Snow began falling in central Indiana during the afternoon hours and continued into the evening. The snow was briefly heavy at times, reducing visibility for travelers.
Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS IND wrote it up.
Snow began falling in central Indiana during the afternoon hours and continued into the evening. The snow was briefly heavy at times, reducing visibility for travelers. Warm ground temperatures melted some of the snow as it fell, and warm road temperatures helped keep most roads clear. As the sun angle decreased during the latter portions of the evening, snow began to stick more readily on elevated surfaces which led to sporadic tree damage and power outages as tree limbs weighed down by spring buds snapped under the weight of the wet snow. Power outages peaked at over 12,000 outages across the state with 2 counties issuing travel advisories during the event. The cold weather that night likely led to damage to spring fruit crops, but the extent and cost is not known at this time.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Indianapolis, IN wrote its last area forecast discussion before the first event at Apr 20, 12:56 PM EST, 1 hour 4 minutes earlier.
Area Forecast Discussion National Weather Service Indianapolis IN 156 PM EDT Tue Apr 20 2021 ...Updated Aviation Discussion... ...SNOW EXPECTED THIS EVENING WITH SUB-FREEZING TEMPS TONIGHT... .Forecast Update... Issued at 959 AM EDT Tue Apr 20 2021 Conditions are evolving as expected this morning...with the cold front that passed last evening now stalled to our south, considerable cloudiness established over most counties, and a few light rain showers approaching the CWA's northwest corner. No changes made past minor tweaks to reflect recent observations. Conditions will deteriorate today from northwest to southeast...with rain chances increasing this morning across northwestern zones. Rain chances will slowly push along and southeast of the I-69 corridor this afternoon, while simultaneously rain mixes with and changes to snow north/west of I-69. A thin coating of snow/slush is likely late today on grassy/elevated surfaces north/west of the Indy metro. Still expecting accumulating snow for essentially the entire CWA this evening. && .Short Term...(Today through Wednesday) Issued at 221 AM EDT Tue Apr 20 2021 As of earlier this evening, the surface front has fully passed through central Indiana and is evidenced by the northerly winds across the area. Surface temperatures have dropped into the upper 30s to low 40s and will drop several more degrees by the morning. Aloft, a broad trough associated with a strong upper level low across eastern Canada continues to slowly approach the area with a well defined deformation zone and frontogenetical band currently stretching from northern Illinois down into eastern Kansas. This band will be the focal point for the expected snow later today. Current expectations for today are that the aforementioned frontogenetical band will arrive to the northwestern counties early this afternoon with precipitation initially falling as rain, but transitioning to all snow very quickly. This band will then slowly advance further into central Indiana through the afternoon into the evening. Temperatures along a line roughly along I-69 will be warmer than points to the northwest as the surface front meanders back to the northwest. How far that front moves will be key in determining where the rain/snow line develops and how long it takes for the rain to transition. Current thoughts are that evaporative cooling from the intense bands of snow will be enough to overpower the warmer temperatures further southeast, but that it may take along the order of a couple of hours vs the much shorter time further northwest. Model guidance continues to suggest that the heaviest amounts of snow is expected across the northeastern counties where 700mb omega values approach 20-ubar/s which indicates that the low to mid level ascent is incredibly strong. The big question will be how much the warm temperatures today and yesterday impact the overall efficiency of snow accumulation. Raw model output suggests 4-6 inches across the north and 2-4 across the central portions of Indiana. With the snow initially falling in temperatures of around 35 and ground temperatures in the mid to upper 50s, do think that a significant amount of the snow will melt as it falls, especially in the western counties. Later in the event and during periods of extremely strong banding, snow should be able to accumulate, but will quickly begin to melt post-event through the overnight hours even with the cool temperatures. Current thoughts are that the total snow depth at the end of the event will be 2-3 inches in the northeast with numbers gradually decreasing further south and more significantly to the west where the snow is falling earlier. Impacts from the snow will be fairly limited