Summer weather continues to drone on across our region with little regard to the steady loss of daylight. Our temperatures have been averaging about 8° above normal for September with every day logging above-normal readings. In fact, the coolest temperature of the entire month is 67°. We got cooler in July and August for crying out loud! The culprit for the 2nd warmest September on record has been a persistent ridge in the jet stream, locking us into a nearly Tropical air mass. But that jet stream pattern is about to change and send some seriously cool air our way later this week.
The legacy of this September may be the morning warmth. No other September has been so warm for morning lows, owing mostly to the oppressive level of moisture in the air with no serious front to remove it. Dewpoint values in the lower 70s are common in mid-summer but are rare by autumn. An exceptionally wet spring and summer has clearly kept our humidity levels high. A moist air mass can only cool so much before saturation so our overnight temperatures can only drop so far. The graph above shows the ongoing 6-day streak of record-breaking morning warmth.
Our daytime highs will not reach record levels but remain about 12° above normal the next few days with those readings reaching 90°. These numbers are also set to tumble as we cross over into October. On Wednesday, a powerful storm system that dumped FEET of snow in Montana will slide into the central Plains, poised to bring us more thunderstorms and temperatures down to near 60° by Thursday morning. The map above shows the big shift in the jet stream this week. Thursday will be the first day it really feels like fall with an even stronger surge of cooler air arriving this weekend. Below is our temperature trend compared to our average over the next 9 days.
Not only will we cool down, the air will also dry out. This could be the end to some seriously muggy air. Moisture return on this side of the calendar is usually less and less after each cold front passage, which will allow for cooler nights and more comfortable days. The jet stream pattern remains very strong and progressive, sending that fast-moving front our way by the weekend. This will further cool us down, dry us out and likely send our lows into the FORTIES a week from now!
These transitions to cooler weather will also come with the risk of more wet weather as well. Rain totals are not expected to be excessive with our midweek and weekend storm systems, but they could still bring a widespread inch or two of rainfall. That wetter than normal trend carries on into mid-October, hinting at a continued active weather pattern for the foreseeable future as shown below.
The outlook for the entire month of October is still calling for a warmer than normal forecast for our region. This incoming cool down may not stick around too long, but we will be unlikely to return to the 90s or levels of mugginess in place now. Hallelujah.
As we go from muggy to mild, remember these cold fronts are just sending our temperatures down to where they “should be” this time of year. At the very least, we’ll get to reacquaint ourselves with our jackets again. Stay cool in the meantime! For more weather updates, be sure to follow me on Twitter: @GroganontheGO and on my Facebook page.