Introduction
Several years ago I wrote a post about Equinox Marathon weather, summarizing the conditions for all 50+ races. Since that post Andrea and I have run the relay twice, and I’ve run the full marathon three more times (if I include last year’s COVID-19 cancelled race). Despite no official race last year, quite a few people came out to run it in the rain and fog. This post updates the statistics and plots to include last year’s weather data.
Conditions on Ester Dome during the 2020 marathon
Methods
Methods and data are the same as in my previous post, except the daily data has been updated to include years through 2020. The R code is available at the end of the previous post.
Results
Race day weather
Temperatures at the airport on race day ranged from 19.9 °F in 1972 to 68 °F in 1969, but the average range is between 34.5 and 53.0 °F. Using our model of Ester Dome temperatures, we get an average range of 29.8 and 47.3 °F and an overall min / max of 16.1 / 61.3 °F up on the Dome. Generally speaking, it will be below freezing on Ester Dome, but usually before most of the runners get up there.
Precipitation (rain, sleet or snow) has fallen on 18 out of 58 race days, or 31% of the time, and measurable snowfall has been recorded on four of those eighteen. The highest amount fell in 2014 with 0.36 inches of liquid precipitation (no snow was recorded and the temperatures were between 45 and 51 °F so it was almost certainly all rain, even on Ester Dome). More than a quarter of an inch of precipitation fell in three of the eighteen years when it rained or snowed (1990, 1993, and 2014), but most rainfall totals are much smaller.
Measurable snow fell at the airport in four years, or seven percent of the time: 4.1 inches in 1993, 2.1 inches in 1985, 1.2 inches in 1996, and 0.4 inches in 1992. But that’s at the airport station. Five of the 14 years where measurable precipitation fell at the airport and no snow fell, had possible minimum temperatures on Ester Dome that were below freezing. It’s likely that some of the precipitation recorded at the airport in those years was coming down as snow up on Ester Dome. If so, that means snow may have fallen on nine race days, bringing the percentage up to sixteen percent.
Wind data from the airport has only been recorded since 1984, but from those years the average wind speed at the airport on race day is 4.8 miles per hour. The highest 2-minute wind speed during Equinox race day was 21 miles per hour in 2003. Unfortunately, no wind data is available for Ester Dome, but it’s likely to be higher than what is recorded at the airport.
Weather from the week prior
It’s also useful to look at the weather from the week before the race, since excessive pre-race rain or snow can make conditions on race day very different, even if the race day weather is pleasant. The first year I ran the full marathon (2013), it snowed the week before and much of the trail in the woods before the water stop near Henderson and all of the out and back were covered in snow.
The most dramatic example of this was 1992 where 23 inches (!) of snow fell at the airport in the week prior to the race, with much higher totals up on the summit of Ester Dome. Measurable snow has been recorded at the airport in the week prior to six races, but all the weekly totals are under an inch except for the snow year of 1992.
Precipitation has fallen in 46 of 58 pre-race weeks (79% of the time). Three years have had more than an inch of precipitation prior to the race: 1.49 inches in 2015, 1.26 inches in 1992 (most of which fell as snow), and 1.05 inches in 2007. On average, just over two tenths of an inch of precipitation falls in the week before the race.
Summary
The following stacked plots shows the weather for all 58 runnings of the Equinox marathon. The top panel shows the range of temperatures on race day from the airport station (wide bars) and estimated on Ester Dome (thin lines below bars). The shaded area at the bottom shows where temperatures are below freezing. The orange horizonal lines represent average high and low temperature in the valley (dashed lines) and on Ester Dome (solid orange lines).
The middle panel shows race day liquid precipitation (rain, melted snow). Bars marked with an asterisk indicate years where snow was also recorded at the airport, but remember that five of the other years with liquid precipitation probably experienced snow on Ester Dome (1977, 1986, 1991, 1994, and 2016) because the temperatures were likely to be below freezing at elevation.
The bottom panel shows precipitation totals from the week prior to the race. Bars marked with an asterisk indicate weeks where snow was also recorded at the airport.
Here’s a table with most of the data from the analysis.
| Date | min t | max t | ED min t | ED max t | awnd | prcp | snow | p prcp | p snow |
|---|---|---|---|---|---|---|---|---|---|
| 1963-09-21 | 32.0 | 54.0 | 27.5 | 48.2 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1964-09-19 | 34.0 | 57.9 | 29.4 | 51.8 | 0.00 | 0.0 | 0.03 | 0.0 | |
| 1965-09-25 | 37.9 | 60.1 | 33.1 | 53.9 | 0.00 | 0.0 | 0.80 | 0.0 | |
| 1966-09-24 | 36.0 | 62.1 | 31.3 | 55.8 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1967-09-23 | 35.1 | 57.9 | 30.4 | 51.8 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1968-09-21 | 23.0 | 44.1 | 19.1 | 38.9 | 0.00 | 0.0 | 0.04 | 0.0 | |
| 1969-09-20 | 35.1 | 68.0 | 30.4 | 61.3 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1970-09-19 | 24.1 | 39.9 | 20.1 | 34.9 | 0.00 | 0.0 | 0.42 | 0.0 | |
| 1971-09-18 | 35.1 | 55.9 | 30.4 | 50.0 | 0.00 | 0.0 | 0.14 | 0.0 | |
| 1972-09-23 | 19.9 | 42.1 | 16.1 | 37.0 | 0.00 | 0.0 | 0.01 | 0.2 | |
| 1973-09-22 | 30.0 | 44.1 | 25.6 | 38.9 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1974-09-21 | 48.0 | 60.1 | 42.5 | 53.9 | 0.08 | 0.0 | 0.00 | 0.0 | |
| 1975-09-20 | 37.9 | 55.9 | 33.1 | 50.0 | 0.02 | 0.0 | 0.02 | 0.0 | |
| 1976-09-18 | 34.0 | 59.0 | 29.4 | 52.9 | 0.00 | 0.0 | 0.54 | 0.0 | |
| 1977-09-24 | 36.0 | 48.9 | 31.3 | 43.4 | 0.06 | 0.0 | 0.20 | 0.0 | |
| 1978-09-23 | 30.0 | 42.1 | 25.6 | 37.0 | 0.00 | 0.0 | 0.10 | 0.3 | |
| 1979-09-22 | 35.1 | 62.1 | 30.4 | 55.8 | 0.00 | 0.0 | 0.17 | 0.0 | |
| 1980-09-20 | 30.9 | 43.0 | 26.5 | 37.8 | 0.00 | 0.0 | 0.35 | 0.0 | |
