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Forecast Discussion for Indianapolis, IN
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634 FXUS63 KIND 281914 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 314 PM EDT Tue Apr 28 2026 .KEY MESSAGES... - Showers and thunderstorms expected tonight with a threat for heavy rainfall and isolated large hail in southern portions of central Indiana. - Flooding threat on area rivers will continue across southern Indiana after multiple rounds of heavy rainfall. - Below normal temps for late this week into the weekend. - Frost possible this weekend. - Slow warm up with rain chances returning early next week. && .DISCUSSION (This evening through Tuesday)... Issued at 314 PM EDT Tue Apr 28 2026 Tonight.... Scattered to numerous TS over Missouri are associated with a broad WAA pattern ahead of a shortwave trough moving through the central Plains. This activity will continue to be supported by elevated instability (MUCAPE from 1000-2000 J/KG) while shifting eastward into southern half of IL into the evening hours. Recent RAP mesoanalysis shows the northward extent of the moderate elevated instability is further north that most of the CAM/12Z HREF guidance suggested. Therefore, unlike the bulk of guidance which shows less than 500 J/KG of MUCAPE across the far south parts of the central IN, expecting with a feed of 8-8.5 C /KM mid level lapse rates coupled with an increasing low level jet expected to form in the wake of the Ozarks this evening, MUCAPE values will be roughly double these values running from 500 J/KG near I-70 to near 1000 J/KG down near the US 50 corridor. Also as a result of the increased instability, the forecast has gone more bullish with TS chances across the southern portions of the forecast area as well as including the mention of locally heavy rainfall. SPC Day 1 outlook maintains a marginal risk for severe hail in the far southern portions of the forecast area, but believe that the severe hail threat is 50-100 mi further north accounting for the greater instability. Regarding the heavy rainfall threat, soil moisture values across the southern portion of the forecast area are running between 50 and 70 percent saturated. Thus it will not take much rain for flash flooding. OHRFC flash flood guidance has most of this area in 1.5 to 2 inch/6hr and 1.5 inch/3 hr. A Flash Flood watch was considered, but given some uncertainty in reaching at least 1.25-1.5 inch QPF overnight, opted to not issue and to let later shifts reassess for the potential for more cell training and higher amounts. Wednesday through Friday... An unsettled and cool pattern will set in for the remainder of the work week as broad NW flow and several weak mid level perturbations move across the region around a longwave trough centered over eastern Canada/CONUS. Just ahead and in the wake of the first shortwave on Wednesday, CAA and wrap around scattered light showers are expected in eastern zones during the afternoon. Skies should be mostly clear Thursday. Low PoPs were added for Thursday Night to account for the consensus timing of another shortwave which will move SE across the region pinwheeling around the closed low centered south of Hudson Bay. Saturday/Sunday... As the closed low/long wave trough move gradually east, surface high pressure will build southward from the northern Plains. The high pressure ridge axis will be just to the northwest of the forecast area on Saturday morning, with the potential for some low clouds and winds remaining 5-10 mph. By Sunday morning, the surface high ridge axis shifts to nearly over central Indiana per the Euro, but slightly south of the central Indiana per the GFS. Either way, temps are expected to be well below normal this weekend with generally light winds and clear skies. A dry airmass with dewpoints near 32F will favor the potential for patchy and possibly more widespread frost, especially in outlying areas both mornings. Highs near 60F (about 10 deg below normal) are expected for afternoon highs. Early next week... Guidance is mixed on the timing of additional shortwave energy moving out of Canada. In the wake of high pressure, expect at least a slight warmup to near normal temperatures Monday and Tuesday. NBM has low PoPs for Monday into Tuesday based on smoothing out the timing of weak shortwaves in the W-NW flow aloft. Given a frontal intrusion in the Gulf this weekend, moisture return will be meager and any precipitation should be primarily showers with isolated sub- severe TS possible. && .AVIATION (18Z TAF Issuance)... Issued at 142 PM EDT Tue Apr 28 2026 Impacts: - MVFR ceilings early this afternoon gradually ending - Scattered TS tonight at all but KLAF. - MVFR ceilings return late tonight at all sites with IFR conditions expected at KBMG. Discussion: MVFR ceilings around 025 will continue to diminish the next few hours, and should end no later than 22Z as an area of cirrus clouds and subsidence move in from IL. Attention turns to the developing round of showers and thunderstorms later tonight. TS Activity is expected to be concentrated over the southern half of Indiana and in these areas have upped the wording to TEMPO for -TSRA overnight, generally in the 03-08Z time period. After the TS threat diminishes, light rain will continue through mid morning Wednesday with lowering ceilings into the MVFR category. Ceilings are expected to fall to upper IFR range at BMG, with the remainder of the TAF sites remaining in lower end MVFR range. Ceilings will improve gradually in the late morning with VFR conditions expected at KIND by early afternoon. Winds will be out of the west this afternoon with a few gusts from 15-18 kts. Winds will gradually shift overnight becoming light and variable as low pressure moves across the Ohio Valley. In the wake of the low passage, winds will shift to the N-NW by late tomorrow morning and increase during the afternoon. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ AVIATION...Crosbie DISCUSSION...Crosbie |
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