Frost Dates for Roundup 15 Sw, MT

Elevation: 1032 m

Frost Dates

Last Spring Frost (50%) iA 50% chance that the last spring frost has already passed by this date. Most gardeners use this as their primary planting guide. May 22
First Fall Frost (50%) iA 50% chance that the first fall frost has occurred by this date. Plan to harvest or protect tender plants before this date. September 15
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

30% Probability iOnly a 30% chance of frost remaining by this date. Use these dates for a safer planting window, especially for tender plants sensitive to cold.

Last Spring Frost May 28
First Fall Frost September 10

Hard Freeze (28°F)

Last Spring Hard Freeze May 11
First Fall Hard Freeze September 26
46.33°N, -108.74°W © OpenStreetMap

Growing Season

116 Days May 22 to September 15

USDA Hardiness Zone iHardiness zones indicate which perennial plants can survive winter in your area. For annual vegetables, frost dates and growing season length matter more than hardiness zone.

Zone 4a

Avg. annual minimum: −30 to −25°F

Learn more

Köppen Climate iThe Köppen climate classification system categorizes climates based on temperature and precipitation patterns.

BSk Cold Semi-Arid (Steppe)

Cool to cold with low rainfall and wide temperature swings. Common in the western Great Plains and central Asia. Short growing seasons benefit from season extension techniques.

Köppen climate map

Temperature

10° 30° 50° 70° 90°
23°
High: 36°F
Avg: 23°F
Low: 11°F
Jan
26°
High: 39°F
Avg: 26°F
Low: 12°F
Feb
33°
High: 48°F
Avg: 33°F
Low: 19°F
Mar
42°
High: 56°F
Avg: 42°F
Low: 27°F
Apr
52°
High: 66°F
Avg: 52°F
Low: 37°F
May
61°
High: 76°F
Avg: 61°F
Low: 46°F
Jun
69°
High: 87°F
Avg: 69°F
Low: 51°F
Jul
67°
High: 86°F
Avg: 67°F
Low: 48°F
Aug
57°
High: 75°F
Avg: 57°F
Low: 39°F
Sep
44°
High: 59°F
Avg: 44°F
Low: 29°F
Oct
33°
High: 46°F
Avg: 33°F
Low: 19°F
Nov
24°
High: 37°F
Avg: 24°F
Low: 12°F
Dec
32°F
28°F
Avg High Avg Temp Avg Low Light Frost (32°F) Hard Frost (28°F)

Precipitation

0" 2" 4" 4.5"
2.1"
2.08"
Jan
1.7"
1.68"
Feb
2.3"
2.26"
Mar
3.2"
3.16"
Apr
4.5"
4.50"
May
3.8"
3.78"
Jun
2.9"
2.92"
Jul
3.1"
3.10"
Aug
3.0"
3.03"
Sep
2.7"
2.72"
Oct
2.0"
1.99"
Nov
1.9"
1.91"
Dec

Sunrise / Sunset

4a7a10a1p4p7p10pNoonJanFebMarAprMayJunJulAugSepOctNovDec9h10h11.5h13.5h15h15.5h15.5h14h12.5h10.5h9h8.5h
Jan: 7:36 AM – 4:24 PM · 8h 48m
Feb: 6:57 AM – 5:03 PM · 10h 05m
Mar: 6:12 AM – 5:48 PM · 11h 36m
Apr: 5:20 AM – 6:40 PM · 13h 20m
May: 4:36 AM – 7:24 PM · 14h 47m
Jun: 4:13 AM – 7:47 PM · 15h 35m
Jul: 4:22 AM – 7:38 PM · 15h 15m
Aug: 5:00 AM – 6:60 PM · 13h 59m
Sep: 5:51 AM – 6:09 PM · 12h 19m
Oct: 6:41 AM – 5:19 PM · 10h 38m
Nov: 7:25 AM – 4:35 PM · 9h 09m
Dec: 7:47 AM – 4:13 PM · 8h 25m
Daylight Longest: 15h 36m · Shortest: 8h 24m

Nearby Stations

Roundup, MTMay 20 - September 21 Ryegate, MTMay 17 - September 23 Ryegate 18 Nnw, MT May 26 - September 18 Rapelje, MTMay 24 - September 21 Pompeys Pillar 15n, MT May 22 - September 22 Huntley Exp Stn, MT May 12 - September 25

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