Indian Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Indian Hill Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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% 12% 4 9% 5% 5% 4 4 5% 7% 30%	104886
	Night	15% 13% 5% 10% 5% 4 4 3 5% 6% 29%	104411
Transparency	Day	51% 8% 12% 19% 10% 1	108562
	Night	53% 7% 11% 17% 10% 1	108874
Seeing	Day	22% 18% 29% 19% 10% 3	14772
	Night	22% 15% 27% 24% 10% 1	24600

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% 23% 9% 16% 5% 3 4 2 4 4 14%	2926
	11th to 20th	Day	12% 24% 9% 16% 7% 6% 3 2 4 4 14%	2930
	21st to end	Day	23% 20% 12% 17% 6% 4 3 2 3 2 7%	3133
February	1st to 10th	Day	15% 20% 7% 14% 8% 4 4 2 3 4 19%	1710
	11th to 20th	Day	14% 16% 7% 15% 8% 6% 5% 3 5% 4 18%	1682
	21st to end	Day	16% 18% 5% 13% 5% 4 4 5% 4 5% 22%	1570
March	1st to 10th	Day	20% 12% 7% 9% 5% 5% 3 3 5% 6% 25%	3391
	11th to 20th	Day	12% 15% 6% 11% 6% 4 4 3 4 5% 31%	3480
	21st to end	Day	19% 13% 6% 9% 4 4 3 3 4 5% 28%	3815
April	1st to 10th	Day	14% 15% 4 9% 4 4 4 3 6% 6% 31%	2152
	11th to 20th	Day	18% 13% 3 7% 5% 4 4 3 5% 5% 33%	2385
	21st to end	Day	19% 13% 3 7% 5% 4 3 3 4 5% 34%	2470
May	1st to 10th	Day	18% 10% 4 8% 5% 5% 5% 4 5% 6% 30%	4082
	11th to 20th	Day	18% 10% 3 7% 4 4 4 3 6% 7% 33%	4081
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 7% 7% 40%	4682
June	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 5% 7% 8% 35%	2660
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 4 7% 9% 38%	2660
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 6% 10% 39%	2660
July	1st to 10th	Day	8% 5% 3 7% 5% 5% 6% 4 7% 10% 39%	4257
	11th to 20th	Day	8% 6% 2 6% 5% 4 5% 5% 7% 11% 42%	4120
	21st to end	Day	9% 6% 3 7% 6% 6% 5% 5% 6% 9% 39%	4466
August	1st to 10th	Day	12% 8% 3 7% 5% 5% 6% 4 6% 10% 34%	4104
	11th to 20th	Day	11% 6% 3 8% 5% 5% 6% 5% 9% 9% 33%	4044
	21st to end	Day	10% 6% 2 6% 5% 6% 5% 4 7% 9% 40%	4419
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 5% 7% 41%	2218
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 6% 8% 42%	2090
	21st to end	Day	19% 9% 3 7% 4 4 4 4 4 6% 36%	2090
October	1st to 10th	Day	16% 6% 3 7% 5% 4 5% 4 6% 6% 37%	1940
	11th to 20th	Day	21% 9% 3 9% 5% 5% 4 4 4 5% 31%	1900
	21st to end	Day	22% 12% 3 9% 5% 5% 4 3 5% 6% 25%	2090
November	1st to 10th	Day	12% 12% 4 9% 5% 5% 4 4 5% 7% 34%	1778
	11th to 20th	Day	16% 19% 4 10% 5% 4 5% 3 4 7% 24%	1705
	21st to end	Day	17% 19% 7% 11% 7% 6% 4 3 5% 5% 16%	1600
December	1st to 10th	Day	15% 19% 9% 15% 7% 5% 5% 3 4 4 13%	2600
	11th to 20th	Day	21% 23% 7% 12% 6% 4 3 4 4 4 12%	2990
	21st to end	Day	22% 25% 7% 16% 6% 4 4 3 3 3 8%	4006
January	1st to 10th	Night	15% 23% 11% 18% 6% 4 4 3 4 4 10%	4239
	11th to 20th	Night	14% 19% 11% 20% 6% 4 4 4 4 4 11%	4250
	21st to end	Night	23% 21% 8% 15% 7% 3 3 2 2 3 12%	4546
February	1st to 10th	Night	18% 17% 4 14% 8% 5% 4 3 4 5% 18%	2470
