Flash flooding kills more people in the U.S. most years than tornadoes do, and the vocabulary around it is worth knowing cold. This page covers flood watches, warnings, and emergencies, plus the hydrology behind them: flash flood guidance, QPF, flood stage, and the WPC products that flag excessive rain days ahead. Hear these called live during coverage in the Xtreme Weather Discord (XWD).
A Flood Watch (FLA) means conditions are favorable for general area flooding — usually slower-developing river or areal flooding over 12–48 hours. Monitor river gauge levels and be ready to evacuate low-lying areas if a Flood Warning (FLW) is issued.
A Flash Flood Watch (FFA) is issued when conditions are favorable for flash flooding — heavy rainfall, slow-moving storms, or saturated ground — but flooding is not yet imminent. EAS code: FFA. Use the watch window to identify escape routes and avoid flood-prone areas.
A Flood Warning (FLW) means flooding is occurring or imminent — either from a river rising above flood stage or from areal flooding. EAS code: FLW. Avoid all flood-prone roads. Turn around, don't drown.
A Flood Statement (FLS) is the follow-up product to an active Flash Flood Warning or Flood Warning, providing updated storm position, rising water levels, and cancellation info. The flood equivalent of an SVS.
A Flash Flood Warning (FFW) is issued when flash flooding is imminent or occurring. Turn around, don't drown — most flood deaths happen in vehicles. 6 inches of moving water can knock you down; 12 inches can sweep a car away.
A Flash Flood Emergency (FFE) is the highest-tier flood wording — issued when a catastrophic, life-threatening flash flood is occurring with significant damage and rescues underway. Equivalent in severity to a Tornado Emergency.
A Coastal Flood Warning (CFW) is issued when tidal surge, wave wash, or storm-related flooding will cause wet conditions 1–2+ feet above normally dry ground in coastal areas. Distinct from Storm Surge Warnings (SSW), which are issued by NHC for tropical cyclone surge. EAS code: CFW.
A Dam Failure warning (product: DMO or appended to Flash Flood Warning) is issued when a dam has failed or is in imminent danger of failing, releasing a surge of water downstream. These are among the most time-critical products in the NWS warning suite — downstream evacuations may have only minutes.
Flood stage is the river gauge level at which a waterway begins to overflow its banks and cause flooding. River Forecast Centers (RFCs) issue crest forecasts and Action/Minor/Moderate/Major stage thresholds. Action stage = begin monitoring; Minor = roads/fields affected; Moderate = structures threatened; Major = significant infrastructure impacted.
Areal flooding is widespread, slower-developing flooding not tied to a specific stream or river — occurring when rainfall exceeds the capacity of saturated soils and stormwater systems. It affects roads, fields, and low-lying urban areas. Often covered by a Flash Flood Warning even when no specific stream is the source.
Flash Flood Guidance (FFG) is the estimated rainfall depth over a given duration (1-, 3-, 6-hour) needed to produce minor flooding on small streams in a given area. When forecast QPF exceeds local FFG, flash flood watches and warnings become likely. It's the key threshold tool hydrologists use to determine warning necessity.
Soil saturation describes how much of the soil's pore space is filled with water. Saturated or near-saturated soils dramatically lower Flash Flood Guidance since any rain runs off immediately rather than infiltrating. Antecedent precipitation (what fell previously) is crucial context for flash flood potential, even if today's rain isn't extreme.
The Excessive Rainfall Outlook (ERO) is the WPC's probabilistic forecast for areas at risk for flash flooding — essentially the flood equivalent of an SPC convective outlook. Categories: Marginal → Slight → Enhanced → Moderate → High. High risk EROs are extremely rare and indicate a serious, life-threatening flood threat.
The Weather Prediction Center (WPC) is the NWS national center responsible for heavy rainfall and flooding forecasts. They issue the Excessive Rainfall Outlook (ERO) — the flood equivalent of an SPC convective outlook — and the Quantitative Precipitation Forecast (QPF). Also issues winter storm forecasts at extended ranges.
A River Forecast Center (RFC) is one of 13 regional NWS offices specializing in hydrological forecasting. RFCs issue river flood forecasts, flash flood guidance, and seasonal water supply outlooks. They sit above individual WFOs in the hydrology hierarchy — the WFO issues the warning based on RFC guidance.