2/16/2017 Surface Analysis – Mon, Aug 8 thru Sun, Aug 14, 2016 Low Pressure Moves from Florida to South Louisiana LA Flooding Episode August 2016 National Weather Service Michael Koziara, Slidell, LA Building a Weather-Ready Nation Building a Weather-Ready Nation National Hurricane Center periodically carried the low pressure system in their Outlooks with a very low chance of Near Record Atmospheric Moisture developing. • Climatology of the moisture content in the atmosphere from all of our office weather balloon releases since 1948 • 3rd highest value on record was recorded during this event. It’s off the chart! • 2.8 inches was observed twice and we were 2.4 inches or higher Aug 9- 12 Building a Weather-Ready Nation Building a Weather-Ready Nation NWS Weather Prediction Center (WPC) NWS Weather Prediction Center (WPC) Quantitative Rainfall Forecasts (QPF) Excessive Rainfall Outlook Quantitative Precipitation Forecasts - used by RFC/WFO to generate QPF-and Excessive Rainfall Guidance used by local WFOs to aid in decision river forecasts. Local Offices does have opportunity to modify for the threat of Flash Flooding and need for Flash Flood Watch Day 2 – Issued Thu Morning Valid 7am Fri thru 7am Sat 48 hour Forecast. Issued48 hour 7AM Forecast. Thu Day 1 - Issued Thu morning Issued 7AM Fri Valid through 7AM Friday Language included “life threatening flash flooding” “Model rainfall truly prolific” “High Risk” used in Day 2 – very unusual 5 6 Building a Weather-Ready Nation Building a Weather-Ready Nation 1 2/16/2017 NASA Visibility Image Radar Loop Aug 11-13, 2016 Aug 12, 2016 Central Dense Overcast (CDO) 8 Building a Weather-Ready Nation 7 Building a Weather-Ready Nation Lower Mississippi River Forecast Center Lower Mississippi River Forecast Center http://www.weather.gov/lmrfcRiver Forecast @NWSLMRFC Center http://www.weather.gov/lmrfcNWS Weather @NWSLMRFC Forecast Office https://www.facebook.com/NWSLMRFCOverview https://www.facebook.com/NWSLMRFCOverview • River Forecast Centers issue precipitation, river and • Issue Outlooks Watches and Warnings flood guidance based on hydrologic/hydraulic • Outlooks – Issued for long lead time notice of days. models (mentioned on Sat Aug 6 and issued special product on Mon Aug 8) • Flood/Flash Flood Watch – Issued 36 to 48 hours in advance • Provide river forecast guidance to Weather Forecast (Initial Watch issued Tue 9 – continued thru event) Offices (WFOs) • River Flood Warnings – Lead time of several days in advance if possible • Develop and calibrate models • Utilize RFC guidance to generate River Forecasts and Warnings. (Wed, Aug 10 – initial river flood warning based strictly on forecasted rainfall) • Flash Flood Warnings – issued for flooding small streams/bayous/local drainages. • Tools – real time precip estimates from radar/gages/satellite, radar trends, reports, and flash flood guidance. Software tools. (Initial Warnings Thu – Aug 11) • Can elevate Warnings to “Emergency” level when there is a particular threat to life. (Fri early morning – Aug 12) Building a Weather-Ready Nation Building a Weather-Ready Nation Lower Mississippi River Forecast Center Lower Mississippi River Forecast Center http://www.weather.gov/lmrfcNWS Weather @NWSLMRFC Forecast Office http://www.weather.gov/lmrfc @NWSLMRFC https://www.facebook.com/NWSLMRFC https://www.facebook.com/NWSLMRFCRainfall Overview - continued • Provide Advice to State and Local Emergency Management • Blast e-mails , webinars, conference calls, direct briefings. (started Mon Aug 8 and continued thru event) • Direct to Media and Public • Media - Conference calls (Wed Aug 10) • Public- thru media as partner/conduit • Public – direct thru Web Page, Social Media, NOAA Weather Radio, phone calls (utilized throughout the event) Building a Weather-Ready Nation Building a Weather-Ready Nation 2 2/16/2017 1. Rainfall – 2 Day Do We Understand the Flood Risk? 2. Annual Exceedance Probabilities • Probability of a least one event over time. • A 1 percent annual risk translates to a 27 percent chance of occurrence over a 30 year mortgage Building a Weather-Ready Nation Building a Weather-Ready Nation 14 Lower Mississippi River Forecast Center http://www.srh.noaa.gov/lmrfcAmite & Comite @NWSLMRFC Forecast & https://www.facebook.com/NWSLMRFC Amite River Hydrographs Support Locations Forecast Locations Support Locations Darlington Grangeville Olive Branch Zachary (Comite) Comite (Joor Road) Magnolia Denham Springs Zachary (White Bayou) Bayou Manchac Milldale Port Vincent (Little Sandy) French Little Prairie Settlement Building a Weather-Ready Nation Building a Weather-Ready Nation Amite River Hydrographs Comite River Hydrographs 17 Building a Weather-Ready Nation Building a Weather-Ready Nation 3 2/16/2017 Comite River Hydrographs Amite River Flood Crests GAGE Event Event Previous Previous Date Crest Record Record Crest Date Darlington 08/12/2016 22.54 22.05 01/25/1990 Grangeville 8/12/2016 44.62 46.47 04/14/1955 Magnolia 08/13/2016 58.56 51.91 04/23/1977 Denham Springs 08/14/2016 46.20 41.50 04/08/1983 Bayou Manchac Point 08/14/2016 E21.5 18.85 04/08/1983 Port Vincent 08/15/2016 E17.5 14.65 04/09/1983 French Settlement 08/16/2016 9.21 7.40 04/25/1977 Building a Weather-Ready Nation Building a Weather-Ready Nation Comite River Flood Crests Flash Flood Verification Storm Based GAGE Record Date Event Previous Previous • POD 0.799 Crest Record Record Crest Date • FAR 0.121 • CSI 0.719 Olive Branch 08/13/2016 26.96 23.37 03/18/1961 • Lead Time 58 min Joor Road 08/14/2016 34.22 30.99 06/09/2001 Building a Weather-Ready Nation Building a Weather-Ready Nation Lower Mississippi River Forecast Center http://www.weather.gov/lmrfc @NWSLMRFC https://www.facebook.com/NWSLMRFCKey Points Contacts Slow moving weak low pressure system produced prolific/record Lower Mississippi River Baton Rouge/New Orleans rainfall. • Slow forward speed of low allowed repetitive bands of showers and Forecast Center Weather Forecast Office thunderstorms over the same area/river basins for approximately 48 hours • Moisture levels were at or near record levels producing extremely efficient www.weather.gov/lmrfc www.weather.gov/lix rainfall. • Flash flooding occurred across much of region’s small streams/bayous/drainages at the onset of the event www.facebook.com/NWSLMRFC www.facebook.com/NWSNewOrleans • 13 total fatalities – most likely related to flash flooding • River flooding ensued as runoff reached larger rivers @NWSLMRFC @NWSNewOrleans • At least 9 record crests were set on gage locations Amite/Comite Rivers. • Back water flooding was widespread at lower end of basins [email protected] [email protected] 24 Building a Weather-Ready Nation Building a Weather-Ready Nation 4.