Friday, Aug. 19 & Saturday, Aug. 20 Outlook

Stalled front across the Southeast produces showers and thunderstorms as far north as WAS; showers and thunderstorms expected Saturday around CHI

Welcome to any new readers! And as a reminder to long-ish time readers, we’re testing a new format for these outlooks. To both old and new—we’re grateful you’re here.

If you have questions about the content of this outlook, the answers might be in this post (we keep adding to it). Otherwise, let us know if something doesn’t make sense (we welcome feedback of all kinds!).

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Friday, August 19

We forecast TSA will screen 2.318 million travelers (± 0.5σ, or a prediction interval of about 38%, is 2.25-2.38 million travelers).

As an aside, the TSA screened fewer than 2 million travelers Tuesday for the first time since June 4, breaking a 74-day streak; and yesterday was the 6th consecutive day where TSA throughput was down by 1.5% or more week-over-week, the first such 6-day streak since early January. It appears summer travel is winding down.

The same weak front we wrote about Tuesday still extends from the Southeast roughly westward to the Southern Plains. Meanwhile, high pressure off the southern Mid Atlantic coast lifts north, drawing moisture towards the Washington area. On the balance, thunderstorm chances are considerably higher at ATL (approaching 40% during late afternoon) than DCA (less than 10%).

Saturday, August 20

We forecast TSA will screen 2.077 million travelers (± 0.5σ, or a prediction interval of about 38%, is 2.01-2.14 million travelers).

By Saturday, a front over the Upper Midwest will have sunk south into the Upper Great Lakes. While showers and thunderstorms are expected, the severe threat looks to be low; the best chance for a strong to marginally severe thunderstorm would be if the front reaches the Chicago area by late afternoon and enough pre-frontal instability has built before sunset. The latter (sufficient instability) may be a tough ask given persistent cloud cover during the day (i.e. an inhibitor to daytime heating).

You can check out¹ hourly estimates in this workbook.

1. While it links to a Google Sheet, it’s an Excel file and relies on the XLOOKUP function, which does not exist in Sheets. You can download the file and open in Excel, which should resolve the #NAME? error; if any readers don’t have Excel, let us know and we can work on a solution.