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 2025-02-21.

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	15% 9% 3 7% 5% 4 4 4 5% 7% 36%	108460
	Night	16% 10% 4 7% 5% 4 4 3 5% 6% 37%	110264
Transparency	Day	45% 7% 12% 22% 13% 2	112101
	Night	46% 6% 11% 21% 15% 2	114763
Seeing	Day	20% 13% 29% 22% 12% 4	15898
	Night	20% 11% 29% 26% 13% 1	25853

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	15% 15% 7% 14% 6% 3 4 3 4 6% 23%	3617
	11th to 20th	Day	13% 14% 8% 15% 8% 7% 5% 4 3 3 21%	3620
	21st to end	Day	21% 17% 8% 11% 4 4 3 3 2 4 23%	4187
February	1st to 10th	Day	18% 15% 6% 9% 5% 5% 4 3 4 5% 26%	2000
	11th to 20th	Day	16% 12% 4 10% 6% 6% 5% 3 5% 6% 28%	1948
	21st to end	Day	18% 15% 5% 8% 5% 3 3 3 5% 5% 31%	1570
March	1st to 10th	Day	22% 18% 4 8% 4 3 3 3 3 4 28%	3120
	11th to 20th	Day	15% 8% 3 6% 4 4 4 3 4 7% 43%	3368
	21st to end	Day	17% 10% 4 8% 5% 5% 5% 4 5% 6% 31%	3989
April	1st to 10th	Day	17% 11% 3 7% 5% 4 4 3 5% 7% 35%	2280
	11th to 20th	Day	17% 9% 2 6% 4 5% 4 3 6% 6% 37%	2254
	21st to end	Day	20% 8% 3 7% 4 4 4 4 4 7% 34%	2441
May	1st to 10th	Day	20% 9% 3 8% 5% 4 5% 4 6% 8% 28%	4082
	11th to 20th	Day	20% 6% 2 6% 4 4 4 3 5% 8% 37%	4081
	21st to end	Day	11% 7% 2 6% 5% 5% 5% 4 8% 9% 38%	4567
June	1st to 10th	Day	12% 6% 2 6% 6% 5% 5% 4 6% 8% 41%	2660
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 9% 45%	2660
	21st to end	Day	10% 6% 2 6% 5% 5% 4 4 7% 9% 41%	2660
July	1st to 10th	Day	14% 7% 2 6% 4 4 4 5% 7% 11% 36%	4440
	11th to 20th	Day	7% 4 2 5% 4 4 5% 5% 7% 12% 45%	4440
	21st to end	Day	10% 6% 2 7% 6% 5% 6% 6% 7% 10% 35%	4666
August	1st to 10th	Day	8% 5% 2 5% 3 4 4 5% 7% 10% 47%	4104
	11th to 20th	Day	9% 5% 2 6% 5% 5% 6% 4 7% 12% 40%	3862
	21st to end	Day	6% 5% 2 5% 4 4 4 3 6% 9% 52%	4180
September	1st to 10th	Day	11% 6% 2 6% 4 4 4 3 5% 7% 46%	2249
	11th to 20th	Day	10% 5% 1 5% 4 4 4 4 6% 7% 49%	2090
	21st to end	Day	13% 5% 2 5% 4 4 4 3 5% 7% 48%	2090
October	1st to 10th	Day	12% 5% 2 5% 4 4 5% 3 5% 7% 48%	2090
	11th to 20th	Day	14% 7% 2 6% 4 3 4 5% 5% 7% 43%	1940
	21st to end	Day	19% 9% 2 7% 4 4 4 3 5% 7% 35%	1881
November	1st to 10th	Day	10% 6% 3 6% 4 3 3 3 5% 6% 50%	1762
	11th to 20th	Day	16% 10% 4 7% 5% 4 4 3 5% 7% 35%	1800
	21st to end	Day	19% 12% 4 7% 4 3 4 3 5% 5% 34%	1800
December	1st to 10th	Day	15% 12% 4 7% 4 4 3 2 3 5% 41%	2930
	11th to 20th	Day	18% 15% 6% 10% 5% 5% 4 3 5% 6% 24%	3050
	21st to end	Day	28% 18% 7% 8% 5% 4 3 3 4 5% 14%	3982
January	1st to 10th	Night	17% 16% 7% 13% 5% 4 4 3 5% 5% 21%	6348
	11th to 20th	Night	14% 19% 7% 14% 8% 6% 5% 3 3 4 19%	6360
	21st to end	Night	21% 14% 5% 7% 5% 4 4 3 4 4 29%	6776
February	1st to 10th	Night	20% 12% 6% 9% 5% 4 4 3 4 5% 28%	2400
	11th to 20th	Night	15% 12% 5% 10% 6% 4 3 3 5% 5% 32%	2338
	21st to end	Night	20% 13% 4 8% 4 4 4 3 4 5% 31%	1885