| 1981-09-19 | 37.0 | 43.0 | 32.2 | 37.8 | 0.15 | 0.0 | 0.04 | 0.0 | |
| 1982-09-18 | 42.1 | 61.0 | 37.0 | 54.8 | 0.02 | 0.0 | 0.22 | 0.0 | |
| 1983-09-17 | 39.9 | 46.9 | 34.9 | 41.5 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1984-09-22 | 28.9 | 60.1 | 24.6 | 53.9 | 5.8 | 0.00 | 0.0 | 0.08 | 0.0 |
| 1985-09-21 | 30.9 | 42.1 | 26.5 | 37.0 | 6.5 | 0.14 | 2.1 | 0.57 | 0.0 |
| 1986-09-20 | 36.0 | 52.0 | 31.3 | 46.3 | 8.3 | 0.07 | 0.0 | 0.21 | 0.0 |
| 1987-09-19 | 37.9 | 61.0 | 33.1 | 54.8 | 6.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1988-09-24 | 37.0 | 45.0 | 32.2 | 39.7 | 4.0 | 0.00 | 0.0 | 0.11 | 0.0 |
| 1989-09-23 | 36.0 | 61.0 | 31.3 | 54.8 | 8.5 | 0.00 | 0.0 | 0.07 | 0.5 |
| 1990-09-22 | 37.9 | 50.0 | 33.1 | 44.4 | 7.8 | 0.26 | 0.0 | 0.00 | 0.0 |
| 1991-09-21 | 36.0 | 57.0 | 31.3 | 51.0 | 4.5 | 0.04 | 0.0 | 0.03 | 0.0 |
| 1992-09-19 | 24.1 | 33.1 | 20.1 | 28.5 | 6.7 | 0.01 | 0.4 | 1.26 | 23.0 |
| 1993-09-18 | 28.0 | 37.0 | 23.8 | 32.2 | 4.9 | 0.29 | 4.1 | 0.37 | 0.3 |
| 1994-09-24 | 27.0 | 51.1 | 22.8 | 45.5 | 6.0 | 0.02 | 0.0 | 0.08 | 0.0 |
| 1995-09-23 | 43.0 | 66.9 | 37.8 | 60.3 | 4.0 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1996-09-21 | 28.9 | 37.9 | 24.6 | 33.1 | 6.9 | 0.06 | 1.2 | 0.26 | 0.0 |
| 1997-09-20 | 27.0 | 55.0 | 22.8 | 49.1 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 1998-09-19 | 42.1 | 60.1 | 37.0 | 53.9 | 4.9 | 0.00 | 0.0 | 0.37 | 0.0 |
| 1999-09-18 | 39.0 | 64.9 | 34.1 | 58.4 | 3.8 | 0.00 | 0.0 | 0.26 | 0.0 |
| 2000-09-16 | 28.9 | 50.0 | 24.6 | 44.4 | 5.6 | 0.00 | 0.0 | 0.30 | 0.0 |
| 2001-09-22 | 33.1 | 57.0 | 28.5 | 51.0 | 1.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2002-09-21 | 33.1 | 48.9 | 28.5 | 43.4 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 2003-09-20 | 26.1 | 46.0 | 22.0 | 40.7 | 9.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2004-09-18 | 26.1 | 48.0 | 22.0 | 42.5 | 4.3 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2005-09-17 | 37.0 | 63.0 | 32.2 | 56.6 | 0.9 | 0.00 | 0.0 | 0.09 | 0.0 |
| 2006-09-16 | 46.0 | 64.0 | 40.7 | 57.6 | 4.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2007-09-22 | 25.0 | 45.0 | 20.9 | 39.7 | 4.7 | 0.00 | 0.0 | 1.05 | 0.0 |
| 2008-09-20 | 34.0 | 51.1 | 29.4 | 45.5 | 4.5 | 0.00 | 0.0 | 0.08 | 0.0 |
| 2009-09-19 | 39.0 | 50.0 | 34.1 | 44.4 | 5.8 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2010-09-18 | 35.1 | 64.9 | 30.4 | 58.4 | 2.5 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2011-09-17 | 39.9 | 57.9 | 34.9 | 51.8 | 1.3 | 0.00 | 0.0 | 0.44 | 0.0 |
| 2012-09-22 | 46.9 | 66.9 | 41.5 | 60.3 | 6.0 | 0.00 | 0.0 | 0.33 | 0.0 |
| 2013-09-21 | 24.3 | 44.1 | 20.3 | 38.9 | 5.1 | 0.00 | 0.0 | 0.13 | 0.6 |
| 2014-09-20 | 45.0 | 51.1 | 39.7 | 45.5 | 1.6 | 0.36 | 0.0 | 0.00 | 0.0 |
| 2015-09-19 | 37.9 | 44.1 | 33.1 | 38.9 | 2.9 | 0.01 | 0.0 | 1.49 | 0.0 |
| 2016-09-17 | 34.0 | 57.9 | 29.4 | 51.8 | 2.2 | 0.01 | 0.0 | 0.61 | 0.0 |
| 2017-09-16 | 33.1 | 66.0 | 28.5 | 59.5 | 3.1 | 0.00 | 0.0 | 0.02 | 0.0 |
| 2018-09-15 | 44.1 | 60.1 | 38.9 | 53.9 | 3.8 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2019-09-21 | 37.0 | 45.0 | 32.2 | 39.7 | 7.6 | 0.13 | 0.0 | 0.40 | 0.0 |
| 2020-09-19 | 39.9 | 53.1 | 34.9 | 47.3 | 2.2 | 0.12 | 0.0 | 0.10 | 0.0 |
Introduction
Several years ago I wrote a post about past Equinox Marathon weather. Since that post Andrea and I have run the relay twice, and I’ve run the full marathon twice. This post updates the statistics and plots to include last year’s weather data.
The official race this year was cancelled due to covid-19, but I will run it anyway, and I have no doubt many others will too. Last year’s race featured rain down in the valley, and high winds and a mixture of snow, sleet, and rain up on Ester Dome.
Conditions on Ester Dome during the 2019 Equinox Marathon
Methods
Methods and data are the same as in my previous post, except the daily data has been updated to include years through 2019. The R code is available at the end of the previous post.
Results
Race day weather
Temperatures at the airport on race day ranged from 19.9 °F in 1972 to 68 °F in 1969, but the average range is between 34.4 and 53.0 °F. Using our model of Ester Dome temperatures, we get an average range of 29.7 and 47.3 °F and an overall min / max of 16.1 / 61.3 °F up on the Dome. Generally speaking, it is below freezing on Ester Dome, but usually before most of the runners get up there.
Precipitation (rain, sleet or snow) has fallen on 17 out of 57 race days, or 30% of the time, and measurable snowfall has been recorded on four of those seventeen. The highest amount fell in 2014 with 0.36 inches of liquid precipitation (no snow was recorded and the temperatures were between 45 and 51 °F so it was almost certainly all rain, even on Ester Dome). More than a quarter of an inch of precipitation fell in three of the seventeen years when it rained or snowed (1990, 1993, and 2014), but most rainfall totals are much smaller.
Measurable snow fell at the airport in four years, or seven percent of the time: 4.1 inches in 1993, 2.1 inches in 1985, 1.2 inches in 1996, and 0.4 inches in 1992. But that’s at the airport station. Five of the 13 years where measurable precipitation fell at the airport and no snow fell, had possible minimum temperatures on Ester Dome that were below freezing. It’s likely that some of the precipitation recorded at the airport in those years was coming down as snow up on Ester Dome. If so, that means snow may have fallen on nine race days, bringing the percentage up to sixteen percent.
Wind data from the airport has only been recorded since 1984, but from those years the average wind speed at the airport on race day is 4.8 miles per hour. The highest 2-minute wind speed during Equinox race day was 21 miles per hour in 2003. Unfortunately, no wind data is available for Ester Dome, but it’s likely to be higher than what is recorded at the airport.
Weather from the week prior
It’s also useful to look at the weather from the week before the race, since excessive pre-race rain or snow can make conditions on race day very different, even if the race day weather is pleasant. The first year I ran the full marathon (2013), it snowed the week before and much of the trail in the woods before the water stop near Henderson and all of the out and back were covered in snow.
