October 1 should be a cool and crisp Sunday in the Twin Cities, as a temperature around the average daily high of 56.7 degrees would be perfect for finding the right pumpkin to carve or getting lost in a corn maze.
Instead, the region slowed to summer-like temperatures that reached a record October high of 92 degrees. Just over a week later, there is frost in the region's forecast for Saturday.
These contrasts will not be found only in Minnesota. A wave of cold air late this week and into the weekend will have an impact almost everywhere east of the Rockies, said Alex Lamars, a meteorologist at the Weather Prediction Center. It will go from sweats to sweaters in a few days.
High temperatures were 15 to 25 degrees above average across the Great Lakes, Ohio Valley and Northeast Wednesday afternoon. However, that warm outlook will change Friday and into the weekend across the east-central United States and toward the East Coast, where highs dropping 10 to 20 degrees below normal are likely.
As cold air sweeps in, rainfall forecast for parts of the Northeast could be boosted by Tropical Storm Philippe, which threatens to wash away anyone's autumn festivities.
Although temperatures are forecast to be below average, only a few places in the east may see daily record low temperatures. Instead, above-average temperatures will continue to be felt in the West, where more than a dozen daily records for warm temperatures could be tied or broken.
Cold air will be an abrupt arrival of the fall season for some, especially in the central and northeastern United States, Mr. Lamars said. These areas have experienced some of the hottest falls ever.
This milder weather pattern comes on the heels of the third warmest summer on record for the United States. The coming blast of fall air will be a refreshing break from the unrelenting heat along the Gulf Coast, especially in Louisiana, which had its hottest summer on record. The last time New Orleans was below 65 degrees was May 2, and temperatures there are forecast to drop into the low 60s, Mr. Lamars said.
Texas and Florida may also feel the relief after a punishing summer that ranked as their second hottest. “The last time Houston had a low temperature even below 65 degrees was May 8,” Mr. Lamars said, adding that they may finally dip into the upper 50s this weekend.
Houston, New Orleans and many other locations in the Gulf Coast region had extremely windy summers and set heat index records for hours above the 110 degree mark. The cooler air mass expected this weekend will also be drier, with humidity levels dropping to some of the lowest these areas have experienced since April or early May.
Sudden changes in temperature are expected as the country moves into more autumnal weather. Even in Minnesota, the cold swing isn't entirely unusual for the arrival of fall, said Tyler Hasenstein, a meteorologist with the National Weather Service in the Twin Cities.
Below-normal high temperatures in the 50s are recorded every three to five years in the Twin Cities in early October, he added. What was unusual this season was the extreme heat at the start of the week. Temperatures rarely reach the 90s in Minneapolis in October, Mr. Hasenstein said.
Conditions expected this weekend in Minnesota are forecast to bring relief from the heat and humidity, Mr. Hasenstein said. Even with frost expected on the ground in places, most areas in the region will remain above freezing.
The first frosts and frosts of the year could occur in other parts of the Northern and Central Plains, the Upper Midwest, the Great Lakes and the inland Northeast, Mr. Lamars said, which “is on par with historical expectations.” ยป. Most of these areas expect to experience the first freeze in late September or early October.
After this weekend, things will change again and above average temperatures will increase across the central United States for the week ahead. However, people on the West Coast may get their turn to get a taste of fall and maybe drink a pumpkin spice latte by the middle of next week.
