Using NOAA-Atlas 14 Return Periods to Aid in Flood Forecasting - Charles Ross and Richard Grumm SOO, NWS State College PA

Topics Covered NOAA Atlas 14 Overview Using the NOAA 14 data Case Studies Review

NOAA Atlas 14 Precipitation Frequency Information - – NOAA Atlas 14 data available for 37 states Pacific NW and Texas not available NE US states in progress but not online yet…but similar data available on NERC website – NWS Hydrometeorological Design Studies Center Precipitation Frequency Data Server (PFDS) website has converted NOAA Atlas 14 data into a point and click interface – Displays PDS based precipitation frequency estimates and 90% confidence interval Durations range from 5-minute to 60-days Average Recurrence Intervals (ARI) Range from 1 year to 1000 years – Data is also available in formats other then web, including GIS

NOAA-14 Data used by NWS State College NWS Phoenix developed a procedure to import this data into NWS AWIPS for use with FFMP NWS State College used this during the summer of 2013 with some success Unfortunately with Awips 2 this data is currently unavailable MRMS/FLASH website used in real time during heavy rain events For last two years used NOAA 14 ARI data in case studies of heavy rain and flooding events

Case #1 – Lebanon County, PA 7/23/13 Record rain event – 3 and 6-hour ARIs close to 1000 year return periods – Flash flooding across the county – Case study:

Case #2 – Flash Flood event central PA 6/27/13 Two Flash Floods on this day – Dubois, PA – Flash Flood Emergency Issued – Beech Creek, PA – 1 Fatality when a man was swept into a creek – Both Floods had ARIs close to 1000 year return periods – Case Study:

Case #3 – Extreme Rain Event – KPHL 7/27-28/13 Philadelphia International Airport received 8.26” of rain – ARIs close to 1000 year return periods – Case Study:

Case #4 – Phoenix Heavy Rain Event – KPHL 9/8/14 Monsoon moisture brought intense heavy rainfall to parts of the Phoenix area. – ARI close to 1000 year 6-hour return period – Case Study:

Case #5 – Long Island, NY Record Deluge – 8/13/14 Intense mesoscale precipitation band sets up over portions of Long Island, New York – 12.92” in 6-hour (13.27” for the day) – NOAA-14 data on PFDS web site unavailable for NYS. Used Northeast Regional Climate Center “Extreme Precipitation in New York and New England Website for ARI data – ARI well over the 500 year 6-hour return period – Case Study:

Review and Discussion Points Using ARIs should be used in flood operations similar in fashion to how we use flash flood guidance – Preferably with access in tools like FFMP Preliminary studies show to look for 1, 3 or 6- hour ARIs exceeding 50 years for moderate flooding to begin with significant flooding on the 100+ year events Currently the FLASH website is the best site to use in near real time