The most dramatic example of this was 1992 where 23 inches (!) of snow fell at the airport in the week prior to the race, with much higher totals up on the summit of Ester Dome. Measurable snow has been recorded at the airport in the week prior to six races, but all the weekly totals are under an inch except for the snow year of 1992.
Precipitation has fallen in 45 of 57 pre-race weeks (79% of the time). Three years have had more than an inch of precipitation prior to the race: 1.49 inches in 2015, 1.26 inches in 1992 (most of which fell as snow), and 1.05 inches in 2007. On average, just over two tenths of an inch of precipitation falls in the week before the race.
Summary
The following stacked plots shows the weather for all 57 runnings of the Equinox marathon. The top panel shows the range of temperatures on race day from the airport station (wide bars) and estimated on Ester Dome (thin lines below bars). The shaded area at the bottom shows where temperatures are below freezing. The orange horizonal lines represent average high and low temperature in the valley (dashed lines) and on Ester Dome (solid orange lines).
The middle panel shows race day liquid precipitation (rain, melted snow). Bars marked with an asterisk indicate years where snow was also recorded at the airport, but remember that five of the other years with liquid precipitation probably experienced snow on Ester Dome (1977, 1986, 1991, 1994, and 2016) because the temperatures were likely to be below freezing at elevation.
The bottom panel shows precipitation totals from the week prior to the race. Bars marked with an asterisk indicate weeks where snow was also recorded at the airport.
Here’s a table with most of the data from the analysis.
| Date | min t | max t | ED min t | ED max t | awnd | prcp | snow | p prcp | p snow |
|---|---|---|---|---|---|---|---|---|---|
| 1963-09-21 | 32.0 | 54.0 | 27.5 | 48.2 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1964-09-19 | 34.0 | 57.9 | 29.4 | 51.8 | 0.00 | 0.0 | 0.03 | 0.0 | |
| 1965-09-25 | 37.9 | 60.1 | 33.1 | 53.9 | 0.00 | 0.0 | 0.80 | 0.0 | |
| 1966-09-24 | 36.0 | 62.1 | 31.3 | 55.8 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1967-09-23 | 35.1 | 57.9 | 30.4 | 51.8 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1968-09-21 | 23.0 | 44.1 | 19.1 | 38.9 | 0.00 | 0.0 | 0.04 | 0.0 | |
| 1969-09-20 | 35.1 | 68.0 | 30.4 | 61.3 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1970-09-19 | 24.1 | 39.9 | 20.1 | 34.9 | 0.00 | 0.0 | 0.42 | 0.0 | |
| 1971-09-18 | 35.1 | 55.9 | 30.4 | 50.0 | 0.00 | 0.0 | 0.14 | 0.0 | |
| 1972-09-23 | 19.9 | 42.1 | 16.1 | 37.0 | 0.00 | 0.0 | 0.01 | 0.2 | |
| 1973-09-22 | 30.0 | 44.1 | 25.6 | 38.9 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1974-09-21 | 48.0 | 60.1 | 42.5 | 53.9 | 0.08 | 0.0 | 0.00 | 0.0 | |
| 1975-09-20 | 37.9 | 55.9 | 33.1 | 50.0 | 0.02 | 0.0 | 0.02 | 0.0 | |
| 1976-09-18 | 34.0 | 59.0 | 29.4 | 52.9 | 0.00 | 0.0 | 0.54 | 0.0 | |
| 1977-09-24 | 36.0 | 48.9 | 31.3 | 43.4 | 0.06 | 0.0 | 0.20 | 0.0 | |
| 1978-09-23 | 30.0 | 42.1 | 25.6 | 37.0 | 0.00 | 0.0 | 0.10 | 0.3 | |
| 1979-09-22 | 35.1 | 62.1 | 30.4 | 55.8 | 0.00 | 0.0 | 0.17 | 0.0 | |
| 1980-09-20 | 30.9 | 43.0 | 26.5 | 37.8 | 0.00 | 0.0 | 0.35 | 0.0 | |
| 1981-09-19 | 37.0 | 43.0 | 32.2 | 37.8 | 0.15 | 0.0 | 0.04 | 0.0 | |
| 1982-09-18 | 42.1 | 61.0 | 37.0 | 54.8 | 0.02 | 0.0 | 0.22 | 0.0 | |
| 1983-09-17 | 39.9 | 46.9 | 34.9 | 41.5 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1984-09-22 | 28.9 | 60.1 | 24.6 | 53.9 | 5.8 | 0.00 | 0.0 | 0.08 | 0.0 |
| 1985-09-21 | 30.9 | 42.1 | 26.5 | 37.0 | 6.5 | 0.14 | 2.1 | 0.57 | 0.0 |
| 1986-09-20 | 36.0 | 52.0 | 31.3 | 46.3 | 8.3 | 0.07 | 0.0 | 0.21 | 0.0 |
| 1987-09-19 | 37.9 | 61.0 | 33.1 | 54.8 | 6.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1988-09-24 | 37.0 | 45.0 | 32.2 | 39.7 | 4.0 | 0.00 | 0.0 | 0.11 | 0.0 |
| 1989-09-23 | 36.0 | 61.0 | 31.3 | 54.8 | 8.5 | 0.00 | 0.0 | 0.07 | 0.5 |
| 1990-09-22 | 37.9 | 50.0 | 33.1 | 44.4 | 7.8 | 0.26 | 0.0 | 0.00 | 0.0 |
| 1991-09-21 | 36.0 | 57.0 | 31.3 | 51.0 | 4.5 | 0.04 | 0.0 | 0.03 | 0.0 |
| 1992-09-19 | 24.1 | 33.1 | 20.1 | 28.5 | 6.7 | 0.01 | 0.4 | 1.26 | 23.0 |
| 1993-09-18 | 28.0 | 37.0 | 23.8 | 32.2 | 4.9 | 0.29 | 4.1 | 0.37 | 0.3 |
| 1994-09-24 | 27.0 | 51.1 | 22.8 | 45.5 | 6.0 | 0.02 | 0.0 | 0.08 | 0.0 |
| 1995-09-23 | 43.0 | 66.9 | 37.8 | 60.3 | 4.0 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1996-09-21 | 28.9 | 37.9 | 24.6 | 33.1 | 6.9 | 0.06 | 1.2 | 0.26 | 0.0 |
| 1997-09-20 | 27.0 | 55.0 | 22.8 | 49.1 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 1998-09-19 | 42.1 | 60.1 | 37.0 | 53.9 | 4.9 | 0.00 | 0.0 | 0.37 | 0.0 |
| 1999-09-18 | 39.0 | 64.9 | 34.1 | 58.4 | 3.8 | 0.00 | 0.0 | 0.26 | 0.0 |
| 2000-09-16 | 28.9 | 50.0 | 24.6 | 44.4 | 5.6 | 0.00 | 0.0 | 0.30 | 0.0 |
| 2001-09-22 | 33.1 | 57.0 | 28.5 | 51.0 | 1.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2002-09-21 | 33.1 | 48.9 | 28.5 | 43.4 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 2003-09-20 | 26.1 | 46.0 | 22.0 | 40.7 | 9.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2004-09-18 | 26.1 | 48.0 | 22.0 | 42.5 | 4.3 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2005-09-17 | 37.0 | 63.0 | 32.2 | 56.6 | 0.9 | 0.00 | 0.0 | 0.09 | 0.0 |