	11th to 20th	Night	14% 16% 6% 14% 7% 6% 4 4 4 5% 19%	2383
	21st to end	Night	18% 14% 5% 13% 6% 5% 4 3 4 4 23%	1884
March	1st to 10th	Night	20% 15% 4 8% 4 4 3 3 4 4 31%	3461
	11th to 20th	Night	14% 12% 5% 10% 5% 5% 4 3 4 5% 32%	3480
	21st to end	Night	17% 12% 5% 9% 5% 4 4 3 4 4 33%	3817
April	1st to 10th	Night	16% 15% 4 8% 5% 5% 3 3 4 5% 31%	2028
	11th to 20th	Night	16% 11% 3 7% 4 5% 5% 4 6% 6% 34%	1760
	21st to end	Night	15% 10% 2 9% 5% 4 5% 4 5% 6% 36%	1710
May	1st to 10th	Night	23% 9% 3 7% 5% 4 4 4 5% 6% 30%	2813
	11th to 20th	Night	13% 10% 3 7% 4 4 4 4 6% 8% 36%	2812
	21st to end	Night	12% 4 1 5% 3 4 4 4 7% 11% 45%	2871
June	1st to 10th	Night	9% 8% 2 8% 5% 6% 4 4 5% 8% 41%	1520
	11th to 20th	Night	8% 5% 3 8% 5% 5% 6% 4 5% 8% 42%	1520
	21st to end	Night	9% 5% 3 7% 4 4 5% 4 7% 10% 41%	1520
July	1st to 10th	Night	8% 6% 3 7% 5% 4 3 4 5% 8% 47%	2698
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 6% 9% 48%	2840
	21st to end	Night	6% 6% 2 7% 5% 5% 5% 4 6% 9% 45%	3087
August	1st to 10th	Night	10% 9% 3 8% 5% 5% 4 4 6% 7% 39%	2825
	11th to 20th	Night	12% 8% 3 8% 4 5% 5% 3 5% 6% 40%	2785
	21st to end	Night	7% 5% 2 7% 6% 5% 5% 5% 7% 9% 43%	3204
September	1st to 10th	Night	13% 6% 2 5% 4 4 4 4 6% 8% 45%	1957
	11th to 20th	Night	10% 5% 2 6% 4 4 3 3 6% 7% 51%	2090
	21st to end	Night	16% 8% 3 7% 5% 5% 4 3 5% 6% 37%	2090
October	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 6% 8% 42%	2238
	11th to 20th	Night	16% 10% 3 8% 5% 4 4 4 5% 7% 33%	2280
	21st to end	Night	23% 11% 3 6% 5% 4 5% 4 6% 6% 29%	2508
November	1st to 10th	Night	13% 10% 3 8% 6% 4 4 3 6% 6% 36%	2517
	11th to 20th	Night	15% 16% 4 11% 6% 5% 4 3 5% 6% 24%	2691
	21st to end	Night	18% 18% 5% 10% 6% 4 4 4 5% 6% 20%	2800
December	1st to 10th	Night	13% 19% 7% 14% 7% 7% 5% 3 5% 4 16%	4580
	11th to 20th	Night	17% 22% 8% 13% 5% 5% 3 3 4 5% 15%	5205
	21st to end	Night	20% 23% 7% 13% 5% 5% 4 3 4 5% 11%	6932

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	74% 6% 10% 8% 2	2927
	11th to 20th	Day	75% 5% 9% 10% 2	2930
	21st to end	Day	84% 4 5% 5% 2	3133
February	1st to 10th	Day	70% 5% 9% 11% 5%	1710
	11th to 20th	Day	68% 6% 9% 11% 6%	1691
	21st to end	Day	63% 7% 11% 12% 6% 2	1570
March	1st to 10th	Day	57% 8% 10% 21% 4	3391
	11th to 20th	Day	53% 9% 15% 17% 6% 1	3480
	21st to end	Day	56% 6% 9% 17% 10% 1	3815
April	1st to 10th	Day	51% 7% 13% 15% 13% 1	2152
	11th to 20th	Day	52% 6% 11% 16% 13% 2	2385
	21st to end	Day	52% 6% 10% 20% 10% 2	2470
May	1st to 10th	Day	51% 8% 9% 22% 8% 1	4120
	11th to 20th	Day	47% 10% 11% 21% 9% 1	4085
	21st to end	Day	38% 11% 12% 20% 15% 5%	4696
June	1st to 10th	Day	44% 8% 12% 24% 12% 1	2660
	11th to 20th	Day	41% 9% 14% 21% 14% 2	2660
	21st to end	Day	39% 7% 13% 24% 15% 1	2660
July	1st to 10th	Day	37% 8% 13% 23% 15% 3	4192
	11th to 20th	Day	33% 9% 14% 26% 17% 1	4051