with the warm road temperatures and the fact that the majority of snow will be falling during the daytime hours or shortly after sunset. Road temperature models show that even across the north, road temperatures remain well above freezing through the period of expected snowfall. The biggest impact to travel will be the visibilities near zero at times with the heaviest bands. With all that in mind, have elected against a Winter Weather Advisory at this time and cut snow amounts to match the expected snow that will stick, vs total amount of snow that will fall. This snow band will be exiting the area shortly after midnight with much cooler air continuing to advect into the area through the overnight hours. No changes planned for the ongoing freeze warning with sub-freezing temperatures expected across the forecast area even with the expected cloud cover and fairly strong winds. Those factors plus the potential for snow on the ground may actually limit the overall effect of sub-freezing temperatures on some less sensitive vegetation. Going into the day Wednesday, scattered rain showers are expected to develop during the afternoon. Model soundings show a very cool airmass aloft with a nearly dry adiabatic lapse rate up to nearly 600mb and non-zero CAPE. Convective temperatures are only 38 near Indianapolis which will easily be achieved by early afternoon. Can't rule out an isolated thunderstorm with this set-up, but with a fairly stable airmass above 600mb, clouds will struggle to get tall enough to produce lightning, but small graupel looks probable in stronger showers. Had this system moved through during the heart of winter, snow squalls would certainly have been in play for Wednesday. Raw models output indicates a snowpack across most of the area through the day Wednesday, but even with the expected cloud cover, this makes no sense with the strong sun angle of April. Increased temperatures quite a bit above guidance to mitigate the feedback caused by the snow. && .Long Term...(Wednesday night through Monday) Issued at 221 AM EDT Tue Apr 20 2021 The unseasonably cold temperatures will be the story to start on Wednesday night with a deep upper level low pressure situated over the eastern Great Lakes. This feature will shift east into New England by Friday but its location in tandem with a cold...cyclonic flow aloft will support another night with subfreezing temperatures across much of central Indiana Wednesday night and Thursday morning. Initially...scattered convective showers that develop Wednesday afternoon will likely linger into the evening hours before diminishing overnight as forcing aloft shifts east. Despite clouds likely lingering in parts of the forecast area for much of Wednesday night...a freeze watch is warranted. Thursday will remain cool but with influence loosening from the departing upper low...return of high pressure...sunshine and drier air will allow temperatures to recover into the 50s. Frost potential is present again Thursday night with light southwest flow... especially across the northeast half of central Indiana where clouds will take longest to arrive in advance of an upper level wave approaching from the mid Mississippi Valley. This feature will drift into the lower Ohio Valley and may bring scattered light rain showers to the western counties as the system interacts with a drier boundary layer. Low pressure will track from the southern Plains on Friday across the Tennessee valley and into the Mid Atlantic states by Saturday evening. Despite northern and southern stream flow aloft being slightly out of phase...deeper moisture will advect across the Ohio and Tennessee Valleys Friday night and Saturday with widespread rain. Drier weather returns for the second half of the weekend into early next week as high pressure moves across the region. Temperatures will remain below normal through the bulk of the extended with highs predominantly ranging from the 50s into the lower 60s. However...there is light at the end of the tunnel as substantial warming takes place once the high pressure shifts east of the area early next week. Broad southerly flow will commence in response to a deep surface wave ejecting out into the High Plains next Tuesday...signaling a shift to a warmer and more active regime for much of the country east of the Rockies into the Great Lakes and Ohio Valley for most of next week. At this early stage...high temperatures likely rise back into the 70s for all of central Indiana by next Tuesday and Wednesday. && .Aviation...