| 2006-09-16 | 46.0 | 64.0 | 40.7 | 57.6 | 4.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2007-09-22 | 25.0 | 45.0 | 20.9 | 39.7 | 4.7 | 0.00 | 0.0 | 1.05 | 0.0 |
| 2008-09-20 | 34.0 | 51.1 | 29.4 | 45.5 | 4.5 | 0.00 | 0.0 | 0.08 | 0.0 |
| 2009-09-19 | 39.0 | 50.0 | 34.1 | 44.4 | 5.8 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2010-09-18 | 35.1 | 64.9 | 30.4 | 58.4 | 2.5 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2011-09-17 | 39.9 | 57.9 | 34.9 | 51.8 | 1.3 | 0.00 | 0.0 | 0.44 | 0.0 |
| 2012-09-22 | 46.9 | 66.9 | 41.5 | 60.3 | 6.0 | 0.00 | 0.0 | 0.33 | 0.0 |
| 2013-09-21 | 24.3 | 44.1 | 20.3 | 38.9 | 5.1 | 0.00 | 0.0 | 0.13 | 0.6 |
| 2014-09-20 | 45.0 | 51.1 | 39.7 | 45.5 | 1.6 | 0.36 | 0.0 | 0.00 | 0.0 |
| 2015-09-19 | 37.9 | 44.1 | 33.1 | 38.9 | 2.9 | 0.01 | 0.0 | 1.49 | 0.0 |
| 2016-09-17 | 34.0 | 57.9 | 29.4 | 51.8 | 2.2 | 0.01 | 0.0 | 0.61 | 0.0 |
| 2017-09-16 | 33.1 | 66.0 | 28.5 | 59.5 | 3.1 | 0.00 | 0.0 | 0.02 | 0.0 |
| 2018-09-15 | 44.1 | 60.1 | 38.9 | 53.9 | 3.8 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2019-09-21 | 37.0 | 45.0 | 32.2 | 39.7 | 7.6 | 0.13 | 0.0 | 0.40 | 0.0 |
Introduction
A couple years ago I wrote a post about past Equinox Marathon weather. Since that post Andrea and I have run the relay twice, and I ran the full marathon. This post updates the statistics and plots to include two more years of the race.
Methods
Methods and data are the same as in my previous post, except the daily data has been updated to include 2018. The R code is available at the end of the previous post.
Results
Race day weather
Temperatures at the airport on race day ranged from 19.9 °F in 1972 to 35.1 °F in 1969, but the average range is between 34.3 and 53.2 °F. Using our model of Ester Dome temperatures, we get an average range of 29.7 and 47.4 °F and an overall min / max of 16.1 / 61.3 °F. Generally speaking, it will be below freezing on Ester Dome, but possibly before most of the runners get up there.
Precipitation (rain, sleet or snow) has fallen on 16 out of 56 race days, or 29% of the time, and measurable snowfall has been recorded on four of those sixteen. The highest amount fell in 2014 with 0.36 inches of liquid precipitation (no snow was recorded and the temperatures were between 45 and 51 °F so it was almost certainly all rain, even on Ester Dome). More than a quarter of an inch of precipitation fell in three of the sixteen years when it rained or snowed (1990, 1993, and 2014), but most rainfall totals are much smaller.
Measurable snow fell at the airport in four years, or seven percent of the time: 4.1 inches in 1993, 2.1 inches in 1985, 1.2 inches in 1996, and 0.4 inches in 1992. But that’s at the airport station. Five of the 12 years where measurable precipitation fell at the airport and no snow fell, had possible minimum temperatures on Ester Dome that were below freezing. It’s likely that some of the precipitation recorded at the airport in those years was coming down as snow up on Ester Dome. If so, that means snow may have fallen on nine race days, bringing the percentage up to sixteen percent.
Wind data from the airport has only been recorded since 1984, but from those years the average wind speed at the airport on race day is 4.8 miles per hour. The highest 2-minute wind speed during Equinox race day was 21 miles per hour in 2003. Unfortunately, no wind data is available for Ester Dome, but it’s likely to be higher than what is recorded at the airport.
Weather from the week prior
It’s also useful to look at the weather from the week before the race, since excessive pre-race rain or snow can make conditions on race day very different, even if the race day weather is pleasant. The year I ran the full marathon (2013), it snowed the week before and much of the trail in the woods before the water stop near Henderson and all of the out and back were covered in snow.
The most dramatic example of this was 1992 where 23 inches (!) of snow fell at the airport in the week prior to the race, with much higher totals up on the summit of Ester Dome. Measurable snow has been recorded at the airport in the week prior to six races, but all the weekly totals are under an inch except for the snow year of 1992.
Precipitation has fallen in 44 of 56 pre-race weeks (79% of the time). Three years have had more than an inch of precipitation prior to the race: 1.49 inches in 2015, 1.26 inches in 1992 (most of which fell as snow), and 1.05 inches in 2007. On average, just over two tenths of an inch of precipitation falls in the week before the race.
Summary
The following stacked plots shows the weather for all 56 runnings of the Equinox marathon. The top panel shows the range of temperatures on race day from the airport station (wide bars) and estimated on Ester Dome (thin lines below bars). The shaded area at the bottom shows where temperatures are below freezing.
The middle panel shows race day liquid precipitation (rain, melted snow). Bars marked with an asterisk indicate years where snow was also recorded at the airport, but remember that five of the other years with liquid precipitation probably experienced snow on Ester Dome (1977, 1986, 1991, 1994, and 2016) because the temperatures were likely to be below freezing at elevation.
The bottom panel shows precipitation totals from the week prior to the race. Bars marked with an asterisk indicate weeks where snow was also recorded at the airport.
