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Post-Processing of Numerical Ozone Model Forecasts: The Land-Sea Problem. Bill Ryan Department of Meteorology The Pennsylvania State University [email protected] 2010 International Workshop on Air Quality Forecasting Research Quebec City, Quebec. The Problem: False Alarms of High O 3.
Department of Meteorology
The Pennsylvania State University
2010 International Workshop on Air Quality Forecasting Research
Quebec City, Quebec
NOAA-EPA Numerical Ozone Forecast Model (www.weather.gov/aq)
Daily maximum 8-Hour Average
Ozone (ppbv), NOAA-EPA Model
average PM2.5 (µg/m3)
~ 1730 UTC
In this case (August 11, 2010) sea breeze circulations developed north of a
frontal boundary and re-circulated the previous day’s polluted air mass.
The Philadelphia Metro Forecast Area, roughly enclosed in rectangle, is peripherally
affected by modeled sea breeze-O3 effects, primarily in southern NJ
Model forecast output is automatically
generated by NOAA-EPA by extracting
peak O3 concentrations over land
areas within designated warning areas
(using zipcodes) that are used for
email/Web notification. This is posted in
timely fashion at AirNow Tech
Millville, NJ monitor location shown at left.
Interstates and zip code boundaries shown.
Simplest post-processing method to
remove land-sea effects is
to extract O3 forecast at locations
near monitors and/or away from the
boundary. This can be quickly
done using point data extraction from the
NOAA forecast web site.
Southern Delaware forecast
area includes monitor along
coast at Lewes.
In 2010, the monitor at Edgewood,
located northeast of Baltimore,
reached the Code Orange range
on 75% of all Code Orange days
in the Baltimore region.
On half of the Code Orange days,
the three bayside monitors
were the only locations reaching
the alert threshold.
2200 UTC hourly O3 observations and wind barbs, June 25, 2009.
Blue: Model Forecast (NAQC)
Red: Post-Processed Model (POST)
Green: Persistence (PERS)
The majority of high O3 events occur at coastal
monitors (62%). Only 5 of 24 observed Code Orange
days did not have a coastal monitor above the
threshold (76 ppbv, 8-hour average).
Model forecasts (NAQC) have a high hit and false alarm rate (high bias) while
the expert forecast (Forecast) is the reverse. The two post-processed forecasts
Mean and Mean plus Gradient straddle the bias threshold but provide
better skill scores (Threat Score, or CSI shown above in green.
NOAA-EPA Model O3 forecast for
August 11, 2010 (1200 UTC run)
HPC Surface Analysis, 1800 UTC,
August 11, 2010
Sea Breeze Verified
(left) 3-hour temperature change
1900 UTC, August 11
SPC Mesoscale Analysis
Scatter plot of observed peak
O3 and mean model
Air Quality Index (AQI) for