Race-day weather · Saturday, June 19, 2027

Grandma's Marathon weather.

26 Grandma's Marathon race mornings since 2000, measured hour by hour: temperature, dew point, wind, rain, and what the weather cost runners. The forecast for the 2027 race goes live here on Jun 13, six days out.

112 Typical score
at the start The median race morning since 2000: 59°F air + 53°F dew point at 7:45am, across 26 race mornings at the Duluth International weather station. Slight penalty: 0.5% to 1% slower.
Start · 7:45am11259° air · 53° dew point
+2 hours · 9:45am11763° air · 54° dew point
+4 hours · 11:45am12067° air · 53° dew point

Your goal pace on a typical race morning

Built from the median race morning since 2000, averaged across the hours you’d be running. Where the weather costs time, each cell gives the adjusted finish time and the pace per mile to run instead. Six days out, the real forecast replaces it.

Goal on a cool dayStarting 7:45amStarting 8:10am
2:456:18/mi2:46 to 2:476:19–6:21/mi0.5% to 1% slower · score 1152:46 to 2:476:19–6:21/mi0.5% to 1% slower · score 116
3:006:52/mi3:01 to 3:026:54–6:56/mi0.5% to 1% slower · score 1163:01 to 3:026:54–6:56/mi0.5% to 1% slower · score 116
3:157:26/mi3:16 to 3:177:28–7:31/mi0.5% to 1% slower · score 1163:16 to 3:177:28–7:31/mi0.5% to 1% slower · score 117
3:308:01/mi3:31 to 3:328:03–8:05/mi0.5% to 1% slower · score 1163:31 to 3:328:03–8:05/mi0.5% to 1% slower · score 117
3:458:35/mi3:46 to 3:478:37–8:40/mi0.5% to 1% slower · score 1163:46 to 3:478:37–8:40/mi0.5% to 1% slower · score 117
4:009:09/mi4:01 to 4:029:12–9:15/mi0.5% to 1% slower · score 1164:01 to 4:029:12–9:15/mi0.5% to 1% slower · score 117
4:3010:18/mi4:31 to 4:3310:21–10:24/mi0.5% to 1% slower · score 1174:31 to 4:3310:21–10:24/mi0.5% to 1% slower · score 117
5:0011:27/mi5:01 to 5:0311:30–11:33/mi0.5% to 1% slower · score 1175:01 to 5:0311:30–11:33/mi0.5% to 1% slower · score 118
How I’d race a typical year

Start 2 to 3 seconds per mile slower than goal through the first 10 miles. Drink early, because by the time you feel the heat the deficit is already there, and race the last 10K on feel.

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Grandma's Marathon weather history: every race morning since 2000

Every row in the table below is a measurement from the Duluth International weather station, taken nearest 7:45am (today’s first-wave start) and again three hours later. Start times have moved over the years, so treat 7:45am as a clock time, not always the gun. Across 26 race mornings:

