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Freezing Date Probabilities | |
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| | Estimating probable freezing dates | Freezing dates for Alberta locations1
This factsheet provides information for estimating probable freezing dates for 114 locations in Alberta. Average dates of frost occurrence have often been used for this purpose. However, averages have limited value because they denote the 50 per cent risk level or the probable occurrence of untimely frost in, for example, five out of ten years. This may well be too much risk for economic viability in the long run.
On the other hand, trying to avoid all frost damage by sticking to a limited number of hardy, short-season crops may not be profitable either. The indirect costs of lost opportunities could be very high. For planning purposes, it may be better to use an intermediate risk level, such as 25 per cent, where the advantages of growing a particular crop outweigh the risks of occasional frost damage.
Estimating Probable Freezing Dates
To estimate probable freezing dates:
| 1. | Determine the average dates (50 per cent risk level) for the last spring frost and the first fall frost for a selected location from the table on the next page.
Freezing dates are based on a recorded minimum air temperature of 0°C or less in standard instrument shelters which are about 150 cm above the ground. Temperatures in a crop are typically lower than the standard values. However grain crops generally freeze at several degrees below 0°C. Thus a standard reading of 0°C is a suitable indicator of damaging frost. Actual damage depends on the temperature, crop type and crop condition. |
| 2. | Next, use the appropriate curve, either Spring or Fall, on the figure to estimate the freezing date adjustment factor for the desired risk level.
The Spring curve indicates the probability of the last spring frost occurring after a certain date. The Fall curve indicates the probability of the first fall frost occurring before a certain date. The two curves are derived from long-term minimum temperature records at stations representing the major agricultural regions in Alberta. Estimates from the curves are generally accurate within one or two days for the 15 per cent to 85 per cent probability range. |
| 3. | Add the freezing date adjustment factor to the average date for the probable frost date at that risk level. |
Example: Estimate spring and fall freezing dates at Vermilion for the 25 per cent risk level
The weather station closest to Vermilion is located at the Vermilion Airport. From the table on the following page, the average date for the last spring frost at the Vermilion Airport is May 25. Using the Spring curve on the figure and the 25 per cent risk level, the adjustment factor is +9 days. Nine days after May 25 is June 3. Similarly, the average date for the first fall frost at the Vermilion Airport is September 9, and the freezing date adjustment factor from the Fall curve is -9 days. Nine days before September 9 is August 31.
Curves for estimating freezing date adjustment factors
Freezing Dates for Alberta Locations1
| Station location | Average date of
last spring frost | Average date of
first fall frost |
| Acme CDA Exp. Farm | May 29 | Sep. 11 |
| Aden | May 12 | Sep. 27 |
| Alliance | May 22 | Sep. 13 |
| Altawan | May 28 | Sep. 9 |
| Andrew | May 22 | Sep. 17 |
| Athabasca 2 | May 23 | Sep. 12 |
| Beaverlodge CDA | May 25 | Sep. 8 |
| Bow Island Rivers Dev. | May 16 | Sep. 20 |
| Breton | May 24 | Sep. 29 |
| Brightview | May 19 | Sep. 14 |
| Brooks AHRC | May 21 | Sep. 14 |
| Brownfield | June 1 | Sep. 2 |
| Caldwell | June 1 | Sep. 11 |
| Calgary International Airport | May 22 | Sep. 16 |
| Calmar | May 22 | Sep. 15 |
| Campsie | June 5 | Aug. 25 |
| Camrose | May 15 | Sep. 17 |
| Cardston | May 25 | Sep. 15 |
| Carway | June 12 | Sep. 5 |
| Claresholm Waterworks | May 27 | Sep. 9 |
