While a significant trough drives autumnal air down across the Northern Plains, Great Lakes, Midwest and eventually the East Coast, ridging is pumping unusual warmth up the western flank of the continent and in fact we may see highs near 100 in Portland, OR and near 90 in Seattle, WA Saturday afternoon. This will be thanks to ridging pushing heat north from the Deserts which could bring record heat all the way up into southern and central British Columbia and Alberta. What’s interesting is that during the first 5 days of September, the high failed to reach 68F (20C) in Edmonton, AB and that hasn’t happened since 2004 according to CBC Meteorologist Josh Classen. Temperatures could top 80 for a few days in Edmonton.

The heat will be short lived however as a trough deepens over Alaska and drops south over Western Canada and the Pacific Northwest Sunday, Monday. Highs go from 88 today, 87 Saturday to only the mid-60s Sunday in Seattle. Snow is expected with this push of chilly air up over the Yukon, NWT and perhaps down over the higher elevations and northern sections of BC and Alberta. Yes, the autumn temperature rollercoaster has begun. You just know that as we progress through September, those cold fronts are just going to get sharper and colder with time.

The northward advance of the western ridge will force the chill over top of North America southeastbound keeping highs in the upper 60s over Minneapolis, Chicago and Detroit with lows falling into the 40s for MSP and low 50s in CHI and DET.

The thing is, it’s only early September and so that heat over the PNW will get shoved east with the SE-bound trough. Temperatures across Idaho, Montana and eventually the Dakotas will rise back into the 90s with near 100 over South Dakota. Temperatures may even push 90 early next week in Minneapolis, baring in mind that today and tomorrow will struggle to hit 70.