DOI: 10.5061/dryad.gxd2547rt
title: Quantitative precipitation estimate (QPE) and forecast (QPF) exceedance comparison with flash flood reports

description: Flash flooding remains a challenging prediction problem, which is
 exacerbated by the lack of a universally accepted definition of the
 phenomenon. In this article, we extend prior analysis to examine the
 correspondence of various combinations of quantitative precipitation
 estimates (QPE) and precipitation thresholds to observed occurrences of
 flash floods, additionally considering short-term quantitative
 precipitation forecasts from a convection-allowing model. Consistent with
 previous studies, there is large variability between QPE datasets in the
 frequency of “heavy” precipitation events. There is also large regional
 variability in the best thresholds for correspondence with reported flash
 floods. In general, Flash Flood Guidance (FFG) exceedances provide the
 best correspondence with observed flash floods, except in the interior
 western US where recurrence interval thresholds (for the southwestern US)
 and static thresholds (for the northern and central Rockies) provide
 better correspondence. Six-hour QPE provides better correspondence with
 observed flash floods than 1-h QPE in all regions except the west coast
 and southwestern US. Exceedances of precipitation thresholds in forecasts
 from the operational High-Resolution Rapid Refresh (HRRR) generally do not
 correspond with observed flash flood events as well as QPE datasets, but
 they outperform QPE datasets in some regions of complex terrain and sparse
 observational coverage such as the southwestern US. These results can
 provide context for forecasters seeking to identify potential flash flood
 events based on QPE or forecast-based exceedances of precipitation
 thresholds. 
description: QPE and QPF data were collected from the NOAA HPSS for the
 seven-year period 2015-2021. All data were interpolated to the 3-km HRRR
 grid. Exceedances of precipitation thresholds (fixed thresholds, average
 recurrence intervals, and ratios of flash flood guidance) were determined
 on the 3-km grid. These exceedances were then upscaled to a 60 km grid for
 contingency table evaluation against flash flood reports. More details are
 provided in the manuscript.
description: Python is the preferred method to handle these netCDF files.
description: # Quantitative Precipitation Estimate (QPE) and Forecast (QPF) exceedances
 of precipitation thresholds --- The dataset consists of a number of QPE
 datasets, in addition to QPF from the High-Resolution Rapid Refresh. The
 data are on a 60 km grid, and represent binary exceedances of various
 precipitation thresholds (fixed, average recurrence intervals, and ratios
 of flash flood guidance thresholds). The grids can be compared with
 observed flash flood reports on the same grid. QPE data have been
 subjected to the automated quality control procedure described in the
 associated paper. ## Description of the data and file structure Data are
 zipped up into files named {qpe}*{duration}*{threshold}.zip. {qpe} can be
 Stage IV QPE (stageIV), radar-only MRMS (mrms), gauge-corrected MRMS
 (mrmsGC), CCPA (ccpa), or HRRR QPF (hrrr). {duration} can be 6h or 1h. For
 HRRR, we also include 6-12h, as well as 3-4h and 6-7h, to examine QPF at
 different forecast lead times. {threshold} varies among fixed threshold,
 average recurrence intervals, and ratios of flash flood guidance. For
 fixed thresholds, {threshold} varies between 1 inch (25.4 mm) and 5 inches
 (127 mm) in {duration}, in increments of half an inch (12.7 mm), with
 labels of 1in, 1p5in, 2in, 2p5in, 3in, 3p5in, 4in, 4p5in, and 5in. For
 average recurrence interval (ARI) thresholds, {threshold} varies between
 1-year ARI and 100-year ARI, with labels of 1yARI, 2yARI, 5yARI, 10yARI,
 25yARI, 50yARI, and 100yARI. For ratios of flash flood guidance (FFG),
 {threshold} varies between 0.25FFG and 5xFFG, with labels of 0p25FFG,
 0p5FFG, 0p75FFG, FFG, 1p5FFG, 2FFG, 2p5FFG, 3FFG, 3p5FFG, 4FFG, 4p5FFG,
 and 5FFG. The flash flood report data (on the same grid) are named
 ffr.zip. Within each zip file, netCDF files are named as
 {qpe}_{yyyymmdd12}.nc, where yyyy = 2-digit year, mm = 2-digit month, and
 dd = 2-digit day of month, and the label is associated with the end of the
 24-h period represented (12 UTC on the label date). For the flash flood
 reports, the files are named LSR_${yyyymmdd12}.nc, where yyyy = 2-digit
 year, mm = 2-digit month, and dd = 2-digit day of month, and the label is
 associated with the end of the 24-h period represented (12 UTC on the
 label date). Each netCDF file contains three 2-D variables: latitude,
 longitude, and precip. Latitude and longitude are in degrees N and E,
 respectively, and precip is a binary (0 or 1) variable indicating the
 occurrence of precipitation exceeding the threshold in the precipitation
 dataset for that day. The precipitation dataset and date are provided in
 the netCDF file name, and the precipitation threshold is provided in the
 zip file name. For the LSR files, the precip variable indicates the
 ocurrence of flash flood reports for that day. ## Sharing/Access
 information Raw data are available in the following locations: Stage IV
 QPE: CCPA QPE:
 HRRR QPF:
 For this project, we
 acquired data from the NOAA High Performance Storage System (HPSS).