THE WEATHER BEAT · EXPLAINER · NOV 2
Flood Warning or Flash Flood Warning: what Monday's Arizona and Florida products say, and how to read them
NWS Flagstaff, Tucson and Miami issued flood products Monday. How a Flood Warning differs from a Flash Flood Warning, and which line to read first.
Key points
- NWS Flagstaff, Tucson and Miami each issued flood products Monday. As of the 1:27 p.m. EST wire pull, 63 Flood Warnings from 11 offices and 7 Flash Flood Warnings from 4 offices were active nationwide.
- The National Weather Service defines a Flash Flood Warning as flash flooding "in progress, imminent, or highly likely." A Flood Warning means flooding that "will pose a serious threat to life and property is occurring, imminent or highly likely." The name tells you about speed only loosely.
- At 11:16 a.m. MST, NWS Flagstaff kept a Flood Warning going in Coconino County after the heavy rain had ended. At 1:02 p.m. EST, NWS Miami issued a Flash Flood Warning for Palm Beach County while radar showed rain falling.
The lesson
Two words, flood and flash flood, sit on warnings that look alike. The National Weather Service glossary separates them like this. A Flash Flood Warning is "issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely." A Flood Warning is for "flooding that will pose a serious threat to life and property is occurring, imminent or highly likely." The matching watches carry the earlier message. A Flood Watch says "flooding with significant impacts is possible." A Flash Flood Watch is for "hydrologic conditions that are favorable for flash flooding," where "the occurrence is neither certain or imminent."
Monday's products show how the labels work in practice.
The Miami warning is the textbook flash flood case. NWS Miami issued it at 1:02 p.m. EST for east central Palm Beach County, until 4:00 p.m. EST. The product says "Doppler radar indicated thunderstorms producing heavy rain," that 1 to 2 inches had fallen, and that 1 to 2 inches more were possible. The source line reads "Radar indicated." The product names the cause, the radar and the clock in a few lines. The warning is short and the rain is the trigger.
The Arizona products read differently. At 11:16 a.m. MST, NWS Flagstaff issued a Flood Warning for Coconino County until 11:30 p.m. MST. Its first line says "Flooding caused by excessive rainfall continues." The text says roads "remain closed within the Flagstaff area due to flooding from earlier heavy rainfall," and that "flooding will remain a threat while water levels decrease through this evening." An earlier Flagstaff product, issued at 6:54 a.m. MST for Coconino, Navajo and Apache counties, said "the heavy rain has ended" and that "flooding is ongoing." So a Flood Warning can follow the rain by hours. It covers the water that is still there.
The third kind is a river with a gauge. NWS Tucson's Flood Warning for the Gila River near Solomon, in Graham County, was issued at 11:10 a.m. MST. At 10:30 a.m. MST the stage was 21.8 feet against a flood stage of 21.0 feet. The forecast was a rise to 24.2 feet late in the afternoon. The product says that at 24.0 feet "several homes and businesses flooded, mostly on north sides of Solomon, Safford, and Thatcher" and that bridges "may be overtopped." The flood stage and the forecast crest are the numbers to read in a river warning. NWS Flagstaff's Little Colorado River warning, issued at 10:48 a.m. MST, gave the same kind of reading for Winslow: a stage of 24.59 feet at 10:00 a.m. against a flood stage of 19.0 feet, and a forecast crest of 46.78 feet around 2:00 p.m. MST.
So the habit that helps is to read the WHAT line, not the title. "Excessive rainfall continues" is a slower flood. "Radar indicated" and "ongoing or expected to begin shortly" is a fast one. A forecast crest with a flood stage is a river. The alert feed is full of all three at once, and the headline alone does not tell you which one is near you.
Today, officially
All times are issue times. As of the 1:27 p.m. EST wire pull, the active-alert list held 63 Flood Warnings across 11 offices, 7 Flash Flood Warnings across 4 offices, 10 Flood Watches across 6 offices and 7 Flood Advisories across 5 offices. Products are replaced through the day, so newer ones may carry different numbers. For your own street, the current product is at weather.gov.
| Product | Office | Issued Mon Nov 2 | Area | What it says |
|---|---|---|---|---|
| Flash Flood Warning | NWS Miami FL | 1:02 p.m. EST, until 4:00 p.m. EST | East central Palm Beach County | Radar indicated heavy rain; 1 to 2 inches had fallen, 1 to 2 more possible |
| Flood Warning | NWS Flagstaff AZ | 11:16 a.m. MST, until 11:30 p.m. MST | Coconino County | Roads closed from earlier heavy rainfall; water levels decreasing through the evening |
| Flood Warning | NWS Tucson AZ | 11:10 a.m. MST, until 11:15 p.m. MST | Gila River near Solomon, Graham County | Stage 21.8 ft at 10:30 a.m.; flood stage 21.0 ft; forecast crest 24.2 ft |
| Flood Warning | NWS Flagstaff AZ | 10:48 a.m. MST, until 10:00 a.m. MST Tuesday | Little Colorado River, Woodruff to Leupp | Winslow stage 24.59 ft at 10:00 a.m.; flood stage 19.0 ft; forecast crest 46.78 ft around 2:00 p.m. |
*Source: api.weather.gov active alerts for Flood Warning and Flash Flood Warning, pulled about 18:30Z Nov 2, and the wire pull at 18:27Z. NWS glossary: https://forecast.weather.gov/glossary.php?word=flood+warning, https://forecast.weather.gov/glossary.php?word=flash+flood+warning, https://forecast.weather.gov/glossary.php?word=flood+watch and https://forecast.weather.gov/glossary.php?word=flash+flood+watch.*
This is a summary of official warnings, not emergency information. For live warnings see weather.gov and your local officials. NWS Flagstaff: https://www.weather.gov/fgz/ NWS Tucson: https://www.weather.gov/twc/ NWS Miami: https://www.weather.gov/mfl/
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