The pattern across the hemisphere is rather interesting these days when you take a step back and look at the broader picture. We’ve just seen two unusually deep lows form in the high latitudes at roughly the same time. One over the Bering Sea between Russia and Alaska which bombed out at around 974mb, the other, was a system which came off Canada, crossed the North Atlantic and then deepened to around 968mb east of Iceland. My thinking about these two systems and others which have deepened beyond depths you would expect for this stage in the year is because of warmer than normal SST’s, energy released into the atmosphere by the El Nino and the gradual building of colder air over the Pole.

Over the next 5 days, we see the first major trough drive into the United States and this will bring cool, refreshing days in the 60s widely across the Northern Plains and Midwest, 70s perhaps all the way down into the Tennessee Valley. Night temperatures could widely fall into the low 50s and 40s.

While this trough drops all the way to central Texas, it will then swing east, pushing the Canadian cool all the way to the Atlantic coast by Monday, Tuesday of next week.

The seesaw has begun and it will be very much a case of as we progress through September, these cold fronts will transport on their backside increasingly cooler air down. I do expect a cold period either in late September or certainly during October, especially over the Rockies and Plains.

Here’s the latest from the ECMWF which shows the deep trough by this weekend over the eastern third.

What’s interesting is that the latest run of the ECMWF shows the return of warmer air back into the East once Leslie strikes Nova Scotia or Newfoundland. The trough leaves and warmer air pushes back north.

First widespread frost since spring possible for UK next week

Interestingly, following a warm weekend, a major trough drops down across the UK, Ireland and Northwest Europe early to mid next week while a ridge tries to build over the North Atlantic and Greenland. While this may bring yet more unsettled weather with wind and rain to the UK, the important aspect for me is the fact the tempeartures are going to be chilly by day and if skies are clear, wind light, we could see a darn cold night by September standards with frost widely outwith towns and cities.

The ECMWF however does show moderation in temperature but no relief from the persistently unsettled pattern.

So, there is two distinct autumnal troughs set to drive below normal temperatures south into the mid-latitudes, 1 over the central, eastern US and the other over Northwest Europe and this marks the start to a rollercoaster temperature pattern over the next couple of months as summer progresses towards winter.

I believe we are very much in for a seesaw in temperature as the ‘stormy’ pattern continues but with each low passing by, we need to get ready for increasingly cooler air working south on their backside.