High temperatures forecast by GFS model for Oct. 5.

If you live in Chicago, Columbus or Charlotte, don’t get used to the touch of fall arriving now. Summer is roaring back by the middle of next week.

After parts of the Midwest and Northeast baked in their hottest late September weather ever recorded, computer models are predicting a second round of abnormally warm conditions to start October in the eastern half of the nation.

Models have consistently simulated the development of a “heat dome” which would be considered intense even by midsummer standards — although it will not produce temperatures nearly as hot because the sun is much lower in the sky in October.

The heat dome is indicated by a sprawling area of high pressure about 20,000 feet high in the atmosphere in which the air sinks, gets compressed and, ultimately, cooks the ground.

On his blog, Guy Walton, a meteorologist retired from the Weather Channel, described the weather pattern as “warm, weird, and spooky.”


GFS model simulation of heat dome over eastern half of United States on Oct. 4. (WeatherBell.com)

So how does this translate to actual conditions?

It means widespread areas are likely to witness temperatures 10 to 20 degree above normal, probably higher in some areas. Because this next warm spell is occurring one to two weeks later than the previous, the ceiling for temperatures isn’t as high.

For example, Chicago isn’t expected to string together seven straight 90-degree days again, but temperatures into the 80s are likely, and you can’t totally rule out 90 degrees on one or two days. The European model predicts highs of 87 degrees Oct. 3 and 4 there. In modern records, Chicago has hit at least 90 degrees as late as Oct. 6, when it was 94 degrees in 1963.

It’s safe to say, given the model consensus for such an intense heat dome, records will be set in some areas. A few locations may even experience all-time highs for the month of October and/or their hottest weather so late in the calendar. However, because this warm spell is still about a week away, it’s too soon to forecast exactly how warm it will get and whether temperatures in particular locations will challenge records.

“This is a really impressive hit,” said Matt Rogers, president of the Commodity Weather Group and contributor to the Capital Weather Gang. “It’s similar to what we just experienced, but we don’t think the humidity will be quite as bad.”

Temperatures probably won’t be as unusually warm as far north as the previous heat wave. So less toasty temperatures are likely in Green Bay, Wis., Burlington, Vt., and northern Maine. However, locations farther south, from St. Louis to Washington, may witness more anomalous warmth compared with last time.


European model forecast of temperature difference from normal at 2 p.m. on Oct. 5. (WeatherBell.com)

Rogers said the District has “a shot” to hit 90 degrees next Thursday and maybe even Wednesday. If Washington reaches 90, it would be the first October case since 2013.

Here are some general expectations for the highest temperatures and their timing next week in a set of cities:

  • St. Louis: 85-90, Monday through Friday.
  • Chicago: 85-90, Tuesday and Wednesday.
  • Cleveland: 80-85, Tuesday and Wednesday.
  • Pittsburgh: 80-85, Wednesday and Thursday.
  • Washington: 85-90, Wednesday and Thursday.

Note that these numbers will need to be fine-tuned as the forecast comes into better focus over the coming days.

Abnormally warm temperatures are likely to persist longest in the nation’s heartland and in parts of the South, where they could linger through next weekend, Oct. 7 and 8.

The presence of this heat dome may help spur the development of tropical activity in the Gulf of Mexico or the western Caribbean. The clockwise flow around the sprawling high pressure center will direct light easterly winds along its southern flank in this vicinity — which is conducive to the development of any tropical disturbances.