Tracking Peak of Summer Heat Waves

We’re entering the historically hottest part of summer and heat waves dominate. SUN/MON maximum temperatures are well into the 90’s in the Northeast, near 100 Washington/Baltimore/Philadelphia the next 2 days and still in the 90’s midweek and 95-100 all week from Atlanta to Richmond. The Midwest heat wave continues today with widespread 90’s Missouri to Ohio ending by tomorrow as a cold front passes.

The next issue is does another heat wave follow? ECMWF says yes and forecasts a stronger event than currently taking place. The GFS is not nearly as hot. The question is whether the hot air source region in the Central U.S. pulses eastward (or not). GFS says no while ECM is (vigorously) yes! The precedent is set as last week’s Midwest heat wave has shifted into the East now. A second event is likely and given peak summer heat the next event could be hotter.

Expected is 102F in Dodge City mid-to-late week as the next heat wave develops. Last week Dodge City peaked at 99F. So…the source region is hotter this time! Chicago reached 90-91F the past 2 days, next weekend 94F is likely. To the east, Richmond reaches 100F tomorrow and possibly 102F one week from tomorrow. NYC is near 96-97 tomorrow and could be close (again) one week from tomorrow.

The ECMWF is the hottest forecast model for the next 10 days, the GFS is somewhat more temperate. But the hot weather precedent forces choosing of the hotter scenario ahead.

Fig. 1: The 16-day MAX/MIN forecast for Chicago, IL using all models.

Fig. 2: The 16-day MAX/MIN forecast for Washington, DC using all models.

Fortunately, waves of thunderstorms fend off drought development in the Midwest to Mid-Atlantic hot weather track. The NOAA/WPC 7-day rainfall forecast (Fig. 3) indicates gully-washer thunderstorms in the Midwest U.S. ahead of the next heat wave and that rainfall will shift into the Mid-Atlantic region this week albeit with less intensity. Storms produce locally heavy rain and a lot of lightning. The most recent daily U.S. soil moisture anomaly analysis reveals a large drought centered on 4 Corners and patchy drought areas in the Midwest including southwest Iowa and the eastern Ohio Valley (Fig. 4). New England, eastern Texas and north-central Florida are each in a drought condition. Areas of dry soils allow over-achieving heat during hot weather episodes.

Fig. 3-4: The NOAA/WPC 7-day rainfall forecast and current soil moisture anomaly analysis across the U.S.

U.S. medium-range forecast: A consensus forecast between the GFS and ECM ENS is indicated in the 6-10 day period (Fig. 6). The 11-15 day forecast is based on the mega-cluster ensemble (Fig. 7).

Fig. 5-6: The Climate Impact Company 6-10/11-15 day forecast.