	21st to end	Day	38% 9% 14% 20% 17% 1	4324
August	1st to 10th	Day	43% 10% 15% 22% 10%	4091
	11th to 20th	Day	41% 10% 12% 29% 7% 1	4083
	21st to end	Day	37% 9% 14% 27% 12% 1	4419
September	1st to 10th	Day	41% 7% 14% 21% 14% 3	2218
	11th to 20th	Day	38% 8% 14% 23% 16% 1	2090
	21st to end	Day	48% 6% 10% 23% 12% 1	2090
October	1st to 10th	Day	33% 7% 16% 25% 18% 1	3226
	11th to 20th	Day	46% 8% 11% 18% 14% 3	3140
	21st to end	Day	44% 6% 14% 23% 12% 1	3428
November	1st to 10th	Day	47% 7% 13% 19% 13% 1	1778
	11th to 20th	Day	60% 6% 12% 13% 7% 3	1705
	21st to end	Day	67% 7% 8% 12% 5%	1600
December	1st to 10th	Day	72% 7% 12% 8% 2	2600
	11th to 20th	Day	74% 7% 8% 9% 2	2986
	21st to end	Day	82% 5% 6% 6% 1	4006
January	1st to 10th	Night	76% 6% 7% 8% 3	4239
	11th to 20th	Night	76% 6% 8% 7% 1	4250
	21st to end	Night	79% 4 7% 7% 2	4546
February	1st to 10th	Night	68% 6% 10% 12% 4	2470
	11th to 20th	Night	66% 6% 9% 14% 5%	2385
	21st to end	Night	64% 6% 8% 14% 7% 1	1884
March	1st to 10th	Night	54% 7% 12% 19% 8%	3461
	11th to 20th	Night	51% 8% 15% 16% 8% 1	3480
	21st to end	Night	51% 8% 10% 20% 10% 1	3817
April	1st to 10th	Night	54% 6% 10% 16% 11% 2	2028
	11th to 20th	Night	49% 6% 11% 19% 12% 2	1760
	21st to end	Night	47% 6% 12% 19% 12% 3	1710
May	1st to 10th	Night	52% 8% 10% 18% 10% 2	2840
	11th to 20th	Night	44% 8% 13% 21% 11% 2	2813
	21st to end	Night	31% 9% 15% 25% 18% 3	2878
June	1st to 10th	Night	40% 8% 11% 24% 15% 2	1520
	11th to 20th	Night	38% 8% 13% 21% 18% 2	1520
	21st to end	Night	36% 10% 12% 25% 17% 1	1520
July	1st to 10th	Night	35% 6% 12% 24% 18% 4	2653
	11th to 20th	Night	30% 8% 14% 27% 18% 2	2786
	21st to end	Night	34% 9% 13% 18% 24% 2	2988
August	1st to 10th	Night	41% 8% 12% 25% 13% 1	2814
	11th to 20th	Night	41% 7% 13% 28% 10% 1	2812
	21st to end	Night	34% 8% 13% 29% 14% 2	3204
September	1st to 10th	Night	35% 8% 13% 25% 15% 3	1957
	11th to 20th	Night	31% 8% 14% 25% 20% 2	2090
	21st to end	Night	47% 7% 10% 21% 15% 1	2090
October	1st to 10th	Night	33% 7% 12% 25% 22% 1	3732
	11th to 20th	Night	43% 9% 11% 19% 15% 3	3779
	21st to end	Night	41% 6% 14% 23% 14% 1	4120
November	1st to 10th	Night	45% 7% 14% 20% 11% 3	2517
	11th to 20th	Night	59% 6% 11% 15% 6% 3	2691
	21st to end	Night	64% 6% 11% 14% 4	2800
December	1st to 10th	Night	67% 9% 12% 8% 3	4580
	11th to 20th	Night	72% 6% 10% 11% 1	5208
	21st to end	Night	74% 7% 10% 8% 1	6932

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	34% 29% 28% 7% 2	300
	11th to 20th	Day	31% 33% 26% 7% 2	300
	21st to end	Day	30% 33% 27% 8% 2	300
February	1st to 10th	Day	36% 23% 34% 6% 1	270
	11th to 20th	Day	33% 34% 25% 7%	270
	21st to end	Day	37% 31% 28% 4	225
March	1st to 10th	Day	30% 24% 30% 13% 4	427
	11th to 20th	Day	29% 23% 32% 13% 3 1	460
	21st to end	Day	36% 22% 26% 13% 4	506
April	1st to 10th	Day	27% 27% 27% 13% 6% 1	460