Here’s a table with most of the data from the analysis. A CSV with this data can be downloaded from all_wx.csv
| Date | min t | max t | ED min t | ED max t | awnd | prcp | snow | p prcp | p snow |
|---|---|---|---|---|---|---|---|---|---|
| 1963-09-21 | 32.0 | 54.0 | 27.5 | 48.2 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1964-09-19 | 34.0 | 57.9 | 29.4 | 51.8 | 0.00 | 0.0 | 0.03 | 0.0 | |
| 1965-09-25 | 37.9 | 60.1 | 33.1 | 53.9 | 0.00 | 0.0 | 0.80 | 0.0 | |
| 1966-09-24 | 36.0 | 62.1 | 31.3 | 55.8 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1967-09-23 | 35.1 | 57.9 | 30.4 | 51.8 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1968-09-21 | 23.0 | 44.1 | 19.1 | 38.9 | 0.00 | 0.0 | 0.04 | 0.0 | |
| 1969-09-20 | 35.1 | 68.0 | 30.4 | 61.3 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1970-09-19 | 24.1 | 39.9 | 20.1 | 34.9 | 0.00 | 0.0 | 0.42 | 0.0 | |
| 1971-09-18 | 35.1 | 55.9 | 30.4 | 50.0 | 0.00 | 0.0 | 0.14 | 0.0 | |
| 1972-09-23 | 19.9 | 42.1 | 16.1 | 37.0 | 0.00 | 0.0 | 0.01 | 0.2 | |
| 1973-09-22 | 30.0 | 44.1 | 25.6 | 38.9 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1974-09-21 | 48.0 | 60.1 | 42.5 | 53.9 | 0.08 | 0.0 | 0.00 | 0.0 | |
| 1975-09-20 | 37.9 | 55.9 | 33.1 | 50.0 | 0.02 | 0.0 | 0.02 | 0.0 | |
| 1976-09-18 | 34.0 | 59.0 | 29.4 | 52.9 | 0.00 | 0.0 | 0.54 | 0.0 | |
| 1977-09-24 | 36.0 | 48.9 | 31.3 | 43.4 | 0.06 | 0.0 | 0.20 | 0.0 | |
| 1978-09-23 | 30.0 | 42.1 | 25.6 | 37.0 | 0.00 | 0.0 | 0.10 | 0.3 | |
| 1979-09-22 | 35.1 | 62.1 | 30.4 | 55.8 | 0.00 | 0.0 | 0.17 | 0.0 | |
| 1980-09-20 | 30.9 | 43.0 | 26.5 | 37.8 | 0.00 | 0.0 | 0.35 | 0.0 | |
| 1981-09-19 | 37.0 | 43.0 | 32.2 | 37.8 | 0.15 | 0.0 | 0.04 | 0.0 | |
| 1982-09-18 | 42.1 | 61.0 | 37.0 | 54.8 | 0.02 | 0.0 | 0.22 | 0.0 | |
| 1983-09-17 | 39.9 | 46.9 | 34.9 | 41.5 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1984-09-22 | 28.9 | 60.1 | 24.6 | 53.9 | 5.8 | 0.00 | 0.0 | 0.08 | 0.0 |
| 1985-09-21 | 30.9 | 42.1 | 26.5 | 37.0 | 6.5 | 0.14 | 2.1 | 0.57 | 0.0 |
| 1986-09-20 | 36.0 | 52.0 | 31.3 | 46.3 | 8.3 | 0.07 | 0.0 | 0.21 | 0.0 |
| 1987-09-19 | 37.9 | 61.0 | 33.1 | 54.8 | 6.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1988-09-24 | 37.0 | 45.0 | 32.2 | 39.7 | 4.0 | 0.00 | 0.0 | 0.11 | 0.0 |
| 1989-09-23 | 36.0 | 61.0 | 31.3 | 54.8 | 8.5 | 0.00 | 0.0 | 0.07 | 0.5 |
| 1990-09-22 | 37.9 | 50.0 | 33.1 | 44.4 | 7.8 | 0.26 | 0.0 | 0.00 | 0.0 |
| 1991-09-21 | 36.0 | 57.0 | 31.3 | 51.0 | 4.5 | 0.04 | 0.0 | 0.03 | 0.0 |
| 1992-09-19 | 24.1 | 33.1 | 20.1 | 28.5 | 6.7 | 0.01 | 0.4 | 1.26 | 23.0 |
| 1993-09-18 | 28.0 | 37.0 | 23.8 | 32.2 | 4.9 | 0.29 | 4.1 | 0.37 | 0.3 |
| 1994-09-24 | 27.0 | 51.1 | 22.8 | 45.5 | 6.0 | 0.02 | 0.0 | 0.08 | 0.0 |
| 1995-09-23 | 43.0 | 66.9 | 37.8 | 60.3 | 4.0 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1996-09-21 | 28.9 | 37.9 | 24.6 | 33.1 | 6.9 | 0.06 | 1.2 | 0.26 | 0.0 |
| 1997-09-20 | 27.0 | 55.0 | 22.8 | 49.1 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 1998-09-19 | 42.1 | 60.1 | 37.0 | 53.9 | 4.9 | 0.00 | 0.0 | 0.37 | 0.0 |
| 1999-09-18 | 39.0 | 64.9 | 34.1 | 58.4 | 3.8 | 0.00 | 0.0 | 0.26 | 0.0 |
| 2000-09-16 | 28.9 | 50.0 | 24.6 | 44.4 | 5.6 | 0.00 | 0.0 | 0.30 | 0.0 |
| 2001-09-22 | 33.1 | 57.0 | 28.5 | 51.0 | 1.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2002-09-21 | 33.1 | 48.9 | 28.5 | 43.4 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 2003-09-20 | 26.1 | 46.0 | 22.0 | 40.7 | 9.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2004-09-18 | 26.1 | 48.0 | 22.0 | 42.5 | 4.3 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2005-09-17 | 37.0 | 63.0 | 32.2 | 56.6 | 0.9 | 0.00 | 0.0 | 0.09 | 0.0 |
| 2006-09-16 | 46.0 | 64.0 | 40.7 | 57.6 | 4.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2007-09-22 | 25.0 | 45.0 | 20.9 | 39.7 | 4.7 | 0.00 | 0.0 | 1.05 | 0.0 |
| 2008-09-20 | 34.0 | 51.1 | 29.4 | 45.5 | 4.5 | 0.00 | 0.0 | 0.08 | 0.0 |
| 2009-09-19 | 39.0 | 50.0 | 34.1 | 44.4 | 5.8 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2010-09-18 | 35.1 | 64.9 | 30.4 | 58.4 | 2.5 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2011-09-17 | 39.9 | 57.9 | 34.9 | 51.8 | 1.3 | 0.00 | 0.0 | 0.44 | 0.0 |
| 2012-09-22 | 46.9 | 66.9 | 41.5 | 60.3 | 6.0 | 0.00 | 0.0 | 0.33 | 0.0 |
| 2013-09-21 | 24.3 | 44.1 | 20.3 | 38.9 | 5.1 | 0.00 | 0.0 | 0.13 | 0.6 |
| 2014-09-20 | 45.0 | 51.1 | 39.7 | 45.5 | 1.6 | 0.36 | 0.0 | 0.00 | 0.0 |
| 2015-09-19 | 37.9 | 44.1 | 33.1 | 38.9 | 2.9 | 0.01 | 0.0 | 1.49 | 0.0 |
| 2016-09-17 | 34.0 | 57.9 | 29.4 | 51.8 | 2.2 | 0.01 | 0.0 | 0.61 | 0.0 |
| 2017-09-16 | 33.1 | 66.0 | 28.5 | 59.5 | 3.1 | 0.00 | 0.0 | 0.02 | 0.0 |
| 2018-09-15 | 44.1 | 60.1 | 38.9 | 53.9 | 3.8 | 0.00 | 0.0 | 0.00 | 0.0 |
Introduction
It’s November 10th in Fairbanks and we have only an inch of snow on the ground. The average depth on this date is 6.1 inches, but that a little deceptive because snow depth doesn’t follow a normal distribution; it can never be below zero, and has a long tail toward deeper snow depths. In the 92 years of snow depth data for the Fairbanks Airport, we’ve had less than an inch of snow only six times (6.5%). At the other end of the distribution, there have been seven years with more than 14 inches of snow on November 10th.
My question is: what does snow depth on November 10th tell us about how much snow we are going to get later on in the winter? Is there a relationship between depth on November 10th and depths later in the winter, and if there is, how much snow can we expect this winter?
Data
We’ll use the 92-year record of snow depth data from the Fairbanks International Airport station that’s in the Global Historical Climate Network.