(18Z TAF Issuance) Issued at 150 PM EDT Tue Apr 20 2021 IMPACTS: -Rain will quickly transition to snow with embedded periods of heavy snow this evening -IFR/MVFR ceilings likely, with brief LIFR visibility possible at all sites this evening -Winds from 350 to 010 around 7 to 11 kts this evening, including brief gusts of 15-20 kts this evening DISCUSSION: A quick-moving, yet briefly potent rain-to-snow event will impact central Indiana this afternoon and evening. Rain, which has been falling around KLAF since 15z, will advance to the southeast this afternoon...before quickly transitioning to snow at all sites... except KBMG where a rain/snow mix should persist. Deteriorating VIS during the main burst/changeover of precipitation will drive down flight rules to IFR/MVFR by 23z at all sites...with brief LIFR during periods of moderate/heavy snow. Mist/fog will also contribute to low visibility. Ceilings meanwhile will also drop to IFR/MVFR during the main batch of precip. Lighter rain showers will precede the main event...with vicinity snow showers as the event tapers off later this evening. Conditions will improve to MVFR by 3-4z at all sites as the system's main forcing pushes eastward. VFR should return pre-dawn at KHUF/KIND as the system's dry conveyor nudges into the region from the southwest. Winds will generally be northerly through the end of the event later this evening...at speeds of 7 to 11 kts, with brief gusts of 15-20 kts during heaviest precipitation. Winds will back to NW/W Wednesday morning at 5-8 kts. && .IND WATCHES/WARNINGS/ADVISORIES... Freeze Watch from late Wednesday night through Thursday morning for INZ021-028>031-035>049-051>057-060>065-067>072. Freeze Warning from 10 PM this evening to 10 AM EDT Wednesday for INZ021-028>031-035>049-051>057-060>065-067>072. && Update...AGM Short Term...White Long Term...Ryan Aviation...AGM
Hazardous Weather Outlook National Weather Service Indianapolis IN 1208 PM EDT Tue Apr 20 2021 INZ028-029-035-036-043>047-051>057-060>065-067>072-211615- Warren-Tippecanoe-Fountain-Montgomery-Vermillion-Parke-Putnam- Hendricks-Marion-Vigo-Clay-Owen-Morgan-Johnson-Shelby-Rush-Sullivan- Greene-Monroe-Brown-Bartholomew-Decatur-Knox-Daviess-Martin-Lawrence- Jackson-Jennings- Including the cities of Williamsport, West Lebanon, Lafayette, West Lafayette, Attica, Covington, Veedersburg, Crawfordsville, Clinton, Newport, Rockville, Greencastle, Plainfield, Brownsburg, Danville, Indianapolis, Terre Haute, Brazil, Clay City, Spencer, Martinsville, Mooresville, Greenwood, Franklin, Shelbyville, Rushville, Sullivan, Linton, Bloomfield, Bloomington, Nashville, Columbus, Greensburg, Vincennes, Washington, Loogootee, Shoals, Bedford, Mitchell, Seymour, Brownstown, and North Vernon 1208 PM EDT Tue Apr 20 2021 ...FREEZE WARNING IN EFFECT FROM 10 PM THIS EVENING TO 10 AM EDT WEDNESDAY... This hazardous weather outlook is for central Indiana. .DAY ONE...This Afternoon and Tonight. Rain will quickly transition to snow this afternoon into the evening. Warm ground temperatures will limit snow accumulations to around an inch or less. During heavier snow showers, visibilities will likely drop below a quarter mile. Temperatures will drop into the upper 20s to low 30s tonight causing a widespread freeze. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Sub-freezing temperatures likely to return Wednesday night. .SPOTTER INFORMATION STATEMENT... Snowfall reports will be appreciated late Tuesday afternoon and night. && More information, along with other weather, hydrological and climate information can be found at http://weather.gov/ind INZ021-030-031-037>042-048-049-211615- Carroll-Clinton-Howard-Boone-Tipton-Hamilton-Madison-Delaware- Randolph-Hancock-Henry- Including the cities of Delphi, Flora, Frankfort, Kokomo, Lebanon, Zionsville, Tipton, Fishers, Carmel, Noblesville, Anderson, Muncie, Winchester, Greenfield, and New Castle 1208 PM EDT Tue Apr 20 2021 ...FREEZE WARNING IN EFFECT FROM 10 PM THIS EVENING TO 10 AM EDT WEDNESDAY... This hazardous weather outlook is for central Indiana. .DAY ONE...This Afternoon and Tonight. Rain will quickly transition to snow this afternoon into the evening. Snow may quickly accumulate to around 1-3 inches before beginning to melt during the overnight hours. During heavier snow showers, visibilities likely will drop under a quarter mile. Temperatures will drop into the upper 20s to low 30s tonight causing a widespread freeze. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Sub-freezing temperatures likely to return Wednesday night. .SPOTTER INFORMATION STATEMENT... Snowfall reports will be appreciated late Tuesday afternoon and night. && More information, along with other weather, hydrological and climate information can be found at http://weather.gov/ind AGM
The national radar mosaic for the moment the first event began.
1 winter weather. Local standard time, as filed.
Widespread minor tree damage across the county as a result of wet snow load on trees that had begun to bud. Snow amounts ranged from 2-4 inches with the higher amounts generally only located on elevated surfaces.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Indiana in 2021Every state in 2021This day in weather historyWarnings in Indiana, April 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 944955.