Hottest May ever featured 25.5-degree jump over April

The National Weather Service has confirmed what a lot of Hoosiers already knew -- May 2018 was the hottest month of May ever recorded in Indiana.

Official totals released by the NWS also report May 2018 as the ninth-driest May in Indiana weather history. The NWS began keeping records in 1871.

Perhaps the most revealing number in the new report is that following one of the coldest Aprils in years -- when the average temperature in the Indianapolis area was 47.1 degrees -- the average May temperature soared to 72.6 degrees. That’s an incredible 25.5-degree difference in one month.

After persistent chilly weather impacted central Indiana in March and April, a complete about-face occurred in May, thanks to a large high pressure ridge that developed across the Ohio Valley. The result was much warmer temperatures all month with highs and lows resembling summer. Average temperatures were generally eight to 10 degrees above normal for the entire month.

The coolest weather of the entire month occurred the first week of May, and wasn’t even all that cool. A combination of increased cloud cover and a few days with at least some rain kept highs in the 70s and low 80s. After May 8, however, the more summer-like pattern took hold and largely persisted the rest of the month.

Amazingly, after May 8 Indianapolis would only have one day, May 18, where highs remained below 80 degrees. Additionally, the first morning of the month would be the only one with a low under 50. Other locations across central Indiana would see a few mornings fall into the 40s during the first 10 days of the month but beyond that, the entire area would see lows no cooler than the 50s.

Indianapolis broke several May records as a result. The average temperature of 72.6 degrees obliterated the previous warmest May on record -- occurring back in May 1896 -- by nearly two degrees.

For the month, 25 days experienced highs at or above 80 -- also a record. All 31 days of the month would end up above normal, the first time that had occurred in any month in Indiana since July 2012, the hottest month on record.

Meanwhile, the high of 88 degrees on May 13 marked the warmest Mothers Day on record, while the sizzling 95 registered on May 28 easily established the warmest Memorial Day ever at Indianapolis, and marked the third warmest May day ever. It was also the warmest temperature experienced in May since May 28, 1911 when the high hit 96.

Meanwhile, monthly rainfall totals ranged from slightly over an inch in central Indiana to nearly 10 inches in southwest and extreme north central Indiana. Monthly rainfall was much below normal across most of the state. It was the driest May since 1988 for Indianapolis.

Rainfall during the first two weeks of May was concentrated in northern Indiana. Much of this area received three to eight inches of rainfall during this time, while most of central and southern Indiana measured less than an inch. A dry spell prevailed over most of the state from May 15-28 with most areas receiving less than an inch of rain.

Rainfall during the first 28 days of May in many areas of central and southern Indiana totaled from 0.5 to 3.0 inches -- less than half of the normal.

Greencastle totaled .71 inches over the May 1-29 period and 1.43 inches for the entire month after .70 inches of rain fell on May 31.

The remains of Tropical Storm Alberto and other weather systems brought needed rains to the state May 29-31 as rainfall ranged from a trace in portions of east-central Indiana to five inches in southwest Indiana.

Looking ahead, the official outlook for June 2018 from the Climate Prediction Center indicates a much greater chance for above normal temperatures for central Indiana. At Indianapolis, the average temperature for the month is 72 degrees.

The June outlook also calls for an equal chance of near, above- or below-normal precipitation. The average precipitation for June at Indianapolis is 4.25 inches.