The correlation coefficients (a 1 means a perfect correlation, and a 0 is no correlation) between snow depth on November 10th, and the first of the months of December, January and February of that same winter are shown below:
| nov_10 | dec_01 | jan_01 | feb_01 | |
|---|---|---|---|---|
| nov_10 | 1.00 | 0.65 | 0.49 | 0.46 |
| dec_01 | 0.65 | 1.00 | 0.60 | 0.39 |
| jan_01 | 0.49 | 0.60 | 1.00 | 0.74 |
| feb_01 | 0.46 | 0.39 | 0.74 | 1.00 |
Looking down the nov_10 column, you can see a high correlation between snow depth on November 10th and depth on December 1st, but lower (and similar) correlations with depths in January and February.
This makes sense. In Fairbanks, snow that falls after the second week in October is likely to be around for the rest of the winter, so all the snow on the ground on November 10th, will still be there in December, and throughout the winter.
But what can a snow depth of one inch on November 10th tell us about how much snow we will have in December or later on?
Here’s the data for those six years with a snow depth of 1 inch on November 10th:
| wyear | dec_01 | jan_01 | feb_01 |
|---|---|---|---|
| 1938 | 5 | 11 | 24 |
| 1940 | 6 | 8 | 9 |
| 1951 | 12 | 22 | 31 |
| 1953 | 1 | 5 | 17 |
| 1954 | 9 | 15 | 12 |
| 1979 | 3 | 8 | 14 |
Not exactly encouraging data for our current situation, although 1951 gives us some hope of a good winter.
Methods
We used Bayesian linear regression to predict snow depth on December 1st, January 1st and February 1st, based on our snow depth data and the current snow depth in Fairbanks. We used the rstanarm R package, which mimics the glm function that’s part of base R.
Because of the non-zero, skewed nature of the distribution of snow depths, a log-linked Gamma distribution is appropriate. We used the rstanarm defaults for priors.
One of the great things about Bayesian linear regression is that it incorporates our uncertainty about the model coefficients to produce a distribution of predicted values. The more uncertainty there is in our model, the wider the range of predicted values. We examine the distribution of these predicted snow depth values and compare them with the distribution of actual values.
The code for the analysis appears at the bottom of the post.
Results
The following figure shows a histogram and density function plot for the predicted snow depth on December 1st (top pane) for this year, and the actual December 1st snow depth data in past years (bottom).
The predicted snow depth ranges from zero to almost 27 inches of snow, but the distribution is concentrated around 5 inches. The lower plot showing the distribution of actual snow depth on December 1st isn’t as smooth, but it has a similar shape and peaks at 9 inches.
If we run the same analysis for January and February, we get a set of frequency distributions that look like the following plot, again with the predicted snow depth distribution on top and the distribution of actual data on the bottom.
The December densities are repeated here, in red, along with the January (green) and February (blue) results. In the top plot, you can clearly see that the shape of the distribution gets more spread out as we get farther from November, indicating our increasing uncertainty in our predictions, although some of that pattern is also from the source data (below), which also gets more spread out in January and February.
Despite our increasing uncertainty, it’s clear from comparing the peaks in these curves that our models expect there to be less snow in December, January and February this year, compared with historical values. By my reckoning, we can expect around 5 inches on December 1st, 10 inches on January 1st, and 12 or 13 inches by February. In an average year, these values would be closer to 9, 12, and 15 inches.
Conclusion
There is a relationship between snow depth on November 10th and depths later in the winter, but the distributions of predicted values are so spread out that we could easily receive as much or more snow as we have in previous years. Last year on this date we had 5 inches, on December 1st we had 11 inches, 13 inches on New Year’s Day, and 20 inches on February 1st. Here’s hoping we quickly reach, and surpass those values in 2018/2019.
Appendix
library(tidyverse)
library(glue)
library(ggpubr)
library(scales)
library(lubridate)
library(RPostgres)
library(rstanarm)
noaa <- dbConnect(Postgres(),
dbname = "noaa")
ghcnd_stations <- noaa %>%
tbl("ghcnd_stations") %>%
filter(station_name == "FAIRBANKS INTL AP")
ghcnd_variables <- noaa %>%
tbl("ghcnd_variables") %>%
filter(variable == "SNWD")
ghcnd_obs <- noaa %>%
tbl("ghcnd_obs") %>%
inner_join(ghcnd_stations, by = "station_id") %>%
inner_join(ghcnd_variables, by = "variable") %>%
mutate(month = date_part("month", dte),
day = date_part("day", dte)) %>%
filter((month == 11 & day == 10) |
(month == 12 & day == 1) |
(month == 1 & day == 1) |
(month == 2 & day == 1),
is.na(meas_flag) | meas_flag == "") %>%
mutate(value = raw_value * raw_multiplier) %>%
select(dte, month, day, variable, value) %>%
collect()
snow_depths <- ghcnd_obs %>%
mutate(wyear = year(dte - days(91)),
mmdd = factor(glue("{str_to_lower(month.abb[month])}",
"_{sprintf('%02d', day)}"),
levels = c("nov_10", "dec_01",
"jan_01", "feb_01")),
value = value / 25.4) %>%
select(wyear, mmdd, value) %>%
spread(mmdd, value) %>%
filter(!is.na(nov_10))
write_csv(snow_depths, "snow_depths.csv", na = "")
dec <- stan_glm(dec_01 ~ nov_10,
data = snow_depths,
family = Gamma(link = "log"),
# prior = normal(0.7, 3),
# prior_intercept = normal(1, 3),
iter = 5000)
