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 2026-05-17.

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% 12% 5% 10% 5% 5% 4 4 5% 6% 29%	131795
	Night	14% 13% 5% 11% 6% 5% 4 3 5% 6% 28%	131001
Transparency	Day	52% 7% 11% 18% 10% 1	135427
	Night	54% 7% 11% 17% 10% 1	135439
Seeing	Day	23% 18% 29% 18% 9% 3	16486
	Night	22% 15% 27% 24% 10% 1	26310

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	14% 21% 8% 26% 6% 4 3 2 3 3 10%	5258
	11th to 20th	Day	9% 20% 9% 22% 9% 7% 4 2 3 3 10%	5280
	21st to end	Day	16% 17% 8% 16% 9% 7% 4 3 4 3 13%	5780
February	1st to 10th	Day	14% 19% 7% 15% 8% 5% 4 2 4 4 19%	1890
	11th to 20th	Day	14% 16% 7% 16% 8% 6% 5% 3 5% 4 18%	1864
	21st to end	Day	15% 18% 5% 14% 5% 4 4 5% 4 5% 21%	1730
March	1st to 10th	Day	16% 10% 8% 12% 4 4 3 3 5% 6% 27%	4971
	11th to 20th	Day	11% 12% 6% 11% 6% 4 4 3 4 5% 34%	5090
	21st to end	Day	17% 14% 6% 11% 5% 5% 4 3 4 5% 27%	5586
April	1st to 10th	Day	15% 15% 4 9% 4 4 4 3 6% 6% 30%	2378
	11th to 20th	Day	17% 13% 3 8% 5% 5% 4 3 5% 6% 32%	2639
	21st to end	Day	18% 13% 3 7% 4 4 3 3 4 5% 35%	2730
May	1st to 10th	Day	19% 9% 4 8% 5% 5% 5% 4 5% 6% 29%	5992
	11th to 20th	Day	18% 10% 3 7% 5% 4 5% 3 6% 7% 32%	5939
	21st to end	Day	17% 7% 3 7% 5% 5% 5% 4 6% 7% 35%	6723
June	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 36%	2800
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 7% 8% 37%	2800
	21st to end	Day	12% 6% 2 6% 5% 4 5% 4 6% 10% 40%	2800
July	1st to 10th	Day	7% 5% 3 7% 5% 5% 5% 4 7% 10% 42%	6093
	11th to 20th	Day	8% 7% 3 7% 5% 5% 5% 5% 7% 10% 37%	5900
	21st to end	Day	10% 5% 2 7% 5% 5% 5% 4 6% 8% 42%	6424
August	1st to 10th	Day	12% 8% 3 7% 5% 5% 6% 4 6% 10% 34%	4234
	11th to 20th	Day	11% 6% 3 8% 5% 5% 6% 5% 9% 9% 33%	4174
	21st to end	Day	9% 6% 2 6% 5% 6% 5% 4 7% 9% 40%	4559
September	1st to 10th	Day	15% 6% 2 6% 4 4 5% 4 5% 7% 41%	2335
	11th to 20th	Day	10% 6% 2 7% 4 5% 5% 4 6% 8% 44%	2200
	21st to end	Day	19% 9% 3 7% 4 4 4 4 4 7% 36%	2200
October	1st to 10th	Day	15% 6% 3 7% 5% 4 5% 4 6% 6% 39%	2042
	11th to 20th	Day	20% 9% 3 9% 5% 5% 4 4 5% 6% 32%	2000
	21st to end	Day	22% 12% 3 9% 5% 5% 4 3 5% 6% 26%	2200
November	1st to 10th	Day	12% 11% 4 9% 5% 5% 4 4 5% 7% 34%	1869
	11th to 20th	Day	15% 19% 4 11% 5% 4 5% 3 4 6% 23%	1790
	21st to end	Day	17% 19% 7% 11% 7% 6% 4 3 5% 5% 16%	1680
December	1st to 10th	Day	15% 19% 9% 15% 6% 5% 5% 3 4 4 13%	2680
	11th to 20th	Day	21% 23% 7% 13% 6% 4 3 4 4 4 12%	3070
	21st to end	Day	22% 25% 7% 16% 6% 4 4 2 3 3 8%	4095
January	1st to 10th	Night	13% 19% 9% 25% 7% 4 4 2 3 3 9%	7635
	11th to 20th	Night	9% 18% 10% 20% 10% 6% 5% 4 4 4 10%	7680
	21st to end	Night	15% 18% 7% 13% 7% 5% 5% 3 3 5% 18%	8401
February	1st to 10th	Night	17% 17% 4 14% 8% 5% 4 3 4 5% 19%	2730
	11th to 20th	Night	15% 15% 6% 15% 8% 6% 4 4 4 5% 19%	2640
