September 2012 Climate Summary

Central Indiana
September 2012
Climate Summary
41st Coolest on record at Indianapolis
5th Wettest on record at Indianapolis
The warmest temperatures of the month occurred over the first week as high temperatures routinely climbed into the 80s. The presence of the remnants of Hurricane Isaac over the region contributed to a humid tropical airmass over central Indiana as well. The passage of a strong cold front on the 7th ushered in cooler and drier air with highs mainly in the 70s and lows in the 50s through the 11th. High temperatures returned to the 80s for the 12th and 13th before another frontal passage knocked highs back into the 70s. For most of central Indiana, the 13th was the last day with highs in the 80s for the month.
The pattern across the lower Great Lakes and Ohio Valley transitioned to an upper level trough during the middle of the month, allowing cold fronts and cooler air to overspread much of the region during the second half of September. High temperatures across central Indiana after the 16th were rarely any higher than 75 degrees and on several days, remained in the 60s. Low temperatures from the 18th through the 22nd dropped into the 40s, culminating with several locations bottoming out in the 30s on the mornings of the 23rd and 24th as cold high pressure set up over the region. Many locations in central Indiana received their first frost on the 24th, making for one of the earliest occurrences on frost on record. Lows at Lafayette and Terre Haute approached the freezing mark on the 24th.
September 2012     Avg Temp
September 2012 Difference from Normal
Lowest Temperature
88 on 4
39 on 23 and 24
88 on 4
33 on 24
86 on 4 and 6
36 on 24
Terre Haute
90 on 4
34 on 24
89 on 4 and 7
35 on 23 and 24
89 on 4
35 on 24
Indy – Eagle Crk.
86 on 4 and 6
37 on 24
At Indianapolis, there were 13 days with above normal average temperatures and17 days with below normal average temperatures.
September 2012 was the 41st coolest in the Indianapolis area since 1871.

The wet weather pattern of August continued in much of Indiana during September.   Monthly rainfall was normal to much above normal in central and southern Indiana and generally below normal in northern Indiana. Precipitation totals ranged from 4 to more than 12 inches in central and southern Indiana, while totals in northern Indiana measured only 1 to 3 inches. Much of southwest, central and east central sections of Indiana were the wettest areas in September. Many locations in these areas received 5 to more than 8 inches of rainfall. As during August, much of northern Indiana missed any significant rainfall and received around 2 inches during the month. Normal rainfall for September is between 2 and 4 inches.
There were two widespread rainfall events during September that covered much of central and southern Indiana. The remnants and moisture from Hurricane Isaac produced rainfall of 1 to more than 4 inches from the 1st through the 8th. The last rainfall event of the month was a result of a series of low pressure areas that moved along a stationary front located in central Indiana. These systems dumped 1 to more than 6 inches from the 25th through the 27th
Between these two widespread rainfall events, there were three lesser events. Rainfall of 1 to 4 inches occurred on the 14th, 17th -18th and the 21st in portions of the state. The storms during the evening of the 21st produced significant hail in parts of central Indiana. Several locations in Hendricks, Marion and Hancock Counties measured hailstones with a diameter of one-half to slightly more than an inch. In a few areas the hail storm lasted for at least 10 minutes and deposited 1 to 2 inches of hail.
Drought conditions were greatly diminished over much of central and southwest Indiana by the end of September. Drought conditions continued to improve in south central and southeast Indiana, but remained largely unchanged in northern Indiana.   At the end of the month, stream flow was above seasonal levels in much of central and southern Indiana, while below normal in northern Indiana and along the Wabash River from Terre Haute to near Vincennes.   Except for Cecil Hardin Reservoir in west central Indiana, local area reservoirs ranged from normal to less than 3 feet below capacity.
September 2012 Precipitation
September 2012 Difference from Normal
Wettest Day
Longest Dry Stretch
2.71 on 7
 5 days 9-13
1.00 on 7
 4 days 27-30
2.20 on 7
 4 days 10-13
Terre Haute
1.55 on 7
 4 days 9-12
2.00 on 2
 5 days 9-13
2.46 on 7
 5 days 9-13
Indy – Eagle Crk.
2.44 on 7
 5 days 9-13
September 2012 was the 5th wettest in the Indianapolis area since weather records began in 1871.
Severe Weather
Strong thunderstorms impacted central Indiana on the 1st and 2nd as the remnants of Hurricane Isaac moved into the Ohio Valley. A weak tornado dropped down briefly near 16th Street and the White River just to the northwest of downtown Indianapolis on the evening of the 2nd. No damage was observed. Two thunderstorm complexes impacted central Indiana on the afternoon and evening of the 7th ahead of a cold front. The first complex moved across northern portions of central Indiana, producing pockets of wind damage and small hail. The second and larger thunderstorm complex moved across much of the area during the evening, producing damaging winds and torrential rainfall producing localized flooding. Wind gusts in excess of 60 mph were reported in Lebanon in Boone County and Hayden in Jennings County as the storms arrived. Several locations received in excess of 3 inches of rainfall from the storms on the evening of the 7th.
A mini-supercell develop over eastern Illinois on the afternoon of the 21st, intensifying and moving across central Indiana during the evening. The storm produced large hail throughout much of its track across the region, including some reports of hail covering the ground. The storm was at its most intense across Hendricks County and especially from near Danville through Brownsburg. Golf ball size hail along with wind gusts of 65 to 70 mph.
For information on severe weather in other areas during September, visit the Storm Prediction Center “Severe Weather Event Summaries” website at
The maximum wind gust at Indianapolis International Airport was 39 mph out of the northwest on the 7th associated with thunderstorms in the vicinity of the airport. A second 39 mph gust was recorded on the 22nd in the wake of a cold frontal passage. Fog or haze was reported at Indianapolis on 22 days during the month, with dense fog recorded on the 6th. Thunder was reported on 3 days during September.
October 2012 Outlook
The official outlook for October 2012 from the Climate Prediction Center indicates a greater chance of below normal temperatures for central Indiana.  At Indianapolis, the average temperature for the month is 55.0 degrees. The outlook also calls for a greater chance of above normal precipitation. The average precipitation for October at Indianapolis is 3.12”.
Data prepared by the Indianapolis Forecast Office.

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