Temperatures in the northern United States will get relatively cool next week, with models suggesting temperatures ranging 10 to 20 degrees below normal. The cause is something we'll call the SummerPolarVortexmageddon, because it sounds cool and (still) nobody knows what a polar vortex is, anyway.
The Current Setup
Temperatures in northern Canada are still pretty cold — this morning's readings dropped off from the low 60s to the low 30s almost instantly across the appropriately-named Arctic Circle, and air temperatures over Hudson Bay are in the upper 30s to low 40s.
Meanwhile, there is currently a potent trough — a large southerly dip in the jet stream — over the western United States, slowly moving to the east. An area of low pressure will form in western Ontario north of Minnesota as a result of this trough, and this low pressure system will be responsible for sucking down cooler Arctic air into the northern part of the country.
As the low begins to lift off to the northeast deeper into the vast recesses of Canada, stiff winds on the western side of the low will drag cold air down into the central United States from Hudson Bay.
This forecast temperature map from the GFS model shows afternoon temperatures on Monday, potentially only reaching the upper 50s as far south as the North Dakota border:
As a result, models are predicting temperatures for the first half of next week to fall 10 to 20 degrees below average, depending on which model you believe.
Here's the GFS (the global American model), which is probably a little extreme as it shows temperatures at noon on July 1 more than 20 degrees below average for this time of year:
And here's the ECMWF (European model) for the same time frame, showing more modest but still below-average temperatures:
The below-average temperatures will migrate to the Great Lakes region by Independence Day:
And by July 6, the European model is showing below-average temperatures finally reaching the I-95 corridor of the northeast:
How cool (or hot) could it get?
The European suggests that highs could only reach the mid- to upper-70s in the northeast on July 6 while the rest of the country bakes in a heat wave — temps in St. Louis could crack the 100s:
Long story short, it's going to cool down in the northern part of the country next week, and if you live anywhere else, it's only going to get hotter.
[Images via WeatherBELL and TwisterData]