Last Modified 18/5/26 18:04 PM
Canterbury Regional Outlook
| Rainfall next 3 days | | | | | | |
| Location | Tue 19 May | | | Wed 20 May | | | Thu 21 May | | |
| | Prob | Low | High | Prob | Low | High | Prob | Low | High |
| Culverden | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 2% | 0.0 | 0.0 |
| Rangiora | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 10% | 0.0 | 0.9 |
| Darfield | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 8% | 0.0 | 0.8 |
| Ashburton | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 6% | 0.0 | 0.4 |
| Methven | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 6% | 0.0 | 0.5 |
| Hinds | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 6% | 0.0 | 0.4 |
| Temuka | 0% | 0.0 | 0.0 | 0% | 0.0 | 0.0 | 16% | 0.0 | 1.8 |
Tuesday morning begins with grey skies across most of the plains, clearing slowly through the day. A light northeasterly develops during the afternoon, mainly on the coast and mid-plains but not penetrating far inland. Ground frost is likely in Culverden and coastal South Canterbury, with frost possible on the inland plains. Temperatures remain in the 9–11°C range on the plains. The Mackenzie Basin stays cold with a hard frost overnight. Tuesday night sees cloud persisting across most areas with light variable winds. Temperatures drop toward 3–5°C on the plains, with the Mackenzie Basin falling below zero again.
Wednesday dawns with ground frost across the plains and a hard frost in the Mackenzie. High cloud moves in, allowing sun to filter through while giving the sky a white, wispy appearance. Winds remain light through the morning. A light nor'wester develops through the afternoon at Darfield and Lincoln, freshening to moderate strength with gusts to 45 km/h on the mid-plains. The Mackenzie Basin remains cold and grey with low cloud. Wednesday night sees the nor'wester build at Akaroa, with sharp gusts to 67 km/h overnight. Elsewhere winds remain light to moderate from the northwest.
| Day | Airflow | High °C | Frost | Watch |
| Tuesday | Light NE, → WNW evening, fine | 9–12 | Hard (Twizel / Mackenzie Basin) | — |
| Wednesday | Moderate NW, fine | 10–16 | Hard (Twizel / Mackenzie Basin) | — |
| Thursday | Moderate NW, → W evening, fine | 16–20 | — | — |
| Friday | Light NW, → WNW evening, fine | 13–17 | Ground inland | — |
| Saturday | Light NE, → SE evening, showers evening | 10–14 | Ground inland | — |
| Sunday | Light NE, → NE evening, patchy drizzle | 10–12 | — | — |
| Next Monday–Next Wednesday | Moderate NW, → NW evening, fine | 11–18 | Ground inland | — |
10-Day Rainfall & Water Balance
Ensemble median rainfall with likely range (middle 50% of outcomes). Water balance = rainfall minus ET₀.
| Station | 10-Day Rainfall | Water Balance |
| Culverden | 8 mm expected, likely 3–13 mm | -7 mm in driest scenario — deficit risk |
| Darfield | 6 mm expected, likely 3–10 mm | -7 mm in driest scenario — deficit risk |
| Temuka | 6 mm expected, likely 4–9 mm | -4 mm in driest scenario — deficit risk |
| Rangiora | 5 mm expected, likely 3–10 mm | -7 mm in driest scenario — deficit risk |
| Ashburton | 4 mm expected, likely 3–9 mm | -7 mm in driest scenario — deficit risk |
| Methven | 4 mm expected, likely 2–9 mm | -6 mm in driest scenario — deficit risk |
| Hinds | 4 mm expected, likely 3–9 mm | -7 mm in driest scenario — deficit risk |
Water balance: ■ comfortable ■ moderate ■ thin ■ deficit risk
Thursday is a warmer day with temperatures reaching the high teens to around 20°C across the plains. A fresh nor'wester develops through the morning, strongest along the foothills with gusts to 45 km/h at Darfield. A dry sou'west change moves through during the late afternoon and evening — arriving at Timaru around 4pm with gusty southerlies to 59 km/h, then pushing north to Christchurch and the inland plains by 8pm. No rain accompanies the change. Winds ease overnight behind the front.
Friday sees light westerly winds across the region following the overnight change. Variable cloud with sunny periods. Temperatures reach the mid-teens. A fresh southerly persists along the South Canterbury coast with gusts to 39 km/h at Timaru. Ground frost possible in the Mackenzie overnight.
Saturday turns grey and gloomy with low cloud spreading across the region. Rain develops during the evening, mainly 1–3 mm across the plains. A fresh northeasterly sea breeze develops during the afternoon, reaching fully inland with gusts to around 40 km/h.
