Indianapolis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Indianapolis clear sky chart from 2005-11-06 to 2026-07-01.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	14% 9% 3 8% 5% 4 4 4 5% 7% 35%	137166
	Night	15% 10% 4 8% 5% 4 4 3 5% 6% 36%	135368
Transparency	Day	45% 7% 12% 22% 13% 2	140763
	Night	46% 6% 11% 22% 14% 2	139846
Seeing	Day	20% 13% 29% 22% 12% 4	17800
	Night	20% 12% 29% 26% 12% 1	27615

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 14% 7% 13% 5% 4 4 3 5% 7% 23%	4691
	11th to 20th	Day	10% 13% 7% 15% 8% 8% 6% 4 4 4 22%	4710
	21st to end	Day	18% 16% 7% 13% 5% 5% 5% 4 3 4 20%	5413
February	1st to 10th	Day	18% 14% 6% 9% 5% 5% 4 3 4 5% 27%	2100
	11th to 20th	Day	15% 13% 4 10% 6% 6% 5% 3 5% 5% 28%	2048
	21st to end	Day	17% 14% 5% 9% 5% 3 3 3 5% 6% 32%	1730
March	1st to 10th	Day	20% 15% 6% 8% 4 3 3 2 3 4 32%	4580
	11th to 20th	Day	13% 10% 2 6% 4 4 4 3 5% 8% 42%	4918
	21st to end	Day	18% 11% 4 8% 5% 5% 4 3 5% 6% 31%	5833
April	1st to 10th	Day	17% 11% 3 8% 5% 4 4 3 5% 7% 34%	2520
	11th to 20th	Day	16% 9% 3 6% 5% 5% 4 3 6% 7% 36%	2494
	21st to end	Day	19% 8% 3 7% 4 4 4 4 4 8% 35%	2698
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 8% 30%	7616
	11th to 20th	Day	17% 6% 3 7% 5% 5% 4 3 5% 7% 39%	7626
	21st to end	Day	16% 8% 3 7% 5% 5% 5% 4 7% 8% 30%	8566
June	1st to 10th	Day	12% 6% 2 6% 6% 5% 5% 4 6% 8% 41%	2940
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 6% 9% 44%	2940
	21st to end	Day	11% 6% 2 6% 5% 5% 4 4 7% 9% 41%	2940
July	1st to 10th	Day	11% 6% 2 6% 4 4 4 5% 6% 11% 41%	6361
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 8% 11% 37%	6360
	21st to end	Day	11% 6% 2 8% 5% 5% 6% 5% 7% 9% 35%	6708
August	1st to 10th	Day	8% 5% 2 5% 3 4 5% 5% 7% 10% 47%	4234
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 4 8% 12% 40%	3986
	21st to end	Day	6% 5% 1 5% 4 4 4 3 6% 9% 52%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 4 4 3 6% 7% 47%	2367
	11th to 20th	Day	9% 5% 1 5% 4 4 4 4 6% 7% 50%	2200
	21st to end	Day	13% 5% 2 5% 4 3 4 3 5% 7% 48%	2200
October	1st to 10th	Day	12% 5% 2 5% 4 4 5% 3 5% 7% 49%	2200
	11th to 20th	Day	14% 7% 2 6% 4 3 4 4 5% 7% 44%	2042
	21st to end	Day	18% 9% 2 8% 4 4 4 3 5% 7% 35%	1980
November	1st to 10th	Day	9% 7% 3 6% 4 4 3 3 5% 6% 50%	1852
	11th to 20th	Day	17% 10% 4 7% 5% 4 4 3 4 6% 36%	1890
	21st to end	Day	20% 12% 4 8% 4 3 4 3 5% 5% 34%	1890
December	1st to 10th	Day	15% 12% 4 7% 4 4 3 2 3 5% 40%	3020
	11th to 20th	Day	18% 15% 5% 10% 5% 5% 5% 3 5% 6% 24%	3131
	21st to end	Day	27% 18% 7% 9% 5% 4 3 3 4 5% 14%	4070
January	1st to 10th	Night	16% 15% 6% 12% 5% 4 4 4 5% 5% 24%	8232
	11th to 20th	Night	11% 17% 6% 15% 7% 6% 5% 3 3 4 22%	8280
	21st to end	Night	18% 13% 5% 7% 5% 5% 4 4 4 5% 29%	8769
February	1st to 10th	Night	19% 12% 6% 9% 5% 4 4 3 5% 5% 28%	2520
	11th to 20th	Night	16% 12% 4 10% 5% 4 3 3 5% 5% 33%	2458
