Photo: Ascended Dreamer · CC BY-SA 4.0Winter nights in Grand Isle are colder than in 94% of U.S. towns
In July the day’s top temperature is typically 81°. Summers stay cool: July afternoons here are cooler than in 89% of U.S. towns. The latest 30-year average runs 1.6° warmer than 1901–2000’s, with December up the most. The heating season runs October to April: each of those months averages under 50°.
A year in Grand Isle at a glance
Each month’s typical high and low, and what it brings.
What stands out about Grand Isle’s climate
Compared with towns across the U.S., with Grand Isle’s place in Vermont beside it.
What a year in Grand Isle feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 174 frost-free days a year
In half of years the last 32° night comes by April 28 and the first by October 20. Frost and day counts come from NOAA’s station at S Hero, VT, 6 miles from the town’s center, at about the same height.
The 2023 USDA map puts Grand Isle’s center in zone 5a: the coldest night of a typical winter, averaged over 1991–2020, reaches about −15°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 50 inches of snow a winter
Snow, measured at S Hero, VT, falls mostly in January, February, March and December. Precipitation (rain plus melted snow) adds up to 35 inches a year; June is the wettest month and February the driest. Rain or snow falls on about 127 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Grand Isle
93% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at S Hero, VT.
Living with Grand Isle’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
174 frost-free days in zone 5a. The last frost comes by Apr 28 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 20.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 5.0 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Grand Isle from natural hazards, river flooding is the largest share (78%); heat waves, cold waves, winter storms and ice storms together are 7%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Grand Isle and its neighbors
Every town next door is within a degree of Grand Isle in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Grand Isle’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Grand Isle, VT | 9° | 81° | 35" | 50" |
| Slinger, WI | 11° | 81° | 34" | 54" |
| Stewartville, MN | 6° | 81° | 36" | 53" |
| Clear Lake, IA | 7° | 82° | 36" | 44" |
| Houghton Lake, MI | 12° | 81° | 33" | 66" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Grand Isle averaged 1.6° warmer than the 1900s. The biggest change is in December (+3.6°).
A bigger shift than in 65% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Grand Isle compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Grand Isle’s place among Vermont’s.
Grand Isle weather by month
Highs, lows and precipitation from NOAA’s grid at Grand Isle’s center; snow, wet days and snow on the ground from S Hero, VT. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 27° | 9° | 2.2" | 11.4" | 11 | 24 | 4° – 27° |
| February | 30° | 11° | 1.8" | 11.6" | 8 | 22 | 6° – 27° |
| March | 39° | 21° | 2.1" | 10.6" | 10 | 16 | 21° – 41° |
| April | 54° | 34° | 2.9" | 2.2" | 11 | 2 | 39° – 50° |
| May | 68° | 46° | 3.3" | 0.0" | 12 | 0 | 51° – 62° |
| June | 76° | 56° | 4.0" | 0.0" | 12 | 0 | 63° – 70° |
| July | 81° | 61° | 3.7" | 0.0" | 12 | 0 | 66° – 75° |
| August | 79° | 59° | 3.5" | 0.0" | 11 | 0 | 66° – 73° |
| September | 71° | 51° | 3.2" | 0.0" | 10 | 0 | 56° – 66° |
| October | 58° | 40° | 3.6" | 0.1" | 11 | 0 | 45° – 57° |
| November | 45° | 30° | 2.5" | 3.3" | 10 | 3 | 32° – 44° |
| December | 34° | 19° | 2.5" | 10.9" | 11 | 14 | 18° – 37° |
| Year | 55° | 36° | 35.4" | 50.1" | 127 | 81 |
How much a month can swing
A normal is an average. January swings the most: from 1991 to 2020 its average ranged from 4° to 27°. August is the most reliable, staying within 7°.
Where Grand Isle’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Grand Isle’s center.
- Snow: S Hero, VT.
- Frost, freezing nights, 90° and 100° days, heating and cooling: S Hero, VT, 6 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Grand Isle’s climate
What is the weather like in Grand Isle?
A typical July afternoon reaches 81°, a January night drops to 9°, and about 50 inches of snow falls in a normal winter. Colder January nights than 94% of U.S. towns; cooler July afternoons than 89% of U.S. towns.
How cold does it get in Grand Isle in winter?
January nights average 9°. About 141 nights a year reach 32° or below and 15 reach 0° or below. In the coldest January of the last 30 years the month averaged 4°.
How much snow does Grand Isle get?
About 50 inches in a normal winter at S Hero, VT, most of it in January, February, March and December, with snow on the ground about 81 days a year.
How hot does it get in Grand Isle?
July, with a typical high of 81° and a low of 61°. About 6 days a year reach 90° (S Hero, VT).
When is the first and last frost in Grand Isle?
In half of years the last spring frost (32°) comes by April 28 and the first fall frost by October 20, about 174 frost-free days, at S Hero, VT.
What growing zone is Grand Isle in?
Zone 5a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −15°.
What is the best time of year to visit Grand Isle?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Grand Isle getting warmer?
Yes: 1991–2020 averaged 1.6° warmer than 1901–2000 on NOAA’s grid. A bigger shift than 65% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Grand Isle.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.