U.S. Frost Dates by Weather Station

NOAA station USC00328913 · North Dakota

Frost Dates for Upham, ND

NOAA weather station Upham 3 N (USC00328913), North Dakota · elevation 1425 ft (434 m) · hardiness zone 3b*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2550% chance of a frost before it
  • Frost-free season132 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Upham, NDSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 25 in half of the years, before October 6 in 9 years out of 10. Typical frost-free season: 132 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 25Frost season at Upham, NDSpring: a frost after May 3 in 9 years out of 10, after May 15 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 25 in half of the years, before October 6 in 9 years out of 10. Typical frost-free season: 132 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 25
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 26September 13
50% (typical)May 15September 25
90% (likely)May 3October 6
Frost-free season (32°F, 50% chance)
132 days
Hard frost (28°F), last in spring, 50% chance after
May 5
Hard frost (28°F), first in fall, 50% chance before
October 1

The last 15 years (2006–2020 normals)

Typical last frost May 12 (3 days earlier than the 30-year normal), typical first fall frost September 28 (3 days later). Frost-free season 138 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Upham: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 22, 30% May 19, 40% May 17, 50% May 15, 60% May 12, 70% May 9, 80% May 6, 90% May 3. Observed last spring frost in recent years: 2021 May 28.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 15May 32021: May 28Fall at Upham: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 17, 30% September 20, 40% September 23, 50% September 25, 60% September 27, 70% September 29, 80% October 1, 90% October 6. Observed first fall frost in recent years: 2021 October 16.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 13Sep 25Oct 62021: October 16
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021May 28October 16
2022no datano data
2023no datano data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

September 13 is the cautious fall date in Upham for finishing the harvest, because only a 10 % chance of a light frost has occurred earlier. In the spring the cautious date for setting out tender crops is May 26, when there is just a 10 % chance that a light frost will still arrive later.

The 50 % dates mark the median odds for a light frost: May 15 in spring and September 25 in fall. A gardener can view these dates as the point at which frost is equally likely to happen or not, providing a reference for timing activities that tolerate some risk. The hard-frost median dates are May 5 and October 1; a hard frost (28 °F) can damage plant tissue that survives a light frost (32 °F), so it represents a greater threat.

Using the cautious dates—May 26 for planting and September 13 for harvest—helps keep the risk of frost to the lowest level recorded for this station.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 26" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 13" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Upham, NDNumbered nearest stations: 1 — Bottineau, ND — 19 mi; 2 — Willow City, ND — 20 mi; 3 — Towner, ND — 23 mi; 4 — Minot (Airport), ND — 35 mi; 5 — Rugby, ND — 38 mi.ND25 mi · 40 km1. Bottineau, ND — 19 mi12. Willow City, ND — 20 mi23. Towner, ND — 23 mi34. Minot (Airport), ND — 35 mi45. Rugby, ND — 38 mi5
  1. Bottineau, ND 19 mi (31 km)
  2. Willow City, ND 20 mi (32 km)
  3. Towner, ND 23 mi (37 km)
  4. Minot (Airport), ND 35 mi (57 km)
  5. Rugby, ND 38 mi (61 km)

Sources

* Hardiness zone 3b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.6147, -100.7264.