Over the next 5-7 days the US pattern overall settles as the jet stream intensifies and roars nearly due west to east across the country. That’s a mild orientation of course with Pacific air crossing the country and locking any cold up in Canada. However these patterns tend to come at a price for the Pacific Northwest as this usually signals a stormier pattern over British Columbia as well as Washington and Oregon.

Sure enough, the first major storm system of the season is on the way and this poses a significant flood risk to urban areas. The trouble is, as it deepens within the Gulf of Alaska, it deepens further as it drops SE towards the West Coast and spreads it’s circulation out as the forward speed slows down. This presents a multi-day barrage of heavy pounding rains driven in by 40-60 mph winds with higher gusts along the coast and over the mountains.

Here’s the GFS surface/precip chart for Sunday and you can see the storm winding up off the BC coast and throwing heavy precip onshore. Note the pressure is down to 972 mb. This will generate big swells at sea and big waves onshore.

The ECMWF 500mb shows a lot of energy streaming onshore.

GFS shows the barrage continuing Monday but the system remains offshore in a weakening state.

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Note by next Wednesday the ECMWF shows a zonal flow with stronger heights further east, suggesting mild conditions coast to coast.

By Wednesday the storm remains OFFSHORE but is barely anything by this point. Note the rest of the country’s weather is very quiet.

A LOT of rain is projected to fall over the next 5 days. Check out these totals according to the ECMWF. These rains are sure to break September rainfall records.

First Shot Of Arctic Air For Lower 48 Around the 5th?

Skipping ahead to next Saturday and another system drops out of the GOA, only this one not only appears to penetrate the coast and push inland but the building cold over western and central Canada, appears to get pulled by this system and by next weekend, the ECMWF shows the FIRST potential shot of ARCTIC ORIGIN AIR entering the Lower 48.

Here’s the surface chart.

Here’s the 500mb chart next Friday.

Check out the wild looking surface chart with impressively low heights driving south into the Plains on the backside of a deepening cross country system. This could have the potential for a severe and wintry side as well as a major up and down temperature setup.

Here’s the 500mb and 850s for Sunday. Now that’s arctic air for sure.

Closer look at those 850 temps

Still a long way out and the model could be going too extreme on this or it may be on to something given the fact the AO is negative and the PNA is set to swing positive while the NAO is negative. In other words the indexes back this up!

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Tags: Pacific Northwest rains, us october forecast, US pattern, Western US weather