	21st to end	Night	17% 15% 5% 13% 6% 5% 4 3 4 4 23%	2076
March	1st to 10th	Night	17% 15% 5% 9% 5% 4 3 3 4 5% 29%	5087
	11th to 20th	Night	11% 10% 5% 10% 5% 4 4 3 4 6% 37%	5090
	21st to end	Night	17% 12% 5% 9% 5% 5% 4 3 4 5% 31%	5588
April	1st to 10th	Night	17% 15% 4 9% 5% 5% 3 3 4 5% 29%	2241
	11th to 20th	Night	15% 11% 3 7% 4 5% 5% 4 6% 6% 33%	1948
	21st to end	Night	14% 10% 2 8% 5% 4 5% 4 6% 6% 36%	1890
May	1st to 10th	Night	23% 10% 3 8% 5% 4 5% 4 5% 6% 28%	4123
	11th to 20th	Night	15% 11% 3 7% 4 4 4 4 6% 7% 37%	4086
	21st to end	Night	17% 8% 2 5% 4 4 4 3 6% 9% 38%	4129
June	1st to 10th	Night	9% 8% 2 8% 5% 6% 4 4 5% 8% 41%	1600
	11th to 20th	Night	9% 6% 3 8% 6% 5% 5% 4 5% 8% 41%	1600
	21st to end	Night	9% 5% 3 7% 4 4 5% 4 7% 10% 41%	1600
July	1st to 10th	Night	7% 6% 2 7% 5% 4 4 4 6% 9% 45%	3860
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 4 7% 9% 43%	4057
	21st to end	Night	7% 6% 2 6% 4 4 4 4 6% 8% 48%	4427
August	1st to 10th	Night	10% 9% 2 8% 5% 5% 4 4 6% 7% 39%	2915
	11th to 20th	Night	12% 8% 3 8% 4 5% 5% 3 5% 6% 41%	2875
	21st to end	Night	7% 5% 2 7% 5% 5% 5% 5% 7% 9% 43%	3305
September	1st to 10th	Night	12% 6% 2 5% 4 4 5% 4 6% 8% 46%	2060
	11th to 20th	Night	10% 4 2 5% 4 4 3 3 5% 7% 52%	2200
	21st to end	Night	17% 8% 3 7% 5% 5% 5% 3 5% 6% 37%	2200
October	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 5% 8% 43%	2356
	11th to 20th	Night	16% 9% 3 8% 5% 4 4 4 5% 7% 34%	2400
	21st to end	Night	23% 10% 3 7% 5% 4 5% 3 6% 6% 29%	2640
November	1st to 10th	Night	13% 10% 3 8% 6% 4 4 3 6% 7% 37%	2646
	11th to 20th	Night	15% 17% 4 11% 6% 5% 4 3 5% 6% 24%	2826
	21st to end	Night	18% 18% 6% 10% 6% 4 4 4 5% 5% 20%	2940
December	1st to 10th	Night	13% 19% 7% 14% 7% 7% 5% 4 5% 4 16%	4720
	11th to 20th	Night	17% 22% 8% 13% 5% 5% 3 3 4 5% 15%	5345
	21st to end	Night	20% 23% 8% 14% 5% 5% 4 3 4 5% 11%	7085

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	79% 6% 8% 5% 2 1	5259
	11th to 20th	Day	79% 5% 7% 7% 2	5280
	21st to end	Day	75% 4 7% 10% 4	5780
February	1st to 10th	Day	69% 5% 8% 12% 5%	1890
	11th to 20th	Day	69% 6% 8% 12% 5%	1873
	21st to end	Day	63% 7% 11% 12% 6% 2	1730
March	1st to 10th	Day	56% 7% 12% 19% 6%	4971
	11th to 20th	Day	51% 8% 14% 20% 6% 2	5090
	21st to end	Day	58% 6% 8% 18% 10% 1	5586
April	1st to 10th	Day	52% 7% 13% 15% 12% 1	2378
	11th to 20th	Day	52% 6% 11% 17% 12% 2	2639
	21st to end	Day	51% 6% 11% 20% 10% 2	2730
May	1st to 10th	Day	53% 8% 8% 18% 9% 4	6027
	11th to 20th	Day	49% 9% 10% 21% 10% 1	5943
	21st to end	Day	44% 10% 11% 19% 12% 3	6738
June	1st to 10th	Day	43% 8% 12% 24% 12% 1	2800
	11th to 20th	Day	42% 9% 14% 20% 14% 2	2800
	21st to end	Day	39% 8% 14% 24% 15% 1	2800
July	1st to 10th	Day	34% 8% 13% 26% 16% 2	6028
	11th to 20th	Day	37% 9% 14% 24% 15% 1	5831
	21st to end	Day	36% 8% 12% 23% 19% 1	6240
August	1st to 10th	Day	42% 10% 15% 22% 11%	4221
