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Farm Tools
Agricultural decision support from live weather data
Spray Conditions
Delta-T: 0.5°CActive rain (0.4 mm/hr) — do not spray
Inversion likely — calm winds after sunset with low Delta-T
Traditional (Boom/Rig) ✗ Avoid
Active rain — do not spray · Too cold — reduced efficacy · Too humid — absorption risk · Low Delta-T — inversion conditions · Temperature inversion likely
Drone ✗ Avoid
Active rain — do not spray · Too cold — reduced efficacy · Too humid — absorption risk · Temperature inversion likely
What is Delta-T?
Delta-T is the difference between the air temperature and the wet-bulb temperature. It's the single best indicator of spray conditions because it captures both temperature and humidity in one number.
Below 2 °C — Inversion likely. Spray hangs and drifts. Do not spray.
2–8 °C — Ideal for traditional spraying.
2–10 °C — Acceptable for drone spraying.
Above 8 °C — Rapid evaporation risk.
Traditional (ground rig/boom)
Wind 3–15 km/h — Below 3 signals inversion; above 15 causes off-target drift.
Temperature 10–28 °C — Cold reduces plant uptake; heat increases evaporation.
Humidity 40–90% — Below 40% droplets evaporate before reaching the target.
Delta-T 2–8 °C — Below 2 indicates inversion; above 8 means rapid evaporation.
Drone (UAV spraying)
Wind up to 25 km/h — Closer to canopy so drift is less of a factor.
Humidity down to 35% — Shorter nozzle-to-target distance means less evaporation.
Delta-T up to 10 °C — Less droplet travel time allows wider tolerance.
Additional checks
Active rain — Rain washes off recently applied spray. Wait for rain to stop and foliage to dry.
Recent rain — Wet leaves dilute spray application and reduce effectiveness.
Inversion risk — Calm winds after sunset with low Delta-T. Spray particles suspend and drift kilometres. One of the most dangerous conditions for off-target damage.
Based on SA agricultural best practice. Always check product labels for specific requirements.
Fire Danger Index
FDI 0 — LowLow fire danger — safe for controlled burns with precautions.
McArthur Grassland FDI (Mark 5) adapted for Free State conditions. Grass curing estimated seasonally. Higher index during dry winter months.
Frost Risk Tonight
HighRisk score: 38/100
Temperature very close to freezing (2.9°C)
Light winds — limited mixing
High frost risk tonight — protect sensitive crops, consider irrigation for heat release.
Based on temperature, humidity, wind, and dew point. Most accurate from mid-afternoon onward. Frost season: April–October.
Fog Risk
Very HighRisk score: 93/100
Dew depression: 0.6°C
Type: Radiation fog
Dew point depression very small (0.6°C) — at saturation
Near saturated air (96%) — fog imminent
Light breeze — fog still possible
Peak fog season (May–Jul)
Pre-dawn — peak fog window
Dense fog expected — very poor visibility, avoid travel if possible.
Radiation fog highly likely. Dew point depression is very small (0.6°C) — expect reduced visibility. Overnight cooling underway. Burn-off expected by 09:00-10:00 SAST if fog forms.
Based on dew point depression, humidity, wind speed, time of day, and season. Radiation fog is most common in the region — forms on clear, calm nights.
Evapotranspiration (ETo)
0.4 mm/day — LowLow water demand — irrigation can wait
Maize (mid-season)
0.5 mm/day
Kc = 1.2
Wheat (mid-season)
0.5 mm/day
Kc = 1.15
Pasture
0.4 mm/day
Kc = 1.0
Crop water need ≈ ETo × crop coefficient (Kc). Values shown are mid-season peaks. Method: penman-monteith (estimated). Based on FAO-56 guidelines.
Livestock Conditions
THI 38
No heat stress — cattle are comfortable.
Normal feeding, production, and behaviour expected.
2.9°C
Effective temperature (wet coat)
High cold stress — shelter essential. Check vulnerable animals (calves, thin cattle, sick animals). Increase feed by 15–25%.
Cattle are wet from rain — cold stress threshold rises significantly
Standard water supply is sufficient.
Temperature-Humidity Index (THI) — cattle stress thresholds: 68 mild, 72 moderate, 80 severe, 90 emergency
THI based on NRC (1971) formula. Cold stress accounts for wind chill and wet coat conditions. Water demand estimates for SA cattle breeds at stated body weight. Calving season: Jul–Sep.
THI 38
No heat stress — sheep are comfortable.
Normal grazing, feed intake and behaviour expected.
2.9°C
Effective temperature (wet fleece)
High cold stress — shelter essential. Check lambs, shorn sheep, and weak animals. Use cover combs at shearing to leave more wool. Wet fleece or bare skin drastically increases heat loss.
Sheep are wet from rain — shorn sheep lose body heat rapidly
Standard water supply is sufficient.
Temperature-Humidity Index (THI) — sheep stress thresholds: 70 mild, 76 moderate, 82 severe, 87 emergency
Sheep THI thresholds adjusted for small ruminants. Cold stress uses shearing-season awareness (Apr–May, Aug–Sep) — shorn sheep lose 3× body heat. Common Eastern FS breeds: Dohne Merino, SAMM, Merino, Afrino, Dorper, Damara. Water demand for 60 kg ewe. Lambing season: Jul–Oct.
Chill Units
Very Low Season active — 202663
Chill Units (Utah)
May 1 – Aug 31
36
Days Recorded
May – Aug 2026
138
CU to Next Milestone
Low-chill peaches & nectarines
Variety Milestones
Very few chill units accumulated. Season may not have started or conditions are too warm.
Utah chill model — estimates hourly temps from daily min/max using sine interpolation. Season: May 1 – Aug 31. Weights: 2.5–9.1°C = 1 CU/hr (optimal), >16°C negates chill.
Rainfall Tracker
Well Below Oct 2025 – Mar 2026255.4
mm this season
600
mm regional average
Full season (Oct–Mar)
43%
of seasonal average
Season complete
Monthly Breakdown
Rainfall well below seasonal average — drought conditions likely. Consider irrigation planning and water conservation.
Rain season: Oct 1 – Mar 31. Regional average: 600 mm/season. Data from DailySummary rain totals.
Farm Tools provide general guidance only — not professional advice. Weather data may be delayed or inaccurate. Always apply your own judgement. Full disclaimer.