Last Modified 16/5/26 18:27 PM
Canterbury Regional Outlook
| Saturday | Risk of Rain (%) | Likely amount (mm) | Winds | | Sunday | Risk of Rain (%) | Likely amount (mm) | Winds |
| Morning | 10% | | Light NE | Morning | 10% | | Light NE |
| Afternoon | 10% | | Moderate NE | Afternoon | 10% | | Moderate NE |
| Evening | 10% | | Light winds | Evening | 10% | | Light winds |
| Night | 10% | | Calm | Night | 10% | | Calm |
| Max | Min | | | Max | Min | |
| Fine | 11 | 0 | | Fine | 12 | 2 | |
Tomorrow morning begins cool with ground frost likely across inland areas including the Selwyn foothills, the mid-plains, Ashburton, and coastal South Canterbury. The Mackenzie Basin has a hard frost with temperatures falling to minus 1°C. Skies are mainly clear as the day begins. Through the afternoon a fresh northeasterly develops, reaching 15 to 20 km/h across the plains and penetrating to the foothills. Temperatures reach 10 to 13°C on the plains. Conditions remain fine.
Tomorrow night winds ease across the region. Cloud increases from the coast overnight. Frost returns to sheltered inland areas, with another hard frost in the Mackenzie Basin.
Monday is similar in character, with light morning winds becoming northeasterly through the afternoon to around 15 km/h. Ground frost again in the morning at Rangiora, Darfield, Ashburton, and Timaru. High temperatures reach 10 to 13°C. Cloud is more persistent, particularly along the Kaikōura Coast and around Timaru. Monday night remains cool with light winds. Ground frost again at Darfield and Rangiora, hard frost in the Mackenzie Basin and Culverden valley.
| Day | Airflow | High °C | Frost | Watch |
| | | | | |
| Sunday | Light NE, → NE evening, fine | 10–13 | Hard (Twizel / Mackenzie Basin) | — |
| Monday | Light NE, → SE evening, fine | 9–13 | Hard (Twizel / Mackenzie Basin) | — |
| Tuesday | Light NE, → NNE evening, fine | 9–13 | Hard (Culverden, Twizel / Mackenzie Basin) | — |
| Wednesday | Light NW, → NNW evening, fine | 11–16 | Hard (Culverden) | — |
| Thursday | Moderate NE, → S evening, showers evening | 14–19 | Ground inland | — |
| Friday | Light NE, → NNE evening, showers | 8–12 | Ground inland | — |
| Next Saturday–Next Monday | Light NE, → NNE evening, fine | 8–15 | Ground inland | Snow Arthur's Pass |
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 |
| Darfield | 19 mm expected, likely 9–32 mm | +0 mm surplus in driest scenario — borderline |
| Methven | 19 mm expected, likely 8–35 mm | +0 mm surplus in driest scenario — borderline |
| Rangiora | 17 mm expected, likely 7–29 mm | -2 mm in driest scenario — deficit risk |
| Ashburton | 17 mm expected, likely 8–35 mm | -1 mm in driest scenario — deficit risk |
| Hinds | 17 mm expected, likely 8–35 mm | -1 mm in driest scenario — deficit risk |
| Culverden | 16 mm expected, likely 6–31 mm | -2 mm in driest scenario — deficit risk |
| Temuka | 15 mm expected, likely 10–33 mm | +1 mm surplus in driest scenario — borderline |
Water balance: ■ comfortable ■ moderate ■ thin ■ deficit risk
Next Tuesday sees light variable winds and grey low cloud across much of the region. Hard frost in the Mackenzie Basin and Culverden valley in the morning. Temperatures reach 9 to 13°C. Akaroa experiences a light northwesterly through the afternoon.
Tuesday night stays cool with frost possible across sheltered inland areas.
Next Wednesday brings a change in character. A light nor'wester develops, reaching around 20 to 25 km/h on the inner plains at Darfield, Lincoln, and Ashburton through the afternoon, while the coast sees a light northeasterly sea breeze. High cloud dominates, allowing good sun beneath. Temperatures reach 14 to 16°C inland, remaining cooler on the coast around 11 to 13°C.
Next Thursday sees a fresh northeasterly developing ahead of an approaching front, reaching 25 to 28 km/h across the plains with gusts to around 50 km/h at the coast. A southerly change moves through during the evening, arriving at coastal South Canterbury around 4pm and pushing north to Rangiora, Darfield, and Lincoln by late evening. A few millimetres of rain accompany the change. Lewis Pass experiences strong gusts to 80 km/h but no snow.
