textproduct: Indianapolis

KEY MESSAGES

- Rain spreads north across much of central Indiana today with continued below normal temperatures. Some potential for localized flooding in SE portions of central Indiana this evening and tonight.

- Rain chances continue through the holiday weekend into next week, but temperatures will become above normal for much of the period.

DISCUSSION (This evening through Friday)

Issued at 128 PM EDT Fri May 22 2026

Today and Tomorrow...

For this weekend, central Indiana will be within an active portion of a subtropical jet streak, of which will aid in the development of shortwaves and therefor multiple chances for rainfall. The first of which is passing through today and tonight. This particular shortwave is ejecting out of the Gulf with abundant moisture throughout. The enhanced diabatic processes of this gulf low will aid in low level pressure depletion over the next 12-24 hours, resulting in a more mature surface low late today and tonight.

Initial rainfall is expected to be associated with weak frontal convergence in the 850-700mb layer as dry NE flow interacts with very moist SE flow over the Ohio Valley. Current radar and IR imagery showcase this well with widespread rain along the OH/IN border quickly surging northward. This rain is expected to be in the Indianapolis area around 2PM Friday afternoon. Consistent light to moderate rainfall is expected to be the norm for most of the afternoon and early evening over the SE half of cenral Indiana with the one exception being a low chance for thermodynamically enforced convection over far southern central Indiana. However, late this evening and tonight, slantwise instability in the front right quadrant of the advancing low will aid upward lift, likely promoting a period of moderate to heavy rainfall and isolated lightning production.

When all is said and done, total rain amounts will vary across the region, but generally those S/E of I-69 are expected to get 0.5-1.5" with lesser amounts to the N/W. The CSI banding potential overnight could lead to narrow corridors of 2-3 inches, of which will create a low end flooding threat given already saturated soils from prior rainfall.

A quasi stationary boundary will linger north of central Indiana following the passage of the wave. Along and south of this boundary, there will be enough moisture and instability for isolated convection to occur, but the only forcing will likely be associated with microscale fluctuations and weak synoptic lift within the entrance region of the subtropical jet. The current expectation is for a large majority of central Indiana to remain dry tomorrow, with a few areas seeing a brief shower or storm in the morning to early afternoon.

Sunday...

The next shortwave will arrive from the West late Saturday night through Sunday. Moisture with this wave passage will not be as abundant, but with antecedent dew points already in the mid to upper 60s, there should be enough instability for convective initiation to occur as the wave passes through. High resolution guidance is mixed on wave timing as of 12Z Friday. Specifically for Indianapolis there is a range from 15-18Z start time and a 20-00z end time for storm chances. Given weak shear within the passing wave along with 500- 1000 J/kg of SBCAPE, isolated strong to severe thunderstorms can also not be ruled out during this timeframe. After the wave passes through Sunday late afternoon/evening modest subsidence should quickly reduce rain chances with dry weather expected Sunday evening and night.

Temperatures will likely be slightly warmer Sunday with weak southerly flow returning, but will greatly depend on where convection and related cloud cover occurs. General expectation is for afternoon highs in the upper 70s.

Memorial Day onward...

Following Sunday's wave passage, amplified ridging will start to build over the Southern Appalachia to the Ohio Valley regions decreasing upper level forcing. However, in the lower levels, a stagnant boundary is expected to develop near the Ohio River. Weak forcing and remnant moisture along the boundary will likely induce a scattered showers Monday through Tuesday over this same area. Areas to the north (a majority of central Indiana) are expected remain dry. Temperatures look to be slightly above normal with some influence from the ridging to the east expected.

Forecast confidence decreases significantly Wednesday onward as ensembles introduce another wave entering the region from the west. Generally, this will increase PoPs for Wednesday, but specifics for this wave passage are still highly variable.

AVIATION (18Z TAF Issuance)

Issued at 128 PM EDT Fri May 22 2026

Impacts:

- Conditions deteriorate to IFR at most sites this afternoon - Showers spread north this afternoon - Wind gusts around 20kt at KLAF today

Discussion:

Moisture will continue to increase today, with gradually lowering ceilings. As low pressure approaches from the south this afternoon, showers will spread north across the sites. By 21Z, IFR ceilings and showers will be common. KLAF will take longer to reach IFR and will have the lowest chances for showers.

Isolated thunderstorms are possible this afternoon and evening, but coverage will be too low to mention in the TAFs. Best chances for thunder will be at KBMG. Low ceilings will persist into Saturday morning. Winds will stay easterly throughout the evening and tonight before quickly switching to westerly tomorrow morning.

IND WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for INZ071-072.