	21st to end	Night	19% 13% 4 8% 4 4 4 3 4 5% 32%	2076
March	1st to 10th	Night	20% 14% 3 6% 3 3 3 2 4 5% 37%	5493
	11th to 20th	Night	14% 7% 2 6% 4 4 4 3 4 7% 46%	5260
	21st to end	Night	19% 9% 3 7% 4 4 4 4 6% 7% 34%	5368
April	1st to 10th	Night	16% 10% 3 5% 4 3 5% 4 5% 7% 38%	2100
	11th to 20th	Night	16% 9% 2 6% 5% 4 4 3 5% 8% 40%	2075
	21st to end	Night	17% 7% 3 6% 4 4 5% 4 6% 6% 37%	1922
May	1st to 10th	Night	21% 9% 3 8% 4 5% 4 3 5% 6% 31%	5237
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 8% 41%	5234
	21st to end	Night	15% 7% 3 7% 5% 5% 6% 4 6% 8% 34%	5590
June	1st to 10th	Night	10% 6% 2 6% 5% 3 4 4 5% 8% 47%	1680
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 3 5% 8% 46%	1680
	21st to end	Night	7% 4 1 5% 5% 4 5% 5% 8% 9% 46%	1680
July	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 9% 47%	3618
	11th to 20th	Night	9% 4 2 6% 4 4 5% 4 7% 9% 46%	3617
	21st to end	Night	10% 6% 2 7% 4 5% 5% 4 6% 11% 39%	4151
August	1st to 10th	Night	10% 6% 2 5% 4 4 3 3 5% 8% 50%	2915
	11th to 20th	Night	8% 5% 2 6% 5% 5% 4 4 7% 8% 46%	3058
	21st to end	Night	4 4 2 5% 4 4 4 3 6% 8% 56%	3586
September	1st to 10th	Night	11% 6% 2 5% 4 4 3 3 5% 7% 50%	2012
	11th to 20th	Night	8% 4 1 5% 4 4 4 4 5% 7% 56%	2200
	21st to end	Night	13% 6% 2 5% 5% 4 3 3 5% 7% 48%	2200
October	1st to 10th	Night	9% 4 2 5% 4 4 4 3 5% 7% 55%	2200
	11th to 20th	Night	17% 6% 1 5% 4 3 4 2 4 6% 47%	2352
	21st to end	Night	18% 8% 2 7% 4 3 3 3 5% 7% 40%	2860
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 6% 5% 49%	2666
	11th to 20th	Night	14% 10% 3 6% 4 4 4 3 5% 6% 40%	2730
	21st to end	Night	20% 14% 4 7% 4 4 3 3 4 4 33%	2730
December	1st to 10th	Night	16% 10% 4 8% 5% 3 3 3 4 5% 38%	4380
	11th to 20th	Night	19% 15% 6% 10% 5% 4 4 3 4 5% 27%	5289
	21st to end	Night	28% 19% 6% 9% 4 4 4 3 4 4 16%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	60% 5% 12% 18% 5% 1	4692
	11th to 20th	Day	64% 6% 9% 12% 8% 2	4710
	21st to end	Day	67% 4 8% 15% 5% 2	5413
February	1st to 10th	Day	60% 5% 9% 17% 9% 1	2100
	11th to 20th	Day	57% 5% 9% 19% 9% 1	2058
	21st to end	Day	54% 4 10% 21% 8% 2	1730
March	1st to 10th	Day	57% 4 6% 19% 11% 2	4580
	11th to 20th	Day	40% 5% 10% 32% 11% 1	4918
	21st to end	Day	52% 6% 13% 18% 9% 1	5835
April	1st to 10th	Day	49% 7% 11% 19% 13% 1	2520
	11th to 20th	Day	47% 5% 11% 23% 10% 3	2494
	21st to end	Day	47% 6% 11% 23% 11% 3	2698
May	1st to 10th	Day	50% 8% 13% 19% 10%	7651
	11th to 20th	Day	45% 6% 12% 22% 14%	7630
	21st to end	Day	46% 9% 12% 19% 12% 2	8580
June	1st to 10th	Day	39% 7% 13% 22% 16% 3	2940
	11th to 20th	Day	35% 8% 12% 23% 20% 2	2940
	21st to end	Day	37% 8% 15% 20% 15% 4	2940
July	1st to 10th	Day	36% 8% 12% 26% 17% 2	6292
	11th to 20th	Day	36% 10% 16% 23% 14% 1	6285
	21st to end	Day	42% 10% 14% 20% 13% 2	6516
August	1st to 10th	Day	29% 9% 17% 30% 14% 1	4221
