NOAA’s National Weather Service

Hydrologic Hazard Communication

Britt Westergard

Service Hydrologist WFO Jackson, KY WAS*IS Workshop, July 2006

NOAA’s National Weather Service

Major Challenges

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NWS issues flood warnings? Really?

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Products vs Information

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Verification vs Perception

(focus on Flash Flood Warnings)

Multi-tiered Concept

Products vs. Information

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Ready

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Outlooks

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Set

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Watches

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Go

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Warnings

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Advisories

NWS Hydrologic Products

Products vs. Information

• • • • • • • • • • • • • • • •

Hydrologic Outlook (ESF) Areal Flood Watch (FFA) Flood Watch for Forecast Points (FFA) Flash Flood Warning (FFW) Flash Flood Statement (FFS) Flood Warning for Forecast Points (FLW) Flood Statement – Follow-up to Flood Warning for Forecast Points (FLS) Areal Flood Warning (FLW) Flood Statement – Follow-up to Areal Flood Warning (FLS) Flood Statement – Areal Advisories (FLS) Flood Statement – Flood Advisory for Forecast Points Hydrologic Statement (RVS) Hydrologic Summary (RVA) River and Lake Forecast Product (RVD) Hydrometeorological Data Products (RRx) Hydrometeorological Data Summary Products (HYx)

Outreach

Products vs. Information We provide:

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Actions to take (“Turn Around, Don’t Drown”)

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Information sources (NWR, internet)

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Call-to-action statements in products But is the public…

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bogged down by flash flood vs. areal flood vs. river flood?

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confused by watches and warnings? What about advisories?

Flash Flood vs. River Flood

Verification vs. Perception

• Short-fused events (FFW) and long-fused events (FLW) • River flood warnings – – –

related to hydrograph - graphical association would be relatively simple to introduce uncertainty graphics verification = perception (exceed flood stage is cut & dried)

• Flash flood warnings – –

less quantifiable Verification and perception diverge?

Verification Guidelines

Verification vs. Perception

A Flash Flood occurs within 6 hours of a causative event: • River or stream flows out of its banks and is a threat to life or property.

• Person or vehicle is swept away by flowing water from runoff that inundates adjacent grounds.

• A maintained county or state road is closed by high water.

• Approximately six inches or more of water flows over a road or bridge. This includes low water crossings in a heavy rain event that is more than localized (i.e., radar and observer reports indicate flooding in nearby locations) and poses a threat to life or property.

• Dam break or ice jam release causes dangerous out of bank stream flows or inundates normally dry areas, creating a hazard to life or property.

• Any amount of water in contact, flowing into or causing damage of an above ground residence or public building and is runoff from adjacent grounds.

• Three feet or more of ponded water that poses a threat to life or property.

• Mudslide, rock slide or debris flow caused by rainfall (could possibly occur in a burned area with only light to moderate rainfall).

Opportunities for Change:

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Bridge gap between products and action taken

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Determine usefulness of product suite?

Modify outreach strategy?

Reach back to concept of products to re-evaluate?

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What is a flash flood anyway?

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Guidelines are based on safety – is there a better basis?

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Convey uncertainty in short- and long-fused products