  • A typical 7:45am reading is 59°F with a 53°F dew point, a combined score of 112.
  • The warmest was 2016: 69°F with a 63°F dew point at 7:45am, a score of 132.
  • The most humid was 2006, with a 64°F dew point.
  • The coldest was 2000, at 46°F.
  • On 23 of 26 race mornings the 7:45am score was above 100, enough to call for a pace adjustment. Three hours later, 25 of 26 were.
  • The weather changed the race itself in 2025 (start delayed 30 minutes by thunderstorms), 2016 (black flag for heat by late morning), 2006 (black flag for heat) and 2002 (start delayed by thunderstorms).
  • The windiest start was 2010: WNW wind at 15 mph, gusting to 23.
  • Rain fell in the first 5 hours on 7 of 26 race mornings (1 more saw only a trace).
Grandma's Marathon weather by year · air / dew point (°F), combined score, wind and rain
YearDateAir / dew at 7:45amScoreAir / dew at 10:45amScoreWind at 7:45amRain
2026Jun 2054° / 52°10661° / 51°112NW 12 mphDry
2025Jun 21Start delayed 30 minutes by thunderstorms63° / 61°12475° / 68°143S 7 mphDry
2024Jun 2256° / 53°10961° / 57°118ENE 12 mph0.04 in
2023Jun 1764° / 54°11873° / 54°127CalmDry
2022Jun 1856° / 38°9461° / 42°103E 9 mphDry
2021Jun 1958° / 52°11062° / 50°112NNE 6 mphDry
2020–Virtual only (COVID-19), no race morning
2019Jun 2257° / 44°10165° / 48°113ESE 11 mphDry
2018Jun 1659° / 57°11656° / 54°110E 8 mphDry
2017Jun 1762° / 56°11870° / 56°126SW 6 mphDry
2016Jun 18Black flag for heat by late morning69° / 63°13275° / 63°138NNE 5 mphDry
2015Jun 2062° / 58°12066° / 59°125SSW 3 mph0.09 in
2014Jun 2152° / 50°10260° / 55°115CalmLight drizzle
2013Jun 2257° / 54°11157° / 54°111E 10 mphLight rain
2012Jun 1664° / 58°12269° / 60°129E 12 mphDry
2011Jun 1853° / 50°10358° / 53°111SE 5 mphLight rain
2010Jun 1961° / 54°11564° / 54°118WNW 15 mphgusts 23Light rain
2009Jun 2068° / 59°12777° / 58°135NW 8 mphDry
2008Jun 2161° / 50°11168° / 49°117NW 10 mphLight rain
2007Jun 1666° / 58°12474° / 56°130NNW 7 mphDry
2006Jun 17Black flag for heat67° / 64°13174° / 64°138SSW 7 mphDry
2005Jun 1857° / 49°10668° / 50°118E 6 mphDry
2004Jun 1953° / 39°9263° / 39°102W 14 mphDry
2003Jun 2162° / 48°11070° / 51°121S 10 mphDry
2002Jun 22Start delayed by thunderstorms53° / 52°10557° / 56°113ESE 13 mphTrace
2001Jun 1657° / 53°11066° / 53°119WNW 8 mphDry
2000Jun 1746° / 40°8654° / 39°93WNW 7 mphDry

Readings from the Duluth International ASOS weather station (NOAA/FAA, via the Iowa Environmental Mesonet), the observation nearest each hour. Scores above 100 call for a pace adjustment. Rain is the total the station measured in the 5 hours after 7:45am. Download every hour as a CSV.

How the score works

Add the air temperature to the dew point, both in Fahrenheit. That combined score is closer to what your body feels than the temperature alone, because dew point decides whether your sweat can evaporate, and evaporating sweat is how you shed heat at race pace. The bands below are the same ones my heat pace calculator uses, and that page has the full chart and the physiology behind it.

Combined score → how much to slow down
  • 100 or lessNo pace adjustment
  • 101 – 1100% to 0.5% slower
  • 111 – 1200.5% to 1% slower
  • 121 – 1301% to 2% slower
  • 131 – 1402% to 3% slower
  • 141 – 1503% to 4.5% slower
  • 151 – 1604.5% to 6% slower
  • 161 – 1706% to 8% slower
  • 171 – 1808% to 10% slower
  • Above 180Hard running is not recommended

The bands are a coach's rule of thumb, not a lab measurement. Treat each range as a starting point and let effort make the final call.

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Other race-day weather pages

Twin Cities MarathonSunday, October 4, 202695Race day at the startNo adjustment needed Chicago MarathonSunday, October 11, 2026113Race day at the startSlight penalty: 0.5% to 1% slower Columbus MarathonSunday, October 18, 202666Forecast at the startNo adjustment needed Detroit MarathonSunday, October 18, 202673Forecast at the startNo adjustment needed Marine Corps MarathonSunday, October 25, 202694Typical startNo adjustment needed NYC MarathonSunday, November 1, 202683Typical startNo adjustment needed Philadelphia MarathonSunday, November 22, 202673Typical startNo adjustment needed California International MarathonSunday, December 6, 202683Typical startNo adjustment needed Honolulu MarathonSunday, December 13, 2026136Typical startReal penalty: 2% to 3% slower Houston MarathonSunday, January 17, 202784Typical startNo adjustment needed LA MarathonSunday, March 7, 202799Typical startNo adjustment needed Boston MarathonMonday, April 19, 202784Typical startNo adjustment needed

All race-day weather pages

RunFitCoach is not affiliated with the Grandma's Marathon or its organizers. Observations from the Duluth International ASOS station (NOAA/FAA) via the Iowa Environmental Mesonet. Data updated Thursday, October 15, 2026.

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