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Apr 19

Snow packs and April forecast

Posted on Apr 19 By: Ralph Wright | Agrometerology Applications and Modelling Unit

Synopsis


Across much of the north-half of the province, spring snow melt is delayed in the wake of several recent snowfalls and unseasonably cold temperatures. During the early morning hours of April 2nd, many stations across the north-half of the province saw temperatures dip below -25oC.

Long range forecasts are predicting a gradual warming trend over the next two weeks, with the south-half of the province warming, sooner than the north-half. Generally, north of Red Deer, temperatures are expected to struggle towards near normal by mid-April.  For the entire month of April, Environment Canada is predicting that there is a 90% chance that temperatures will be colder than normal (map 1).

If the forecasts are correct, and temperatures remain near to below normal for a few weeks, it’s likely that snow packs across the north-half of the province will linger in fields until at least late April. However, long range forecasts are not always correct, and Alberta’s weather is often full of surprises.

Given recent memory, this may seem unusual to see snow linger so long. However, this occurs relatively often. For Grande Prairie, looking back as far as 1961, snow packs have persisted into early May approximately 10 times. For the same period in the Edmonton area, snows have persisted beyond April 25th on six occasions.

Snow pack development

 
Snow pack water equivalent (SWE) describes the depth of water contained in the current snow pack if it was to be melted (map 2). As of March 31st, south of Drumheller, most of the agricultural areas across the province were largely snow free.  North of this, snow packs increase rapidly with areas around Edmonton having between 80 to 90 mm SWE. The deepest snowpacks are located through the extreme southern Peace Region, where upwards of 200mm of SWE exists. This means that many of these areas will have over one meter of snow covering the landscape.

Compared to the long term normal (map 3), this year’s snow packs currently range from near normal across the east half of the province to above normal west of Highway 2. Across the extreme southern Peace region, snow packs are estimated to be this deep less than once in 12 years.

Note that the above normal snow packs shown across parts of the southern region on map 3 reflect a recent snow storm and the fact that even a small amount of snow cover at this time of year is relatively infrequent.

Perspective

Ideally, a relatively slow melt at this time of year is desirable to prevent localized flooding in areas with significant snow packs. As a result, cooler than normal forecast temperatures may well be desirable over a sudden warm spell that brings above normal temperatures and extremely rapid melt. This is particularly true across the southern Peace Region and through parts of the North West. However, this is tempered by the need to complete last year’s harvest as wet fall weather left some fields unharvested. A return to at least near normal weather in early May will help to speed access to land and allow farming operations to continue in a timely fashion.

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