The first major storm of autumn is well underway across British Columbia, Washington and Oregon and has been bringing problems throughout the region with power outages being reported by the tens of thousands from parts of Vancouver and Victoria all the way down to Portland, OR with winds in excess of 60 mph and 24 hour rains in excess of 2-3 inches in places, much more locally and this has indeed broken both daily and even monthly rainfall records. Both Seattle and Olympia have seen their heaviest 24 hour rains for the month of September on record.

It’s all thanks to a powerful Gulf of Alaska storm which has dove into the region and this system will continue to bombard the BC-PNW region for the next 72 hours before the new trough that will carve out, spreads east bringing ridging and warmer, more settled conditions back in towards next weekend. Snow is falling above 7 or 8,000ft and like the rains, could mount up.

Here’s a current water vapour image showing the swirl off the BC coast with TWO ribbons of cloud extending from the central Pacific and merging over the BC-WA-OR coast.

As for the rest of the country, except for a fairly vigorous but weakening cold front crossing the Midwest bringing isolated severe weather and a big 20-30 degree temperate drop, there’s little to speak of with a largely zonal upper air pattern setting up across the country through the first half of the week. Heights are set to rise over the Plains and Eastern half of the country in the coming days as powerful westerly winds and a Pacific flow takes charge but a western trough will begin to carve out mid to late this week once again sending the coldest air of the season into the Great Basin and Rockies while a surge of heat lifts north, northeast into the Midwest and eventually the East.

That’s the -PNA signal dictating once again.

Check out the ECMWF surface/precipitation charts for the next 3 days and you can see the bulls eye of wild weather focused on the Pacific Northwest while a weakening front slides across the Ohio and Tennessee Valleys as a much lesser feature. The rest of the country is pretty quiet.

24 hrs (Mon)

48 hrs (Tue)

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72 hrs (Wed)

Total rainfall over the next 72 hrs

The ECMWF is much bolder with the snow with this next system compared to the one which just brought heavy snows to Idaho, Montana, Wyoming into parts of Utah and Colorado and by that I mean the coverage. This system could bring a slushy coating or an inch to Metro Denver mid or late week but it may be strictly confined to grassy surfaces as roads be too warm for it to stick. Nonetheless the model has a fairly large area extending from the Cascades down to southern Colorado covered.

GFS shows a similar coverage but indicates more clearly the fairly significant totals expected in the mountains. 1-2 feet is quite likely in the higher elevations.

By late week the upper pattern returns to a more amplified state as the trough deepens.

Interestingly the GFS 500mb is much deeper with the trough and colder with the 5,000ft temperatures compared to the ECMWF.

Here’s Friday!

5,000ft temperatures at 120 hours.

The 156 hour GFS brings the first accumulating snow to the Upper Midwest.

Here’s the 5,000ft temperatures by next Sunday which shows the storm to the east and driving cold air out of Canada into the Upper Midwest.

Also notice the warming both to the west and east.

While we see the trough slide east through the mid and later stages of the upcoming week, we’ll see temperatures initially rise, fall then rise again as the overall upper pattern remains fluid or progressive. It will be interesting to see what will take place in the 2-3 week period as the PNA is projected to go positive and it the NAO and particularly the AO was to hold negative then we could see some much colder air dive in the eastern half of the continent. Right now the bias is on the western trough and eastern ridge.

Here’s the 6-10 temperatures according to the CPC.

The modelling is all over the place these days and while I’ve been strong on the idea of a fairly cold October in the central and eastern US, there’s little guidance in the longer range models and given the fluid nature of the pattern these days, October is tough to call. Clearly the opening few days to the month in the West will be cold and snowy with warmth in the East but we could see a flip week 2 into 3 for the East.

Here’s the latest CFSv2 temperatures for October which suggests a +PNA signal and with that western ridge and warmth, one would think troughiness and cool shots into the East.

The abnormally warm water off the West Coast certainly supports a +PNA and ridge.

As already mentioned, the models in the longer term are very much all over the place, wildly back and forth from wild northern blocking to none at all but check out the latest CFS 500mb heights for Nov, Dec and Jan.

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Tags: Rockies Snow, september snow