. | Issued each morning | A daily readout covers the day's rain, month-to-date and year-to-date totals, the normal for each window, and the date's record. That readout exists for 138 of the 145 cities; the others use the station record only. |
| Year to date and day log | GHCN-Daily station observations from NOAA NCEI | 1 to 3 days behind | The calendar year starts January 1. Quality-flag handling follows the snow rule: a daily total above 43 inches is dropped. Years with fewer than 330 observations do not count toward averages or the driest-year ranking. Rebuilt each January. |
| Records | GHCN-Daily station observations from NOAA NCEI | 1 to 3 days behind | Under the same quality rules, the station record supplies the average year since observations began, the driest and wettest years, and the wettest single day. The calendar-date record comes from the climate report row above. Rebuilt each January. |
| Normals | U.S. Climate Normals 1991-2020 | Static climatology | Monthly and annual normals. |
Hail
Hailstone records for the largest stones begin in 1996, when the NOAA NCEI Storm Events Database took its modern form. For averages, the period is 2005 to 2025. Reporting density shifted in 2010, when the 1-inch severe threshold was set, and again in 2012, when phone reporting became common.
| Figure | Source | Lag or refresh | Note |
|---|---|---|---|
| Live reports by state | National Weather Service Local Storm Reports via Iowa Environmental Mesonet | State pages every 5 minutes | The last 24 hours are shown per state in inches. On the NWS scale, 1.00 inches corresponds to a quarter, which is also the severe threshold. Golf balls are 1.75 inches, baseballs 2.75, softballs 4.00. |
| Last 7 days grid | National Weather Service Local Storm Reports via Iowa Environmental Mesonet | Homepage and hub every 15 to 30 minutes | Because hail is episodic, the grid shows each state's reports from the last 7 days. |
| City circle this year | National Weather Service Local Storm Reports via Iowa Environmental Mesonet | City pages every 30 minutes | The 25-mile circle around the city counts reports from the past week and from this year to date. |
| Records | NOAA NCEI Storm Events Database | 2 to 3 months behind | Reviewed log of reports. Largest stones counted from 1996. |
| Averages | NOAA NCEI Storm Events Database | Rebuilt roughly monthly, when NCEI republishes | The 2005 to 2025 data gives reports per year, reporting days per year, reports by month, and counties. |
Aurora
Aurora visibility starts with the Kp index from the NOAA Space Weather Prediction Center. Each state is placed by geomagnetic latitude, and the auroral oval's southern edge is projected for the current Kp. A margin for the altitude of the lights, roughly 100 km up, lets the aurora be seen south of the oval.
- Kp source: 1-minute estimated value, 3-hour official value, and 3-day forecast, refreshed every 15 minutes.
- Geomagnetic latitude: a state's position comes from converting its northernmost latitude with a centered dipole.
- Oval edge and margin: the southern edge of the oval comes from a standard SWPC table: at Kp 0 it sits near 66.5 degrees geomagnetic latitude, at Kp 5 near 56.3, and at Kp 9 near 48.1. The aurora remains visible roughly 5 degrees south of that edge.
- Kp needed: reaching the state requires the oval plus that margin; the lowest Kp at which that happens is the needed value.
- Likelihood bands: the labels none, low, moderate, high, and extreme form five fixed bands of the same margin, based on how far the current Kp sits above or below the line.
- Cloud cover: the National Weather Service gridpoint forecast supplies it for each dark-sky spot at that location.
Rounding and units
- Snow totals are given to 0.1 inch.
- Rain totals are given to 0.01 inch, and a trace shows as T.
- Hail diameters are given to 0.01 inch. All dates are in US form, and all times are in the state's own time zone.
Corrections
If something looks wrong, send the page address and the figure to contact page. We correct the page and re-check the source.