Moisture Update - August 19, 2024

Maps 1-4: In the 12-days since the last report, rainfall has been extremely variable.  Across each of the four regions, some areas received over 20 mm of rainfall, with upwards of 30 mm seen across many parts of the North West Region (Map 1). In contrast, relatively large areas in each of the four regions remained dry, with under 5 mm reported at several locations. The driest areas include the central-western portions of the Peace Region, large parts of the North East Region, as well as the shared border areas between the Central and Southern Regions. Following a relatively wet May (Map 2), many of these lands have been dry since June (Map 3), with the drying trend intensifying in July (Map 4).  

Over the last few weeks, there is an increasing number of reports of highly variable crop conditions across short distances, that appear to be primarily related to seeding date and highly localized moisture conditions that existed in the face of the July heat, which came at a critical time during crop development. For some areas, success, or lack thereof, was related to a few storms that either supplied just enough moisture at the right time, or simply rolled across the sky off in the distance.

Looking out over the next 10-days, temperatures are expected to cool across most areas, along with the promise of some moderate rainfall accumulations, particularly for those parts of the province lying north of the TransCanada Highway. However, this remains to be seen. At the very least, it’s better than a forecast predicting persistently dry and warm weather in the upper 20s or low 30s. 

Maps 5-8: Over the past 30-days, most of the North West and much of the Peace Region, have received at least near-normal moisture for this time of year (Map 5). This is significant, as the wet season tends to persist well into August in these areas, and dry conditions are beginning to ease, at least temporarily. Across the North East, Central, and Southern Regions, roughly 50 percent of the lands have received near-normal precipitation, albeit on the drier end of the normal scale, with relatively large areas in the normal category receiving only 70 to 90 percent of the 1991-2020 historical average rainfall for this time frame (Map 6). In contrast, large parts of each of these three regions are still lingering in the dry spell that started in June. Lands around Lloydminster, Red Deer, Medicine Hat, and a few other widely scattered areas, are still in the low category, which is estimated to occur on average once every 6 to 12 years.

Looking back over the past 90-days (Map 7), even the rains across the North West and parts of the Peace Regions were still not sufficient to bring longer term moisture trends to near-normal. It is worth noting that the central Peace Region has received the most moisture this season, and crops are doing very well here.

Looking back over the past 365 days (Map 8), in aggregate most of the Southern Region, the eastern portions of the Special Areas, and the eastern portions of the Peace Region, have been trending to near-normal with respect to longer term precipitation patterns. In contrast, across much the Central, North West, North East, and the western-half of the Peace Region, deep deficits exist as a result of the drought of 2023, and the dry winter that followed, along with the long, dry stretches of weather seen this season. These areas will need good moisture this fall that help build depleted soil moisture reserves and, of course, healthy snow packs, to encourage spring runoff and fill surface water supplies for next year. 

As fall approaches, significant moisture is needed across many areas of the province. This will help perennial crops, soil moisture reserves, native vegetation, and the landscape as a whole begin the recovery after several years without significantly long wet spells or successive wet years.  

As a special attachment to this report there is a series of maps, showing yearly precipitation accumulations relative to normal, from 1901 to 2023.  Please note, that station density was quite low during the first half of the 20th century, and these early maps are not necessarily directly comparable to the maps we are able to produce today.  

During the 1901-1940 period, widespread drought was very persistent, arguably in many years worse than what we have experienced in the last two decades. During the 1940s, we transitioned into a 50-year wet period, that lasted from the 1950s through to the late 1990s. Since the 2000s, there has been a relative balance between wet and dry years, punctuated by some serious drought years. The last provincewide wet year occurred in 2016.  

Since about 2021, most of the province has now seen nearly four years without significantly above normal annual precipitation accumulations. This takes a toll on all surface water supplies and perhaps even ground water. The meteorological record teaches us that this could change abruptly and we could hit a wet spell anytime. Hopefully this occurs soon as we are long overdue one. The meteorological record also strongly enforces the notion that the weather of last week, last month, or last year, is not a good predictor of the weather next week, next month, or next year. As always, it’s wise to prepare for the worst and hope for the best.

For more maps describing our current and past weather back as far as 1901, please visit the Map Library on the Alberta Climate Information Service.