Read severe-weather and rainfall outlooks

Start with the issuer and valid period

The severe-weather collection on the homepage uses NOAA Storm Prediction Center products. The excessive-rainfall collection uses NOAA Weather Prediction Center products. Mammatus presents and renders those fields; the issuing agencies remain responsible for the outlooks.

Read the map’s valid period and update time before interpreting its outline. A Day 1 label refers to the issuer’s defined outlook period, not necessarily the next 24 hours counted from when you open the page. Use the source link for the full official product and discussion.

A categorical outlook summarizes a severe-weather risk

The categorical severe-weather map is a broad summary. Separate tornado, wind, and hail probability views describe different hazards. Switching between them can change both the legend and the meaning of a percentage, even while the same area stays in view.

Do not read a tornado probability as the chance of rain at your house. SPC outlook probabilities use their own event and distance definitions. The NWS product definitions explain these distinctions, including the distance around a forecast point. Keep the hazard’s legend with a downloaded graphic.

Rainfall outlooks describe flood-producing potential

The WPC Excessive Rainfall Outlook describes the probability that rainfall will exceed flash-flood guidance within 25 miles of a point. It is not a map of expected inches of rain, and it is not the same quantity as the rain chance in a local forecast. WPC explains the product here.

Rainfall that causes problems in one place may have different impacts elsewhere. An outlook helps frame that wider hazard; it does not replace a local warning, knowledge of a flood-prone route, or instructions from emergency officials.

Outlook, watch, and warning are different stages

The NWS watch and warning guide explains severe-thunderstorm alerts. Treat the warning’s actual text, area, and expiration time as the operational information, rather than assuming an outlook color tells you whether a warning applies.

A useful sequence in Mammatus

1. Choose your location on the homepage and read any local alerts.
2. Use the national outlook for context, then choose the particular hazard and day you want to examine.
3. Confirm the legend, valid period, and official source.
4. Return to the local forecast and active warning text before making plans.

A model forecast can help explain a possible scenario, but it does not become an official warning when it resembles an outlook. If you share an image, keep its source and timestamp visible and describe which product it is.