Plan by the numbers, not the guesswork
A century of daily temperatures from the U of I campus weather station, turned into growing degree days, frost odds and year-over-year comparisons for Palouse crops.
- 1Pick a crop (or a custom base / cap temperature)
- 2Choose a planting date and watch the GDD curve
- 3Check frost odds and the season leaderboard before you commit
Tip: hover or tap the GDD and frost charts (or any calendar day) for details, and click a leaderboard row to load that year into the planner and calendar.
Growing degree day planner
Cumulative GDD from the planting date, vs the median year of the 1991–2020 normals, with crop growth-stage markers.
GDD base 32°F, cap 86°F
GDD accumulates from this day forward.
Frost & freeze risk
Spring curve: share of years whose last freeze is still to come on or after each date. Fall curve: share of years whose first freeze has already happened by each date.
The ◇ markers are NOAA's official 1991–2020 freeze dates (from NCEI normals methods: gap-filling plus their own probability fit). They sit a few weeks from the station curve — even for 1991–2020 — because that is a different, shorter period than the full record and the sources use different methods; use the period toggle above to compare like with like.
Temperature anomaly calendar
Each day’s mean temperature ((max+min)/2) for the selected year, minus the 1991–2020 normal for that calendar day.
Hatched cells mark days with no observation; plain empty cells are days not yet reported. Hover or tap a day for its temperatures.
Season leaderboard
Warmest and coldest seasons on record. Click a row to load that year into the GDD planner and the anomaly calendar.
Data & sources
- Daily temperatures. Daily max/min air temperature, MOSCOW U OF I, ID
(GHCN USC00106152 / COOP 106152), 1893–2026, from the
NOAA Regional Climate Centers, ACIS StnData web service
(retrieved 2026-09-13). Per the NOAA disclaimer, near-real-time data are preliminary — 2026 values may change.
- Normal band. 1991–2020 mean per calendar day, computed from the ACIS record (same window as NOAA’s 1991–2020 U.S. Climate Normals). Calendar anomalies subtract a 7-day-centred (wrap-around) smoothed version of this normal. The normal curve and 10–90 % band are the median and percentiles of per-year cumulative GDD from the same planting date, at the chosen base/cap, over 1991–2020. Daily GDD follows the NDAWN method: raise each day's tmax and tmin to the base if below it, cap both at the upper limit (86 °F for all presets except canola, which has no cap), then take the mean and subtract the base; the stored normals use the default 86 °F cap.
- Freeze odds. Computed from the full ACIS record (1893–2026): last spring freeze = last day with tmin ≤ threshold in Jan 1–Jun 30; first fall freeze = first such day in Jul 1–Dec 31. A year only counts with ≥ 20 tmin observations in that half-year (133 spring- and 131 fall-eligible years). The ◇ markers are NOAA NCEI’s official 1991–2020 freeze dates (probability of first/last freeze) from NCEI Climate Normals. The ◇ dates are 1991–2020-only and use NCEI's methods (gap-filling from neighbouring stations, their own probability fit), so they sit weeks from the full-record curve — recomputed for 1991–2020 alone, the station's own median last spring freeze (≤ 28 °F) shifts from ≈ Apr 27 (full record) to ≈ May 4, and the first fall freeze from ≈ Oct 12 to ≈ Sep 28. Use the period toggle on the frost chart to compare like with like.
- Anomalies. Each calendar day’s mean ((max+min)/2) minus the smoothed 1991–2020 normal for that calendar day. A day is treated as missing when its max or min is missing.
- Leaderboards. A year is left out of a ranking when its window for the metric has more than 5 days with a missing max or min, so data gaps cannot fake an extreme rank. Winters run Nov 1 of the previous year through Mar 31.
- Crop stages. Base temperatures: wheat 32 °F; dry peas 40 °F; lentils 34 °F; canola 41 °F; sweet corn 50 °F (86 °F cap); potatoes 45 °F; canola has no upper cap — as reviewed in “Base and upper temperature thresholds … FAO56rev” (ScienceDirect, 2025). Wheat stages per the NDAWN wheat table (tillers begin 538, flag leaf visible 1,181, heading begins 1,567, flowering begins 1,739, kernel watery ripe 1,825 °F GDD since planting); canola stage thresholds are the start of each stage's GDD range from the NDAWN canola table. The UDel weekly crop update is the source of the base-50 GDD idea for corn. Sweet corn silking ≈ 1,075 and harvest ≈ 1,425 GDD (base 50) are not published figures — approximate planning values. Likewise, dry pea, lentil, and potato stages (all marked ≈ in the table) are not published figures — approximate planning values calibrated to the 1991–2020 median GDD so the stages land on typical Palouse dates: peas flower mid/late June and mature late July–early August; lentils flower in June and mature late July–early August; potatoes initiate tubers mid/late June and mature in September.
All figures on this page derive from the station record unless labelled otherwise. The app makes no network requests; data are embedded at build time.