Great Falls weather in May

In May, Great Falls sees average daytime highs of 65°F and overnight lows near 43°F, with 2.4 in of precipitation across 10.8 wet days and about 14.9 hours of daylight. It is the 5th-warmest and 2nd-wettest month of the year here.

Highs climb over the month, from about 61°F in the first days to 68°F by the end. The sky is clear or mostly clear about 23% of the time in May, and the air most often feels dry.

Daylight stretches from about 14 h 12 min at the start of May to 15 h 24 min by month's end. Set against the rest of the year, May is Great Falls's 10th-clearest and 8th-windiest month. For the whole year in context, see Great Falls's year-round climate.

Daytime high
65°
5th warmest
Overnight low
43°
8th coldest
Precipitation
2.4 in
10.8 wet days
Daylight
14 h 54 min
4:55 AM – 7:48 PM
Cloud cover
63%
10th clearest
Wind
8 mph
8th windiest
Solar energy
6.3 kWh/m²
Travel score
5.7
out of 10

Great Falls is city in and county seat of Cascade County, Montana, United States.

Density
985/km²
people per km²
Founded
1883

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in May

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 61°F in the first days to 68°F by the end.

A typical May day in Great Falls reaches about 65°F in the afternoon and slips back to 43°F overnight — a 22°F spread between the day's warmth and the night's chill. On most days the high lands between 51°F and 80°F. Set against its neighbours, May runs about 10°F warmer than April and about 8°F cooler than June.

20°40°60°80°151015202531
Avg high (°F)Avg low (°F)
16038
26039
36139
46139
56139
66240
76240
86240
96341
106341
116441
126442
136442
146542
156543
166543
176544
186644
196644
206644
216645
226745
236745
246746
256746
266746
276846
286847
296847
306947
316947

How May really feels in Great Falls

Once humidity and wind are folded in, May averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
0
wind chill below the day's low

May sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Great Falls weather by month

How May compares with the rest of the year at a glance. May is the 5th-warmest and 2nd-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan33° / 18°0.85.75.78.70.0
Feb36° / 19°0.75.85.99.90.0
Mar45° / 26°1.075.311.61.2
Apr55° / 34°2.09.44.213.33.5
May65° / 43°2.410.81.114.95.7
Jun73° / 50°2.910.50.115.76.6
Jul84° / 56°0.95.1015.46.5
Aug83° / 55°1.14.8014.17.0
Sep71° / 47°1.46.30.212.47.3
Oct57° / 37°1.372.510.64.3
Nov43° / 27°0.95.84.79.10.7
Dec34° / 20°0.85.75.68.30.0

Cloud cover in May

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 23% of the time in May.

Beyond those clear spells, partly cloudy skies cover about 20% of May, with mostly cloudy or overcast conditions the remaining 57%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
14159
24159
34159
44159
54258
64258
74258
84357
94456
104456
114357
124357
134357
144258
154357
164258
174258
184357
194357
204357
214357
224357
234456
244456
254456
264456
274555
284555
294555
304555
314555

Chance of precipitation in May

Any precipitationSnow

Great Falls gets around 2.4 in of rain and snow over 10.8 wet days in May. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 35% and peaks near 40% on the wettest days, and about 1 day brings snow. The odds climb toward the end of the month.

0%10%20%30%40%50%151015202531
Rain chance (%)Snow chance (%)
1339
2339
3339
4328
5328
6327
7327
8326
9326
10326
11325
12325
13334
14334
15344
16343
17353
18363
19362
20372
21382
22392
23391
24391
25391
26391
27391
28391
29391
30391
31401

Humidity in May

DryComfortableHumidMuggyOppressiveMiserable

Most of May feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, May lands in the dry band about 100% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
11000
21000
31000
41000
51000
61000
71000
81000
91000
101000
111000
121000
131000
141000
151000
161000
171000
181000
191000
201000
211000
221000
231000
241000
251000
261000
271000
281000
291000
30991
31991

Wind in May

Winds average 8 mph in May.