March	1st to 10th	Night	21% 15% 3 6% 3 3 3 3 4 5% 34%	3733
	11th to 20th	Night	14% 7% 2 5% 3 4 4 3 4 6% 47%	3590
	21st to end	Night	19% 8% 3 7% 4 4 3 3 5% 6% 38%	3671
April	1st to 10th	Night	15% 10% 3 6% 4 3 5% 3 5% 7% 39%	1900
	11th to 20th	Night	17% 9% 2 5% 5% 4 4 3 5% 8% 40%	1875
	21st to end	Night	18% 7% 3 6% 5% 4 5% 4 6% 5% 37%	1739
May	1st to 10th	Night	20% 11% 3 8% 4 5% 4 4 6% 7% 29%	2813
	11th to 20th	Night	20% 6% 2 5% 4 3 4 3 5% 7% 40%	2812
	21st to end	Night	11% 5% 2 5% 5% 4 5% 4 6% 10% 44%	2986
June	1st to 10th	Night	9% 6% 2 6% 5% 3 4 4 5% 8% 48%	1520
	11th to 20th	Night	10% 6% 2 6% 4 3 4 4 5% 8% 48%	1520
	21st to end	Night	7% 4 1 5% 5% 4 5% 5% 9% 9% 45%	1520
July	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 6% 9% 48%	2530
	11th to 20th	Night	6% 3 2 4 3 4 4 4 7% 8% 56%	2530
	21st to end	Night	11% 7% 2 7% 4 5% 5% 4 6% 10% 40%	2889
August	1st to 10th	Night	10% 6% 2 5% 4 4 3 3 5% 8% 50%	2825
	11th to 20th	Night	8% 5% 2 6% 5% 5% 5% 5% 7% 8% 45%	2963
	21st to end	Night	5% 4 2 6% 4 4 4 3 6% 8% 56%	3476
September	1st to 10th	Night	12% 6% 3 5% 4 4 4 3 5% 7% 49%	1911
	11th to 20th	Night	8% 4 1 4 4 4 4 4 5% 7% 55%	2090
	21st to end	Night	13% 6% 2 5% 5% 4 3 3 5% 7% 48%	2090
October	1st to 10th	Night	9% 4 2 5% 4 4 4 3 5% 7% 54%	2090
	11th to 20th	Night	17% 6% 1 5% 4 3 4 3 4 6% 47%	2234
	21st to end	Night	19% 8% 2 6% 4 3 3 3 5% 7% 40%	2717
November	1st to 10th	Night	13% 7% 2 5% 3 3 3 3 6% 5% 49%	2536
	11th to 20th	Night	15% 10% 3 6% 4 4 4 3 5% 6% 40%	2600
	21st to end	Night	20% 14% 4 7% 4 4 3 3 4 4 33%	2600
December	1st to 10th	Night	16% 10% 4 8% 5% 3 3 3 4 6% 39%	4250
	11th to 20th	Night	19% 15% 6% 10% 5% 4 3 3 4 5% 27%	5151
	21st to end	Night	28% 19% 6% 9% 4 4 4 3 4 4 16%	6996

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	63% 4 8% 19% 6% 1	3618
	11th to 20th	Day	67% 5% 9% 10% 8% 2	3620
	21st to end	Day	66% 4 7% 15% 6% 2	4187
February	1st to 10th	Day	60% 5% 9% 16% 9% 1	2000
	11th to 20th	Day	57% 5% 9% 19% 9% 1	1958
	21st to end	Day	56% 4 9% 20% 8% 2	1570
March	1st to 10th	Day	60% 5% 7% 17% 10% 1	3120
	11th to 20th	Day	41% 5% 11% 29% 13% 1	3368
	21st to end	Day	51% 8% 14% 21% 6%	3989
April	1st to 10th	Day	48% 7% 11% 20% 13% 1	2280
	11th to 20th	Day	47% 5% 11% 23% 10% 3	2254
	21st to end	Day	49% 6% 11% 21% 11% 3	2441
May	1st to 10th	Day	51% 9% 13% 20% 6%	4120
	11th to 20th	Day	45% 7% 13% 25% 10%	4085
	21st to end	Day	37% 10% 14% 20% 18% 1	4580
June	1st to 10th	Day	39% 7% 13% 23% 15% 3	2660
	11th to 20th	Day	34% 7% 13% 23% 21% 2	2660
	21st to end	Day	37% 8% 15% 20% 16% 4	2660
July	1st to 10th	Day	41% 8% 12% 22% 15% 2	4371
	11th to 20th	Day	28% 9% 16% 28% 19% 1	4365
	21st to end	Day	40% 11% 15% 17% 14% 3	4518
August	1st to 10th	Day	29% 9% 17% 29% 14% 1	4091
	11th to 20th	Day	33% 9% 13% 31% 14% 1	3901
	21st to end	Day	27% 7% 14% 30% 18% 4	4179
