Fig. 10.21. Estimated snow accumulation (inches) from the LEDWI
sensor on the left axis and liquid precipitation (inches) from the tipping
bucket gauge, both located at the METAR site.
Also examined is the method used to forecast the snowfall within the RWFS. Using both
the tipping bucket at the METAR site as well as the LAPS data, a 20:1 snow-to-liquid
ratio was found to be appropriate for this case. Fig. 10.22 compares the approximate
actual snow depth from this method to the forecasted snow depth from the RWFS. The
estimated actual snow depth was approximately 6.5 inches while the forecast was only
2.5 inches. In the RWFS a straight 10:1 ratio is used for all cases regardless of the
atmospheric conditions. Since this case had closer to a 20:1 ratio the forecasts were a
factor of 2 off. If a 20:1 ratio had been applied to the forecast the forecasted snow depth
would have been around 5 inches, which was much closer to reality. The NWS forecast
from 18 UTC 25 January called for 8 inches of snow, which was a good very good
forecast compared to the observations.