Warm Start to Autumn About to Come to Abrupt End

Temperature anomaly across the US from mid-September to mid-October.

Temperature anomaly across the US from mid-September to mid-October. (Click to enlarge this and all other images.)

Cooler than normal temperatures have lingered in the West while much of the middle and eastern part of the nation enjoyed a rather warm and pleasant beginning to Autumn.  As is often the case in transitional seasons, all good things must come to an end.  In this instance, not one, but two shots of cold air are expected to impact much of the country, with the second shot serving as the Winter wake-up call, so to speak.

610temp_new

814temp_new

Remember not to pay too much attention to how deep the blue colors are – they merely reflecting higher probabilities.  These charts don’t actually tell us anything about how cold it’s going to be.  They simply state the likelihood of temperatures being below normal during a certain period.  To get a better visual of the first shot of cold air this weekend into early next week, here’s a look at the GFS 850mb temperatures on Sunday morning:

gblav_c850_h090

If you look closely at the wind vectors, you can see the cold air (deep blue and purple/pink) being ushered in from central Canada and the Arctic.  Now take a look at what the model is seeing late next week:

gblav_c850_h192

Again you can see the cold air coming from Canada and the Arctic, but this time it’s colder and more widespread.  Will it be cold enough for snow?  Perhaps in some of the northernmost states, but at this time of year, it’s hard to get it to stick.  (Unless, of course, there’s an intense blizzard like the one in Wyoming/South Dakota a few weeks ago.  I don’t see that right now and, even if I did, I’d have a hard time trusting it until I saw it for several successive runs into this weekend.)

How cold it will be on Halloween in your neighborhood is a little tough to say right now, but it’s probably worth considering how to keep yourself and any children warm in the event of cold temperatures.  By the way, “cold temperatures” is a relative term – it depends on where you live and what you’re used to for Halloween.

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