Across May, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

051015151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
257light breeze
267light breeze
277light breeze
287light breeze
297light breeze
307light breeze
317light breeze

Sunrise & sunset in May

DaylightNight

Daylight runs from about 14 h 12 min at the start of May to 15 h 24 min by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 72 minutes over May. Sunrise moves from 5:17 AM to 4:40 AM, and sunset from 7:28 PM to 8:06 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.25:177:28
214.25:157:29
314.35:147:31
414.35:127:32
514.45:107:34
614.45:097:35
714.55:077:36
814.55:067:38
914.65:047:39
1014.65:037:40
1114.75:017:42
1214.75:007:43
1314.84:597:44
1414.84:577:46
1514.94:567:47
1614.94:557:48
1714.94:537:50
1815.04:527:51
1915.04:517:52
2015.14:507:53
2115.14:497:55
2215.14:487:56
2315.24:477:57
2415.24:467:58
2515.24:457:59
2615.34:448:00
2715.34:438:01
2815.34:428:02
2915.44:418:04
3015.44:408:05
3115.44:408:06

Solar energy in May

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in May, about 6.3 kWh/m².

For context, solar energy here swings from a low near 1.39 kWh/m² to a high of 7.32 kWh/m² in July across the year — May's 6.3 kWh/m² falls in the middle.

0246151015202531
Solar energy (kWh/m²)Level
16.0Intense
26.0Intense
36.1Intense
46.1Intense
56.1Intense
66.2Intense
76.2Intense
86.2Intense
96.2Intense
106.2Intense
116.2Intense
126.3Intense
136.3Intense
146.3Intense
156.3Intense
166.3Intense
176.3Intense
186.3Intense
196.3Intense
206.3Intense
216.3Intense
226.3Intense
236.3Intense
246.3Intense
256.3Intense
266.4Intense
276.4Intense
286.4Intense
296.4Intense
306.5Intense
316.5Intense
Planning a trip in May

Is May a good time to visit Great Falls?

Our two travel scores rate May for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

5.7
Sightseeing
5th-best month of the year
2.0
Beach & pool
5th-best month of the year

May is a reasonable time to visit Great Falls for sightseeing.

What to pack for Great Falls in May

From May's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In May, Great Falls sees daytime highs around 65°F and nights near 43°F. Pack sun protection. Worth having: a warm layer and rain gear. About 11 days see rain.

sun protectiona warm layerrain gear

UV index in Great Falls in May

LowModerateHighVery highExtreme

Clear-sky midday UV in May peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Great Falls peaks around July 14 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 17 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 14UV 8Dec 17UV 1
UV index (midday)Level
Jan1Low
Feb2Low
Mar3Moderate
Apr4Moderate
May7High
Jun7Very high
Jul8Very high
Aug6High
Sep5Moderate
Oct4Moderate
Nov1Low
Dec1Low

Air quality in Great Falls in May

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where May falls, not just the annual average.

Air quality in Great Falls is worst in August — around 23 µg/m³ PM2.5 (moderate), about 3.8× the cleanest month (December, 6 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodModerateGoodAug 1323 µg/m³Dec 106 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb6Good
Mar11Good
Apr13Moderate
May12Good
Jun9Good
Jul20Moderate
Aug23Moderate
Sep16Moderate
Oct8Good
Nov6Good
Dec6Good
Location & terrain

Where is Great Falls?

Great Falls sits at 47.5°N, 111.3°W, 3,330 ft above sea level, in United States. The nearest listed city is Helena, 71 mi away.

Topography around Great Falls

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Great Falls.

Within 2 miles, the terrain around Great Falls has only modest variations in elevation — a maximum elevation change of 217 ft around an average of 3,366 ft above sea level; within 10 miles, significant variations in elevation — a maximum elevation change of 1,270 ft; within 50 miles, very significant variations in elevation — a maximum elevation change of 6,588 ft.

The land around Great Falls is covered by artificial surfaces (52%) and grassland (22%) within 2 miles, grassland (51%) and cropland (38%) within 10 miles, and grassland (55%) and cropland (31%) within 50 miles.

2 miles
217 ft
10 miles
1,270 ft
50 miles
6,588 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
May weather nearby: Helena 71 mi · Butte 119 mi · Bozeman 126 mi · Missoula 134 mi · Kalispell 148 mi · Whitefish 154 mi · Lethbridge 167 mi · Medicine Hat 178 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Great Falls (47.5002°, -111.3008°, elevation 3,330 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).