Ag Weather Forum

As another week has gone by and crops continue to develop and mature across the Canadian Prairies, we will take a look at the potential or risk of a significant cold weather outbreak occurring during the first 10 days to two weeks of September.

Crop development remains behind normal in some locations. I again believe that the canola crop is most at risk if a serious freeze occurs during early September.

The short-range forecast for the Prairies calls for below-normal temperatures during the next few days gradually giving way to somewhat higher readings during the weekend and early next week. These is no significant risk of a freeze during this period, although I cannot rule out some lows reaching the upper 30s Fahrenheit.

Showers or rain will occur this coming Sunday into Monday, especially northern and eastern areas. This added moisture works to limit the potential for lower temperatures occurring at night. The cool weather during the next few days is more for the daytime highs rather than the lows at nights. This does slow crop maturity in the region, but it should not harm the crop.

The six-to-10-day outlook for the region which covers the period Sept. 3-7 features a setup that would support below-normal temperatures for eastern Canada while the west looks to be warmer. The included graphic shows the mean map at upper levels of the atmosphere for this five-day period. The first aspect of this map that I would like to point out is the above-normal heights aloft northwest of Hudson Bay and the corresponding below-normal heights southeast of Hudson Bay. This represents a weak high-latitude blocking pattern. The weak ridge northwest of Hudson Bay serves to force the trough that would normally be in that area well to the south. This is the type of pattern that frequently leads to cold weather in southern Canada during winter. The flow around the eastern trough shows the direction of movement of any cold weather coming south. This suggest that any cool to cold weather will be directed towards the Ontario area. This means the highest risk for colder weather would be in that area, rather than the Canadian Prairies to the west during this time frame. The second aspect of this map is the relatively strong late-season upper level ridge over the U.S. Rockies. The west-to-east flow north of this ridge and the above-normal heights over southwest Canada suggests a generally warmer-than-normal temperature pattern for this area. The bottom line during this period is that the chance for a significant freeze occurring in the Canadian Prairies is on the low side during the first week of the month.

The longer-range chart, covering the 11-to-15-day period or Sunday-through-Thursday of the following week, shows the high latitude ridge weakening and shifting west towards Siberia. If real this would allow the east Canada trough to lift northward and it would lead to a more west-to-east flow across southern Canada.

This would suggest that the chances for a significant freeze during the second week of September may also be on the lower side as well. The longer-range charts also show a weakening of the western U.S. ridge. This, by itself, does not affect the weather in the Canadian Prairies much at all -- except that it removes a system that could block any colder weather from moving south over Western Canada during that time frame. However, without the high latitude blocking system in northwest Canada, this is of less importance during this time period.

The outlook for the first 10 days to two weeks of September points to somewhat less risk of a hard freeze occurring in the Canadian Prairies. This does not mean frost is not possible since the normal lows will continue to fall during this time. It just means that damaging cold weather is less likely. The high latitude ridge will need to be watched. If it continues longer than is currently indicated, or is located a little west of where it is forecasted to be, it could be a more important factor in the longer-range freeze potential for the area.

Joel Burgio can be reached at joel.burgio@dtn.com

(ES)

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