# What does the model day about 2018?
dec_prediction_mat <- posterior_predict(dec,
newdata = tibble(nov_10 = 1))
dec_prediction <- tibble(pred_dec_01 = dec_prediction_mat[,1])
dec_hist <- ggplot(data = dec_prediction,
aes(x = pred_dec_01, y = ..density..)) +
theme_bw() +
geom_histogram(binwidth = 0.25, color = 'black',
fill = 'darkorange') +
geom_density() +
scale_x_continuous(name = "Snow depth (inches)",
limits = c(0, 40),
breaks = seq(0, 40, 5)) +
scale_y_continuous(name = "Frequency") +
theme(plot.margin = unit(c(1, 1, 0, 0.5), 'lines')) +
theme(axis.text.x = element_blank(),
axis.title.x = element_blank(),
axis.ticks.x = element_blank()) +
labs(title = "December Snow Depth",
subtitle = "Fairbanks Airport Station")
actual_december <- ggplot(data = snow_depths,
aes(x = dec_01, y = ..density..)) +
theme_bw() +
geom_histogram(binwidth = 1, color = 'black',
fill = 'darkorange') +
geom_density() +
scale_x_continuous(name = "Snow depth (inches)",
limits = c(0, 40),
breaks = seq(0, 40, 5)) +
scale_y_continuous(name = "Frequency") +
theme(plot.margin = unit(c(0, 1, 0.5, 0.5), 'lines'))
height <- 9
width <- 16
rescale <- 0.75
heights <- c(0.5, 0.5) * height
gt <- ggarrange(dec_hist, actual_december,
ncol = 1, nrow = 2, align = "v",
widths = c(1, 1), heights = heights)
svg('december_comparison.svg',
width=width*rescale, height=height*rescale)
gt
dev.off()
jan <- stan_glm(jan_01 ~ nov_10,
data = snow_depths,
# family = gaussian(link = "identity"),
family = Gamma(link = "log"),
# prior = normal(0.7, 3),
# prior_intercept = normal(1, 3),
iter = 5000)
jan_prediction_mat <- posterior_predict(jan,
newdata = tibble(nov_10 = 1))
jan_prediction <- tibble(pred_jan_01 = jan_prediction_mat[,1])
feb <- stan_glm(feb_01 ~ nov_10,
data = snow_depths,
# family = gaussian(link = "identity"),
family = Gamma(link = "log"),
# family = poisson(link = "identity"),
# prior = normal(0.7, 3),
# prior_intercept = normal(1, 3),
iter = 5000)
feb_prediction_mat <- posterior_predict(feb,
newdata = tibble(nov_10 = 1))
feb_prediction <- tibble(pred_feb_01 = feb_prediction_mat[,1])
all_predictions <- bind_cols(dec_prediction,
jan_prediction,
feb_prediction) %>%
rename(`Dec 1` = pred_dec_01,
`Jan 1` = pred_jan_01,
`Feb 1` = pred_feb_01) %>%
gather(prediction, snow_depth_inches) %>%
mutate(prediction = factor(prediction,
levels = c("Dec 1", "Jan 1", "Feb 1")))
pred_density_plot <- ggplot(data = all_predictions,
aes(x = snow_depth_inches, colour = prediction)) +
theme_bw() +
geom_density() +
scale_x_continuous(name = "Snow depth (inches)",
limits = c(0, 55),
breaks = pretty_breaks(n = 10)) +
theme(axis.text.x = element_blank(), axis.title.x = element_blank(),
axis.ticks.x = element_blank()) +
labs(title = "Predicted and actual snow depths based on November 10 depth",
subtitle = "Fairbanks Airport Station")
actual_data <- snow_depths %>%
transmute(`Dec 1` = dec_01,
`Jan 1` = jan_01,
`Feb 1` = feb_01) %>%
gather(actual, snow_depth_inches) %>%
mutate(actual = factor(actual, levels = c("Dec 1", "Jan 1", "Feb 1")))
actual_density_plot <- ggplot(data = actual_data,
aes(x = snow_depth_inches, colour = actual)) +
theme_bw() +
geom_density() +
scale_x_continuous(name = "Snow depth (inches)",
limits = c(0, 55),
breaks = pretty_breaks(n = 10)) +
theme(plot.margin = unit(c(0, 1, 0.5, 0.5), 'lines'))
height <- 9
width <- 16
rescale <- 0.75
heights <- c(0.5, 0.5) * height
gt <- ggarrange(pred_density_plot, actual_density_plot,
ncol = 1, nrow = 2, align = "v",
widths = c(1, 1), heights = heights)
svg('dec_jan_feb.svg',
width=width*rescale, height=height*rescale)
gt
dev.off()
Introduction
A couple years ago I wrote a post about past Equinox Marathon weather. Since that post Andrea and I have run the relay twice, and I plan on running the full marathon in a couple days. This post updates the statistics and plots to include two more years of the race.
Methods
Methods and data are the same as in my previous post, except the daily data has been updated to include 2016 and 2017. The R code is available at the end of the previous post.
Results
Race day weather
Temperatures at the airport on race day ranged from 19.9 °F in 1972 to 35.1 °F in 1969, but the average range is between 34.1 and 53.1 °F. Using our model of Ester Dome temperatures, we get an average range of 29.5 and 47.3 °F and an overall min / max of 16.1 / 61.3 °F. Generally speaking, it will be below freezing on Ester Dome, but possibly before most of the runners get up there.
Precipitation (rain, sleet or snow) has fallen on 16 out of 55 race days, or 29% of the time, and measurable snowfall has been recorded on four of those sixteen. The highest amount fell in 2014 with 0.36 inches of liquid precipitation (no snow was recorded and the temperatures were between 45 and 51 °F so it was almost certainly all rain, even on Ester Dome). More than a quarter of an inch of precipitation fell in three of the sixteen years when it rained or snowed (1990, 1993, and 2014), but most rainfall totals are much smaller.
Measurable snow fell at the airport in four years, or seven percent of the time: 4.1 inches in 1993, 2.1 inches in 1985, 1.2 inches in 1996, and 0.4 inches in 1992. But that’s at the airport station. Five of the 12 years where measurable precipitation fell at the airport and no snow fell, had possible minimum temperatures on Ester Dome that were below freezing. It’s likely that some of the precipitation recorded at the airport in those years was coming down as snow up on Ester Dome. If so, that means snow may have fallen on nine race days, bringing the percentage up to sixteen percent.
Wind data from the airport has only been recorded since 1984, but from those years the average wind speed at the airport on race day is 4.8 miles per hour. The highest 2-minute wind speed during Equinox race day was 21 miles per hour in 2003. Unfortunately, no wind data is available for Ester Dome, but it’s likely to be higher than what is recorded at the airport.
Weather from the week prior
It’s also useful to look at the weather from the week before the race, since excessive pre-race rain or snow can make conditions on race day very different, even if the race day weather is pleasant. The year I ran the full marathon (2013), it snowed the week before and much of the trail in the woods before the water stop near Henderson and all of the out and back were covered in snow.
The most dramatic example of this was 1992 where 23 inches (!) of snow fell at the airport in the week prior to the race, with much higher totals up on the summit of Ester Dome. Measurable snow has been recorded at the airport in the week prior to six races, but all the weekly totals are under an inch except for the snow year of 1992.
Precipitation has fallen in 44 of 55 pre-race weeks (80% of the time). Three years have had more than an inch of precipitation prior to the race: 1.49 inches in 2015, 1.26 inches in 1992 (most of which fell as snow), and 1.05 inches in 2007. On average, just over two tenths of an inch of precipitation falls in the week before the race.
Summary
The following stacked plots shows the weather for all 55 runnings of the Equinox marathon. The top panel shows the range of temperatures on race day from the airport station (wide bars) and estimated on Ester Dome (thin lines below bars). The shaded area at the bottom shows where temperatures are below freezing.
The middle panel shows race day liquid precipitation (rain, melted snow). Bars marked with an asterisk indicate years where snow was also recorded at the airport, but remember that five of the other years with liquid precipitation probably experienced snow on Ester Dome (1977, 1986, 1991, 1994, and 2016) because the temperatures were likely to be below freezing at elevation.
The bottom panel shows precipitation totals from the week prior to the race. Bars marked with an asterisk indicate weeks where snow was also recorded at the airport.