September	1st to 10th	Day	36% 7% 11% 25% 17% 5%	2249
	11th to 20th	Day	32% 6% 12% 26% 21% 4	2090
	21st to end	Day	35% 5% 11% 25% 22% 1	2090
October	1st to 10th	Day	23% 4 9% 31% 30% 2	3480
	11th to 20th	Day	32% 6% 8% 27% 25% 1	3195
	21st to end	Day	40% 4 10% 24% 21% 1	3081
November	1st to 10th	Day	34% 5% 12% 28% 17% 4	1762
	11th to 20th	Day	49% 5% 8% 20% 14% 4	1800
	21st to end	Day	53% 4 10% 22% 10% 2	1800
December	1st to 10th	Day	48% 4 10% 27% 12%	2930
	11th to 20th	Day	61% 6% 10% 17% 6%	3047
	21st to end	Day	72% 5% 9% 10% 4	3982
January	1st to 10th	Night	63% 5% 8% 15% 7%	6348
	11th to 20th	Night	70% 5% 7% 10% 7% 2	6360
	21st to end	Night	59% 4 10% 18% 8% 1	6776
February	1st to 10th	Night	59% 4 11% 17% 8% 1	2400
	11th to 20th	Night	54% 4 10% 18% 12% 1	2339
	21st to end	Night	56% 5% 10% 17% 10% 2	1885
March	1st to 10th	Night	53% 4 8% 23% 10% 1	3733
	11th to 20th	Night	37% 7% 11% 25% 18% 2	3590
	21st to end	Night	46% 7% 11% 28% 7% 1	3671
April	1st to 10th	Night	44% 7% 11% 23% 14% 2	1900
	11th to 20th	Night	44% 5% 9% 21% 17% 5%	1875
	21st to end	Night	45% 7% 10% 21% 14% 3	1739
May	1st to 10th	Night	53% 9% 10% 19% 7% 1	2840
	11th to 20th	Night	42% 7% 14% 25% 10% 1	2813
	21st to end	Night	32% 9% 16% 23% 15% 4	2994
June	1st to 10th	Night	34% 6% 11% 26% 20% 3	1520
	11th to 20th	Night	33% 7% 11% 24% 21% 4	1520
	21st to end	Night	30% 9% 16% 23% 18% 4	1520
July	1st to 10th	Night	33% 7% 11% 27% 17% 5%	2490
	11th to 20th	Night	23% 7% 15% 31% 22% 2	2482
	21st to end	Night	38% 7% 15% 20% 15% 4	2797
August	1st to 10th	Night	31% 7% 15% 32% 13% 1	2814
	11th to 20th	Night	33% 9% 14% 27% 17% 1	2990
	21st to end	Night	26% 7% 14% 28% 22% 4	3476
September	1st to 10th	Night	33% 7% 12% 22% 21% 6%	1911
	11th to 20th	Night	27% 6% 10% 27% 26% 4	2090
	21st to end	Night	35% 7% 9% 23% 23% 4	2090
October	1st to 10th	Night	20% 4 8% 26% 40% 2	3480
	11th to 20th	Night	28% 4 8% 25% 34% 2	3718
	21st to end	Night	33% 4 9% 25% 24% 4	4467
November	1st to 10th	Night	36% 4 10% 25% 21% 3	2536
	11th to 20th	Night	44% 5% 10% 22% 17% 3	2600
	21st to end	Night	55% 4 9% 21% 10%	2600
December	1st to 10th	Night	46% 5% 12% 26% 11%	4250
	11th to 20th	Night	59% 5% 10% 16% 9% 1	5153
	21st to end	Night	72% 5% 9% 10% 4	6996

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% 20% 33% 15% 3	300
	11th to 20th	Day	31% 20% 36% 9% 3	300
	21st to end	Day	31% 21% 33% 12% 3	330
February	1st to 10th	Day	28% 25% 32% 14% 1	300
	11th to 20th	Day	29% 26% 30% 13% 3	300
	21st to end	Day	32% 26% 33% 8%	225
March	1st to 10th	Day	30% 25% 36% 8% 1	270
	11th to 20th	Day	31% 19% 33% 12% 5% 1	387
	21st to end	Day	34% 18% 29% 13% 5% 1	506
April	1st to 10th	Day	22% 21% 33% 17% 6% 1	460
	11th to 20th	Day	27% 18% 27% 19% 8% 1	452
	21st to end	Day	28% 19% 31% 13% 7% 2	460
