Heat, humidity and storms for Wednesday

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Humidity surges, along with temperatures, Wednesday ahead of a cold front. The front is located approximately 700 miles from Indianapolis as of Tuesday evening.

A narrow line of decaying thunderstorms may enter western portions of Indiana around sunrise Wednesday morning, bring a small chance of rain for some.

Temperatures will quickly warm up through the day with high temperatures topping out in the lower to middle 90°s – thanks in part to compressional warming from the cold front approaching central Indiana.

Forecast high temperature Wednesday.

Once you factor in the higher humidity, the heat index will climb to the upper 90°s to around 100° by late afternoon.

With the amount of heat and humidity in place, the atmosphere should become very unstable, especially late afternoon and in to the evening.

Forecast Convective Available Potential Energy Wednesday evening.

The one thing needed to get thunderstorms going in this kind of environment is some lift.  We can get that from the cold front, however the problem is that the front is not expected to move through central Indiana until late Wednesday night in to early Thursday morning.  We will have to keep an eye back in to Illinois to see if a line of thunderstorms flares up and moves in to Indiana Wednesday night.

At this time there is some question if a line of thunderstorms can make it in to the Hoosier state.

The Storm Prediction Center (SPC) does include portions of central Indiana in a “Slight Risk” for severe thunderstorms Wednesday evening.  That being said, the latest data from SPC suggests a 1%-2% probability for severe thunderstorms in Indiana for any three hour period Wednesday afternoon and in to the night.  Right now, I think the best chance for severe thunderstorms will be back in Iowa and Illinois.

If we do have thunderstorms in Indiana during the afternoon and in to the night, the main threat will be damaging winds and small hail.  The storms will also have the potential to drop copious amounts of rain if you get caught underneath one.


If you’ve thought it has felt humid this month you aren’t wrong.  I went back and looked at hourly weather observations over the previous 30 years.  It turns out that this ranks as the 4th highest humid July to date in 30 years for Indianapolis.  I defined “humid” as the number of hours spent at or above a 70° dew point temperature.  Through 6 p.m. Tuesday the capital city has spent 121 hours with 70°+ dew points this month.  In comparison, the 30-year average is 54 hours.

Number of hours spent at 70°+ dew points July 1-9:

  1. 1993: 150
  2. 1999: 145
  3. 2018: 124
  4. 2019: 121


The cold front that passes early Thursday morning will bring some relief in the humidity Thursday and Friday.  While it won’t completely dry out the air, dew points will fall from the 70°s Wednesday to the middle 60°s Thursday evening to the upper 50°s by early Friday morning.

Humidity will begin to come back Friday night and stick around through at least the middle of next week as dew points are projected to rise in to the lower and middle 70°s.  Combine that with temperatures in to the lower 90°s this weekend through early next week and the heat index – or the feels like temperature – should top out around 100°.

We will keep an eye on what could become Tropical Storm Barry, along the Gulf Coast, to see if it will impact central Indiana.  Long range computer models suggest it could bring rain to central Indiana middle of next week.

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