	11th to 20th	Day	40% 10% 13% 29% 8% 1	4213
	21st to end	Day	36% 9% 15% 27% 12% 1	4559
September	1st to 10th	Day	40% 7% 14% 22% 14% 3	2335
	11th to 20th	Day	36% 8% 14% 25% 16% 1	2200
	21st to end	Day	48% 6% 11% 22% 12% 1	2200
October	1st to 10th	Day	32% 7% 16% 25% 19% 1	3328
	11th to 20th	Day	45% 8% 12% 19% 14% 3	3240
	21st to end	Day	44% 6% 14% 23% 12% 1	3538
November	1st to 10th	Day	48% 7% 13% 19% 12% 1	1869
	11th to 20th	Day	60% 6% 11% 13% 7% 2	1790
	21st to end	Day	68% 7% 8% 12% 5%	1680
December	1st to 10th	Day	71% 7% 12% 8% 2	2680
	11th to 20th	Day	74% 7% 9% 9% 2	3066
	21st to end	Day	81% 5% 7% 6% 1	4095
January	1st to 10th	Night	78% 6% 6% 7% 3	7636
	11th to 20th	Night	75% 6% 8% 7% 2 1	7680
	21st to end	Night	68% 5% 9% 13% 5%	8401
February	1st to 10th	Night	67% 6% 10% 12% 4	2730
	11th to 20th	Night	66% 7% 9% 14% 5%	2642
	21st to end	Night	64% 6% 8% 14% 7% 1	2076
March	1st to 10th	Night	55% 6% 14% 17% 8%	5087
	11th to 20th	Night	46% 7% 14% 22% 10% 1	5090
	21st to end	Night	52% 7% 10% 17% 12% 1	5588
April	1st to 10th	Night	56% 6% 10% 15% 11% 2	2241
	11th to 20th	Night	49% 7% 11% 19% 12% 2	1948
	21st to end	Night	47% 6% 12% 20% 12% 3	1890
May	1st to 10th	Night	54% 8% 9% 14% 9% 5%	4150
	11th to 20th	Night	45% 7% 11% 23% 12% 1	4087
	21st to end	Night	40% 8% 13% 23% 14% 2	4136
June	1st to 10th	Night	40% 8% 11% 24% 15% 3	1600
	11th to 20th	Night	39% 8% 13% 21% 17% 2	1600
	21st to end	Night	35% 10% 12% 24% 17% 1	1600
July	1st to 10th	Night	34% 7% 13% 24% 19% 3	3817
	11th to 20th	Night	34% 9% 14% 25% 15% 2	4006
	21st to end	Night	32% 8% 12% 20% 26% 2	4297
August	1st to 10th	Night	40% 8% 12% 25% 14% 1	2904
	11th to 20th	Night	41% 7% 13% 29% 11% 1	2902
	21st to end	Night	34% 8% 13% 29% 14% 2	3305
September	1st to 10th	Night	35% 8% 13% 26% 15% 3	2060
	11th to 20th	Night	30% 8% 14% 26% 20% 2	2200
	21st to end	Night	46% 7% 11% 20% 16% 1	2200
October	1st to 10th	Night	33% 7% 11% 26% 22% 1	3850
	11th to 20th	Night	42% 8% 11% 19% 16% 3	3899
	21st to end	Night	41% 7% 14% 23% 14% 1	4252
November	1st to 10th	Night	45% 7% 13% 20% 12% 2	2646
	11th to 20th	Night	59% 6% 11% 15% 6% 3	2826
	21st to end	Night	65% 6% 11% 14% 4	2940
December	1st to 10th	Night	67% 9% 12% 8% 3	4720
	11th to 20th	Night	71% 6% 10% 12% 1	5348
	21st to end	Night	74% 7% 10% 8% 1	7085

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% 28% 29% 6% 2	330
	11th to 20th	Day	35% 32% 24% 6% 2	330
	21st to end	Day	31% 33% 27% 7% 1	363
February	1st to 10th	Day	34% 25% 33% 8% 1	330
	11th to 20th	Day	36% 32% 25% 7%	330
	21st to end	Day	34% 33% 29% 4	273
March	1st to 10th	Day	29% 25% 31% 11% 3	503
	11th to 20th	Day	31% 24% 30% 12% 3 1	540
	21st to end	Day	36% 22% 28% 12% 3	594
April	1st to 10th	Day	30% 26% 27% 12% 5% 1	540
	11th to 20th	Day	31% 21% 25% 14% 8% 1	532
	21st to end	Day	29% 20% 30% 15% 5% 1	540