May	1st to 10th	Day	24% 14% 33% 19% 8% 2	463
	11th to 20th	Day	22% 12% 31% 19% 9% 6%	487
	21st to end	Day	15% 10% 29% 22% 15% 8%	581
June	1st to 10th	Day	14% 9% 32% 28% 13% 4	680
	11th to 20th	Day	13% 7% 31% 31% 13% 5%	680
	21st to end	Day	14% 8% 33% 26% 15% 4	680
July	1st to 10th	Day	14% 4 24% 27% 21% 11%	671
	11th to 20th	Day	8% 5% 29% 32% 19% 8%	668
	21st to end	Day	10% 5% 23% 35% 18% 9%	654
August	1st to 10th	Day	10% 5% 19% 31% 24% 11%	486
	11th to 20th	Day	14% 4 24% 27% 21% 9%	479
	21st to end	Day	8% 3 17% 34% 29% 9%	539
September	1st to 10th	Day	13% 7% 18% 30% 26% 6%	490
	11th to 20th	Day	9% 3 18% 28% 31% 11%	490
	21st to end	Day	19% 10% 22% 20% 21% 8%	490
October	1st to 10th	Day	14% 7% 28% 28% 16% 6%	490
	11th to 20th	Day	17% 19% 32% 20% 11% 1	420
	21st to end	Day	30% 15% 38% 16% 1	330
November	1st to 10th	Day	15% 23% 33% 21% 7% 1	300
	11th to 20th	Day	28% 21% 29% 17% 5% 1	300
	21st to end	Day	28% 18% 37% 16% 2	300
December	1st to 10th	Day	24% 27% 35% 10% 3 1	300
	11th to 20th	Day	25% 22% 37% 13% 4	300
	21st to end	Day	35% 18% 29% 14% 3	330
January	1st to 10th	Night	25% 20% 30% 21% 4	1000
	11th to 20th	Night	27% 17% 36% 16% 4	1000
	21st to end	Night	24% 20% 31% 23% 3	1015
February	1st to 10th	Night	27% 16% 34% 20% 2	800
	11th to 20th	Night	23% 22% 32% 19% 3	783
	21st to end	Night	28% 16% 34% 19% 3	629
March	1st to 10th	Night	23% 17% 34% 21% 5%	760
	11th to 20th	Night	22% 16% 37% 20% 5% 1	760
	21st to end	Night	27% 12% 33% 23% 5% 1	754
April	1st to 10th	Night	20% 16% 31% 26% 6% 1	570
	11th to 20th	Night	22% 12% 32% 25% 9%	563
	21st to end	Night	23% 14% 36% 20% 7% 1	570
May	1st to 10th	Night	20% 10% 36% 25% 8%	570
	11th to 20th	Night	21% 7% 25% 30% 14% 2	561
	21st to end	Night	10% 4 30% 34% 20% 1	617
June	1st to 10th	Night	11% 5% 29% 41% 14% 1	570
	11th to 20th	Night	14% 3 27% 36% 19% 1	570
	21st to end	Night	7% 4 30% 35% 23% 1	570
July	1st to 10th	Night	10% 2 18% 33% 31% 6%	555
	11th to 20th	Night	9% 3 23% 34% 27% 4	552
	21st to end	Night	11% 3 20% 36% 29% 2	624
August	1st to 10th	Night	10% 2 17% 36% 31% 4	567
	11th to 20th	Night	8% 3 16% 38% 31% 4	564
	21st to end	Night	7% 2 20% 32% 35% 4	627
September	1st to 10th	Night	15% 4 17% 33% 27% 4	581
	11th to 20th	Night	9% 4 18% 32% 33% 4	760
	21st to end	Night	16% 7% 21% 29% 24% 3	760
October	1st to 10th	Night	11% 7% 26% 32% 19% 5%	760
	11th to 20th	Night	20% 12% 29% 24% 13% 1	760
	21st to end	Night	23% 13% 34% 24% 6%	836
November	1st to 10th	Night	17% 12% 34% 25% 11% 1	780
	11th to 20th	Night	19% 18% 29% 26% 7% 1	800
	21st to end	Night	28% 15% 28% 24% 7%	800
December	1st to 10th	Night	25% 15% 36% 20% 5%	800
	11th to 20th	Night	28% 14% 30% 23% 6%	965
	21st to end	Night	33% 15% 29% 19% 3	1100

Page generated at 2025-02-18 03:26:31. Version ac07

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