| Cold Lake Airport | May 22 | Sep. 13 |
| Coronation Airport | May 20 | Sep. 14 |
| Cowley | June 7 | Sep. 3 |
| Craigmyle | May 29 | Sep. 8 |
| Crossfield | June 2 | Sep. 2 |
| Dakota West | May 31 | Aug. 30 |
| Drumheller City | May 19 | Sep. 17 |
| Duchess | May 8 | Sep. 18 |
| Eckville South | June 1 | Sep. 6 |
| Edmonton International Airport | May 24 | Sep. 10 |
| Edmonton/Namao Airport | May 12 | Sep. 21 |
| Edmonton/Stony Plain | May 10 | Sep. 21 |
| Edson Airport | June 13 | Aug. 29 |
| Elk Point | June 1 | Sep. 1 |
| Ellerslie | May 25 | Sep. 11 |
| Empress | May 19 | Sep. 15 |
| Fabyan | May 25 | Sep. 7 |
| Fairview | May 16 | Sep. 17 |
| Falher | May 24 | Sep. 11 |
| Foremost | May 15 | Sep. 22 |
| Forestburg Plant Site | May 9 | Sep. 25 |
| Fort Chipewyan Airport | June 4 | Sep. 2 |
| Fort Macleod | May 19 | Sep. 18 |
| Fort McMurray Airport | June 2 | Sep. 4 |
| Fort Saskatchewan | May 16 | Sep. 14 |
| Fort Vermilion CDA | May 25 | Sep. 4 |
| Gleichen | May 21 | Sep. 14 |
| Glenevis | May 26 | Sep. 14 |
| Grande Prairie Airport | May 17 | Sep. 14 |
| Gwynne | June 4 | Sep. 8 |
| Hanna | May 10 | Sep. 18 |
| Herronton East | May 19 | Sep. 14 |
| High Level Airport | June 2 | Aug. 29 |
| High Prairie | May 30 | Sep. 6 |
| High River | June 10 | Aug. 30 |
| Hinton | June 9 | Aug. 25 |
| Horseshoe Lake | May 13 | Sep. 14 |
| Hughenden | May 25 | Sep. 3 |
| Kinsella Ranch | May 18 | Sep. 13 |
| Kitscoty | May 18 | Sep. 19 |
| Lac La Biche (automatic) | May 25 | Sep. 11 |
| Lacombe CDA | May 28 | Sep. 8 |
| Lethbridge Airport | May 16 | Sep. 19 |
| Madden | May 26 | Sep. 17 |
| Manyberries CDA | May 16 | Sep. 16 |
| Marwayne | June 6 | Aug. 29 |
| Medicine Hat Airport | May 15 | Sep. 23 |
| Milk River | May 17 | Sep. 21 |
| Millarville | June 28 | Aug. 20 |
| Newbrook | June 14 | Aug. 22 |
| Olds | May 23 | Sep. 13 |
| Oliver Tree Nursery | May 23 | Sep. 13 |
| Oyen Cappon | May 16 | Sep. 20 |
| Paradise Valley | May 25 | Sep. 9 |
| Peace River Airport | May 25 | Sep. 4 |
| Pincher Creek | May 29 | Sep. 11 |
| Pine Lake | June 9 | Aug. 28 |
| Pollockville | May 24 | Sep. 5 |
| Prairie Creek Ranger Station | July 9 | July 28 |
| Queenstown | May 19 | Sep. 22 |
| Rainier | May 24 | Sep. 15 |
| Ranfurly | May 24 | Sep. 5 |
| Raymond | May 17 | Sep. 14 |
| Red Deer Airport | May 25 | Sep. 10 |
| Rimbey | May 25 | Sep. 13 |
| Rocky Mountain House | May 18 | Sep. 12 |
| Scotfield | June 1 | Aug. 31 |
| Sedalia East | May 21 | Sep. 18 |
| Sedgewick | May 27 | Aug. 30 |
| Sibbald | May 28 | Sep. 7 |
| Sion | May 23 | Sep. 12 |
| St. Lina | June 5 | Aug. 24 |
| Stettler | May 16 | Sep. 14 |
| Strathmore East | May 22 | Sep. 11 |
| Suffield Airport | May 17 | Sep. 19 |
| Sundre Ranger Station | June 18 | Aug. 26 |
| Taber | May 14 | Sep. 22 |
| Three Hills | June 3 | Aug. 23 |
| Tofield North | May 24 | Sep. 14 |
| Trochu Equity | May 22 | Sep. 14 |
| Tulliby Lake | May 24 | Sep. 5 |
| Turner Valley | June 4 | Sep. 3 |
| Vauxhall CDA | May 24 | Sep. 13 |
| Vegreville CDA | June 5 | Aug. 29 |
| Vermilion Airport | May 25 | Sep. 9 |
| Viking | May 18 | Sep. 13 |
| Vulcan | May 19 | Sep. 19 |
| Wainwright Heath | May 22 | Sep. 2 |
| Warwick | June 5 | Aug. 27 |
| Wastina Hemaruka | June 7 | Sep. 6 |
| Watino | May 16 | Sep. 18 |
| Wetaskiwin | May 17 | Sep. 13 |
| Whitecourt Airport | May 24 | Sep. 4 |
| Winfield | June 1 | Sept. 1 |
1Stations used in this table have data for 13 or more years during the period from 1961 to 1990.
Data analysis by the Conservation and Development Branch of Alberta Agriculture, Food and Rural Development; climate data obtained from Environment Canada.
Source: Agdex 075-2. Revised January 1998. |
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For more information about the content of this document, contact Ralph Wright.
This document is maintained by Jennifer Rutter.
This information published to the web on January 1, 1998.
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