Fall 2018 summary reveals odd season in central Indiana

Tuesday, December 18, 2018

The advent of December marks the conclusion of meteorological fall and the welcoming of meteorological winter, although in central Indiana it’s been difficult to tell the difference this year.

Temperatures remained above average throughout much of the first half of the fall, before cooling to below-normal levels by mid-October prior to a much colder November.

Overall, fall 2018 saw average temperatures within a degree either side of normal. A very wet September was aided by the remnants of Tropical Storm Gordon early in the month. Drier conditions settled in from late September through October before turning wetter again in November.

Most of central Indiana saw the first snowflakes of the season in October, followed by one of the more wintry Novembers in recent memory. A rare early season ice storm impacted the region on Nov. 15, followed by additional snow threats through the second half of the month.

The fall of 2018 was tied for the 75th coolest fall ever at Indianapolis with an average temperature of 55 degrees, only 0.2 degrees below the normal fall average temperature of 55.2 degrees.

September started out hot across central Indiana, with much of the area getting to 90 degrees or warmer five out of the first six days of the month. The average temperature 0f 80.8 degrees in Indianapolis through the first six days was the second warmest start to a September on record, behind only Sept. 1-6, 1922. But the heat wave came to an abrupt end on the 7th as remnants of Tropical Storm Gordon brought clouds and heavy rain.

Cooler temperatures would arrive the last week of the month, with highs generally in the 60s and 70s. The coolest nights of September would come during the last few days of the month as lows fell into the 40s for the first time since early May.

At Indianapolis, eight days at or above 90 degrees were recorded, the most in September since 1999. There were also eight nights where lows remained above 70 degrees, the most in the city in September since 1936.

October was truly a tale of two seasons as unseasonably hot and humid conditions for the first 10 days transitioned into a much cooler pattern that would largely extend through the remainder of the month.

The month had one of the warmest starts to an October on record as highs consistently warmed into the mid and upper 80s with a few locations making it to 90 on a day or two. The Columbus Day weekend was exceptionally warm and humid with average temperatures running up to 20 degrees above normal. The first 10 days of October were the second warmest on record at Indianapolis, bested only by Oct. 1-10, 1879.

The passage of a cold front on Oct. 10 effectively flipped the script as high temperatures in the days to follow were 30 to 35 degrees below the high temperatures experienced just a few days prior. This pattern would linger for the rest of the month with highs predominantly in the 50s and lows in the 30s.

At Indianapolis, only five days would even rise above 60 degrees from Oct. 11 through the end of the month.

Many locations experienced their first of several frosty mornings Oct. 12-13 with a hard freeze impacting central Indiana on the morning of the 18th and effectively ending the growing season.

The cool weather experienced throughout the second half of October continued right on into November, producing one of the colder Novembers on record in recent memory and highlighting that there would not really be a true fall across the area this year. In fact, other than November 2014, this was the coldest November on record in Indianapolis over the last two decades.

A raw and wet start to the month gave way to a brief milder period with highs in the 50s to around 60 from Nov. 3-6. As the second week of November began however, temperatures tumbled, with daily highs in the 30s and 40s common over the following two weeks lasting through Thanksgiving Day.

Low temperatures were frequently in the 20s with even a few nights in the teens throughout this period. Temperatures turned mild once again right after Thanksgiving, albeit briefly, with highs warming into the 50s.

Indianapolis only made it to 60 on one day during the month, the first time there had been so few 60 degree-plus days in November since 1976. Ten days during the month had highs at or below 40, the second most in November since 1997. Maybe even more remarkable, there have only been seven days in November since 1970 with highs at or below 25. One of those days came on the 27th when the high reached just 25 in Indianapolis.

Overall it was the 33rd wettest fall on record at Indianapolis. The total rainfall this fall was 11.45 inches, 1.51 inches above the normal fall rainfall total of 9.94 inches.

Record monthly rainfall fell in portions of south central Indiana during September with totals in central Indiana above normal. Monthly amounts ranged from less than 1.50 inches in portions of northeast Indiana to near 14 inches in south central Indiana. Much of central and southern Indiana received between 4 and 8 inches of rainfall in September, while northern Indiana received only 2 to 4 inches in most areas.

A trace of wintry precipitation fell in portions of central Indiana on Oct. 12, the earliest the Indianapolis area had seen wintry precipitation since Oct. 9, 1925.

Much of the precipitation the first 10 days of October fell in west-central and northern Indiana. Rainfall totaled 2-5 inches for the six-day period from Oct. 5-10.

Ice accumulations of 2 to 3 tenths of an inch from the evening of Nov. 14 through the next morning were highly unusual for November in central and southern Indiana and necessitated the issuance of a rare Ice Storm Warning.

The official outlook for the 2018-19 winter season (December-February) from the Climate Prediction Center, indicates slightly better chances for near to below-normal temperatures across central Indiana. At Indianapolis, the average temperature for the winter season is 30.5 degrees. The outlook also calls for a greater chance of below-normal precipitation. The average precipitation is 8.15 inches with 22 inches of snowfall.

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