	11th to 20th	Day	33% 9% 14% 31% 14% 1	4025
	21st to end	Day	27% 7% 14% 31% 18% 4	4311
September	1st to 10th	Day	35% 7% 11% 26% 17% 4	2367
	11th to 20th	Day	31% 6% 12% 27% 21% 3	2200
	21st to end	Day	35% 5% 11% 24% 23% 2	2200
October	1st to 10th	Day	23% 4 9% 31% 31% 2	3590
	11th to 20th	Day	32% 6% 9% 27% 25% 1	3297
	21st to end	Day	41% 4 10% 24% 21% 1	3180
November	1st to 10th	Day	34% 5% 12% 28% 17% 4	1852
	11th to 20th	Day	49% 5% 8% 21% 14% 3	1890
	21st to end	Day	54% 4 10% 22% 10% 1	1890
December	1st to 10th	Day	48% 4 10% 26% 12%	3020
	11th to 20th	Day	61% 6% 10% 17% 6% 1	3128
	21st to end	Day	72% 5% 9% 10% 4	4070
January	1st to 10th	Night	61% 5% 11% 17% 7%	8233
	11th to 20th	Night	65% 5% 8% 11% 9% 2	8280
	21st to end	Night	56% 5% 11% 20% 8% 1	8769
February	1st to 10th	Night	58% 5% 11% 18% 8% 1	2520
	11th to 20th	Night	53% 4 11% 19% 12% 1	2459
	21st to end	Night	55% 6% 10% 18% 10% 2	2076
March	1st to 10th	Night	50% 4 7% 25% 12% 3	5493
	11th to 20th	Night	38% 6% 10% 27% 16% 2	5260
	21st to end	Night	49% 6% 10% 27% 8% 1	5368
April	1st to 10th	Night	44% 6% 11% 23% 13% 2	2100
	11th to 20th	Night	43% 6% 10% 21% 16% 5%	2075
	21st to end	Night	44% 7% 10% 23% 13% 3	1922
May	1st to 10th	Night	52% 8% 9% 19% 10% 1	5264
	11th to 20th	Night	41% 6% 12% 25% 15% 1	5235
	21st to end	Night	44% 8% 15% 19% 11% 3	5600
June	1st to 10th	Night	35% 6% 11% 24% 21% 3	1680
	11th to 20th	Night	35% 7% 10% 24% 20% 4	1680
	21st to end	Night	30% 9% 16% 23% 18% 4	1680
July	1st to 10th	Night	32% 8% 12% 26% 18% 4	3580
	11th to 20th	Night	31% 9% 16% 27% 16% 1	3572
	21st to end	Night	38% 8% 15% 24% 13% 3	4030
August	1st to 10th	Night	31% 7% 15% 32% 13% 1	2904
	11th to 20th	Night	32% 9% 14% 27% 17% 1	3085
	21st to end	Night	25% 7% 14% 29% 22% 3	3586
September	1st to 10th	Night	32% 7% 11% 23% 21% 6%	2012
	11th to 20th	Night	27% 6% 10% 27% 27% 4	2200
	21st to end	Night	36% 7% 9% 22% 24% 3	2200
October	1st to 10th	Night	20% 4 8% 25% 41% 2	3590
	11th to 20th	Night	28% 4 8% 25% 34% 2	3836
	21st to end	Night	34% 4 9% 25% 25% 4	4610
November	1st to 10th	Night	36% 4 11% 25% 21% 3	2666
	11th to 20th	Night	44% 4 10% 22% 17% 3	2730
	21st to end	Night	55% 4 9% 21% 10%	2730
December	1st to 10th	Night	47% 5% 12% 26% 11%	4380
	11th to 20th	Night	59% 5% 10% 16% 9%	5291
	21st to end	Night	72% 5% 9% 10% 4	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	28% 19% 34% 15% 3	330
	11th to 20th	Day	33% 21% 34% 8% 3	330
	21st to end	Day	32% 21% 32% 12% 2	363
February	1st to 10th	Day	27% 24% 32% 16% 2	330
	11th to 20th	Day	28% 26% 30% 12% 3	330
	21st to end	Day	31% 25% 36% 8%	273
March	1st to 10th	Day	29% 25% 37% 7% 1	330
	11th to 20th	Day	32% 20% 32% 11% 4	459
	21st to end	Day	32% 21% 29% 13% 4 1	594
April	1st to 10th	Day	24% 22% 32% 16% 5% 1	540
	11th to 20th	Day	28% 19% 27% 18% 7% 1	532
	21st to end	Day	26% 19% 32% 16% 6% 1	540