Here’s a table with most of the data from the analysis. A CSV with this data can be downloaded from all_wx.csv
| Date | min t | max t | ED min t | ED max t | awnd | prcp | snow | p prcp | p snow |
|---|---|---|---|---|---|---|---|---|---|
| 1963-09-21 | 32.0 | 54.0 | 27.5 | 48.2 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1964-09-19 | 34.0 | 57.9 | 29.4 | 51.8 | 0.00 | 0.0 | 0.03 | 0.0 | |
| 1965-09-25 | 37.9 | 60.1 | 33.1 | 53.9 | 0.00 | 0.0 | 0.80 | 0.0 | |
| 1966-09-24 | 36.0 | 62.1 | 31.3 | 55.8 | 0.00 | 0.0 | 0.01 | 0.0 | |
| 1967-09-23 | 35.1 | 57.9 | 30.4 | 51.8 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1968-09-21 | 23.0 | 44.1 | 19.1 | 38.9 | 0.00 | 0.0 | 0.04 | 0.0 | |
| 1969-09-20 | 35.1 | 68.0 | 30.4 | 61.3 | 0.00 | 0.0 | 0.00 | 0.0 | |
| 1970-09-19 | 24.1 | 39.9 | 20.1 | 34.9 | 0.00 | 0.0 | 0.42 | 0.0 | |
| 1971-09-18 | 35.1 | 55.9 | 30.4 | 50.0 | 0.00 | 0.0 | 0.14 | 0.0 | |
| 1972-09-23 | 19.9 | 42.1 | 16.1 | 37.0 | 0.00 | 0.0 | 0.01 | 0.2 | |
| 1973-09-22 | 30.0 | 44.1 | 25.6 | 38.9 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1974-09-21 | 48.0 | 60.1 | 42.5 | 53.9 | 0.08 | 0.0 | 0.00 | 0.0 | |
| 1975-09-20 | 37.9 | 55.9 | 33.1 | 50.0 | 0.02 | 0.0 | 0.02 | 0.0 | |
| 1976-09-18 | 34.0 | 59.0 | 29.4 | 52.9 | 0.00 | 0.0 | 0.54 | 0.0 | |
| 1977-09-24 | 36.0 | 48.9 | 31.3 | 43.4 | 0.06 | 0.0 | 0.20 | 0.0 | |
| 1978-09-23 | 30.0 | 42.1 | 25.6 | 37.0 | 0.00 | 0.0 | 0.10 | 0.3 | |
| 1979-09-22 | 35.1 | 62.1 | 30.4 | 55.8 | 0.00 | 0.0 | 0.17 | 0.0 | |
| 1980-09-20 | 30.9 | 43.0 | 26.5 | 37.8 | 0.00 | 0.0 | 0.35 | 0.0 | |
| 1981-09-19 | 37.0 | 43.0 | 32.2 | 37.8 | 0.15 | 0.0 | 0.04 | 0.0 | |
| 1982-09-18 | 42.1 | 61.0 | 37.0 | 54.8 | 0.02 | 0.0 | 0.22 | 0.0 | |
| 1983-09-17 | 39.9 | 46.9 | 34.9 | 41.5 | 0.00 | 0.0 | 0.05 | 0.0 | |
| 1984-09-22 | 28.9 | 60.1 | 24.6 | 53.9 | 5.8 | 0.00 | 0.0 | 0.08 | 0.0 |
| 1985-09-21 | 30.9 | 42.1 | 26.5 | 37.0 | 6.5 | 0.14 | 2.1 | 0.57 | 0.0 |
| 1986-09-20 | 36.0 | 52.0 | 31.3 | 46.3 | 8.3 | 0.07 | 0.0 | 0.21 | 0.0 |
| 1987-09-19 | 37.9 | 61.0 | 33.1 | 54.8 | 6.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1988-09-24 | 37.0 | 45.0 | 32.2 | 39.7 | 4.0 | 0.00 | 0.0 | 0.11 | 0.0 |
| 1989-09-23 | 36.0 | 61.0 | 31.3 | 54.8 | 8.5 | 0.00 | 0.0 | 0.07 | 0.5 |
| 1990-09-22 | 37.9 | 50.0 | 33.1 | 44.4 | 7.8 | 0.26 | 0.0 | 0.00 | 0.0 |
| 1991-09-21 | 36.0 | 57.0 | 31.3 | 51.0 | 4.5 | 0.04 | 0.0 | 0.03 | 0.0 |
| 1992-09-19 | 24.1 | 33.1 | 20.1 | 28.5 | 6.7 | 0.01 | 0.4 | 1.26 | 23.0 |
| 1993-09-18 | 28.0 | 37.0 | 23.8 | 32.2 | 4.9 | 0.29 | 4.1 | 0.37 | 0.3 |
| 1994-09-24 | 27.0 | 51.1 | 22.8 | 45.5 | 6.0 | 0.02 | 0.0 | 0.08 | 0.0 |
| 1995-09-23 | 43.0 | 66.9 | 37.8 | 60.3 | 4.0 | 0.00 | 0.0 | 0.00 | 0.0 |
| 1996-09-21 | 28.9 | 37.9 | 24.6 | 33.1 | 6.9 | 0.06 | 1.2 | 0.26 | 0.0 |
| 1997-09-20 | 27.0 | 55.0 | 22.8 | 49.1 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 1998-09-19 | 42.1 | 60.1 | 37.0 | 53.9 | 4.9 | 0.00 | 0.0 | 0.37 | 0.0 |
| 1999-09-18 | 39.0 | 64.9 | 34.1 | 58.4 | 3.8 | 0.00 | 0.0 | 0.26 | 0.0 |
| 2000-09-16 | 28.9 | 50.0 | 24.6 | 44.4 | 5.6 | 0.00 | 0.0 | 0.30 | 0.0 |
| 2001-09-22 | 33.1 | 57.0 | 28.5 | 51.0 | 1.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2002-09-21 | 33.1 | 48.9 | 28.5 | 43.4 | 3.8 | 0.00 | 0.0 | 0.03 | 0.0 |
| 2003-09-20 | 26.1 | 46.0 | 22.0 | 40.7 | 9.6 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2004-09-18 | 26.1 | 48.0 | 22.0 | 42.5 | 4.3 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2005-09-17 | 37.0 | 63.0 | 32.2 | 56.6 | 0.9 | 0.00 | 0.0 | 0.09 | 0.0 |
| 2006-09-16 | 46.0 | 64.0 | 40.7 | 57.6 | 4.3 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2007-09-22 | 25.0 | 45.0 | 20.9 | 39.7 | 4.7 | 0.00 | 0.0 | 1.05 | 0.0 |
| 2008-09-20 | 34.0 | 51.1 | 29.4 | 45.5 | 4.5 | 0.00 | 0.0 | 0.08 | 0.0 |
| 2009-09-19 | 39.0 | 50.0 | 34.1 | 44.4 | 5.8 | 0.00 | 0.0 | 0.25 | 0.0 |
| 2010-09-18 | 35.1 | 64.9 | 30.4 | 58.4 | 2.5 | 0.00 | 0.0 | 0.00 | 0.0 |
| 2011-09-17 | 39.9 | 57.9 | 34.9 | 51.8 | 1.3 | 0.00 | 0.0 | 0.44 | 0.0 |
| 2012-09-22 | 46.9 | 66.9 | 41.5 | 60.3 | 6.0 | 0.00 | 0.0 | 0.33 | 0.0 |
| 2013-09-21 | 24.3 | 44.1 | 20.3 | 38.9 | 5.1 | 0.00 | 0.0 | 0.13 | 0.6 |
| 2014-09-20 | 45.0 | 51.1 | 39.7 | 45.5 | 1.6 | 0.36 | 0.0 | 0.00 | 0.0 |
| 2015-09-19 | 37.9 | 44.1 | 33.1 | 38.9 | 2.9 | 0.01 | 0.0 | 1.49 | 0.0 |
| 2016-09-17 | 34.0 | 57.9 | 29.4 | 51.8 | 2.2 | 0.01 | 0.0 | 0.61 | 0.0 |
| 2017-09-16 | 33.1 | 66.0 | 28.5 | 59.5 | 3.1 | 0.00 | 0.0 | 0.02 | 0.0 |