Ag Weather Forum

During the late winter and spring western Canada was dominated by a weather pattern that featured strong high latitude blocking high pressure resulting in heavy snows and very cold temperatures. This pattern broke down during May and June allowing for a late, but generally good start to the crop season. During the past 10 days to 2 weeks we have seen a return of a similar blocking pattern to what was observed earlier in the spring.

To refresh, high latitude blocking refers to an upper level high pressure system located across northern latitudes such as northern Canada that deflects the jet stream southward. The blocking high in the early spring as well as the current time is located across northwest and northern Canada and has been diverting the jet stream to far southern parts of western Canada then falling into a trough across the Midwest and Great Lakes region of the U.S. Surface high pressure across northwest Canada tends to keep a flow of cooler air moving southward across central Canada into the north-central U.S. as well as through the Canadian Prairies.

Since the mid portion of July this pattern has resulted in a downturn in temperatures for much of the Prairie crop region with the coolest readings found from Manitoba to Saskatchewan. Alberta has seen a few periods of more moderate readings during this time. Temperature departures have been generally in the 2 to 5 degree C (4-10 F) below normal category since late July for most areas.

Rainfall has been mostly near normal but with the jet stream passing mostly across the Prairies we have seen a couple of episodes of showers develop that produce a little more rain than initial forecasts would expect. The rainfall has also been variable with some areas seeing rather heavy totals while others seeing minimal amounts. This is a normal summer pattern since summer showers tend to be local and can be quite heavy versus the large scale winter rains and snows that deposit fairly even totals across a large area.

Crops continue to be a good condition from Alberta to Manitoba but the cool weather has slowed growth during the recent couple of weeks raising the threat for an early season frost to bring an unfortunate end to maturing crops. Average dates for season ending freezes across the Prairies are mostly during early September but a few of the colder locations are as early as the tail end of August.

That leaves about another month for crops to develop and mature fully and for harvest to begin before potential freeze problems can arise. Obviously the weather is the main player here and if a warmer pattern takes hold as we move through mid August and the seasons' first freezes are late we could avoid any problems.

Current weather forecasts show an easing to the chilly pattern as we move into next week and beyond with mostly seasonable temperatures expected to return. In fact a few rather warm days could arrive by later next week as the high pressure block weakens across northwest Canada. The question remains as to whether this block returns later in the month or early September and if crops can make some faster advancement when we see some warmth return.

Hopefully the milder scenario plays out allowing the currently rather good summer crops to advance to maturity before frosts and freezes take their toll.

Doug Webster can be reached at doug.webster@telventdtn.com

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