Sunday remains grey with a fresh northeasterly established across the plains, gusting to 48 km/h on the coast and 42 km/h at Lincoln. Light patchy drizzle possible. Temperatures in the 10–12°C range.
Next Monday brings a return to nor'west conditions with a moderate to fresh nor'wester developing across the plains, strongest at Darfield with gusts to 67 km/h. Temperatures rise to the mid to high teens. Ground frost inland overnight. Next Tuesday sees light to moderate nor'west winds persisting with mostly fine weather. A cold easterly develops on the coast with gusts to 49 km/h at Christchurch. Ground frost widespread inland overnight. Next Wednesday shows continued unsettled conditions with moderate southwest winds and patchy light rain. Sharp gusts to 66 km/h possible at Akaroa and 60 km/h in the Culverden valley.
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Water Balance
| Evapotranspiration ET₀ (mm/day) | |
| Location | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Tue 26 May | Wed 27 May | Mean |
| Culverden | 0.93 | 0.93 | 1.22 | 1.20 | 0.94 | 0.35 | 0.48 | 1.03 | 0.92 | 1.18 | 0.92 |
| Rangiora | 1.10 | 0.83 | 0.99 | 1.57 | 0.91 | 0.59 | 0.52 | 0.87 | 1.06 | 1.00 | 0.94 |
| Darfield | 0.99 | 0.80 | 1.53 | 1.70 | 0.88 | 0.51 | 0.55 | 1.56 | 0.95 | 1.11 | 1.06 |
| Ashburton | 0.95 | 0.74 | 1.23 | 1.69 | 0.97 | 0.67 | 0.58 | 1.64 | 1.00 | 1.08 | 1.06 |
| Methven | 0.96 | 0.88 | 1.12 | 0.99 | 0.95 | 0.59 | 0.66 | 0.71 | 0.93 | 0.86 | 0.86 |
| Hinds | 0.93 | 0.67 | 0.99 | 2.04 | 0.99 | 0.75 | 0.60 | 1.51 | 1.04 | 1.15 | 1.07 |
| Temuka | 0.70 | 0.76 | 0.83 | 1.17 | 0.84 | 0.84 | 0.67 | 0.90 | 1.19 | 1.19 | 0.91 |
| | | | | | | | | | | |
| Rainfall (mm) | |
| Location | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Tue 26 May | Wed 27 May | Total |
| Culverden | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.5 | 1.3 | 0.0 | 0.0 | 0.6 | 2.4 |
| Rangiora | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 2.0 | 0.0 | 0.0 | 0.6 | 3.6 |
| Darfield | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 0.2 | 0.0 | 0.0 | 0.0 | 1.2 |
| Ashburton | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 0.2 | 0.0 | 0.0 | 0.0 | 1.2 |
| Methven | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 2.8 | 1.1 | 0.0 | 0.0 | 0.6 | 4.5 |
| Hinds | 0.0 | 0.0 | 0.0 | 0.0 | 0.3 | 1.0 | 1.4 | 0.0 | 0.0 | 0.0 | 2.7 |
| Temuka | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.0 | 3.8 | 0.0 | 0.0 | 0.6 | 5.4 |
| | | | | | | | | | | |
| Cumulative Water Balance (mm) | |
| Location | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Tue 26 May | Wed 27 May | Final |
| Culverden | -0.9 | -1.9 | -3.1 | -4.3 | -5.2 | -5.1 | -4.2 | -5.3 | -6.2 | -6.8 | -6.8 |
| Rangiora | -1.1 | -1.9 | -2.9 | -4.5 | -5.4 | -5.0 | -3.5 | -4.4 | -5.4 | -5.8 | -5.8 |
| Darfield | -1.0 | -1.8 | -3.3 | -5.0 | -5.9 | -5.4 | -5.8 | -7.3 | -8.3 | -9.4 | -9.4 |
| Ashburton | -0.9 | -1.7 | -2.9 | -4.6 | -5.6 | -5.2 | -5.6 | -7.3 | -8.3 | -9.3 | -9.3 |
| Methven | -1.0 | -1.8 | -3.0 | -4.0 | -4.9 | -2.7 | -2.3 | -3.0 | -3.9 | -4.2 | -4.2 |
| Hinds | -0.9 | -1.6 | -2.6 | -4.6 | -5.3 | -5.1 | -4.3 | -5.8 | -6.8 | -8.0 | -8.0 |
| Temuka | -0.7 | -1.5 | -2.3 | -3.5 | -4.3 | -4.1 | -1.0 | -1.9 | -3.1 | -3.7 | -3.7 |
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