Freezing Date Probabilities

Download 241K pdf file ("075-2.pdf")PDF
     Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
 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 0C 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 0C. Thus a standard reading of 0C 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.

Curves for estimating freezing date adjustment factors

Freezing Dates for Alberta Locations1

Station locationAverage date of
last spring frost
Average date of
first fall frost
Acme CDA Exp. FarmMay 29Sep. 11
AdenMay 12Sep. 27
AllianceMay 22Sep. 13
AltawanMay 28Sep. 9
AndrewMay 22Sep. 17
Athabasca 2May 23Sep. 12
Beaverlodge CDAMay 25Sep. 8
Bow Island Rivers Dev.May 16Sep. 20
BretonMay 24Sep. 29
BrightviewMay 19Sep. 14
Brooks AHRCMay 21Sep. 14
BrownfieldJune 1Sep. 2
CaldwellJune 1Sep. 11
Calgary International Airport May 22Sep. 16
CalmarMay 22Sep. 15
CampsieJune 5Aug. 25
CamroseMay 15Sep. 17
CardstonMay 25Sep. 15
CarwayJune 12Sep. 5
Claresholm WaterworksMay 27Sep. 9
Cold Lake AirportMay 22Sep. 13
Coronation AirportMay 20Sep. 14
CowleyJune 7Sep. 3
CraigmyleMay 29Sep. 8
CrossfieldJune 2Sep. 2
Dakota WestMay 31Aug. 30
Drumheller CityMay 19Sep. 17
DuchessMay 8Sep. 18
Eckville SouthJune 1Sep. 6
Edmonton International AirportMay 24Sep. 10
Edmonton/Namao AirportMay 12Sep. 21
Edmonton/Stony PlainMay 10Sep. 21
Edson AirportJune 13Aug. 29
Elk PointJune 1Sep. 1
EllerslieMay 25Sep. 11
EmpressMay 19Sep. 15
FabyanMay 25Sep. 7
FairviewMay 16Sep. 17
FalherMay 24Sep. 11
ForemostMay 15Sep. 22
Forestburg Plant SiteMay 9Sep. 25
Fort Chipewyan AirportJune 4Sep. 2
Fort MacleodMay 19Sep. 18
Fort McMurray AirportJune 2Sep. 4
Fort SaskatchewanMay 16Sep. 14
Fort Vermilion CDAMay 25Sep. 4
GleichenMay 21Sep. 14
GlenevisMay 26Sep. 14
Grande Prairie AirportMay 17Sep. 14
GwynneJune 4Sep. 8
HannaMay 10Sep. 18
Herronton EastMay 19Sep. 14
High Level AirportJune 2Aug. 29
High PrairieMay 30Sep. 6
High RiverJune 10Aug. 30
HintonJune 9Aug. 25
Horseshoe LakeMay 13Sep. 14
HughendenMay 25Sep. 3
Kinsella RanchMay 18Sep. 13
KitscotyMay 18Sep. 19
Lac La Biche (automatic)May 25Sep. 11
Lacombe CDAMay 28Sep. 8
Lethbridge AirportMay 16Sep. 19
MaddenMay 26Sep. 17
Manyberries CDAMay 16Sep. 16
MarwayneJune 6Aug. 29
Medicine Hat AirportMay 15Sep. 23
Milk RiverMay 17Sep. 21
MillarvilleJune 28Aug. 20
NewbrookJune 14Aug. 22
OldsMay 23Sep. 13
Oliver Tree NurseryMay 23Sep. 13
Oyen CapponMay 16Sep. 20
Paradise ValleyMay 25Sep. 9
Peace River AirportMay 25Sep. 4
Pincher CreekMay 29Sep. 11
Pine LakeJune 9Aug. 28
PollockvilleMay 24Sep. 5
Prairie Creek Ranger StationJuly 9July 28
QueenstownMay 19Sep. 22
RainierMay 24Sep. 15
RanfurlyMay 24Sep. 5
RaymondMay 17Sep. 14
Red Deer AirportMay 25Sep. 10
RimbeyMay 25Sep. 13
Rocky Mountain HouseMay 18Sep. 12
ScotfieldJune 1Aug. 31
Sedalia EastMay 21Sep. 18
SedgewickMay 27Aug. 30
SibbaldMay 28Sep. 7
SionMay 23Sep. 12
St. LinaJune 5Aug. 24
Stettler May 16Sep. 14
Strathmore EastMay 22Sep. 11
Suffield AirportMay 17Sep. 19
Sundre Ranger StationJune 18Aug. 26
TaberMay 14Sep. 22
Three HillsJune 3Aug. 23
Tofield NorthMay 24Sep. 14
Trochu EquityMay 22Sep. 14
Tulliby LakeMay 24Sep. 5
Turner ValleyJune 4Sep. 3
Vauxhall CDAMay 24Sep. 13
Vegreville CDAJune 5Aug. 29
Vermilion AirportMay 25Sep. 9
VikingMay 18Sep. 13
VulcanMay 19Sep. 19
Wainwright HeathMay 22Sep. 2
WarwickJune 5Aug. 27
Wastina HemarukaJune 7Sep. 6
WatinoMay 16Sep. 18
WetaskiwinMay 17Sep. 13
Whitecourt AirportMay 24Sep. 4
WinfieldJune 1Sept. 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.
Share via
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.