May	1st to 10th	Day	24% 15% 34% 18% 8% 2	543
	11th to 20th	Day	23% 14% 30% 19% 8% 5%	567
	21st to end	Day	17% 11% 29% 22% 14% 7%	675
June	1st to 10th	Day	14% 10% 33% 27% 12% 4	780
	11th to 20th	Day	14% 9% 32% 28% 12% 4	780
	21st to end	Day	15% 8% 31% 28% 15% 4	780
July	1st to 10th	Day	13% 4 23% 28% 21% 11%	722
	11th to 20th	Day	8% 5% 29% 32% 18% 8%	718
	21st to end	Day	11% 4 22% 36% 18% 9%	704
August	1st to 10th	Day	10% 5% 19% 31% 25% 11%	526
	11th to 20th	Day	13% 4 23% 27% 23% 9%	519
	21st to end	Day	7% 3 18% 35% 28% 9%	583
September	1st to 10th	Day	12% 8% 18% 29% 27% 6%	530
	11th to 20th	Day	8% 3 17% 27% 32% 12%	530
	21st to end	Day	19% 10% 22% 21% 22% 8%	530
October	1st to 10th	Day	13% 7% 27% 30% 17% 6%	530
	11th to 20th	Day	17% 18% 31% 21% 12% 1	456
	21st to end	Day	30% 16% 38% 15% 1	363
November	1st to 10th	Day	15% 24% 33% 20% 6% 1	330
	11th to 20th	Day	28% 21% 28% 17% 5% 1	330
	21st to end	Day	30% 17% 36% 15% 2	330
December	1st to 10th	Day	24% 26% 36% 10% 3 1	330
	11th to 20th	Day	25% 22% 36% 12% 4	330
	21st to end	Day	35% 19% 30% 13% 3	363
January	1st to 10th	Night	25% 19% 31% 21% 4	1050
	11th to 20th	Night	26% 18% 36% 15% 4	1050
	21st to end	Night	24% 21% 31% 22% 2	1065
February	1st to 10th	Night	26% 16% 34% 21% 3	840
	11th to 20th	Night	23% 22% 33% 20% 3	823
	21st to end	Night	27% 17% 35% 18% 2	692
March	1st to 10th	Night	25% 18% 33% 20% 4	840
	11th to 20th	Night	22% 17% 36% 20% 5% 1	840
	21st to end	Night	27% 12% 34% 22% 5%	833
April	1st to 10th	Night	21% 17% 30% 24% 6% 1	630
	11th to 20th	Night	22% 13% 32% 24% 8%	623
	21st to end	Night	22% 13% 37% 21% 6% 1	630
May	1st to 10th	Night	22% 10% 36% 24% 8%	630
	11th to 20th	Night	20% 8% 28% 29% 14% 1	621
	21st to end	Night	10% 5% 31% 33% 19% 1	683
June	1st to 10th	Night	12% 5% 29% 40% 14% 1	630
	11th to 20th	Night	15% 3 27% 36% 18% 1	630
	21st to end	Night	8% 4 28% 35% 23% 1	630
July	1st to 10th	Night	10% 2 17% 34% 31% 6%	585
	11th to 20th	Night	9% 4 23% 34% 27% 3	582
	21st to end	Night	11% 3 19% 36% 29% 2	657
August	1st to 10th	Night	10% 2 17% 36% 31% 3	597
	11th to 20th	Night	8% 3 15% 38% 32% 4	594
	21st to end	Night	7% 2 21% 33% 34% 4	660
September	1st to 10th	Night	15% 4 16% 34% 27% 4	612
	11th to 20th	Night	9% 4 17% 32% 33% 5%	800
	21st to end	Night	16% 7% 21% 29% 24% 3	800
October	1st to 10th	Night	11% 7% 26% 33% 20% 5%	800
	11th to 20th	Night	20% 12% 28% 26% 13% 1	800
	21st to end	Night	23% 13% 34% 23% 6%	880
November	1st to 10th	Night	17% 12% 35% 25% 10% 1	820
	11th to 20th	Night	20% 18% 30% 25% 7%	840
	21st to end	Night	28% 15% 27% 24% 7%	840
December	1st to 10th	Night	25% 15% 37% 19% 4	840
	11th to 20th	Night	27% 15% 30% 22% 5%	1013
	21st to end	Night	34% 15% 29% 18% 3	1155

Page generated at 2026-06-28 02:10:44. Version ac07

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