Last week it was snow.  This week, it’s rain.  Last week, it was mainly Alberta.  This week, it’s also mainly Alberta.

A major rainfall event begins Monday.

An upper level low coming in from the Oregon coast, along with a surface low to develop in northern Montana, will lead to plenty of rain starting Monday in southern and central Alberta, along with southwestern Saskatchewan.  The biggest rain threat will occur Tuesday in central and southern Alberta, with up to 80 mm of rain expected near Medicine Hat and the Cypress Hills. Thunderstorms, and possibly severe thunderstorms, can’t be ruled out.  Beneath those storms, local rainfall amounts will be even higher.   This will be a soaking rain, and the runoff may cause localized flooding in ditches, underpasses, and other low lying areas in southern Alberta.   While the heaviest rain will occur near Medicine Hat, and along the Alberta-Saskatchewan boundary, significant rainfall can be expected all the way west to the foothills, and east across southern Saskatchewan and Manitoba.   This map shows expected rainfall accumulations by early Wednesday morning:

The map shows a widespread area of 50-75 mm of rain across central and southern Alberta east of Highway 22, extending to the Swift Current area.  East of there, amounts range from 10-50 mm across southern Saskatchewan.  In southeastern Alberta, the areas shaded purple on the map above indicate rainfall totals exceeding 75 mm.

It will be cold and windy during the rain event, particularly on Tuesday, with a strong north wind drawing in cold air that will limit temperatures to the single digits in southern Alberta and southwestern Saskatchewan.  Low double digit highs can be expected elsewhere across the prairies.

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The rain is expected to taper off during the day Wednesday.   The Montana surface low will stall for the duration of the event, so the storm is unlikely to move east, meaning Manitoba will be largely left out of the heavier rainfall, which would have been so beneficial to the region.  Still, some parts of southwestern Manitoba can expect 10-30 mm of rain through early Wednesday.

These types of systems are very dynamic, so for updated information as the event progresses, check out Environment Canada’s website.   You’ll find rainfall warnings posted there.

Some of this rain will fall on soil already moistened by last week’s snowfall.   The higher amounts of snow fell in the foothills and mountains from Jasper to Waterton, but some agricultural lands received snowy moisture as well.   Again, Manitoba was largely left out of that event.  Here is a table showing snowfall totals as measured by CocoRahs volunteers.  The Calgary measurement is from ECCC.

Saskatchewan snow totals:

After the Monday/Tuesday rain event, here’s how the rest of the week plays out:

Wednesday:

This is the day the stalled Low in Montana weakens and drifts southward.  The rain in Alberta and Saskatchewan will taper off.  The last few drops of rain will fall near midnight Thursday morning in the Cypress Hills.  There will be a rebound in temperatures in Saskatchewan and Manitoba, with some areas reaching 15-20 degrees, though it will remain cool in the rain-soaked areas of southwestern Saskatchewan and Alberta, which will continue to be under cloud cover.

Thursday:

 It becomes mainly sunny over the agricultural regions of all three prairie provinces.  A few scattered clouds are likely over southern Saskatchewan, with temperatures climbing to the high teens in Alberta and Saskatchewan, and the low 20s in southern Manitoba.

Friday:

No significant weather is expected Friday in Alberta and Saskatchewan, though southern Manitoba will see a mix of sun and cloud.   Convective clouds may produce showers or thunderstorms in southwestern Manitoba, with the passage of a weak cold front.   Temperatures in the area will be below average.   In the Peace country of Alberta and BC, temperatures will likely climb to the 20s under sunshine.

Saturday and Sunday:

 No significant weather is expected over the weekend, with bright sunshine across all three prairie provinces, and temperatures reaching the high teens or low 20s.

COMPARE TO LAST WEEK: Prairie Weather This Week: Apr 29