Hot Summer Forecast to End with (Relative) Cold Stretch (UPDATED)

After a dry and warm start to Summer in June, the following month managed to set the record for the hottest July in recorded US history.  Most Americans living east of the Rockies don’t need charts, graphs, maps, or numbers to tell you this Summer has been brutal.  If you just watch the weather, you know the stretch of above-normal temperatures seemed unending through much of the Summer.

But this story has some semblance of a happy ending.  As noted earlier this week, temperatures began to cool toward normal (and even below normal) in the past week across many of the places that were sweltering earlier this Summer.  In fact, it appears the heat has meandered westward in the inter-mountain west and along the coast.

UPDATE: I found a nice map to prove this point from the High Plains Regional Climate Center:

Temperature anomaly for the past 7 days.

The 14-day forecast from the Climate Prediction Center called for below-normal temperatures across much of the nation’s heartland and it appears that forecast applies through the end of August.  The GFS ensemble mean forecast for the next 16 days, which covers the rest of August, shows below normal temperatures for much of the eastern 2/3 of the country.

16 day mean 2-meter temperature anomaly from the Global Ensemble Forecast System (GEFS). Valid 12Z 8/16 through 12Z 9/1.

The coolest temperature anomaly is forecast for parts of Missouri, Iowa, and Illinois – almost exactly where the CPC forecast the greatest chance for above-normal temperatures during the month of August:

August temperature outlook for the US from the Climate Prediction Center.

Granted, the GEFS forecast is only for a 16-day stretch, not the entire month.  Still, as pointed out earlier this week, it’s going to be hard to validate this outlook if half the month is below normal.

For a more detailed look at this forecast cool down across the central and eastern US, I looked at the break down between days 0-7 and 8-16:

7 day mean temperature anomaly from the GEFS valid 12Z 8/16 to 12Z 8/23.

Day 8-16 mean temperature anomaly from the GEFS valid 12Z 8/24 to 12Z 9/1.

You can see the intensity of the below-normal temps (as well as the western heat wave) wanes as we get later in the forecast, although it is still forecast to be cool in the central and eastern US while staying warm in the inter-mountain west.  Remember what we’re looking at: means of ensemble forecasts over a period of time.  Thus, it’s the average temperature over a period of time (7, 9, or 16 days) over approximately 20 different, individual model runs.  As time goes further out, you would expect ensemble means to trend toward climatology (although this isn’t always the case).  So, the softening in the anomalies would be expected in days 8-16.  Reality may differ when we get there.

Some people may look at this and point to an early start to Fall.  I would caution against that line of thinking.  I can recall a couple different years in which September was warmer than August in the location I was living at the time.  And August was much cooler in those instances than it will likely be this year.  Plus, the CPC outlook for September forecasts a reasonable chance for above-normal temperatures throughout much of the country.  Granted, their August forecast was similar and that’s looking shaky, at best, right now.

(Disclaimer/Side note: The GEFS images are from WeatherBell’s model page, which is currently available for free.  At some point, presumably in the near future, it will go back to being available only to subscribers.  I would suggest any weather enthusiast who spends time looking at models visit this page.  I am quite impressed by the graphics and collection of model data available.  I am guessing it will only expand once behind the subscriber wall.)

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