Next Friday remains unsettled with persistent grey cloud and a few spots of rain, mainly in the morning. Light easterly winds. Temperatures reach only 8 to 12°C. Ground frost at Darfield in the morning.
Confidence decreases from next Saturday — the following is indicative only. Next Saturday and Sunday see a return to light northeasterly conditions with grey low cloud. Ground frost overnight inland. A westerly change may move through late Sunday with possible snow above 900m on Arthur's Pass and Lindis Pass. Current risk indicators for hill-level snow next weekend or in the days after are rising, currently at 20-25% risk. Worth keeping an eye on.
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Water Balance
| Evapotranspiration ET₀ (mm/day) | | | | | | | | | |
| Location | Sat 16 May | Sun 17 May | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Mean |
| Culverden | 0.86 | 0.98 | 0.85 | 0.92 | 1.20 | 1.03 | 0.30 | 0.68 | 0.98 | 0.96 | 0.88 |
| Rangiora | 0.97 | 1.11 | 1.05 | 0.73 | 0.98 | 1.80 | 0.45 | 0.84 | 0.71 | 1.17 | 0.98 |
| Darfield | 0.98 | 1.05 | 0.90 | 0.75 | 1.62 | 1.34 | 0.44 | 0.78 | 0.84 | 0.80 | 0.95 |
| Ashburton | 0.97 | 1.06 | 0.89 | 0.64 | 1.25 | 1.31 | 0.45 | 1.00 | 0.89 | 0.92 | 0.94 |
| Methven | 0.89 | 0.99 | 0.95 | 0.88 | 1.06 | 0.69 | 0.37 | 1.00 | 0.94 | 0.62 | 0.84 |
| Hinds | 0.98 | 1.07 | 0.88 | 0.56 | 0.98 | 1.51 | 0.54 | 1.02 | 0.82 | 0.82 | 0.92 |
| Temuka | 0.99 | 0.93 | 0.76 | 0.55 | 0.76 | 0.97 | 0.41 | 0.83 | 0.61 | 0.85 | 0.77 |
| | | | | | | | | | | | |
| Rainfall (mm) | | | | | | | | | | | |
| Location | Sat 16 May | Sun 17 May | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Total |
| Culverden | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 15.0 | 0.0 | 0.0 | 0.6 | 15.6 |
| Rangiora | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 3.0 | 0.0 | 0.0 | 0.0 | 3.0 |
| Darfield | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.2 | 2.5 | 0.0 | 0.0 | 0.0 | 2.7 |
| Ashburton | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.6 | 0.0 | 0.0 | 0.0 | 0.6 |
| Methven | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 3.0 | 0.0 | 0.0 | 0.6 | 3.6 |
| Hinds | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.6 | 0.6 |
| Temuka | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.2 | 0.0 | 0.0 | 1.2 | 2.4 |
| | | | | | | | | | | | |
| Cumulative Water Balance (mm) | | | | | | | | | | |
| Location | Sat 16 May | Sun 17 May | Mon 18 May | Tue 19 May | Wed 20 May | Thu 21 May | Fri 22 May | Sat 23 May | Sun 24 May | Mon 25 May | Final |
| Culverden | -0.9 | -1.8 | -2.7 | -3.6 | -4.8 | -5.8 | +8.9 | +8.2 | +7.2 | +6.8 | +6.8 |
| Rangiora | -1.0 | -2.1 | -3.1 | -3.9 | -4.8 | -6.6 | -4.1 | -4.9 | -5.6 | -6.8 | -6.8 |
| Darfield | -1.0 | -2.0 | -2.9 | -3.7 | -5.3 | -6.4 | -4.4 | -5.2 | -6.0 | -6.8 | -6.8 |
| Ashburton | -1.0 | -2.0 | -2.9 | -3.6 | -4.8 | -6.1 | -6.0 | -7.0 | -7.9 | -8.8 | -8.8 |
| Methven | -0.9 | -1.9 | -2.8 | -3.7 | -4.8 | -5.5 | -2.8 | -3.8 | -4.8 | -4.8 | -4.8 |
| Hinds | -1.0 | -2.0 | -2.9 | -3.5 | -4.5 | -6.0 | -6.5 | -7.5 | -8.4 | -8.6 | -8.6 |
| Temuka | -1.0 | -1.9 | -2.7 | -3.2 | -4.0 | -5.0 | -4.2 | -5.0 | -5.6 | -5.3 | -5.3 |
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