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Tuesday, May 8 • 3:30pm - 4:00pm
PRESENTATION: Using Gazpacho and ArcGIS to Create Forecast Snowfall Bias, Error, and Composite Maps Stratified by Flow Regime

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AUTHORS: Joseph P. Villani, NOAA/National Weather Service Albany, NY

ABSTRACT: In order to evaluate patterns of snowfall forecast error, the Gridded Automated Zonal Precipitation and Complete Hi-Res Output (GAZPACHO) verification program and ArcGIS were used to create maps of observed snowfall, zone-average snowfall and forecast error maps for 56 snowfall events in the National Weather Service Albany, NY County Warning Area (ALY CWA; eastern New York and western New England). Events from the 2013-2017 winter seasons were used for the study. The criteria for an event was when at least advisory level snow fell or advisory level snow was forecast (around 4 inches or greater somewhere in the ALY CWA). Each event was categorized by determining a representative wind direction and speed at 925 and 850 mb. The wind direction categories were 0-90, 90-180, 180-270, and 270-360. The wind speed categories were 0-19 kt, 20-39 kt, and 40 kt or greater. Twelve categories were defined based on the various direction and speed combinations. The winds were derived from Albany, NY (ALY) observed sounding data for each snowfall event. The wind direction and speed (at 0000 or 1200 UTC) closest to the midpoint time of each event was used to categorize each event. Forecast bias, mean absolute error (MAE), and snowfall composite maps were created for each of the twelve wind categories from the 56 total snowfall events using ArcGIS. Since there were 12 wind categories and 56 total snowfall events, some of the categories only contained a few events. However, there were several wind categories with five or more events. Results from a few of the wind categories using 925 mb winds will be presented, with some discernible patterns noted in the forecast bias, MAE and snowfall composite maps. It is hypothesized that some of the larger forecast biases can be attributed to terrain influences based on the over/under forecast of snowfall in favored upslope/downslope areas in the ALY CWA.

Tuesday May 8, 2018 3:30pm - 4:00pm EDT
Room 201

Attendees (5)