textproduct: Indianapolis

KEY MESSAGES

- Patchy fog, locally dense, this morning

- Warm and dry this weekend

- Severe thunderstorms possible from mid afternoon Monday into Monday night

- Cooler temperatures expected late next week

FORECAST UPDATE

Issued at 921 AM EDT Sat Apr 25 2026

Surface analysis this morning shows strong high pressure in place over WI, providing cooler northerly flow across Central Indiana. GOES16 shows some lake cloud over NW Indiana. A stream of higher clouds were found across the southern and eastern half of Indiana...associated with the departure of yesterday's system. Aloft, water vapor showed deep low pressure aloft over Saskatchewan, and weak ridging in place over Illinois, Indiana and the Great Lakes. This was resulting in west-southwest flow aloft over the plains streaming toward Indiana. Temperatures were mainly in the 50s.

This afternoon with the upper ridge in place over Illinois and Indiana, subsidence will be predominate. This results in a very dry air mass as indicated by forecast soundings. Thus a mostly sunny afternoon with highs in the middle 70s is expected. Overall, ongoing forecast remains in good shape.

DISCUSSION (Today through Friday)

Issued at 304 AM EDT Sat Apr 25 2026

A cold front passed through Indiana yesterday, but the air mass change has yet to occur. Winds have diminished becoming light and variable. High boundary layer moisture content remains following widespread rainfall earlier. Despite thin cirrus, fog has been gradually developing across much of the area. Fog has become locally dense, especially in favored areas such as within river valleys. Thickening cirrus and a gradually increasing northerly wind should help keep dense fog patchy through morning.

Surface high pressure builds to our north allowing winds to become northeasterly later today. Mainly clear skies should help temperatures rebound nicely even with cooler air advecting from the Great Lakes region. Highs both today and tomorrow are expected to climb into the mid 70s. Lows dip into the upper 40s/low 50s each night.

MONDAY'S SEVERE WEATHER POTENTIAL

Guidance is in good agreement showing a potent shortwave trough ejecting out of the Rockies late Sunday. This feature moves northeastward fairly quickly, passing to our north Monday evening. Surface cyclogenesis progresses rapidly on Monday over the Great Plains, with the resulting low strengthening to between 990-998mb. Such deepening will help drive a potent mass response, lifting a broad warm/moist sector rapidly northward. Additionally, a developing low-level jet (LLJ) is modeled to strengthen through the day Monday and especially into Monday evening.

Convection fires up over Illinois later Monday afternoon. Most of the day looks to be dry here in Indiana, with storms arriving as early as 6-8pm at the Indiana/Illinois state line. The environment within the warm sector can be characterized by moderate to high levels of instability and strong effective wind shear. Model soundings show steep lapse rates with MLCAPE values between 2000-300 J/Kg, though this decreases a bit after sunset to 1000-2000 J/Kg. Model hodographs are long and curved during the afternoon, elongating further as the LLJ ramps up after 00z. Corresponding 0- 1km SRH values between 200-300 m2/s2 are shown, peaking after 00z.

Model shear vectors are roughly SW to NE, which aligns with the system's surface cold front. Given the shear present and the shape of the hodograph, convection over Illinois likely becomes supercellular quickly after initiation. Given the orientation of the shear vector, however, quick upscale growth also appears likely. Looking at potential hazards, all hazards appear possible especially over Illinois. Large hail, tornadoes, severe wind gusts, and flooding are possible with any supercell that develops and remains discrete. Upscale growth into a line/MCS is probable by the time convection reaches Indiana. Severe wind gusts are likely the primary hazard over Indiana. However, given the very large amounts of 0-1km SRH, relatively low LCLs, and a strengthening south to north LLJ...a QLCS tornado threat may develop and mesoscale conditions will need to be monitored very closely.

Storms likely weaken with eastward extent as they outpace the best forcing and instability. Therefore, the best chance of severe weather currently looks to be over the western half of our CWA, though this could easily change.

TUESDAY ONWARD

A second shortwave ejecting from the Rockies closely behind Monday's may provide another chance at showers and storms. However, given the potency of Monday's system, much of the moist unstable air will have been swept away by the time the second system arrives. Sufficient moisture return may be possible for storms over the southern half of Indiana late Tuesday. Severe weather may again be possible should this occur, especially further south, but this depends on how quickly moisture and instability can advect back northward.

After Tuesday, persistent troughing aloft takes hold and cooler conditions are favored for the second half of the week. High temperatures in the 60s (which is right around average) and lows in the 40s appear likely Wednesday through Saturday.

AVIATION (12Z TAF Issuance)

Issued at 638 AM EDT Sat Apr 25 2026

Impacts:

- Fog this morning before 12z at BMG. LIFR conditions possible.

- IFR stratus near LAF this morning. - Becoming breezy this morning, wind gusts up to 20kt.

Discussion:

Patchy fog has diminished across most of central Indiana, with only BMG under 1 mile visibility as of 11z. Fog has lifted into a low stratus deck near LAF, with ceilings around 800 feet. Improvement is expected after sunrise with a quick return to VFR.

Some diurnal cumulus likely develops this afternoon but will remain FEW or SCT. Guidance hints at low-level stratus arriving from the northeast overnight into Sunday morning, potentially becoming BKN at times.

Winds become east-northeasterly overnight tonight into Sunday morning, remaining breezy between 5-10kt.

IND WATCHES/WARNINGS/ADVISORIES

None.