May	1st to 10th	Day	27% 23% 29% 16% 4 2	543
	11th to 20th	Day	21% 17% 31% 22% 8% 2	551
	21st to end	Day	17% 12% 30% 23% 13% 4	573
June	1st to 10th	Day	17% 15% 36% 21% 9% 2	530
	11th to 20th	Day	15% 15% 30% 25% 13% 2	530
	21st to end	Day	13% 12% 34% 27% 11% 3	530
July	1st to 10th	Day	10% 9% 24% 29% 22% 6%	525
	11th to 20th	Day	13% 10% 29% 25% 17% 6%	524
	21st to end	Day	10% 7% 32% 28% 16% 7%	576
August	1st to 10th	Day	9% 9% 26% 28% 21% 7%	526
	11th to 20th	Day	11% 10% 28% 26% 16% 9%	519
	21st to end	Day	10% 10% 28% 26% 18% 8%	583
September	1st to 10th	Day	15% 10% 23% 25% 21% 6%	530
	11th to 20th	Day	8% 6% 23% 29% 23% 11%	530
	21st to end	Day	22% 14% 26% 20% 13% 5%	530
October	1st to 10th	Day	15% 13% 29% 21% 18% 3	530
	11th to 20th	Day	24% 22% 32% 16% 5% 2	530
	21st to end	Day	32% 19% 30% 16% 3	583
November	1st to 10th	Day	27% 23% 27% 16% 6% 1	347
	11th to 20th	Day	38% 19% 28% 12% 4	278
	21st to end	Day	32% 24% 36% 8%	220
December	1st to 10th	Day	28% 30% 30% 10% 2 1	220
	11th to 20th	Day	32% 26% 31% 9% 2	220
	21st to end	Day	37% 26% 27% 8% 1	253
January	1st to 10th	Night	29% 26% 31% 12% 2	840
	11th to 20th	Night	32% 25% 29% 12% 2	840
	21st to end	Night	25% 25% 31% 16% 2	924
February	1st to 10th	Night	30% 20% 30% 18% 2	840
	11th to 20th	Night	29% 23% 31% 15% 2	823
	21st to end	Night	30% 23% 32% 13% 2	692
March	1st to 10th	Night	25% 22% 32% 19% 3	840
	11th to 20th	Night	26% 22% 27% 19% 5% 1	840
	21st to end	Night	25% 19% 30% 21% 5%	924
April	1st to 10th	Night	27% 15% 33% 20% 4	840
	11th to 20th	Night	22% 17% 34% 20% 6% 1	704
	21st to end	Night	18% 13% 34% 28% 5%	630
May	1st to 10th	Night	23% 11% 28% 29% 9%	630
	11th to 20th	Night	17% 11% 29% 32% 10% 1	609
	21st to end	Night	13% 7% 27% 35% 17% 1	526
June	1st to 10th	Night	12% 5% 33% 38% 13% 1	400
	11th to 20th	Night	11% 8% 27% 39% 15% 1	400
	21st to end	Night	10% 9% 25% 39% 18%	400
July	1st to 10th	Night	6% 5% 19% 40% 25% 4	491
	11th to 20th	Night	10% 4 22% 36% 24% 4	582
	21st to end	Night	9% 5% 19% 41% 25% 2	657
August	1st to 10th	Night	10% 5% 17% 41% 25% 3	597
	11th to 20th	Night	10% 6% 14% 38% 28% 3	594
	21st to end	Night	10% 6% 21% 32% 28% 3	703
September	1st to 10th	Night	14% 7% 18% 33% 25% 3	800
	11th to 20th	Night	12% 4 16% 36% 28% 4	800
	21st to end	Night	20% 10% 23% 28% 17% 3	800
October	1st to 10th	Night	17% 10% 26% 26% 19% 3	800
	11th to 20th	Night	21% 16% 29% 25% 7% 1	800
	21st to end	Night	29% 15% 31% 20% 4	880
November	1st to 10th	Night	20% 17% 29% 26% 7% 1	820
	11th to 20th	Night	28% 20% 29% 17% 5% 1	840
	21st to end	Night	32% 21% 29% 14% 4	840
December	1st to 10th	Night	32% 22% 29% 14% 4	840
	11th to 20th	Night	28% 25% 30% 14% 2	840
	21st to end	Night	31% 22% 31% 15% 1	924

Page generated at 2026-05-14 01:58:53. Version ac07

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