1. The elevation dependence of snowfall in the Appalachian Ridge and Valley Region of Northeast Pennsylvania
Mike Evans – NOAA / NWS BGM
Mike Jurewicz – NOAA / NWS BGM
Rachael Kline – SUNY Binghamton

2. Topography in northeast Pennsylvania
Study Area

3. Research Goals and Methodology
Determine impacts of elevation on snowfall in northeast Pennsylvania
Examine cases from (snowfall at last 4 inches)
For each case, determine a “high-elevation” snowfall (from an average of stations above 1000 ft ASL) and “low-elevation” snowfall (from an average of stations below 1000 ft ASL).
Examine model and observational data to determine characteristics of events with high vs. low elevation dependence.
Derive an equation to predict the snowfall ratio of high elevation vs. low elevation snowfall.

4. Median snowfall

5. Ratio by season

6. Define low-elevation dependence vs. high elevation dependence
high elevation snowfall / low elevation snowfall < (1st quartile)
High-elevation dependence:
High elevation snowfall / low elevation snowfall > (4th quartile)

7. High elevation dependence cases

8. Low elevation dependence cases
Low elevation (12 cases)
High elevation (12 cases)
Elevation Dependence

9. Surface temperature at AVP

10. Surface wind at AVP

11. 0-1 km wind component perpendicular to the sw-ne oriented ridges

12. hPa lapse rate

13. Surface wind speed / 0-1 km wind speed

14. Froude number

15. A predictive equation R2 = 0.53
Y = (Surface Temp) (surface wind) (0-1 km wind) (surface wind / 0-1 km wind) – (N)

16. Example – February 2, 2015

17. Ratio forecasts Average surface temperature 31 °F
Surface wind speed kt
0-1 km wind kt
Sfc / 0-1 km wind
N (stability factor)
Predicted ratio
Observed ratio (8.4/5.5)
High-resolution ensemble forecast ratio approximately 2.0 to 2.5

18. Research to operations
Before
After

19. Summary
The median high elevation vs. low elevation ratio for the cases in the study was about 1.25.
However – many cases depart substantially from the median
The biggest factor that determines the ratio is wind speed. Temperature and stability are also factors.
Examination of the Froude number is a good way to determine elevation dependence of snowfall.
Use of the equation derived in this study also appears to be a promising method – in combination with high resolution model output.