28-29 July 2013 Philadelphia Heavy Rainfall Event Colleen McHugh

Motivation On 29 July 2013, Philadelphia International Airport (PHL) recorded a record breaking daily rainfall total of 203.7 mm The previous record was 168.4 mm set on 16 September 1999 (Hurricane Floyd) Made July 2013 the second wettest month on record behind August 2011 (Hurricane Irene) and ahead of September 1999 Record occurred in the presence of a frontal passage and heavy rainfall embedded in slow moving thunderstorms, not a tropical cyclone 186.7mm fell in a four hour period from 2000 UTC to 0000 UTC 203.7 mm =8.02” 168.4mm = 6.63” 186.7 mm = 7.35”

Methodology Synoptic conditions Surface analysis plots from WPC Archived radar from NCAR MMM shows the rain fell between 2000 UTC 28 July and 0600 UTC 29 July CFS reanalysis Mesoscale conditions SPC RAP archive Soundings from University of Wyoming Stage IV Precipitation Data Analyzed conditions from 1200 UTC 28 July to 0600 UTC 29 July 2013

Key Findings MUCAPE at 1800 on the 28th

Key Findings

Conclusions Constant southerly flow due to a surface cyclone over the Great Lakes and 500 hPa heights that were -3.5 sigma 850-300 hPa mean wind was also southerly PHL in a right entrance region of the jet High PWAT values transported into the region by the southerly flow Moderate MUCAPE values helped initiate convection and constant southerly flow and IVT helped to add to training effect and record breaking rainfall