	11th to 20th	Day	31% 20% 25% 14% 8% 1	452
	21st to end	Day	29% 21% 29% 15% 5% 1	460
May	1st to 10th	Day	26% 22% 28% 17% 4 2	463
	11th to 20th	Day	21% 16% 31% 22% 8% 2	487
	21st to end	Day	14% 12% 32% 24% 14% 5%	529
June	1st to 10th	Day	16% 14% 36% 22% 10% 2	490
	11th to 20th	Day	14% 13% 31% 25% 14% 2	490
	21st to end	Day	14% 12% 36% 26% 10% 3	490
July	1st to 10th	Day	9% 9% 24% 29% 21% 7%	485
	11th to 20th	Day	13% 10% 30% 25% 17% 6%	484
	21st to end	Day	10% 8% 32% 29% 15% 7%	532
August	1st to 10th	Day	9% 10% 27% 27% 20% 8%	486
	11th to 20th	Day	11% 11% 29% 25% 15% 9%	479
	21st to end	Day	10% 9% 27% 26% 19% 8%	539
September	1st to 10th	Day	15% 9% 24% 26% 20% 5%	490
	11th to 20th	Day	9% 7% 23% 29% 22% 10%	490
	21st to end	Day	22% 14% 27% 20% 12% 5%	490
October	1st to 10th	Day	15% 14% 30% 20% 16% 3	490
	11th to 20th	Day	24% 21% 30% 17% 5% 2	490
	21st to end	Day	33% 19% 29% 16% 3	539
November	1st to 10th	Day	26% 22% 27% 16% 7% 2	316
	11th to 20th	Day	36% 20% 28% 11% 4	253
	21st to end	Day	30% 24% 39% 9%	200
December	1st to 10th	Day	28% 30% 29% 10% 3 1	200
	11th to 20th	Day	31% 27% 32% 9% 2	200
	21st to end	Day	35% 27% 28% 8% 1	230
January	1st to 10th	Night	29% 26% 32% 11% 2	800
	11th to 20th	Night	32% 24% 30% 13% 2	800
	21st to end	Night	25% 24% 32% 17% 2	841
February	1st to 10th	Night	31% 20% 29% 18% 2	760
	11th to 20th	Night	29% 23% 31% 15% 2	743
	21st to end	Night	31% 22% 32% 14% 2	628
March	1st to 10th	Night	24% 21% 31% 20% 3	760
	11th to 20th	Night	26% 22% 26% 20% 5% 1	760
	21st to end	Night	25% 18% 30% 21% 5%	836
April	1st to 10th	Night	25% 15% 34% 21% 4	760
	11th to 20th	Night	23% 16% 34% 20% 6% 1	636
	21st to end	Night	18% 13% 36% 28% 5%	570
May	1st to 10th	Night	22% 11% 28% 29% 9% 1	570
	11th to 20th	Night	17% 10% 28% 33% 10% 2	561
	21st to end	Night	12% 6% 27% 36% 18% 1	499
June	1st to 10th	Night	12% 4 33% 37% 13% 1	380
	11th to 20th	Night	11% 8% 26% 40% 15% 1	380
	21st to end	Night	11% 9% 25% 39% 16%	380
July	1st to 10th	Night	6% 5% 20% 39% 25% 5%	465
	11th to 20th	Night	10% 4 22% 36% 24% 4	552
	21st to end	Night	9% 5% 19% 42% 24% 2	624
August	1st to 10th	Night	10% 5% 17% 40% 25% 3	567
	11th to 20th	Night	10% 6% 15% 38% 28% 3	564
	21st to end	Night	10% 6% 22% 31% 28% 3	668
September	1st to 10th	Night	15% 7% 18% 32% 25% 3	760
	11th to 20th	Night	13% 4 16% 37% 26% 4	760
	21st to end	Night	20% 10% 24% 27% 16% 4	760
October	1st to 10th	Night	17% 11% 26% 25% 18% 3	760
	11th to 20th	Night	22% 16% 29% 25% 8% 1	760
	21st to end	Night	29% 16% 30% 21% 4	836
November	1st to 10th	Night	20% 17% 29% 26% 8% 1	780
	11th to 20th	Night	27% 21% 29% 17% 5% 1	800
	21st to end	Night	31% 22% 29% 14% 4	800
December	1st to 10th	Night	33% 22% 29% 13% 4	800
	11th to 20th	Night	29% 25% 30% 14% 2	800
	21st to end	Night	31% 21% 30% 16% 1	880

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