By AccuWeather senior meteorologist
June started off on a scorching note for the Midwest and was marked by searing stretches of 90-degree days with AccuWeather RealFeel® Temperatures frequently climbing into the 100s over a large portion of the north-central United States. However, for those that mind the heat, AccuWeather meteorologists have some good news. Temperatures are expected to swing in the opposite direction for a prolonged stretch as several waves of cooler air sweep across the region.
The blistering pattern caused extraordinary departures from the average temperature through the midpoint in June. Minneapolis experienced an average temperature 14 degrees above normal during the first 15 days of the month.
However, that trend will not continue.
A shift in the jet stream pattern will allow batches of much cooler air to dive southeastward from central Canada and across a large part of the region in the coming days, AccuWeather Lead Long-Range Meteorologist Paul Pastelok stated.
The cooler weather could chip away at the heat enough to halve the temperature departures by the end of June, according to Pastelok.
Pastelok and his team of long-range meteorologists are projecting that the temperature departure in Minneapolis will drop to about 7.5 degrees above average by June 30.
AccuWeather forecasters expect other major cities to face a similarly dramatic swing in temperatures.
"Chicago experienced a temperature departure of 9.4 degrees above average during the 15 days of June, but by the end of June, enough waves of cool air should impact the city to knock the overall monthly departure to about 5.0 degrees above average," Pastelok explained.
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"Just as extreme as the heat was the first half of the month, this anticipated slash in the June temperature departure will be a testament to the magnitudes of the cool waves anticipated during the latter half of the month for a good chunk of the region," Pastelok said.
Some relief already arrived for some areas at the start of the week as temperatures dropped by about 5-10 degrees Fahrenheit. For example, Minneapolis recorded a high of 97 Sunday and a high of 88 degrees Monday. Chicago climbed to 93 Saturday, but the high came in at 87 Sunday and then 83 Monday.
Heat will also sound the retreat farther west over portions of the northern High Plains as the week progresses as another brief cooldown is in store for much of the region late this week.
"Temperatures will average 4-8 degrees below normal" across the Dakotas and much of the Midwest with that second push of cooler air this week, Pastelok said.
During the third week of June, normal high temperatures range from the lower to middle 70s across the upper Great Lakes to the lower to middle 80s across the Ohio Valley and portions of the central Plains.
"Low temperatures for Bismarck, North Dakota, can be in the middle 50s Thursday morning, but as low as the upper 40s Friday morning just outside of town," he added.
Another blast of cool air will arrive right after the summer season officially gets underway on June 20. Temperatures will fall to 6-12 degrees below normal from the Dakotas and on through much of the Midwest beginning around Monday, June 21. This cool snap could also stick around and last for several days.
"During the early and middle parts of next week, highs will generally be in the 60s to lower 70s in this zone," Pastelok said, adding that normal highs are in the upper 70s to lower 80s for comparison.
During that same cool air outbreak next week, nighttime lows are forecast to range from the lower 40s across the northern tier to near 50 or so over parts of the Ohio Valley.
The greatest temperature departures from average next week are likely from eastern North Dakota to Minnesota and Wisconsin.
In between the doses of cool air, temperatures can recover to or even a bit above average, but overall there will be more days with below-average temperatures than above average through the end of June.
When and where the sky is clear during the day, intense June sunshine will go to work on the cool waves and allow temperatures to fight back in some cases. However, even the strong sunshine effect this time of the year may not be enough to prevent a number of days with below-average temperatures, and episodes of clouds and wet weather can make for even much cooler conditions.
One such rainy episode may progress from west to east from Sunday, June 20, to Monday, June 21. This storm system may trigger a thorough soaking across parts of the northern Plains and Midwest that are in need of precipitation. Soil conditions over much of the North Central states range from near average over the central Plains and the Ohio Valley to exceptional drought over North Dakota, according to the United States Drought Monitor.
That same storm system is the one that will unleash the reinforcing dose of cool air next week. After that, it's possible temperatures moderate back toward normal.
Prior to the storm this weekend, a round of severe thunderstorms is possible on Thursday and Thursday night from portions of eastern south Dakota to northern Illinois, northern Indiana and the Lower Peninsula of Michigan.
"Late month, the temperature departures are not likely to be as extreme on the cool side," Pastelok said.
There is the possibility that some of the heat from the West may try to push northward and eastward to some extent, while cool air keeps eastern Canada and the northeastern U.S. in its grips. The Midwest will teeter on the edge of the clashing air masses and may experience back-and-forth temperature swings and the potential for thunderstorms in between.
During the first half of June, Minneapolis experienced nine days in a row of high temperatures of 90 degrees or higher. This is the first time the city endured a streak of nine days with 90-degree temperatures since 2006, according to the NWS. At the peak of the heat wave, the temperature stopped just shy of the 100-degree mark on June 5. Three days of record high temperatures were set in the pattern on June 4, 5 and 9.
Chicago stopped short of breaking record highs during the pattern, but it did experience six days with highs at or above the 90-degree mark. The normal high in Chicago ranges from 75 on June 1 to 80 on June 15.
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